Fall 2021 Season in Review

Overall, fall was warmer and wetter than normal. Temperatures were generally above normal in September and October, and above or much above normal in November. September precipitation ranged from above to below normal. In October the entire area was wetter or much wetter than normal. The trend reversed in November, with below normal precipitation nearly everywhere.

September

September 2021 precipitation

September 2021 temperature

Temperatures were above normal over more than half of the area. Precipitation presented a patchwork pattern, reflecting the predominantly convective nature of the heavier precipitation events.

A weak upper level low pressure trough hanging over the northwest U.S. kept temperatures 5-10 degrees below normal through the 3rd.

A warming trend commenced on the 4th as an upper level high pressure ridge built over the Intermountain Region. Temperatures topped out at 10-15 degrees above normal on the 9th. Wildfire smoke limited heating to some extent, but temperatures still managed to reach the 93 at Baker City, Burns, and Twin Falls, 94 at Ontario, 95 at Jerome, and 98 at Boise. Except for Ontario, these were all records for the date.

The high the following day was 20 degrees cooler as a Pacific cold front and upper level trough crossed our area. Many locations experienced wind gusts in the 40-50 mph range as the front passed.

Following the trough, temperatures remained cool on the 11th. Slightly warmer westerly flow aloft from the 12th through the 15th provided highs in the lower 80s at lower elevations…near normal for mid September.

Another Pacific cold front passed on the evening of the 15th, lowering highs on the 16th by around 10 degrees.

Southwest flow aloft ahead of a much stronger Pacific cold front added 10-15 degrees to highs on the 17th and 18th. As the front passed, gusts of 40 to 55 mph were measured at many locations. Precipitation with the front was generally light, but a bit more fell on the 19th under the upper level trough which followed the cold front. Highs on the 19th and 20th were mostly in the 50s and 60s, the coolest of the season so far.

A high pressure ridge brought a warming trend on the 21st and 22nd. Warming was briefly interrupted on the 23rd as a weak trough crossed our area. The ridge strengthened behind the trough, and highs rose into the 80s at lower elevations from the 25th through the 27th.

During the afternoon of the 27th, desert winds from the south brought dry air with humidity dropping into the single digits at several locations.

On the 27th gusts of 45-50 mph were reported at many locations following a strong cold front. On the 28th the winterlike trough following  the front lowered snow levels to around 5000 feet. At Bogus Basin, nearly 3 inches had accumulated at the snow stake just before 11 am MDT.

Temperatures in the north Pacific air that afternoon were as much as 30 degrees cooler than the previous day`s highs.

By sunrise on the 29th, cool air and clear skies allowed the temperature to drop into the mid and upper 30s in the Treasure and Magic Valleys. Since winds were light, that was cold enough for patchy frost. McCall froze with 29 degrees, but the coldest readings were in eastern Oregon, with 23 at Baker City and 20 at Burns.

The month ended under a high pressure ridge which brought sunny skies and near normal temperatures.

October

October 2021 prepitation October 2021 temperature

October was noteworthy for heavy rainfall events. Precipitation was over 150 percent of normal across wide areas of southeast Oregon and southwest Idaho. Significant areas had over 300 percent of normal.

During the first five days of the month, temperatures rose to summerlike values under a high pressure ridge. On the 4th, southwest flow aloft ahead of a low pressure trough raised the temperatures into the 80s at many valley locations.

After reaching the coast, the trough deepened far enough south on the 6th and 7th to pick up tropical moisture. As the system moved inland on the 8th, precipitation was hit and miss. Ontario reported no rain, only .04 inch was measured at Baker City, and Burns got only a trace. But Boise picked up .46 inch, Jerome .65 inch, McCall .63 inch, and Twin Falls received a total of .71 inch on the  7th and 8th.

Cool showery weather persisted through the 10th.

A colder trough moved inland on the 11th. Temperatures averaged 10-15 degrees below normal through the 14th. There was only light of precipitation.

During the next couple of days, a ridge brought a warming trend. As it shifted east, southwest flow ahead of the next Pacific cold front raised the temperature from the upper 60s to the mid 75s on the 17th.  Cool air behind the front lowered highs on the 18th by 10-15 degrees.

By the 19th a weak ridge had again built over the Intermountain Region.

Southwest flow aloft intensified as the next trough approached the coast. Like the system earlier in the month, it had entrained tropical moisture. As it moved inland over the northwest states on the 22nd, rainfall totals ranged from a quarter inch to over half an inch in the valleys. McCall got .88 inch.

Another even deeper trough from the Aleutians intensified as it approached the coast on the 24th, resulting in even stronger southwest flow from the tropics to the Pacific Northwest and Northern Rockies by way of California.

This cool-season phenomenon is known as an “atmospheric river” or AR. It is a narrow region of poleward transport of moisture, where strong flow taps very moist air from the tropics and carries it to higher latitudes. An intense low pressure system developing on the west side of the AR, plus the associated cold front and warm front, lend lift to the extremely moist and potentially unstable air. So the northern Sierra Nevada, Cascade, and Owyhee ranges, which usually create “rain shadows”, have limited effect on the amount of rain falling downwind.

Heavy precipitation was widespread on the 24th and 25th. By far the heaviest amounts fell in the Boise mountains, where totals exceeding 2 inches were common. The winning totals were 3.05 inches 4 miles southwest of Featherville, and 4.83 inches 1 mile south-southeast of Featherville.

The 24th was not only wet, but very windy. Gusts over 40 mph were common. Several locations experienced gusts over 50 mph. A gust of 65 mph was measured at a location 6 miles north of Wagontire in Harney County, Oregon. In Washington County, Idaho, a gust of 64 mph was measured 15 miles west-northwest of Cambridge.

The ridge warmed temperatures to 10-15 degrees above normal on the 28th and 29th. Then another Pacific cold front dropped temperatures to near normal on the the 30th.

November

November 2021 precipitation November 2021 temperature

November was unseasonably warm and dry.  The month began with above normal temperatures under an upper level high pressure ridge. Disturbances moving into the ridge brought only light precipitation.

Southwest flow aloft brought more light showers on the 5th and 6th, and temperatures cooled to near normal on the 7th following another weak Pacific cold front.

On the 9th moderate amounts of precipitation accompanied a Pacific cold front and upper level low pressure trough. Totals from a quarter to a half inch were common, the largest one day precipitation totals of the month at many locations.

On the 11th a high pressure ridge initiated a warming trend, and temperatures averaged 10-15 degrees above normal through the 15th. Disturbances moving around the northern periphery of the ridge brought light showers from the 11th through the 14th.

During the night of the 16th, a strong but dry cold front from the Gulf of Alaska was followed by the coldest air so far this season, with lows below freezing at nearly all locations. Both Burns and McCall registered lows of 15 degrees.

On  the 19th a Pacific cold front triggered scattered thunderstorms. In the Boise area, small hail was reported at a few locations, and there were a couple of reports of wind gusts over 50 mph.

A high pressure ridge built in from the southwest on the 20th and kept our area dry through the 22nd.

On the 23rd another pacific cold front brought showers and cooler temperatures.

A high pressure ridge centered off the California coast expanded north on the 24th. It kept the area dry through the end of the month, but it created a temperature inversion, resulting in air stagnation in the lower valleys. Despite the inversion, afternoon heating under mostly sunny skies pushed temperatures above normal during the final week of the month.

https://twitter.com/NWSBoise/status/1465115860431867906

Season in Review – Summer 2021

Summer was, in a word, hot…the hottest on record at several locations. Many monthly and daily temperature records were broken or tied. It was also drier than normal overall, with the notable exception of the Treasure Valley.

June-August 2021 3-Month Averages vs  Previous Warmest              
               Summer 2021         Previous warmest
Boise              78.0                   76.6/2015
Baker City         67.2                   69.0/1961  
Burns              69.6                   69.2/1961
Jerome             74.2                   74.2/1961
McCall             65.6                   65.3/1961
Ontario            79.4                   78.5/1961
Rome               71.0                   72.4/2007
Twin Falls         73.9                   75.1/2013
June-August 2021 Monthly Averages vs Previous Warmest
             June               July               August
Boise        75.9  70.5/2007    83.8  83.1/2007    74.4  78.7/2001
Baker City   65.4  66.0/1961    71.3  72.3/1985    64.9  71.3/1961
Burns        66.9  66.9/2015    74.5  73.2/1960    67.3  72.3/1967
Jerome       73.5  71.8/1974    79.0  77.9/1985    70.1  77.3/1967
McCall       62.9  63.3/2015    71.1  68.7/2017    62.8  67.9/1961
Ontario      75.9  80.0/1971    85.1  82.3/2007    75.9  80.0/1971
Rome         68.9  72.4/2015    75.2  78.1/2007    68.8  74.2/1967
Twin Falls   72.2  73.5/2015    78.8  79.6/2007    70.6  77.1/2013
2021 Monthly Highs vs Previous Monthly Highs
             June               July              August
Boise        105  110/2015      107  111/1960     105  110/2018
Baker City   103  102/1961      101  105/2020      98  109/2018
Burns        103  102/2015      102  107/2002     101  103/2018
Jerome       100  110/1940      100  108/1973      99  107/1940
McCall        96   97/2015       95  102/1928      93  104/1928
Ontario      107  109/2015      107  113/1967     106  113/1961
Rome         101  107/2015      105  110/2002     103  107/2018
Twin Falls   100  103/2013      100  107/2003      96  102/2013

June

June temp anomalyJune precip anomaly

A persistent and very warm upper level high pressure ridge resulted in a number of record highs. It was the warmest June on record at Boise, Burns (tied), and Jerome.  The high of 103 at Boise on the 3rd was not only a new record for the date, it was also the highest for so early in the season.

A dry pacific cold front crossed the Boise area on the 4th, and temperatures were back to near normal from the 6th through the 9th.

A cold upper level low pressure trough from the Aleutians arrived at the northwest coast on the 7th. After deepening southward, it moved inland over the Pacific Northwest and northern California on the 9th and crossed the Intermountain Region on the 10th. The 0.71 inch of rain at Boise that day was only 0.04 inch short of Boise’s normal precipitation for the entire month of June.

Temperatures rose from the 11th through the 13th under southwest flow aloft ahead of an offshore trough.

As the trough moved inland on the 14th and 15th, the coolest air was diverted north of our area by an expanding upper level high pressure ridge over the four corners. So the trough brought only slight cooling, lowering temperatures to near normal on the 16th.

As the ridge amplified, temperatures rose again.

A low pressure trough formed off the California coast on the 20th. A disturbance generated by the trough lifted north, heading for southeast Oregon and southwest Idaho. It spawned strong, but mostly dry, thunderstorms in southeast Oregon on the 22nd. Cloud cover and cool air in the trough kept temperatures in the 60s and lower 70s in Harney County, while Boise`s high soared to 98 degrees. The increased pressure gradient caused by the temperature difference enhanced outflow from the storms as they drifted north, resulting in strong west winds in the Treasure Valley. A gust of 59 mph was measured at the Boise Airport, but there were reports of even stronger gusts elsewhere in the valley.

On the 23rd, an upper level ridge began to build off the coast. By the 26th it had moved inland over B.C. and the northwest U.S., unusually far north for such a strong and very warm ridge. Temperatures responded with a number of record highs from the 28th through the 30th.

During the hottest part of the day, humidities were low, falling into the teens and single digits.

Moisture circulating around the ridge resulted in numerous showers and thunderstorms around the region on the 30th, but many locations reported only sparse precipitation.

jun2021recs

July

July temp anomalyJuly precip anomaly

July 2021 was the warmest on record at several locations, including Boise, Burns, Jerome, McCall, and Ontario.  It could have been even warmer. Persistent smoke from wildfires restricted sunlight from reaching the surface, so highs were slightly lower than they would have been under clear skies.

At Boise, several other temperature records were broken, tied, or approached.

Consecutive days
     highs >= 90...44(6/17 - 7/31) ranks 2nd (50 in 1875 ranks 1st)
           >= 100...9(6/28 - 7/6) ties 2015, 2006, and 2003 
     lows  >= 60...43(6/19 - 7/31) ranks 1st (37 in 2007 ranks 2nd)
           >= 70...11(6/27 - 7/7) ranks 1st (5 in 2015 ranks 2nd)
Number of days
     highs >= 90...31...ties July 2017 (30-year average is 22)
           >= 100...12...ranks 4th (15 in 2003 ranks 1st)
     lows  >= 60...31...ties July 2007 (30-year average is 20)
           >= 70...16...ranks 1st (9 in 2007 ranks 2nd)
                                 (30-year average is 3)

It was a dry month overall, but a storm on the 31st brought significant rain to many Idaho locations.

An upper level warm high pressure ridge was responsible for the heat. Weak cold fronts associated with Pacific weather systems crossing western Canada occasionally pushed far enough south to lower temperatures by a few degrees. But other than breezy northwest winds, they had little noticeable effect.

By the 20th the ridge had shifted east and was centered over Colorado. Southwest flow between the ridge and an upper level trough centered over the B.C. coast transported monsoon moisture north of the Nevada border. The resulting thunderstorms brought generally light precipitation, along with gusty winds.

On the morning of the 22nd, a cold front passed our area as the upper level flow began to shift into the west, carrying the monsoon moisture east. Cooler drier air following the front resulted in the below normal average daily temperatures from the 22nd through the 24th.

On the 28th a brief influx of monsoon moisture generated early morning showers and thunderstorms, but precipitation was sparse. Skies cleared, and it was another hot afternoon and evening. Drier southerly flow brought even higher temperatures on the 29th and 30th.

By the 26th the center of the upper level ridge had migrated to the central Great Plains. Easterly flow south of the ridge picked up very moist air from the Gulf of Mexico and carried it west to New Mexico and Arizona. Southerly flow on the west side of the ridge then transported it north to the northern Intermountain Region.

On the 31st a low pressure system formed over Nevada. As it moved north, it interacted with the Gulf moisture, setting off numerous showers and thunderstorms with locally heavy rain. The Boise and Ontario areas, the Magic Valley, southern Twin Falls County, and the central Idaho mountains got the brunt of the rain.

 

jul2021recs

August

August temp anomalyAugust precip anomaly

 

In contrast to June and July, August was a relatively wet month with near normal temperatures, although it certainly had its share of record daily high temperatures. But smoky skies prevented highs from reaching their full potential. Temperatures were mostly above normal for the first half of the month and mostly below normal for the last half.

An upper level high pressure ridge kept temperatures hot from the 2nd through the 5th.

On the 6th a cold front and weak upper level trough crossed our area. Temperatures warmed briefly on the 7th ahead of a stronger trough from the Gulf of Alaska. That trough, and the northwest flow that followed, cleared the smoke and kept temperatures below normal through the 10th.

The heat returned on the 11th as an upper level ridge centered off the coast built inland. The heat persisted through the 16th. By the 14th the smoke had overspread our area again.

A major pattern change on the 17th ended the heat. An upper level trough deepened south from Canada over the Pacific Northwest and the Intermountain Region as an upper level ridge between Alaska and Hawaii strengthened and expanded north. The resulting northwest flow aloft put us in the path of more troughs coming out of Alaska. One of these systems brought light but measurable rain on the 20th and 21st, plus another brief respite from the smoke.

 

aug2021recs

Winter 2020-2021 in Review

December

Temperatures were above normal in the mountains and below normal at lower elevations due to temperature inversions.  The entire region was drier or much drier than normal. The driest areas were the central Snake River Valley, the Camas Prairie, and the Boise Mountains.   An upper-level high pressure ridge dominated through the 10th, keeping our region dry. Burns was an exception, where a weak upper level low pressure trough brought light snow on the 6th.  From the 11th through the 16th, a temperature inversion resulted in areas of night and morning fog. A trough from the Gulf of Alaska brought light snow on the 13th and 14th. It was too weak to mix out the inversion, as most of its energy crossed the Intermountain Region well south of our area. 

The inversion finally broke as a stronger trough crossed the area on the 17th, bringing 5-10 inches of snow to the mountains, but only light precipitation in the valleys. An exception was the .55 inch rainfall at Jerome, which established a new record for the date.  Mild westerly flow aloft brought a warming trend from the 18th through the 22nd.  High temperature records were tied or broken at several locations on the 21st and 22nd

City New Record Old Record Year
Baker City 56 55 1972
Burns 53 51 1972
Jerome 58 58 1969
McCall 43 43 2019
Twin Falls (21st) 59 53 2014
Twin Falls (22nd) 50 50 2005

A strong Pacific cold front crossed the area on the 22nd, followed by a 10-20 degree temperature drop. Strong northwest winds gusting to 40-50 mph followed the front. A gust of 57 mph was measured north of Andrews in Harney County.  The trough which followed the front produced light precipitation at lower elevations. Moderate amounts of snow fell in the mountains, including 5 inches at Brundage.  

https://twitter.com/NWSBoise/status/1341508962311688197/

Following this system, a strong ridge kept skies mostly clear through Christmas eve.

A weak trough brought mainly light precipitation on the 25th and 26th. Boise was an exception, where a third of an inch of precipitation fell on the 26th, which included half an inch of snow. A few inches of snow fell in the mountains. 

Another temperature inversion formed on the 26th, and locally dense fog returned to the valleys.  With cold air trapped in the valleys, temperatures failed to reach the freezing mark at many of the usually warmer locations in the 28th and 29th

https://twitter.com/NWSBoise/status/1343759866368675842?s=20

The final trough of the month weakened as it moved inland on the 31st, but it was able to drop several inches of snow on the mountains, including 8 inches at McCall and 6 inches at Tamarack.

DecemberDecemberp

January

Temperatures were above normal across the region, and much above normal in the Snake River Valley and parts of southeast Oregon.  Most of southern Idaho and parts of Baker and Harney Counties in Oregon were drier than normal, while the Treasure Valley and west central Idaho received above normal precipitation.  

https://twitter.com/NWSBoise/status/1345922598413062145

Strong westerly flow across the Pacific was charged with abundant moisture as it swept inland with a warm front on the 3rd, resulting in heavy precipitation. Totals from a half inch to an inch of water were common, falling as rain at lower elevations and snow in the mountains. Bogus Basin accumulated 7 inches.  Strong west winds, mostly in the 40 to 50 mph range, followed a cold front on the 4th.  A gust of 63 mph was measured at Wagontire in Harney County.  On the 5th another warm front brought heavy snow to the mountains. Banner Summit got 14 inches. Bogus Basin and Tamarack received 10 inches. Atlanta also got 10 inches. Bogus Basin got 7 additional inches on the 7th as a trough crossed the area. Little if any precipitation fell at lower elevations from the 5th through the 7thOn the 12th a weak but moist trough embedded in the westerly flow brought more snow to the mountains, while relatively light precipitation fell at lower elevations. At Council 7 inches was measured, and 6 inches fell at Brundage and McCall.  A cold front crossed the area on the 13th, followed by wind gusts of 30-45 mph.

High pressure kept the area mostly dry from the 14th through the 20th.  From the 21st through the 26th, weak troughs moving down the coast from the Gulf of Alaska brought only light precipitation to our valleys and a few inches of snow to the higher elevations.  A record low temperature of 10 degrees was set at Twin Falls on the 25th, breaking the old record of 12 set in 2008.  On the 27th a stronger trough centered over southeast Alaska deepened southward just offshore. Southerly flow aloft on the east flank of the trough was felt at the surface as gusty south to southeast winds, generally in the 40 to 50 mph range. A gust of 68 mph was measured at Trail Gulch, 14 miles east-southeast of Hollister.   Also on the 27th, moderate amounts of snow fell in eastern Oregon and west-central Idaho, due mainly to lifting of the air by the mountains. At McCall 9 inches was measured, and 7 inches fell at Midvale. At Huntington in Baker County 5 inches was reported. 

Januaryp

January

February

February was a month of very active weather. Temperatures were near or above normal at most locations. February is normally warmer than January, but this year it was actually colder than January at Boise, McCall, Mountain Home, and Ontario. It’s not the first time this has happened, but at Boise it was the fourth year in a row.

On average, February is the driest winter month, but this year it was the wettest in the Treasure Valley and eastern Oregon. However, the Boise Mountains, Camas Prairie, and Magic Valley were drier than normal.  The month began with above-normal temperatures under southwest flow aloft ahead of an offshore trough. As the trough moved inland, a cold front crossed our area during the afternoon and evening of the 2nd.  This marked the beginning of a pattern change which would lead to long overdue winter weather for the valleys. Northwest flow aloft developed on the 4th and strengthened during the following days.  On the 5th, a fast-moving trough from the Gulf of Alaska brought a few inches of snow to the mountains, but its main impact was strong west to northwest wind. Gusts of 45-55 mph were common, but by far the strongest wind measured was 92 mph at Soldier Mountain.  Meanwhile on the 3rd, arctic air had plunged south across the Canadian border east of the Rockies. The mountains, and strong northwest winds aloft, kept it out of Idaho. A second invasion of even colder arctic air entered Montana on the 5th. By the 6th, its western margin had stalled along the Montana border.  Meanwhile, the “milder” western portion of the same arctic airmass was drifting south through the mountains of British Columbia. It entered Washington on the 8th and northeast Oregon on the 9th.  The front marking its leading edge reached eastern Oregon and southern Idaho on the 11th.  Moist air streaming inland ahead of an approaching trough was lifted over the cold air north of the front, resulting in snow which became heavier as the trough drew closer on the 12th and crossed our area on the 13th.  Snowfalls of 3 to 6 inches were common in the valleys on the 12th.  Up to 6 more inches fell on the 13th, with heavier accumulations in the mountains. By the time the snow ended, 7 to 10 inches had accumulated in the Treasure Valley. McCall, which nearly always gets way more snow than Boise, also reported a storm total of 10 inches. Totals of 13 inches were measured at both Bogus Basin and Magic Mountain ski areas, while Twin Falls reported only 2 inches.  The 4.4 inches which fell at the Boise airport on the 12th broke the old record for the date of 1.3 inches set in 1966, and the 5.5 inches on the 13th broke the old record of 4.3 inches set in 1995.  

On the 15th another trough from the Pacific brought more snow, with 1 to 4 inches in the valleys and 5 to 10 inches in the mountains. Wind gusts of 40 to 55 mph were observed in Harney County and the Magic Valley.  From the 16th through the 22nd, Pacific systems brought more snow to the mountains but generally light precipitation in the valleys. With afternoon temperatures above freezing, there was little if any snow accumulation in the lower valleys.  On the 23rd, a cold front was followed by a wind event which mainly affected southeast Oregon and areas east of Boise. There were many reports of gusts in the 45 to 55 mph range, but a gust of 67 mph was measured at Twin Falls.  On the 26th, another strong cold front swept across the region. One of the stronger gusts was 59 mph from the west-northwest at the Boise airport. A brief snow squall followed the front, but less than half an inch fell at the airport.  

On the 27th a trough from the Gulf of Alaska brought heavy snow to the mountains. Some of the heavier totals were 12 inches at Mores Creek Summit, 15 inches at Banner Summit, 20 inches at Tamarack, and 22 inches at Brundage.

November 2020 Weather Summary

November’s temperatures averaged close to normal.  Precipitation was generally above normal, although there were areas near the Nevada border where precipitation was less than 50 percent of normal.  A strong upper level high pressure ridge over the Intermountain Region on the 1st and 2nd weakened on the 3rd, but above-normal temperatures continued through the 6th ahead of a Pacific cold front.

On the 2nd, the highs of 70 at Burns and Twin Falls tied their records for the date. The 74 at Jerome set a new record, as did the 68 at Baker City.  On the 4th, new records were set at both Burns and Baker City with highs of 70 and 71 respectively.  On the 5th, Boise’s high of 76 set a new record for the date, as did the highs of 75 at Burns, 69 at Ontario, and 72 at Baker City.
On the 6th, the high of 67 at Ontario set a new record for the date. The high of 71 at Mountain Home tied their record.
The cold front crossed southeast Oregon and southwest Idaho on the 6th with little if any precipitation. The cold upper-level low pressure trough behind the front drifted south over California before settling over the Great basin on the 7th. At the same time, a second trough from Alaska was deepening over western Canada.
On the 8th, light to moderate amounts of snow fell as the Canadian trough joined forces with the Great Basin trough. Snowfalls in the Boise area ranged from 1 to 4 inches. The 2.7 inches at the Boise Airport set a new record for the date.
Yet another trough, this time from the Gulf of Alaska, arrived over the northwest U.S. on the 10th with only light snow. Meanwhile, a band of westerly flow aloft, aka the jet stream, was strengthening south of the Aleutians. Its arrival over the northwest coast on the 13th was preceded by a very active weather disturbance.
Rainfall amounts with this system included over two-thirds of an inch at Jerome and McCall, nearly a half inch at Boise, and a third of an inch at Burns and Ontario.
Heavy snow fell in the mountains, including 9 inches east of New Meadows, 8 inches northwest of McCall, and 10 inches near Halfway and Sumpter in Baker County.

Also in eastern Oregon on the 13th, a wind gust of 66 mph was measured north of Wagontire, and a gust of 63 mph was measured north of Andrews.
On the 15th, copious Pacific moisture accompanying a warm front brought more rain. The 0.46 inch at Boise and the 0.28 at Twin Falls were new records for the date.
More snow fell in the mountains, including 4 inches east of New Meadows and 9 inches at Cuprum in western Adams County.
Temperatures had been below normal since the 7th, but an upper-level high pressure ridge following the warm front raised temperatures above normal on the 16th.
On the 17th, a cold upper-level low pressure trough, which had been deepening off the B.C. coast, generated a strong cold front which pushed rapidly inland. The front, energized by the jet stream, was accompanied by thunderstorms with abundant lightning as it roared across southwest Idaho during late afternoon on the 18th.


Storm reports in the Boise area included brief heavy showers which produced from a quarter to a half inch of precipitation, small hail covering the ground at some locations, and wind gusts exceeding 40 mph. An inch of rain fell at Placerville and three-quarters of an inch near Horseshoe Bend.
The cold front caused only slight cooling, and temperatures remained above normal through the 19th under southwest flow aloft.
The next several days were much less dramatic as a series of relatively weak troughs and ridges crossed our area. During the morning of the 25th, a better organized trough brought light snow. One inch was measured at the Boise airport. Most of it melted during the afternoon.


By the 27th, a high pressure ridge had built over the northern Intermountain Region. As is typical of this time of year, the warm air aloft and nighttime cooling in the valleys resulted in an inversion which kept temperatures below normal from the 28th through the 30th.

On the 30th, a weather disturbance brought more light snow. It was not strong enough to break the inversion.

Snow across the mountains was well above normal for November standards.


November temperature anomaly
November precipitation departure

October 2020 Weather Statistics

October was generally warmer than normal when temperatures for the entire month were averaged. But that average gives no indication of the extremes.
October precipitation departureOctober temperature anomaly
As in September, precipitation was below normal.
From the 1st through the 9th, the ridge kept temperatures around 10 degrees above normal. As in September, smoke and haze kept highs from achieving their full potential.
On the 2nd, the high of 87 at Ontario tied their record for the date. And on the 3rd, the high of 87 at Burns set a new record for the date. On the 4th, the high of 85 at Twin Falls set a new daily record.
On the 10th, strong westerly flow aloft flattened the ridge as it carried a cold front inland from the northwest coast. As it crossed southeast Oregon and southwest Idaho, the front routed the smoke as it pushed east. Rain which followed the front washed out most of the remaining aerosols.

Seasonable temperatures followed the front, but an impending major pattern change would bring an early taste of winter.
The high pressure ridge, which had provided summer-like temperatures early in the month, shifted west off the coast and expanded north toward Alaska, resulting in northerly flow aloft over the Intermountain Region.
The first cold front from Canada crossed our area on the 21st. By sunrise on the 22nd, temperatures had dropped below 32, the first freezing readings of the season at many lower valley locations. An even stronger cold front followed on the 24th, delivering an early season blast of Arctic air from northwest Canada.
On the 25th, record lows for the date were set at Jerome and Twin Falls, with 22 and 15 respectively.
The low of 17 at Boise on the 26th set a new record for the date. The temperature dropped to a frigid 3 above at Burns, setting a new record. It was 10 above at McCall, tying their record for the date. The 10 above at Mountain Home set a new record. The 16 at both Jerome and Twin Falls broke their old records.
It is interesting to note that just last year a nearly identical late October weather pattern also resulted in record lows, along with some light snow in the lower valleys.
The high pressure ridge began to drift back over the western U.S. on the 27th, bringing a warming trend.
The 71 at Burns on the 30th set a new record.

September 2020 Weather Summary

September was warmer than normal. On the 4th, record highs of 102 were set at Boise and Burns. The 99 at Ontario tied the record for the date. On the 5th, the high of 100 at Boise tied the record for the date, and the 98 at Twin Falls set a new record.
Screen Shot 2020-12-28 at 12.08.10 PMScreen Shot 2020-12-28 at 12.08.22 PMScreen Shot 2020-12-28 at 12.08.36 PMScreen Shot 2020-12-28 at 12.09.28 PMScreen Shot 2020-12-28 at 12.09.52 PMScreen Shot 2020-12-28 at 12.09.11 PM
It would have been even warmer had it not been for widespread smoke and haze from wildfires.


It was a dry month, especially in southcentral and southeast Oregon, where totals were less than 5 percent of normal across a wide area.
September precipitation departure
September temperature anomaly
A very warm upper-level high pressure ridge anchored over the western region kept temperatures above normal during the first week of the month. By the 8th the ridge had migrated far enough west to allow a very cool upper-level low pressure trough to drop south from Canada.


The cold front ahead of the trough crossed our area on the 7th. Following the front, northwest winds in the 40-50 mph range were common. A gust of 54 mph from the northwest was measured near Boise.
https://twitter.com/NWSBoise/status/1303333613392388097?s=20
The trough kept temperatures below normal. Highs failed to reach 70 at a number of locations on the 8th.
Following the trough, the ridge built inland, and temperatures were above normal again on the 11th. The ridge dominated through the 17th, with highs in the 80s at many lower valley locations.
The northern part of the ridge gave way to a Pacific cold front on the 18th. Most locations received only light precipitation. Isolated thunderstorms generated outflow winds over 40 mph.
From the 20th through the 25th, the ridge was alive and well over the southwest U.S., while southwest flow aloft on its northern periphery kept temperatures in our region above normal.
Meanwhile, a more fall-like pattern was developing as westerly flow aloft strengthened across the North Pacific.
The upper-level winds carried a fast-moving weather disturbance inland on the 25th. While rainfall was generally light in the valleys, McCall set a record for the date with .54 inch.


Temperatures stayed below normal through the 27th. On the 28th the ridge, now resurrected over the west coast, brought a warming trend. It would guarantee above-normal temperatures through the 30th and beyond.

August 2020 Climate

August was warmer than normal across the area, and a number of record highs were set.
August 2020 temperature (2)
August 2020 precipitation

On the 15th, the high of 99 at Burns set a daily record.

On the 16th, the high of 103 at Boise set a daily record. A record of 100 was set at Burns.

On the 17th, the high of 102 set a record for the date at Boise. Other record highs include 106 at Mountain Home and 99 at Baker City.

On the 18th, the 98 at Baker City tied the daily record.

On the 19th, the 97 at Twin Falls was a record for the date.

It was drier than normal nearly everywhere, but, as mentioned in the July summary, that’s actually normal.

Monsoon thunderstorms brought more wind than rain.

On the 15th, a thunderstorm near Andrews, Oregon broke off dead tree limbs and did other minor damage. At Little McCoy Creek in Harney County, a gust of 63 mph was measured by automated equipment.

On the 17th, a gust of 70 mph was measured by a spotter. A spotter in Fields, Oregon measured a sustained speed of 44 mph with a gust of 58 mph. A spotter in Fields measured a 54 mph gust which resulted in lost power. There were numerous other reports of gusts exceeding 50 mph.

On the 18th a spotter in Oreana reported half-inch diameter hail.

As usual, the seasonal upper level high pressure ridge over the southwest states was the main source of the heat. An occasional Pacific cold front provided some respite, but there was no significant cooling Until the end of the month.

Had the air been clear, it would have been even hotter. But widespread smoke from wildfires limited high temperatures on many days. Persistent southwest flow aloft transported the smoke from its California source.

The monsoonal moisture brought high dewpoints to the region, which helped fuel afternoon and evening thunderstorms from August 24th through the 29th. Boise recorded the highest dewpoint since September 5th, 2013 on August 25th.

On August 26th, a long-lived supercell thunderstorm tracked across Owyhee County with 2″ diameter hail.

Overnight on the 29th, a dry cold front brought much cooler air from western Canada. Highs were around 15 degrees lower than on the previous day.

Northwest winds at the surface and aloft behind the front temporarily swept away most of the smoke.

On the 31st, a weather system from British Columbia brought clouds, a breezy afternoon, and slightly cooler air.

July 2020 Climate

The temperature, when averaged across the area, was slightly above normal. The greatest departures were at Baker City (+3.5 degrees), McCall (+2.5 degrees), and Rome (+2.1 degrees).
July 2020 temperature
Precipitation was below normal nearly everywhere. July is one of the two driest months of the year (the other being August), so dry is actually normal.
July 2020 precipitation
During most of the month, upper-level low pressure troughs moving inland over western Canada would play a role in our weather, as they vied for dominance with the very warm seasonal upper-level high pressure ridge over the southwest U.S.

Precipitation is usually associated with troughs, but during July they produced little if any rain south of the Canadian border, bringing only brief periods of slightly cooler weather.

Between troughs, the high pressure ridge to our south made its presence felt as it expanded northward.

Increasing amounts of monsoon moisture circulating within the ridge eventually managed to reach our area on the 22nd and 23rd, and again on the 27th and 28th, carried north ahead of weak low pressure troughs over California.

On the 23rd, thunderstorms brought locally strong gusty winds. At Rome, numerous tree branches were blown down and garbage cans were knocked over. A gust of 64 mph was measured 21 miles north of Murphy Hot Springs. Numerous other locations reported gusts in excess of 50 mph.

On the evening of the 28th, thunderstorms crossed the Owyhee Mountains, bringing spotty but locally heavy showers to the Boise area.

The ridge made a major northward expansion on the 30th and 31st, bringing the hottest weather of the summer.

At Baker City on the 30th, the high temperature of 101 tied the daily record set in 2003. And the 105 on the 31st set a new record for the date.

On the 31st at Burns, the high of 99 tied the record set in 1949. At Ontario, the high of 107 tied the record set in 1971.


Pocatello tied their all time record high temperature of 104 degrees as well.

 

 

June 2020 Climate

Temperatures varied widely during the month. Most of southwest Idaho was cooler than normal. Most of southeast Oregon had near or slightly below normal temperatures, but Baker City, Burns, and Rome averaged warmer than normal.

From the 1st through the 4th, temperatures were above normal under dry and relatively warm westerly flow aloft. On the 5th, southwesterly flow ahead of a Pacific cold front brought even warmer air.

Gusty west winds followed the cold front. Many locations reported gusts in the 50-70 mph range. The strongest was 77 mph at an automatic observing site 10 miles southwest of Hill City.

https://twitter.com/NWSBoise/status/1269481164642738178

A cold upper level trough from the Gulf of Alaska followed the front. High temperatures were as much as 30 degrees cooler from the 6th through the 8th. Tamarack Ski recorded 17″ of snow, while 15″ fell at Brundage and 8″ at Bogus Basin.

Except for northern Harney County, and a narrow strip between the Snake River and the Owyhee Mountains, June was wet, especially in a corridor from southern Malheur County across the central Idaho mountains. The Treasure Valley was the wettest area in the region. Boise had the third wettest June on record.

On the 7th, rainfall set new records for the date at McCall (1.13 inches), Ontario (.35 inch), and Twin Falls (.28 inch). During the three day period from the 6th through the 8th, McCall measured 1.75 inches and Boise 1.11 inches of rain. Much less fell elsewhere. Baker City and Burns received only traces.

Following the trough, a high pressure ridge brought dry and warmer weather from the 9th through the 12th. The high of 90 at Twin Falls on the 12th set a record for the date.

The cold front ahead of the next trough arrived on the the 12th. Following the front, west winds gusted over 50 mph at many locations. The strongest reported gust was 61 mph at Grassy Mountain 19 miles southeast of Rome.

On the 13th, an upper level low pressure trough lifted north from California, generating a band of heavy rain which was mainly confined to the Treasure Valley. Many reporting points in Ada, Baker, and Washington Counties measured just over one inch. Record rainfalls for the date were set at Boise (1.21 inches) and Ontario (.74 inch).

https://twitter.com/HeyMzWilliams/status/1271904256530907136

Rainfall from the 13th through the 17th totaled 1.81 inches at Boise, 1.11 inches at McCall, .83 inches at Ontario, and 1.31 inches at Rome. On the 13th, rainfall amounts set records for the date at Boise (1.21 inches) and Ontario (.74 inch). Outside of the heavy rain band, other locations in southeast Oregon received between a quarter and a half inch. Southeast of Boise, Mountain Home got only .11 inch and Jerome .12 inch.
On the 16th, yet another trough arrived from the Gulf of Alaska, keeping temperatures unseasonably cool through the 18th.

On the 24th, thunderstorms brought hail and strong gusts to a few locations. Four miles south of Jamieson in Malheur County, hail one inch in diameter covered the ground and caused damage to crops. Quarter inch hail fell nine miles north of Vale. Thunderstorm winds exceeded 50 mph at a few locations in Owyhee County.

On the 25th, the high of 94 at Twin Falls tied the record for the date set in 2015.

On the 27th another unseasonably cold low pressure trough was bearing down from the north.

The cold front ahead of this trough crossed our area late on the 27th. The air behind the front was much cooler and initially dry. but as the trough settled over the northern Intermountain Region, it entrained a plume of moisture from across the Pacific, resulting in moderate amounts of rain at several locations on the 29th and 30th. The most reported was .77 inch at Ontario.

At Twin Falls on the 28th, a daily rainfall record was set (.25 inch), and a record low temperature was set (42).

On the 29th, daily rainfall records were set at Ontario (.74 inch) and Twin Falls (.18 inch).

https://twitter.com/IdahoITD/status/1277704643385016320

Also on the 29th, the low of 41 at Twin Falls set a new record low for the date.

 


June 2020 temperatureJune 2020 precipitation

April 2020 Climate Statistics

boi

Precipitation was near normal, and temperatures averaged slightly warmer than normal.

A cold upper level low pressure trough over western Canada and the Northwest states during the first three days of the month held temperatures below normal.

Southwest flow aloft ahead of a low pressure trough off the Pacific Northwest coast started a warming trend on the 4th.  As the trough moved south along the California coast on the 5th and 6th, showers spread inland, but the Boise area received only light precipitation.  The air was unstable enough for thunderstorms both days.

With our area between the low pressure system over the southwest states and the jet stream to our north and east, weak high pressure kept temperatures above normal from the 5th through the 11th.

A cool down was on the way as the flow over western Canada shifted into the north on the east flank of a high pressure ridge off the west coast of North America.

A cold front from British Columbia passed Boise during the evening of the 11th, accompanied by a wind gust of 45 mph from the north.  Temperatures the following day were 10 to 15 degrees cooler, and temperatures stayed below normal through the 14th.

Boise fared better than eastern Idaho, and much better than states to the east, where a late season arctic outbreak brought snow and winter temperatures.

After a brief warmup on the 15th, another cold front from British Columbia crossed the Boise area that evening. Compared to the previous front, the cool down was minor.  A convergence zone in the Snake River Basin near Mountain Home created show showers on the morning of the 16th.

A warming trend began on the 17th as the high pressure ridge began to move inland from the coast.

Increasing westerly flow aloft gradually weakened the ridge, and on the 22nd and 23rd a disturbance embedded in the flow brought the largest amount of precipitation for the month. Most of it fell on the 23rd with scattered convective showers, some of which produced brief heavy rain and small hail.

On the 25th and 27th a couple of weak disturbances dropped most of their precipitation over north Idaho, with only light showers at Boise.

On the 28th a strong high pressure ridge developed over the western U.S. as it amplified and drifted east, it provided the season’s warmest weather so far.

On the 29th strong southwest flow aloft on the west flank of the ridge, down valley flow at the surface, and mostly sunny skies helped boost the temperature at Boise to 88 degrees, one degree shy of the record set in 1992. Severe thunderstorms containing 1″ hail were reported in Baker City.

On the 30th the southwest flow carried an energetic weather disturbance across southeast Oregon and southwest Idaho. Late that morning a line of thunderstorms formed over Harney County.  The storms intensified rapidly as they approached Idaho. They crossed the border at about 1:45 pm, and strong outflow ahead of the storms arrived at the Boise airport at 2:30 pm.  Five minutes later a gust of 61 mph was measured just ahead of the rain, which was heavy at times.  Golf-ball size hail (1.75″) was reported at Oreana, ID (40 miles southwest of Boise).

 

The winds were likely stronger in some parts of town, as there were reports of power outages, downed trees, and other damage. Large trees across the Treasure Valley toward the Boise Mountains and Magic Valley were knocked down as a result of this storm.  Numerous large trees were knocked down from Prairie to Pine to Featherville with this storm.

 

Here are the rest of the climate graphics for southwest Idaho and southeast Oregon.  McCall was cooler than average due to a deep snow pack on the ground within the valley, which kept their temperatures lower than other areas.

ONO

MYL

JER

BNO