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Winter 2021-2022 in Review

Although December was warmer or much warmer than normal area wide, temperature inversions which prevailed in January and February caused the winter as a whole to average colder than normal in the Baker Valley and much of the Snake River Valley. Higher elevations, which were above the inversion, averaged warmer than normal for the season. 

This winter was drier than normal primarily due to one of the driest Februarys on record, although some areas were actually wetter than normal in December and January. 

3 month temp anomaly 3 month precip anomaly

December

The first three and a half weeks of December were relatively mild. Then real winter arrived on the 27th, lowering the average temperature for the month only slightly. December as a whole still averaged warmer or much warmer than normal nearly everywhere.

Precipitation was below normal in some areas and above normal in others. Some valley locations received more snow than usual. The month’s total of 15 inches at Boise was nearly three times normal, making it the snowiest December since 2008.

Weak high pressure aloft kept temperatures mild through the 5th. On the 1st,  a new record high of 62 was set at Burns. The 53 at McCall tied their record for the date.  On the 3rd, the high of 58 at Twin Falls set a new record for the date. 

On the 5th, a strong high pressure ridge building northward off the coast put our area under northwest flow aloft, allowing a cold front to push south from B.C. On the 6th a disturbance following the cold front brought a mix of rain and snow. 

Highs rose 10-15 degrees between the 6th and the 8th under a weak high pressure ridge. Then a fast moving Pacific cold front cooled highs by 10-15 degrees on the 9th and 10th. 

Temperatures began to recover on the 11th under westerly flow aloft through a transitory high pressure ridge.  As the ridge shifted east on the 12th, the flow backed into the southwest, and highs rose above normal from the 12th through the 14th ahead of another Pacific cold front.

Following that front, a pair of low pressure troughs brought snow to most of our area.  Boise received 2.1 inches, a record for the date.

A weak high pressure ridge contributed to above normal temperature on the 20th.

Showers began on the 22nd ahead of a deep low pressure trough. The unsettled weather continued through the 27th.  Precipitation totals were quite variable:

Boise .64
Jerome .59
McCall .95
Mountain Home .09
Ontario .14
Baker .05
Burns .37 (inches). 

Meanwhile, back on the 17th, a high pressure ridge was building just south of the Aleutians. By the 24th, it had grown into a massive feature between Alaska and Hawaii. It would contribute to much colder weather for the end of the month.

By the 28th, the trough had moved east of the Rockies, leaving our area under north-northwest flow aloft between the ridge and the trough. On the 29th and 30th,  disturbances embedded in this flow brought several inches of snow to the lower valleys and heavier accumulations in the mountains. 

On the 31st, Arctic air which had been residing in B.C. and adjacent areas of northern Washington began to filter into southeast Oregon and southwest Idaho, bringing clearing skies and falling temperatures. Although temperatures that day averaged only around 10 degrees below normal, temperatures on New Year’s Day averaged around 20 degrees below normal. 

December 2021 temp anomaly December 2021 precip anomaly

January

It was the coldest January since 2017 at many valley locations, although temperatures in the mountains averaged above normal because of a stubborn temperature inversion.  

Precipitation showed just the opposite pattern, with above normal totals in the lower valleys and below normal amounts in the mountains. 

On the 1st,  Arctic air from British Columbia provided the winter’s coldest weather. With clear skies, light winds, and snow cover, conditions were ideal for radiative cooling.

 

At Boise, the low at the “official” location at the airport was -3. It was the first subzero reading since January 2017. It wasn`t quite that cold elsewhere around Boise. The “warmest” reported low was 8 above zero in town in an area near the Boise River.

Lows at other locations include:

Baker City -20
Burns -16
Challis -12
Idaho Falls -13
Jerome -3
McCall -15
Mountain Home 2
Ontario -3
Rexburg -9
Salmon -12
Stanley -29.

On the 3rd, an upper level trough was approaching the Washington coast. Ahead of the trough strong mid-Level flow from the southwest mixed down to the surface, replacing the Arctic air with milder Pacific air. 

The trough weakened as it crossed the Northwest on the 4th, but strong flow from the Pacific continued to transport relatively warm air inland.  

The 7th was the “warmest” day of the month at some locations, but  there was a wind chill, so temperatures in the 40s felt more like the 20s. Here are some high temperatures plus peak winds and gusts (mph) that day. 

Boise 49 W33G50
Baker City 47 NW29G48
Burns 44 W35G47
Jerome WSW22G29
McCall 38 SSW26G34
Mountain Home E18
Ontario 49 SW16G26

By the 8th only traces of snow remained in the lower valleys.

On the 9th an upper level high pressure ridge found a home near the west coast. It would be the dominant feature for the rest of the month.

As expected at this time of year, a temperature inversion developed under the ridge. Pacific systems weakened as they passed around and through the ridge, so there was no precipitation until the 20th.

On the 20th a stronger Pacific system crossed our area from the northwest,  causing the ridge to shift offshore. Light amounts of snow fell, but it disappeared in the lower valleys the next day as temperatures rose above freezing.

The ridge was alive and well as it expanded back inland on the 21st and 22nd, and the inversion remained. Low stratus and night and morning fog plagued the valleys. 

With surface high pressure centered over southwest Idaho and southeast Oregon, the pressure gradient was too weak to generate enough wind to sweep the stratus out. Finally on the 27th, high pressure strengthened over eastern Idaho, resulting in easterly winds strong enough to clear the valleys.

The following days were sunny, but nights were clear and cold without the protective blanket of low clouds. 

January 2022 temp anomalyJanuary 2022 precip anomaly

February

It was the coldest February since 1993, and also one of the driest on record. At Boise, it was the second driest February in 145 years. And it was the driest ever at the airport, where records go back to 1940. 

A persistent upper level high pressure ridge, centered to our west through most of the month, was the main cause of both anomalies. 

The temperature inversion which formed in January persisted through February 8th. Although highs managed to rise above freezing on most days, the cold nights were mainly responsible for keeping daily averages below normal. 

On the 4th the low of 10 on Twin Falls tied the record for the date. 

On the 9th the ridge shifted farther inland. Clear skies, along with increasing sun angle and longer days, generated enough mixing to bring some of the warmer air aloft down to the surface. 

At Burns the highs of 57 on the 9th and 62 on the 10th set a new record for those dates.

Temperatures averaged right around normal through the 20th.

On the 19th an upper level trough moved down the coast from the Gulf of Alaska as an upper level ridge amplified south of the Aleutians. The trough arrived over the Pacific Northwest on the 20th. As it amplified southward over the western U.S. on the 21st, Arctic air east of the Rockies had already penetrated as far south as Nebraska. Farther west, a lobe of the same Arctic air was entering Washington from British Columbia. On the 22nd Arctic air from both sources converged over southwest Idaho. The resulting precipitation was hit and miss. Some valley locations received from 1 to 4 inches of snow.

The coldest temperatures of the month were recorded between the 21st and the 27th. 

On the 23rd the low of 0 at Burns set a new record for the date. The 10 at Twin Falls tied the record set in 2018. 

On the 25th the low of 7 at Twin Falls set a new record for the date,  and the low of 9 at Baker tied the record set in 1933. 

On the 26th the low of 0 at Twin Falls set a new record for the date. 

Temperatures gradually moderated as an upper level high pressure ridge moved inland. On the 28th highs were above normal. 

February 2022 precip anomaly February 2022 temp anomaly

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

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.

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.

 

 

October 2019 coldest on record in some places across SE Oregon and SW Idaho

Temperatures were well below normal during October 2019. Jerome, ID, Fairfield, ID, Burns, OR, Halfway, OR and Ontario, OR recorded the coldest October on record.  Fairfield, ID had snow cover at the end of the month, and shattered their previous October record by 5.6 degrees, finishing 10.3 degrees below normal for the month.  Idaho as a whole, ranked as the coldest October on record.

It was a dry month, with below normal precipitation across most of southeast Oregon and southwest Idaho.  But a few locations, mainly in Harney County, were actually wetter than normal.

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Baker City, OR ranked as 3rd coldest October on record.
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McCall, ID ranked as 4th coldest October on record.

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It was the third coldest October in 80 years of airport records, and 6th coldest on record at Boise. Temperatures averaged above normal on only five days.

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The low of 23 on the 10th eclipsed the old record for the date of 26 set in 1985.

The high of 35 on the 29th broke the previous record for the date of 37 set in 1991. It was also the coldest daily high temperature for so early in the season.

The low of 16 on the 30th tied the old record set in 1991. It was the coldest temperature since the 10 degrees on February 22, which was last winter’s low.

It was a dry month, tying 1965 as the 12th driest October in Boise Airport records. Measurable precipitation fell on only five days at Boise.

The unseasonable cold can be blamed on the persistent pattern of cold upper level low pressure troughs interspersed with cool northwest flow aloft.  The northwest flow was a result of a strong high pressure ridge off western North America, directing the storm track into Alaska.  Since most of the troughs came from northwest Canada and the cold waters of the Gulf of Alaska, they brought little moisture.

15

There were a couple of exceptions to the predominately cold and dry weather.

On the 15th an upper level high pressure ridge built over the western U.S. and southwest Canada. As the ridge drifted east on the 16th, temperatures rose to summerlike values in southwest Idaho. Boise, Jerome, and Twin Falls all recorded highs of 80 degrees under warm southwest flow aloft.

t2anom-mslp_na-lc_2019_d289

On the 19th a broad jet stream over the north Pacific pushed a fast-moving upper level trough inland across Idaho. There was enough moisture and energy with this system to generate thunderstorms with strong gusty winds. There were numerous reports of gusts over 50 mph. At some locations in the Magic Valley, including Twin Falls and Hazelton, gusts exceeded 60 mph.

Power poles were knocked down near Wendell and at Caldwell. Around 30 poles were knocked over along Highway 93 between Twin Falls and Jerome. At Kuna, several large trees were down, fences were blown over, cars were damaged, and power lines were down. Northeast of Boise in Ada County, lightning struck a house, causing a fire. Two people were injured.

And it snowed. McCall got 4 inches and Tamarack 6 inches. A spotter northeast of Featherville reported 7 inches that day.

Even more snow fell on the 20th.  Tamarack got an additional 4 inches, making their storm total 10 inches. Other storm totals in the mountains ranged from 6 inches at Mores Creek Summit to 12 inches at Atlanta Summit.

https://twitter.com/NWSBoise/status/1186319069416280064?s=20

Real winter cold arrived at the end of the month.

Winter weather arrived very early during the final week of the month.  By the 26th northwest flow aloft had transported cooler air from British Columbia to southwest Idaho.  From the 26th through the 28th, A very cold upper level low pressure trough moved from north of Alaska through central Canada to the U.S. Border, causing the flow over western Canada to strengthen and shift into the north.  Arctic air was on the way.  The arctic front passed Boise around 4 am on the 29th. Behind the front, very cold high pressure centers moving south on both sides of the Rockies caused northwest and northeast surface winds to converge over the Snake River valley.

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snowband10292019

The convergence zone approached Boise from the east later that morning, generating the first snow flurries of the season at the airport and in southeast Boise, while the sun shone on the rest of the city.  At the airport nearly half an inch of very dry snow briefly covered the ground.

t2anom-mslp_na-lc_2019_d303

Temperatures stayed well below normal through the 31st.  Here are some record temperatures during the cold spell.

October 29: lows…Burns 1, Ontario 15, Baker City 6.

October 30: high…Boise 35 (coldest high temperature for the date and so early in the season) lows…Boise 16 (tied 1991), McCall 4 (tied 1991), Ontario 9, Mountain Home AFB 9, Jerome 8, Baker City 4

Below are graphics of mean temperature percentiles and departure from normal across the Pacific Northwest for October 2019.

201910_pnw_cl (1)

201910_pnw_cl

Idaho as a whole ranked as the coldest October on record.

Capture

For more information about the U.S. Climate in October 2019, see Assessing the U.S. Climate in October 2019.

September 2019 Climate Statistics

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Unseasonably cool weather at the end of the month compensated for hot weather at the beginning and middle of the month, so the average temperature was exactly normal. Total precipitation was a quarter inch above normal.

It was wet nearly everywhere, with parts of Malheur County getting over three times normal precipitation.

Summer weather persisted through the first week of September, with a strong upper level high pressure ridge anchored over the western half of the nation.

A record high of 101 was set at Ontario on the 5th.

The 99 degrees on the 5th was the culmination of a streak of 9 consecutive days with highs over 90.

Airflow from the Desert Southwest brought enough monsoon moisture for isolated thunderstorms on the 5th and 6th. On the 6th, 0.15 inch of rain fell, exceeding our total summer rainfall by a hundredth of an inch.

Thunderstorms on the 5th was preceded by gusts over 55 mph near Swan Falls, in the Boise area, and at Glenns Ferry. In Boise, a microburst knocked down numerous trees from Broadway to Apple Street, some falling on houses. At Timberline High School fences were knocked down, and a batting cage was lifted over a baseball field fence and thrown into an adjacent parking lot.

On the 6th large tree branches were blown down near Buhl and at Glenns Ferry.

On the 8th a Pacific cold front dropped a third of an inch of rain at Boise. The .52 inch total at Mountain Home AFB set a record for the date.

On the 9th one-inch diameter hail fell at several locations near Twin Falls and Eden in Jerome County. Near Hansen in Twin Falls County 1.5 inch diameter hail was reported.

The upper level trough following the front kept temperatures a few degrees below normal through the 11th.

After the trough exited on the 12th, warm dry air south of the jet stream raised temperatures above normal. In the Treasure Valley the last 90-degree highs of the summer were recorded on the 14th and 15th. The 95 at Ontario on the 15th tied the record for the date set in 1956.

On the 16th an upper level trough from the Gulf of Alaska, followed by a second trough on the 19th, maintained cool showery weather through the 21st.

After the trough departed, temperatures were slightly above normal from the 22nd through the 27th.

During the early morning hours of the 28th, a strong cold front imported much cooler air from Alaska as a major upper level trough deepened over the northwest U.S. Temperatures averaged nearly 15 degrees below normal for the final three days of the month.

At Burns on the 30th the low of 23 tied the record set in 1981.

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August 2019 Climate Statistics

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Temperatures averaged slightly above normal. Measurable rain fell on 3 days, totaling 0.09 inch. August is normally the driest month of the year, averaging 0.24 inch.

Precipitation for June, July, and August totaled only .14 inch, making this the second driest summer on record at the airport.

A massive upper level high pressure ridge covering the west kept the first week of August hot. Temperatures at Boise topped out at 100 on the 5th and 101 on the 6th.

Southerly flow aloft brought enough monsoon moisture for light showers on the 2nd and again on the 8th, plus enough cloud cover on the 8th to prevent the temperature from reaching 90.

On the 9th and 10th, a low pressure trough which had resided off the West coast since late July moved inland. As the associated cold front interacted with the monsoon moisture, it triggered thunderstorms which produced light but measurable precipitation and gusty outflow winds. A gust of 40 mph was measured at the airport on
The 9th.

With a high of only 78, the 11th was the coolest day of the month, thanks to the north Pacific air which accompanied the trough.

Following the trough, highs were back in the 90s from the 13th through the 15th, and dry westerly flow aloft blocked monsoon moisture from invading southwest Idaho.

On the 16th and 17th, a weak cold front trailing south from a low pressure system over Canada lowered temperatures a few degrees.

The high pressure ridge expanded north again, and highs were in the 90s from the 18th through the 21st.

On the 22nd and 23rd, a Pacific cold front, followed by an upper Level low pressure trough from the the Gulf of Alaska, brought a trace of rain and kept highs from exceeding the 80s. A dry cold front followed on the 25th, keeping temperatures below normal through the 26th.

A warming trend commenced on the 27th as the high pressure ridge rebuilt and persisted through the end of the month, with temperatures around 10 degrees above normal.

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July 2019 Climate Statistics

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The average temperature for the month was less than one degree above
normal. No temperature records were broken, but the low of 76 on the
23rd tied the record high low for that date set in 1994.

At the airport, the only triple digit high was the 102 on the 22nd.
The normal for July is 4 days of 100 or higher. The normal for
summer (June-August) is 7. Last summer had 14, with 9 in July and
the rest in August, including the 110 on August 10.

Only 0.01 inch of rain fell at the National Weather Service office in Boise,
which ranks in the driest 15 percent of Julys.

July and August are normally the driest months, averaging 0.33 inch
and 0.24 inch respectively.

As is common at this time of year, upper level troughs from the
north Pacific weakened as they encountered the strong summer high
pressure ridge over the western U.S. The ridge diverted these
systems too far north to bring measurable rain to the Boise area.

Upper-level winds were usually from the southwest, with enough
westerly component to shunt monsoon moisture east before it reached
the Treasure Valley. When it did manage to drift this far north and
west, it usually brought only cloud cover, which hindered the
heating that drives convection, so only a few sprinkles resulted.

Weak cold fronts accompanying the Pacific systems were followed by
slightly cooler and much drier air. For example, the afternoon
humidity dropped to 7 percent on the 19th and 8 percent on the 24th
after frontal passages. On the other days minimum humidities were in
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Record February Precipitation in 2019

February 2019 precipitation ranged 200-300% of normal across southern and central Idaho, southeast Washington, and across eastern Oregon. Several places recorded their February precipitation record.

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McCall set the all-time precipitation record for February at 7.57″ (normal 2.42″). McCall set the all-time snowfall record for Feb at 74.0″ (normal 22.5″), the most in Feb since 1975 when 70.0″ fell. Records began in 1906. Courtesy of COOP observer.

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Boise set the all-time precipitation record for February at 3.71″ (Normal is 0.99″). Boise received 11.6″ of snow in February, the most in February since 1949 when 25.2″ fell. Records began in 1877.

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Baker City, OR and Ontario, OR both broke their all-time February records for precipitation. Burns, OR came in at 4th most all-time for February.

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Mores Creek Summit and Bogus Basin snow surveys reported the biggest change in snow depth and snow water equivalent in February since records began in 1942. 360-370% of normal.

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September 2018 Climate Statistics

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With only a trace of rain, September 2018 was one of the driest Septembers on record. There were only 9 others with no measurable precipitation in 152 years of Boise area records, and only 5 others in 78 years of airport records.

Total precipitation for the four months from June through September was only 0.36 inch. June-September periods with so little precipitation are unusual, but not unique. For example:

1994 .44
1901 .39
1898 .37
2018 .36
1957 .31
2012 .31
1933 .27
1966 .27
1935 .19

Temperatures averaged only slightly above normal.  September began with near normal temperatures under dry westerly flow aloft. The flow backed into the southwest on the 5th as a high-pressure ridge built over the northern Rockies. This resulted in the last 90-degree highs of the summer on the 5th, 6th, and 7th.

A cooling trend commenced on the 8th as an upper-level low-pressure trough from the Gulf of Alaska approached the British Columbia Coast. As the trough edged closer, a dry cold front passed Boise on the 10th, followed by cooler north Pacific air. Highs were only in the low 70s from the 11th through the 13th.

The trough remained parked over the west coast through the 18th, keeping temperatures a few degrees below normal. It finally moved inland on the 19th, then continued east out of our area on the 20th.

Brief warming followed on the 21st and 22nd, with highs in the low 80s, but another north Pacific trough was on the way.

Rather than stalling over the coast, this trough continued on an eastward track, pushed along by a building upper-level high-pressure ridge offshore. The trough was east of our area on the 24th. Like its predecessors, it produced no rain in the Boise area.

East of the ridge, northwest flow aloft over the Pacific Northwest states kept temperatures 5 to 10 degrees below normal, with highs of only 69 on the 24th and 25th, the first highs in the 60s since June 17. The low of 38 on the 24th was the first low in the 30s since May 2.

As the eastern portion of the ridge edged inland, warmer air raised temperatures above normal from the 27th through the 29th, with highs in the low 80s.

During that time, an upper-level low was drifting slowly eastward toward California. By the morning of the 30th, it was centered over the Oregon-northern California coast. Its only effect on Boise was a few clouds and slightly cooler temperatures.

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