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

Winter 2019-2020 in Review

Winter 2019-2020 was much warmer than normal, with the greatest departures in the western portion of our County Warning Area (CWA). The average temperature for December through February at Ontario, Oregon was 7.4 degrees above normal, making it their third warmest winter on record. 

Snowfall was generally below normal, mainly because of the unusually warm temperatures, but below-normal precipitation in some areas also played a part.

Most of our forecast area had near normal precipitation for the season. Camas, Twin Falls, Gooding, and Jerome Counties, and the Owyhee Mountains, were drier than normal. Southern portions of Harney, Malheur, Owyhee, and Ada Counties were wetter than normal, as was Baker County, with the notable exception of the Baker Valley, which was significantly drier than normal.

One of the large-scale controlling mechanisms for winter weather in the Northern Hemisphere is the Arctic Oscillation (AO). It is characterized by a counterclockwise circulation of winds around the Arctic, centered at about 55 degrees north latitude. This winter it was in its positive phase, meaning that the winds were strong and consolidated.  This tends to hinder arctic air from moving south into the lower 48 states.  Most of this winter the AO was strongly positive, especially in January and February.  In fact it set all-time records twice in February.  

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New Daily Records

Dec 21 – McCall – record high temperature of 43 (old record 42 in 1906)
Dec 22 – McCall – record high temperature of 48 (old record 46 in 1940)
Jan 26 – Boise – record rainfall of .74 inch (old record .40 inch in 1970)
Feb 5 – Boise – record snowfall 2.6 inches (old record 2.1 inches in 1948)
Feb 5 – Baker City – record rainfall of .25 inch (old record .16 inch in 2010)

December

Temperatures were relatively mild, especially in the Treasure Valley. Ontario had its sixth warmest December on record. Baker City had its eleventh warmest. 

Aside from portions of Harney County, most of our CWA was drier than normal. Factors contributing to the precipitation deficit included a split in the jet stream, leaving our area between northern and southern branches. Most of the Pacific moisture moved south over the southwest states instead of east over our area. During periods of west or southwest flow over our CWA, some valleys were in the precipitation shadows of mountain ranges. This effect was especially pronounced at Baker City and Mountain Home, downwind from the Elkhorn and Owyhee Mountains. However,  precipitation at McCall was enhanced by lifting over the higher terrain to their east. 

Despite widespread below-normal precipitation, there were several storms which produced significant snowfalls. 

On the 1st and 2nd, 5 to 10 inches of snow fell in southeast Oregon and the mountains of southwest Idaho. Amounts were lighter in the Treasure and Magic Valleys, where only 1 to 3 inch amounts were reported.  

On the 8th, heavy snow fell in the mountains of Baker County Oregon and the west central Idaho and Boise Mountains. The greatest reported amount was 13 inches at Atlanta Summit and Deadwood. 

On the 12th, Bogus Basin received a 9-inch snowfall. Tamarack ski area got 14 inches, and Brundage accumulated 12 inches. The heaviest amount was 15 inches at Mores Creek Summit. 

From the 13th through the 16th there were relatively light amounts of snow across most of the area. Exceptions included 7 inches near Frenchglen in Harney County, 12 inches east of Three Creek in southern Twin Falls County, and 8 inches near Murphy Hot Springs in Owyhee County, all on the 14th. 

On the 19th, 6 inches was measured at Council in Adams County and at Placerville in Boise County, while 9 inches fell at Bear Saddle Snotel in Washington County.

On the 20th, 8 inches fell east of Meadows in Adams County and at Halfway in Baker County. Tamarack in Valley County picked up 11 inches. 

December 2019 precipitation

December 2019 temperature

January

Temperatures were above normal across nearly all of our CWA, and much above normal in the Treasure and Magic Valleys and southern Malheur County. Boise was +6.2° F above normal for the month – making it the fifth warmest January on record.

Strong westerly flow aloft maintained a progressive pattern which brought Pacific weather systems across our area at frequent intervals. This hindered the formation of long-lasting temperature inversions and discouraged arctic air from pushing south.

A persistent ridge of high pressure off the California coast steered storm systems, including a series of atmospheric rivers, into the Pacific Northwest. Atmospheric rivers are long narrow streams of air carrying large amounts of moisture. They are responsible for most of the water vapor transport outside the tropics. 

Most of our region was wetter or much wetter than normal. The mountains of central and northern Idaho and northeast Oregon saw a significant improvement in snowpack. 

Snow fell nearly every day in the mountains.

A storm on New Year’s Day dropped heavy snow on the mountains of Baker County and central Idaho. Storm totals included 14 inches at Tamarack and McCall, 15 inches at Brundage, and 5 inches at Bogus Basin. 

Strong winds were reported at many locations that day, including gusts of 67 mph  east of Van in northern Harney County, and 65 mph south of Rogerson in Twin Falls County. Elsewhere, gusts of 45 to 55 mph were common.

From the 9th and 14th, snowfall was heavy in the mountains. Even in the lower valleys moderate amounts fell. 

A storm total of 18 inches was reported at Centerville in Boise County.  In Valley County storm totals included 23 inches near Donnelly, 17 inches at Yellow Pine, and 9 inches at Cascade. In Baker County Halfway’s total was 17 inches. Featherville in Elmore County accumulated a total of 36 inches. 

Total snowfall at Boise for the six days was 8 inches, more than half the total this winter. The most on the ground was 4 inches on the morning of the 15th. 

A couple of places reported strong winds on the 14th, including a gust of 63 mph at Rome in Malheur County and 58 mph at Twin Falls.

January 2020 precipitation

January 2020 temperature

February

February was colder than January at several locations. Normally  February is around 5 degrees warmer than January. Still, Februrary was warmer than normal across most of our area. 

On the 5th and 6th a warm front, which had entrained tropical moisture from east of Hawaii, brought heavy snow to the mounains and moderate amounts of rain and snow to the valleys. 

In Baker County, 7 to 8 inches of snow fell near Baker City, and 12 inches was measured at Sumpter.  In Valley County 17 inches fell near McCall and at Yellow Pine. Near Donelly 9 inches was reported. In Adams County New Meadows got over 25 inches. The storm total at Brundage was 40 inches. 

A storm on the 16th dropped 4 to 5 inches of snow on Boise County. McCall received only 3 inches. Rain fell in the lower valleys. By far the greatest reported amount was 0.53 inch at Boise, which set a new record for the date.

During the afternoon and evening of the 23rd, gusty northwest winds followed a strong cold front. Some the the stronger gusts reported included 67 mph at Baker City, 77 mph at Wagontire in Harney County, 67 mph at Midvale Hill in Washington County, 53 mph at Burns in Harney County, 56 mph at Black Canyon in Payette County, and 65 mph near Hammett in Elmore County.

February 2020 precipitation

February 2020 temperature

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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June 2019 Climate Statistics

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It was the second driest June at the Boise Airport, where records go back to 1940. It was the fourth driest June at all Boise locations going back to 1864. Measurable rain fell on only two days.

The average temperature for the month was very close to normal.

June began with above normal temperatures, with highs in the 80s under an upper level high pressure ridge.

On the 7th a pacific cold front, followed by an upper level low pressure trough, brought a brief break in the warm weather. Highs were only in the lower 60s on the 7th and 8th.

By the 10th temperatures had risen above normal again as another high pressure ridge began to build over the west coast. Highs were in the 80s from the 10th through the 19th, with the exception of the 91 on the 12th. That was the first 90 degree reading since September 7.

Following the 80 degrees on the 19th, much cooler air spread south following a cold front as an upper level trough deepened over southwest Canada and the northwest U.S. Highs were only in the mid 60s on the 20th and 21st.

After a chilly 42 degree low on the 22nd, temperatures began a slow recovery as the trough exited to the east. By the 25th milder west-southwest flow aloft had returned temperatures to near normal.

On the 26th an upper level trough from the Gulf of Alaska had arrived off the Washington-Oregon coast. Coming from the cold waters of the northeast Pacific, it contained little moisture.

Ahead of the trough, southwest flow aloft helped the temperature warm to 89 on the 26th.

As the trough edged further east that day, thunderstorms developed in northeast Oregon along a weak cold front. But they never got as far as Boise, and that night the front produced no precipitation as it crossed southwest Idaho.

The trough gradually weakened and moved offshore. It continued to have little effect on our area, although on the 28th a stationary band of dense high clouds prevented temperatures from rising above the lower 70s.

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May 2019 Climate Statistics

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It was the wettest May since 2005, and the 6th wettest on record, with a total of 3.98 inches. In addition, the period from January 1 through May 31 is the wettest on record at the Boise Airport, at 12.07 inches. It ranks in second place for the entire period of record in the Boise area (behind 1896 at 14.27 inches), and even exceeds Boise’s average annual precipitation of 11.73 inches.

No rain fell during the first two weeks of the month. During the rest of the month most days had measurable rain.

Northwest flow aloft kept temperatures below normal for the first two days of the month. A warming trend began on the 3rd as a warm upper level high pressure ridge centered offshore began to extend its influence inland. The ridge kept our area warm and dry as it moved inland over the next several days. By the 15th it was east of the Rockies, and a Pacific cold front was approaching.

Unseasonably cool and wet weather followed the front on the 16th as an upper level trough settled over the inter mountain region, where it remained for the rest of the month. The moist and unstable air provided favorable conditions for daily rounds of showers and thunderstorms, some of which produced locally heavy showers.

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September 2016 Climate Stats at Boise

Sept2016
September’s average temperature was slightly below normal due to cool upper-level troughs which dominated the inter-mountain region for most of the month.

Highs were only the 60s on six days.  The high of 63°F on the 14th was the coolest day since June 15.

A very warm upper-level ridge built over the region on the 25th and 26th, bringing Boise the highest temperatures of the month.  The 93°F on the 28th was only two degrees shy of the record for that date.

As the ridge moved east on the 29th and 30th, southwest flow aloft on its western flank, combined with southeast surface winds, continued the warm weather.

Precipitation was one third of normal. For most of the month, Boise was on the western margin of moist air moving up from the south, so upper-level troughs interacting with this moisture dumped most of their rain on south-central and southeast Idaho.

Locations east of Boise received substantial monthly precipitation totals, ranging from just under an inch at Mountain Home to over two inches at Twin Falls and Pocatello, much of that from the 21st through the 23rd.

August 2016 Climate Stats at Boise

AUG2016

August 2016 was dry and seasonably warm, with the average temperature within one degree of normal. There were no record high or lows set.  Only traces of rain fell at the airport. That’s not unusual, because August is generally the driest month at Boise.  Historically at Boise, 25% of Augusts had no measurable rainfall and 50% had no more than a 0.10″.

Weather patterns were typical of this time of year. Pacific systems were relatively weak, mainly moving inland north of our area with precipitation confined to northern and central Idaho and adjacent sections of eastern Washington, northern Oregon, and western Montana.  But even those areas were drier than normal, and little if any rain fell on southwest Idaho.

Incursions of monsoon moisture were usually deflected to the east ahead of trailing pacific cold fronts, so measurable rain from that source came no closer than the Nevada border and eastern Idaho.

At the Boise Airport, where records go back to 1940, June-August 2016 ranked among the driest 15% of summers.

July 2016 Weather Stats at Boise

JUL2016

July 2016 was the first month with below normal temperatures since November 2015. Although July’s average temperature and total precipitation were close to normal in Boise, it was an unusual month.  The average temperature of 75.4°F was the lowest July average since 2001.  The low temperature of 47°F on July 11th was the coolest July temperature in Boise since 2000.  The high temperature of 69°F on July 10th was the coolest July daily high temperature since 2001.  The hottest day of July 2016, 101°F on the 27th, was the lowest monthly July maximum since 1997. There were no record daily high or low temperatures set in July 2016.  A daily precipitation record was set on July 10th, when the total rainfall of the month fell (0.27in) in one day. Even heavier amounts were measured elsewhere in the Boise area, including 0.76in at Eagle and 0.61in at Meridian and over an inch was measured in surrounding areas.