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.
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:
Mountain Home .09
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.
Check out this monster blocking high pressure off the West Coast that is directing the jet stream up into Alaska and down into the Western U.S. The lack of clouds underneath this high pressure, shows the anomalous strength. #idwx #orwx #wawx pic.twitter.com/VdcbTuefw4
— NWS Boise (@NWSBoise) December 28, 2021
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.
Before and after in Placerville pic.twitter.com/qCuK3Wtk4i
— Gary Salzman (@gsalzman) December 29, 2021
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.
— NWS Boise (@NWSBoise) January 3, 2022
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
Idaho Falls -13
Mountain Home 2
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.
— NWS Boise (@NWSBoise) January 5, 2022
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
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.
— Stef Henry (@stefferology) January 20, 2022
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.
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.
At the Boise Airport, it has been the driest February on record at 0.08". If Baker City does not reach 0.10" today, they will also have the driest February.
— NWS Boise (@NWSBoise) February 28, 2022