February was colder than January for the third consecutive year. Normally December is the coldest month, with January half a degree warmer, and February about 5 degrees warmer than January.
With an average temperature of 36.9, winter (Dec-Feb) 2019-20 was the fifth warmest at the airport (80 years of records) and the eleventh warmest at all official observing locations in Boise (156 year of records). The season’s low was 16 on October 30 and January 15. The only other time the coldest “Winter” temperature occurred in October was in 2002, when the low was 13 on the 31st.
Snowfall for the season so far has been 15.4 inches, compared to the normal of 17.6 inches for October through February.
On the 1st an upper-level high pressure ridge kept temperatures above normal. A cold front passed Boise just after midnight that night. Northwest winds gusted to over 30 mph just behind the front. The strongest gust was 38 mph at 10:26 am MST on the 3rd. An upper-level low pressure trough, followed by northerly flow aloft, kept temperatures below normal from the 2nd through the 5th.
On the 5th and 6th a warm front, which had entrained tropical moisture from east of Hawaii, brought nearly half an inch of precipitation over the two-day period, including nearly 3 inches of snow ahead of the front on the 5th.
Impressive stream of moisture has led to heavy precipitation over the the mountains of the Pacific Northwest the past 48 hours. #PineappleExpress #AtmosphericRiver #orwx #idwx pic.twitter.com/5q4MN1Rv2u
— NWS Boise (@NWSBoise) February 6, 2020
The central Idaho and northeast mountains had 36+” of snow with this system.
Impressive snowfall @BrundageMtn since Wednesday with 39.5"! #idwx #orwx pic.twitter.com/6mTSgbSje4
— NWS Boise (@NWSBoise) February 7, 2020
Here's an analysis of 72-hr snowfall (ending this afternoon) over the region. There are large areas that got over 36" of snow in just 72 hours! #orwx #idwx pic.twitter.com/Q1jLmHwJPt
— NWS Boise (@NWSBoise) February 8, 2020
Following the warm front, temperatures stayed above normal starting on the 6th under the influence of an upper-level high pressure ridge parked off the west coast. The ridge moved inland on the 12th and 13th, followed by fast and relatively mild westerly flow aloft on the 14th and 15th.
On the 16th a very moist disturbance embedded in the westerly flow brought a record amount of rain, most of which fell between 12:30 am and 12:30 pm MST. A cold front crossed the Boise area at about 12:45 pm MST, ending the main rain event. Unstable air behind the front set off a brief thunderstorm with small hail around 3:30 pm MST. The total precipitation of.53 inch set a new record for the date, exceeding the previous record of .40 inch in 1976.
340 PM – Showers with small hail are moving through portions of the Treasure Valley. #idwx pic.twitter.com/nmFNmVlrsT
— NWS Boise (@NWSBoise) February 16, 2020
Temperatures stayed below normal from the 17th through the 21st due to northwest flow aloft and cool surface high pressure.
A brief warmup followed on the 22nd and 23rd ahead of a strong cold front. The front crossed the Boise area at 6:19 pm MST on the 23rd with only a trace of rain. The main impact was strong north-northwest wind which gusted to 48 mph at the airport at 6:46 pm MST. Temperatures stayed below normal through the 25th.
Temperatures gradually warmed from the 26th through the 28th as an upper-level high pressure ridge crossed the intermountain region. The high for the month was 63 on the 28th.
Temperatures will be around 20 degrees above normal today! The next weather system will bring cooler temperatures and snow flurries to the mountains on Saturday. #idwx #orwx pic.twitter.com/bNdZ0xpBDb
— NWS Boise (@NWSBoise) February 28, 2020
A dry cold front moved through early on the morning of the 29th, and the high that day was 15 degrees cooler. Here are the climate graphics for selected cities across southeast Oregon and southwest Idaho.