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.
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.
— NWS Boise (@NWSBoise) June 8, 2020
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).
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.
⚠️Severe Thunderstorm Warning for NE Harney County & SW Washington County until 5:00pm PDT/4:00pm MDT. 1" hail and wind gusts to 70 mph possible in the core of these storms. #orwx #idwx pic.twitter.com/5wVzX726GL
— NWS Boise (@NWSBoise) June 24, 2020
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).
Also on the 29th, the low of 41 at Twin Falls set a new record low for the date.
— NWS Boise (@NWSBoise) July 2, 2020
— NWS Boise (@NWSBoise) July 2, 2020