A shortwave trough ahead of the main upper low off the coast of Oregon tapped enough moisture for heavy snow across parts of Eastern Oregon.
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Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS BOI wrote it up.
A shortwave trough ahead of the main upper low off the coast of Oregon tapped enough moisture for heavy snow across parts of Eastern Oregon.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Boise, ID wrote its last area forecast discussion before the first event at Dec 30, 9:31 AM MST, 29 minutes earlier.
Area Forecast Discussion National Weather Service Boise ID 931 AM MST Wed Dec 30 2020 .DISCUSSION...Our next weather system is starting to make its presence felt with light snow falling across lower valleys. Snowfall will increase tonight into Thursday morning with lower valleys seeing 1 to 2 inches. A brief break for New Years day ahead of a series of systems that will impact us beginning Saturday. No updates expected at this time. && .AVIATION...generally VFR near BOI MUO TWF and JER through 03z/Thu, with MVFR to IFR in snow showers north of a line from BNO and BOI. Mountains obscured. MVFR-IFR snow showers increasing across the rest of the area after 03z/Thu. Surface winds: east-southeast 5-15kt, strongest near BOI and BKE. Winds aloft at 10kft MSL: W-SW 30-45kt becoming NW 15-25kt by 12z/Thu. && .PREV DISCUSSION... SHORT TERM...Today through Friday night...Fog has lifted to a low stratus deck in most areas, while higher clouds are spreading in from the northwest ahead of the next Pacific storm. Models develop light snow across northern areas this morning and southern areas this evening as a Pacific upper trough comes in from the northwest. The system will spread enough snow for a low-end winter weather advisory today and tonight in Baker County, the West- Central Idaho Mountains, and Upper Weiser River Valley. Southern areas will get accumulations tonight and early Thursday ranging from around an inch in the Treasure Valley to near two inches in the Western Magic Valley. Southeast Oregon should get less than one inch, except in the mountains where up to 3 inches will fall. Same amounts for the southwest Idaho Highlands and Owyhee Mountains. Clearing Thursday night (New Years Eve) but patchy fog forming in the valleys during the night and New Years morning. New Years morning will be mostly sunny but clouds will spread in from the west New Years afternoon, with light snow in northern areas Friday night. Daytime high temperatures will be near normal through Friday but nights will be milder than they have been. Light winds through Friday night. LONG TERM...Saturday through Wednesday...An active pattern will continue, with westerly flow aloft bringing weather systems inland across our area at about 24-hour intervals. Models show most of the precipitation falling Saturday night and Sunday, with snow levels around 4000 feet, and Monday night and Tuesday, with snow levels closer to 3000 feet. Relatively mild Pacific air will keep temperatures 5-10 degrees above normal, with Sunday the warmest day. && .BOI WATCHES/WARNINGS/ADVISORIES... ID...Winter Weather Advisory until 2 AM MST Thursday IDZ011-033. OR...Winter Weather Advisory until 1 AM PST Thursday ORZ062. && www.weather.gov/Boise www.facebook.com/NWSBoise www.twitter.com/NWSBoise DISCUSSION...JC AVIATION.....KA PREV SHORT TERM...LC PREV LONG TERM....JT
The national radar mosaic for the moment the first event began.
1 heavy snow. Local standard time, as filed.
The COOP observer at Halfway, OR reported 6 inches of new snow at 6:00 PM PST, on the 30th and 3 more inches overnight while reports of 6 to 9 inches were received from the public and social media around Baker County.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Oregon in 2020Every state in 2020This day in weather historyWarnings in Oregon, December 2020
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 934567.