On December 17-18 2020, a 972 mb low in the Northern Gulf of Alaska brought heavy snowfall, winds gusting in excess of 60 mph, and wind chills approaching 30 below zero to the Richardson Highway through Thompson Pass.
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 AFC wrote it up.
On December 17-18 2020, a 972 mb low in the Northern Gulf of Alaska brought heavy snowfall, winds gusting in excess of 60 mph, and wind chills approaching 30 below zero to the Richardson Highway through Thompson Pass.
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 Anchorage, AK wrote its last area forecast discussion before the first event at Dec 17, 4:30 PM AKST, 4 hours 30 minutes earlier.
Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 430 PM AKST Thu Dec 17 2020 .ANALYSIS AND UPPER LEVELS... At 300 mb, a strong upper level jet remains in place south of the Aleutian Chain. An upper level trough over the Northern Gulf is anchored by a surface low centered south of Kodiak Island. This low gradually continues to track toward the northeast, spreading in cloud cover across Southcentral. Meanwhile out west, an upper level trough over the central Bering continues to lift northeastward. At the surface, a low centered just southwest of the Pribilofs is spreading clouds and precipitation across the central and eastern Bering. Light snow showers are falling across the northern Alaska Peninsula this afternoon. && .MODEL DISCUSSION... Model solutions are generally in good synoptic agreement for the immediate short term through early Friday. A key difference that arises in the upper levels Friday afternoon is the interaction between two upper level troughs over the Gulf. Right now the GFS continues to advertise these two troughs will phase, thus steering a surface low farther west over Southcentral. Meanwhile the NAM and Canadian models maintain two distinct upper level troughs, thus sending the bulk of the energy farther east. However, this was a recent development in the 18Z NAM, as the previous 12Z run was advertising these troughs phasing. This major difference will drive the track of the surface low into Southcentral. With this in mind, and given the drastic changes across run to run, forecast confidence remains low. By the weekend, models do seem to be locking onto a broad complex low over the western Bering very well with great synoptic agreement. && .AVIATION... PANC...North winds will continue through the evening hours. VFR conditions are expected overnight until midday Friday when MVFR ceilings are likely. && .SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Thursday through Saturday)... The area of low pressure we have been monitoring is currently east of Kodiak Island, moving towards the northern Gulf coast. Warm sea surface temperatures have kept Kodiak City as mostly rain, therefore, a wintry mix of rain/snow is anticipated as the backside of the low (and cold air) move over the area. As long as this low stays the course, there is a chance for a quick shot of snow for the Anchorage Bowl tomorrow afternoon/evening. Due to the intricate details of the low track, however, there is high uncertainty this will occur at this time. The Winter Storm Watch for Thompson Pass has been upgraded to a Blizzard Warning in effect from 9 p.m. this evening until noon tomorrow. Total snow accumulations of 4 to 8 inches, 50 mph winds and visibility to a quarter mile or less are expected. A foot of transportable snow on the ground combined with the aforementioned wind and new snowfall, will work together to keep visibilities at or below the quarter mile threshold. Following this low, models are all over the place with the formation of two upper level shortwaves and their phasing, or not phasing, together. The 12Z NAM and GFS phase these two together and spin up another low, heading west towards Southcentral. The Canadian, the EC and the 18Z NAM do not phase these two together, with the track of any low spun up clipping the southern Gulf and moving to the east. This accounts for uncertainty with the low possibly moving as far north as Kodiak Island or as far south as through the southern Gulf. All of these solutions have various potential impacts including: chances for snow in Anchorage Saturday, another round of wind/snow for Thompson Pass or no impacts whatsoever. For now, the GFS solution was preferred, but further refinement is necessary to really hone in on the details. && .SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Friday through Sunday)... A weakening low continues traveling eastward across the Southern Bering towards Bristol Bay through Saturday, pushing onshore by Sunday. Once it makes landfall the low fizzles out and becomes an open wave. On Friday, the front off the Bering low will push approach the Southwest coast, bringing a round of light snow showers to the coastal areas. QPF and accumulations are unimpressive so no significant amounts are expected. A second strong low enters the Western Bering Sunday morning. The associated leading front is expected to track across the Bering through Sunday night and reach the Southwest coast by Monday. This will be the next system of concern for the Southwest region and will be monitored over the next couple days. && .SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3: Friday through Sunday)... A weakening low continues traveling eastward across the Southern Bering towards Bristol Bay through Saturday, pushing onshore by Sunday. Impacts will be minimal with this, mainly looking at gales south of the low, weakening to small craft by tomorrow night. Tonight and tomorrow the low lingers briefly over the Pribilof Islands so consistent light rain/snow showers are expected during that time. By Sunday morning, the leading front of an incoming storm force low west of Shemya enters the Western Bering. This front will push across the Bering Sunday into Monday with a band of gales and precipitation, mostly rain and a rain snow mix. A brief period of storms are expected south of the Central Aleutians Sunday as well. && .MARINE (Days 3 through 5/Sunday through Tuesday)... Gulf of Alaska: There is high confidence an area of low pressure will exist over the Prince William Sound through Monday morning. Westerly winds up to 35 kts are possible but most of the Gulf will remain within small craft advisory criteria. On Monday afternoon there is high confidence a gale force front will move into the western Gulf where it will slowly move east at gale force through Tuesday. Long fetch southerly winds will result in waves greater than 20 feet. Bering Sea: A strong, complex low with multiple centers is expected to move into the western Bering on Sunday, moving slowly into the central Bering by Tuesday. There is high confidence the front will move across the Bering at gale force through Monday morning. Gales are expected to persist around the low with isolated areas of storms possible near the individual low centers. Forecast confidence is low in regards to the location of the meso-lows and therefore the area(s) of stronger winds. && .LONG TERM FORECAST (Days 4 through 7/Monday through Thursday)... A deep trough is expected to remain over the Bering Sea while a high amplitude ridge builds over western Alaska Monday and moves east over Southeast Alaska through Thursday. This pattern will result in active weather throughout the AOR. Over the Bering, a broad low with multiple centers is expected to persist through Thursday. The main feature for southern Alaska will be the large warm front expected to reach Southwest Alaska on Monday. The moisture feed extends down into the tropics, so moderate to heavy rain is possible for the AKPen and portions of Southwest. A transition to snow is likely over the interior but the exact location of the transition remains uncertain at this time. The front then reaches Southcentral on Tuesday, with rain likely over lower coastal elevations. The exact rain/snow line is uncertain at this time due to the large number of upper level and potential surface lows developing along the front. By Wednesday forecast confidence remains low; however, active weather should continue as Southcentral will remain in a region of upper level divergence and therefore favors storm development. && .AFC WATCHES/WARNINGS/ADVISORIES... PUBLIC...WSW 131. MARINE...Gales 119,120,131,132,170,173,35,352,413,414. FIRE WEATHER...NONE. && SYNOPSIS AND MODEL DISCUSSION...KO SOUTHCENTRAL ALASKA...CK SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KM MARINE/LONG TERM...CJ
1 blizzard. Local standard time, as filed.
The AK DOT RWIS site at Thompson Pass (Richardson Hwy MP 2) reported winds higher than 35 mph for a 26 hr period on Dec 17-18. While area SNOTELs indicated snowfall. With temperatures in the single digits, this also produced wind chills as low as 30 below zero.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Alaska in 2020Every state in 2020This day in weather historyWarnings in Alaska, 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: 932154.