Another Big Anchorage Snowfall
Another Big Anchorage Snowfall
Fourth Major Storm Past Two Years
The Anchorage area received very heavy snowfall November 8ᵗʰ and 9ᵗʰ, 2023, making this the third time in the past 12 months and the fourth time since March 2022 with more than a foot of snow in a single storm (my posts about the December 2022 storms here and here).
Snow totals
As usually happens, there was a wide range in snowfall totals in the metro Anchorage area, with the lower amounts in West Anchorage and higher amounts east of the Seward Highway, and the highest amounts on the Hillside. Many of the final total snowfall reports are plotted in Fig. 1. In order to get as many observations as possible to plot I’ve made the font size small, but hopefully it’s clear enough to tell the story (clicking on the image should make it a bit larger). These observations are from a variety of sources and are mostly “unofficial but reliable”. Because temperatures were near freezing the entire event, there was considerable compaction and so some of the differences in adjacent observations may merely reflect how soon after the snow ended that the observations were made. Elevation is often a significant factor in Anchorage area snowfall, but as the precipitation remain all snow in this event elevation was a secondary influence in this storm.
Figure 2 nicely illustrates the heavy snow in south Anchorage at an elevation of about 750 ft (230 m) MSL. Nearly all of this 28 inches (71cm) of snow fell between 8am AKST November 8ᵗʰ and 3pm AKST November 9ᵗʰ.
Meteorological setting
The weather set-up that produced this event was a classic for heavy snow in Anchorage, with the surface low pressure track from the the Gulf of Alaska northward through Prince William Sound. This track means there’s no downsloping winds from the Chugach Mountains into the Anchorage bowl to limit precipitation and there’s less chance for above freezing air aloft to be wrapped in from the southeast and change snow to rain. Figure 3 presents the surface weather analysis valid for 3pm AKST November 8th, showing complex and strengthening low pressure and associated fronts in the northern Gulf of Alaska, and importantly for Anchorage, a trough extending into Prince William Sound.
Climate perspective
From the climate perspective, this storm was especially notable for its occurrence so early in the season. From Anchorage Airport observations,1 only two other snowstorms earlier in the season saw accumulations exceed 12 inches (30cm): October 7-8, 1982 (12.2" inches, 31cm) and the October 12-13, 1996 storm, which with 17.6 inches (45cm) remains the highest early season snowfall on record.
A foot or more of snow in a single storm at Anchorage Airport is unusual. Since the winter of 1953-54, there have been 32 separate storms that produced 12 inches (30cm) or more of snow in two days or less. That's an average of less than once every two years. But there have now been four such storms in the past 20 months:
March 5, 2022: 12.2" (31cm)
Dec 5-6, 2022: 12.2" (31cm)
Dec 11-12, 2022: 16.2" (41cm)
Nov 8-9, 2023: 17.2" (44cm)
While in one way this is just random variability, e.g. calendar year 1996 had four separate 12 inches plus storms, in another way this is completely consistent with what we expect to happen in a warming world: warmer air can hold more water vapor, and when storms come along that can convert that into precipitation, the result is bound to be more precipitation. And in climates (like Anchorage) where typical cold season temperatures are still significantly below freezing, even with above normal temperatures, like three of four most recent events, big snowstorms are bound to happen.
Historic level snowfall in the eastern Chugach Mountains
This storm also produced one of the highest single event snowfall totals ever reported in Alaska. Around Prince William Sound there was very little snow near sea level: the cooperative observer at Valdez reported over 3.5 inches (90mm) of precipitation but nearly all of the that came as a cold rain, with only 0.2 inches (0.5cm) of snow. The Sugarloaf Mountain SNOTel above the Alyseka Pipeline Terminal at about 500 ft (165 m) MSL reported over four inches of precipitation but only a two inch snow depth increase. Both the Esther Island (east of Whittier) and Tatitlek (south of Valdez) SNOTels reported several inches of precipitation with temperatures in the 30s and 40s, and the Esther Island snow depth sensor reported no change (Tatitlek does not have a snow depth sensor).
It was different story out the Richardson Highway east and northeast of Valdez, where the roads weaves through the Chugach Mountains before dropping down into the Copper River basin. The Alaska Department of Transportation and Public Facilities reported 48 inches of snow near the top of Thompson Pass (elevation 2700 ft, 820 m MSL) as of 5pm AKST November 8, and it’s quite likely more snow fell after that. The bigger news though was even more extreme snowfall east of the Pass.
The Anchorage National Weather Service Forecast Office issued a storm report with some details of the snowfall at Richardson Highway Mile 46, elevation about 1150 ft (350m) MSL. An Alaska DOT highway maintenance station is located here. Summarizing the NWS report shown in Fig. 4: 72 inches (183cm) of snow fell midnight to 730pm Wednesday November 8ᵗʰ and a storm total of ~87 inches (221cm) by 7am Thursday November 9ᵗʰ. Now you might reasonably wonder if this is credible or if maybe some exaggeration is involved. But considering the larger scale weather set-up and that this is the same area that reported 78 inches (198cm) of snow on February 7, 1963, (the Alaska record for one-day snowfall), this report seems quite plausible to me.
There are also two SNOTel stations in the Thompson Pass area (southwest of Richardson Highway Mile 46). Both the higher elevation Nick’s Valley and the lower elevation Upper Tsaina River stations reported snow depth increases of 48 inches (122cm) during the storm.
Technical details: Storm snow totals from:
NWS Anchorage Local Storm Reports, readily accessible from the Iowa Enviromental Mesonet here.
CoCoRaHS here:
Natural Resources Conservation Service SNOTels (snow depth changes only) here.
NWS Ocean Prediction Center Alaska/Arctic Analyses here, although online analyses are only available back 15 days.
Anchorage has been Alaska’s most populous city since World War 2 but the area is a climate observation desert: International Airport is the only place within 30 miles of downtown Anchorage with 50 years or more of climate observations. Because of the strong influence of Cook Inlet waters and mountains immediately to the east and on the west side of Cook Inlet, dramatic differences in precipitation and snowfall in very short distances are the rule.
I've been wondering about climate change, air moisture and the future of big snow in Anchorage. Amongst all the other great information, thank you for covering that aspect.