January Climate Review, Part 2
January Climate Review, Part 2
Precipitation, Snow and Sea Surface Temperatures
This is the second installment of the January 2023 climate review. Part 1, Temperatures and sea ice is here and has been updated since first published on February 1.
Precipitation
Precipitation varies greatly over short distances, even after accounting for huge range in climatology: NOAA published normal precipitation in January for places near sea level ranges vary by more than a factor of 100: from 0.15 inches at Kuparuk (North Slope, Prudhoe Bay area) to 28 inches at Little Port Walter (Southeast, Baranof Island).
With that in mind, Fig. 1 shows the January percent of average precipitation from the ERA5 reanalysis courtesy of ECMWF/Copernicus. Shows significantly higher than average preciptation across much of the North Slope and eastern Interior. Remember though that because normals are quite low in these regions, 1.5 to 2 times normal is still not a lot in absolute terms. Southeast was, overall, wetter than normal too. The Bering Sea coast and Aleutians had less precipitation than usual, while Southwest and Southcentral Alaska saw mixed departures.
At the station level, the only really outstanding monthly total was at Eagle, where the NWS cooperative observer reported 1.60 inches precipitation for the month, the second highest January total on record (only 1963 with 1.63 inches higher). Climate observations at or very near Eagle have been made since the Gold Rush Days but there are several multi-year gaps.
Snowfall
Snowfall as conventionally reported in the US is the solid depth of snow that falls over a given time. Think of this as “how much snow you have to brush off your car each morning” (assuming no melting or wind). The relationship between precipitation and solid depth of snow is often expressed as a ratio, expressed in the conventional maxim of “1 inch of rain equals 10 inches of snow”. Typically in meteorology/climatology this is expressed the other way around, so “10 inches snow equal 1 inch of water”. In reality, this for any given event this ratio is dependent on many factors, including in-cloud temperatures, winds and, if it’s above freezing, temperatures below the cloud base. As a result, real world ratios for all-snow precipitation events vary from maybe 5 to 1 (basically falling slush) to 50 to 1, or even higher with very low precipitation events.
While the number and distribution of locations reporting daily snowfall in Alaska decreased dramatically in the past 30 years, from the observations at are available, the highest snowfalls in January were 51.8 inches at Annex Creek (Taku River east of Juneau) and 48.2 inches at Valdez. Both these are below normal. Relative to normal, Eagle was the most outstanding report: 27.7 inches of snow is the highest January total on record, easily exceeding the 23.0 inches in January 1929.
Figure 2. shows the ERA5 water equivalent of the precipitation that the ERA5 “thinks” fell as snow in January, as a percent of the 1991-2020 average. For most land areas away from the coast in January this is functionally the same as Fig. 1, since rain is extremely rare in January. However, southern coastal areas, the Alaska Peninsula, Aleutian Island and Southeast Alaska, where rain is a normal part of the January climate, there are some big differences. Southeast Alaska is especially notable: total precipitation was generally above normal, but the amount of that which fell as snow was near normal along the Canadian border to much less the below normal on the outer coast.
Sea Surface Temperatures
Sea surface temperatures in January south of sea ice edge in the Bering Sea were warmer than normal. This is quite a different pattern than last winter, when the “warm” water was largely confined to southwest Bering Sea.
Gulf of Alaska sea surface temperatures were very close to average north of 54°N.
Technical details: Precipitation and snowfall analysis spatial maps from ERA5 reanalysis data from ECMWF/Copernicus. Note that ERA5 does NOT ingest any in-situ direct precipitation or snowfall observations. Sea surface temperatures from NOAA 0.25 degree daily Optimum Interpolation Sea Surface Temperature (OISST) version 2.1.
The below normal temperatures in the northern Bering Sea are largely an artifact of 1) the natural lower limit of sea water temperature that isn’t ice (-1.8C) and 2) this particular database and how it handles water temperatures in ice areas.