Cold Outbreak

The first serious cold spell of the winter is now under way for Alaska, as strong northerly flow has brought cold air plunging down from the Arctic in the past day or so.  Temperatures have dropped below -40° at the usual cold spots, and Fairbanks airport is sitting around -30°F this morning for the first time since last January.

The immediate cause of the cold outbreak is a powerful high pressure ridge that ballooned up over the Bering Sea and far eastern Russia in the past couple of days, driving a sharp change to northerly flow over Alaska.  The shift in the flow pattern has been very dramatic: check out the 500mb flow change over Alaska from Thursday morning to this morning:

The north-south pressure gradient across Alaska is extreme today, with MSLP near 1040mb on the Beaufort Sea coast and near 980mb on the south coast of the Kenai Peninsula.  As a result, strong winds are producing ground blizzard conditions and nasty wind chill in exposed locations.

Remarkably, today's near-60mb north-south pressure difference is close to (or may be) an all-time record; here's a chart showing the annual maximum and minimum MSLP difference between Deadhorse and Seward, based on daily mean data.

The ERA5 record for the daily mean pressure difference is 55.8 mb on December 8, 1955.  I need to rerun the analysis using hourly data and compare it to today's conditions.  Note that very strong pressure differences like this are found in winter, when the jet stream is strongest and flow anomalies are greatest.

Looking ahead, there are strong signs that the Bering Ridge setup could have some serious staying power, judging from model forecasts.  For example, here's a diagram of 500mb heights averaged over the 50-80°N latitude band, with the time progression from top to bottom.  Look at the yellow/orange colors at the left and right sides in the forecast section (below the dashed line): the ECMWF model expects a ridge to persist near the Date Line all the way into mid-January.

This would mean persistent, significantly below-normal temperatures for southeastern Alaska and western Canada.  The CPC forecast is locked into this signal for their 6-10 day, 8-14 day, and week 3-4 forecasts:

Declining Alaska Observations

Yesterday UAF's ACCAP announced the results of a study evaluating the availability of weather data from FAA and NWS observing sites in Alaska:

https://uaf-accap.org/projects/alaska-weather-station-data-availability/

Unfortunately the results are not pretty: there has been a serious decline in availability of hourly weather data in recent years.  The number of sites reporting consistently on an hourly basis has dropped by about 40% in the last decade, and only 19 reliable FAA/NWS sites remain in off-road-network locations.  Check out the linked article for some striking graphics.

It's not difficult to observe the trend in the data.  Here's a chart for Utqiaġvik showing the percentage of days each year with temperature and wind data from at least 18 of 24 hours (not necessarily at the top of the hour):

Last year the observation reliability fell of a cliff, with virtually the entire summer missing data in the overnight period.  This year the same thing happened in March and April, but not in summer.

From a scientific standpoint it's a shame to see the lack of commitment to maintaining weather and climate monitoring with the FAA/NWS instrumentation, and from a public service standpoint it's bad news, as reliable real-time ground-level weather data is important for forecasting and decision making.

A significant counterpoint, however, is that NOAA's Climate Reference Network has expanded its coverage across Alaska in the last 20 years.  There are now 25 sites installed, and while several aren't reporting currently, the overall volume of data has become substantial in recent years.  The chart below shows the annual number of daily observations with maximum and minimum temperature across all the sites:

With the CRN sites being located preferentially in stable and often remote locations, and with high-quality instrumentation, the scientific value for long-term climate monitoring is potentially much higher than with airport instruments; but for real-time weather monitoring and forecasting, the CRN network can't replace the loss of FAA/NWS data in recent years.