Medium-range Forecast Verification of North America Temperature Forecasts Too Cold So Far in 2021

Northern Hemisphere Late Winter Arctic Air Masses
02/01/2021, 12:31 pm EST
January 2021 Global Soil Moisture Outlook
02/05/2021, 8:17 am EST
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Fig. 1: U.S. gas population weight HDD forecast from overnight using all models, their consensus and comparing vs. the 30-year/10-year normal.

HDD discussion: Natural gas market prices are on the rise again as overnight models indicate the incoming cold pattern achieves a stronger East (where high-demand consumption is located) signature. The U.S. gas population weight HDD forecast is MUCH colder for the middle third of February overnight (Fig. 1). The forecast is also colder for the week (beginning today). The peak of winter 2020-21 cold for the U.S. is obviously next week. Note the ending of the big chill for the week of Feb. 19-25.

Forecast error: The colder overnight trend is reasonably confident but has potential for changes over-the-weekend. Why? Take a look at the average temperature error the past 30 days by the GFS for days 6-10 (Fig. 2) and days 11-15 (Fig. 3). The bias is clearly too cold in west/central portions of Canada. This region is where arctic air tends to pool and also a cold zone during a La Nina climate. Clearly, the GFS has forecast this zone consistently too cold. That’s the problem forecast arctic air regimes. Arctic air is 15F to 40F colder than normal. If the arctic air fails to emerge or is delayed and temperatures are close to or warmer than normal instead a LARGE forecast error emerges.

Fig. 2-3: GFS days 6-10/days 11-15 temperature error for the past 30 days.

Fig. 4: NOAA/NWS weather watch, warning and advisory areas.

Setting the stage for cold: Setting the stage for cold…increasing snow cover. Nowadays, snow cover is the be all-end all for any chance at cold weather. Across the northern U.S. snow cover has been increasing of late and that trend will continue. Currently, Winter Storm Warnings for heavy snow and Winter Weather Advisories for moderate snow are in effect for 19 states (Fig. 4). The southern edge of the cold air mass is indicated by high wind with arctic air across the northern Great Plains. In stages, these conditions will spread south through next week.