U.S. Winter 2020-21 Heating Degree Day Pattern

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Fig. 1: The percent departure from normal of gas population weight HDD for the U.S. and regions of the U.S. in February 2021.

The winter 2020-21 U.S. gas population weight discussion: Of course, winter 2020-21 will be remembered for the February arctic outbreak. The U.S. gas population weight HDD during February was 892 which is 4th coldest since 2000. The coldest February since 2000 occurred during the “polar vortex” winter of 2014-15 when 954 HDD’s were observed. Not far behind was frigid February 2007 at 923 HDD’s and the first of two “polar vortex” winter seasons in 2013-14 produced 896 HDD’s. Not surprisingly, the region hardest hit in February was the Texas region where 137% of the 30-year normal HDD were observed (Fig. 1). The Upper Midwest and Ohio Valley were also quite cold. New England and the Mid-Atlantic region were not hard-hit by the arctic blast with marginally warm HDD’s for the month of February. If the Northeast U.S. was also hit by the Siberian Express in February a record cold month may have occurred.

Fig. 2: The U.S. gas population weight HDD observations (and March forecast) compared to the 10-year and 30-year climatology.

Fig. 3: Today’s U.S. gas population weight HDD forecast trends cooler for the first half of March since yesterday.

The winter 2020-21 U.S. gas population weight HDD observations by month identify interesting changeability (Fig. 2). The cold season started with a warm November followed by a December which was also warm coming-in near the 10-year normal. Mid-winter was very warm, almost as warm as November regarding the HDD departure. February is the only cold month of the season while March is projected warmer than normal. The tendency for extremes dominated as observed with a very warm November and January and a frigid February.

In the current forecast extending to March 12-18, 2021 the warm forecasts of this week have trended notably less warm overnight (Fig. 3). Lead by the European Ensemble the consensus forecast is on average about 10 HDD cooler for March 5-11 and March 12-18 compared to 24 hours ago.

Yesterday Climate Impact Company mentioned that an emerging Madden Julian oscillation phase_1 in the extended-range favored a cooler East regime. Not surprisingly, the extended-range forecasts ease back on the previous warm forecast for the East and the ECM Ensemble completely dissipates that warmth.