Charts of the day: Sharply less cold HDD forecast and why.
Discussion: The U.S. gas population weight HDD forecast has shifted moderately less cold for next week, which is the cold week in the upcoming colder pattern change. However, the Feb. 3-9 cold forecast from 48 hours ago is now producing a sharp reduction in HDD. The forecast is still colder than normal but nowhere near the previously indicated extreme. In the 5-day forecast, ECM demonstrates a developing cross-polar flow at 500 MB and at the surface which brings an extremely narrow channel of arctic air into North America. The polar vortex strengthens and causes a cold release into the U.S. However, in the medium-range, the cold northerly flow in the mid-troposphere and at ground level is cutoff by milder Pacific influence which subtracts the cold sting from the previous forecast.
Medium-range 6-10 Day Forecast Valid January 31-February 4, 2023 (24-hour change)
Discussion: A very cold forecast remains for the West and Central U.S. with a colder trend for the Northeast. However, the arctic sting is subtracted from the forecast consequently the extreme cold character of previous outlooks eases.
Medium-range 11-15 Day Forecast Valid February 5-9, 2023 (24-hour change)
Discussion: As previously indicated, there is an increasing Pacific component to the upper air flow for the first third of February which limits the effectiveness of potential cold. The 11-15-day forecast reveals that issue as the Interior West, protected by mountains, pools cold air but east of the Divide trends much warmer.
U.S. Medium-range Precipitation Forecast
Discussion: The 6-10-day forecast vividly indicates a potent storm track stretching from Texas to the Mid-Atlantic States. There are questions on how much snowfall is generated. Increased snow = colder temperatures; less snow = milder forecast. In the 11-15-day period, the Mid-south States could receive wintery precipitation while the primary storm track shifts south to Southern Florida.
Days 16-20 Extended range Forecast valid February 10-14, 2023
Discussion: The GFS ENS shifts into a warmer pattern in the East. Cold air remains over snow cover of the Northern Rockies and North-central U.S. The storm track features snow in the Midwest and rain for the Mid-south sectors. Certainly, a warmer trend is indicated.