Beginning midweek the northern hemisphere jet stream will trough on the U.S. West Coast and re-strengthen in western Europe. In-between the two vigorous trough patterns a third trough resides south of Greenland. By late January the pattern still remains although with slightly less amplitude. These features shape the last third of January 2021 climate for the northern hemisphere.

A December 2020 stratospheric warming event across Northeast Asia spawned a frigid polar vortex stretching from Mongolia to Northeast Asia. Beneath the polar vortex increasingly cold air was generated taking on arctic intensity. In late DEC/early JAN the cold air mass was ejected southeastward into China bringing historic snows and cold.

The more conservative view (by the HRRR model) indicates the heaviest snowfall in west-central Texas (6-10 in.) while GFS is much heavier northwest of Houston area (up to 10-12 in.). Given the strength of the upper trough and rapid cooling of the lower atmosphere late today/this evening the heavier (GFS) totals are favored!

Forecast models have shown (at times) a trail of snow storms across the East U.S. in recent days. Each model run varies, sometimes widely. How do you make an assessment for planning purposes given the variability of operational models? The mega-cluster ensemble accounts for ALL models including their prevailing skill level to put-together a daily “most likely” projection of the weather. The model also assigns a confidence level and identifies which operational model was used most influentially.

The first month of meteorological winter 2020-21 was much warmer than normal. HOWEVER, due to cold spikes related to increased snow cover or surface wind advecting over snow cover (and into the Southeast U.S.) plus above normal number of cloudy days much of the eastern third of the U.S. observed near to above normal heating degree days.