Fig. 1: Current NOAA/NWS weather watch, warning and advisories.
The Climate Cause: A massive arctic air reservoir caused by several stratospheric warming events set-up early-to-mid-winter across Russia. To compensate for that massive chill in the northern latitudes, Canada was unusually mild in December and January. During late January/early February a large mass of tropical convection near the Dateline released heat poleward to cause the northeast Pacific Ocean upper ridge to amplify and consequently a downstream “polar vortex” trough to develop in central North America. Cross-polar arctic air flow from Siberia into this polar vortex pattern caused the unusually intense cold air mass which is able to expand into the southern latitudes as U.S. snow cover expands southward across Texas. The pattern described is representative of negative arctic oscillation (-AO). The winter 2020-21 AO pattern has been sharply negative each month one of only 4 winter seasons to produce that regime in the historical record.
Fig. 2-3: The northern hemisphere temperature anomalies for DEC/JAN 2020-21 identifying the Russia source region for arctic air (left) and the cross polar flow of arctic air into North America in the 5-day forecast (right).
Regional Weather Discussion
The Great Plains into Texas is where the historical weather is where the historical weather will occur. Although other “never seen before” weather events taking place such as ice accretion in the Richmond, VA area. The temperature anomalies across the Great Plains range from 20F to 40F below normal for the evolving arctic outbreak. The severity and aerial coverage of the intense cold is due to the full-latitude (North Dakota to Texas) snow cover.
Currently, a Winter Storm Warning for heavy snow, sleet and freezing rain/ice accretion is issued across the southern Great Plains and across much of Texas. The incoming storminess and cold for Texas are likely a first-time experience for many residents. The arctic is into western Texas and the entire Great Plains now. The second wave arrives late tomorrow with a major snow storm affecting all of Texas. Prior to that second wave much of eastern Texas (except the coast) receives more freezing rain/drizzle.
Let’s take a look at the snowfall forecast for Texas (Fig. 3) and the historic cold that follows for Tuesday morning (Fig. 4).
Fig. 4-5: The Texas/Mid-south U.S. snowstorm amount forecast (left) and projected minimum temperature for Tuesday morning (right).
In Richmond, VA. A historic ice storm is occurring. Central to northeast Virginia are involved. So far about 3 to 4 tenths of an inch of ice has accreted in parts of this region. NOAA/WPC forecasts another 0.25 to 0.30 in. of liquid today/tonight and all of it will be ice. Total ice accretion will exceed one-half inch and could approach 3/4 in. for some locations. Ice accretion at this level is considered severe and will lead to widespread power outages due to weight on trees/tree limbs causing collapse that can knock down power lines. Travel is nearly impossible in this condition.
The coldest temperatures in the Great Plains are Sunday morning with -30F to -35F in Minnesota. Monday morning low temperatures in this region are almost as cold. The farthest southern extent of subzero temperatures (into Texas) is on Tuesday morning.
Fig. 6-7: The coldest temperature of the outbreak are in Minnesota Sunday morning (left) while the subzero line expands into Texas Tuesday morning (right).
Northwest mountains to the southern Rockies pick-up 1-3 feet of snow over-the-weekend. So far this winter, the West has observed a lot of snow but much of which is low water content leaving long-term water shortages largely intact.
Fig. 8-9: The 84-hour snowfall forecast across the West (left) and water supply for the West in the new water year (right.
Northeast U.S. snows are on the way. The GFS forecasts two moderate to major snowfall events for Tuesday and again later this week. The Northeast is quiet today but that won’t last long.
Fig. 10-11: The GFS snowfall forecast in the Northeast for a Tuesday and late week storm.