January 20, 2025 Monday Winter Weather

Arctic blast to combine with Gulf of Mexico moisture for historic snowfall

Good Evening!

The Lower 48 is in the grips of a major Arctic blast — lobe of the tropospheric circumpolar vortex — with coldest air east of the Rockies.

Lower 48 average temperature at 6:30 PM ET was only 18.2°F with 213 million below freezing and 15 million subzero.

Of course January 20 climatology is cold — depths of winter. We are 19.2°F below normal with 30°F to 35°F below from the Midwest to South Texas. Brutal.

850 mb Temperature — minimum is -37°C

850 mb Temperature Anomaly — coldest compared to normal centered on South Dakota almost 30°C below normal.

The 500 mb Height Anomaly doesn’t look so ominous, just a positively tilted, oblong looking trough axis from the U.S. Southwest to the Great Lakes.

And, at 500 mb the temperatures are easily seen to be connected to the Arctic or polar regions. This is the tropospheric polar vortex unabated into the Lower 48.

And, one of my favorite parameters, the Dynamic Tropopause Potential Temperature nicely outlines the boundary of the extremely cold and dry polar air.

Weather on Tuesday

And, that cold air has plunged southward but the Gulf of Mexico (America) moisture plume is trying its hardest to surge northward, isentropic upglide to form very strong, convective winter precipitation all along the coast from Houston to Florida.

This is a generational surface frontal forecast for Tuesday Jan 21, 2025 7 PM ET

The State of Florida does not own its own fleet of snowplows, but contracts from a service that provides them on-demand. Interstate 10 probably will be closed until Wednesday afternoon if this winter weather forecast comes to fruition. The exit and on-ramps are going to be too slippery for travel.

State of Florida DOT Contracted Snow Plows

HRRR 18z — through 48-hours — will update a few more times through the entire event to highlight the accumulations of snowfall, freezing rain, and sleet.