Mid December Storm Set-Up Could be a Repeat of 2021’s Christmas Tornadoes

December 9, 2022

One year ago on December 15, the central US experienced a record shattering tornado outbreak. (above)
Something similar setting up for next week. Heads up.

Bob Henson in Yale Climate Connections:

A rash of tornadoes and other severe weather appears increasingly likely to erupt from Texas to the Mississippi Valley early in the week of December 12-16. As an unusually strong upper-level storm approaches, plenty of mild, moist air is expected to be in place to fuel severe thunderstorms. 

The same upper-level storm could help bring much-needed moisture to parts of California and the Southwest.

No month of the year is immune to U.S. severe weather – especially in the south – but the factors expected to come into play next week will be unusually potent for December. Multiple forecast models have become increasingly emphatic about the imminent threat.

On Thursday, December 8, the NOAA/NWS Storm Prediction Center outlined risk areas for severe weather valid on Day 5 (Monday, December 12) and Day 6 (Tuesday, December 13). The Day 6 outlook includes the equivalent of an enhanced risk – which is the highest tier allowed in SPC outlooks beyond Day 3. 

According to SPC’s Elizabeth Leitman, such a strong Day 5 outlook has been issued only five times in the nine years of probabilistic outlooks for that time range. The other four examples were all issued in April, not in December!

In contrast, the two record-smashing severe events that closed out 2021 were not flagged at all in SPC risk areas until Day 3. These included the deadliest December tornadoes on record, which killed at least 89 people in and around western Kentucky on December 10-11, and the most widespread December tornadoes on record, a derecho-driven swarm of 120 twisters that swept across the central and northern Plains as far north as Minnesota on December 15. 

Forecast confidence in an upcoming event is not necessarily a sign of how strong that event will be, but the two tend to be highly correlated.

Both the ECMWF and GFS model have consistently shown that vertical wind structures favoring formation of tornadic supercell thunderstorms—including winds that strengthen and veer with height—will sweep across the Southern Plains and toward the Southeast from late Monday into Wednesday, December 12-14.

Below, Youtube Meteorologist Ryan Hall doesn’t do a good job relating weather to climate, but he does have good explainers of severe events as they develop.

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