A Gulf air mass with record heat and humidity has been blown into the northern plains by very strong southerly winds driven by an extreme pressure gradient between a massive Bermuda high pressure area and an intense storm rapidly moving from the Rocky mountains into the northern plains. Heat and humidity levels in Iowa are already high enough to support the development of tornadoes. Intense winds at levels just above the surface will be pulled downwards as storms develop ahead of a cold front/dry line. These winds will be extreme.
I checked the weather models yesterday night and wondered if what I was seeing was right. In all my over fifty years of tracking weather I have never seen anything like this one. However, I am no expert on tornadoes or the severe weather systems that impact the mid-continent region. I wanted to see what the experts said before writing about the situation. Now the experts are warning us of a rare historic event.
The forecast office in La Crosse Wisconsin has warned:
A storm system will bring severe storms to the region this evening with damaging winds and possibly a few tornadoes. Historically rare very strong winds will then impact the area through the night. The winds will start out of the south, swinging around to the west later in the evening and overnight hours. Wind gusts to 65 mph are likely.
NOAA’s Storm Prediction Center has raised the warning level for severe thunderstorms to the next to highest level “moderate”. That’s the same forecast level that was given before the massive tornadoes that caused widespread destruction in Kentucky and Illinois last week. There has never been a “moderate” severe storm warning in December for Iowa, Minnesota and Wisconsin before.
The SPC’s discussion warns of exceedingly high winds and a few possible strong tornadoes.
...SUMMARY... Widespread severe wind gusts of 60-75 mph along with at least a few tornadoes are likely from mid afternoon through early tonight across the Mid-Missouri Valley to the Upper Mississippi Valley. Embedded gusts of 75-100 mph and a strong tornado or two are also possible, particularly from extreme eastern Nebraska across western to northern Iowa and southeastern Minnesota.
...A rapidly evolving outbreak of severe storms with widespread damaging winds and a few tornadoes is expected to begin by mid afternoon across eastern NE and continue northeastward into the upper MS Valley by early tonight...
Wind shear levels and helicity (a measure of near surface wind gradients) levels are very high. It’s not uncommon in December and the winter months to have high levels of spin in the atmosphere. This situation is unprecedented because a warm humid spring like air mass is so far north in the middle of December. The combination of spring like Gulf air being slammed by winter like winds and shear aloft makes for an extremely dangerous situation as the intensifying low pressure area tracks rapidly towards Canada.
Pay attention to your local trusted weather forecasters. This situation will evolve so rapidly that people who live in the affected areas will have very little time to react, so be prepared. Do not expect national forecasters or weather amateurs like me to help you. You need to pay close attention to a local expert who is tracking your local situation in real time. What’s clear now is that there will be very strong winds. The potential is there for intense tornadoes that have a very high forward speed. At night. If you might be affected, have a plan and get ready to make it happen quickly.
Epilogue
The forecast verified. There were more 75 mph and above wind gusts reported than any day since reliable statistics on wind gusts became available in 2004. The title to this diary which focused on 3 states understated the scale of this event which included Colorado, Nebraska, Kansas, Missouri and other states. This was an historic weather event. We are in a climate crisis.