(12:15AM - 12/1/18) Given recent snows and colder temperatures across the state the past several weeks, severe weather is the last thing on the mind of most, but the threat exists Saturday into Saturday night across portions of the state.
A storm system moving through the region will help set the stage for a late season severe weather event across portions of the state. By afternoon a cold from will be sweeping east from Western Missouri into Western and Southwest Illinois. Ahead of this front will be a moderately favorable environment for this time of year. This environment will feature moderate instability (1000-1500 CAPE), moderate moisture (Upper 50's dew points), favorable upper level environment, a nice push of higher lapse rates, and nicely curved hodographs.
Scattered thunderstorms will develop in the vicinity of the front across portions of Western Missouri, Western and Southwest Illinois during the afternoon. This activity will push northeast across portions of Central and Southern Illinois through the rest of the afternoon and evening, posing a severe threat. All modes of severe weather will be possible, including a tornado threat, given a favorable environment. All of this activity will weaken and the severe threat will end, as it pushes into Northern and Eastern Illinois by early Saturday night.
Below is our latest updated severe threat TAM. You may notice the severe threat extends across some areas impacted with high snowfall totals during the recent blizzard, where snow still exists on the ground.
(11/29/18 - 6:00PM) Another major storm system will be affecting the state this weekend, as it pushes through the region. This system will bring the chance for heavy rain, flooding, severe weather and snow to different portions of the state from Friday afternoon into Monday morning.
Things will start off Friday afternoon into Saturday evening, with heavy rain and flooding potential across a good portion of the state. Widespread rainfall amounts of 0.50-1.50" are likely across much of the state, with higher totals possible across portions of Southern Illinois. Minor flooding potential is likely across portions of Central and Southern Illinois, where conditions have been somewhat abnormally wet over the past several weeks. Additionally, minor to moderate flood potential is likely across portions of Northern and Western Illinois. Across this area, the combination of snow melt due to mild temperatures, frozen ground due to recently cold temps, and the expected heavy rainfall, will lead to an increased risk for flooding. Sewers/drains covered with ice and snow may lead to abnormal and increased flood potential on roads.
A thunderstorm and severe weather threat will likely exist across portions of the state on Saturday and Saturday night. In the wake of early heavy heavy rains, some clearing may occur, in addition to some destabilization. By mid-afternoon moderate instability and moisture will be in place for this time of year. With favorable upper level conditions and an approaching cold front, a broken line of thunderstorms will likely develop across far Eastern Missouri on into Southwest Illinois. This activity will push northeast, across a good portion of Central and Southern Illinois Saturday evening and early night. Given the environment in place, an isolated severe threat is likely. Further updates regarding the severe potential may be needed.
This storm system will end with rain showers turning to snow showers across portions of Northern and Central Illinois Sunday afternoon, continuing into Monday morning. Only minor accumulations of snow are likely, less than 1".