Friday, April 25, 2014

April 26-30 Severe Weather Outbreak: Monday Outlook

This forecast is solely for the severe weather on Monday, April 28th. For the Sunday, Monday and Tuesday outlooks, please look at the bottom of this post for links.

The Storm Prediction Center has outlined a rather large area of potential severe weather to kick off the workweek on Monday, April 28th. This is a continuation of the severe weather events on Saturday and Sunday, as a strong upper level low continues to ravage the country. When the SPC issues these sorts of long range outlooks, they highlight areas with a 30% chance or more of observing severe weather within 25 miles of any given point. This means that any of the areas highlighted in Arkansas, Louisiana, Mississippi, Alabama, Tennessee, Kentucky, Indiana, Illinois and Missouri may see some formidable severe weather, with a lesser-but-still-present severe weather threat surrounding this circular shape.

A look at the projected 500mb isobars and wind speeds for late Monday evening continues to exemplify why this event will be a multi-day, potentially significant severe weather outbreak. We see a long strand of anomalously high wind speeds extending from Oregon, rounding the closed low and punching into the area we're watching for Monday's severe weather risk around Missouri and Illinois. Although the closed low does not have a negative tilt that could then intensity the situation further, it does look like this piece of the Pacific jet stream will be what keeps the severe weather going, even though the closed low won't be doing much, other than continuing to pull moisture up from the Gulf of Mexico.

A look at 700mb winds, just a few thousand feet off the ground for the same time as the 500mb image shows strong lower-level winds over the area we're watching for the severe weather threat Monday evening. Considering the streak of 40 to 60 knot winds in the Midwest and southern Plains will only continue to intensity during Monday evening, as it is the nocturnal Lower Level Jet stream (LLJ), the severe weather threat will likely continue as well, at least through Monday evening.

A look at projected dewpoints and the Lifted Index for Monday evening really emphasizes the moisture this system has to work with. We see the projected dewpoints in shaded colors, and the dark blues represent the highest dewpoints, and thus some pretty muggy air. This all bodes well for severe weather potential, which is confirmed by the very low Lifted Index values, some as low as -9. The Lifted Index, also called the LI, is a measure of buoyancy of the air- in other words, when the LI is negative, air tends to rise and thus create thunderstorms. When the LI is positive, it indicates a stable atmosphere, suppressing thunderstorms. Seeing numbers close to double-digit negatives tells me this closed low will be keeping the severe weather fireworks going well into the workweek.

To summarize:
• A potentially significant severe weather event is possible on Monday.
• Those in the outlined area may want to review severe weather preparations and watch for further updates on this situation.

Other posts pertaining to the April 26-30 Severe Weather Outbreak:
• Saturday Severe Weather Outlook: Click Here 
• Sunday Severe Weather Outlook: Click Here
• Tuesday Severe Weather Outlook: Click Here (Coming soon)


1 comment:

matt zuro said...

Local weather men are saying chicago could see some severe weather also? Is this true or false? I'm excited for this upcoming event!