TRACKING A REGIONAL SEVERE OUTBREAK MONDAY

Monday continues to look ominous across the Upper Midwest with severe weather likely, but significant questions remain on how early-day thunderstorm activity will impact the severe weather potential this far north. As I mentioned last night outflow from the morning activity likely will send stable air down towards the St. Louis metro before we see a surge of southerlies recovering the atmosphere. The magnitude of instability that builds back in is questionable - and that is clear in the latest outlook from the Storm Prediction Center.

The Level 3 of 5 risk, an Enhanced Risk, was pushed farther south into southeast Iowa, eastern Missouri and central/southern Illinois. While the risk level has fallen for the Quad Cities, Cedar Rapids and Iowa City metro areas, we still have the Level 2 of 5 risk, a Slight Risk, to cover the potential recover following the morning storms.

Thunderstorms in Kansas Sunday night are forecast to move into our area Monday morning. The HRRR model has heavy rain, and potentially strong wind gusts and large hail, with this line of storms moving through the late morning hours. While not the main event it could still be on the stronger side at times while also producing locally heavy rain. The strongest storms appear to be about US34 and points south in Iowa/Illinois.

The latest severe weather ensemble forecast, the HREF, shows a signal for some recovery of the level of instability in southeast Iowa by late afternoon Monday. This would be critical for a severe weather threat to materialize. The highest degree of instability will be farther south into Missouri where we anticipate more widespread and significant severe weather.

Using the HREF again we can see the greatest likelihood of robust thunderstorms will be farther south of our area - mainly Missouri and Illinois through the evening hours. The strongest storms could produce large hail and strong tornadoes, in addition to a damaging wind threat as the the threat of supercells transitions into more of a line of thunderstorms.

The latest tornado threat from the Storm Prediction Center has the highest chances to the south. This is the area confidence is higher in recovery of instability and a threat of supercells. Towards the Quad Cities there is considerable uncertainty. Once the morning thunderstorms pass through late Monday morning we will have a better handle of the evening severe threat. Keep an eye on official sources for the latest watches and warnings as this could change rapidly.

I think for eastern Iowa and Northwest Illinois the most significant severe weather will be to the south, however it cannot be ruled out entirely given the robust wind shear and upper air support. Instability is the one limiting factor due to the early morning convection.

Once we get passed this severe weather event Monday the pattern shuts down and we can take a break from the rain and severe weather. Northwest flow takes over sending in drier and cooler air to the region as we end the month of April and beginning of May. The latest GEFS shows below-normal precipitation through May 5.

Analogs support this dry and cool pattern as well. Latest probabilities of below-normal temepratures May 1-4 are well over 80% across the eastern half of the CONUS. Much needed time to dry out.

Have a great week, friends!

-Meteorologist Nick Stewart