Sunday-Monday Midwest/Great Lakes/Ohio Valley Severe Threat

For record keeping purposes, here is a post I made on an online weather forum regarding the upcoming severe threat.

Just from an ingredients based perspective, I’d have to think there’s pretty good potential in the sub-forum Monday-Monday night.

Fairly persistent low-mid level ridging over the south and especially southwest US through the weekend will allow for strong surface heating over the Rockies/High Plains during the day which will allow a good EML to form…and the strong mid-upper level ridge over the south suggests there won’t be much organized convection to overturn that as it moves east on the northern edge of the low-mid level ridging.

Closer to the surface, an already moisture rich airmass is in place across much of the south-central and southeastern US, and a persistent anti-cyclonic flow near the central Gulf Coast through the weekend and into early next week will allow more moisture to continue to advect into the Plains and then east towards the Mississippi Valley/OH Valley/Great Lakes.

The combination of an EML and moisture rich low levels definitely supports the strong-extreme instability numbers spit out by both the GFS/NAM at this stage outside of any ongoing convection on any given day.

In addition to the instability, the combination of the enhanced flow on the northern edge of the mid-upper level ridge over the southern US and shortwaves diving south into central Canada thanks to a fairly stout ridge over Alaska should be enough to cause seasonably strong bulk shear over the northern portion of the very unstable airmass. In addition, the seasonably strong shortwaves should provide enough large scale ascent for areas of surface low pressure to develop that help undulate the quasi-stationary front’s position as they go by and also enhance low level shear.

So, from just looking at the ingredients potentially in place, things seem lined up for a moderate-high end event somewhere in the subforum Monday-Monday night, although as we get closer mesoscale details/ongoing convection may ultimately throw some wrinkles into that.

As has been mentioned…the speed max/shortwave that will move across the upper Mississippi Valley/Great Lakes Monday afternoon-night will eject out into the northern Plains on Sunday, and I’d have to suspect that adequate instability and shear will be in place for an MCS to develop somewhere over maybe SD or NE Sunday evening that moves ESE Sunday night. Although the nose of the 850mb jet is progged to get into southern MN by Monday morning, the shear vectors and MUCAPE gradient Sunday night suggest the MCS will likely track towards IA/MO/IL by Monday morning if it develops. Rich low level moisture…a decent EML…and strong low level jet should allow for quick recovery behind this potential MCS…however, if the MCS dives too far south it may limit moisture return farther east (IE MI/OH). In addition to creating moisture return questions…if the MCS doesn’t “get out of the way” quickly enough, getting enough surface heating to break the cap associated with the EML may become harder to do and limit the threat farther south/east. In addition, recent model runs have trended somewhat stronger with the proceeding shortwave over the eastern lakes on Sunday, and are trying to show an interaction with Bill’s remnants over the NE Sunday night into Monday. If this shortwave and associated surface low trend stronger/slower, then the surface cold front may get driven farther south Sunday-Sunday night over the eastern portions of the sub forum, also casting some doubt into the magnitude of the threat later Monday farther east.

As things stand now, I’d feel decent about some sort of an overnight MCS with at least a marginal severe threat over SD/NE/IA and perhaps into northern MO/parts of IL Sunday evening into Monday morning. For Monday, there’s reasonable agreement in the ingredients coming together for a sizable event, with only modest differences in timing of the short wave and associated mid-level speed max. With strong airmass recovery likely behind any nocturnal MCS on Monday and decent shear likely being in place, I’d have to feel fairly decent from eastern IA into WI/ northern IL…shear vectors support some southward component of motion Monday night with whatever the convection grows upscale into which puts lower MI/IN possibly into play and perhaps OH…although farther east questions about timely moisture return do grow some. The one wild card is the cap not breaking if nocturnal stuff hangs around long enough to significantly limit surface heating.

So, I see a fairly high end potential and feel fairly good about a decent event occurring somewhere, however I won’t feel great until the mesoscale details become clearer.

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