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The 12z ECMWF is Sounding Alarm Bells in the Midwest

There's nothing quite like overreacting to one single weather model run multiple days out from a potential weather event, and I am ready to do exactly that to this morning's run of the ECMWF with respect to the forecast for Tue, Feb 27th.

The potential for severe weather across the Midwest has been highlighted for several days now with the Storm Prediction Center introducing risk areas on their days 6 & 7 outlooks on Thursday and global ensembles having hinted at this potential a week ago.

What has been catching my eye the last day or so has been the tendency for the ECMWF to depict a Pacific front that acts the part of a Midwestern dryline - an initiation zone for thunderstorms well ahead of the trailing, strongly forced cold front.

Simply put, if the trailing cold front were the primary storm initiation mechanism for this event, a squall line and linear storm mode would likely result.

A Pacific front/pre-frontal trough/dryline feature allows more subtle, but still adequate forcing to initiate thunderstorms but allow them to an opportunity to remain discrete.

There are other factors that can strongly dictate tornadic vs non-tornadic storms when it comes to strongly forced convection and Professor of Atmospheric Sciences Jeff Frame did an excellent deep dive on this yesterday. Read it here:

Additionally, this isn't your typical cold season, or early, early season big bomb cyclone that gives you <12 hours of just-in-time, barely-enough moisture return. We're doing a one-and-done cold sunny day in Illinois today (Sat Feb 24) before we shoot back up to 60-degrees tomorrow (Sunday) and begin nearly 72 hours of moisture return and air mass modification over the Midwest. That means this system will be swinging into a mature, healthy warm sector that is ready to erupt more akin to a mid-spring environment.

We're seeing forecast soundings depicting t/td spreads of 72F/60F across Central Illinois on Tuesday afternoon - that is seriously mid-April stuff.

The synoptics displayed by the ECMWF remind me of a few high-end Illinois tornado days of the past, but given that there are still disagreements amongst global models and some of the mesoscale models that are starting to grab onto the system I'm going to at least steer away from doing any annoying "this looks just like XX/XX/20XX" comps for now.

We're 84 hours out... but this is "I've seen enough" stuff on my end. Again - note the dry punch in western Illinois well out ahead of the cold front which is still way back by Kansas City, MO. Surface low in eastern Iowa, warm front draped across north-central Illinois beneath a belt of 70-80 knot flow at 500 mb. That's another thing. That's a lot of flow, but, it's not 100+ knots of too-much flow associated with a digging trough and rapid cyclogenesis. This effectively halves expected forward motion on any hypothetical storms on Tuesday with storm motions perhaps a very chaseable 35-40 MPH. Tornadic supercells on outbreak days featuring rapidly deepening cyclones such as March 31, 2023 and December 10th, 2021 were traveling at speeds of 60-75 MPH across the Midwest.

Screaming internally for now, but may be getting louder and louder on this one if trends continue through the weekend. At the very least, I've told my wife that this is serving as a solid nudge to spend part of the weekend making sure our basement is in storm shelter mode as we head into the spring.


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