Severe Risk in the I-States Today

Let me get this out there right away - I respect the crap out of the brilliant meteorologists over at the Storm Prediction Center and could never do what they do 365 days out of the year. It's also just the nature of the science that meteorologists aren't going to agree with each other in perfect harmony all 365 days of the year. I agree with the folks at the SPC more days than I don't, and often when I disagree with them it's me that's eating humble pie at the end of the day.

My meteorological stubbornness will have me disagreeing with them for not being aggressive enough about a day I think has sneaky tornado potential in the Midwest, and other days, like today, I just don't see what they're seeing when they go hard after a tornado risk in my backyard.

The RAP/HRRR forecast for Wednesday, March 19th has been volatile at times across portions of northern and central Illinois, depicting an environment extremely favorable for low-topped supercells capable of all severe hazards, including a few tornadoes. It's a profile I've seen several times in recent years - December 1st, 2018 came to mind, February 27th 2023 as well - both days on which I documented wintertime tornadoes in Illinois. Sure surface air temperatures are in the lower to middle 60s with dew points only in the middle 50s, but it's the SHAPE of the thermal profile that makes the day, not the numbers associated with it.

Several things didn't pass the eye test for me, however. First of all, I love a good recency bias with the weather models, a "what have you done for me lately?". I might be living alone in my own universe where I actually respect the NAM suite more than I do the RAP/HRRR. For placement of important surface features, timing, and overall environment, my own anecdotal experience has been that the NAM does a better job consistently helping me hone in on "the zone". The NAM suite outperformed the RAP/HRRR during the recent Friday, March 14th severe weather outbreak across the Midwest. The 3km NAM correctly depicted forecasting soundings and subsequent messier, rainier (but still tornadic!) storms across central and southeast Illinois during that event, while the RAP/HRRR showed a more aggressive scenario with long-track, intense supercells remaining semi-discrete into the night across all of central Illinois.

I'm faced with the same thing today - the RAP/HRRR has chosen violence, while the NAM suite offers a more tempered solution.

At a quick glance, I immediately like the placement of surface features on the NAM suite better. I think the warm front will be much further south and much sharper than the RAP/HRRR depict, with the warm front and volatile tornadic region surging northward toward the Wisconsin border. A very sharp thermal gradient is more likely to exist along the Interstate 80 corridor, shutting the northern 1/4 of Illinois off to anything other than elevated hailers today.

The NAM3 likely offers a much more realistic scenario, with a very sharp baroclinic zone along Interstate 80 in northern Illinois. Sharp warm fronts are much less supportive of tornado production vs a more subtle, gradual baroclinic zone. Storms quickly become elevated upon reaching/crossing the front.

Next, I think the NAM offers a more reasonable forecast of the warm sector environment. It's one with plenty of juice in the middle and upper levels of the atmosphere to support intense convection, but the lower levels differ wildly on the NAM with a more saturated sounding offering more cloudiness during the day and a more muted 0-3 km thermal profile. Instead of "fat cape" in the lowest few km, you've got rather puney thermals near the surface, and that makes the entire difference between tornadic mini-supercells and fast-moving, outflow dominant storms.

Could the more aggressive RAP/HRRR scenario come to fruition and have me eating meteorological crow this evening? Absolutely.

But it's on an island all by itself right now, and I just would not have gone all-in with that scenario alone before seeing how the morning evolved.

In fact, I think we're already beginning to see the RAP/HRRR trending (read, caving) to the NAM suite in the early morning hours.

Here's the 4 PM dew point forecast from the HRRR from 18z on Tuesday:

Here's the 4 PM dew point forecast from the HRRR from 11z this morning:

That's a sharp drop in dew points in the warm sector which eliminates the low-level 0-3 km cape driving the significant tornado risk.

Here's the theta-e forecast for 5 PM from the 3z RAP:

Here's the 5 PM theta-e forecast from the 9z RAP:

That's a big shift south, and a hard sharpening of the baroclinic zone across northern Illinois over a 6 hour span.

We'll see how the day goes, but you live with the HRRR, you often die with the HRRR. In a few hours the models won't matter, and it'll have everything to do with visible satellite and surface map trends.

My gut leans toward an early tornado risk right on the surface low from 12-2 PM in eastern Iowa or far northwest Illinois, with a few intense severe thunderstorms and a low tornado risk along the warm front and ahead of the effective dryline in north-central Illiniois during the mid-afternoon, followed by a broken line of fast-moving, likely non-tornadic storms along Interstate 57 in eastern Illinois early this afternoon headed into western Indiana in the evening.