CheeselandSkies

3K NAM, RRFS suggest the Sycamore area could well be in the bulls-eye.

Obviously Thursday is the more immediate issue, but next Tuesday looks like another potential severe threat in the region given general surface/500mb pattern. Parameter space doesn't look impressive on the 18Z GFS because the model blows out the warm sector with a huge amount of simulated convection.

Notable slowdown of the system across 18Z hi-res guidance. One of my main concerns with previous runs of models such as the GFS was their wanting to sweep the cold front practically all the way to Lake Michigan by 21Z (4 PM) Thursday (if nothing else, for the simple fact of giving me enough time to get on a storm after getting off work at 1 PM). SPC noted in their Day 4 outlook yesterday that it was possibly exhibiting its fast bias, and so far things would indeed seem to be trending in that direction. As noted there are concerns with dry EML and mixing for Thursday; however, the difference in CAM initiation at this range between that and April 28 is quite stark. 3K NAM, MPAS and RRFS all develop discrete convection with pronounced UH swaths. Very bizarre seeing that be the main failure mode; around here 99 times out of 100 it'll be excessive early convection working over the atmosphere and preventing destabilization.

Fair. I agree S. WI looks like the most favorable area and that happens to be my backyard. I prefer to stay local on a work day and although the terrain isn't great, there are workable spots and I'm familiar with where they are. As long as the best storm(s) don't track through the Driftless area (especially Sauk/Vernon/Crawford/Richland Counties, which are pretty much all solidly tree-covered steep hills/ridgelines, river valleys and winding roads that seldom lead directly from anywhere to anywhere). ...and I wasn't necessarily calling for a balls to the wall approach from SPC. However I think a 30%/Enh with an all-hazards hatched area would have been warranted. Anyway, looks like they're doing that now with the new Day 3 update. Further north than I would have liked to see, but the hatching does extend throughout the rest of S. WI and into IL/IN.

What doesn't look great about it to you? There are some potential failure modes to be sure but I think it checks a lot more boxes than that day did. *Edit Annnnnd 12Z 3K NAM coming in hot (unlike any of the CAMs at this range for 4/28). Unusual for this model to resolve semi-discrete convection like this. These simulated cells are moving through a strongly unstable and sheared environment. The solution verbatim would also resolve a lot of the timing issues that have been shown on the coarser models (especially the GFS).

Initial Day 3 outlook was surprisingly underwhelming. Gun-shy after the one they put out for April 28? But this setup looks a lot more concerning simply from a trough geometry standpoint.

Been hoping you would chime in here and/or TW.

12Z NAM came in pretty spicy. Again, there are some pattern fundamentals that suggest this one has a better chance of verifying a threat than 4/28, namely a pronounced negative tilt and a potent LLJ with a more southerly component. Still some details yet to iron out which held SPC back from pulling the trigger on a 30% zone.

Would really need to see the timing of the system slow down (by just about 3 hours) compared to recent GFS solutions to maximize the severe threat in Wisconsin/Illinois Thursday afternoon. Today's SPC outlook notes that is in fact a bias with the model, but it continues to hold consistent with that through the current (06Z) run.

SPC introduced a Day 6 risk yesterday for this coming Thursday the 15th and maintains it today. No surprise as GFS and Euro have been relatively consistent with a pattern that would support severe weather primarily across Wisconsin, northern into central Illinois, western Indiana and perhaps far eastern Iowa. Here's the 500mb forecast from the most recent GFS, nice negative tilt with the left exit region pointed squarely into the region. That alone would suggest a higher likelihood of actually producing than April 28th.

Does this bleed over into other NCEP models as well? NAM, CFS, RAP? If so, going to make forecasting the rest of chase season a b****.

So as we know Monday April 28th was not a big day. I found the initial, quite strongly worded Day 3 moderate risk a bit of a head-scratcher from the get-go given the lack of a CAM signal for initiating discrete convection. However I had already booked the PTO from a week out when the setup looked potentially higher-ceiling so I went anyway given that there eventually was a signal for some storm development.

To me a bad April is like 2018 when it was still snowing regularly almost until the 20th. However, a really good April needs at least one threat into this region (that verifies, not Monday's overhyped trash).

Puke. Classic dreaded spring omega block that prevents western troughs from maturing and ejecting properly for events.

Not sure if I've ever seen SPC go so hard against the CAMs before. Used to those models being overly bullish with supercells that don't happen (such as the meme-worthy HRRR run from the morning of 5/20/2019).

Where'd you get that? Furthest range RAP run I know of right now is today's 15Z which goes out 51 hours to 18Z Monday.

Copy/paste of what I just posted on TW: There are some weird things about this setup. It's certainly not going to be your absolutely classic 500mb pattern for a tornado outbreak (like, say 3/31/23 and 4/26/24 were). At first glance the 500mb looks way too positively tilted. However, it doesn't seem to have the big problem you usually get with a strong positive tilt, which is a SW-NE oriented front with all the strong 500mb flow parallel to and relegated to largely along/behind it. With Monday, at the surface we still have a more N-S oriented cold front/dryline with the flow extending out over the warm sector. NAM/3K NAM are also doing weird things with the thermos (surprise) which makes it tough to get a good handle on what the warm sector environment will actually be like over Iowa/Wisconsin going into Monday evening. All in all I think the Day 3 MDT was a bold call given all this (seems to be based solely on the jet translation speed), but they're the ones who have been doing the work on it.

As of this past Monday the signal was strong enough for me to book PTO for this coming Monday-Wednesday so that I can chase Sunday-Monday and perhaps Tuesday. Based on modeling over the last few days, currently will probably target somewhere along the central to western KS/NE border on Sunday and north-central to northeast Iowa for Monday, although tornado parameters look potentially dangerous into Wisconsin.

I was living in Milwaukee at the time and I recall it being bone dry from "Morch" onward.

Getting a nice round moving through the state line region this AM. After drought concerns in the late winter due to the lack of snow, April showers have been in plentiful supply. This ain't gonna be 2012, at least around here.

12Z HRRR and 3K NAM both fire a supercell in south-central WI this afternoon, and this one has some surface-based instability to work with... Chase mode activated? We shall see.

As per the other posts, was a pretty significant hail event by our standards. The station I work at was wall-to-wall or nearly wall-to-wall from shortly after the first thunderstorm warning went out at around 5:10, until the storms cleared the Madison broadcast market shortly before 8:00.

3K NAM has been reluctant to fire convection tomorrow since it came into range, but 18Z HRRR actually doesn't look terrible parameter space-wise around the WI/IL border region, and fires storms around 23-00Z.

Today's Euro runs would have a decent threat into parts of the sub on Sunday. GFS is nowhere near as impressive. Basically a complete 180 from their respective positions on tomorrow's threat at a similar range.

12Z NAM is way slower, has the greatest threat back in central NE/KS at 0Z Friday (Thursday evening). Meanwhile Euro shows pretty meager moisture. GFS has looked pretty good over IA for a few runs, but it's really by itself with that. If the GFS is in fact being too progressive, I could see Friday actually being a significant day somewhere in the E IA/N IL/S WI region.