4/28 and 4/29 Severe Weather

[nvck]

Figure it's probably time to start a thread for what looks to be a 2-day severe weather event across the region. CSU (per usual) is pretty aggressive with it's probabilities, but is outlining much of the same area as the SPC has. It's looking like all severe modes are possible on both Monday and Tuesday, and Tuesday has been uptrending over the past couple days, so I'd expect higher probs coming from the SPC.

[sbnwx85]

I'm worried I'll get stuck between the two risks. Maybe I can get initiation to occur overhead on Tuesday. The GFS is more hopeful than the Euro at last check.

[CheeselandSkies]

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.

[yoda]

Oh... okay then

 

 

 

[A-L-E-K]

Jelly

[nvck]

I think the decision to pull the trigger on a day3 MDT was at least partially supported by Broyles et al. findings in the OMEGA project, which found that jet streak translation speeds >40kt are associated with higher-end tornado events. Doing some rough math, from the 6z NAM, it looks like at 6z monday the core of the 500mb jet is over eastern NM, and by 6z Tuesday it's not as obvious where the core of the jet is, but it appears to be somewhere around the northern shore of  Lake Superior. This would suggest a translation speed of around 49kts, well above the threshold mentioned in the paper.

The SPC also mentions the jet translation speed in the outlook: 

 A strong mid-level jet streak will move rapidly northeastward from
   the Southwest to the Upper Midwest on Monday.

I could be wrong, but this is my best guess as to why they went moderate today instead of pulling the trigger tomorrow

Here's the paper if you're interested: https://prod-west-spc.woc.noaa.gov/publications/broyles/omega.pdf

[CheeselandSkies]

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.

[mnchaserguy]

I haven’t been a believer because something has just seemed off. Probably mostly the lack of better heating and narrow cape ribbons. However the RAP is screaming outbreak. If it’s correct or even somewhat close then we could be in real trouble. This is the RAP at
21z in western MN on Monday.


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[CheeselandSkies]

23 minutes ago, mnchaserguy said:

I haven’t been a believer because something has just seemed off. Probably mostly the lack of better heating and narrow cape ribbons. However the RAP is screaming outbreak. If it’s correct or even somewhat close then we could be in real trouble. This is the RAP at
21z in western MN on Monday.


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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.

[mnchaserguy]

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.

Whoops. Mislabeled. It is 18z on Monday.


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