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4/28 and 4/29 Severe Weather

nvck

By nvck,
in Lakes/Ohio Valley

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nvck

nvck

Posted
Posted

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.

Screenshot 2025-04-25 at 09-20-18 Models EPS — Pivotal Weather.png

Screenshot 2025-04-25 at 09-19-35 CSU-MLP Severe.png

Screenshot 2025-04-25 at 09-19-28 CSU-MLP Severe.png

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CheeselandSkies

CheeselandSkies

Posted
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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.

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nvck

nvck

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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.

1129842096_Screenshot2025-04-26at10-02-24cincywxgraphics-GoogleSlides.thumb.png.f343c48e4cbe3a1f78e7915a9ad26584.png

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

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CheeselandSkies

CheeselandSkies

Posted
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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.

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CheeselandSkies

CheeselandSkies

Posted
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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.


.

IMG_0456.png

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.

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mnchaserguy

mnchaserguy

Posted
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Despite the warm, moist air surging north into Iowa, most models show little, if any, storm activity around here.  Are we capped or something?

Seems like the issue is a lack a forcing. Looks like weak convergence on the dryline and the cold front is way out west.


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Powerball

Powerball

Posted
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13 hours ago, CheeselandSkies said:

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).

 

It's definitely a thread the needle kind of setup with decent bust potential.

Part of the problem (which the CAMs are likely picking up on) is that the better ascent/forcing will start to peel away by late afternoon/early evening before convective temps are achieved.

There is, however, a 6 hour window from 18z to 00z though where sky's the limit if everything aligns just right.

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nvck

nvck

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Watch issued: 

SEL0

   URGENT - IMMEDIATE BROADCAST REQUESTED
   Tornado Watch Number 180
   NWS Storm Prediction Center Norman OK
   1230 PM CDT Mon Apr 28 2025

   The NWS Storm Prediction Center has issued a

   * Tornado Watch for portions of 
     Northwest Iowa
     Southwest Minnesota
     Extreme Southeast South Dakota

   * Effective this Monday afternoon and evening from 1230 PM until
     800 PM CDT.

   * Primary threats include...
     A few tornadoes likely with a couple intense tornadoes possible
     Widespread large hail and scattered very large hail events to 3
       inches in diameter likely
     Scattered damaging winds likely with isolated significant gusts
       to 80 mph possible

   SUMMARY...Isolated to scattered thunderstorms developing along a
   surface front will develop east/northeast through the afternoon.
   These storms will have the potential to produce large to very large
   hail, damaging wind gusts, and a few tornadoes.

   The tornado watch area is approximately along and 40 statute miles
   east and west of a line from 85 miles north of Redwood Falls MN to
   30 miles west of Storm Lake IA. For a complete depiction of the
   watch see the associated watch outline update (WOUS64 KWNS WOU0).

   PRECAUTIONARY/PREPAREDNESS ACTIONS...

   REMEMBER...A Tornado Watch means conditions are favorable for
   tornadoes and severe thunderstorms in and close to the watch
   area. Persons in these areas should be on the lookout for
   threatening weather conditions and listen for later statements
   and possible warnings.

   &&

   AVIATION...Tornadoes and a few severe thunderstorms with hail
   surface and aloft to 3 inches. Extreme turbulence and surface wind
   gusts to 70 knots. A few cumulonimbi with maximum tops to 500. Mean
   storm motion vector 24035.

   ...Leitman
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