Strong Storms Ending Overnight

Timeframe:6:00 AM THU to 3:00 AM FRI
Confidence:Above Average
Primary Hazard:Severe Thunderstorms
Class: 3 - Moderate
Forecaster:Justin Poublon

Last Update: 10:42 PM - Thu June 27, 2019

Summary

Severe thunderstorms possible Thursday afternoon or evening in portions of Wisconsin.

Member Only Discussion


12:00 PM -

8:18 AM - Expanded target area further a little further north. Not ready to bump to "Severe". Did bump event up to a 3-Moderate. Confidence raised to above average.

8AM mesoanalysis showing the main instability pool pointing into SE MN/NE IA. For severe in WI IDEALLY I'd like to see that pointing into WI. SOUTHERN WI still unstable but not the maximum amount.
8AM mesoanalysis showing the main instability pool pointing into SE MN/NE IA. For severe in WI IDEALLY I'd like to see that pointing into WI. SOUTHERN WI still unstable but not the maximum amount.


7:00 AM - Video Update


9:50 PM WED - well not making any changes tonight. Only looked at 00NAM so far and it's not any more clear. Will need to see how that complex looks coming out of the Dakotas in the AM. Next update in the AM. Pretty sure this complex will be the main event for the afternoon hours.

PREVIOUS UPDATE 1:30PM WED - There is plenty of uncertainty regarding the evolution of thunderstorm activity on Thursday. There are probably two main ways it could go. The strategy for 2019 is to wait until the last minute because of poor model performance. Despite potential shaping up; shouldn't jump in guns blazing now either.

Most models show a complex of storms pushing through Wisconsin during the mid-day hour, then redevelopment late in the day west of I-90 near the WI/IA/MN intersection. I used the "Target" zone across southwest WI out of respect for model uncertainty. There has been general consistency. I want to see more from the 00Z run and will consider bumping to a severe risk threat at that point if necessary.

EARLY THURSDAY

NAM predicts a complex of storms will move through Wisconsin during the middle of the day. This complex may intensify and could become the main event.
NAM predicts a complex of storms will move through Wisconsin during the middle of the day. This complex may intensify and could become the main event.

A convective complex will pass over the state from west to east during the day. Most models bring that through northern/central Wisconsin. With timing squarely on peak heating we may see intensification of this system in the afternoon. GFS a bit slower and could act to diffuse the situation somewhat. Convective models are faster with most 12Z CAM's showing pretty much the same thing. Not sure about instability as models have been too aggressive with moisture influx in 2019. Either way; could see a strong storm during the day...it this could become the main event if the GFS is correct.

THURS NIGHT - FRI AM

NAM simulation for Thursday night showing worst case scenario of complex forming and bowing out to the southeast. This is far from certain.
NAM simulation for Thursday night showing worst case scenario of complex forming and bowing out to the southeast. This is far from certain.

Most models show redevelopment of t-storm activity on Thursday night into Fri AM back west, likely in the form of a convective system propagating east and south after dark. The primary threats would be damaging wind gusts and large hail. In the worst case scenario I foresee the complex riding an outflow boundary from early Thursday complex. Short range models show this but are just a little cool at the surface which suggests we would get a rotating mesoscale system but maybe not connecting all the way to the surface. With nicely veered soundings and good moisture flow in from the southwest, I think severe storms will be possible. The only thing that could disrupt it would be an overly aggressive early Thursday complex acting to cool the boundary layer.

Will consider boosting to 3-Moderate class tomorrow morning depending on which path mother nature takes. If we go there then will likely need a blog post. But we'll see. The plan is to update this storm event as we get closer and will resend if severe risk/confidence increases.


Blog Posts

Regions: Northeast IA, Central MN, Southeast MN, Northeast WI, Northwest WI, Southeast WI, Southwest WI, Western WI

Notes(admin only)

Forecast Grade: -

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Images

June 27
8AM mesoanalysis showing the main instability pool pointing into SE MN/NE IA. For severe in WI IDEALLY I'd like to see that pointing into WI. SOUTHERN WI still unstable but not the maximum amount.
photo by Wisconsin Weather
June 26
NAM predicts a complex of storms will move through Wisconsin during the middle of the day. This complex may intensify and could become the main event.
photo by Wisconsin Weather
June 26
NAM simulation for Thursday night showing worst case scenario of complex forming and bowing out to the southeast. This is far from certain.
photo by Wisconsin Weather

Thunderstorm Outlook Types

What is the outlook forecast timeframe?
Forecast timeframes change and are defined by start and end dates which differ by storm event.
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Tornadoes are possible today, but your outlook only shows a Strong t-storm threat?
Tornadoes can occur in non-severe storms with no lightning, hail, or gusty winds. We would call that a strong thunderstorm. Severe and Significant thunderstorm threats would suggest mulitple tornadoes and/or strong tornadoes.Matter of semantics but also designed to suppress "cry-wolf" ideology.
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