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Wisconsin Weather

JUL 18, 2020 | Severe T-storms Possible Overnight Ending

LAST UPDATE : JUL 19, 2020

11:00AM VIDEO FORECAST (see text below)

SAT 10:30AM - Confidence is LOW for today and overnight. Potential exists for severe t-storms SOMEWHERE over Wisconsin but because of numerous possible scenarios; hard to say exactly who is most at risk. I kept the t-storm forecast broad & vague with STRONG TARGET...will have to take this one into the trenches and tackle it as it evolves. I almost did a broad SEVERE zone instead but don't want to risk overdoing it.

Models are struggling greatly with morning convective complex in southern Wisco. This lowers confidence in all models going forward. I don't think you can rule anything out. Most of the CAMS blow up convection across MUCH OF WI tonight & overnight. I guess this makes sense given available instability returning this afternoon (near 4500 j/kg SB). I still think NORTHERN WI is most at risk tonight relatively speaking. Models generally show severe t-storms moving in from southern MN. With convective complex in southern WI now...I think that will take the edge off?

Looking at wind profiles...shear magnitudes are good but mostly unidirectional (+ thermodynamic dominated environment) which suggests damaging wind threat primarily. Pretty common situation this time of year and TIME OF DAY[NIGHT]. Large hail or even a tornado is possible too.

In conclusion; I won't rule anything out right now. The narrative is "strong to severe storms possible tonight". Spatial risk area is large. Will have to add detail tonight as the situation unfolds.


FRI 10:30PM - quite a variety of solutions on the latest 00z NAM model. Low res showing a totally disjointed setup with supercells firing at 09z SUN over NC WI???..meanwhile high res NAM shoves SE propagating MCS through central WI by that same time? Not sure what to believe yet so let's keep confidence LOW. The pieces are there for a widespread event (low end?). Just not yet convinced it will come together correctly. Watching closely how tonight goes. Will plan for an update tomorrow around mid day.


FRI 1:30PM - Severe t-storms are likely [expected] somewhere across Wisconsin Saturday NIGHT into SUN AM. Confidence LOW because of location uncertainty.

Where the highest risk will be depends on TIMING & LOCATION of morning convective complex. Faster/further north will tend to focus storms north(GFS/NAM). Slower, further south solutions(CAMS) would open door for all of Wisconsin. Damaging wind gusts are the primary concern, large hail and perhaps a tornado possible.

Severe T-storms are likely SOMEWHERE across WI overnight Saturday into Sunday morning.
Severe T-storms are likely SOMEWHERE across WI overnight Saturday into Sunday morning.

On Saturday night; strong instability will be paired with strong upper level flow pushing through WI. Storms most likely during the overnight hours [after sunset]. GFS/NAM try to constrain most of the activity in northern WI. Short range CAMS are further south covering pretty much all of WI with t-storm threat. At least want to blend the two scenarios. Both scenarios are on the table. Looks like a nocturnal MCS event of some form (would like to see a stronger 850mb jet for bigger threat). Given the size and strength of the instability pool, storms could form as far south as the WI/IL overnight Saturday. I'm leaning towards a further south focused solution due to presence of SAT AM convective complex.

So...I will cover Wisconsin with a large STRONG zone for now...add in focused SEVERE zone tomorrow.

Forecast Maps

Storm Details

Hazards
Severe T-Storms, Heavy Rain
Start
SAT 12:00 PM - Jul 18, 2020
End
SUN 8:00 AM - Jul 19, 2020
Confidence Level
Storm Class

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