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May 22-? Severe weather


MNstorms

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3:06pm(EST) latest MSD for northwest WI highlights linear-mode with wind and hail as primary threats

and further south CINH is higher

MODIFIED FCST SOUNDINGS SUGGEST MLCAPE 1000-1500 J/KG WITH

50-100 NM AHEAD OF FRONT...ATOP WELL-MIXED/INVERTED-V THERMODYNAMIC

PROFILE IN BOUNDARY LAYER. THIS REGIME...SET AMIDST 50-70 KT

EFFECTIVE SHEAR MAGNITUDE AND STG DEEP-LAYER WINDS ALIGNED NEARLY

PARALLEL TO FRONT...INDICATES QUASI-LINEAR CONVECTIVE MODE WITH

DAMAGING WIND POSSIBLE. STRONGEST MID-UPPER LEVEL SUPPORT AND

LOW-LEVEL FRONTAL ASCENT SHOULD REMAIN N OF MO THROUGH

AFTERNOON...WHILE CINH INCREASES WITH SWD EXTENT. THIS INDICATES

ANY CONVECTION S OF IA SHOULD REMAIN RELATIVELY SHORT-LIVED AND NOT

AS INTENSE AS FARTHER N.

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Does it look like a tornado outbreak today, Reed? Never stop chasing!

In all seriousness, hope it gets better for you guys...

he's resorted to posting video from may 24, 2011 tornadoes on his facebook page "while we're waiting on these storms in Wisconsin"

very frustrating May all around...

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Does it look like a tornado outbreak today, Reed? Never stop chasing!

In all seriousness, hope it gets better for you guys...

I really should market my anti tornado abilities.

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Definitely going to be a low topped day. The shear out there is incredible...storms are extremely tilted...50 dbz is not even pushing 20k feet on the Preston, MN storm.

A good example for determining warning thresholds. I am a huge fan of the 50 dBZ height for warning on hail, but in a situation like this it can be misleading. You may not have 50 dBZ topping 20 kft today, but if you were to straighten out that updraft in the vertical it may actually be 35-40 kft. So cross-section and volume products go a long way to helping you see weak echo regions/echo overhang, etc.

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The storm near Allison IA looks like it has 1-2" hail. All other warned storms, I would say a 50-100% chance of wind damage in the area. Storm near Lewiston MN doesn't look to be taking on supercell characteristics, although it has sort of the right shape.

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I Just pulled this off the ARX AFD last night, has the shear in fact over whelmed the low cape values, if that's the case who ever wrote this deserves a ata boy/girl.

DEBRIS CLOUDS FROM ONGOING CONVECTION

BEHIND THE FRONT WILL BE A PROBLEM FOR STRONG WARMING/

DESTABILIZATION THIS AFTERNOON...ESPECIALLY OVER THE WEST HALF OF

THE FCST AREA. MOST MODELS WITH A RATHER NARROW BAND OF ONLY 500-

1000 J/KG OF MU CAPE OVER WESTERN WI AHEAD OF THE FRONT THIS

AFTERNOON. THE STRONG SHEAR MAY OVERWHELM WHAT COULD BE LIMITED CAPE

AND ANY TSRA MAY STRUGGLE TO ORGANIZE OR BE TORN APART BY THE STRONG

SHEAR.

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That storm riding the Iowa/Missouri border should be producing near baseball size hail. Really large core of 65+ dBZ aloft.

Wow. GR3 hail detection is seeing 4" hail. I haven't seen that in a while.

It might be a nice day to try out the new dual-pol capabilities in GR3 version 2.

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I Just pulled this off the ARX AFD last night, has the shear in fact over whelmed the low cape values, if that's the case who ever wrote this deserves a ata boy/girl.

DEBRIS CLOUDS FROM ONGOING CONVECTION

BEHIND THE FRONT WILL BE A PROBLEM FOR STRONG WARMING/

DESTABILIZATION THIS AFTERNOON...ESPECIALLY OVER THE WEST HALF OF

THE FCST AREA. MOST MODELS WITH A RATHER NARROW BAND OF ONLY 500-

1000 J/KG OF MU CAPE OVER WESTERN WI AHEAD OF THE FRONT THIS

AFTERNOON. THE STRONG SHEAR MAY OVERWHELM WHAT COULD BE LIMITED CAPE

AND ANY TSRA MAY STRUGGLE TO ORGANIZE OR BE TORN APART BY THE STRONG

SHEAR.

great find

perhaps premature, but an early post-mortem (this was advertised as potentially "historic" by some) would include:

- low cape + too strong shear that rips apart any discrete storms that develop

- insufficient dewpoints

- a predominantly linear storm organization very early in the game

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Highlighting the moisture problems today: compare 12Z NAM forecast sounding valid 21Z (right) vs. 21Z RAP analysis (left), for areas in SW WI.

post-674-0-61864100-1337898915_thumb.png

RAP shows Tds around 11 degrees C (52 degrees F) at the surface, whereas NAM shows Tds around 19 degrees C (66 degrees F). Verdict?

Verdict is NAM/GFS have been grossly too moist with boundary layer dews and nearly worthless for any type of thermodynamic analysis of storm environments. The good thing is they have been wrong basically every day anywhere north of TX, it seems. Usually whack about 5-10 degrees F off the NAM/GFS, and that will get you to some reasonable value. RAP and ECMWF have been the only useful dewpoint guidance...as well as bias-corrected guidance we have running at the local offices. But I totally agree, they have both been absolutely worthless. GFS has been especially awful. The biggest bomb event was a week or so ago when the GFS was progging dews 20+ degrees too high across the Great Lakes...with CAPE values around 2500 j/kg. Resultant CAPE that afternoon was more around 500-750 j/kg, SPC had a slight that they dropped that afternoon when it became apparent the evapotranspiration was not going to produce anything of the sort.

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