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SEMIweather

May 21-22 Midwest & Great Lakes Severe Threat

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Models have been showing a decent threat for a few days now.

:thumbsup: for starting a separate thread. As I said on the original one, the Cape looks like it has increased for Sunday, expected to be 1500 j/kg yesterday, and now the AFD stated they're expecting 2-3K, as well as 40 knots of bulk shear. Overall, looks like a decent threat, which is much better than it looked a few days ago.

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One or more days in the Sunday-Wednesday period looks to be chase worthy.

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The Sunday-Wednesday period looks to be chase worthy.

Where do you think the storms on Monday thru Wednesday will fire up? It seems like the front will stall out just south of the Great Lakes region, so maybe the Northern Ohio Valley, although there is still enough instability in the Southern Great Lakes on Monday to perhaps warrant a threat.

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Where do you think the storms on Monday thru Wednesday will fire up? It seems like the front will stall out just south of the Great Lakes region, so maybe the Northern Ohio Valley, although there is still enough instability in the Southern Great Lakes on Monday to perhaps warrant a threat.

An early target for Sun/Mon looks to be IA/IL.

For Tue/Wed, the ECMWF is much farther north than the GFS is with the setup.

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Ya was just looking at the 12z Euro and it as well has alot of juice in central IL (near 4000 j/kg) and the PIA sounding sunday evening had over 90 degrees of turning from the sfc to H5 but only 30kts of H5 flow, nice low-level shear though.

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Gotta start somewhere. :P

post-855-0-10247700-1305866130.gif

Well, I like where that little nook or cranny is located. I assume it's normal for the probs to start out low three days ahead and slowly increase as things become a little more certain?

In regards to Central Illinois, I'm sure the instability will be there, but the better forcing seems to be further north.

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Pretty large day 3 slight with 30% probabilities too.

day3prob_0730.gif

DAY 3 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0230 AM CDT FRI MAY 20 2011

VALID 221200Z - 231200Z

...THERE IS A SLGT RISK OF SVR TSTMS SUN FROM THE SOUTHERN PLAINS

THROUGH THE MIDDLE MISSISSIPPI...OHIO AND TENNESSEE VALLEYS...

...SYNOPSIS...

MODELS INDICATE THAT CIRCULATION AROUND LOW-LEVEL RIDGING DEVELOPING

ALONG THE ATLANTIC SEABOARD WILL AID THE INLAND RETURN FLOW OF A

MOIST GULF BOUNDARY LAYER DURING THE NEXT FEW DAYS. LOWER/MID 70S

SURFACE DEW POINTS ARE NOW PRESENT ACROSS MUCH OF THE GULF OF MEXICO

INTO THE WESTERN GULF COAST REGION...AND...BY SUNDAY...DEW POINTS

NEAR 70F MAY ADVECT THROUGH PORTIONS OF THE SOUTHERN PLAINS AND

OZARK PLATEAU...INTO THE MIDDLE MISSISSIPPI AND LOWER OHIO VALLEYS.

THIS APPEARS LIKELY TO OCCUR COINCIDENT WITH THE NORTHEASTWARD

ADVECTION OF ELEVATED MIXED LAYER AIR FROM THE SOUTHERN PLAINS AND

PLATEAU REGION. MODEST WEST SOUTHWESTERLY MID/UPPER FLOW IS

EXPECTED TO PERSIST FROM THE SOUTHERN PLATEAU INTO THE NORTH

ATLANTIC COAST STATES...JUST AHEAD OF LARGE-SCALE TROUGHING

MIGRATING INLAND ACROSS THE PACIFIC COAST...AND SOUTH/ EAST OF A

REMNANT CLOSED LOW ACCELERATING FROM THE NORTHERN PLAINS INTO THE

UPPER MIDWEST...IN ADVANCE OF A SIGNIFICANT SHORT WAVE IMPULSE

DIGGING ACROSS MANITOBA/ONTARIO.

GUIDANCE IS SUGGESTIVE THAT MODERATE TO STRONG DESTABILIZATION WILL

OCCUR OVER A RATHER BROAD AREA FROM THE SOUTHERN PLAINS INTO THE

OHIO VALLEY...AND ADJACENT PORTIONS OF THE MISSISSIPPI AND TENNESSEE

VALLEYS...BY EARLY SUNDAY AFTERNOON. GIVEN ANTICIPATED WEAK TO

MODEST INHIBITION AND FAVORABLE LARGE-SCALE FORCING FOR UPWARD

VERTICAL MOTION...THIS IS EXPECTED TO ALLOW THE DEVELOPMENT OF

CONSIDERABLE THUNDERSTORM ACTIVITY. DEEP LAYER FLOW AND SHEAR

...WHILE NOT PARTICULARLY STRONG /PERHAPS ON THE ORDER OF 30-40

KT/...IS EXPECTED TO BE SUFFICIENT FOR ORGANIZED CONVECTIVE

DEVELOPMENT...INCLUDING ISOLATED SUPERCELLS...A COUPLE WHICH MAY BE

CAPABLE OF PRODUCING TORNADOES...AND PERHAPS SEVERAL STORM CLUSTERS

CAPABLE OF PRODUCING DAMAGING WINDS AND LARGE HAIL. SEVERE STORMS

COULD BECOME FAIRLY NUMEROUS BEFORE DIMINISHING WITH BOUNDARY LAYER

STABILIZATION SUNDAY EVENING.

..KERR.. 05/20/2011

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MKX still seems convinced about chance of severe weather on Sunday, and perhaps Monday. SPC does not seem so bullish, only indicating 5% chances Saturday and Sunday. Given temps will warm into the upper 70s and low 80s, dewpoints into the 60s, and there should be a minimal amount of CIN on Sunday night, I tend to believe the local WFO over SPC.

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18z NAM again...east of PIA for sunday evening. I will tkae that turning anyday. DVN is mentioning possible sups but forming into a line.

All I know is I can chase sunday :)

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18z NAM again...east of PIA for sunday evening. I will tkae that turning anyday. DVN is mentioning possible sups but forming into a line.

All I know is I can chase sunday :)

That looks nice...I like that there are no weak spots in the flow aloft.

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18z NAM again...east of PIA for sunday evening. I will tkae that turning anyday. DVN is mentioning possible sups but forming into a line.

All I know is I can chase sunday :)

Is that where you're taking me chasing? :popcorn:

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I actually like south-central Iowa/north-central Missouri for Sunday. Great instability, and better mid level forcing. Just not sure if anything will fire in Illinois, but obviously it's too early to see if there will be any leftover boundaries etc. With the overall synoptic setup further west I'm thinking that's the better bet. Unfortunately with the stronger forcing comes the likelihood that storms will organize into more of a linear wind threat, but there should be a brief window of discrete sups with as much directional shear that will be in place. It's all speculation at this point though. I'm sure things will be tweaked as we get closer.

12z NAM forecast sounding for near Lamoni late Sunday. This is under 3500j/kg of cape.

NAM_218_2011052012_F60_40.5000N_94.0000W.png

NAM_218_2011052012_F60_40.5000N_94.0000W_HODO_SM.png

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I actually like south-central Iowa/north-central Missouri for Sunday. Great instability, and better mid level forcing. Just not sure if anything will fire in Illinois, but obviously it's too early to see if there will be any leftover boundaries etc. With the overall synoptic setup further west I'm thinking that's the better bet. Unfortunately with the stronger forcing comes the likelihood that storms will organize into more of a linear wind threat, but there should be a brief window of discrete sups with as much directional shear that will be in place. It's all speculation at this point though. I'm sure things will be tweaked as we get closer.

Your right about the better forcing, stronger mid-level winds further west but the problem with that is you have weaker sfc flow and weaker low-level shear/not as good as a low-level hodograph. Now if we can back the sfc winds under the better mid-level flow than its a different story.

Right now just off models alone I like Keokuk, IA as a starting tonight.

Def will be up for the new day 2.

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Your right about the better forcing, stronger mid-level winds further west but the problem with that is you have weaker sfc flow and weaker low-level shear/not as good as a low-level hodograph. Now if we can back the sfc winds under the better mid-level flow than its a different story.

Right now just off models alone I like Keokuk, IA as a starting tonight.

Def will be up for the new day 2.

Yeah, sure would like to get those better low-level winds further west into the better instability/forcing. Hopefully things line up a little better as we get closer.

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Yeah, sure would like to get those better low-level winds further west into the better instability/forcing. Hopefully things line up a little better as we get closer.

Ya looking more at the 18z NAM id be near the GBG/MQB area.

the cap is breakable and you can see on the H7 RH plots, that the model showing some pretty good ascent taking place in that area.

Also there isn't that much of a difference in the H5 flow between southern IA over into central IL, maybe 5-10kts difference.

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The 18z GFS has a stronger s/w and is hinting at a confluent axis ahead of the front in southeast IA around BRL up through DVN..

also, please give the LLJ the GFS has rather than the NAM.

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0z NAM in the Sterling/Princeton/La Salle/Amboy area...

hahaha wow I just texted you the wind profile/hodo just south of Sterling is damn nice, too funny.

The 0z NAM develops a line of storms at 18z in eastern IA which races east to chicagoland but quickly destablizes behind this small complex and then lights up from DBQ on down into MO by 0z.

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