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May 21-22 Midwest & Great Lakes Severe Threat


SEMIweather

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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.

Looks good... It took a step in the right direction.

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I almost think it might be a good thing to be in the screw zone right now with the thunderstorms this weekend: most of the convection tomorrow passes just to our north, and most of the convection Sunday just to our south. Then again, my morale for prospects of severe is pretty low.

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I know it's just one piece of the pie but we'll see if that's a trend none the less. Definitely a marked increase at that time frame.

So, does SPC shift the slight risk north when it does the new Day 2 SWO? 5% probs for parts of N. Illinois and all of S. Wisconsin seem a bit low considering the local discussions and maps like this.

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So, does SPC shift the slight risk north when it does the new Day 2 SWO? 5% probs for parts of N. Illinois and all of S. Wisconsin seem a bit low considering the local discussions and maps like this.

I have to think it would shift north at least a bit. They could also potentially defer to the 1730 Day 2 tomorrow before doing anything too drastic.

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The GFS is coming in stronger with the s/w and a bit further south/stronger with the associated sfc reflection by 12z sunday....sounds like were tracking a winter storm lol

Shouldn't it realistically come in further NW if the system is stronger? Of course it would trend in the direction we don't need it.

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something that caught my eye with the new GFS compared to the 12z run is that its stronger aloft and quicker...just look at H7. The new run closes off the 700mb low in central MN where the 12z run hangs it back along with the jet max. If the 0z run were to verfiy we will have no problem getting convection and possibly too much, that is a strong 700mb wave.

0z

12z

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I don't think I've ever seen this before in the sfc wind field...The NAM blows up a serious MCS by 3z late sunday night over northern IL and check out the wind fields its putting out.

It's showing 70kts at 900mb at 3z over northern IL..oh hey LLJ

HOLY ****! That's pretty impressive. Looks like there's been quite a few changes with the new 00z runs based on all your guys posts. I'm gonna start digging into them here in a sec. That sounding from the Sterling area was pretty sick. That's not too far away from here either lol.

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The 00z models have definitely sped things up compared to the 12z runs. Forcing in the mid levels is further east. Overall the whole setup took a big step in the right direction IMO. Wind profiles from the surface on up look very nice. That combined with moderate instability will about guarantee severe convection over a huge part of the Midwest. Directional shear profiles look more than adequate for tornadic supercells. The big question is will the strong forcing lead to too much storm competition and eventual linear squall line evolution? With such deep directional shear I'm guessing we should get at least a period of discrete supercells before they all organize into a quasi-linear MCS type thing. Tornadoes would still be possible with the QLCS, but the best shot at photogenic tornadoes would obviously be before the QLCS takes over.

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The 00z models have definitely sped things up compared to the 12z runs. Forcing in the mid levels is further east. Overall the whole setup took a big step in the right direction IMO. Wind profiles from the surface on up look very nice. That combined with moderate instability will about guarantee severe convection over a huge part of the Midwest. Directional shear profiles look more than adequate for tornadic supercells. The big question is will the strong forcing lead to too much storm competition and eventual linear squall line evolution? With such deep directional shear I'm guessing we should get at least a period of discrete supercells before they all organize into a quasi-linear MCS type thing. Tornadoes would still be possible with the QLCS, but the best shot at photogenic tornadoes would obviously be before the QLCS takes over.

At this point, from my point of view, I just want severe storms. The quicker nature of these new models is very good for further east locations like Chicago and Milwaukee, as the convection was looking more like a nocturnal event previously (and it still might be). It's interesting, though, b/c it seems like the initial convection tomorrow is actually going to be delayed, which seems divergent from the trend in the 0z models to speed the jet up.

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The 00z models have definitely sped things up compared to the 12z runs. Forcing in the mid levels is further east. Overall the whole setup took a big step in the right direction IMO. Wind profiles from the surface on up look very nice. That combined with moderate instability will about guarantee severe convection over a huge part of the Midwest. Directional shear profiles look more than adequate for tornadic supercells. The big question is will the strong forcing lead to too much storm competition and eventual linear squall line evolution? With such deep directional shear I'm guessing we should get at least a period of discrete supercells before they all organize into a quasi-linear MCS type thing. Tornadoes would still be possible with the QLCS, but the best shot at photogenic tornadoes would obviously be before the QLCS takes over.

I think we could have a tornadic window until about 3z Monday, whether in discrete cell or QLCS form. Low level CINH increases markedly after that per the NAM. I haven't spent more than 10 minutes on this setup to be honest...just can't get into it for some reason. Hopefully that will change tomorrow. ;)

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DAY 2 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

1235 AM CDT SAT MAY 21 2011

VALID 221200Z - 231200Z

...THERE IS A SLGT RISK OF SVR TSTMS SUNDAY OVER A BROAD AREA FROM

THE SOUTHERN PLAINS THROUGH THE MID/UPPER MISSISSIPPI VALLEY AND

MUCH OF THE OHIO/TENNESSEE VALLEYS...

..SYNOPSIS

MODELS INDICATE THAT LARGE-SCALE TROUGHING WILL CONTINUE TO EVOLVE

OVER THE WESTERN U.S. DURING THIS FORECAST PERIOD...AS A SERIES OF

VIGOROUS SHORT WAVE IMPULSES/ASSOCIATED JET STREAKS DIG INLAND

ACROSS THE PACIFIC COAST. NEAR THE BASE OF THE POLAR

TROUGH...ANOTHER SIGNIFICANT HIGH-LEVEL JET STREAK EMERGING FROM THE

SUBTROPICAL EASTERN PACIFIC APPEARS LIKELY TO CONTINUE

EASTWARD...BUT SOME WEAKENING IS PROGGED AS IT NOSES ACROSS THE

NORTHERN MEXICAN PLATEAU/SOUTHWEST AND CENTRAL TEXAS. FARTHER

EAST...LOWER/MID-LEVEL RIDGING IS EXPECTED TO REMAIN GENERALLY

STRONG ACROSS THE GULF OF MEXICO AND SOUTHEAST. BUT GUIDANCE

SUGGESTS THAT A REMNANT CLOSED LOW MAY BEGIN ACCELERATING MORE

RAPIDLY EASTWARD OUT OF THE NORTHERN PLAINS THROUGH MUCH OF THE

UPPER MIDWEST...AHEAD OF A STRONG SHORT WAVE TROUGH DIGGING ACROSS

THE HUDSON BAY/NORTHERN MANITOBA AND ONTARIO REGION.

IN RESPONSE TO THESE DEVELOPMENTS...MODELS CONTINUE TO INDICATE THAT

MODERATE TO STRONG DESTABILIZATION WILL OCCUR SUNDAY OVER A RATHER

BROAD AREA FROM THE SOUTHERN PLAINS THROUGH A LARGE PORTION OF THE

MID/UPPER MISSISSIPPI VALLEY...AND MUCH OF THE OHIO AND TENNESSEE

VALLEYS. AN INFLUX OF MID 60S TO NEAR 70F SURFACE DEW POINTS FROM

THE GULF OF MEXICO...BENEATH STEEPENING MID-LEVEL LAPSE RATES

ASSOCIATED WITH NORTHEASTWARD ADVECTING ELEVATED MIXED LAYER

AIR...IS EXPECTED TO YIELD MIXED LAYER CAPE ON THE ORDER OF

2000-4000 J/KG. IN THE PRESENCE OF AT LEAST MODERATE

SHEAR...BENEATH A COUPLE OF BROAD BELTS OF 30-50 KT WEST

SOUTHWESTERLY 500 MB FLOW...CONVECTION COULD BECOME

WIDESPREAD...INCLUDING ORGANIZED STORM CLUSTERS AND ISOLATED

SUPERCELLS.

..LWR OH/TENNESSEE VALLEYS INTO PARTS OF THE SRN PLAINS

VIGOROUS STORM DEVELOPMENT MAY OCCUR FIRST...POSSIBLY AS EARLY AS

MID DAY...FROM PORTIONS OF KENTUCKY/TENNESSEE WEST SOUTHWESTWARD

INTO PARTS OF NORTHEAST TEXAS. THIS IS EXPECTED TO BE SUPPORTED BY

FORCING ASSOCIATED WITH WEAK SHORT WAVE IMPULSES...PERHAPS A REMNANT

CONVECTIVELY GENERATED OR ENHANCED PERTURBATION OR TWO...ON THE

SOUTHERN FRINGE OF THE STRONGER WESTERLIES. UPSCALE GROWTH INTO

SEVERAL SMALL BUT ORGANIZED MESOSCALE CONVECTIVE SYSTEMS MAY OCCUR

BY THE PEAK HEATING HOURS...TRACKING EASTWARD AND GENERATING SWATHS

OF POTENTIALLY DAMAGING WIND GUSTS AND HAIL BEFORE DIMINISHING WITH

BOUNDARY LAYER STABILIZATION DURING THE EVENING.

..UPPER MS VALLEY INTO THE SRN PLAINS

AS A SURFACE LOW MIGRATES EASTWARD WITH THE REMNANT UPPER LOW INTO

THE UPPER MIDWEST...AN AXIS OF STRONGER DESTABILIZATION AHEAD OF A

WEAK SOUTHWARD TRAILING SURFACE FRONT INTO THE LOWER MISSOURI

VALLEY...AND AHEAD OF A DRY LINE ACROSS THE SOUTHEASTERN PLAINS...IS

EXPECTED TO BE THE FOCUS FOR HIGHER SEVERE PROBABILITIES SUNDAY. A

STRENGTHENING SOUTHERLY PRE-FRONTAL LOW-LEVEL JET...COUPLED WITH A

BELT OF ENHANCED WESTERLY MID-LEVEL FLOW TO THE SOUTHEAST OF THE

UPPER LOW...COULD YIELD FAVORABLE HODOGRAPHS FOR SUPERCELLS CAPABLE

OF PRODUCING TORNADOES...PARTICULARLY ACROSS PARTS OF EASTERN

IOWA/SOUTHERN WISCONSIN INTO NORTHERN ILLINOIS.

A DIFLUENT/DIVERGENT REGIME NEAR THE EXIT REGION OF THE SUBTROPICAL

JET STREAK PROBABLY WILL ENHANCE STORMS NEAR THE SOUTHERN PLAINS RED

RIVER VALLEY REGION. A FEW SUPERCELLS ARE LIKELY...BUT MORE MODEST

LOWER/MID TROPOSPHERIC FLOW MAY LIMIT THE TORNADIC POTENTIAL.

..KERR.. 05/21/2011

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something that caught my eye with the new GFS compared to the 12z run is that its stronger aloft and quicker...just look at H7. The new run closes off the 700mb low in central MN where the 12z run hangs it back along with the jet max. If the 0z run were to verfiy we will have no problem getting convection and possibly too much, that is a strong 700mb wave.

0z

12z

Pretty small scale sub-synoptic differences yielding a rather large wind field spreads associated with the small anomaly aloft.

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DAY 2 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

1235 AM CDT SAT MAY 21 2011

VALID 221200Z - 231200Z

...THERE IS A SLGT RISK OF SVR TSTMS SUNDAY OVER A BROAD AREA FROM

THE SOUTHERN PLAINS THROUGH THE MID/UPPER MISSISSIPPI VALLEY AND

MUCH OF THE OHIO/TENNESSEE VALLEYS...

..SYNOPSIS

MODELS INDICATE THAT LARGE-SCALE TROUGHING WILL CONTINUE TO EVOLVE

OVER THE WESTERN U.S. DURING THIS FORECAST PERIOD...AS A SERIES OF

VIGOROUS SHORT WAVE IMPULSES/ASSOCIATED JET STREAKS DIG INLAND

ACROSS THE PACIFIC COAST. NEAR THE BASE OF THE POLAR

TROUGH...ANOTHER SIGNIFICANT HIGH-LEVEL JET STREAK EMERGING FROM THE

SUBTROPICAL EASTERN PACIFIC APPEARS LIKELY TO CONTINUE

EASTWARD...BUT SOME WEAKENING IS PROGGED AS IT NOSES ACROSS THE

NORTHERN MEXICAN PLATEAU/SOUTHWEST AND CENTRAL TEXAS. FARTHER

EAST...LOWER/MID-LEVEL RIDGING IS EXPECTED TO REMAIN GENERALLY

STRONG ACROSS THE GULF OF MEXICO AND SOUTHEAST. BUT GUIDANCE

SUGGESTS THAT A REMNANT CLOSED LOW MAY BEGIN ACCELERATING MORE

RAPIDLY EASTWARD OUT OF THE NORTHERN PLAINS THROUGH MUCH OF THE

UPPER MIDWEST...AHEAD OF A STRONG SHORT WAVE TROUGH DIGGING ACROSS

THE HUDSON BAY/NORTHERN MANITOBA AND ONTARIO REGION.

IN RESPONSE TO THESE DEVELOPMENTS...MODELS CONTINUE TO INDICATE THAT

MODERATE TO STRONG DESTABILIZATION WILL OCCUR SUNDAY OVER A RATHER

BROAD AREA FROM THE SOUTHERN PLAINS THROUGH A LARGE PORTION OF THE

MID/UPPER MISSISSIPPI VALLEY...AND MUCH OF THE OHIO AND TENNESSEE

VALLEYS. AN INFLUX OF MID 60S TO NEAR 70F SURFACE DEW POINTS FROM

THE GULF OF MEXICO...BENEATH STEEPENING MID-LEVEL LAPSE RATES

ASSOCIATED WITH NORTHEASTWARD ADVECTING ELEVATED MIXED LAYER

AIR...IS EXPECTED TO YIELD MIXED LAYER CAPE ON THE ORDER OF

2000-4000 J/KG. IN THE PRESENCE OF AT LEAST MODERATE

SHEAR...BENEATH A COUPLE OF BROAD BELTS OF 30-50 KT WEST

SOUTHWESTERLY 500 MB FLOW...CONVECTION COULD BECOME

WIDESPREAD...INCLUDING ORGANIZED STORM CLUSTERS AND ISOLATED

SUPERCELLS.

..LWR OH/TENNESSEE VALLEYS INTO PARTS OF THE SRN PLAINS

VIGOROUS STORM DEVELOPMENT MAY OCCUR FIRST...POSSIBLY AS EARLY AS

MID DAY...FROM PORTIONS OF KENTUCKY/TENNESSEE WEST SOUTHWESTWARD

INTO PARTS OF NORTHEAST TEXAS. THIS IS EXPECTED TO BE SUPPORTED BY

FORCING ASSOCIATED WITH WEAK SHORT WAVE IMPULSES...PERHAPS A REMNANT

CONVECTIVELY GENERATED OR ENHANCED PERTURBATION OR TWO...ON THE

SOUTHERN FRINGE OF THE STRONGER WESTERLIES. UPSCALE GROWTH INTO

SEVERAL SMALL BUT ORGANIZED MESOSCALE CONVECTIVE SYSTEMS MAY OCCUR

BY THE PEAK HEATING HOURS...TRACKING EASTWARD AND GENERATING SWATHS

OF POTENTIALLY DAMAGING WIND GUSTS AND HAIL BEFORE DIMINISHING WITH

BOUNDARY LAYER STABILIZATION DURING THE EVENING.

..UPPER MS VALLEY INTO THE SRN PLAINS

AS A SURFACE LOW MIGRATES EASTWARD WITH THE REMNANT UPPER LOW INTO

THE UPPER MIDWEST...AN AXIS OF STRONGER DESTABILIZATION AHEAD OF A

WEAK SOUTHWARD TRAILING SURFACE FRONT INTO THE LOWER MISSOURI

VALLEY...AND AHEAD OF A DRY LINE ACROSS THE SOUTHEASTERN PLAINS...IS

EXPECTED TO BE THE FOCUS FOR HIGHER SEVERE PROBABILITIES SUNDAY. A

STRENGTHENING SOUTHERLY PRE-FRONTAL LOW-LEVEL JET...COUPLED WITH A

BELT OF ENHANCED WESTERLY MID-LEVEL FLOW TO THE SOUTHEAST OF THE

UPPER LOW...COULD YIELD FAVORABLE HODOGRAPHS FOR SUPERCELLS CAPABLE

OF PRODUCING TORNADOES...PARTICULARLY ACROSS PARTS OF EASTERN

IOWA/SOUTHERN WISCONSIN INTO NORTHERN ILLINOIS.

A DIFLUENT/DIVERGENT REGIME NEAR THE EXIT REGION OF THE SUBTROPICAL

JET STREAK PROBABLY WILL ENHANCE STORMS NEAR THE SOUTHERN PLAINS RED

RIVER VALLEY REGION. A FEW SUPERCELLS ARE LIKELY...BUT MORE MODEST

LOWER/MID TROPOSPHERIC FLOW MAY LIMIT THE TORNADIC POTENTIAL.

..KERR.. 05/21/2011

They haven't updated the NWS site where the SWOs are found for me yet. Where do you find the discussions so early?

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