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September 3rd-5th Severe Weather Threat


Brewers

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I am not sure why there is all this negativity in this thread this morning, I still see a really good opportunity this afternoon for most of us. I mean hell it is only 1PM/2PM...

mlcape is still under 500 across Chicagoland which is well under what was being modeled yesterday for this time....better instability is lurking close by though

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hopefully. Can't leave work till 4 15pm.

Yeah, this was going to be an evening event from what I had been seeing anyways. Furthermore the upper support is still back over MN/W WI. Also looking at the shear values I'd argue that they are better than expected for today. A couple good hours of sunshine across N IL/S WI will do wonders to this potential, which I expect we will be seeing that sunshine.

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I am not sure why there is all this negativity in this thread this morning, I still see a really good opportunity this afternoon for most of us. I mean hell it is only 1PM/2PM...

I do have some cautious optimism. My temp has been skyrocketing since I got some clearing around 10am. Up to 85 at the moment. A few more hours of heating and lets see where the instability goes.

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FWIW, the crapvection that just came through did nothing to work over the atmosphere.

LI's increased to -6 and CAPE values are still 1500-2000 J/KG.

But despite that, I do have to wonder how much of an impact the subsidence behind this "wave" will have on development for the rest of the day, especially since the best instability/moisture has been shunted to the SW and we're just beyond peak heating.

With a relative extensive stratocumulus deck filling in just east of LM and along the WI/IL border, there's clearly still a decent inversion in place from this morning's storms.

20120905_1910_DTW_vis.jpg

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AREA FORECAST DISCUSSION

NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL

259 PM CDT WED SEP 5 2012

MESOSCALE DISCUSSION

145 PM CDT

A COMPLEX WEATHER PATTERN EXISTS OVER THE LOCAL AREA. POTENTIAL

FOR SEVERE THUNDERSTORMS REMAINS THIS AFTERNOON AND EVENING...WITH

THE MOST FAVORABLE TIME WINDOW BETWEEN 4 AND 8 PM...BUT

CONFIDENCE ON OVERALL EVOLUTION REMAINS SOMEWHAT LOW.

THE SURFACE COLD FRONT IS GRADUALLY TAKING SHAPE FROM WESTERN WI

INTO CENTRAL IA EARLY THIS AFTERNOON AS THE LOW-LEVEL NORTHWEST

FLOW MOVES INTO THE UPPER MISSISSIPPI VALLEY. SURFACE LOW

PRESSURE...PARTLY AS A RESULT OF THE EARLIER WAKE LOW...IS

ANALYZED WITHIN THE SURFACE PRESSURE AND WIND FIELDS ACROSS

SOUTHERN WI. THIS HAS HELPED TO INCREASE WESTERLY WINDS ACROSS

SOUTHERN WI/FAR NORTHERN IL EARLY THIS AFTERNOON...WITH SOME

LOCATIONS GUSTING IN EXCESS OF 20 KT. THIS IS OF COURSE AHEAD OF

THE MAIN BOUNDARY AND THE ALREADY WESTERLY WINDS MAY CREATE

PROBLEMS FOR DEEPER CONVERGENCE ALONG THE PRIMARY BOUNDARY. CLOUD

COVER HAS THINNED AND SCOURED IN MANY AREAS AND ALLOWED FOR

FAIRLY RAPID WARMING IN THE NORTHWEST CWA. ADAPTING AN AMDAR

SOUNDING FOR THE ROCKFORD 1 PM OBSERVATION INDICATES THE SURFACE

BASED CIN IS DOWN TO 100 J/KG. /DOWN 400 J/KG IN THE PAST THREE

HOURS/.

VISIBLE SATELLITE IS INDICATING THE FIRST CUMULUS ACROSS

NORTHEAST IA/SOUTHWEST WI/FAR NORTHWEST IL ASSOCIATED WITH WEAK

CONVERGENCE DEVELOPING AHEAD OF THE MAIN SURFACE FRONT. WHILE THIS

IS STABLE LOOKING INITIALLY...CONVERGENCE IS EXPECTED TO INCREASE

AS THE SURFACE FRONT STRENGTHENS WITH ITS EASTWARD PROGRESSION AND

BE IN TANDEM WITH THE RETURN OF INSTABILITY AROUND THE BACK SIDE

OF THE REMNANT COLD POOL. FURTHER AIDING THIS WILL BE THE FORCING

OF A MID-LEVEL JET STREAK AND ASSOCIATED DRYING ON WATER VAPOR

MOVING EAST SOUTHEAST FROM WESTERN WI/SOUTHERN MN. EXPLICIT

CONVECTIVE MODELS ARE IN FAIRLY GOOD AGREEMENT ON DEVELOPING

DISCRETE ACTIVITY OVER THE SOUTHERN WI/NORTH CENTRAL IL. AHEAD OF

THIS FEATURE...ALONG THE WESTERLY WIND SHIFT MENTIONED EARLIER NOW

ACROSS THE NORTH METRO MAY SERVE AS A FOCUS FOR DEVELOPMENT TOO.

DESPITE THE AGGRESSION OF THE MODELS AND THE DIMINISHING

CIN...SATELLITE TRENDS ARE NOT POSITIVE FOR IMMEDIATE DEVELOPMENT.

ANY DEVELOPMENT NEAR OR ACROSS THE NORTHERN FORECAST AREA DURING

THE MIDDLE TO LATTER PART OF THIS AFTERNOON WOULD LIKELY BE

LIMITED IN COVERAGE INITIALLY AS WELL...BUT COULD IMPROVE AS THE

NORTHWESTERLY PUSH CATCHES UP TO THE SURFACE TROUGH AIDING IN MORE

SEGMENT TYPE STRUCTURE. HOW FAR SOUTH ANY ACTIVITY WOULD DEVELOP

OR MAKES IT INTO THE FORECAST AREA AS IT EVOLVES EAST IS

CHALLENGING TO TELL AT THIS TIME. IN ADDITION...A CONTINUED

ELEVATED INSTABILITY GRADIENT AND TRAILING SHORT WAVE ACROSS THE

SOUTHERN FORECAST AREA COULD LEAD TO ISOLATED CONVECTIVE

DEVELOPMENT IN THAT REGION. CONFIDENCE ON DEVELOPMENT IN THIS AREA

AND HOW IT WOULD BEHAVE IS LOW.

WITH EFFECTIVE DEEP LAYER SHEAR ANTICIPATED TO INCREASE TO 40-50

KT AND AT LEAST MUCAPE OF 1000-2000 J/KG...SUPERCELLS ARE

CERTAINLY POSSIBLE IF DEVELOPMENT CAN HAPPEN THIS AFTERNOON. WITH

STEEP MID-LEVEL LAPSE RATES AND LARGE CAPE IN THE -10C TO -30C

HAIL GROWTH AREA...LARGE HAIL WOULD SEEM LIKE THE GREATER THREAT

INITIALLY...WITH WINDS GRADUALLY INCREASING WITH ANY ORGANIZATION.

THE 0-1 KM SHEAR HAS GRADUALLY DIMINISHED AS THE DIRECTIONAL

COMPONENT AT THE SURFACE HAS BECOME MORE SOUTHWEST/WEST ACROSS

NORTHERN IL. CANT RULE OUT THE TORNADO POSSIBILITY...BUT MAY NEED

TO SEE SOME STORM DEVELOPMENT SOON ACROSS THE AREA FOR THAT TO

OCCUR. WILL SEE WHAT THE SOUNDINGS FROM 19Z SPECIAL RAOB RELEASES

AT DVN AND ILX LOOK LIKE.

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Hope you can get some nice t storm action from your hi rise view, Alek, I was surprised with the intensity of the storms last night in sw WI. Really did not expect that. Hope the upper air support and other factors come together for this evening's potential. Had a good soaking heavy rain from the dying MCS this morning around 10 am EDT as it passed through Elkhart.

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Hope you can get some nice t storm action from your hi rise view, Alek, I was surprised with the intensity of the storms last night in sw WI. Really did not expect that. Hope the upper air support and other factors come together for this evening's potential. Had a good soaking heavy rain from the dying MCS this morning around 10 am EDT as it passed through Elkhart.

I was playing video games when that line came through...sounded pretty solid but nothing epic. I should be better attuned to this action.

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MESOSCALE DISCUSSION 1896

NWS STORM PREDICTION CENTER NORMAN OK

0402 PM CDT WED SEP 05 2012

AREAS AFFECTED...NRN IL...SRN WI

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 052102Z - 052230Z

PROBABILITY OF WATCH ISSUANCE...40 PERCENT

SUMMARY...A CONDITIONAL THREAT OF SUPERCELLS WITH LARGE HAIL AND

DAMAGING WINDS EXISTS ACROSS FAR NRN IL AND SRN WI...AND THE AREA IS

BEING MONITORED FOR POSSIBLE DEVELOPMENT.

DISCUSSION...THE AIR MASS ACROSS THE REGION WAS AFFECTED BY EARLY

DAY CONVECTION...BUT SOME RECOVERY HAS TAKEN PLACE. STREAMLINES ARE

CONVERGING OVER THE AREA BUT SOME CAPPING EXISTS. THE SURFACE

THETA-E AXIS REMAINS W OF THE AREA...BUT MORE BUOYANT AIR MAY

EVENTUALLY MOVE IN SLOWLY FROM THE SW. IT IS UNCLEAR IF THE FORCING

WILL OVERCOME CAPPING...BUT IF IT DOES...CONDITIONS WILL BE QUITE

FAVORABLE FOR HAIL AND WIND.

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