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July 12-15, 2014 Severe Weather Threat


Chicago WX

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Tornado watch likely coming for N IL/Chicagoland.

 

MESOSCALE DISCUSSION 1347
NWS STORM PREDICTION CENTER NORMAN OK
0551 PM CDT SAT JUL 12 2014

AREAS AFFECTED...N IL...SE IA...FAR NW IND

CONCERNING...TORNADO WATCH 411...

VALID 122251Z - 130015Z

THE SEVERE WEATHER THREAT FOR TORNADO WATCH 411 CONTINUES.

SUMMARY...WW ISSUANCE IS LIKELY DOWNSTREAM OF WW 411 ACROSS MUCH OF
NRN IL IN THE NEXT HOUR OR TWO. DAMAGING WINDS WILL BE THE PRIMARY
HAZARD...BUT ISOLATED SEVERE HAIL AND A TORNADO OR TWO WILL BE
POSSIBLE.

DISCUSSION...A PREVIOUSLY INTENSE STORM WITHIN WW 411 OVER CLINTON
COUNTY IA LIKELY PRODUCED A SEVERE DOWNBURST WITH 49 KT WINDS
MEASURED AT 2220Z AT THE DEWITT RWIS SITE. DOWNSTREAM AIR MASS HAS
BECOME MODERATELY UNSTABLE OVER MUCH OF IL WITH SURFACE TEMPERATURES
IN THE 80S AND DEW POINTS IN THE LOWER TO MIDDLE 70S.
MID/UPPER-LEVEL LAPSE RATES WILL REMAIN MARGINAL...AROUND 6 DEG C/KM
FROM 700-500 MB PER 18Z DVN RAOB. BUT LOW/MID-LEVEL SHEAR WILL BE
FAVORABLE FOR UPDRAFT ROTATION WITH 0-6 KM VALUES AROUND 40 KT PER
LOT/DVN VWP DATA. STRENGTHENING OF WINDS IS ANTICIPATED IN RESPONSE
TO THE VIGOROUS SHORTWAVE TROUGH NEAR THE S-CNTRL CANADIAN/N-CNTRL
CONUS BORDER. SUPERCELLS AND MULTICELL CLUSTERS WILL LIKELY DEVELOP
EWD THROUGH THE EVENING CAPABLE OF ALL SEVERE HAZARDS.

..GRAMS.. 07/12/2014
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Rainfall is predicted to be around 2 to 5 inches, I don't see the need for a tornado watch. At least as of right now.

 

 

Parameters are decent enough with a strengthening LLJ and storms have already developed.  Really not more time to wait to issue one.

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Thinking the cell merger about to take place on the Lee County IL cell might do the trick.  Eff sig tor 2-3 and incredibly high humidity through the column should allow for a sustained tornado threat for several hours into the night if this storm can really organize itself.

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Mesoscale Discussion 1350

< Previous MD

mcd1350.gif


MESOSCALE DISCUSSION 1350

NWS STORM PREDICTION CENTER NORMAN OK

0909 PM CDT SAT JUL 12 2014

AREAS AFFECTED...N IL...SE IA/WI

CONCERNING...TORNADO WATCH 411...

VALID 130209Z - 130315Z

THE SEVERE WEATHER THREAT FOR TORNADO WATCH 411 CONTINUES.

SUMMARY...OVERALL SEVERE RISK MAY REMAIN TOO MARGINAL TO WARRANT

DOWNSTREAM WW ISSUANCE. STILL...ISOLATED DAMAGING WINDS WILL BE THE

PRIMARY HAZARD...ESPECIALLY WITH A CLUSTER EVOLVING E/SE FROM NW IL.

DISCUSSION...DESPITE A FAVORABLE COMBINATION OF CAPE/SHEAR...TSTM

CLUSTERS HAVE STRUGGLED TO YIELD ORGANIZED SEVERE STORMS BEYOND

LOCALIZED DAMAGING WINDS. THIS IS PROBABLY IN PART DUE TO MARGINAL

LAPSE RATES BETWEEN 700-500 MB SAMPLED IN 00Z DVN/ILX RAOBS AND

RELATIVELY WEAK CONVERGENCE ALONG THE FRONT. OVERALL STORM INTENSITY

HAS LARGELY DIMINISHED...EXCEPT FOR A STRONG TO LOCALLY SEVERE

CLUSTER OVER STEPHENSON/CARROLL COUNTY IL. AMIDST LARGEST GREATEST

SURFACE PRESSURE FALLS ACROSS N IL TO FAR S WI...POTENTIAL WILL

EXIST FOR THIS CLUSTER TO PRODUCE ISOLATED DAMAGING WINDS AS IT

MOVES TOWARD CHICAGOLAND.

..GRAMS.. 07/13/2014

ATTN...WFO...LOT...ILX...MKX...DVN...DMX...

LAT...LON 40599195 40719221 40849228 41029215 41569078 42268993

42918868 42898775 42258751 41748740 41438765 40948865

40558972 40499074 40599195

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