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April 18-20th Severe Weather


Chicago Storm

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Definitely have had alot of rain down in southern indiana in spots this morning..

0921 AM FLASH FLOOD BROWNSTOWN 38.88N 86.05W 04/19/2011 JACKSON IN CO-OP OBSERVER BROWNSTOWN HIGH SCHOOL RECEIVED 4.26 INCHES OF RAINFALL. INDIANA HIGHWAY 250 BETWEEN BROWNSTOWN AND UNIONTOWN HAD WATER OVER IT.

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Interesting that the headline mentions a few potentially strong tornadoes, but there is no hatching on the maps.

I think the lack of hatching is SPC's lack of confidence in storm mode or how long storms are discrete. I'd be they hatch it in the next update if their uncertainty has been reduced.

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DAY 1 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

1129 AM CDT TUE APR 19 2011

VALID 191630Z - 201200Z

...THERE IS A MDT RISK OF SVR TSTMS THIS AFTERNOON AND TONIGHT OVER

PARTS OF ERN OK...AR...CNTRL/SRN MO...WRN TN...KY...IL...IND AND WRN

OH...

...THERE IS A SLGT RISK OF SVR TSTMS FROM THE LOWER GREAT LAKES SWWD

INTO SRN TX...

...OUTBREAK OF SEVERE THUNDERSTORMS CAPABLE OF WIDESPREAD

HAIL...DAMAGING WINDS AND A FEW STRONG TORNADOES POSSIBLE THIS

AFTERNOON THROUGH TONIGHT...

..OH VALLEY/LOWER GREAT LAKES SWWD INTO ERN OK/AR

SHORTWAVE TROUGH OBSERVED OVER THE CNTRL/SRN HIGH PLAINS THIS

MORNING WILL CONTINUE NEWD...CONTRIBUTING TO A CORRIDOR OF 30-60 M

HEIGHT FALLS PER 12-HR AT 500 MB FROM THE CNTRL PLAINS THROUGH THE

MID MS VALLEY INTO UPPER GREAT LAKES. IN THE LOW-LEVELS...SURFACE

LOW ATTENDANT TO THIS SYSTEM ANALYZED OVER W-CNTRL MO AS OF 16Z WILL

DEVELOP NNEWD TO N OF STL BY 19/21Z...THE IL/IND BORDER NEAR DNV BY

20/03Z TO LAKE ERIE BY 20/12Z. A WARM FRONT WILL PRECEDE THE

LOW...GRADUALLY LIFTING NWD THROUGH IL/IND/OH/PA. TRAILING COLD

FRONT WILL ADVANCE SEWD...LIKELY EXTENDING FROM SURFACE LOW OVER

CNTRL IL SWWD THROUGH E-CNTRL MO...NWRN AR AND SERN OK BY 20/00Z.

THIS COLD FRONT WILL SERVE AS THE PRIMARY FOCUS FOR SEVERE

THUNDERSTORM DEVELOPMENT THIS AFTERNOON INTO TONIGHT.

12Z REGIONAL SOUNDINGS SHOWED THE PRESENCE OF STEEP MIDLEVEL LAPSE

RATES/EML IN PLACE FROM THE CNTRL/SRN PLAINS EWD THROUGH THE

MID/LOWER MS VALLEYS. THESE LAPSE RATES RESIDE ABOVE A MOIST AND

RATHER BROAD WARM SECTOR CHARACTERIZED BY PW VALUES OF 1.0-1.5

INCHES AND BOUNDARY LAYER DEWPOINTS IN THE 60S. ASIDE FROM ISOLATED

OCCURRENCES OF HAIL N OF WARM FRONT OVER THE OH VALLEY TODAY...A CAP

AT THE BASE OF THE EML IS EXPECTED TO DELAY SURFACE-BASED TSTM

DEVELOPMENT UNTIL THIS AFTERNOON.

ABUNDANT SUNSHINE...THE STEEP LAPSE RATES AND INCREASING LOW-LEVEL

MOISTURE WILL YIELD A MODERATELY TO STRONG UNSTABLE WARM SECTOR

TODAY WITH MLCAPE VALUES RANGING FROM 1000-2000 J/KG S OF THE WARM

FRONT IN THE OH VALLEY...TO 3000-4000+ J/KG AHEAD OF COLD FRONT FROM

SRN MO INTO ERN OK/WRN AR. FRONTAL UPLIFT COUPLED WITH INCREASED

FORCING FOR ASCENT ATTENDANT TO MIDLEVEL TROUGH ARE EXPECTED TO

FOSTER TSTM DEVELOPMENT BY MID AFTERNOON FROM THE VICINITY OF THE

SURFACE LOW OVER CNTRL/E-CNTRL MO SWWD TO ERN OK/WRN AR.

AN ISALLOBARICALLY BACKED WIND FIELD AHEAD OF SURFACE LOW WILL

RESULT IN A CORRIDOR OF ENHANCED LOW-LEVEL SHEAR FROM E-CNTRL MO EWD

THROUGH CNTRL PARTS OF IL/IND. GIVEN MORE DISCRETE STORM MODES

/I.E. SUPERCELLS/...THIS AREA WILL REPRESENT THE GREATEST RISK FOR

TORNADOES /SOME POSSIBLY STRONG/ FROM LATE THIS AFTERNOON INTO

TONIGHT. OTHERWISE...EXPECT THE DEVELOPMENT OF SUPERCELLS AND LINE

SEGMENTS ALONG COLD FRONT WITH EVENTUAL UPSCALE GROWTH INTO ONE OR

MULTIPLE MCSS/QLCSS. WIDESPREAD OCCURRENCES OF HAIL AND DAMAGING

WINDS /SOME SIGNIFICANT/ ARE EXPECTED ACROSS THE MODERATE RISK AREA

INTO EARLY WEDNESDAY DUE TO THE PRESENCE OF STEEP LAPSE RATES AND

THE WIDE...UNSTABLE WARM SECTOR.

..TX

TSTM POTENTIAL AND ATTENDANT SEVERE WEATHER THREAT IS MORE UNCERTAIN

WITH SWD EXTENT ALONG THE DRYLINE THIS AFTERNOON OWING TO WEAK OR

NEGLIGIBLE LARGE-SCALE FORCING FOR ASCENT. NONETHELESS...MORNING

VISIBLE SATELLITE IMAGERY DOES SUGGEST THAT STRONG DIABATIC HEATING

WILL OCCUR TODAY ALONG AND W OF DRYLINE...BOOSTING SURFACE

TEMPERATURES INTO THE 90S. SHOULD SUFFICIENT HEATING/CONVERGENCE

DEVELOP TO INITIATE ISOLATED STORMS...THE PRESENCE OF MLCAPE VALUES

OF 3000-4000+ J/KG AND 30-40 KT OF DEEP WLY SHEAR WILL BE SUPPORTIVE

OF SUPERCELLS CAPABLE OF LARGE HAIL. ANY STORMS THAT MAY DEVELOP

WOULD LIKELY WEAKEN BY LATE EVENING AS THE BOUNDARY LAYER BEGINS TO

COOL AND CONVECTIVE INHIBITION INCREASES

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A good chunk of the 10% hatched tornado area is in the 40's right now, but it's a different world south of the warm front. I always feel like these days are a bit more dangerous from a public perception standpoint.

Almost looks like two warm fronts on satellite. You can see where the true surface front is by where the low level cumulus field starts. North of that there's about a 50-75 mile wide clear swath where temps are warmer than further north, but still not as warm as further south. This area will probably will probably mix out and become much warmer over the next few hours.

Still really cool here in Peoria at 42. Gonna head down towards Litchfield Illinois.

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Update from IND:

.NEAR TERM /TODAY AND TONIGHT/... INCREDIBLY TIGHT WARM FRONT LOCATED ROUGHLY ALONG THE SOUTHERN BOUNDARY OF THE FORECAST AREA THIS MORNING. SECOND ROUND OF SHOWERS AND THUNDERSTORMS AFTER THE OVERNIGHT ACTIVITY IS PROCEEDING ACROSS THE NORTHERN HALF OF THE AREA WITH HEAVY RAIN AND SOME HAIL. NORTHWARD PROGRESS OF THE BOUNDARY HAS BEEN DELAYED BY THIS MORNING CONVECTION...AND THIS WILL SIGNIFICANTLY IMPACT EXPECTED HIGH TEMPERATURES THIS AFTERNOON...WHICH IS A MAJOR BUST POTENTIAL AREA OF THE FORECAST AS GRADIENT ACROSS THE BOUNDARY IS ON THE ORDER OF 15-20 DEGREES OVER A 1-2 COUNTY WIDE AREA. HAVE DELAYED THE NORTHWARD PROGRESS OF THE BOUNDARY A FEW HOURS AND THUS LOWERED MAX TEMPS ACROSS MUCH OF THE CENTRAL AND NORTHERN PORTION OF THE AREA. AFTER THE CURRENT ROUND OF THUNDERSTORMS CONCLUDES...ATTENTION WILL SHIFT TO THE WARM FRONT...AS THIS MAY SERVE AS THE FOCUS FOR ADDITIONAL DEVELOPMENT LATER THIS AFTERNOON INTO THE EARLY EVENING...WITH POTENTIAL FOR TORNADIC STORMS...LARGE HAIL...DAMAGING WINDS...AND HEAVY RAIN. STILL EXPECT ADDITIONAL SEVERE STORMS IN THE FORM OF A QUICKLY PROGRESSING LINE OR BOW COMPLEX SWEEPING ACROSS THE AREA OVERNIGHT...WITH CONTINUED TORNADO/LARGE HAIL/HEAVY RAIN POTENTIAL...IN ADDITION TO AN EVEN GREATER DAMAGING WIND POTENTIAL.

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