Severe Thunderstorm Warning 28, NWS Chicago, IL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
655 PM CDT THU APR 13 2006

.DISCUSSION FOR AFTERNOON GRIDS/ZFP...
322 PM CDT

MAIN FOCUS IS ON SHORT TERM...AND CONVECTIVE/SEVERE POTENTIAL
TONIGHT...THEN PRECIP AND TEMP TRENDS THROUGH WEEKEND.

SFC WARM FRONT CONTINUES TO SURGE NORTH INTO THE MID MISSISSIPPI
VALLEY THIS AFTERNOON...WITH 19 UTC SFC ANALYSIS INDICATING BOUNDARY
ROUGHLY ALONG KDSM...KOTM...KIRK TO WEST OF KSTL LINE. SFC DEW
POINTS INTO THE LOWER 60S IN WARM SECTOR...WITH TEMPS SOLIDLY IN THE
MID 80S. SPC RUC ANALYSIS INDICATES MLCAPE VALUES IN EXCESS OF 2500
J/KG IN WARM SECTOR OVER MO...WITH DEEP LAYER MOIST CONVERGENCE MAX
FROM NE MO INTO SE IA. VIS SAT PICS SHOW CU CONGESTUS FINALLY DVLPG
OVER EASTERN MO. APPEARS ALSO WEAK PSUEDO WARM FRONT ALONG TRAILING
EDGE OF MID LEVEL CLOUD DECK OVER NERN IL...LIKELY ENHANCED BY
DIFFERENTIAL HEATING DUE TO CLOUD COVER. ALOFT...VAPOR LOOPS
INDICATE MID LEVEL SHORT WAVE/SPEED MAX TRANSLATING EAST NORTHERN
PLAINS TO UPPER MIDWEST...EXPECTED TO AID CONVECTIVE INITIALIZATION
VERY LATE AFTN/EARLY EVENING ALONG WRM FRONT ACROSS ERN IA/MO. THIS
ACTIVITY EXPECTED TO SPREAD SOUTHEAST ALONG FRONTAL ZONE...AS LOW
LEVEL MOIST/WARM ADVECTION CONTNUES INTO WFO LOT FCST AREA. SPECIAL
18Z AND 20Z SOUNDINGS FROM DVN AND ILX RESPECTIVELY INDICATE STEEP
LAPSE RATES AND DRY LOW LEVELS NORTH OF WARM FRONT...SUGGESTING
POTENTIAL FOR DAMAGING WINDS AND LARGE HAIL IF/WHEN ORGANIZED
CONVECTION GETS GOING. WILL HAVE CHANCE POPS WEST THIS EVENING
CLOSER TO VCNTY WRMFRNT...WHILE WILL MAINTAIN LIKELY POPS FOR TRW
OVERNIGHT ESPECIALLY 03-08Z TIME FRAME. SHORT WAVE TROUGH AXIS THEN
MOVES THROUGH IN PREDAWN HOURS...DIMINISHING THREAT FROM WEST TO
EAST.

FRONT EXPECTED TO LINGER ACROSS SOUTHERN CWA OR CNTRL IL
FRIDAY...AIDED BY OUTFLOW FROM OVRNGT ACTIVITY. ANOTHER WEAKER VORT
DEPICTED BY GFS/NAM SAT AFTN...AND WILL CARRY CHC AFTN POPS
GENERALLY SOUTH OF INTERSTATE 88. UPPER RIDGE BEGINS TO DVLP ACROSS
MS VLY FRIDAY NIGHT AS MORE AMPLIFIED UPPER TROUGH EMERGES ACROSS
SOUTHWESTERN US. IN LOW LEVELS...SFC HIGH ACROSS NRN LAKES/ONTARIO
TO HELP PUSH BOUNDARY SOUTH OF CWA...WITH COOL/DRIER NORTH/NORTHEAST
LOW LEVEL FLOW PUSHING MAIN FOCUS OF PRECIP SOUTH OF FCST AREA.
FRONT BEGINS TO COME BACK NORTH LATE SATURDAY AND SUNDAY
HOWEVER...AS THIS MORE AMPLIFIED SHORT WAVE MOVES ACROSS THE PLAINS.
THIS BRINGS RETURN OF PRECIP THREAT FOR EASTER HOLIDAY. SOME TIMING
DIFFERENCES BETWEEN GFS/ECMWF IN MID RANGE OF FCST RUN...WITH ECMWF
SUGGESTING SLOWER PROGRESSION. WILL MAINTAIN CHANCE POPS FROM MAINLY
SAT NIGHT THROUGH SUNDAY AS SYSTEM PASSES ACROSS REGION. UPPER RIDGE
DEVELOPS IN ITS WAKE MONDAY...THOUGH APPEARS NEXT AMPLIFED WAVE
APPROACHES TUES NGT/WED.

GFS RUNS DVLP PESKY CLOSED UPPER LOW WHICH WOBBLES ACROSS MIDWEST IN
LATER PERIODS NEXT WEEK...SUGGESTING COOLER/SHOWERY WX.

TEMP WISE...WILL BE TRICKY WITH FRONTAL BOUNDARY STRETCHED ACROSS
CWA ESPECIALLY THROUGH EARLY THIS WEEKEND. LARGER TEMP RANGE FROM
NORTH TO SOUTH REALLY SHOWS SATURDAY...WITH MORE NE/E FLOW SUPPLYING
LAKE COOLING TO NORTHERN PARTS OF FA. WILL SETTLE ON RANGE 60S NORTH
TO 70S/AROUND 80 SOUTH...OF COURSE SOMEWHAT COOLER ALONG LAKE SHORE.

RATZER

&&

.AVIATION...
655 PM CDT

00Z TAFS...FEATURES OF NOTE ARE LK BRZ WHICH IS BEING OVERWHELMED BY
ADVANCING WMFNT...ESPECIALLY WITH DEC IN HEATING AND STRONG SURGE OF
LLVL MOISTURE ACROSS MO INTO SRN AND E CNTRL IA. ELEVATED CONVECTION
N OF WMNFT MOVG ESE ACROSS SERN WI AND EXPECTED TO CONT ACROSS SRN
LK MI INTO LWR MI THIS EVE. SFC BASED TSRA DVLPD IN CNTRL IA 21-22Z
AT NOSE OF STG LLVL THETA-E ADVECTION AND WHERE DEEP UVV OCCURING AS
SHRTWV TROF MOVS E INTO WRN MN AND IA. SHRTWV FCST TO MOV GENERALLY
EWRD AND THRU ERN WI AND IL OVR TOP OF BROAD UPR RDG CNTRD OVR SRN
AND CNTRL PLAINS. WHILE MID LVL FLO SUGGESTS EWRD MVMT OF IA TSRA
ACROSS NRN IL...EXPECT CONVECTION TO TAKE A TURN TO MORE SERLY THIS
EVE STAYING CLOSER TO MOISTURE DISCONTINUITY AS IT GRADUALLY SHIFTS
E INTO IL. THUS EXPECT SOME TSRA IN VC OF TERMINALS MID TO LATE
EVE...FEEL BEST COVERAGE TO BE A LTL FURTHER TO THE S AND SW.

TRS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
.IL...NONE.
.IN...NONE.
.LM...NONE.

&&

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
430 PM CDT THU APR 13 2006

ILZ003>006-008-010>014-019>022-023-032-033-039-INZ001-002-010-011-
019-140930-
WINNEBAGO-BOONE-MCHENRY-LAKE IL-OGLE-LEE-DE KALB-KANE-DU PAGE-COOK-
LA SALLE-KENDALL-GRUNDY-WILL-KANKAKEE-LIVINGSTON-IROQUOIS-FORD-
LAKE IN-PORTER-NEWTON-JASPER-BENTON-
430 PM CDT THU APR 13 2006

THIS PORTION OF THE HAZARDOUS WEATHER OUTLOOK IS FOR NORTH CENTRAL
AND NORTHEAST ILLINOIS...AND NORTHWEST INDIANA.

.DAY ONE... TONIGHT

THUNDERSTORMS ARE LIKELY ACROSS THE OUTLOOK AREA TONIGHT. THERE IS A
SLIGHT RISK THAT SOME OF THESE STORMS COULD BE SEVERE...WITH LARGE
HAIL AND DAMAGING WINDS THE PRIMARY SEVERE WEATHER THREATS.

THUNDERSTORMS ARE EXPECTED TO DEVELOP ACROSS PARTS OF EASTERN IOWA
AND NORTHEAST MISSOURI THIS EVENING...AND SPREAD EAST ALONG A WARM
FRONT ACROSS NORTHERN ILLINOIS AND NORTHWEST INDIANA DURING THE LATE
EVENING AND OVERNIGHT HOURS.

.DAYS TWO THROUGH SEVEN... FRIDAY THROUGH WEDNESDAY

THERE IS A CHANCE OF THUNDERSTORMS FRIDAY AFTERNOON AND EVENING
ACROSS PARTS OF THE OUTLOOK AREA...MAINLY SOUTH OF INTERSTATE 80.
THERE IS A SLIGHT RISK THAT SOME OF THESE STORMS COULD BE SEVERE.

THERE IS A CHANCE OF THUNDERSTORMS AGAIN LATE SATURDAY THROUGH
SUNDAY. THERE IS A SLIGHT RISK THAT SOME OF THESE STORMS COULD BE
SEVERE...MAINLY ACROSS EASTERN PARTS OF THE OUTLOOK AREA SUNDAY
AFTERNOON.

ISOLATED THUNDERSTORMS ARE AGAIN POSSIBLE LATE TUESDAY INTO
WEDNESDAY.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE REQUESTED TONIGHT.

&&

COMPLETE FORECAST INFORMATION IS AVAILABLE ON THE
NWS CHICAGO WEBPAGE: WEATHER.GOV/CHICAGO (LOWER CASE)

LMZ740>745-766-140930-
WINTHROP HARBOR IL TO MICHIGAN CITY IN-
LAKE MICHIGAN-
430 PM CDT THU APR 13 2006

THIS PORTION OF THE HAZARDOUS WEATHER OUTLOOK IS FOR THE ILLINOIS
AND INDIANA WATERS OF LAKE MICHIGAN.

.DAY ONE... TONIGHT

THERE IS A CHANCE OF THUNDERSTORMS TONIGHT. THERE IS A SLIGHT RISK
THAT SOME OF THESE STORMS COULD BE SEVERE...WITH LARGE HAIL AND
STRONG GUSTY WINDS THE MAIN SEVERE WEATHER THREATS.

.DAYS TWO THROUGH SEVEN... FRIDAY THROUGH WEDNESDAY

THERE IS A CHANCE OF THUNDERSTORMS OVER FAR SOUTHERN LAKE MICHIGAN
FRIDAY AFTERNOON...AND AGAIN LATE SATURDAY INTO SUNDAY.

ISOLATED THUNDERSTORMS ARE AGAIN POSSIBLE LATE TUESDAY INTO
WEDNESDAY.

&&

COMPLETE FORECAST INFORMATION IS AVAILABLE ON THE
NWS CHICAGO WEBPAGE: WEATHER.GOV/CHICAGO (LOWER CASE)