Severe Thunderstorm Warning 8, NWS Chicago, IL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO IL
245 AM CDT MON APR 23 2001

DEEP(ENING) LOW NORTHWEST OF OMAHA THIS MORNING WITH WARM FRONT
NORTHEAST AND EAST TO SOUTHERN WISCONSIN AND COLD FRONT TRAILING TO
WEST OF TOPEKA/OKC.  WEAKENING LINE OF SHOWERS/NOT A LOT OF TSTORMS
HAS MOVED OUT WELL AHEAD OF COLD FRONT, ESPECIALLY NORTHERN END, AND
IS LOCATED NEARER DIFFUSE MOIST AXIS.  WOULD NOT EXPECT TO SEE THIS
WEAKENING TREND REVERSE AS AIR AHEAD OF LINE IS DRIER.  LINE
PROBABLY WILL DISSIPATE IN THE EARLY MORNING IN OUR WESTERN COUNTIES.

MODEL FORECASTS AGAIN PRETTY SIMILAR IN THE FIRST 24-36 HOURS.
SURFACE THERMAL BOUNDARY TO PUSH INTO WESTERN COUNTIES BY MIDDAY AND
OUT OF THE FAR EASTERN COUNTIES BY EARLY EVENING.  MODEST (FOR THE
ETA) CAPES AND SOME LOW LEVEL MOISTURE CONVERGENCE STILL ARGUE FOR
POSSIBLE REDEVELOPMENT IN THE AFTERNOON WITH INCREASING POPS AS LINE
PROGRESSES FROM CENTRAL INTO SOUTHEASTERN PORTION OF CWFA. FORECAST
UVV INCREASES THROUGH THE DAY AND IS FAIRLY IMPRESSIVE MAINLY EAST
OF OUR AREA BY 00Z IN THE AVN/ETA. UPPER SUPPORT RATHER WEAK AND LOW
LEVEL INSTABILITY/CONVERGENCE NOT EXCEPTIONAL, SO POPS IN THE CHANCE
CATEGORY CENTRAL TO LIKELY FAR EAST LOOK REASONABLE.  SEVERE CHANCES
ARE PROBABLY BEST IN THE EAST AS WELL.

HOWEVER, EVEN IN THE ABSENCE OF THUNDERSTORMS, WINDS WILL BE A
PROBLEM TODAY.  ETA STILL SHOWING NEAR 60 KNOT WINDS POTENTIALLY
MIXING DOWN DURING THE AFTERNOON AS COOLING AT 850 KICKS IN ALTHOUGH
OTHER MODELS ARE WEAKER.  THIS REMAINS STRONGER FORECAST WIND
PROFILE THAN SATURDAYS, WHICH PROVED TO BE A BORDERLINE ADVISORY
EVENT. AND THIS MORNINGS SURFACE LOW IS IN IDENTICAL POSITION TO
THE ONE 48 HOURS AGO AND FORECAST ON A SIMILAR TRACK TO THAT ONE.
NOCTURNAL GUSTS IN EASTERN IA ALREADY PUSHING ADVISORY CRITERIA, IN
PART BEING DRIVEN BY LARGE PRESSURE FALLS.  WHILE ISALLOBARIC
CONTRIBUTION MAY BE LESS OF A FACTOR IN OUR AREA, BELIEVE MIXING
ALONE SHOULD BE ENOUGH TO PUSH SOME GUSTS OVER 45 IN THE LATE
MORNING AND AFTERNOON OVER MOST OF THE CWFA.

TEMPS, WITH WARM FRONT NO LONGER IN CWFA SHOULD BE A LITTLE EASIER.
WITH A WARM START AND EXPECTED FRONTAL TIMING NOTED, THIS SHOULD
ALLOW TEMPS TO REACH NEAR MAV VALUES THIS AFTERNOON, MAYBE JUST A
TAD BELOW CONSIDERING UPSTREAM TEMPS YESTERDAY.  BEYOND THE FIRST
PERIOD MOS S CLOSE...AND CLOSE TO GOING FORECAST...AND WONT STRAY
TOO FAR.

EXTENDED...
GOING EXTENDED MAY BE A LITTLE SLOW WITH WARM UP BASED ON 00Z AVN
RUN. WEDNESDAY TEMPS DEPEND ON HOW QUICKLY CLOUDS MOVE OUT IN THE
AFTERNOON.  MAV S QUITE A BIT WARMER THAN GOING FORECAST BUT CANT
SEE GOING THAT WARM WITH UNCERTAINTY OF TIMING ON CLOUDS.  WILL BUMP
TEMPS UP A CATEGORY OR SO.  AVN/UKMET ALSO SUGGEST TEMPS ON THURSDAY
MAY BE TOO LOW, BUT I DONT USUALLY MESS WITH FORECAST THAT FAR OUT
FOR A FEW DEGREES.

COORD...MKX/DVN/ILX.

.CHI...GALE WARNING LAKE MICHIGAN
       WIND ADVISORY LATE MORNING AND AFTERNOON ENTIRE CWFA

KAPLAN

ILZ003>006-008-010>014-019>023-032>033-039-INZ001>002-010>011-019-
241100-

SEVERE WEATHER OUTLOOK
NATIONAL WEATHER SERVICE CHICAGO IL
1200 PM CDT/EST MON APR 23 2001

FOR NORTH CENTRAL AND NORTHEAST ILLINOIS AND NORTHWEST INDIANA...

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON AND
VERY EARLY THIS EVENING EAST OF INTERSTATE 39.

A COLD FRONT NOW MOVING THROUGH NORTHWEST AND WEST CENTRAL ILLINOIS
WILL CONTINUE TO SURGE EASTWARD ACROSS NORTHERN ILLINOIS THIS
AFTERNOON...EXITING NORTHWEST INDIANA BY EARLY THIS EVENING.
SHOWERS AND THUNDERSTORMS ARE PRESENTLY MOVING ACROSS THE WESTERN
PORTIONS OF THE CWA.  THESE WILL BE OVERSPREADING THE CHICAGO AREA
BY 1 PM CDT AND NORTHWEST INDIANA BY 2 PM CDT.   SOME OF THESE
STORMS MAY ORGANIZE THEMSELVES INTO SMALL BOW ECHOES CAPABLE OF
DAMAGING STRAIGHT LINE WIND GUSTS.

THE SEVERE WEATHER THREAT WILL END WITH THE PASSAGE OF THE COLD
FRONT.  AT PRESENT THE TIMING ON THIS FRONT WOULD BRING IT THROUGH
THE ROCKFORD AREA BY 100 PM...CHICAGO AROUND 300 PM AND VALPARAISO
BY 500 PM CDT.

IN ADDITION TO THE POSSIBILITY OF THUNDERSTORM INDUCED WIND
GUSTS...A WIND ADVISORY WILL REMAIN IN EFFECT UNTIL 7 PM CDT FOR THE
ENTIRE AREA.  NON THUNDERSTORM WINDS GUSTING ROM THE SOUTH UP TO 35
MPH WILL BECOME SOUTHWEST WITH THE FRONTAL PASSAGE AND INCREASE TO
GUSTS OCCASIONALLY IN EXCESS OF 45 MPH.

MERZLOCK