Tornado Warning 6, NWS Chicago, IL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO IL
258 PM CDT TUE JUL 24 2001

PRECIP CHANCES AND TEMPS MAIN FORECAST ISSUES THIS TIME AROUND. 18Z
SURFACE ANALYSIS SHOWS DIFFUSE GRADIENT OVER FORECAST AREA...WITH
FRONTAL POSITION SUGGESTED BY DEWPOINTS POOLING INTO THE MIDDLE AND
UPPER 70S ACROSS CENTRAL ILLINOIS AND CENTRAL INDIANA. BEST
DEWPOINT GRADIENT REMAINS ALONG ILLINOIS/WISCONSIN BORDER
HOWEVER...WITH DEWPOINTS STILL IN THE LOWER 70S ACROSS ALL BUT
EXTREME NORTHEAST IL. SATELLITE LOOPS SHOW GOOD VORT MOVING INTO
WESTERN IOWA...WITH ATTENDANT THUNDERSTORM CLUSTER AND SURFACE LOW
PRESSURE. WINDS TRYING TO BECOMING SOUTHEAST INTO NORTH CENTRAL IL
AHEAD OF THE SURFACE LOW...SUGGESTING A SLIGHT RETURN NORTHWARD OF
THE SURFACE FRONT. ETA/AVN/NGM ALL AGREE IN BRINGING THIS WAVE INTO
ILLINOIS LATER THIS EVENING INTO WEDNESDAY...AND WILL LEAN TOWARD
THE HIGHER POPS OF THE AVN MAV GUIDANCE. WESTERN HALF OF FORECAST
AREA IN SLIGHT RISK PER SPC DAY 1 OUTLOOK AND THIS LOOKS GOOD GIVEN
MID LEVEL SPEED MAX...UPPER DIVERGENCE IN RIGHT ENTRANCE TO UPPER
JET AND POOLING DEWPOINTS ALONG BOUNDARY. RADAR LOOPS OUT OF CENTRAL
IOWA SHOWS CONVECTION BEGINNING TO TAKE ON LEWP/BOW CONFIGURATION.

WAVE TRAVERSES FORECAST AREA WEDNESDAY...WITH ALL MODELS BRINING
PRECIP ACROSS THE AREA. ETA 305K ISENTROPIC SURFACE FORECAST SHOWS
BEST LIFT OCCURRING THROUGH 18Z WED...WITH WEAK SINKING IN THE
AFTERNOON. WILL CONTINUE TO GO WITH OR ABOVE MAV POPS FOR WEDNESDAY.
FRONT THEN SHOULD PUSH THROUGH THE FORECAST AREA WITH THE LESS HUMID
AIR FINALLY PUSHING IN FOR THE REMAINDER OF THE WEEK.

BIG GUIDANCE DISCREPANCY SHOWS UP WITH MAX TEMP FORECAST FOR
WEDNESDAY. MAV MUCH COOLER WITH LOW TO MID 70S...ALTHOUGH THIS UP A
FEW DEGREES FROM 00Z RUN. FWC A COUPLE OF CATEGORIES HIGHER...WITH
LOW 80S FORECAST. GIVEN CONDITIONS IN RAIN COOLED AIR OUT WEST TODAY
WILL TREND TOWARD LOWER MAV NUMBERS...BUT STILL A BIT HIGHER THAN
GOING FORECAST.

IN THE EXTENDED...WAVE MOVES OUT WEDNESDAY EVENING...WITH SURFACE
HIGH BUILDING EAST ACROSS THE UPPER LAKES. THIS SHOULD PROVIDE A
COUPLE OF NICE DAYS WITH DRIER NORTHEASTERLY FLOW...SUNSHINE AND
SEASONABLE TEMPS. HIGH SHIFTS EAST THIS WEEKEND...WITH GRADUAL WARM
UP AND SLOW RETURN OF MOISTURE. LOW CHANCE POPS SUNDAY THROUGH
TUESDAY AS WARM ADVECTION RETURNS...BUT BEST CHANCES REMAIN
NORTHWEST OF THE FORECAST AREA...IN AREA OF BETTER MOISTURE
CONVERGENCE ALONG AND AHEAD OF SURFACE COLD FRONT.

.CHI...NONE

RATZER

ILZ003>006-008-010>014-020>023-250325-

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE CHICAGO IL
925 PM CDT TUE JUL 24 2001

...SEVERE THUNDERSTORM WATCH CANCELLATION...

THE SEVERE THUNDERSTORM WATCH ISSUED EARLIER THIS EVENING FOR MOST OF
NORTHERN ILLINOIS HAS BEEN CANCELED FOR THE ROCKFORD AND CHICAGO
AREAS.   ALTHOUGH SHOWERS AND THUNDERSTORMS ARE STILL FORECAST TO MOVE
INTO THE AREA DURING THE OVERNIGHT HOURS...THEY ARE NOT EXPECTED TO BE
SEVERE.

MERZLOCK