Severe Thunderstorm Warning 29, NWS Chicago, IL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO IL
142 PM CDT WED AUG 21 2002

SYNOPSIS...SLOW MOVING COOL FRONT WILL SAG INTO NORTHERN ILLINOIS AND
LINGER FOR A DAY OR SO.  VERY MOIST AND UNSTABLE AIR ALONG STIRRED UP
BY A COUPLE MID LEVEL DISTURBANCES PROMISES A PERIOD OF WET
CONDITIONS TONIGHT THROUGH MUCH OF FRIDAY.  LOCALLY HEAVY RAIN MAY
OCCUR LATER TONIGHT AND AGAIN THURSDAY NIGHT INTO FRIDAY MORNING.

DISCUSSION...POTENTIALLY EXCESSIVE RAINFALL SITUATION SHAPING UP
ACROSS CWA NEXT TWO DAYS OR SO. MODELS HAVE BEEN CONSISTENT IN
SAGGING COOL FRONT INTO NORTHERN ILL LATE THUR MORNING OR EARLY
AFTERNOON. VERY WET AIRMASS NOW SPREADING INTO THE REGION WITH PRECIP
WATER VALUES FORECAST TO RANGE OVER 2.5 INCHES ON THUR.  THIS IS THE
UPPER RANGE OF VALUES FOR THESE LATITUDES AND SUGGESTS POTENTIAL FOR
EXCESSIVE RAINS WHERE OR IF CELLS FORM AND ECHO-TRAIN.

AT THIS POINT TWO MAIN PERIODS APPEAR THE BEST FOR RAINFALL...LATER
TONIGHT AND THURSDAY MRNG THEN 24HRS LATER...THUR NIGHT AND FRIDAY
MORNING.  BETWEEN ACTIVITY COULD BE MORE DISORGANIZED BUT NOT NIL.
CONVECTION ACROSS WISC INTO NRN IOWA WILL RE-ENFORCE LOW LEVEL
BAROCLINIC ZONE THIS AFTERNOON. SHORT WAVE MOVING OUT OF IOWA THIS
EVENING WILL INTENSIFY AND BACK LOW LEVEL JET INTO THIS REGION.
WINCHESTER PROFILER ALREADY REFLECTS THIS. EXPECT CONVECTION TO
INCREASE ALONG THE BOUNDARY BY SUNSET AND THIS EVENING AND SAG INTO
NRN ILL. COULD BE FEW APPRCHG SVR STORMS FAR NW SINCE WIND FIELD SO
STRONG BUT THOSE SHOULD COLLAPSE INTO RAIN EVENTS SOON. WITH RR QUAD
OF JET CORE EASING SOUTHWARD FULL VERTICAL CIRCULATION PROMISES SOME
WELL DEVELOPED AREAS OF R+.  SOILS OVER NRN ILL QUITE DRY THOUGH AND
SHOULD HANDLE 2-3 RAINS WHERE THEY OCCUR...IF NOT IN AN HOUR.

NEXT SHORT WAVE PROGGED TO SLIDE NEAR OR OVER NRN ILL THURSDAY NIGHT
AND FRIDAY.  AVN HAS THIS SYSTEM FURTHER N THAN ETA WITH A MUCH
BETTER INFLOW WIND FIELD. BY THAT TIME SURFACE FRONT SHOULD BE S OF
I-80 BUT OVERALL DYNAMICS BOTH SURFACE AND ALOFT SUGGEST ANOTHER
ROUND OF POTENTIAL R+. THIS TIME SOILS MAY BE TOO WET AND THATS WHEN
FLOODING WILL LIKELY BE MORE OF A CONCERN.  HOW RAPIDLY CONDS IMRPOVE
LATER FRIDAY INTO SAT REMAINS TO BE SEEN BUT BY THEN SURFACE FNT
SHOULD BE WELL INTO OHIO VALLEY ALONG WITH DEEPEST MOISTURE FIELD.

AFTER THIS SITUATION IS RESOLVED A MORE AMPLIFIED TROUGH INTO THE
EASTERN STATES WILL STABILIZE GT LAKES REGIONS WITH RE-ENFORECED HIGH
PRESSURE AND NEAR AVE TEMPS.  MODEL GUIDANCE APPEARS TOO LOW WITH THE
POPS NEXT 48HRS ALONG WITH TEMPS BEING TOO HIGH GIVEN THE EXPECTED
CLOUD COVER THE RAIN DROPS.  ESFCHI HAS BEEN ISSUED FOR FLOOD
POTENTIAL. MAY ISSUE PRODUCTS EARLY DUE TO POWER/GENERATOR SWITCHING.
KML

.CHI...NONE

ILZ003>006-008-010>014-019>023-032>033-039-INZ001>002-010>011-
019-221100-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE CHICAGO IL
1200 PM MDT WED AUG 21 2002

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

NO HAZARDOUS WEATHER IS EXPECTED THIS AFTERNOON.  THERE IS A SLIGHT
CHANCE OF SEVERE THUNDERSTORMS THIS EVENING OVER NORTH CENTRAL
ILLINOIS ..AS WELL AS THE POTENTIAL FOR HEAVY RAIN...ACROSS NORTHERN
ILLINOIS AND NORTHWEST INDIANA LATER TONIGHT AND THURSDAY MORNING.
THE RISK AREA FOR BOTH THE SEVERE THUNDERSTORMS AND THE HEAVY RAIN
IS MAINLY ALONG AND NORTH OF THE KANKAKEE AND ILLINOIS RIVERS.

VERY WARM AND MOIST AIR WILL OVERSPREAD THE REGION THIS AFTERNOON
RESULTING IN AN INCREASINGLY UNSTABLE AND WATER-CHARGED AIRMASS.
THUNDERSTORMS ARE EXPECTED TO SPREAD SOUTHEASTWARD FROM WISCONSIN
AND INTO NORTHERN ILLINOIS LATE THIS AFTERNOON AND THIS EVENING AS A
COLD FRONT SAGS SOUTH THROUGH THE UPPER MIDWEST...AND INTO NORTHERN
ILLINOIS OVERNIGHT. THERE IS A SLIGHT RISK OF DAMAGING WINDS FROM
THESE STORMS THIS EVENING OVER THE NORTH CENTRAL PORTION OF THE
STATE.

THE SURFACE FRONT IS EXPECTED TO LINGER ACROSS NORTHERN ILLINOIS
THROUGH FRIDAY. A SERIES OF WEAK DISTURBANCES COMBINED WITH AN
EXCEPTIONALLY WET AIRMASS RAISES THE POTENTIAL FOR FLOODING RAINS
THURSDAY NIGHT INTO FRIDAY.  THE RAIN EXPECTED TONIGHT AND EARLY
THURSDAY SHOULD BE ABSORBED BUT SUBSTATIAL RAINS LATER MAY NOT
BE.

THE RAINS SHOULD RETREAT TO THE SOUTH ON SATURDAY WITH THE FIRST
PART OF NEXT WEEK RETURNING TO SEASONABLE TEMPERATURES AND DRY
CONDITIONS.

KML