Severe Thunderstorm Warning 90, NWS Chicago, IL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO IL
315 PM CDT MON JUL 7 2003

AVIATION DISCUSSION FOR THE 00 UTC TAFS

THE GOES SOUNDING AT 22Z AND THE ACARS SOUNDING AT 2345 UTC SHOW
LARGE POSITIVE AREAS. BELOW 727 MB ON THE ACARS SOUNDING THERE
IS SOME CIN. THE ATMOSPHERE WILL SUPPORT THUNDERSTORMS BUT A
A TRIGGER IS NEEDED. THIS WILL BE A WEAK COLD FRONT THAT EXTENDS
FROM EAST IOWA THROUGH NORTHWEST ILLINOIS. THE FRONT WILL
MOVE SOUTHEAST AND BY TUESDAY MORNING WILL STRETCH FROM DVN
TO JUST SOUTH OF CHICAGO. THIS WILL CAUSE THE THUNDERSTORMS
AROUND 03 UTC TO 05 UTC. THEN BEING SO LATE THE ATMOSPHERE
MAY STABILIZE A LITTLE AS THE FRONT MOVES SOUTH OF THE TAFS
AREA.  WILL KEEP THUNDERSTORMS IN THE VICINITY FROM 10 TO 14
AS THE FRONT CONTINUES SOUTHWARD AND STALLS SOUTH OF THE
TAFS. A SHORT WAVE IS INDICATED ON THE ETA 500 MB FORECAST
HEIGHT AND VORTICITY FIELD. THE VORTICITY IS ESPECIALLY
HAS A LARGE GRADIENT. THIS WILL MOVE THE FRONT NORTH AND
PROVIDE ENOUGH VERTICAL LIFT TO SET OFF THUNDERSTORMS IN
THE AFTERNOON.

WHW

PUBLIC DISCUSSION FOR AFTERNOON ZONES/GRIDS:

AMS HAS RECOVERED QUICKLY FROM THIS MORNINGS CONVECTION.  SFC
ANALYSES SHOW TEMPS IN LOWER 90S IMMEDIATELY UPSTREAM OVER NORTHWEST
AND CENTRAL ILLINOIS...WITH MID 70S DEW POINTS POOLING ALG
RETREATING OUTFLOW BOUNDARY FROM NEAR DBQ-ARR-JOT.  SATLT IMAGERY
SHOWS WIDESPREAD CU DVLPMT OVR FA...BUT NO IMMEDIATE SIGNS OF TSTM
DVLPMT ATTM XCP NR DSM AT INTERSECTION OF OLD BOUNDARIES. AMS FROM
ERN IA-CNTRL IL IS QUITE UNSTABLE WITH SFC BASED LI/S NR -13 AND MU
CAPES OVR 4000 J/KG.    THINKING IS THAT SCT TSTMS WILL DVLP NXT FEW
HRS FROM SRN WI-NRN IL-ERN IA.  MORE ORGANIZED STMS MAY FORM NR SFC
COLD FRONT OVR UPPER MIDWEST.  THIS FRONT SAGS DOWN INTO FA ON TUES
AS LO LVL FLOW BEGINS TO BACK ACROSS AREA BY AFTERNOON.  THIS IS
EXPECTED TO SET UP PERIODS OF TSTMS.  THIS ZONE OF CONVECTION THEN
SAGS SWD INTO SRN CWA TUES NGT AS HI PRES BUILDS OVR ERN ONTARIO IN
RESPONSE TO BUCKLE IN WLYS.  LINGERING SHWRS TO CONT OVR WED INTO
WED EVENING.  THEN DRY...SEASONABLE WX UNTIL NXT SHORT WAVE MOVES
IN.  RIGHT NOW MED RANGE GFS BRINGS THIS SYS IN SAT NGT OR SUN.

.CHI...NONE

MERZLOCK

FXUS63 KLOT 080048 RRA
AFDCHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO IL
740 PM CDT MON JUL 7 2003

AVIATION DISCUSSION FOR THE 00 UTC TAFS

THE GOES SOUNDING AT 22Z AND THE ACARS SOUNDING AT 2345 UTC SHOW
LARGE POSITIVE AREAS. BELOW 727 MB ON THE ACARS SOUNDING THERE
IS SOME CIN. THE ATMOSPHERE WILL SUPPORT THUNDERSTORMS BUT A
A TRIGGER IS NEEDED. THIS WILL BE A WEAK COLD FRONT THAT EXTENDS
FROM EAST IOWA THROUGH NORTHWEST ILLINOIS. THE FRONT WILL
MOVE SOUTHEAST AND BY TUESDAY MORNING WILL STRETCH FROM DVN
TO JUST SOUTH OF CHICAGO. THIS WILL CAUSE THE THUNDERSTORMS
AROUND 03 UTC TO 05 UTC. THEN BEING SO LATE THE ATMOSPHERE
MAY STABILIZE A LITTLE AS THE FRONT MOVES SOUTH OF THE TAFS
AREA.  WILL KEEP THUNDERSTORMS IN THE VICINITY FROM 10 TO 14
AS THE FRONT CONTINUES SOUTHWARD AND STALLS SOUTH OF THE
TAFS. A SHORT WAVE IS INDICATED ON THE ETA 500 MB FORECAST
HEIGHT AND VORTICITY FIELD. THE VORTICITY IS ESPECIALLY
HAS A LARGE GRADIENT. THIS WILL MOVE THE FRONT NORTH AND
PROVIDE ENOUGH VERTICAL LIFT TO SET OFF THUNDERSTORMS IN
THE AFTERNOON.

WHW

PUBLIC DISCUSSION FOR AFTERNOON ZONES/GRIDS:

AMS HAS RECOVERED QUICKLY FROM THIS MORNINGS CONVECTION.  SFC
ANALYSES SHOW TEMPS IN LOWER 90S IMMEDIATELY UPSTREAM OVER NORTHWEST
AND CENTRAL ILLINOIS...WITH MID 70S DEW POINTS POOLING ALG
RETREATING OUTFLOW BOUNDARY FROM NEAR DBQ-ARR-JOT.  SATLT IMAGERY
SHOWS WIDESPREAD CU DVLPMT OVR FA...BUT NO IMMEDIATE SIGNS OF TSTM
DVLPMT ATTM XCP NR DSM AT INTERSECTION OF OLD BOUNDARIES. AMS FROM
ERN IA-CNTRL IL IS QUITE UNSTABLE WITH SFC BASED LI/S NR -13 AND MU
CAPES OVR 4000 J/KG.    THINKING IS THAT SCT TSTMS WILL DVLP NXT FEW
HRS FROM SRN WI-NRN IL-ERN IA.  MORE ORGANIZED STMS MAY FORM NR SFC
COLD FRONT OVR UPPER MIDWEST.  THIS FRONT SAGS DOWN INTO FA ON TUES
AS LO LVL FLOW BEGINS TO BACK ACROSS AREA BY AFTERNOON.  THIS IS
EXPECTED TO SET UP PERIODS OF TSTMS.  THIS ZONE OF CONVECTION THEN
SAGS SWD INTO SRN CWA TUES NGT AS HI PRES BUILDS OVR ERN ONTARIO IN
RESPONSE TO BUCKLE IN WLYS.  LINGERING SHWRS TO CONT OVR WED INTO
WED EVENING.  THEN DRY...SEASONABLE WX UNTIL NXT SHORT WAVE MOVES
IN.  RIGHT NOW MED RANGE GFS BRINGS THIS SYS IN SAT NGT OR SUN.

.CHI...NONE

MERZLOCK

ILZ003>006-008-010>014-019-020>023-032-033-039-INZ001-002-010-011-019
-081100-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE CHICAGO IL
400 PM CDT MON JUL 7 2003

THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTH CENTRAL AND NORTHEAST
ILLINOIS...NORTHWEST INDIANA...AND THE ADJACENT WATERS OF LAKE
MICHIGAN.

.DAY ONE... TONIGHT

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS TONIGHT.  THE LATEST
IN A SERIES OF SHORTWAVES WILL BE MOVING THROUGH THE UPPER LAKES
REGION TONIGHT...ENHANCING CHANCES FOR ORGANIZED CONVECTION OVER THE
OUTLOOK AREA. THE BEST CHANCE FOR SEVERE STORMS WILL BE BETWEEN 10
PM AND 6 AM TONIGHT AND TUESDAY MORNING. DAMAGING WINDS AND LARGE
HAIL ARE THE MAIN SEVERE THREATS.

.DAYS TWO THROUGH SEVEN... TUESDAY THROUGH SUNDAY

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS AGAIN TUESDAY AND
TUESDAY NIGHT FOR MOST OF THE AREA.  HEAVY RAIN IS POSSIBLE
ESPECIALLY IN SOUTHERN PORTIONS...WHICH COULD CAUSE AT LEAST SMALL
STREAM FLOODING DUE TO ALREADY SATURATED SOILS FROM THE WEEKEND
RAINS...PRIMARILY SOUTHEAST OF A BLOOMINGTON...WATSEKA...RENSSELAER
LINE.

SHOWERS AND THUNDERSTORMS WILL LINGER THROUGH WEDNESDAY...BUT ARE
NOT EXPECTED TO BE SEVERE. MORE THUNDERSTORMS COULD RETURN SATURDAY.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS MAY BE NEEDED THIS AFTERNOON...FROM MID AFTERNOON ON...AND
TONIGHT.

&&

           NWS CHICAGO WEBPAGE

    HTTP://WWW.CRH.NOAA.GOV/LOT (LOWER CASE)
OR  HTTP://WEATHER.NOAA.GOV/CHICAGO (LOWER CASE)