Severe Thunderstorm Warning 163, NWS Chicago, IL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO IL
642 PM CDT THU JUL 31 2003

AVIATION DISCUSSION FOR 00Z TAFS

TS FIRING OVER WI AND FAR NORTHERN IL THIS EVENING. EXPECT EVENING
ACTIVITY TO REMAIN MAINLY NORTH OF CHICAGO TERMINALS...GETTING CLOSE
TO DPA/ORD. AS SHORTWAVE SWINGS ACROSS MIDWEST OVERNIGHT...BETTER
CHANCE OF TS AFTER 08Z OR SO AND WILL MAINTAIN CURRENT TIMING OF
PROB30 GROUP. SOUTHERLY WINDS UNTIL EARLY FRI AFTERNOON WHEN WINDS
SWING AROUND TO WNW.

CMS

PUBLIC DISCUSSION FOR AFTERNOON ZONES AND GRIDS...

SHORT TERM...THROUGH 02/12Z
MODELS IN EXCELLENT AGREEMENT ON UPPER LOW VICINITY LAKE OF THE
WOODS TO WOBBLE VERY SLOWLY SOUTHEAST DURING THIS TIME WITH ANY
NUMBER OF MINOR RIPPLES ROTATING AROUND IT AS IT DOES TO KEEP THINGS
QUITE UNSETTLED.

FOR THE VERY SHORT TERM VERY UNSTABLE SURFACE AIRMASS FROM CENTRAL
WI TO CENTRAL IOWA HAS BEGUN TO ERUPT AS WEAK SURFACE CONVERGENCE IS
HELPED BY APPROACHING MID LEVEL TROUGH.  THIS SHOULD BRING SCATTERED
THUNDER OVERSPREADING THE AREA BY AROUND MIDNIGHT. AFTER THIS
EVENING, HAVE PUT LITTLE REFINEMENT IN TIMING OR AREAL DISTRIBUTION,
EXCEPT THAT AS A RESULT OF FIRST 24-36 HOURS OF ACTIVITY, A BOUNDARY
MAY TEND TO FOCUS ACTIVITY TO THE SOUTH BY FRIDAY NIGHT.

LITTLE CHANGE TO GOING TEMPS WHICH ARE IN CLOSE AGREEMENT WITH THE
VERY SIMILAR MOS #S.

KAPLAN

LONG TERM...AFTER 02/12Z

UPPER LOW PROGGED TO MOVE FROM NEAR DULUTH AT 02/12Z TO TO SOUTHERN
WISCONSIN BY 03/12Z...WITH THE GFS DEVELOPING A DUMBBELL LOW OVER
LAKE SUPERIOR AT THIS TIME. LOWS THEN CONVERGE OVER THE NORTHERN END
OF LAKE MICHIGAN BY THE END OF THE PERIOD. TIMING AND LOCATION ARE
IN QUESTION...BUT MAIN RESULT OF THIS ACTION REMAINS THE
SAME...UNSEASONABLY COOL TEMPERATURES ALOFT WITH PERSISTENT CYCLONIC
FLOW. NOT COMPLETELY CONVINCED THAT CWFA WILL DRY OUT AFTER DUMBBELL
FORMS AND CENTER OF CIRCULATION TRANSLATES BACK NORTH...BUT WILL
LEAVE GRIDS DRY FROM TUESDAY ONWARD FOR THE TIME BEING.

TEMPERATURES TO REMAIN AOB NORMALS THROUGH THE PERIOD.

.CHI...NONE

JHV

ILZ003>006-008-010>014-019-020>023-032-033-039-INZ001-002-010-011-019
-011100-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE CHICAGO IL
430 PM CDT THU JUL 31 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 ACROSS EXTREME
NORTHERN ILLINOIS THIS EVENING...MAINLY BETWEEN 500 PM AND
MIDNIGHT.  THE SLIGHT RISK AREA IS GENERALLY ALONG AND NORTH OF A
LINE FROM DOWNTOWN CHICAGO TO PEORIA.

AN UPPER LEVEL LOW PRESSURE SYSTEM IN NORTHERN MINNESOTA WILL MOVE
VERY SLOWLY SOUTHEAST...WITH A SERIES OF DISTURBANCES ROTATING
AROUND THE MAIN SYSTEM.  THE AIR AHEAD OF THIS SYSTEM IS UNSTABLE
ENOUGH TO SUPPORT SCATTERED SEVERE THUNDERSTORMS.

AFTER MIDNIGHT...AS THE UPPER LEVEL SYSTEM MOVES CLOSER...
ADDITIONAL STORMS MAY DEVELOP...FORMING SHORT LINES.  THESE LINES OF
STORMS MAY CONTAIN HAIL AND DAMAGING WINDS.

.DAYS TWO THROUGH SEVEN... FRIDAY THROUGH WEDNESDAY

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER ALL OF THE
REGION FRIDAY AFTERNOON AND EVENING.   ISOLATED DAMAGING WIND GUSTS
AND HAIL WILL BE THE PRIMARY THREATS.

ON SATURDAY AND SUNDAY...SCATTERED THUNDERSTORMS WILL CONTINUE TO
DEVELOP FROM TIME TO TIME AS THE PERSISTENT UPPER LEVEL WEATHER
SYSTEM REMAINS OVER THE UPPER MIDWEST.  AT THIS TIME...THESE STORMS
ARE EXPECTED TO PRODUCE BRIEF GUSTY WINDS AND SMALL HAIL.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BECOME NECESSARY LATER THIS EVENING AND AGAIN
FRIDAY AFTERNOON AND EVENING.

&&

           NWS CHICAGO WEBPAGE

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

MERZLOCK

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