Severe Thunderstorm Warning 90, NWS Chicago, IL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO IL
230 PM CDT SUN AUG 6 2000

WW 649 IN FULL BLOOM ACROSS ERN IA/NWRN IL. THIS MOVING ACROSS NRN
IL THIS AFTN AND ERY TONIGHT AHEAD OF COLD FRONT RUNNING THROUGH
THAT AREA. HAVE BEEN WAITING FOR THE SHOE TO DROP ALL MORNING AND
APPEARS UNSTABLE ENVIRONMENT HAS BEEN TIPPED OVER. DRY STABILIZING
AIR BEHIND COLD FRONT TONIGHT WILL CLEAR US OF THIS THREAT. MAIN
UPPER AIR SUPPORT FROM RRQ OF UPPER JET OVER CENTRAL AND SRN IL INTO
CENTRAL INDIANA. BUT CONTINUED CLOUD COVER DURING THE DAY HAS
STYMIED GROWTH INTO SEVERE STAGE WHEREAS WIDE OPEN SKIES IN NRN IL
HAS FORCED TEMPS TO NEAR 90 WHERE THE CONVECTIVE TEMPERATURE RESIDES
AS PER THE MORNING SOUNDINGS.

AS MENTIONED ABOVE...COLD FRONT SHOULD SWEEP SEWD THRU NRN IL/NWRN
IN BY MIDNIGHT...CLEARING OUT THE ALREADY DISIPATING STORMS AND
MAKING FOR A DRY DAY ON MONDAY. HOWEVER AS UPPER JET SHIFTS TO THE
NORTHEAST ON MONDAY...UPPER LEVEL DIVERGENCE COUPLES WELL WITH
INCREASING LOW LEVEL SOUTHWEST FLOW IN PLAINS FROM ANOTHER
DEVELOPING SYSTEM AND ASSOCIATED SHORT WAVE. THIS WILL BRING TONIGHTS
COLD FRONT BACK NORTH AS A WARM FRONT...ALONG WITH THOSE 70
DEWPOINTS.

SO ANOTHER GOOD CHANCE OF THUNDERSTORMS CALLED FOR MONDAY NIGHT
THROUGH TUESDAY. THIS HALTED BY NEXT COLD FRONT TUESDAY NIGHT OR
EARLY WEDNESDAY. DRY AGAIN FOR THURSDAY AS HIGH PRESSURE BUILDS
ACROSS ONTARIO AND DOWN THE GREAT LAKES FOR FRIDAY.

HIGHS TOMORROW WILL DEPEND ON AVAILABLE SUNSHINE. FWCS ARE
PREDICTING OUR FIRST 90 DEGREE HIGH BUT FANS CONSERVATIVE TO THE
MIDDLE 80S. MIDDLE GROUND WOULD BE UPPER 80S. DEWPOINTS IN MIDDLE
60S TOMORROW STILL HUMID ALTHO A RESPITE FROM LOWER 70S. BUT
MOISTURE STILL AVAILABLE TO RETARD TEMPERATURE RISES...ESPECIALLY
WITHOUT A GOOD STRONG SOUTHWEST WIND. SAME CONDITIONS FOR TUESDAY.

.CHI...WW 649

BRUMER

ILZ003>006-008-010>014-019>023-032>033-039-INZ001>002-
010>011-019-071100-

SEVERE WEATHER OUTLOOK
NATIONAL WEATHER SERVICE CHICAGO IL
NOON CDT/EST SUN AUG 6 2000

FOR NORTH CENTRAL AND NORTHEAST ILLINOIS AND NORTHWEST INDIANA.

THUNDERSTORMS HAVE BLOSSOMED ACROSS CENTRAL AND SOUTHERN ILLINOIS...
JUST SOUTH OF NORTHEAST ILLINOIS AND NORTHWEST INDIANA. BUT LITTLE
IS HAPPENING ACROSS OUR AREA AT THIS TIME. THERE IS HOWEVER THE
POTENTIAL FOR STORM DEVELOPMENT SHOULD SOME TRIGGER MOVE THROUGH TO
UPSET A DELICATE BALANCE OF INSTABILITY.

VERY HUMID AIR IS IN PLACE OVER THE REGION. ALTHOUGH THE AREA IS
THERMALLY CAPPED ALOFT... IT MAY TAKE LITTLE MORE THAN A WEAK OUTFLOW
FROM THESE STORMS IN CENTRAL ILLINOIS TO PROVIDE THAT TRIGGER.

AS A RESULT OF THE LOOMING INSTABILITY... THERE IS A SLIGHT RISK OF
SEVERE THUNDERSTORMS TODAY AND TONIGHT SOUTH OF A LINE FROM WAUKEGAN
THROUGH DE KALB THROUGH AMBOY IN NORTHERN ILLINOIS. EVEN FURTHER...
THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS SOUTH OF A LINE
FROM VALPARAISO THROUGH MERRILLVILLE IN NORTHWEST INDIANA THROUGH
MANHATTAN... SENECA... AND TONICA IN NORTHEAST ILLINOIS.

A COLD FRONT SHOULD DROP THROUGH THE AREA FROM THE NORTHWEST LATE
TONIGHT. THIS SHOULD HELP STABILIZE THE LOWER LAYERS MORE BY
BRINGING IN A LITTLE DRIER AIR.

THIS FRONT WILL RETURN MONDAY NIGHT AS A WARM FRONT...RETURNING US
INTO AN UNSTABLE ENVIRONMENT ONCE AGAIN.

BRUMER