Severe Thunderstorm Warning 100, NWS Quad Cities, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
251 PM CDT SUN JUL 20 2001

SITUATION THIS AFTERNOON SOMEWHAT SIMILAR TO YESTERDAY WITH
ORGANIZED CONVECTION TOPPING UPPER RIDGE STREAMING EAST ACROSS
NORTHERN IOWA WITH SLIGHT SOUTHEAST TREND. BIGGEST DIFFERENCE TODAY
IS STRONGER OUTFLOW BOUNDARIES EVIDENT ON 88DS THAT WILL ACT AS
BETTER FOCUS FOR THUNDERSTORM DEVELOPMENT LATE THIS AFTERNOON AND
EVENING. FORECAST CHALLENGE REMAINS THUNDERSTORM CHANCES AND
NECESSITY FOR HEAT ADVISORY THROUGH MONDAY.

UPPER LEVEL RIDGE REMAINED OVER EAST TX TO WESTERN IA AXIS THIS
MORNING WITH WEAK TROUGH IN THE NORTHEAST AND STRONGER PAC NW
TROUGH. H7 SHORTWAVE EVIDENT ON WATER VAPOR IMAGERY MOVING INTO SE
NEB AT 18Z NOT HANDLED WELL BY MODELS AND THINK THIS MAY PROVIDE
ADDED SUPPORT FOR THUNDERSTORMS LATER THIS EVENING AS IT ROTATES
THROUGH RIDGE INTO SOUTH CENTRAL IOWA. ALL MODELS GENERATING QPF TOO
FAR SOUTH THIS AFTERNOON. ETA HAD CLOSEST FIT IN SHORT TERM...THEN
MAIN MODEL DIFFERENCE WAS AVN NOW PUSHING FRONT ACROSS IA/IL FASTER
THAN PREVIOUS RUN. WENT WITH COMPROMISE OF ETA AND AVN ON TIMING
OF FRONT ACROSS FORECAST AREA MONDAY NIGHT AND ENDING OF POPS AS
HIGH DECENDS INTO NORTHERN PLAINS TO BRING DRIER...THEN AVN FOLLOWED
FOR MEDIUM RANGE.

STRONGEST OUTFLOW MOVING SE FROM SE OF DBQ TO CID AT 19Z WITH LESS
OBVIOUS BOUNDARY ACROSS S CENTRAL IA TO CENTRAL IL. ABUNDANT
SUNSHINE TODAY HAS RESULTED IN LAPS CAPES AS HIGH AS 5K TO 7K J/KG
ACROSS EASTERN IA AND EXPECT NUMEROUS THUNDERSTORMS LATE AFTERNOON
AND EARLY EVENING ALONG BOUNDARY INTERSECTIONS. MUCH LIKE IN CENTRAL
IA THIS AFTERNOON...EXPECT THESE TO BE MAINLY SHORT-LIVED PULSE
STORMS AS MID LEVEL FLOW IS WEAK. CONVECTION SHOULD CONTINUE AFTER
SUNSET AS SHORTWAVE APPROACHES AND FLOW AT H85 INCREASES. BEST
CHANCES WILL BE ALONG AND NORTH OF I-80 TONIGHT AND WILL GO WITH
50 TO 60 POPS THERE AND 40 TO SOUTH. SURFACE DEWPOINTS STAYING IN
MID 70S THROUGH NIGHT AND MID LEVEL CONVECTIVE DEBRIS WILL KEEP HEAT
INDICES ABOVE ADVISORY CRITERIA IN SOUTH. ALONG AND NORTH OF HIGHWAY
30 WILL BE MORE MARGINAL DUE TO SLIGHTLY COOLER AIR FROM
THUNDERSTORMS TO NORTH...BUT WILL BE NEEDED AGAIN FOR MONDAY WITH
FRONT NOT MOVING THROUGH UNTIL LATE IN DAY AND TO KEEP THINGS SIMPLE
WILL REISSUE HEAT ADVISORY FOR ENTIRE CWA FOR TONIGHT AND MONDAY.

ON MONDAY H5 RIDGE BEGINS TO FLATTEN AS STRONG SHORTWAVE PUSHES S
INTO NORTHERN PLAINS. THIS CAUSES TROUGH CURRENTLY IN HIGH PLAINS TO
PUSH E-SE. WILL KEEP HIGH SCATTERED POPS GOING FOR MONDAY AHEAD OF
FRONT DURING DAY AND THEN MAINLY ISOLATED FOR EVENING AS FRONT
PUSHES TO SOUTH. SURFACE DEWPOINTS AND H85 TEMPERATURES SIMILAR TO
TODAY OVER FORECAST AREA AND EXPECT HEAT INDICES BACK INTO 105 TO
110 RANGE TO WARRANT ADVISORY. SHOULD BE MAINLY DRY TUESDAY
WITH DRIER LOW LEVEL NE FLOW. BUT WITH PROXIMITY OF FRONT TO SOUTH
AND WEAK WAVES IN WESTERLIES...CANNOT RULE OUT ISOLATED
THUNDERSTORMS AND LEFT IN WORDING FOR LATE AFTERNOON AND EVENING.

.DVN...
IA...IL...MO...HEAT ADVISORY TONIGHT AND MONDAY.

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