Severe Thunderstorm Warning 103, NWS Quad Cities, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
255 PM CDT SAT JUL 21 2001

OF IMMEDIATE CONCERN IS SEVERE POTENTIAL FOR LATE THIS AFTERNOON AND
EARLY EVENING AS MCC MOVING ACROSS SOUTHERN MN SINCE AM BEGINS TO
TURN MORE SE. LINE OF ELEVATED CONVECTION TRIGGERED FROM MN COMPLEX
OUTFLOW THIS MORNING EXTENDING SW INTO W CENTRAL IA AT 18Z ALSO
MOVING E-SE AND EXPECT STORMS TO STRENGTHEN BY FORECAST ISSUANCE AS
THEY MOVE INTO AREA OF LAPS SURFACE BASED CAPES OF 4 TO 6K J/KG.
SEVERE CONVECTION MAY BE ON-GOING AT FORECAST ISSUANCE NW OF DBQ-CID
LINE AND ANTICIPATE MOVEMENT TO SE SIMILAR TO EARLY AM CONVECTION.
MAIN CHALLENGE THROUGH ENTIRE FORECAST IS POPS WITH LITTLE CHANGE IN
UPPER PATTERN THROUGH SHORT TERM. HIGH HEAT INDICES ALSO A CONCERN
THROUGH MONDAY.

UPPER RIDGE AXIS REMAINS ANCHORED FROM TX TO EASTERN NEB WITH
MONSOONAL MOISTURE PLUME SEEN ON WATER VAPOR IMAGERY FROM AZ INTO SW
MN. H85 THERMAL RIDGE WITH H85 TEMPERATURES OF 30C OVER HIGH PLAINS
WITH BAROCLINIC AXIS FROM SD INTO WRN IA AT 12Z. NONE OF THE SHORT
TERM MODELS HAD GOOD HANDLE ON CURRENT CONVECTION...BUT ETA AND AVN
FARED BETTER THAN NGM WITH QPF PLACEMENT. WILL MAINLY FOLLOW AVN DUE
TO BETTER PERFORMANCE PAST FEW WEEKS IN THIS PATTERN.

H5 SHORTWAVE TOPPING RIDGE AND AIDING CURRENT MCC MOVES SE ACROSS
FORECAST AREA THIS EVENING...THEN NEXT H5 VORTICITY MAX PROGGED TO
MOVE THROUGH MONDAY NIGHT. AFTER INITIAL ROUND OF CONVECTION THIS
EVENING...FORCING WILL BE LIMITED TO WHERE LOW LEVEL BOUNDARIES
LINGER AND TAP INTO NOCTURNAL JET. WILL KEEP IN LOW POPS FOR LATE
TONIGHT FOR ALL ZONES. NO MAJOR FOCUS EXPECTED FOR CONVECTION
EXPECTED FOR SUNDAY...BUT WITH VERY MOIST AND UNSTABLE AIRMASS...
WILL LEAVE IN ISOLATED POPS. BETTER CHANCES WILL OCCUR WITH
SHORTWAVE SUNDAY NIGHT AND THEN MONDAY WHEN STRONGER SHORTWAVE IN
WESTERLIES PUSHES THE TROUGH CURRENTLY OVER HIGH PLAINS SE ACROSS
FORECAST AREA.

HEAT ADVISORY WAS ISSUED EARLIER FOR THIS AFTERNOON FOR SOUTH OF
HIGHWAY 30 AND WILL BE NECESSARY CWA WIDE FOR SUNDAY. SURFACE
DEWPOINTS IN UPPER 70S TO AROUND 80 COMMON ACROSS IA AND MO ZONES
BOOSTING HEAT INDICES INTO 105 TO 115 RANGE. WESTERN IL ZONES NOT AS
OPPRESSIVE WITH DEWPOINTS IN LOWER TO MID 70S AND INDICES IN 90 TO
100 RANGE. EVENING CONVECTION MAY COOL TEMPERATURES SOMEWHAT
THIS EVENING...BUT DEWPOINTS TO REMAIN HIGH. ONLY NORTHERN HALF CWA
DIPPED BELOW 80 HEAT INDEX LAST NIGHT AND THINK TONIGHT WILL BE EVEN
WARMER DUE TO MORE SUNSHINE TODAY AND WARMER MAXES. WILL GO AHEAD
AND ISSUE HEAT ADVISORY FOR TONIGHT THROUGH SUNDAY AND EXTEND TO
ENTIRE FORECAST AREA. TEMPERATURES SHOULD REACH LOWER TO MID 90S
SUNDAY WITH WARM ADVECTION AT H85 BOOSTING TEMPERATURES ABOUT 2 C
WARMER INTO RANGE OF 22 TO 24 DEG C. EXPECT CONDITIONS CLOSE TO
ADVISORY CRITERIA TO EXTEND INTO SUNDAY NIGHT AS DEWPOINTS REMAIN
HIGH BUT WILL LET LATER FORECASTS EXTEND THE ADVISORY AS NEEDED.
HIGHS MONDAY WILL BE A BIT COOLER...ESPECIALLY NORTH DUE TO MORE
CLOUD AND AFTERNOON CONVECTION AS TROUGH APPROACHES FROM NW.

UPPER RIDGE FLATTENS AND RETROGRADES WESTWARD TOWARD MIWEEK WITH
NUMEROUS SHORTWAVES IN WESTERLIES TO BRING ALMOST DAILY CHANCES FOR
RAIN. AVN AND MRF SHOW FRONT HANGING EAST TO WEST TO OUR SOUTH WITH
SURFACE HIGH MOVING INTO NE GREAT LAKES PROVIDING COOLER
TEMPERATURES. TEMPERATURES TRENDED DOWNWARD SOME...BUT NOT AS LOW AS
LATEST MEDIUM RANGE GUIDANCE.  THANKS TO DMX AND CHI FOR
COORDINATION.

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

SHEETS