Severe Thunderstorm Warning 109, NWS Quad Cities, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
400 AM CDT TUE AUG 3 2004

.SYNOPSIS...AT 06Z STNRY FRONT STRETCHED FROM SD/NE BORDER E THROUGH
NW IA AND SW MN INTO CNTRL WI. A WK SURFACE LOW WAS LOCATED OVER
CNTRL NE WITH A WRM FRNT EXTDG E INTO E CNTRL MO.  AIRMASS OVER MUCH
OF THE REGION WAS QUITE JUICY WITH 70+ DEWPOINTS COVERING MUCH OF MO
ERN KS WRN IA ERN NE AND SRN MN.  NORTH OF THE STNRY FRONT DEWPOINTS
TAPERED OFF RAPIDLY ACRS CNTRL MN. 00Z SOUNDINGS SHOWED A RATHER
STRONG CAP A KDVN/KOAX AND WAS SUPPORTED BY H7 TEMPS RANGING FROM
13C AT KDVN TO 15C AT KOAX.  HOWEVER...DESPITE THE CAP...ISOLD
ELEVATED SEVERE TSRA DVLPD OVER NW IA JUST AFTER MIDNIGHT AND WAS
FORMING INTO THE A SMALL CONVECTIVE COMPLEX ATM FROM W OF KFOD
TO NR KTNU...JUST WEST OF CWA. THE COMPLEX WAS BACKBUILDING ON
THE NW END. TSRA WAS COINCIDENT WITH NARROW PRESSURE FALL MAXIMA
FROM FROM NERN NE INTO SE IA AND ALSO LINED UP WITH DEEP CONVERGENCE
ZONE FROM H8 THROUGH H7 FROM NW IA INTO ECNTRL AND SE IA.

&&

.NEAR TERM (TODAY AND TONIGHT)...CONVECTIVE TRENDS CONTINUE TO BE THE
FOCUS FOR TODAY AND TONIGHT. MODELS ARE NOT PROVIDING MUCH HELP WITH
CONVECTIVE FEEDBACK ISSUES CONTAMINATING THE SOLUTIONS AND IMPACTING
THE LARGE SCALE FEATURES. BELIEVE CAP WILL KEEP ANY CONVECTION FROM
DEVELOPING OVER THE SW THIRD OF THE CWA TODAY. WHILE ON GOING ISOLD/
SCT TSRA WILL CONTINUE TO DEVELOP SE INTO ECNTRL IA THIS MORNING.
WILL HAVE TO WATCH THESE TSRA FOR HAIL...DESPITE HIGH WET BULB ZEROS
(AROUND 13KFT AT KDVN AT 00Z). HVY RAIN WILL ALSO BE A THREAT THIS
MORNING WITH PWS AROUND 1.5...WEAK FLOW AND NEARLY STNRY FORCING
THROUGH MID MORNING.  FEEL TSRA THREAT FOR THE AFTERNOON WILL BE
MINIMAL AS FORCING IN THE FORM OF THE MID LEVEL CONVERGENCE ZONES
ROTATES TO THE NE AS UPPER RIDGE BUILDS AHEAD OF S/W ENERGY MOVING
THROUGH THE PLAINS. TSRA THREAT WILL INCREASE BY LATE EVENING INTO
THE OVERNIGHT HOURS AS THE S/W MOVES INTO THE MID MO RIVER VALLEY AND
SENDS A SURFACE WAVE ALONG THE FRONT...WHICH SHOULD BE OVER SRN IA OR
NRN MO.  CONVECTIVE FEED BACK ON THE ETA/GFS MAKE IT DIFFICULT TO PIN
POINT WHERE THE FRONT AND HEAVIEST QPF WILL OCCUR TONIGHT...SO WILL
GO WITH HEAVY RAIN WORDING FOR THE ENTIRE CWA.     ..DLF..

&&

.LONGER TERM (WEDNESDAY THROUGH NEXT MONDAY)...WILL WALK OUT
EXPECTED MCS THAT SHOULD BE GOING ACRS MUCH OF THE CWA AT START OF
THIS PERIOD ON WED...WITH FEEDBACK POLLUTED MODELS VARYING WITH
EXTENT OF NORTH-SOUTH BOUNDARY PLACEMENT AND SFC WAVE STRENGTH AND
PROPAGATION ALONG THIS FEATURE. ALTHOUGH EVERYBODY IS MENTIONING
THAT THE QPF IS ENHANCED BY THIS FEEDBACK...LOCALLY HEAVY RAIN OF
AT LEAST A FEW INCHES STILL A VERY REAL THREAT FOR PART OF WED
LOOKING AT PWS AND THTA-E FEED/CONVERGENCE ACRS THE AREA. TEMPS ON
WED A BIG CRAP SHOOT DEPENDING ON HOW FAR NORTH BOUNDARY/SFC LOW
MOVES ACRS THE AREA AND EXTENT OF CLOUD COVER/PRECIP...BUT WILL TRY
TO MUDDLE OUT A GENERAL RANGE FROM NORTH TO SOUTH. ETA REALLY SUCKS
THE COOL AIR IN ACRS THE NORTHERN CWA ON WED AND HAS HIGHS ONLY IN
THE LOW 60S AT DBQ. FEEL THIS EXTENT OF CAA OVERDONE...BUT WOULD
NOT BE SURPRISED IF NORTHERN CWA DOESNT GET MUCH ABOVE 70.

THE LATEST SHORT(AND MEDIUM RANGE) MODEL RUN ENSEMBLE SUGGESTS
UPPER TROUGH/CYCLONIC FLOW PATTERN TO DEEPEN ACRS THE GRT LKS AND
UPPER MS RVR VALLEY LATE WED INTO THU MORNING AS UPPER RIDGE
AMPLIFIES ACRS THE ROCKIES. ADDITIONAL VORT ENERGY WILL LOOK TO GET
SHUTTLED DOWN ACRS THE CWA IN STEEPENING NORTHWEST FLOW WITH THIS
PROCESS...BUT  WILL BE TO NO AVAIL AS SEASONABLY STRONG LLVL RIDGE
BUILDS SOUTH OF OF CANADA AND PLOWS DOWN ACRS THE NORTHERN PLAINS.
AS THIS HIGH PRESSURE CONTINUES TO ENGULF THE WESTERN GRT LKS THU
INTO WED...ANOTHER ROUND OF FAIR BUT UNSEASONABLY COOL WX ON TAP TO
END THE WEEK. MODELS SUGGEST SINGLE DIGIT H85 ISOTHERMS INTO THE
CWA POSSIBLY BY THU...AND HIGHS MAY BE HELD IN THE 70S FOR BOTH THU
AND FRI. AS RIDGE AXIS CLOSES IN ON THE CWA LATE THU NIGHT...
POTENTIAL FOR TEMPS TO DIP CLOSE TO RECORD LEVELS(UPPER 40S- AROUND
50) FOR FRI MORNING/AUGUST 6TH LOWS. WILL FOLLOW THE LATEST ECMWFS
LEAD WITH DIGGING TROUGH ACRS THE UPPER MS RVR VALLEY EARLY NEXT WEEK
IN WARMING RETURN FLOW FOR NEXT PRECIP THREAT ON MONDAY.
 ..12..

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.

&&

DLF/12

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
515 AM CDT TUE AUG 3 2004

IAZ040>042-051>054-063>068-076>078-087>089-098-099-ILZ001-002-007-
009-015>018-024>026-034-035-MOZ009-010-041000-
BENTON IA-BUCHANAN IA-BUREAU IL-CARROLL IL-CEDAR IA-CLARK MO-
CLINTON IA-DELAWARE IA-DES MOINES IA-DUBUQUE IA-HANCOCK IL-
HENDERSON IL-HENRY IA-HENRY IL-IOWA IA-JACKSON IA-JEFFERSON IA-
JO DAVIESS IL-JOHNSON IA-JONES IA-KEOKUK IA-LEE IA-LINN IA-LOUISA IA-
MCDONOUGH IL-MERCER IL-MUSCATINE IA-PUTNAM IL-ROCK ISLAND IL-
SCOTLAND MO-SCOTT IA-STEPHENSON IL-VAN BUREN IA-WARREN IL-
WASHINGTON IA-WHITESIDE IL-
515 AM CDT TUE AUG 3 2004

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTHEAST...EAST
CENTRAL...AND SOUTHEAST IOWA...NORTHWEST...NORTH CENTRAL...AND WEST
CENTRAL ILLINOIS...AND NORTHEAST MISSOURI.

.DAY ONE...TODAY AND TONIGHT

SEVERE THUNDERSTORMS WILL BE POSSIBLE THIS MORNING IN SOUTHEAST IOWA
BETWEEN HIGHWAY 34 AND INTERSTATE 80. IF THE SEVERE THUNDERSTORMS
DEVELOP...THEY WILL HAVE THE POTENTIAL OF PRODUCING HAIL THE SIZE OF
GOLFBALLS...60 TO 70 MPH WINDS AND HEAVY RAIN.

THERE WILL BE A THREAT OF MORE SEVERE THUNDERSTORMS AGAIN FROM THIS
EVENING INTO THE OVERNIGHT HOURS OVER MUCH OF THE AREA. THE GREATEST
THREAT OF SEVERE THUNDERSTORMS WILL BE MAINLY AFTER MIDNIGHT. ANY
SEVERE STORMS THAT DEVELOP TONIGHT WILL PRODUCE DAMAGING WINDS AND
LARGE HAIL. HEAVY RAIN WILL ALSO BE POSSIBLE AND COULD RESULT IN
LOCALIZED FLOODING OF SMALL STREAMS AND LOW LYING AREAS.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

NUMEROUS STORM CLUSTERS OR COMPLEXES SHOULD BE OCCURRING ACROSS
THE AREA WEDNESDAY MORNING AS A LOW PRESSURE STORM SYSTEM SHIFTS
EAST OVER EASTERN IOWA AND NORTHWEST ILLINOIS. LATEST INDICATIONS
SUGGEST THERE WILL BE THE POTENTIAL FOR SOME OF THESE STORMS TO
BE SEVERE WEDNESDAY MORNING THROUGH THE MIDDAY PERIOD...BEFORE THE
STORM COMPLEXES MOVE EAST OUT OF THE AREA. THE STRONGEST STORMS
COULD PRODUCE DAMAGING WINDS OF 60 TO 70 MPH AND LARGE HAIL UP TO THE
SIZE OF GOLFBALLS. HEAVY RAIN WILL ALSO BE A THREAT WITH SOME
LOCATIONS POSSIBLY EXPERIENCING AN ADDITIONAL 2 TO 3 INCHES OF
RAINFALL BY EARLY WEDNESDAY AFTERNOON...PRODUCING THE RISK OF
FLOODING.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS MAY BE NEEDED THIS MORNING IN PARTS OF SOUTHEAST AND EAST
CENTRAL IOWA. SPOTTER ACTIVATION MAY BE NECESSARY AGAIN TONIGHT
OVER MUCH OF THE AREA.

DLF/12