Damaging Winds in Iowa, August 27, 2003

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
155 PM CDT THU AUG 27 2003

SHORT TERM...
CAPE AND MOISTURE POOL LINE UP NICELY WITH DEVELOPING CU FIELD FROM
JUST SW OF DNS THROUGH CSQ TO THE MO BORDER E OF LWD.  EXPECT ISOLD
TRSA THROUGH EARLY EVENING. DIFFUSE AND RATHER CHAOTIC FLOW ON THE
SLATER PROFILER, WITH ANY UPDRAFTS LEANING ONLY SLIGHTLY TO THE E.
SOME THREAT OF LOCALIZED STRONG WINDS WITH THESE STORMS AS THEY
COLLAPSE WITH 1300 J/KG DCAPE NOTED.  WILL ALSO CARRY SLIGHT CHANCE
MOST OF TONIGHT AS WARM FRONT LIFTS NE.  BELIEVE THE MODELS ARE TOO
BULLISH HOWEVER AS MAIN THETA-E ADVECTION AND LLJ CONVERGENCE ARE
WELL N AND NE OF IA.

LONGER TERM...
FEEL THE META HAS A BETTER HANDLE ON TIMING OF THE FRONT MOVING IN
WITH MAIN MID LEVEL PUNCH IN THE NORTHERN PLAINS AND NORTHERN MS
VALLEY.  AGAIN, I FEEL THE CONVECTION AND QPF ARE WAY OVERDONE
THROUGH MUCH OF THURSDAY, SO AM EXPECTING PRETTY DECENT HEATING AS
WIND FLOW BECOMES S AND SSW THURSDAY AFTERNOON. THEREFORE, HAVE
EXCEEDED EVEN ETA TEMPS, GOING WITH PERSISTENCE AND CURRENT OBS AS A
GUIDE IN SW/SC IA WHERE READINGS ARE ALREADY IN THE LOWER TO MID 90S.

PRE FRONTAL TROF WILL FOCUS CONVERGENCE FOR ISOLATED DEVELOPMENT BY
21Z IN WESTERN IA, WITH HIGHER THREAT FURTHER NE ALONG THE FRONT
WHERE EHI, DEEPER LAYER SHEAR AND WARM FRONT INTERSECT IN NORTH
CENTRAL IA INTO MN.  THIS IS WHERE SUPERCELLS WOULD INITALLY BE MORE
LIKELY, WITH SMALLER LEWP STRUCTURES FURTHER SW ALONG THE FRONT.
THESE CELLS COULD EASILY WEAKEN BY EVENING, WITH REINTENSIFICATION
OR NEW DEVELOPMENT LATER THURSDAY EVENING AS LLJ IMPINGES BOUNDARY
AS IT BECOMES ORIENTED WSW-ENE IN SOUTHERN AND EASTERN IA.  CORFIDI
AND 1000-500MB THICKNESS DIFFLUENCE WOULD SUGGEST BACKWARD
PROPOGATION AND SLOWER MOVEMENT AS MID LEVEL WIND STRENGTH OF 30KT
OR HIGHER STAYS N.

WITH BOUNDARY SOUTH OF THE STATE, HAVE REMOVED PRECIP CHANCES
SATURDAY.  WILL INTRODUCE SOME HIGH CLOUDS THOUGH ASSOCIATED WITH
MID LEVEL BAROCLINIC ZONE.  WILL HAVE TO WATCH THIS AS DECENT RRQ
JET FORCING MAY KEEP POST FRONTAL PRECIP GOING CLOSE TO OUR SOUTHERN
BORDER.  HAVE ALSO ADJUSTED TEMPS WARMER ON SATURDAY PER OAX
COORDINATION, ALTHOUGH WIDESPREAD RAINFALL MAY LIMIT WARMING AS
DECENT COLD ADVECTION ARRIVES.

EXTENDED...
LIMITED MEDIUM RANGE DATA THIS MORNING WILL KEEP CHANGES TO A
MINIMUM.  MAIN CHANGES WERE TO INCREASE TEMPS TUE-WED TIME FRAME.
NOT INTRODUCING PRECIP AT THIS TIME.  SOUTHERLY FLOW RETURNS AHEAD
OF NEXT SURFACE TROF AND SHOULD INSTITUTE DECENT WARMUP AGAIN.
RECENT AND LONGER TERM HISTORY OF MEX GUIDANCE, INCLUDING 15-20
DEGREE BUSTS LAST WEEK, AND HOT/DROUGHT CONDITIONS FAVOR THIS
ADJUSTMENT.

.DSM...NONE
KULA

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-081>086-
092>097-281100-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
227 PM CDT WED AUG 27 2003

THIS HAZARDOUS WEATHER OUTLOOK IS FOR CENTRAL IOWA.

.DAY ONE...THIS AFTERNOON AND TONIGHT

ISOLATED THUNDERSTORMS ARE EXPECTED THIS AFTERNOON INTO THIS EVENING
ALONG A WEAK BOUNDARY IN SOUTHERN IOWA.  THE THUNDERSTORMS ARE
EXPECTED TO REMAIN SOUTH OF A LINE FROM CENTERVILLE THROUGH WINTERSET
TO DENISON.  ALTHOUGH THE STORMS ARE EXPECTED TO REMAIN BELOW SEVERE
LIMITS...A FEW WIND GUSTS MAY EXCEED 50 MPH.  THE STORMS SHOULD
DISSIPATE BY LATER THIS EVENING AS DAYTIME HEATING SUBSIDES.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

A SLIGHT RISK OF SEVERE THUNDERSTORMS EXISTS FOR THURSDAY AFTERNOON
AND EVENING AS A COLD FRONT MAKES IT WAY THROUGH THE STATE. DAYTIME
HEATING WILL DESTABILIZE THE ATMOSPHERE AND WITH PLENTY OF MOISTURE
AVAILABLE THERE IS THE LIKELIHOOD OF A SQUALL LINE TO DEVELOP AHEAD
OF OR ON THE COLD FRONT.  THE MAIN THREAT WOULD BE DAMAGING WINDS
AND LARGE HAIL. HOWEVER AN ISOLATED STORM COULD PRODUCE A BRIEF
TORNADO.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS POSSIBLE THURSDAY AFTERNOON AND EVENING.

&&

MORE INFORMATION CAN BE OBTAINED AT WWW.CRH.NOAA.GOV/DMX (ALL LOWER
CASE).

COGIL