Severe Thunderstorm Warning 209, NWS Des Moines, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
313 PM CDT THU AUG 22 2002

PRIMARY FCST CONCERN WL BE TSTM AND HVY RAIN TRENDS TNGT.  WATER
VAPOR IMAGERY SHOWS ELONGATED SHEAR AXIS/TROF FM NE INTO KS...OK AND
TX WITH LRG SCALE UVM INCRG AHEAD OF FEATURE.  EXTRAPOLATION PLACES
THIS LIFT INTO FA ARND 02Z.  COMBINATION OF VISIBLE STLT
DATA...RADAR DATA...AND MESONET INDC BNDRY ALG KDNS-KDSM-KMUT LN AT
19Z.  LRGR SFC ANLYS AT SAME TIME SHOWS THIS AS WRMFNT FM LOW ACRS
NERN NE AND PRES FALL CNTR ACRS SWRN IA.  MSTR CNVGNC HAS BEEN INCRG
PAST FEW HRS AS HAS CU DVLPMT...BUT SEEMS TO HAVE LTL VERTICAL
EXTENT PER STLT AND LOOK OUTSIDE.  THIS MAKES SENSE WITH LAPS/RUC
SOUNDINGS SHOWING WRM LYR UP TO ARND 750 MB.  THUS XPC INITIATION TO
WAIT TIL THIS EVEN WITH INCRG LOW LVL JET AS UPR LVL FORCING APCHS.
SPC RUC PAGE SHOWS MLCAPES/CINS ARND ARND 1000/25 J/KG RESPECTIVELY
SO IT SHOULD NOT TAKE MUCH TO GET THINGS GOING...SPCLLY WITH UPR LVL
SUPPORT.  SLA PROFILER ALREADY SHOWS MOD WRM ADVCTN IN PLACE.
RUC/ETA TAKE SFC BNDRY SWD REACHING NRN MO 03Z-06Z SO WL GO WITH
LIKELY POPS ACRS SRN ZNS TNGT.  WL ALSO KEEP LOWER CHCS N IN CASE
CNVGNC AREA INVOF KSUX LIGHTS UP SOONER THAN XPCD AND TSTMS ADVECT
ACRS NRN SXNS.  FLOW SHOULD VEER OVNGT SO WOULD XPC PCPN TO PUSH S
AND E OF FA OVNGT BUT HVY RAINS POSSIBLE IN THE MEANTIME.  PWS AOA 2
INCHES YET AGN SO WL MENTION IN SRN ZNS.  DO NOT FEEL WATCH
NECESSARY WITH RELATIVELY SHRT DURATION (COORDINATION W/DVN).  XPC
PCPN ASSOCD WITH SHRT WV OVR DAKOTAS TO PUSH EWD STAYING N OF FA.

AMS QUITE UNSTABLE AGN TMRW BUT CNVGNC WEAK SO WL LEAVE FCST DRY
ATTM.  CVRG WOULD NOT BE GREAT IF SOMETHING POPPED.  NEXT PCPN CHCS
SEEM TO BE LATE SAT AS WV DROPS DOWN MO VLY.  MUCH OF CNVGNC AND
FORCING RMNS SW OF FA...SO ALTHOUGH ETA CLIPS SWRN PTNS WITH
EVOLUTION OF MATURE MCS DO NOT FEEL CHCS GREAT ENOUGH TO INTRODUCE
AS OF YET.  GENERALLY FOLLOWED NGM MOS FOR TEMPS.  WITH FNTL BNDRY
SLIDING SWD WOULD XPC AT OR BLO PERSISTENCE NEXT SVRL DAYS.

FCST FOR NEXT WEEK PROBLEMATIC WITH SHRT WVS MEANDERING BTWN WLYS
ACRS CANADA AND SWRN RDG.  ALTHOUGH THERE CERTAINLY ARE
DIFFERENCES...MED RANGE MDLS IN BETTER AGREEMENT THAN YOU WOULD XPC
WITH THESE FEATURES CONSIDERING POOR RUN TO RUN CONTINUITY.
TEMPORAL AND SPACIAL DIFFERENCES ARE APPARENT BUT GENERAL TRENDS
APPR SIMILAR.  CANNOT FIND MUCH REASON TO CHG FM AVN WITH 00Z AND
12Z RUNS NOT ALL THAT DIFFERENT IN MOST FIELDS...BUT QPF LOWER.
THIS WOULD LEAD TO TWO PCPN WINDOWS WITH LOW CONFIDENCE.  1ST OVER
THE WEEKEND WITH PCPN POSSIBLE FM SAT NGT INTO EARLY MON AS PTNS OF
NWRN CONUS SHRT WV DRIFT INTO MO VLY.  FORCING WOULD LIKELY COME FM
MID LVL THETA-E ADVCTN AND KINEMATICS RATHER THAN LOW LVL CNVGNC
WHICH IS WEAK...AND MAINLY SW OF FA.  HWVR CANNOT SEE LEAVING FCST
DRY CONSIDERING MDLS QPF SO WL INTRODUCE CHCS SUN WHICH LOOKS TO BE
A GOOD PLACE TO START.  NEXT CHCS LOOK TO BE TUE NGT AND WED WITH
SIMILAR SUBTLE FORCING.

FLOW WL BE RELATIVELY WEAK SO TO NOT XPC MUCH IN THE WAY OF TEMP
EXTREMES.  GENERALLY STAYED AT OR JUST ABV AVN MOS WHICH IS NR CLIMO
AND WOULD MAKE SENSE CONSIDERING NR NORMAL H85 TEMPS.

.DSM...NONE

SMALL

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
810 PM CDT THU AUG 22 2002

A WARM FRONT WAS SITUATED FROM THE IOWA AND NEBRASKA BORDER ...NEAR
ONAWA EAST INTO WEST CENTRAL ILLINOIS TONIGHT. THUNDERSTORMS ARE
EXPECTED TO RAPIDLY DEVELOP ALONG AND SOUTH OF THIS WARM FRONT OVER
EASTERN NEBRASKA. THE STORMS WILL THEN SPREAD EAST THROUGH IOWA
OVERNIGHT. SEVERE WEATHER IS POSSIBLE THIS EVENING ALONG AND SOUTH
OF HIGHWAY 30 FROM DENSION EAST TO NEAR AMES...AND WEST OF
INTERSTATE 35. THE PRIMARY THREAT TONIGHT WILL BE FROM LARGE HAIL
AND AS THE EVENT EVOLVES POSSIBLY DAMAGING WINDS. FLASH FLOODING IS
ALSO POSSIBLE AS TRAINING THUNDERSTORMS ARE EXPECTED.

SEE SITE SPECIFIC DETAILS BELOW FOR MORE INFORMATION.

IAZ044>048-057>060-070>073-081>083-092>094-230715-
ADAIR-ADAMS-AUDUBON-BOONE-CARROLL-CASS-CLARKE-CRAWFORD-DALLAS-
DECATUR-GREENE-GUTHRIE-MADISON-POLK-RINGGOLD-STORY-TAYLOR-UNION-
WARREN-
INCLUDING THE CITIES OF...AMES...ATLANTIC...BOONE...CARROLL...
CRESTON...DENISON...DES MOINES...INDIANOLA...LAMONI...MOUNT AYR
810 PM CDT THU AUG 22 2002

THREAT                         PROBABILITY      EVENT TIMING
------                         -----------      ------------
THUNDERSTORMS
  TORNADO                      NONE
  DAMAGING WINDS (58+ MPH)     MODERATE          TONIGHT
  LARGE HAIL (3/4+)           MODERATE          TONIGHT
  FLASH FLOODING               MODERATE          TONIGHT

* SPOTTER ACTIVATION OUTLOOK
  TONIGHT...MODERATE

IAZ004>007-015>017-023>028-033>039-049-050-061-062-074-075-084>086-
095>097-230715-
APPANOOSE-BLACK HAWK-BREMER-BUTLER-CALHOUN-CERRO GORDO-DAVIS-EMMET-
FRANKLIN-GRUNDY-HAMILTON-HANCOCK-HARDIN-HUMBOLDT-JASPER-KOSSUTH-
LUCAS-MAHASKA-MARION-MARSHALL-MONROE-PALO ALTO-POCAHONTAS-POWESHIEK-
SAC-TAMA-WAPELLO-WAYNE-WEBSTER-WINNEBAGO-WORTH-WRIGHT-
INCLUDING THE CITIES OF...ALGONA...CENTERVILLE...CHARITON...
ESTHERVILLE...FORT DODGE...GRINNELL...IOWA FALLS...KNOXVILLE...
MARSHALLTOWN...MASON CITY...NEWTON...OSKALOOSA...OTTUMWA...
WATERLOO/CEDAR FALLS
810 PM CDT THU AUG 22 2002

THREAT                         PROBABILITY      EVENT TIMING
------                         -----------      ------------
THUNDERSTORMS
  TORNADO                      NONE
  DAMAGING WINDS (58+ MPH)     NONE
  LARGE HAIL (3/4+)           NONE
  FLASH FLOODING               NONE

* SPOTTER ACTIVATION OUTLOOK
  TONIGHT...NOT EXPECTED

BARLOW