Severe Thunderstorm Warning 198, NWS Des Moines, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
235 PM CDT WED SEP 13 2000

FORECAST PROBLEMS FOR THIS PACKAGE INCLUDE POPS FOR TONIGHT AND
TEMPERATURES IN OUT PERIODS.  MODELS ALL FORECAST A DEEPENING S/WV
TO MOVE ACROSS THE UPPER MIDWEST TONIGHT AND THEN AMPLIFY INTO A
DEEP UPR LOW WELL TO THE EAST.  UPR DYNAMICS AND ASSOCIATED UVV
STRONGEST ACRS NE IA TONIGHT.  VORT MAX FCST TO PASS JUST TO THE N
OF THE CWA WHICH SHUD PLACE THE MAX AREA OF ST PCPN N OF DMX CWA.
WL THEREFORE FCST MODERATE POPS FOR -RA NRN/NERN CWA.  SFC LOW FCST
TO DEEPEN AND MOVE ACROS SRN IA TONIGHT.  RAPID LOW-LVL MOISTURE
RETURN TDY WITH LOW 60S DEWPOINTS INTO WRN IA AHEAD OF THE SFC
SYSTEM.  BASED ON POSITION OF STRONGEST  PRES FALLS...MESO-ETA LOOKS
REASONABLE REGARDING MOVEMENT OF SFC LOW.  WITH LOW-LVL MOISTURE IN
PLACE...AMS SHOULD BE SOMEWHAT UNSTABLE TONIGHT ACROSS SRN IA.  CNVG
ALONG BOUNDARY AND DYNAMICS SHUD BE ENOUGH TO GENERATE SCT TSTMS NR
SFC BOUNDARY OVERNIGHT AS IT MOVES THRU CWA.  WL ADD POPS SRN IA FOR
THIS.

N/NW FLOW ALFT DURG OUT PDS WL KEEP FCST DRY THROUGHOUT.  COOL DRY
AMS AND POSITION OF SFC HIGH SHUD RESULT IN TEMPS REACHING THE 30S
ACROSS PARTS OF NRN/NERN CWA FRIDAY NIGHT.

MRF FCST REINFORCING SHOT OF COOL AIR LATE SATURDAY AND SUNDAY THEN
WARMER MONDAY AHEAD OF STRONGER LOOKING S/WV DIVING SE.   WL KEEP NO
PCPN IN EXTENDED WITH FAIRLY LARGE DIURNAL TEMP CHANkGES DUE TO DRY
AMS.

.DSM...NONE.

JOHNSON

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-081>086-
092>097-141100-

CENTRAL IOWA THUNDERSTORM OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
333 PM CDT WED SEP 13 2000

HAZARD--SCATTERED THUNDERSTORMS WITH THE POTENTIAL FOR ONE INCH HAIL.
SOME STORMS COULD PRODUCE WIND GUSTS BETWEEN 50 AND 60 MPH.

AREA OF CONCERN--ALL OF CENTRAL IOWA.

TIMING DETAILS--AFTER 10PM.

METEOROLOGICAL COMMENTS--INSTABILITIES HAVE BEEN INCREASING
THROUGHOUT THE DAY AND 60 PLUS DEWPOINTS HAVE REALLY SURGED
NORTHWARD INTO WESTERN IOWA THROUGH THE AFTERNOON.  IN ADDITION
SOUTHWEST WIND AT 15 TO 25 MPH HAVE TRANSPORTED VERY WARM AIR INTO
THE STATE.  A WARM FRONT WILL PUSH SOUTHEAST THIS EVENING AS SUFACE
CYCLOGENESIS DEEPENS FOLLOWED BY THE PASSAGE OF A PRETTY STRONG COLD
FRONT.  THERE WILL BE STRONG CONVERGENCE ALONG THE FRONT AND AN
IMPRESSIVE AMOUNT OF LIFT.  THIS COMBINED WITH THE COLD AIR ALOFT
WILL CREATE THE THREAT FOR LARGE HAIL.

PRECAUTIONS--SKYWARN SPOTTER GROUPS AND AMATEUR RADIO GROUPS MAY BE
REQUIRED LATER THIS EVENING AND OVERNIGHT. STAY TUNED FOR LATER UPDATES
AND STATEMENT.

FAB