Severe Thunderstorm Warning 88, NWS Des Moines, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
310 AM CDT FRI JUN 23 2000

WITH NOT MUCH CONFIDENCE IN MODELS EARLY THIS MORNING DUE TO
UPPERAIR DATA SHORTAGE FOR THE EVENING RUN...DECIDED TO LEAVE
YESTERDAYS ZONE FORECAST PACKAGE ESSENTIALLY ALONE.  THUS...MADE
MINOR CHANGES TO TEMPERATURES AND INTRODUCED HEAVY RAIN WORDING.
NONETHELESS...MY WEATHER DISCUSSION CENTERS AROUND A MIX BETWEEN THE
AVN/ETA SOLUTIONS.

MAIN FORECAST CHALLENGES IN THE FIRST FOUR PERIODS ARE TIMING OF
CONVECTIVCE INITIATION TODAY ACROSS CWA AND SETUP OF HEAVY RAINS
THROUGH SATURDAY.  LEFT EXTENDED ALONE...AS GOING FORECAST LOOKS
GOOD...WITH COLD FRONT PUSHING CONVECTION TO THE SOUTH OF CWA BY
LATE SUNDAY INTO MONDAY WITH ANOTHER FRONT AFFECTING IA ON
TUESDAY.

TODAY...NOT TOO CONCERNED ABOUT DIEING NE MCS GETTING INTO WESTERN
KDSM CWA THIS MORNING.  850-300MB THICKNESS SUGGESTS A CONTINUING
ESE TRACK OF MCS ACROSS SOUTHERN NE...NORTHERN KS INTO NW MO IF IT
HOLDS TOGETHER.  HOWEVER...THE MCS IS MOVING INTO A VERY UNSTABLE
AIRMASS AS IT MOVES EASTERLY AROUND 35 MPH.  IF IT DOES HOLD
TOGETHER...IT COULD REACH THE SW PORTION OF CWA AROUND 11Z.  THE
PROBLEM IS HOW WILL THE MCS AFFECT THE SFC WARM FRONT ACROSS
SOUTHERN IA/NORTHERN MO BORDER TODAY.  AVN/ETA SOLUTIONS WANT TO
TAKE WARM FRONT NORTH AND STALL IT OUT ACROSS SOUTHERN MN AND
SOUTHERN WISCONSIN LATER TODAY.  I FAVOR THE SLIGHTLY FASTER ETA
SOLUTION...AS CURRENT WARM FRONTAL POSITION IS EVER SO SLOWLY MOVING
NORTH AS DEWPOINTS IN THE MIDDLE 70S HAVE ALREADY REACHED SW IA BY
07Z.  ETA SOLUTION INDICATES THAT CONVECTION WOULD INITIATE LATE
THIS AFTERNOON OVER SOUTHERN MN/WI AND NORTHERN IA...AND MOVE SOUTH
ALONG WARM FRONTAL BOUNDARY TONIGHT AND EXPAND.  THEREFORE...WILL
KEEP GOING ZONE PACKAGE WORDING AS IT REMAINS CONSISTENT WITH THE
00Z ETA SOLUTION.  ALSO...CONCERNED ABOUT HEAVY RAINS LATER
TODAY...ESPECIALLY NORTHERN ZONES.  WILL ISSUE AN ESF THIS MORNING
FOR POSSIBLE FLOODING RAINS LATER TODAY.  WILL LEAVE DECISION TO
DAYTIME SHIFT FOR POTENTIAL FLASH FLOOD WATCH FOR TONIGHT ACROSS
PORTIONS OF CWA.

SATURDAY...00Z AVN/ETA SOLUTIONS ARE SIMILAR IN TIMING OF INITIATION
OF CONVECTION AND AREAL EXTENT OF PRECIPITATION FIELD ACROSS CWA.
THIS IS ONLINE WITH GOING ZONE FORECAST PACKAGE...SO I MADE MINOR
ADJUSTMENTS.  EXPECT SITUATION TO SETUP IN THE LATE AFTERNOON
SIMILAR TO TODAY.  AGAIN HEAVY RAINS MAY BE POSSIBLE.

.DSM...NONE

KNOLLHOFF

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-081>086-
092>097-241100-

CENTRAL IOWA THUNDERSTORM OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
607 AM CDT FRI JUN 23 2000

HAZARD--SCATTERED THUNDERSTORMS WITH SOME REACHING SEVERE CRITERIA
AND PRODUCING LOCALLY HEAVY RAINS.

TIMING--THUNDERSTORMS AFTER 1 PM CDT THROUGH 6 AM CDT SATURDAY.
POTENTIAL SEVERE WEATHER ANYTIME AFTER 1 PM CDT THROUGH 9 PM CDT.

AREA OF CONCERN--ALL OF CENTRAL IOWA

METEOROLOGICAL COMMENTS--PLENTIFUL MOISTURE MIXED TOGETHER WITH
A VERY UNSTABLE AIRMASS AND MULTIPLE SURFACE BOUNDARIES ARE THE
INGREDIENTS THAT WILL AID IN THE DEVELOPMENT OF SHOWERS AND
THUNDERSTORMS ACROSS CENTRAL IOWA TODAY...ESPECIALLY THIS AFTERNOON
AND TONIGHT.  WITH HIGH DEW POINTS SPREADING ACROSS IOWA AND A
WARM FRONT STALLING OVER NORTHERN IOWA LATER TODAY...THESE
FACTORS WILL COMBINE TO PRODUCE A FEW SEVERE STORMS WITH
DAMAGING WINDS AND HAIL...ESPECIALLY THIS AFTERNOON.  A FEW
TORNADOES ARE ALSO POSSIBLE.  HOWEVER...THE SEVERE WEATHER THREAT
WILL DIMINISH TONIGHT AS THE STORMS TRANSITION INTO HEAVY RAIN
PRODUCERS. SEVERAL INCHES OF RAIN COULD FALL ACROSS CENTRAL IOWA
TODAY AND TONIGHT ANYTIME CAUSING FLASH FLOODING.  THE HIGHEST THREAT
OF FLOODING RAINS WILL BE IN NORTHERN PORTIONS OF IOWA...WHERE THE
GROUND SOIL IS RELATIVELY SATURATED.

PRECAUTIONS--SPOTTER ACTIVATION MAY BE NEEDED TODAY AND TONIGHT.

KNOLLHOFF