Severe Thunderstorm Warning 306, NWS Des Moines, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
235 PM CDT SUN JUL 22 2001

SHORT TERM...
TOUGH FORECAST TODAY DEALING WITH HEAVY RAIN THREAT AND REMAINING HEAT
IN SOUTHERN IA.  PUSHING 100 DEGREE TEMPS IN SOUTHERN IA TODAY AND
HEAT INDICES GETTING CLOSE TO WARNING CRITERIA.  WILL HOLD ONTO THE
HEAT ADVISORY THROUGH THIS EVENING S HALF BASED ON UNCERTAINTY OF
CONVECTIVE/OUTFLOW TRENDS FOR LATER TONIGHT.  WELL DEFINED OUTFLOW
BOUNDARY IN PLACE AS OBSERVED BY IMAGERY AND OBS, BASICALLY JUST N
OF I-80.  COULD SEE SOME NEW ISOLD CONVECTION ALONG IT AS
CONVERGENCE A BIT BETTER THAN YESTERRDAY.  SOME WEAKENING TO
NORTHERN IA CONVECTION, BUT IT HAS STOPPED DEVELOPING INTO NE NEBR
WHERE 850 MB FRONTOGENEIS IS INCREASING UP THROUGH THE BLACK HILLS
REGION.  META IS MODEL OF CHOICE, BUT WILL RELY MORE ON CONCEPTUAL
THINKING FOR TONIGHT.  SHORTWAVE COMING UP THROUGH KS INTO SW IA MAY
BECOME A PLAYER AS FASTER MOVING WAVE IN NW NEBRASKA INTERACTS WITH
OUTFLOW BOUNDARY.  SURFACE GEOSTROPHIC WINDS AT 18Z ARE CONCERNING
ME WITH 30KT IN KS AND A FORECAST LLJ OF 35-40 KT TONIGHT.  THIS
SHOULD ENHANCE ISENTROPIC ASCENT OVER OUTFLOW BOUNDARY IN NORTHERN
NE INTO SOUTHERN SD.  CURRENT CONVECTION MAY JUST EXPAND, WITH
TRAINING LIKELY ALONG BOUNDARY PER CORFIDI VECTORS, AND PERSISTENT
RADAR TRENDS TODAY.  MADDOX MESOHIGH TYPOLOGY LOOKING GOOD.  AS
RIDGE BEGINS TO FLATTEN THROUGH MONDAY, THIS MAY SIGNAL THE
BEGINNING OF RINGING OUT THIS SOAKED 2.0 INCH PWAT ATMOSPHERE.
MEASURED RAINFALL RATES THE LAST COUPLE DAYS AND ANY TRAINING WOULD
EQUATE TO LOCAL FLASH FLOOD PROBLEMS, ESPECIALLY IN NC/NE IA WHERE
FFG VALUES HAVE FALLEN.  COULD EASILY SEE 3-6 INCH RAIN LOCALLY
WHERE TRAINING OCCURS.  DAMAGING WIND THREAT STILL EXISTS WITH HIGH
CAPES AND A BIT MORE MID LEVEL PUSH WITH SHORTWAVE.  AFTER
COORDINATION, WILL ISSUE FFA N OF HIGHWAY 30 TONIGHT.  WILL GO
CATEGORICAL WORDING N AND 40 POPS LATE FAR SOUTH BARRING DEVELOPMENT
THE NEXT COUPLE OF HOURS.

LONGER TERM...
MODELS PUSH OUTFLOW BOUNDARY INTO SOUTHERN IA, SO NOT OUT OF THE
WOODS S HALF MONDAY OR MONDAY NIGHT.  MCS ACTION SHOULD DEVELOP IN
THE HIGHER TERRAIN OF NE/WY MOVING INTO IA TOWARD TUESDAY MORNING.
WILL KEEP POPS LOW N AND A BIT HIGHER S.  TUESDAY COULD BE AN ACTIVE
AND WET DAY, SO WILL BE ABLE TO COOL TEMPS AND KEEP POPS UP.  NEW
LONGER RANGE INFORMATION SUGGEST WED/THU MAY BE A DRIER PERIOD WITH
FRI/SAT WETTER.  WOULD LIKE MORE CONSISTENCY BEFORE CHANGING MUCH TO
THE EXTENDED, SO WILL GO THAT ROUTE FOR NOW.

COORDINATION WITH FSD/MPX/ARX.

.DSM...FLASH FLOOD WATCH TONIGHT ALONG AND N OF KDNS-KAMW-KMIW
HEAT ADVISORY TIL 9 PM  ALONG AND S OF KADU-DSM-KTNU

KULA