Tornado Warning 44, NWS Des Moines, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
230 PM CDT MON JUL 19 1999

SHORT TERM...
SETTING UP FOR A MADDOX FRONTAL FLASH FLOOD TYPOLOGY FOR TONIGHT,
MUCH LIKE LAST NIGHT.  E-W FRONT WHICH SAGGED S TO ABOUT HIGHWAY 30
HAS NOW BECOME STATIONARY AS PRESSURE RISES TO ITS NORTH HAVE
CEASED.  GOES SOUNDER PWATS ARE AROUND 2 INCHES ALONG THIS BOUNDARY,
WITH EXCEPTIONALLY HIGH SURFACE DEW POINTS OF 73-79 DEGREES.  CAPES
ARE INCREASING INTO THE 4000-5000 J/KG RANGE AS SUCH WITH SFC
PARCELS WARMING TO THE LOWER 90S S OF FRONT.  EXPECT DEVELOPMENT
ALONG ENTIRE STRETCH OF FRONT THIS EVENING AS LLJ OF 20-25 KT
DEVELOPS AND INCREASES CONVERGENCE ALONG LARGE STRETCH OF BOUNDARY.
DEVELOPMENT OVER NEBR WILL BE AIDED BY WEAK SHORTWAVE ROUNDING THE
UPPER RIDGE THROUGH KS, THEN BE DIRECTED EAST ALONG BOUNDARY INTO IA
INTO TUESDAY.  SHEAR VECTORS CURRENTLY ARE DIRECTING NEBR CONVECTION
NE, BUT SHOULD BEGIN TO TURN E SOON.  ALSO OF NOTE IS SOME COOLING
AT 700 AND 500 MB ON THIS MORNING'S CHARTS OVER WESTERN SD AND NE
WHICH SHOULD TRACK E INTO NORTHERN IA TONIGHT.  I LOOK FOR EXPLOSIVE
DEVELOPMENT AT THAT POINT WITH SUCH HIGH POTENTIAL INSTABILITY.
ECHO TRAINING AGAIN LIKELY ALONG SURFACE BOUNDARY.  IT WAS A
CHALLENGE DEFINING FF WATCH FOR TONIGHT.  94E SEEMED A BIT TOO FAR
SW GIVEN FRONT STALLING.  FFG VALUES ARE NOT TOO LOW OVER SC AND SE
CWA, SO HAVE LEFT THEM OUT OF WATCH FOR NOW, BUT WILL INCLUDE
LOCALLY HEAVY RAIN LATE TONIGHT FOR THOSE AREAS.  THE CURRENT
BOUNDARY POSITION ALSO LESSENS THE THREAT FOR THE NORTHERN TIERS OF
COUNTIES, BUT 1.0 FFG VALUES ARE LIKE A LOADED GUN IF ANY CONVECTION
CAN MAKE IT THAT FAR N LATE TONIGHT, SO WILL CARRY THE WATCH TO THE
MN BORDER AND E TO I-35.  TEMPS STAYED RATHER WARM WITH THE HIGH DEW
POINTS LAST NIGHT, MAKING A GOOD CASE TO GO ABOVE FWC GUIDANCE.

LONGER TERM...
SITUATION DOES NOT APPEAR MUCH DIFFERENT TUESDAY AND TUESDAY NIGHT
WITH THE EXCEPTION THAT THE NGM FORECAST IS A BIT BETTER WITH THE
FRONTAL POSITION CURRENTLY, AND IT SHOULD BE OVER NORTHERN IA OR
SOUTHERN MN BY 36-48 HOURS.  THIS WILL AGAIN PUT THE HIGHEST THREAT
OF HEAVY RAIN OVER THE NORTHERN TIERS OF COUNTIES.  WILL KEEP 40-50
POPS FOR N AND NE CWA COUNTIES WITH 30 POPS CENTRAL SECTIONS, AND
LEAVE AREAS S AND SW DRY.  TEMPS SHOULD START HEATING UP OVER
SOUTHERN PORTIONS OF IA ALSO, WITH 95-97 OBTAINABLE SW AND SC
SECTIONS TUESDAY AND WED.  CAP SHOULD START TO BUILD NE, WITH NE IA
STILL AT RISK OF CONVECTION THAT DEVELOPS OVER SOUTHERN MN AND
SPILLING SE INTO THE STATE.  IN THE EXTENDED, THE MRF, ALTHOUGH
SHOWING BUILDING UPPER RIDGE, SHOWS POTENTIAL FOR NOCTURNAL SW LLJ
WHICH COULD KICK OFF SOME NIGHT TIME CONVECTIVE DEVELOPMENT AT EDGE
OF CAP OVER MN AND WRN WI.  THIS COULD SPILLOVER INTO EASTERN IA.
WILL KEEP CHANCES GOING FOR FRIDAY AND SATURDAY NE SECTIONS, BUT DRY
SW.  HOT AND HUMID WEATHER ALSO ON THE WAY.

COORDINATI\ON WITH DVN, OAX, FSD, MPX, AND ARX.

.DSM...FLASH FLOOD WATCH TONIGHT
IAZ004>007-015>017-023>026-033>037-044>049-057>061

KULA