Severe Thunderstorm Warning 120, NWS Des Moines, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
245 PM CDT SUN JUL 2 2000

FOR TONIGHT...SFC BOUNDARY MOVING S INTO ERN IA ATOM PROBABLY IN
RESPONSE TO S/WV MOVG ACRS THE STATE.  WATER VAPOR IMAGERY SHOWS
DRYING MOVING INTO WARN IA ATOM SUGGESTING MID LVL DRY AIR MOVG OVR
VERY UNSTABLE AMS. UPR FLOW SHUD ALSO BECOME NW WHICH SHUD INCREASE
VERTICAL WIND SHEAR.  BOUNDARY FCST TO MOV SE INTO CWA THIS EVENING.
RISE/FALL PRESSURE COUPLET NOTED OVER THE PAST FEW HOURS IN NRN
IA/SRN MN.  ALL OF THESE FACTORS POINT TOWARDS INCREASING SEVERE
POTENTIAL ESPECIALLY FOR DOWNBURST WINDS.  WL GO SCT WORDING IN
ZONES AND WL MENTION SVR.  AFTER SUNSET...LOW LVL JET NOT VERY
IMPRESSIVE BASED ON MODELS BUT THERE SHUD BE ENOUGH TO SUPPORT TSTMS
INTO SC IA.

AFTER TONIGHT...UPR RIDGE BUILDS INTO IA MONDAY.  THINK THIS WL HELP
SUPPRESS THUNDERSTORMS MONDAY AND MONDAY NIGHT.  WL KEEP SML POP
GOING NE CORNER OF CWA.  NEXT BEST CHANCE FOR TSTMS APPEARS TO BE IN
THE EXTENDED WHEN A S/WV IS FCST TO DROP THE FNT BACK INTO IA.
OTHERWISE...VRY WARM AND HUMID UNDER THE RIDGE.  SE SFC FLOW NOT
GREAT FOR HOT TEMPS SO MODEST TEMPS IN FWC/FAN GUIDANCE MAY NOT BE
TO FAR OFF.

.DSM...NONE
JOHNSON

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-081>086-
092>097-031100-

CENTRAL IOWA THUNDERSTORM OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
1210 PM CDT SUN JUL 2 2000

HAZARD--SCATTERED THUNDERSTORMS WITH LOCALLY HEAVY RAIN.  SOME MAY
BE SEVERE AS WELL WITH DAMAGING WINDS AND LARGE HAIL.  TORNADOES ARE
NOT LIKELY.

AREA OF CONCERN--ALL OF THE DES MOINES NATIONAL WEATHER SERVICE
FORECAST AREA.

TIMING DETAILS--INITIAL THUNDERSTORM DEVELOP IS POSSIBLE NORTH OF
HIGHWAY 30 ACROSS NORTHERN IOWA THROUGH 6 PM THIS EVENING.  A HIGHER
PROBABILITY OF THUNDERSTORM DEVELOP IS JUST NORTH AND NORTHWEST OF
THE DES MOINES...NATIONAL WEATHER SERVICE...COUNTY WARNING AREA IN
FAR NORTHWEST IOWA AND SOUTHERN MINNESOTA.

ONCE DEVELOPED...THE STORMS SHOULD MOVE SLOWLY SOUTHEAST ACROSS
CENTRAL IOWA THROUGH THE NIGHT. THE BEST CHANCE FOR STORMS SOUTH OF
I80 WILL BE DURING THE OVERNIGHT HOURS.

METEOROLOGICAL COMMENTS-- A STATIONARY FRONT WAS ACROSS SOUTHERN
MINNESOTA INTO SOUTHEAST SOUTH DAKOTA LATE THIS MORNING.  IN
ADDITION...AN OUTFLOW BOUNDARY WAS MOVING SLOWLY NORTH ACROSS NORTH
CENTRAL IOWA.  THE AIRMASS SOUTH OF THESE BOUNDARIES WAS VERY
UNSTABLE AT 1200 PM CDT...BUT THERE WAS ALSO A FAIRLY STRONG CAP
OVER THE STATE.  THUNDERSTORMS MAY DEVELOP ALONG THE OUTFLOW
BOUNDARY IN NORTHERN IOWA OR ALONG THE STRONGER FRONT JUST TO THE
NORTHWEST.  IN EITHER EVENT...ONCE FORMED...SCATTTERED STORMS SHOULD
MOVE SOUTHEAST INTO AND ACROSS IOWA.  THE LOW-LEVEL JET ORIENTATION
TONIGHT WILL NOT BE OVERLY FAVORABLE WHICH SHOULD LIMIT THE THREAT
OF SEVERE WEATHER AFTER SUNSET.

THE WIND SHEAR PROFILE IS NOT VERY FAVORABLE FOR ORGANIZED STORMS.
HOWEVER...MID LEVEL DRY AND A LARGE AMOUNT OF INSTABILITY MAY ALLOW
SOME STORMS TO REACH SEVERE LIMITS THIS EVENING.  THE BEST CHANCE
FOR SEVERE WEATHER IS NORTH OF I80 BEFORE DARK.  THE SLOW MOVEMENT
OF THE THUNDERSTORMS SHOULD PRODUCE LOCALLY HEAVY RAIN.

PRECAUTIONS--SPOTTER ACTIVATION MAY BE NEEDED THIS AFTERNOON AND
TONIGHT...ESPECIALLY NORTH OF I80.

JOHNSON