Severe Thunderstorm Warning 319, NWS Des Moines, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
317 PM CDT FRI AUG 17 2001

...MAIN CHALLENGES THOUGH PERIOD TO BE PRECIP IN 1ST TWO PERIODS AND
LATER IN EXTENDED...

VAPOR LOOP INDICATING VARIOUS SHORT WAVES OF INTEREST...SOME WEAK
OVER NEB/SD AND THE OTHER STRONGER OVER SRN MANITOBA TO NRN MN AND
ERN ND.  AT THE SFC/80H...WARM FRONT OVR KS THIS AFTERNOON...AND
WEAK RIDGING ASSOC WITH DYING CONVECTION OVR MO.  AT 80H THIS
MORNING...10-13 DEWPOINTS POOLED OVR KS INTO SGF AREA...AND WOULD
EXPECT THESE TO PUSH FARTHER NORTH TONIGHT ON LLJ.

SHORT TERM...
QUESTION TNGT WL BE WHEN TO DVLP PCPN.  SVRL SFC TROFS NOTED
UPSTREAM AND TOUGH TO PICK OUT TRUE CDFNT.  MSTR AND CNVGNC
RELATIVELY WEAK AND LAPS ANLYS SHOWING ENOUGH CIN TO HOLD BACK SFC
DVLPMT...AT LEAST IN OUR FA.  NE CONVECTION SHOULD RMN JUST SW.
THUS WL LEAVE EVE DRY AS PCPN WL LIKELY WAIT TIL STG SHRT WV OVR
CANADA/MN BORDER DROPS SWD.  DIFFERENTAL PVA SHOULD MODIFY
ENVIRONMENT ENOUGH TO KEEP TSTMS ACRS MN GOING OVNGT DROPPING SWD
INTO IA WITH DYNAMICS AND DECENT WRM ADVCTN AHD OF SHRT WV.  DID NOT
WANT TO JUMP INTO LIKELY CATEGORY AS PCPN MAY DMSH SOMEWHAT WITH
LOSS OF HEATING...BUT DID RAISE CHCS.  SAW NO REASON TO DEVIATE FM
TEMP GUIDANCE.

LONG TERM...LITTLE REASON TO ARGUE WITH ETA/AVN TIMING HERE.  SOME
DIFFERENCES EARLY...BUT BY SAT...ETA CATCHES UP WITH AVN.  FWC/MAV
TEMPS NOT MUCH DIFFERENT THAN GOING ZFP EITHER.  EXPECT LINGERING
CONVECTION ALONG AND JUST BEHIND FRONT OVER CWA IN MORNING HOURS.
LIKELY NOT TO SEE MUCH THO IN WEST OF LINE FROM DNS TO MCW...THO
WILL CARRY A SMALL MORNING MENTION OF CONVECTION IN NW.
ELSEWHERE...CONVECTION SHOULD BE OVER BY 18Z OR SO WITH
DOWNGLIDE...DIV OF Q...AND SO FORTH. WITH COLD POOL ALOFT AND CAA AT
80H...WILL NOT GET RID OF CLOUDS TOO FAST THOUGH.

SAT NIGHT INTO MONDAY...LOOKS QUIET. EXPECT SOME CONVECTION OVER
PLAINS SUN NIGHT MAYBE IN WAA AND LLJ...BUT SHOULD STAY WEST OF CWA.

IN THE EXTENDED...TROFFINESS IN EAST FILLS WITH SOME PUSH TO THE
EAST OF THE WRN RIDGE.  EXPECT POTENTIAL FOR SOME SCT CONVECTION IN
VCNTY OF WRM FRONT AND TROF ON TUES.  FOR WED...LOOKS LIKE BEST
POTENTIAL FOR LL CONV HAS PUSHED NORTH...THOUGH THIS ISNT SET IN
STONE.  WILL GO DRY FOR WED NOW.  THU/FRI...AGAIN LOOKS LIKE
NIGHTTIME MCS POTENTIAL WITH RIDGE AXIS TO OUR EAST AND SOME
TROPICAL MOISTURE INFLUENCE.  SEASONABLE TEMPS.

.DSM...NONE

SMALL/SEARCY

CENTRAL IOWA THUNDERSTORM OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE DES MOINES IA
545 PM CDT FRI AUG 17 2001

SYNOPSIS
A COLD FRONT EXTENDING FROM MINNESOTA INTO SOUTH DAKOTA AND EASTERN
NEBRASKA WILL MOVE INTO NORTHWEST IOWA LATER THIS EVENING...AND PASS
SOUTHEAST OF THE STATE ON SATURDAY.  THE AIRMASS IS MARGINALLY
UNSTABLE THIS EVENING AS LOW LEVEL MOISTURE INCREASES AND
TEMPERATURES FALL ALOFT.  ALTHOUGH THERE WILL BE SOME THREAT FOR
WIND AND TORNADOES...THE
PREDOMINANT SEVERE WEATHER THREAT WILL BE FOR HAIL.

SEE SITE SPECIFIC DETAILS BELOW FOR MORE INFORMATION.

IAZ004>007-015>017-023>025-033>035-044-181100-
CALHOUN-CERRO GORDO-CRAWFORD-EMMET-HANCOCK-HUMBOLDT-KOSSUTH-PALO
ALTO-POCAHONTAS-SAC-WEBSTER-WINNEBAGO-WORTH-WRIGHT-
INCLUDING THE CITIES OF...ALGONA...DENISON...ESTHERVILLE...FORT DODGE
AND MASON CITY
536 AM CDT FRI AUG 17 2001

* EVENT TIMING... FROM 630 PM THROUGH 1100 PM

* THREAT CATEGORIES...
     TORNADO.......... LOW
     DAMAGING WINDS... LOW
     LARGE HAIL....... LOW
     FLASH FLOODING... NOT EXPECTED

* SPOTTER ACTIVATION OUTLOOK... LOW

IAZ026>028-036>039-045>050-057>061-070>072-181100-
ADAIR-AUDUBON-BLACK
HAWK-BOONE-BREMER-BUTLER-CARROLL-CASS-DALLAS-FRANKLIN-GREENE-GRUNDY-
GUTHRIE-HAMILTON-HARDIN-JASPER-MADISON-MARSHALL-POLK-STORY-TAMA-
INCLUDING THE CITIES OF...AMES...ATLANTIC...BOONE...CARROLL...DES
MOINES...IOWA FALLS...MARSHALLTOWN...NEWTON...PERRY...WATERLOO...
WAVERLY AND WEBSTER CITY
536 AM CDT FRI AUG 17 2001

* EVENT TIMING... FROM 1000 PM UNTIL 400 AM

* THREAT CATEGORIES...
     TORNADO.......... NOT EXPECTED
     DAMAGING WINDS... LOW
     LARGE HAIL....... LOW
     FLASH FLOODING... NOT EXPECTED

* SPOTTER ACTIVATION OUTLOOK... LOW

IAZ062-073>075-081>086-092>097-181100-
ADAMS-APPANOOSE-CLARKE-DAVIS-DECATUR-LUCAS-MAHASKA-MARION-MONROE-
POWESHIEK-RINGGOLD-TAYLOR-UNION-WAPELLO-WARREN-WAYNE-
INCLUDING THE CITIES OF...CENTERVILLE...CHARITON...CRESTON...
GRINNELL...INDIANOLA...KNOXVILLE...LAMONI...OSKALOOSA...OTTUMWA AND
PELLA
536 AM CDT FRI AUG 17 2001

* EVENT TIMING... FROM 100 AM UNTIL 600 AM

* THREAT CATEGORIES...
     TORNADO.......... NOT EXPECTED
     DAMAGING WINDS... NOT EXPECTED
     LARGE HAIL....... LOW
     FLASH FLOODING... NOT EXPECTED

* SPOTTER ACTIVATION OUTLOOK... NOT EXPECTED

-------------------------------------------------------------------

THREAT KEY:
    TORNADO.......... ANY TORNADO OCCURRENCE
    DAMAGING WINDS... WINDS >= 58 MPH
    LARGE HAIL....... HAIL >= 3/4 INCH DIAMETER
    FLASH FLOODING... FLOODING CAUSED BY HEAVY RAINS WITHIN 6 HOURS
                      OF RAIN EVENT. POSES THREAT TO LIFE OR
                      PROPERTY.

THREAT CATEGORY KEY:  PROBABILITY OF THREAT OCCURRING WITHIN 25
                      MILES OF POINT WITHIN FORECAST AREA
    NONE....... NOT EXPECTED.  LESS THAN 5% ( 2% FOR TORNADOES)
    LOW........ 5-15% (2-15% FOR TORNADOES)
    MODERATE... 25-35%
    HIGH....... 45% OR GREATER

SPOTTER ACTIVATION OUTLOOK KEY:
    NOT EXPECTED
    LOW........ ACTIVATION POSSIBLE BUT NOT LIKELY
    MODERATE... POSSIBILITIES ABOUT 50-50
    HIGH....... ACTIVATION LIKELY

FOR MORE INFORMATION ON PROBABILISTIC SEVERE WEATHER OUTLOOKS...GO
TO THE STORM PREDICTION CENTER WEBSITE AT
WWW.SPC.NOAA.GOV/PRODUCTS/OUTLOOK/PROBINFO.HTML .

KNOLLHOFF