Severe Thunderstorm Warning 145, NWS Des Moines, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
307 AM CDT SUN MAY 13 2001

MAIN FCST PROBLEM WL AGN BE CONVECTIVE TRENDS FOR NEXT SVRL DAYS.
MDLS IN DECENT AGREEMENT BUT DO DVRG SOMEWHAT BY MON NGT...SPCLLY
WITH LOW LVL FEATURES.  CURRENT ZNS SEEM TO HAVE GOOD HANDLE ON
THESE TRENDS AND ONLY MINOR CHGS XPCD.

STLT AND RADAR DATA INDC TWO DISTINCT PCPN AREAS ATTM.  ONE ALG AND
E OF KAXA-KDSM-KCNC LN...AND ANOTHER INVOF MO RVR.  ETA 305K ISENT
SFC SHOWS THIS WELL.  TRAJECTORIES FM ERN PCPN ARE MORE ELEVATED AND
ORIGINATE FM DAKOTAS AND MINNESOTA...SO PCPN WILL LIKELY RMN WEAK.
WRN BAND MORE DIURNALLY DRIVEN FM LOW LVL JET ENHANCEMENT AND MAY BE
MORE SGFNT.  THESE TRAJECTORIES TRACK FM DEEPER MSTR 00Z UPR AIR
ANLYS INDCS OVR HIGH PLAINS AOB H85 FM KLBF-KDDC-KAMA.  MSTR CNVG
AND ADVCTN MAXES ALG 305K SFC STAY IN THIS LOCATION THRU 12Z SO WL
HAVE TO BE WATCHED.  KOMA LAPS SOUNDING INDCS PLENTY OF POSITIVE
AREA ABV 750MB IF MSTR INCRS ADEQUATELY TO DMSH CIN.  NET ISENT
OMEGA DMSHS TWRD 18Z SO XPC THIS WDLY SCT CONVECTION TO LINGER INTO
THE MRNG AND END DRNG AFTN.

BY TNGT FOCUS TURNS TO THE N.  RIGHT ENTRANCE RGN OF UPR LVL JET
SHIFTS INTO GTLKS BY 12Z MON AND SHOULD AID UVM THRU UPR MS VLY.
H85/H7 QG FORCING WEAKENS AND LINGERS OVR IA TDA THEN INTENSIFIES
LATE TNGT ALG MS RVR INVOF KLSE...MAINLY DUE TO QG FRONTOGENESIS AND
QN RESPONSE.  XPC MCS TO DVLP OVR MN TNGT AND THEN GRDLLY BUILD SWD
DROPPING INTO NERN IA AFT 06Z PER H85 THETA-E ADVCTN.  SHOWALTER
INDICES DMSH OVNGT SO TNGTS CONVECTION SHOULD BE MORE SGFNT...BUT
MAINLY N OF FA.

WRMR TEMPS WL BE MAIN WX FEATURE MON.  AVN MOS MORE AGRESSIVE WITH
WRM UP AND MAY BE TOO HIGH LOOKING AT MDL TEMPS EVEN WITH DECENT
MIXING.  WL TAKE THE MIDDLE ROAD AND PLAY COMPROMISE BTWN NGM AND
AVN MOS FOR NOW.  PCPN WISE...BACLIN ZN SHOULD PUSH E WITH LTL LOW
LVL CNVGNC.  AMS APPRS CAPPED PER CAPE/CIN FIELDS.  BNDRY DOES
SLIDE INTO NRN PTNS MON NGT BUT CAP STILL LOOKS TO BE IN PLACE.
STILL WORTH LOW POPS NRN SXNS WHICH IS ALREADY INCLUDED IN ZNS.  BY
12Z TUE...ETA PUSHES LOW AND ASSOCD FNT FARTHER S THAN AVN RESULTING
IN COOLER TEMPS AND DMSHD CONFIDENCE.  CERTAINLY SVRL CHCS FOR MORE
SFC BASED DVLPMT WITH BNDRYS DANCING BACK AND FORTH ACRS FA AND AMS
UNSTABLE.  HWVR CAP WL STILL BE PLAYING A ROLE WITH NERN SXNS MORE
LIKELY LOCATIONS FOR PCPN.  CURRENT FCST HAS TUE DRY BUT FEEL CHCS
GOOD ENOUGH TO MENTION IN N AND ERN ZNS MUCH LIKE IS GOING FOR WED.
NO CHGS TO EXTEND BY TUE.  WL SHADE BACK AVN MOS TEMPS FOR TUE AS
WELL.

.DSM...NONE

SMALL

CENTRAL IOWA THUNDERSTORM OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
545 AM CDT SUN MAY 13 2001

A WARM FRONT FROM THE NEBRASKA AND SOUTH DAKOTA BORDER INTO EXTREME
WESTERN IOWA WILL SURGE NORTHEAST TODAY REACHING THE UPPER
MISSISSIPPI RIVER VALLEY BY TONIGHT.  SCATTERED SHOWERS AND
THUNDERSTORMS CAN BE EXPECTED ALONG AND NORTHEAST OF THE
FRONT...ESPECIALLY DURING THE OVERNIGHT HOURS.  SOME OF THE STORMS
MAY PRODUCE LARGE HAIL AND BRIEF STRONG AND GUSTY WINDS...BUT
WIDESPREAD HEAVY RAINS ARE NOT ANTICIPATED.

SEE SITE SPECIFIC DETAILS BELOW FOR MORE INFORMATION.

IAZ004>007-016-017-024>028-035>039-047>050-060>062-073>075-084>086-
095>097-141100-
APPANOOSE-BLACK HAWK-BOONE-BREMER-BUTLER-CERRO
GORDO-DAVIS-EMMET-FRANKLIN-GRUNDY-HAMILTON-HANCOCK-HARDIN-HUMBOLDT-
JASPER-KOSSUTH-LUCAS-MAHASKA-MARION-MARSHALL-MONROE-POLK-POWESHIEK-
STORY-TAMA-WAPELLO-WARREN-WAYNE-WEBSTER-WINNEBAGO-WORTH-WRIGHT-
INCLUDING THE CITIES OF...ALGONA...AMES...BOONE...CENTERVILLE...
CHARITON...DES MOINES...ESTHERVILLE...FORT DODGE...GRINNELL...
INDIANOLA...IOWA FALLS...KNOXVILLE...MARSHALLTOWN...MASON CITY...
NEWTON...OSKALOOSA...OTTUMWA...PELLA...WATERLOO...WAVERLY AND WEBSTER
CITY
545 AM CDT SUN MAY 13 2001

* EVENT TIMING... THIS MORNING...AND AGAIN OVERNIGHT.

* THREAT CATEGORIES...
     TORNADO.......... NONE
     DAMAGING WINDS... NONE
     LARGE HAIL....... LOW
     FLASH FLOODING... NONE

* SPOTTER ACTIVATION OUTLOOK... LOW

* THE STORMS THIS MORNING SHOULD BE MINIMAL...ISOLATED...AND
  EMBEDDED WITHIN AREAS OF SHOWERS.  THERE ARE BETTER CHANCES FOR
  STRONGER STORMS OVERNIGHT.

IAZ015-023-033-034-044>046-057>059-070>072-081>083-092>094-141100-
ADAIR-ADAMS-AUDUBON-CALHOUN-CARROLL-CASS-CLARKE-CRAWFORD-DALLAS-
DECATUR-GREENE-GUTHRIE-MADISON-PALO
ALTO-POCAHONTAS-RINGGOLD-SAC-TAYLOR-UNION-
INCLUDING THE CITIES OF...ATLANTIC...CARROLL...CRESTON...DENISON...
LAMONI AND PERRY
545 AM CDT SUN MAY 13 2001

* EVENT TIMING... THIS MORNING

* THREAT CATEGORIES...
     TORNADO.......... NONE
     DAMAGING WINDS... LOW
     LARGE HAIL....... LOW
     FLASH FLOODING... NONE

* SPOTTER ACTIVATION OUTLOOK... LOW

* THUNDERSTORMS ARE EXPECTED TO MOVE SOUTHEAST AT 25 TO 30 MPH ACROSS
  WESTERN IOWA THIS MORNING.  A FEW OF THE STORMS MAY BE SEVERE...
  WITH LARGE HAIL THE GREATEST THREAT.  A FEW SEVERE THUNDERSTORM
  WARNINGS HAVE ALREADY BEEN ISSUED OVER EASTERN NEBRASKA AND WESTERN
  IOWA.

SMALL

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

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 .