Hail in Iowa, April 18, 2002

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
245 PM CDT THU APR 18 2002

COLD FRONT EXTENDS FROM NORTHWEST IOWA THROUGH SOUTHEAST NEBRASKA
AT 18Z WITH MUCH DRIER AIR BEHIND IT. FRONT IS EXPECTED TO CONTINUE
SLOW SE MOVEMENT INTO THE EVENING.  SOME CHANCE OF TRW DURING THIS
TIME FOR SERN AREAS BUT MAIN ACTION EXPECTED EAST OF THE CWA.

HIGH BUILDS INTO THE NORTHERN PLAINS REGION TONIGHT THROUGH
SATURDAY BEHIND THIS SYSTEM WITH SURFACE FRONT GETTING PUSHED INTO
THE SOUTHERN PLAINS BY MODELS.  BREEZY AND COOL PERIOD WITH POSSIBLE
SHOWERS INDICATED INTO FIRST PART OF THE WEEKEND.  SOUTHERN PARTS OF
CWA APPEAR TO BE ON NORTHERN EDGE OF OVERRUNNING H85 PATTERN
SATURDAY AFTERNOON AND NIGHT.  WILL TREND TEMPERATURES IN THE SHORT
TERM TOWARD ETA. SUNDAY INTO MONDAY LOOKS MAINLY DRY WITH AVN
PUSHING HIGH INTO SERN CONUS.  NEXT SYSTEM SWEEPS ACROSS IN THE
TUE-WED TIME FRAME WITH SOME CHANCE PRECIP AT THAT TIME.

FOBERT
...

920 AM CDT THU APR 18 2002

UPDATED FCST FOR EXPIRATION OF WIND ADVISORY.  CDFNT WILL CONT TO
PUSH EWD TODAY.  KEPT CHANCE OF TSTMS GOING FOR THIS AFTN IN SERN
NE...WHERE DEWPOINTS ARE CURRENTLY IN THE 60S.  REST OF FCST
BASICALLY UNCHANGED OTHER THAN MINOR WORDING TWEAKS.  AIRMASS TO
THE NORTH IS MUCH COLDER.

MILLER
...

315 AM CDT THU APR 18 2002

FORECAST CHALLENGES...DAMAGING WINDS VERY SHORT TERM. ASSESS NEED
FOR WIND ADVISOR THIS AM.  RISK OF TSRA/PASSAGE OF COLD FNT THIS AFT
AND TEMPERATURES.

SYNOPSIS...H85 PROGS SHOW 50-60KT WNDS ERLY DECREASING TO 30KT WNDS
BY LATE MORNING.  WILL EXTEND WIND ADVISORY WITH THE MAIN EMPHASIS
ON THE SE NEB AND SW IA COUNTIES.

LATEST SUBJECTIVE SURFACE ANALYSIS SHOWED LOW PRESSURE
OVER SOUTHWEST SOUTH DAKOTA WITH A WARM FRONT INTO NORTHERN NEB AND
CNTRL IA.  RETREATING DRYLINE OVR WCNTRL NEB/WRN KS SOUTHWARD. AS
DISCUSSED IN SPC SWO AMORPHOUS LARGE SCALE ASCENT DIURNALLY DRIVING
CONVECTION TO OUR SOUTH.  VERY STG LOW LEVEL JET SHOWING UP ON
PROFILERS WITH 70KTS AT H85 JUST TO THE E OF DDC.  SEVERAL ACTIVE
AREAS FROM KS TO TX AND BEST CORRELATES WITH AXIS OF DEEPER
MOISTURE/INSTABILITY AXIS.  IMPRESSIVE SUPERCELL RAPIDLY DEVELOPED
OVER DODGE CO IN OUR FCST AREA AND BECAME TORNADIC OVER GREENE CO IN
IA...JUST EAST OF CARROLL CO. STORMS CONTINUE TO ADVANCE ACROSS THE
NEB/KS BORDER.

THE LATEST UA ANALYSIS SHOWED THE UPR TROF WITH LOW CNTRS OVR WA/IA
AND THE MOST SIGNIFICANT FEATURE HERE WERE THE COLD -30 TO -35 DEG C
TEMPS AT H50.

FORECAST...IN THE SHORT TERM...REST OF TONIGHT...CAPE VALUES RANGE
FROM 1000-2500 J/KG FM CNTRL KS-WRN IA AND ANOTHER AREA OF HIGHER
VALUES FOR MO.  THUNDERSTORMS PRODUCING DAMAGING WINDS FOR SE NEB
AND SW IA.  BY 18Z THIS AREA OF INSTABILITY EXTENDS FM SE NEB INTO
CNTRL IA AND BY 00Z THE WRN EDGE IS OVR SE NEB.  EXPECT THE
THUNDERSTORM THREAT TO SHIFT E THIS AM...HOWEVER...WILL REDEVELOP
ALONG THE FNT AND INCLUDE SOME CHC WITH THE CDFNT TAF.  WITH VERY
WARM H85 TEMPS

SHORT TERM MODELS SHOW THE NRN PORTION OF THE TROF ADVANCING
FASTER...WITH THE SRN STREAM PORITON OF THE TROF LAGGING AND THE
OVERALL SYSTEM WEAKENING.  THE SHORT TERM MODELS HAVE COME INTO
CLOSER AGREEMENT ON THE SFC PATTERN.  THE SFC LOW CONTINUES TO
DEEPEN OVER SD TODAY AND LIFTS NE TO THE UPR GRTLKS BY 00Z...WITH A
TRAILING LOW NRN THE KS/CO BORDER.  THE FNT RMNS TO THE S FM KS-THRU
MO AND IL BY FRI AM AS SFC HI PRES BUILDS IN FOR LATER FRI AND SAT.

ETA SHOWING POST FRONTAL PRECIP SE NEB/SW IA THRU FRI AM AND AVN
SIMILAR IF NOT FARTHER N.  WITH THE APPROACH OF THE NEXT TROF WILL
HOLD ON TO POPS INTO SAT...BUT MAIN PRECIP WITH BETTER AMOUNTS WELL
TO THE SE OF THE FCST AREA.

EXTENDED...SUN-WED...THE AVN SHIFTS THE WEAK UPR LVL TROF THRU THE
AREA.  AT THE SFC...HIGH PRES RMNS OVR THE FCST AREA SUN AS
PRESSURES BEGIN TO LOWER ACRS THE NRN PLNS.  DO NOT HAVE ACCESS TO
THE 84HR EXTENSION OF THE ETA...HOWEVER...THE NEW AVN HAS A BROAD
AREA OF LOW PRES OVR THE PLNS MON.

ZAPOTOCNY

IF YOU HAVE COMMENTS ON THE NEW FORECAST DISCUSSION FORMAT...PLEASE
E-MAIL THEM TO W-OAX.WEBMASTER@NOAA.GOV OR CALL DAVE THEOPHILUS AT
402 359-5166.

.OMA...NONE.
FOBERT

IAZ043-055-056-069-079-080-090-091-NEZ011-012-015>018-030>034-
042>045-050>053-065>068-078-088>093-182330-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
1120 AM CDT THU APR 18 2002

STORM SPOTTERS MAY BE REQUIRED IN SOUTHEAST NEBRASKA AND
SOUTHWEST IOWA THIS AFTERNOON AND EARLY THIS EVENING.

A COLD FRONT WILL MOVE ACROSS SOUTHEAST NEBRASKA AND SOUTHWEST
IOWA THIS AFTERNOON AND EARLY THIS EVENING.  SCATTERED
THUNDERSTORMS MAY DEVELOP AHEAD OF THE FRONT EAST OF AN
OMAHA TO FAIRBURY LINE LATER THIS AFTERNOON.  SOME OF THE
STORMS MAY BE SEVERE WITH LARGE HAIL AND DAMAGING WINDS
THE PRIMARY THREAT.

THIS PRODUCT...ALONG WITH OTHER WEATHER...HYDROLOGIC AND CLIMATIC
INFORMATION...IS AVAILABLE ON THE INTERNET AT
WWW.CRH.NOAA.GOV/OAX OR AT WEATHER.GOV (LOWER CASE).

FOBERT