Severe Thunderstorm Warning 69, NWS Des Moines, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
105 PM CDT SUN MAY 2 2010

...UPDATED FOR 18Z AVIATION DISCUSSION...

.SHORT TERM /TODAY/...
AREA OF -RN OVR THE SERN PART OF THE STATE HAS MOVED OUT OF THE CWA
AND ATTM AM NOT PLANNING TO RUN A PRE FIRST PD FCST ON THAT. WX
QUITE WITH INC WNDS THIS MRNG. FEEL WE'LL MIX OUT...BUT DO NOT
EXPECT TO SEE WNDS LIKE YDA. COLD AIRMASS ALF WILL YIELD STEEP LAPSE
RATES WITH PROFILE BCMG NEARLY DRY ADIABATIC TO H7 THIS AFTN. MID
LVL LAPSE RATES 7 TO 7.5 C...HOWEVER MOISTURE IS LACKING WITH PWATS
SCANTY...ONLY REACHING 20MM THIS AFTN. WITH CDFNT MOVG THRU EXPECT
TO SEE ISOLD TO SCT TSRA DVLP LATE THIS AFTN INTO THE EVE. MEAGER
CAPE IN THE 500 TO 1000 J/KG RANGE...BUT SHOULD BE ENUF FOR SOME
CONVECTION. PUT IN MNTN OF SMALL HAIL FOR A BRIEF PD THIS AFTN WITH
FZG LVL AOB 8000 MSL THIS AFTN.

.LONG TERM /TONIGHT THROUGH SATURDAY/...
SOME CONVECTION SHOULD BE ONGOING AT BEGINNING OF TONIGHT PERIOD AS
ALLUDED TO ABOVE. EXPECT THAT THESE STORMS WILL BE DIURNALLY DRIVEN
AND DIMINISH AFTER SUNSET...WITH SCATTERED LIGHT SHOWERS PERSISTING
NEAR THE FRONT OVERNIGHT AS IT MOVES TO THE SOUTHEAST. HAVE KEPT
POPS SOMEWHAT BROADBRUSHED TONIGHT AS THERE IS CONSIDERABLE
UNCERTAINTY AS TO WHERE THE FRONT/STORMS WILL BE LOCATED AT THE
BEGINNING OF THE PERIOD. THIS WILL LIKELY BE REFINED THROUGH THE
COURSE OF TODAY.

BEHIND THIS WEAK FRONT IT STILL APPEARS RELATIVELY QUIET FOR A FEW
DAYS AS A BRIEF PERIOD OF RIDGING SETS IN...PARTICULARLY MONDAY
NIGHT/TUESDAY WHEN WINDS WILL COME AROUND TO SOUTH SOUTHWEST AHEAD
OF AN APPROACHING SURFACE TROUGH. STILL EXPECT SOUTHWEST WINDS TO BE
FAIRLY STRONG ON TUESDAY PROMOTING GOOD MIXING AND WAA. THE NEXT
COLD FRONT WILL APPROACH OUR NORTHWEST LATE TUESDAY...TRAILING FROM
A MID/UPPER LOW MOVING ACROSS FAR SOUTHERN MANITOBA. AS ASSOCIATED
SHORTWAVE SKIRTS BY TO OUR NORTH EXPECT SHOWERS/THUNDERSTORMS NEAR
THE FRONT TUESDAY NIGHT...ESPECIALLY ACROSS OUR NORTHERN THIRD OR
SO...WITH THE FRONT WASHING OUT OVER MISSOURI ON WEDNESDAY. VERY
LITTLE HAS CHANGED IN FORECAST THINKING FOR THESE PERIODS SINCE LAST
NIGHT...AND VERY FEW CHANGES WERE MADE TO THE FORECAST AS A RESULT.

THINGS GET MORE INTERESTING AND VASTLY MORE UNPREDICTABLE TOWARD THE
AND OF THE WEEK. THERE IS GOOD AGREEMENT AMONG THE LONG RANGE MODELS
THAT BY THURSDAY MORNING THE AFOREMENTIONED SOUTHERN MANITOBA LOW
WILL HAVE MOVED NORTHEAST TO AROUND JAMES BAY CANADA...WHILE THE
NEXT LOW WILL HAVE DROPPED SOUTHEAST INTO THE IDAHO/UTAH REGION.
AFTER THIS POINT HOWEVER THE MODELS BEGIN TO DIVERGE
SIGNIFICANTLY...WITH THE GFS/GEFS/SREF FILLING IN THE LOW AND
BRINGING IT ACROSS OUR REGION AS A SHORTWAVE WHILE THE GEM AND NOW
THE ECMWF AS WELL KEEP THE 500 MB LOW CLOSED OFF AS IT MOVES BY JUST
TO OUR NORTHWEST. AT THE SURFACE THIS DISCREPANCY RESULTS IN A RANGE
OF POSSIBILITIES FOR PRECIP...TEMPS...AND WINDS FROM THURSDAY
THROUGH THE END OF THE WEEK. FEEL THAT OUR TEMPERATURES MAY BE TOO
WARM FROM THURSDAY NIGHT ONWARD REGARDLESS OF WHICH SOLUTION IS
PREFERRED AS THERE APPEARS TO BE SUBSTANTIAL COLD AIR BEHIND THE
EVENTUAL SYSTEM...AND HAVE BEGUN TO TREND THURSDAY NIGHT TEMPS
DOWNWARD SOMEWHAT. WILL HOLD OFF FOR FURTHER SHIFTS/MODEL RUNS TO
TRY TO FIND SOME MORE CONSISTENT SIGNAL BEFORE MAKING FURTHER
CHANGES.

&&

.AVIATION...
02/18Z...WEAK BOUNDARY WILL PASS THROUGH THE STATE LATE THIS
AFTERNOON INTO TONIGHT.  WEAK CONVERGENCE AND INSTABILITY SHOULD
LEAD TO SOME ISOLD/SCT TSRA DEVELOPMENT BY MID AFTERNOON AND
CONTINUE INTO THIS EVENING.  SOUNDING PRESENT AS INVERTED V AND
GUSTY WINDS AND SOME SMALL HAIL WILL BE POSSIBLE WITH THE STRONGER
CELLS.  OTHERWISE...WIDESPREAD VFR CONDITIONS ARE FORECAST DURING
THE PERIOD WITH ONLY EXCEPTION IN AND NEAR THUNDERSTORMS.  SFC WINDS
WL WEAKEN TONIGHT BEFORE STRENGTHENING AFTER 14Z ON MONDAY.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...NONE.

SHORT TERM...MS MAY 10
AVIATION...COGIL
LONG TERM...LEE

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
502 AM CDT SUN MAY 2 2010

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-081>086-
092>097-031100-
EMMET-KOSSUTH-WINNEBAGO-WORTH-PALO ALTO-HANCOCK-CERRO GORDO-
POCAHONTAS-HUMBOLDT-WRIGHT-FRANKLIN-BUTLER-BREMER-SAC-CALHOUN-
WEBSTER-HAMILTON-HARDIN-GRUNDY-BLACK HAWK-CRAWFORD-CARROLL-GREENE-
BOONE-STORY-MARSHALL-TAMA-AUDUBON-GUTHRIE-DALLAS-POLK-JASPER-
POWESHIEK-CASS-ADAIR-MADISON-WARREN-MARION-MAHASKA-ADAMS-UNION-
CLARKE-LUCAS-MONROE-WAPELLO-TAYLOR-RINGGOLD-DECATUR-WAYNE-APPANOOSE-
DAVIS-
502 AM CDT SUN MAY 2 2010

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA.

.DAY ONE...TODAY AND TONIGHT

ISOLATED TO SCATTERED THUNDERSTORMS WILL DEVELOP LATER THIS
AFTERNOON AND EVENING AHEAD OF AN APPROACHING COLD FRONT. SOME
STORMS WILL LIKELY PRODUCE SMALL HAIL...HOWEVER THE POTENTIAL FOR
SEVERE WEATHER APPEARS LIMITED.

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

THUNDERSTORM CHANCES WILL RETURN FROM LATE TUESDAY THROUGH TUESDAY
NIGHT...MAINLY NORTH OF HIGHWAY 30. SEVERE WEATHER IS NOT
EXPECTED AT THIS TIME. THERE MAY BE ADDITIONAL NON SEVERE
THUNDERSTORMS ACROSS FAR SOUTHERN IOWA THURSDAY INTO THURSDAY
NIGHT.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT ANTICIPATED...HOWEVER ANY HAIL REPORTS
THIS AFTERNOON AND EVENING WOULD BE APPRECIATED.

LEE

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