Severe Thunderstorm Warning 69, NWS Des Moines, IA

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE DES MOINES IA
645 AM CDT SUN APR 2 2006

.UPDATE...
ALTHOUGH FORECAST WORDING AND SEVERE MENTION HAS NOT CHANGED FROM
EARLIER RELEASE...HAVE UPDATED HWO WITH LARGER AREA OF SIGNFICANT
THREAT THAN PREVIOUSLY ANTICIPATED.

.DISCUSSION...
PREVIOUS THINKING WAS BANKING ON 06Z RUC AND ASSOCIATED INSTABILITY
PARAMETERS...BUT SUBSEQUENT 09Z RELEASE DOES NOT SEEM REALISTIC
KEEPING TEMPS DOWN IN SERN IA AND BLANKETING AREA IN STRATUS.
ALTHOUGH VIS/FOG STLT IMAGERY DOES SHOW SOME STRATUS DEVELOPMENT
BEHIND CLEARING OF DEEPER CLOUD LAYER OVER NE AND KS...FEEL THIS
WILL NOT BE WIDESPREAD ENOUGH TO PROHIBIT DESTABILIZATION INTO SERN
IA.  11Z SFC ANLYS SHOWS PRES FALLS AGGRESSIVELY SPREADING INTO IA
WITH LOWER 60S TEMPS ALREADY INTO CENTRAL MO JUST SOUTH OF WRMFNT.
AXIS OF MID 50/LOWER 60S SFC DEWPOINTS STILL BACK INTO THE ERN HALF
OF KS AND MUCH OF OK SO AMS INTO SERN IA MAY QUICKLY DESTABILIZE BY
AFTERNOON MORE IN LINE OF NAM/GFS THINKING.  ALTHOUGH STRONG
MECHANICAL FORCING IS NOT APPARENT AHEAD OF SHRT WV ENTERING
KS...HAVE RELEASED HWO WITH LINE OF THOUGHT THAT LOW LEVEL
CONVERGENCE COUPLED WITH INSTABILTY WILL BE ADEQUATE FOR
REDEVELOPMENT ALONG AND S OF MOUNT AYR TO GRINNELL LINE.  11Z SFC
ANLYS HAS STRONG MOISTURE CONVERGENCE BULLSEYE OVER ERN KS WITH WELL
DEFINED WRMFNT ACROSS MO.  AS THESE FEATURES LIFT NEWD...THIS
PATTERN SHOULD BE FAVORABLE FOR DEVELOPMENT OF TORNADIC SUPERCELLS
INTO SERN IA CONSIDERING SHALLOW AND DEEP SHEAR.  PRECIP N OF
ADVANCING WRMFNT IS OFTEN PREVIOUSLY NOTED ON TORNADO DAYS...KEEPING
LFCS RELATIVELY LOW.

.PREV DISCUSSION...
LINGERING QUESTION REMAINS NWD EXTENT OF SVR THREAT THIS AFTERNOON
WITH ELEVATED PULSEY HAILERS IN PROGRESS.  DIVERGENCE IN RIGHT
ENTRANCE REGION OF DAKOTAS/MN JET AIDING WEAK MCS AND UVM OVER IA AT
THE MOMENT.  SHRT WVS NOTED BEHIND MCS WITH OTHER STRONGER WVS
CARVING TROUGH OVER WY AND ALSO NEAR NM/TX/OK BORDERS.  KINEMATIC
FORCING NON-DESCRIPT AHEAD OF THESE FEATURES FOR THE TIME BEING
HOWEVER AND NAM/GFS SEEM TO SPLIT LARGE SCALE FORCING TO OUR S BY
AFTERNOON WITH DEF ZN ACROSS THE N.  STRONG LOW LEVEL CONVERGENCE
WOULD BE NEEDED AND THAT STILL APPEARS TO BE THE CASE OVER S CENTRAL
IA BY 18Z.  QUESTION WILL BE AMOUNT OF RECOVERY BEHIND DEPARTING
MCS.  EXTRAPOLATION BRINGS BACK EDGE TO S CENTRAL IA BY 11Z WITH SFC
LOW STILL OVER SERN NE...SO THERE MAY STILL BE SEVERAL HOURS OF
HEATING.  PRES FALLS AND MLCAPE AXIS APPEAR TO BE MOVING ONLY
SLIGHTLY N OF E HOWEVER SO ONLY EXTREME SERN PORTIONS OF FORECAST
AREA MAY BE UNDER THE GUN.  08Z SPC MESOANLYS PLACES MLCAPE AXIS FM
KMKC METRO SWD SO SURGE MAY ONLY MAKE IT INTO FAR SERN SECTIONS BY
AFTERNOON.  06Z RUC SEEMS TO HAVE GOOD HANDLE ON INSTABILITY AND
ALTHOUGH I DO NOT HAVE ANY DATA BEYOND 18Z...OVERLAY OF THETA-E
CONVERGENCE AND NOSE OF MLCAPE AXIS WOULD POINT TOWARD ONLY 8 OR SO
COUNTIES IN THE FAR SOUTHEAST HAVING MUCH OF A TORNADO THREAT.
NAM/GFS INSTABILITY CERTAINLY MORE AGGRESSIVE...BUT ALSO APPEAR TO
BE OVERDOING DEWPOINTS.  HAVE EITHER HIGH CHANCES OR LIKELIES GOING
W BLENDING INTO CATEGORICAL NERN HALF.  FORECAST PROCESS CUT
SOMEWHAT SHORT BY SWITCH TO CDT...BUT FOR THE TIME BEING WILL KEEP
SEVERE WORDING GOING IN SPC MODERATE AREA...BUT TAPER STRONGER HWO
WORDING FARTHER SE.  WILL RESERVE THE RIGHT TO CHANGE THAT THINKING
BY 6AM ISSUANCE TIME HOWEVER IF FASTER RECOVERY SEEMS TO BE TAKING
PLACE.

LITTLE CHANGES TO GOING FORECAST TONIGHT AS WE LOSE OUR INSTABILITY
AND DEF ZN CROSSES IA...ESPECIALLY NORTHERN PORTIONS.  CONFIDENCE IN
CURRENT FLOOD WATCH NOT THE GREATEST WITH MCS APPEARING TO BE
TRANSIENT AND INFLUENCED MORE BY LARGER SCALE FORCING RATHER THAN
LOW LEVEL JET.  HOWEVER RAIN WILL BE ONGOING AND A FEW RIVERS
ALREADY AT OR APPROACHING FLOOD STAGE SO WILL LEAVE WATCH IN EFFECT.
WIND THREAT STILL THERE TONIGHT BUT SPEEDS HAVE DIMINISHED IN
SHALLOW MIXED LAYER FROM YESTERDAY.  MAY STILL NEED AN
ADVISORY...BUT DO NOT WANT TO CREATE CONFUSION WITH POTENTIAL
CONVECTIVE WATCHES SO WILL LEAVE THAT TO DAY SHIFT.

LITTLE CHANGES TO TEMPS TODAY...BUT LOWERED MON SOMEWHAT.  EXPECT
MIXING MORE THAN SOUNDINGS SUGGEST WITH PLENTY OF APRIL SUN BUT THAT
STILL ONLY SUPPORTS LOWER END OF GUIDANCE.  LEFT EXTENDED ALONE TOO
WITH SHORTER TIME WINDOW.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...FLOOD WATCH TIL 00Z MON ALONG AND
NORTH OF KADU-KBNW-KALO LINE.

&&

SMALL

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
1133 AM CDT SUN APR 2 2006

IAZ062-074-075-083>086-093>097-031100-
POWESHIEK-MARION-MAHASKA-CLARKE-LUCAS-MONROE-WAPELLO-RINGGOLD-
DECATUR-WAYNE-APPANOOSE-DAVIS-
1133 AM CDT SUN APR 2 2006

...SEVERE WEATHER OUTBREAK POSSIBLE THIS AFTERNOON...

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTHEAST
IOWA...ALONG AND SOUTH OF A MOUNT AYR TO GRINNELL LINE.

.DAY ONE...TODAY AND TONIGHT

AFTERNOON THUNDERSTORMS ARE FORECAST TO DEVELOP BEFORE 3 PM. THESE
STORMS WILL LIKELY PRODUCE LARGE HAIL...DAMAGING WINDS AND POSSIBLY
AN ISOLATED TORNADO. THE BEST THREAT AREA HAS SHIFTED A BIT MORE
SOUTHWARD...IN THE SOUTHERN MOST ONE OR TWO TIERS OF COUNTIES AS A
SURFACE LOW MOVES EAST ALONG A WARM FRONT. AFTER THE THUNDERSTORMS
DIMINISH THIS EVENING...NORTHWEST WINDS WILL INCREASE WITH GUSTS TO
40 MPH.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

ANOTHER ROUND OF THUNDERSTORM MAY OCCUR FROM WEDNESDAY NIGHT INTO
FRIDAY WITH SEVERE WEATHER AGAIN POSSIBLE.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS LIKELY THIS AFTERNOON. DUE TO THE PROJECTED
FAST MOVEMENT OF THE STORMS...SPOTTERS SHOULD BE DEPLOYED QUICKLY.

IAZ004>007-015>017-023>028-033>039-044>050-057>061-070>073-081-
082-092-031100-
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-CASS-
ADAIR-MADISON-WARREN-ADAMS-UNION-TAYLOR-
1133 AM CDT SUN APR 2 2006

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA.

.DAY ONE...TODAY AND TONIGHT

SHOWERS AND A FEW THUNDERSTORMS ARE EXPECTED THIS AFTERNOON AND INTO
THE EVENING. SOME AREAS MAY SEE HEAVY RAINFALL AND HAIL. AFTER THE
THUNDERSTORMS DIMINISH THIS EVENING...NORTHWEST WINDS WILL INCREASE
WITH GUSTS TO 40 MPH.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

ANOTHER ROUND OF THUNDERSTORM MAY OCCUR FROM WEDNESDAY NIGHT INTO
FRIDAY WITH SEVERE WEATHER AGAIN POSSIBLE.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED THIS AFTERNOON...AND AGAIN IN THE
LATER HALF OF THE COMING WORK WEEK.

MYERS