Funnel Clouds in Iowa, May 2, 2008

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
346 AM CDT FRI MAY 2 2008

.SHORT TERM...THROUGH SUNDAY

MAIN FORECAST CONCERN IS WITH THE RAIN CHANCES THROUGH SATURDAY.

SURFACE ANALYSIS THIS MORNING SHOWS ONE AREA OF LOW PRESSURE OVER
SOUTH CENTRAL SOUTH DAKOTA AND A SECOND AREA OF LOW PRESSURE OVER
EASTERN KANSAS. A COLD FRONT EXTENDS EAST FROM THE SOUTH DAKOTA
LOW INTO NORTHWEST IOWA AND THEN SOUTH TO THE SECOND LOW. A WARM
FRONT EXTENDS EAST FROM NORTHWEST IOWA INTO SOUTHERN LOWER MICHIGAN.

THE SHORT TERM OPERATIONAL MODELS ARE NOT APPEAR TO HAVE A VERY
GOOD HANDLE ON THE CURRENT SYSTEM. THE NAM LOOKS TO CARRY THE
SURFACE LOW COMING OUT OF KANSAS NORTHEAST TOO FAST SATURDAY TRYING
TO GET THE WHOLE SYSTEM VERTICALLY STACKED. THE GFS IS LIKELY TOO
SLOW AS IT SHOWS SIGNS OF CONVECTIVE FEEDBACK. THE 01.21Z AND
02.03Z SREF MEANS AVERAGE OUT THE DIFFERENCES BETWEEN THE TWO
OPERATIONAL MODELS AND GIVE A REASONABLE SOLUTION.

THE UPPER LEVEL LOW IS EXPECTED TO START TRANSLATING EAST TODAY
SHIFTING FROM NEBRASKA INTO IOWA. SEVERAL SHORT WAVE TROUGHS WILL
ROTATE AROUND THE UPPER LEVEL LOW AND BOTH THE NAM AND GFS SHOW
STRONG PV ADVECTION IN THE 500-300 MB LAYER COMING INTO THE AREA THIS
AFTERNOON. THIS LIFT WILL BE AIDED BY SOME GOOD AGEOSTROPHIC
MOTIONS IN THE DIVERGENT ZONE AHEAD OF THE UPPER LEVEL LOW.
STRONG AND DEEP QG CONVERGENCE IS ALSO EXPECTED TO BE OVER THE
AREA TODAY. GOOD LOW LEVEL THERMODYNAMIC FORCING SHOULD ALSO OCCUR
WITH 2 TO 4 MICROBARS/S OF UPGLIDE ON THE 300K ISENTROPIC SURFACE.
THE SURFACE LOW OVER SOUTH DAKOTA IS EXPECTED TO DISSIPATE DURING
THE DAY AS THE LOW OVER KANSAS ADVANCES QUICKLY NORTHEAST INTO
NORTHERN IOWA OR SOUTHERN MINNESOTA. RAIN SHIELD AHEAD OF THE
KANSAS LOW IS ALREADY ADVANCING INTO SOUTHWEST AND CENTRAL IOWA
AND SHOULD START TO MOVE INTO NORTHEAST IOWA EARLY THIS MORNING
AND QUICKLY OVER SPREAD THE REST OF THE AREA. CAN NOT TOTALLY RULE
OUT THE POSSIBILITY OF SEVERE WEATHER TODAY BUT INSTABILITY WILL
BE RATHER LIMITED AND SHOULD BE LESS THAN A 1000 J/KG AND CONFINED
TO AREAS SOUTH OF INTERSTATE 90. THE BEST SHEAR WILL BE IN THE
0-3KM LAYER AND MAY BE UP TO 30 KNOTS AND WOULD BE SUPPORTIVE OF
STORMS PRODUCING WIND GUSTS AND LARGE HAIL.

AS THE UPPER LEVEL LOW CONTINUES TO MOVE NORTHEAST TOWARD THE
GREAT LAKES TONIGHT THE MODELS ARE INDICATING A STRONG DRY SLOT
WILL QUICKLY ADVANCE NORTH AHEAD OF THE LOW AND WILL HELP TO SHUT
DOWN THE RAIN. THE BETTER FORCING WILL ALSO BE LIFTING NORTHEAST
OUT OF THE AREA AND WILL ONLY HAVE CHANCE POPS ACROSS THE AREA
AFTER 06Z SATURDAY. ONCE THE LOW GETS BY THE AREA...ONE LAST SHORT
WAVE TROUGH WILL COME ACROSS THE AREA ON THE BACK SIDE OF THE LOW
AND BRING SOME WEAK PV ADVECTION TO THE AREA DURING THE DAY
SATURDAY. THIS COMBINED WITH THE CYCLONIC FLOW AND THE COLD POOL
ALOFT SHOULD CONTINUE TO PRODUCE SCATTERED SHOWERS IN THE
DEFORMATION AREA OF THE DEPARTING SURFACE LOW. WILL CONTINUE THE
CHANCE POPS FOR THE ENTIRE AREA SATURDAY. ALL OF THIS LOOKS TO
LIFT OUT OF THE AREA SATURDAY EVENING AND FOR NOW WILL MAINTAIN A
DRY FORECAST BUT DEPENDING ON HOW FAST ALL THIS OCCURS...MAY NEED
SOME POPS FOR SATURDAY EVENING.

.LONG TERM...TUESDAY NIGHT THROUGH THURSDAY

BOTH THE 02.00Z GFS AND ECMWF INDICATE A SURFACE LOW WILL TRACK
NORTHEAST ALONG A STALLED SURFACE BOUNDARY. HOWEVER...THE TWO
MODEL DISAGREE ON THE TIMING OF THIS OCCURRING WITH THE GFS BEING
QUICKER THAN THE ECMWF. CURRENT DATABASE ACCOUNTS FOR THESE RAIN
CHANCES BY BRINGING SOME POPS TO THE AREA TUESDAY AND THEN
CONTINUES THEM THROUGH THURSDAY. GIVEN THE DIFFERENCES IN THE
MODELS...NO CHANGES MADE AT THIS TIME.

&&

.AVIATION...

AN AREA OF LOW PRESSURE WILL PUSH NORTHEAST INTO SOUTHEAST
MN/WESTERN WI BY 00Z THIS EVENING...WITH A COLD FRONT RUNNING SOUTH
OF IT. MORE SHRA/TSRA WILL FIRE ALONG AND HEAD OF IT...WITH AMPLE
MOISTURE LEADING TO SOME PERIODS OF HEAVY RAIN. SEVERE WEATHER IS
ALSO A POSSIBILITY...WITH THE BETTER CHANCES SOUTH OF KRST/KLSE AND
MOSTLY BETWEEN 21-03Z. THERE WILL BE A BREAK FROM CONVECTION EARLY
TODAY...WITH PCPN CHANCES INCREASING BETWEEN 15-18Z. GRADUALLY...MID
LEVEL DRY PUNCH INTO THE LOW SHOULD BRING ANOTHER BREAK FROM PCPN
FOR KRST/KLSE TONIGHT...WITH WRAP AROUND MOISTURE LEADING TO SOME
-SHRA CHANCES AS THE LOW MOVES AWAY ON SAT. VFR CONDITIONS WILL BE
THE RULE UNTIL THE PCPN MOVES BACK IN...WITH MVFR AND SOME IFR
CONDITIONS THEN LIKELY.
&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...NONE.
MN...NONE.
IA...NONE.
&&

SHORT/LONG TERM...04
AVIATON...RIECK

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE LA CROSSE WI
1021 AM CDT FRI MAY 2 2008

IAZ008>011-018-019-029-030-MNZ079-086>088-094>096-WIZ017-029-032>034-
041>044-053>055-061-031000-
ADAMS-ALLAMAKEE-BUFFALO-CHICKASAW-CLARK-CLAYTON-CRAWFORD-DODGE-
FAYETTE-FILLMORE-FLOYD-GRANT-HOUSTON-HOWARD-JACKSON-JUNEAU-LA CROSSE-
MITCHELL-MONROE-MOWER-OLMSTED-RICHLAND-TAYLOR-TREMPEALEAU-VERNON-
WABASHA-WINNESHIEK-WINONA-
1021 AM CDT FRI MAY 2 2008

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PARTS OF SOUTHEAST
MINNESOTA...NORTHEAST IOWA AND SOUTHWEST INTO CENTRAL WISCONSIN.

.DAY ONE...TODAY AND TONIGHT

OCCASIONAL THUNDERSTORMS ARE EXPECTED ACROSS THE REGION TODAY AS AN
AREA OF LOW PRESSURE TRACKS NORTHEAST FROM WESTERN IOWA INTO WEST
CENTRAL WISCONSIN. IF ENOUGH INSTABILITY DEVELOPS AHEAD OF THE
LOW...THERE IS THE POTENTIAL FOR A FEW SEVERE STORMS. THE TIMING FOR
THIS SEVERE THREAT WOULD BE MAINLY FROM 1 PM TO 8 PM. THE PRIMARY
SEVERE THREATS WOULD BE LARGE HAIL AND DAMAGING WINDS. A FEW
TORNADOES COULD ALSO OCCUR. THE HIGHEST SEVERE THREAT SHOULD ACROSS
THE SOUTH...MAINLY SOUTH OF A LINE FROM ROCHESTER MINNESOTA THROUGH
BLACK RIVER FALLS WISCONSIN.

IN ADDITION...HEAVY RAIN WILL ACCOMPANY THE STRONGER STORMS...AND
AMOUNTS UP TO AN INCH OR SO WILL BE POSSIBLE. THIS MAY EXASPERATE
ALREADY HIGHER THAN NORMAL RIVER LEVELS. THOSE WITH INTEREST ALONG
AREA RIVERS MAY WANT TO PAY CLOSE ATTENTION TO THE RIVER LEVELS.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED THIS AFTERNOON THROUGH EARLY THIS
EVENING. AGAIN...THE MAIN SEVERE THREAT AND NEED FOR SPOTTER
ACTIVATION WILL BE FOR AREAS ALONG AND SOUTH OF A LINE FROM
ROCHESTER MINNESOTA THROUGH BLACK RIVER FALLS WISCONSIN. IN
ADDITION...REPORTS OF RAINFALL AND RIVER LEVELS WOULD ALSO BE
APPRECIATED THROUGH SATURDAY.

.EMERGENCY MANAGEMENT COORDINATION...

NO CALL IS SCHEDULED.

DAS/RIECK

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE LA CROSSE WI
0105 PM CDT FRI MAY 02 2008

...TIME...  ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
...DATE...  ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE...
            ..REMARKS..

0103 PM     HEAVY RAIN       LA CROSSE 2E            43.82N 91.19W
05/02/2008  E0.05 INCH       LA CROSSE          WI   OFFICIAL NWS OBS

            0.05 SINCE 7 AM CDT