698
FXUS63 KARX 091125 AAA
AFDARX
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE LA CROSSE WI
625 AM CDT WED JUL 9 2008
UPDATE
TODAY
SCATTERED SHOWERS HAVE ALREADY DEVELOPED ACROSS SOUTH CENTRAL AND
SOUTHWEST MINNESOTA. IF THEY KEEP UP THERE PRESENT SPEED AND CAN
HOLD TOGETHER THEY WILL BE IN SOUTHEAST MINNESOTA AND NORTHEAST IOWA BY
MID MORNING. AS A RESULT...WE HAVE UPDATED THE FORECAST TO ACCOUNT
FOR THIS POSSIBILITY.
PREV DISCUSSION
/ISSUED 416 AM CDT WED JUL 9 2008/
SHORT TERM...TODAY THROUGH FRIDAY
SEVERE WEATHER POSSIBILITIES ON THURSDAY AND AGAIN ON FRIDAY
AFTERNOON ARE THE MAIN CONCERNS WITH PART OF THE FORECAST.
THE 09.00Z AND 09.06Z MODELS CONTINUE HINT THAT THERE WILL BE
ENOUGH INSTABILITY AND LOW LEVEL MOISTURE CONVERGENCE FOR THE
DEVELOPMENT OF WIDELY SCATTERED SHOWERS AND THUNDERSTORMS ACROSS
PARTS OF NORTHEAST IOWA AND SOUTHEAST MINNESOTA THIS AFTERNOON.
THE NAM/WRF HAS BEEN SUGGESTING THIS FOR THE LAST 3 DAYS AND THE
GFS SINCE 08.00Z. SINCE THERE WAS SOME CONVECTION ACROSS THE
DAKOTAS ON TUESDAY AND THE MODELS HAVE HAD A CONSISTENT SIGNAL...
I DID ADD A SMALL PRECIPITATION CHANCE FOR THESE AREAS.
ON THURSDAY...THE 09.00Z MODELS DIFFERED ON THE EVOLUTION OF A
MESOSCALE CONVECTIVE COMPLEX THAT WILL BE MOVING SOUTHEAST THROUGH
THE UPPER MISSISSIPPI RIVER VALLEY. THE GFS CONTINUE TO SHOW A
MUCH FURTHER NORTH AND LESS IMPRESSIVE COMPLEX. MEANWHILE THE
NAM/WRF...GEM...AND ARW WRF...SUGGESTS THAT THIS SYSTEM WILL TRACK
RIGHT THROUGH THE ENTIRE FORECAST AREA. THEY ARE IN GOOD AGREEMENT
THAT THIS SYSTEM WILL MOVE INTO THE AREA DURING THE MORNING. THE
ECMWF HAS ALSO BEEN SHOWING THIS SCENARIO FOR THE LAST THREE DAYS.
HOWEVER WITH THIS RUN...IT DID HINT THAT THIS SYSTEM MAY INFLUENCE
NORTHEAST IOWA...SOUTHEAST MINNESOTA...AND SOUTHWEST WISCONSIN
MORE THAN THE REMAINDER OF WESTERN AND NORTHERN WISCONSIN. FOR
THIS PACKAGE...I STAYED WITH THE NAM/WRF...GEM...AND ARW WRF
SOLUTIONS. WITH INCREASING SHEAR DURING THE DAY...THERE WILL BE
THE POTENTIAL OF SEVERE WEATHER WITH THIS SYSTEM. THE MAIN SEVERE
WEATHER THREATS WILL BE LARGE HAIL AND DAMAGING WINDS.
ON THURSDAY NIGHT...THE MODELS DIFFER ON WHERE THE CONVECTION WILL
BE LOCATED ACROSS THE UPPER MISSISSIPPI RIVER VALLEY. BOTH THE
ECMWF AND NAM WOULD SUGGEST THAT THIS PRECIPITATION WILL BE MUCH
FURTHER SOUTHEAST THAN THE GFS. THIS MAKES A LOT OF SENSE WHEN
CONSIDERING THE COLD POOL THAT WILL BE GENERATED FROM THE
THUNDERSTORM COMPLEX EARLIER IN THE DAY. SINCE I LIKED THE NAM/WRF
BETTER ON THURSDAY...I TRENDED TOWARD IT.
ON FRIDAY...THE 09.00Z MODELS CONTINUE TO SHOW THAT OUR AREA WILL
BE LOCATED IN THE WARM SECTOR OF AN APPROACHING LOW PRESSURE
SYSTEM. SOUTHERLY WINDS IN THE 15 TO 25 MPH RANGE WILL USHER IN
VERY WARM AND MOIST AIR INTO THE REGION. BOTH THE NAM/WRF AND GFS
SUGGEST THAT OUR MEAN LAYER DEW POINTS WILL CLIMB INTO THE UPPER
60S AND LOWER 70S. THE COMBINATION OF THESE DEW POINTS AND
TEMPERATURES AROUND 90 WILL LIKELY PRODUCE HEAT INDEXES INTO THE
95 TO 100 DEGREE RANGE. THIS IS SLIGHTLY BELOW THE NEW HEAT ADVISORY
CRITERIA OF DAY TIME HEAT INDEX OF 100 DEGREES OR HIGHER. IN
ADDITION...THE MEAN LAYER CAPES WILL INCREASE INTO THE 3000 TO
4000 J/KG. THIS VERY UNSTABLE AIR MASS WILL LIKELY REMAINED CAPPED
THROUGH 3 PM AND THEN THIS CAP WILL GRADUALLY WEAKEN AS A RATHER
VIGOROUS 500 MB SHORT WAVE TROUGH BRINGS IN SLIGHTLY COOLER AIR
ALOFT AND THE TEMPERATURES ALOFT ARE ALSO COOLING THROUGH LIFTING.
ONCE THE CAP BREAKS...THUNDERSTORM SHOULD RAPIDLY DEVELOP. WITH
0-6 KM SHEAR AROUND 45 KNOTS...THESE THUNDERSTORMS SHOULD RAPIDLY
DEVELOP INTO SUPERCELLS. WITH THE SIGNIFICANT TORNADO PARAMETER
OVER 3 ACROSS NORTH CENTRAL WISCONSIN...SOUTHEAST MINNESOTA...AND
NORTHEAST IOWA...THEY WILL HAVE THE POTENTIAL OF PRODUCING
TORNADOES. IN ADDITION TO THIS THREAT...THERE WILL ALSO BE THE
POSSIBILITY OF DAMAGING WINDS AND LARGE HAIL. AT THIS TIME...IT
LOOKS LIKE THERE WOULD BE A POSSIBILITY OF SEVERE WEATHER FROM
4 PM INTO THE EVENING. MORE ON THE EVOLUTION OF THIS SEVERE
WEATHER EVENT CAN BE FOUND INTO THE LONG TERM SECTION OF THIS
DISCUSSION.
LONG TERM...FRIDAY NIGHT THROUGH TUESDAY
THE MEDIUM RANGE MODELS CONTINUE TO SHOW THAT A RATHER VIGOROUS
500 MB SHORT WAVE AND COLD FRONT WILL MOVE THROUGH THE REGION ON
FRIDAY NIGHT. BY THE START OF THIS PERIOD...THERE SHOULD BE
ALREADY SUPERCELL THUNDERSTORMS DEVELOPED ACROSS THE SOUTHERN AND
EASTERN PARTS OF MINNESOTA...AND ACROSS NORTH CENTRAL IOWA. A FEW
OF THESE THUNDERSTORM MAY BE SEVERE. THE MAIN SEVERE WEATHER
THREATS WILL INITIALLY BE ISOLATED TORNADOES...DAMAGING
WINDS...AND LARGE HAIL. TI LOOKS LIKE AS THE EVENING GOES
ON...THESE THUNDERSTORMS WILL CONSOLIDATE INTO A SEVERE MESOSCALE
CONVECTIVE COMPLEX. ONCE THIS OCCURS...THE SEVERE WEATHER THREAT
SHOULD SHIFT TO WIND. AT THIS TIME...IT APPEARS MUCH OF THE SEVERE
WEATHER SHOULD BE PROBABLY OUT OF THE AREA BY MIDNIGHT.
MUCH COOLER AND DRIER AIR WILL FILTRATE INTO THE REGION THIS
WEEKEND AS 850 MB TEMPERATURES COOL INTO THE 6C TO 10C RANGE BY
SUNDAY. MOST OF THE 09.00Z MODELS ARE DRY THIS WEEKEND. HOWEVER
THE ECMWF DOES HINT AT THE POSSIBILITY OF SOME SHOWERS AND
THUNDERSTORMS ON SUNDAY AS THE COLD POOL MOVES OVERHEAD. FOR THE
TIME BEING...THE ONLY CHANGES MADE TO THIS TIME PERIOD WAS TO
LOWER THE TEMPERATURES.
EARLY NEXT WEEK...IT CONTINUES TO LOOK LIKE WE WILL BE ON THE
NORTH AND NORTHWEST PERIPHERY OF A 500 MB HIGH. THIS MAY RESULT IN
OCCASIONAL MESOSCALE CONVECTIVE COMPLEXES MOVING THROUGH THE
REGION. THIS LOOKS WELL HANDLED IN THE CURRENT GRIDS...SO NO
CHANGES WERE MADE.
AVIATION...TODAY AND TONIGHT
DRY WESTERLY FLOW EXPECTED TO CONTINUE TODAY...WITH VFR CONDITIONS
PREVALENT. SCATTERED TO BROKEN CLOUDS ANTICIPATED...GENERALLY 6-8K
FEET OR ABOVE. VFR CONDITIONS SHOULD PREVAIL INTO TONIGHT...WHILE
SOUTHERLY FLOW BEGINS TO RETURN IN EARNEST DURING THE OVERNIGHT
HOURS.
ARX WATCHES/WARNINGS/ADVISORIES
WI...NONE.
MN...NONE.
IA...NONE.
UPDATE - BOYNE
PREV DISCUSSION - BOYNE/THOMPSON
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page