000
FXUS63 KARX 121714
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1214 PM CDT WED JUN 12 2013

.UPDATE...
ISSUED AT 1214 PM CDT WED JUN 12 2013

INCREASING THREAT FOR SEVERE THUNDERSTORMS ACROSS PORTIONS OF THE
FORECAST AREA THIS AFTERNOON. THE HIGHEST CHANCES FOR SEVERE
THUNDERSTORMS WILL BE ALONG AND SOUTH OF THE INTERSTATE 94 CORRIDOR.
DAMAGING WINDS...LARGE HAIL...AND A FEW TORNADOES ARE POSSIBLE
THIS AFTERNOON...ESPECIALLY ACROSS NORTHEAST IOWA INTO FAR
SOUTHWEST WISCONSIN. FAYEETTE...CLAYTON...AND GRANT COUNTIES HAVE
THE HIGHEST CHANCES OF SEEING A TORNADO THIS AFTERNOON. A LARGE
TORNADO OR TWO IS POSSIBLE...ESPECIALLY NORTHEAST OF THE SURFACE
LOW.

AT THIS TIME...A POTENT SHORTWAVE WAS DRIVING SOUTHEAST ACROSS
EASTERN SOUTH DAKOTA/SOUTHWEST MINNESOTA AND LOOKED RATHER
IMPRESSIVE ON WATER VAPOR. MEANWHILE...SURFACE LOW PRESSURE WAS
DEEPENING OVER CENTRAL IOWA WITH A WARM FRONT EXTENDING FROM
CENTRAL IOWA EAST ACROSS NORTHERN ILLINOIS. THE LOW WILL LIFT
NORTHEAST THIS AFTERNOON PULLING THE WARM FRONT NORTH INTO
NORTHEAST IOWA/SOUTHWEST WISCONSIN. MEANWHILE...THE SHORTWAVE WILL
TRACK SOUTHEAST ACROSS NORTHER IOWA/SOUTHERN MINNESOTA. THE
TIMING OF THE WAVE AND THE PROXIMITY OF THE WARM FRONT...ALONG
WITH INCREASING INSTABILITY....WILL CREATE FAVORABLE CONDITIONS
FOR SEVERE THUNDERSTORMS. 0-6 KM SHEAR OF 60 KTS AND 0-1 KM SHEAR
OF AROUND 20KTS...LOCALLY ENHANCED NEAR THE WARM FRONT/SURFACE
LOW...WILL BE VERY FAVORABLE FOR DISCRETE SUPERCELLS CAPABLE OF
PRODUCING TORNADOES. A FEW STORMS MAY ALSO PRODUCE LOCALIZED FLASH
FLOODING.

&&

.SHORT TERM...(TODAY THROUGH THURSDAY)
ISSUED AT 318 AM CDT WED JUN 12 2013

MAIN CONCERN FOR TODAY INTO THIS EARLY EVENING WILL BE SEVERE
THUNDERSTORM THREAT ACROSS THE SOUTH.

WATER VAPOR IMAGERY/RAP 500MB HEIGHT FIELD SHOWS A VIGOROUS
SHORTWAVE TROUGH MOVING OUT OF MT/WY INTO WESTERN ND/SD/NE. SURFACE
MAP AS OF 2 AM HAD AN AREA OF LOW PRESSURE ALONG THE KS/NE BORDER
WITH A WARM FRONT EXTENDING ENE ALONG I-80 IN IA AND IL. 850MB
MOISTURE TRANSPORT/ISENTROPIC LIFT AHEAD OF THE LOW AND OVER THE
WARM FRONT WAS PRODUCING SCATTERED ELEVATED SHRA/TS ACROSS OUR
FORECAST AREA...WITH A MORE INVIGORATED N-S LINE OF STORMS ACROSS
CENTRAL SD WHICH WAS HEADED EAST AROUND 50KT. RAP CORFIDI VECTORS
TAKE THIS COMPLEX OF STORMS DUE EAST AT 55-65KT THIS MORNING...WHICH
WOULD BRING IT INTO OUR AREA IN THE 7-9 AM TIME FRAME. MEANWHILE...A
NEW COMPLEX OF THUNDERSTORMS WERE FIRING ACROSS NORTHWEST
IA...MOVING TOWARD THE EAST. THIS CONVECTION WAS ROOTED A BIT CLOSER
TO THE CAPE POOL JUST NORTH OF THE 925-850MB WARM FRONT. A COUPLE
OBS IN SD WHERE THIS LINE PASSED RECORDED 43/48KT. HOWEVER...WRF
MODELS...NAMELY THE 12.00Z NSSL WRF WHICH SEEMS TO HAVE THE BEST
HANDLE ON THE CONVECTION RIGHT NOW...HAS THIS CONVECTION DECAYING AS
IT MOVES INTO THE AREA IN THE 5-8AM TIME FRAME. WITH 0-3KM BULK
SHEAR IN THE 40-50KT RANGE AND 0-3KM ML MUCAPE HOVERING IN THE
1000-2000J/KG...WILL HAVE TO WATCH THIS ONGOING CONVECTION CAREFULLY
FOR A SEVERE WIND THREAT EARLY THIS MORNING.

THERE THEN SEEMS TO BE A BREAK IN THE ACTION FROM MID-MORNING UNTIL
EARLY AFTERNOON BEFORE THE MID-LEVEL TROUGH AND SURFACE LOW MOVE
ACROSS EASTERN IA IN THE 18Z-21Z TIME FRAME. THIS TROUGH/STEEPENING
MID LEVEL LAPSE RATES THEN INTERACTS WITH 2000-3500J/KG 0-1KM ML
MUCAPE POOL IN PLACE SOUTH OF I-90 TO FIRE VIGOROUS/DEEP
CONVECTION. COOLING MID LEVEL/STEEPER LAPSE RATES AND 0-3KM BULK
SHEAR IN THE 20-40KT RANGE WILL SUPPORT A SEVERE HAIL/WIND THREAT
SOUTH OF I-90. AND...WITH THE JUXTAPOSITION OF THE LOW/WARM FRONT
PRODUCING FAVORABLE 0-3KM SRH...CANNOT RULE OUT A TORNADIC THREAT
ACROSS PORTIONS OF NORTHEAST IA INTO FAR SOUTHWEST WI...NAMELY
FAYETTE AND CLAYTON COUNTIES IN NORTHEAST IA AND GRANT COUNTY IN WI.
LOCALIZED FLOODING IS ALSO A CONCERN WITH THIS CONVECTION AS
PRECIPITABLE WATER VALUES HOVER IN THE 1.5 TO 2 INCH RANGE. SEE
HYDROLOGY SECTION BELOW FOR FURTHER DETAILS ON HEAVY RAIN POTENTIAL
AND IMPACTS. PLAN ON THE LOW AND ASSOCIATED CONVECTION TO MOVE
SOUTHEAST OF THE REGION AROUND MIDNIGHT TONIGHT. HIGH PRESSURE THEN
STARTS NOSING IN AFTER MIDNIGHT FROM THE NORTHERN PLAINS FOR
CLEARING SKIES.

HIGH PRESSURE WILL BE IN CONTROL ON THURSDAY WITH PLEASANT
TEMPERATURES IN THE 70S AND LOWER HUMIDITY LEVELS.

.LONG TERM...(THURSDAY NIGHT THROUGH TUESDAY)
ISSUED AT 318 AM CDT WED JUN 12 2013

HIGH PRESSURE REMAINS IN CONTROL ACROSS THE AREA THURSDAY NIGHT
THROUGH FRIDAY MORNING FOR A CONTINUED DRY RESPITE. BY FRIDAY
AFTERNOON THOUGH...A TROUGH OF LOW PRESSURE OVER THE PLAINS BEGINS TO
SHOVE MOISTURE BACK INTO THE AREA...MAINLY WEST OF THE MISSISSIPPI
RIVER FOR A CHANCE OF SHOWERS/ISOLATED THUNDER. FOR FRIDAY NIGHT
THROUGH SATURDAY EVENING...LOOK FOR LOW PRESSURE OVER CANADA TO SEND
A COLD FRONT THROUGH THE AREA. THIS WILL PRODUCE THE LIKELIHOOD OF
SHOWERS AND THUNDERSTORMS. WILL NEED TO WATCH FOR THE POSSIBILITY OF
SEVERE WEATHER GIVEN 0-1KM ML MUCAPE IN THE 1500-3500J/KG AND MODEST
AMOUNT OF 0-3KM BULK SHEAR. LINGERING MID-LEVEL TROUGH/FAIRLY STEEP
LAPSE RATES ENOUGH TO WARRANT A LOWER-END SHRA/TS CHANCE SUNDAY
THROUGH MONDAY. NORTHWEST FLOW AND ANOTHER WEAK MID-LEVEL TROUGH IN
THIS FLOW PRODUCE ANOTHER SHRA/TS CHANCE ON TUESDAY. OTHERWISE...
LOOKS LIKE TEMPERATURES WILL BE RIGHT AROUND NORMAL THROUGH THE
PERIOD...MAINLY IN THE 70S.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)
ISSUED AT 1214 PM CDT WED JUN 12 2013

A VIGOROUS UPPER LEVEL DISTURBANCE WILL BRING SHOWERS AND
THUNDERSTORMS TO THE TAF SITES THIS AFTERNOON INTO EARLY THIS
EVENING. A FEW STORMS COULD BECOME SEVERE WITH LARGE
HAIL...DAMAGING WINDS. AN ISOLATED TORNADO IS ALSO POSSIBLE BUT
THE HIGHER CHANCES WILL BE ACROSS NORTHEAST IOWA AND FAR SOUTHWEST
WISCONSIN. MVFR TO IFR CONDITIONS ARE POSSIBLE IN THE
THUNDERSTORMS THIS AFTERNOON. A COLD FRONT WILL PUSH ACROSS THE
AREA THIS EVENING WITH WINDS SWITCHING TO THE NORTHWEST. AFTER A
BRIEF PERIOD OF MVFR STRATUS RIGHT BEHIND THE FRONT...VFR
CONDITIONS ARE EXPECTED LATE TONIGHT INTO THURSDAY MORNING.

&&

.HYDROLOGY...TODAY INTO THIS EVENING
ISSUED AT 318 AM CDT WED JUN 12 2013

FOR AREAS MAINLY ALONG AND SOUTH OF I-90...EXPECTING RAINFALL
AMOUNTS FROM TODAY INTO THIS EVENING IN THE 0.75 TO 1.25 INCH RANGE
WITH THE POSSIBILITY OF LOCALLY HIGHER AMOUNTS IN THUNDERSTORM
ACTIVITY. GIVEN THE WET SOILS IN PLACE...PLAN ON SOME RUNOFF ISSUES
WITH PONDING OF WATER AND SOME SIGNIFICANT WITHIN BANK RIVER RISES.
ANY LONGER DURATION/HIGHER RAINFALL RATES WOULD INCREASE THE
FLOODING POTENTIAL. STAY TUNED.

&&

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

$$

UPDATE...WETENKAMP
SHORT TERM...DAS
LONG TERM....DAS
AVIATION...WETENKAMP
HYDROLOGY....DAS