Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 030000
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
700 PM CDT SAT MAY 2 2015

.SHORT TERM...(THIS EVENING THROUGH SUNDAY NIGHT)
ISSUED AT 341 PM CDT SAT MAY 2 2015

FORECAST FOCUS IS ON SMALL RAIN CHANCES TONIGHT...AND BETTER RISK
FOR SHOWERS AND STRONG THUNDERSTORMS ON SUNDAY.

WEAK SHORT WAVE TROUGH MOVING THROUGH IA THIS AFTERNOON WITH A FEW
SHOWERS AND ISOLATED THUNDERSTORMS OCCURRING. MODELS HAVING SOME
ISSUES WITH HOW TO HANDLE THIS FEATURE. DISTURBANCE IS MOVING DUE
EAST AND SHOULD CONTINUE TO DO SO THIS EVENING. SOME MODELS INSIST
ON NEW DEVELOPMENT OVERNIGHT IN THE DEFORMATION AREA ON THE BACK
SIDE OF THE WAVE...LIKELY AS THE LOW LEVEL JET ENHANCES MOISTURE
TRANSPORT INTO THE REGION. BUT NOT SOLD ON THAT HAPPENING. HAVE
MAINTAINED A LOW CHANCE OVER OUR FAR SOUTHERN AREA BUT OTHERWISE
LEAVING THE FORECAST DRY TONIGHT.

OF LARGER CONCERN IS THE COLD FRONT MOVING THROUGH THE AREA
SUNDAY AFTERNOON AND EVENING. A POTENT SHORT WAVE TROUGH WILL PASS
INTO FAR NORTHERN MN LATE SUNDAY...HELPING SUPPORT THE FRONT AS IT
DROPS SOUTHWARD. FRONTAL PASSAGE IN THE MOST OPPORTUNE TIME OF
DAY...AND AMPLE MOISTURE LOOKS TO BE AVAILABLE AS SOUTHERLY WINDS
CONTINUE TO ENHANCE TRANSPORT AHEAD OF THE BOUNDARY. MODEL CAPE
FORECAST SUGGESTS AS MUCH AS 2500-3000 J/KG...BUT THIS LIKELY
OVERDONE AS MODEL DEWPOINTS APPEAR TO BE INFLATED A BUT. BUT
SUFFICE TO SAY THERE WILL BE ENOUGH INSTABILITY TO SUPPORT STRONG
UPDRAFTS. BETTER SHEAR LOOKS TO LAG BEHIND THE FRONT...BUT ENOUGH
PRESENT FOR STRONG STORMS...ESPECIALLY GIVEN THE COLD AIR MOVING
IN BEHIND. HAIL AND STRONG WIND ARE A POSSIBILITY AND SPC INCLUDES
OUR AREA IN THE DAY 2 SLIGHT RISK.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 341 PM CDT SAT MAY 2 2015

FRONT CONTINUES SOUTH THROUGH THE AREA EARLY MONDAY...BUT THEN
STALLS OUT. BOUNDARY LOOKS TO LINGER AROUND THE GENERAL AREA ALL
THE WAY INTO WEDNESDAY. WITH THIS BOUNDARY SERVING AS A FOCAL
POINT...COULD SEE PERIODIC SHOWERS AND ISOLATED THUNDERSTORMS INTO
MID WEEK. MEDIUM RANGE MODELS THEN IN GOOD AGREEMENT THAT A
SIGNIFICANT SHORT WAVE TROUGH WILL EJECT NORTHEAST UP AND ACROSS
OUR REGION OUT OF THE MEAN WEST COAST LONG WAVE TROUGH. THIS WILL
PASS LATE WEDNESDAY AND THURSDAY. THIS WILL RESULT IN A COUPLE OF
PERIODS OF SHOWERS AND THUNDERSTORMS. YET ANOTHER SIGNIFICANT
SYSTEM LOOKS TO MOVE IN FOR NEXT WEEKEND...SO A PERIOD OF ACTIVE
WEATHER LOOKS TO BE IN THE OFFING.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SUNDAY EVENING)
ISSUED AT 659 PM CDT SAT MAY 2 2015

A MODERATE PRESSURE GRADIENT IN THE LOW LEVELS WILL CAUSE SOME
LLWS APPROACHING VALUES TO INCLUDE IN THE TAF OVERNIGHT AT KLSE.
1KFT WINDS WILL BE 220 DEG AT 30 KTS. THIS GRADIENT WILL ALSO
CAUSE SOME GUSTING WINDS AGAIN THROUGH SUNDAY AS A COLD FRONT
APPROACHES FROM THE NORTHWEST.

AT THE VERY END OF THE PERIOD...00Z MAY 3 OR 7 PM SUNDAY
EVENING...A BROKEN LINE OF THUNDERSTORMS IS LIKELY TO BE VERY
NEAR THE KRST AIRFIELD. INSTABILITY WILL GROW DURING THE DAYTIME
HOURS AND A COLD FRONT WILL PROVIDE THE SPARK NEEDED TO DEVELOP
TSRA. ISOLATED STORMS WITH HAIL UP TO GOLF BALLS AND WINDS GUSTING
TO 60-65MPH ARE POSSIBLE.

DUE TO THE VARIABILITY IN TIMING /PROBABLY A 22-01Z WINDOW/...DID
NOT INCLUDE VCTS IN THE KRST TAF. HOWEVER...THE NEXT TAF ISSUANCE
AT 06Z WILL INCLUDE ABOUT A 2 HOUR TEMPO TSRA AT BOTH KLSE AND
KRST SOMEWHERE IN THE 00-03Z AND 22-02Z WINDOW RESPECTIVELY.

&&

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

$$

SHORT TERM...MW
LONG TERM...MW
AVIATION...DB



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