Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 241907
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
207 PM CDT FRI JUL 24 2015

.SHORT TERM...(TODAY THROUGH SATURDAY NIGHT)
ISSUED AT 207 PM CDT FRI JUL 24 2015

IMMEDIATE CONCERN IS SEVERE CONVECTION POTENTIAL THIS EVENING WITH
COLD FROPA.

SURFACE MAP THIS AFTERNOON SHOWS THE COLD FRONT EXTENDING FROM THE
ARROWHEAD OF MN THROUGH NORTHWEST WI INTO SOUTHEAST MN INTO NORTH
CENTRAL IA. RAP PUSHES CORRIDOR OF 0-1KM MUCAPE IN THE 1500-3000J/KG
RANGE (NE-SE RESPECTIVELY) ALONG THE FRONT AS IT MOVES INTO THE AREA
BY 7PM. HOWEVER...RAP/NAM SOUNDING CONTINUE TO SHOW A STRONG 700-
800MB CAP IN PLACE TO INHIBIT SURFACE BASED CONVECTION. THE ONLY
MODEL SHOWING CONVECTIVE REFLECTIVITY OUTPUT WITH THE FROPA IS THE
NAM...BUT THIS IS WITH MUCH HIGHER PROGGED DEW POINTS IN THE 75-80
DEGREE RANGE WHICH SEEMS A BIT OVERDONE. AS A RESULT...CONVECTION
ALONG THE FRONT WILL BE VERY CONDITIONAL DUE TO THE CAP IN PLACE. IF
THE CAP DOES WEAKEN SOME...SCATTERED STRONG TO SEVERE STORMS COULD
FIRE WITH LARGE HAIL AND DAMAGING WINDS BEING THE MAIN THREAT. AS A
RESULT OF THE CONDITIONAL NATURE TO THIS SCENARIO...KEEPING POP
CATEGORY IN THE CHANCE RANGE...WITH HIGHER PROBABILITIES OVER THE
EAST WHERE CAP WILL BE WEAKEST. LOOK FOR STORM THREAT TO SUBSIDE
AFTER MIDNIGHT AS THE FRONT EXITS THE AREA.

SATURDAY LOOKS LIKE A DRIER DAY AS HIGH PRESSURE/SUBSIDENCE TAKES
CONTROL ACROSS THE AREA. PLAN ON HIGHS IN THE 80S.

SHOWER/THUNDERSTORM CHANCES RETURN LATE SATURDAY NIGHT/AFTER
MIDNIGHT AS A SHORTWAVE TROUGH ROUNDS THE TOP OF THE HEAT RIDGE IN
PLACE ACROSS THE PLAINS. NAM MOST AGGRESSIVE WITH THIS FEATURE WHILE
THE ECMWF IS MUCH WEAKER AND FARTHER SOUTH. WILL GO WITH 20-40 PPS
FOR NOW AND MAINLY WEST OF THE MISSISSIPPI RIVER.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 207 PM CDT FRI JUL 24 2015

LOOK FOR THAT MID-LEVEL TROUGH TO CONTINUE PUSHING EAST INTO/THROUGH
THE AREA SUNDAY INTO SUNDAY NIGHT FOR A CONTINUED CHANCE OF
SHOWERS/THUNDERSTORMS. THIS CONVECTION LOOKS TO BE SUB-SEVERE AT
THIS TIME WITH JUST LIGHTNING AND SOME HEAVY DOWNPOURS BEING THE
MAIN IMPACTS. OTHERWISE...LOOK FOR HIGHS IN THE LOWER TO MIDDLE 80S.

MONDAY HOLDS A LOWER-END CHANCE FOR SOME AIRMASS SHOWERS AND
THUNDERSTORMS AS THERE WILL STILL BE A SLIGHT WEAKNESS IN THE HEAT
RIDGE IN PLACE AS HIGHS TOP OFF WELL INTO THE 80S.

FOR MONDAY NIGHT THROUGH TUESDAY...THE REGION WILL BE IN AN AREA OF
WARM AIR ADVECTION/ISENTROPIC LIFT AHEAD OF LOW PRESSURE CROSSING
THE NORTHERN PLAINS. THIS WILL SPREAD MORE SHOWER/THUNDERSTORM
CHANCES INTO THE AREA. HIGHS ON TUESDAY LOOKS LIKE THEY COULD TOP
90S DEGREES AT SOME LOCATIONS. THEN FOR TUESDAY NIGHT INTO
WEDNESDAY...A COLD FRONT WILL MOVE ACROSS THE AREA FOR A CONTINUED
CHANCE OF SHOWERS AND STORMS.

THURSDAY LOOKS TO BE DRY AS A WEAK RIDGE OF HIGH PRESSURE
ESTABLISHES ITSELF OVER THE REGION. OTHERWISE...PLEASANT WITH HIGHS
IN THE UPPER 7S0 TO THE LOWER 80S.

SMALL-END SHOWER/THUNDER CHANCE RETURN ON FRIDAY AS BOTH THE
GFS/ECMWF SHOW A TROUGH/COLD FRONT MOVING ACROSS MN INTO NORTHWEST
WI. LOOK FOR TEMPERATURES AGAIN IN THE UPPER 70S/LOWER 80S.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)
ISSUED AT 1208 PM CDT FRI JUL 24 2015

SKIES ARE BEGINNING TO CLEAR OUT BEHIND THE EARLY MORNING ROUND OF
SHOWERS AND STORMS AND EXPECT TO SEE SCATTERED OR SOME BROKEN MID
LEVEL CLOUDS OVER THE AREA. THE COLD FRONT IS STILL WEST OF THE
AREA AND IS EXPECTED TO SLIDE THROUGH DURING THE EVENING HOURS.
THE CONCERN BECOMES WHETHER ADDITIONAL STORMS WILL DEVELOP AS THE
COLD FRONT COMES IN. BOTH THE 24.12Z NAM AND 24.15Z RAP FORECAST
SOUNDINGS SUGGEST A CAP WILL DEVELOP THIS AFTERNOON AHEAD OF THE
FRONT AS WARM AIR ALOFT MOVES IN AND THAT THIS CAP WILL REMAIN IN
PLACE UNTIL AFTER THE FRONT MOVES THROUGH. THE BEST CHANCES FOR
THE CAP TO BE DISPLACED LOOK TO BE OVER CENTRAL INTO SOUTHWEST
WISCONSIN. BASED ON THIS...PLAN TO SHOW SOME LATE AFTERNOON
CUMULUS CLOUDS DEVELOPING THAT COULD GO TO A VFR CEILING FOR A
WHILE BUT WILL NOT INCLUDE ANY MENTION OF SHOWERS OR STORMS. SKIES
SHOULD BECOME CLEAR FAIRLY QUICKLY BEHIND THE FRONT WITH THE WINDS
DROPPING UNDER 10 KNOTS FROM THE NORTHWEST.

&&

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

$$

SHORT TERM...DAS
LONG TERM...DAS
AVIATION...04



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