Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 241800
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
100 PM CDT FRI APR 24 2015

.SHORT TERM...(TODAY THROUGH SATURDAY)
ISSUED AT 245 AM CDT FRI APR 24 2015

A 500 MB LOW TROUGH IS SLATED TO MOVE NORTHEAST OUT OF THE DESERT
SOUTHWEST...MOVING ACROSS THE MID MISSISSIPPI RIVER VALLEY BY 18Z
SAT. THE TROUGH/S ASSOCIATED SFC LOW WILL HOLD WITH THE
TROUGH...MOVING FROM THE SOUTHERN PLAINS TOWARD THE OH RIVER VALLEY
BY 00Z SUN. WHILE THE HEART OF THE SYSTEM WILL STAY SOUTH...OTHER
PARTS WILL PROVIDE A GOOD SHOT AT SOME RAIN...ESPECIALLY FOR
NORTHEAST IA/SOUTHWEST WI.

FIRST...STRENGTHENING 900-800 MB FRONTOGENETIC REGION WITH A NICE
NORTH-SOUTH RUNNING SWATH OF 850 MB WARM AIR ADVECTION MOVES INTO
EASTERN MN THIS AFTERNOON...WEAKENING AS THEY MOVE INTO WESTERN WI
TONIGHT. SOME LOW LEVEL MOISTURE TRANSPORT WITH THE
THERMODYNAMICS...AND EXPECT AREAS OF SHOWERS AS A RESULT.
HOWEVER...HOW FAR EAST THESE ADVANCE IS IN QUESTION. BUFKIT
SOUNDINGS AND RH FIELDS POINT TO A LOT OF DRY AIR ACROSS
WI...ACTING AS AN INHIBITOR TO THE RAIN/S EASTWARD MARCH.
THAT...WITH WEAKENING FORCING MAKE CHANCES OVER WESTERN A BIT LESS
COMPARED TO EASTERN MN.

SECOND...AS THE SFC LOW MOVES SOUTH OF THE FORECAST AREA...ITS
DEFORMATION REGION WITH SLOPING FRONTOGENETIC LIFT WILL EXTEND
ACROSS IA AND ILL. MOISTURE WRAPS AROUND THE LOW AND THERE SHOULD BE
AMPLE SATURATION FOR A BROAD AREA OF RAIN. HOW FAR NORTH THE BEST
RAIN CHANCES EXTEND IS THE BIGGEST QUESTION...AND NAM/GFS/EC ALL
SEEM TO FAVOR THE I-90 CORRIDOR SOUTH. LOOKS REASONABLE AT THE
MOMENT. SOME SOUNDINGS SUGGEST ICE COULD BE LOST FOR A PERIOD OF
TIME OVERNIGHT...MAKING DRIZZLE MORE LIKELY. GOING TO STICK WITH
RAIN AS THE PTYPE. THIS AREA OF RAIN LOOKS MOST LIKELY SAT MORNING.

DON/T SEE MUCH OF A THUNDER THREAT AT THIS TIME...MINIMAL IF ANY
INSTABILITY...AND WHAT COULD BE THERE IS AWFULLY SKINNY. BEST
CHANCES FOR ISOLATED THUNDER WOULD BE PARTS OF SOUTHEAST
MN/NORTHEAST IA THIS AFTERNOON. CONFIDENCE LOW...SO GOING TO LEAVE
OUT OF THE FORECAST FOR THE MOMENT.

THERE COULD BE SOME SNOW IN THE NORTH...BUT CHANCES FOR PCPN ARE
MUCH LESS...AND THE SUB CLOUD LAYER IS RATHER DRY...INHIBITING ANY
PCPN TYPE FROM REACHING THE GROUND.

.LONG TERM...(SUNDAY THROUGH THURSDAY)
ISSUED AT 245 AM CDT FRI APR 24 2015

THE GFS HAS TRENDED TOWARD THE EC/GEM SOLUTION OF BUILDING A
SHORTWAVE UPPER LEVEL RIDGE ACROSS THE REGION FOR THE END OF THE
WEEKEND. SOLUTIONS THEN FAVOR A LONG WAVE RIDGE TAKING OVER FOR NEXT
WEEK...WITH VARIOUS RIDGE RUNNERS WORKING THROUGH/ACROSS IT.
PLACEMENT AND TIMING OF THESE SHORTWAVE TROUGHS ARE DUBIOUS AT
BEST...BUT THE VARIOUS SOLUTIONS ALL POINT TO DRY FOR THE BETTER
PART OF NEXT WEEK.

WITH THE SWING BACK TO RIDGING...TEMPS SHOULD FOLLOW SUIT. EXPECTING
AT OR ABOVE NORMAL HIGHS.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)
ISSUED AT 1259 PM CDT FRI APR 24 2015

INITIAL ROUND OF SHOWERS MOVING ACROSS THE AREA IN A REGION OF
SOME ISENTROPIC UP GLIDE AND FRONTOGENESIS IN THE 1000-700 MB
LAYER. THESE HAVE BEEN ABLE TO PRODUCE SOME SHORT PERIODS OF MVFR
CONDITIONS. LOOKING AT THE 24.15Z HRRR AND 24.18Z NAM...THESE
SHOWERS WILL CONTINUE TO PROGRESS NORTHEAST BUT WILL HAVE A TOUGH
TIME GETTING VERY FAR INTO WESTERN WISCONSIN WHERE DEW POINTS
HAVE REMAINED IN THE TEENS. PLAN TO SHOW TEMPO GROUPS FOR BOTH TAF
SITES THROUGH THE MIDDLE OF THE AFTERNOON WITH THE SHOWERS AROUND
AND THE POTENTIAL FOR MVFR CONDITIONS. AFTER THAT...THE FORCING
BEGINS TO REFOCUS FARTHER TO THE SOUTH WITH THE FRONTOGENESIS
FOCUSING OVER EXTREME SOUTHERN WISCONSIN INTO IOWA AS THE MAIN
SURFACE LOW TRACKS ACROSS KANSAS INTO MISSOURI. THIS SHOULD TAKE
MOST OF THE RAIN SOUTH OF BOTH TAF SITES AND WENT BACK TO JUST
VCSH FOR THE LATE AFTERNOON INTO THE EARLY EVENING. AFTER
THAT...THINK THE ACTIVITY WILL BE TO THE SOUTH AND HAVE GONE DRY
FOR THE REMAINDER OF THE PERIOD. WITH THE LOW LEVEL FLOW TURNING
MORE TO THE EAST...THIS WILL HELP TO BRING IN THE LOW LEVEL DRY
AIR WHICH SHOULD SERVE TO KEEP CEILINGS VFR ONCE THE SHOWERS ARE
OUT OF THE AREA.

&&

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

$$

SHORT TERM.....RIECK
LONG TERM......RIECK
AVIATION...04



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