Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 231919
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
219 PM CDT THU JUL 23 2015

.SHORT TERM...(TONIGHT THROUGH FRIDAY NIGHT)
ISSUED AT 219 PM CDT THU JUL 23 2015

MAIN FOCUS IS ON LIKELIHOOD OF SHOWERS/STORM MOVING INTO THE AREA
EARLY FRIDAY MORNING...AND THEN SEVERE THUNDERSTORM POTENTIAL LATE
FRIDAY AFTERNOON INTO FRIDAY EVENING WITH COLD FRONTAL PASSAGE.

SURFACE MAP THIS AFTERNOON HAD HIGH PRESSURE CENTERED OVER SOUTHERN
LAKE MICHIGAN WITH RIDGING INTO WI. VISIBLE SATELLITE SHOWING FAIRLY
EXTENSIVE FIELD OF CUMULUS ACROSS THE REGION WITH MOIST SOUTHERLY
FLOW ADVECTING IN ON RETURN FLOW ON THE BACKSIDE OF THE HIGH.
OTHERWISE...TEMPERATURES THIS AFTERNOON WERE IN THE 80-85 DEGREE
RANGE.

FOR TONIGHT INTO FRIDAY MORNING...MID-LEVEL SHORTWAVE
TROUGH/THUNDERSTORMS OVER THE DAKOTAS THIS AFTERNOON EXPECTED TO
UPSCALE AND ADVANCE SOUTHEAST TOWARD THE REGION BY EARLY FRIDAY
MORNING AS 850MB MOISTURE TRANSPORT CONTINUES TO FUEL THE
CONVECTION. APPEARS THIS COMPLEX OF STORMS COULD BECOME SEVERE WITH
DAMAGING WINDS/LARGE HAIL AS IT MOVES INTO MN...THEN BE ON A
WEAKENING TREND AS THEY HEAD INTO OUR AREA AFTER 12Z. THIS IS DUE TO
THE STORMS MOVING AWAY FROM THE BETTER CAPE AXIS/SOURCE WHICH WILL
BE IN PLACE ACROSS SOUTH CENTRAL MN/WESTERN IA. HAVE BUMPED POPS
INTO LIKELY CATEGORY FROM SOUTHEAST MN INTO NORTH CENTRAL WI IN THE
12-16Z TIME FRAME...TAPERING OFF TO CHANCY POPS AFTERWARDS AS THE
COMPLEX FALLS APART/MOVES EAST OF THE AREA.

WILL THEN BE FOCUSING ATTENTION TO INCOMING COLD FRONT BY LATER
FRIDAY AFTERNOON/FRIDAY NIGHT. PLENTY OF CAPE AND WIND SHEAR FOR A
SEVERE RISK. HOWEVER...SEVERE THREAT WILL BE CONDITIONAL DUE TO A
FAIRLY STRONG CAP THAT WILL BE IN PLACE DUE TO SOME SUBSIDENCE
BEHIND PASSING SHORTWAVE TROUGH. NAM/ARW MESOWRF MODEL REFLECTIVITY
DOES SHOW SCATTERED CONVECTION FIRING MAINLY AFTER 23Z WITH
WEAKENING CAP...BUT OTHER MODELS LESS ENTHUSED. DAMAGING WINDS AND
LARGE HAIL WOULD BE THE MAIN THREATS IF STORMS DO DEVELOP. WILL HAVE
TO KEEP A CLOSE EYE ON THIS SCENARIO WHICH WILL DEPEND HIGHLY ON
DEGREE OF CLEARING/RECOVERY BEHIND THE MORNING CONVECTION.

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 219 PM CDT THU JUL 23 2015

RIDGE OF HIGH PRESSURE DRIES THINGS OUT ON SATURDAY WITH HIGHS
CLIMBING INTO THE 80S.

SHOWER AND THUNDERSTORM CHANCES MAKE A RETURN LATER SATURDAY NIGHT
THROUGH SUNDAY NIGHT AS MODELS SHOW A WEAK MID-LEVEL TROUGH MOVING
OUT OF THE CENTRAL/NORTHERN PLAINS AND THROUGH THE UPPER MISSISSIPPI
RIVER VALLEY REGION. PLAN ON HIGHS SUNDAY AGAIN IN THE 80S.

FOR MONDAY THROUGH THURSDAY...MODELS DEPICTING A SOMEWHAT OF A
PATTERN SHIFT AS UPPER LEVEL RIDGE OF HIGH PRESSURE SHIFTS EAST AND
TROUGH OF LOW PRESSURE MOVES ACROSS THE NORTHERN PLAINS INTO THE
UPPER MISSISSIPPI RIVER VALLEY/GREAT LAKES REGION. LATEST ECMWF/GFS
SHOWING LOW PRESSURE OVER SOUTHERN CANADA PUSHING A COLD FRONT
THROUGH THE REGION MONDAY NIGHT/TUESDAY TIME FRAME FOR A CHANCE OF
SHOWERS/THUNDERSTORMS.

LOOKS LIKE SLIGHTLY COOLER CONDITIONS THEN FOR WEDNESDAY INTO
THURSDAY AS MID-LEVEL TROUGHING SETS UP ACROSS THE AREA. EXPECT QUITE A BIT OF
DAYTIME CUMULUS WITH ISOLATED SHOWERS/THUNDERSTORMS ON WEDNESDAY.
PLAN ON HIGHS WEDNESDAY IN THE 80-85 DEGREE RANGE AND IN THE UPPER
70S/LOWER 80S ON THURSDAY.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)
ISSUED AT 1211 PM CDT THU JUL 23 2015

SHORT WAVE TROUGH CURRENTLY COMING ACROSS MONTANA AND WYOMING IS
EXPECTED TO CONTINUE MOVING EAST/NORTHEAST THROUGH THE PERIOD OVER
THE TOP OF THE UPPER LEVEL RIDGE THAT IS IN PLACE OVER THE CENTRAL
PART OF THE COUNTRY. THE 23.12Z NAM SUGGESTS THE BEST FORCING FROM
THIS WAVE WILL REMAIN TO THE NORTH OF BOTH TAF SITES BUT THERE
COULD STILL BE SOME WEAK TO MODERATE PV ADVECTION IN THE 500-300
MB LAYER THAT COMES ACROSS AFTER 12Z. THE LOW LEVEL MOISTURE
TRANSPORT AXIS WILL BE THROUGH THE AREA AS IT IS PULLED NORTH
TOWARD THE SHORT WAVE TROUGH...BUT THE LOCAL AREA SHOULD STILL GET
INTO THE EASTERN AND CONVERGENT SIDE OF THIS AXIS AFTER 12Z.
EXPECTING A COMPLEX OF STORMS TO DEVELOP OVER THE DAKOTAS TODAY
AND THEN MOVE EAST WITH THE WAVE AND MOISTURE TRANSPORT. THE
QUESTION BECOMES HOW MUCH OF THIS COMPLEX WILL MAKE IT SOUTH TO
THE TAF SITES. THE 23.12Z CR-NAM NEST SHOWS A BROKEN LINE OF
WEAKENING CONVECTION GETTING INTO BOTH TAF SITES WHILE THE 23.12Z
HI-RES ARW AND NMM SHOW A LITTLE MORE AND STRONGER CONVECTION
COMING THROUGH. THE TIMING OF THE NMM IS PRETTY SIMILAR TO THE
CR-NAM NEST WHILE THE ARW IS A LITTLE QUICKER. FOR NOW...OVERALL
CONFIDENCE IS NOT THAT HIGH ON HOW FAR SOUTH THE CONVECTION WILL
GET...SO WILL START BY INTRODUCING A VCSH IN THE MIDDLE OF THE
MORNING WITH VFR CEILINGS. LATER FORECASTS MAY HAVE TO UPGRADE TO
INCLUDE THUNDER AND MVFR CEILINGS IF THE TRENDS SHOW THE
CONVECTIVE COMPLEX COULD COME THROUGH IMPACTING THE TAF SITES.

&&

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

$$

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



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