Area Forecast Discussion
Issued by NWS La Crosse, WI

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215
FXUS63 KARX 171118
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
618 AM CDT SUN MAY 17 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 350 AM CDT SUN MAY 17 2015

AT 3 AM...WATER VAPOR AND RADAR SHOWED A MESOSCALE VORTICITY JUST
NORTHWEST OF DES MOINES. THE 17.00Z MODELS ARE IN FAIRLY GOOD
AGREEMENT THAT THIS SYSTEM WILL MOVE NORTH NORTHEAST THROUGH THE
AREA THIS MORNING. MANY OF THE MESO MODELS SHOW THAT A WEAKENING
LINE OF CONVECTION WILL MOVE ACROSS THE AREA THIS MORNING. WITH
MOST UNSTABLE CAPES RUNNING BETWEEN 500 AND 1000 J/KG AND
EFFECTIVE SHEAR LESS THAN 40 KNOTS ALONG AND AHEAD OF THIS BAND...
NOT ANTICIPATING ANY SEVERE WEATHER WITH THIS INITIAL BAND OF
CONVECTION.

FOR THIS AFTERNOON AND EARLY EVENING...THERE IS QUITE A BIT OF
UNCERTAINTY AS MESO MODELS ARE SHOWING A VARIETY OF SOLUTIONS AND
THEY ARE ALL EQUALLY PLAUSIBLE. SOME OF THIS HAS TO DEAL WITH HOW
MUCH THE DEBRIS CLOUDS WILL LIMIT INSTABILITY. THE 17.03Z SUGGEST
THAT MOST UNSTABLE CAPES SHOULD BE ABLE TO RECOVER INTO THE 1500
TO 2000 J/KG RANGE. IN ADDITION...SOUNDINGS SHOW AN UNCAPPED
ATMOSPHERE WHICH WILL ALLOW ANY CONVERGENT AREA TO GENERATE
SHOWERS AND STORMS. THESE COULD USE UP THE AVAILABLE CAPE PRIOR TO
THE ARRIVAL OF A MESOSCALE CONVECTIVE COMPLEX FROM NORTHWEST
OKLAHOMA LATE IN THE AFTERNOON AND EVENING. WITH THE 0-6 KM
EFFECTIVE SHEAR GREATER THAN 40 KNOTS...ANY STORM WILL HAVE THE
POTENTIAL BECOME SUPER CELLULAR. WITH A MAJORITY OF THE SHEAR
BEING LOCATED IN THE 0-3 KM LAYER...STILL THINKING THAT THERE
COULD BE SEVERAL BROKEN LINES THAT MOVE QUICKLY ACROSS THE AREA.
WILL HAVE TO WATCH OUT FOR DAMAGING WIND POTENTIAL DESPITE THE
LACK OF DRY AIR IN THE SUB CLOUD LAYER. SOUNDINGS /ESPECIALLY
NAM/ SUGGEST THAT THERE COULD BE FAT CAPE WHICH COULD AID IN THE
DEVELOPMENT OF LARGE HAIL. WITH 0-1 KM SHEAR GREATER THAN 20 KNOTS
AND HELICITY CLIMBING INTO THE 200 TO 400 J/KG...THERE IS A
CONCERN FOR ISOLATED TORNADOES ESPECIALLY NORTH OF INTERSTATE 94.
AT THIS TIME...THINKING THE GREATEST RISK OF SEVERE WEATHER WILL
BE ACROSS SOUTHEAST MINNESOTA AND NORTHEAST IOWA THIS AFTERNOON...
AND FROM THIS AFTERNOON THROUGH EARLY EVENING FOR WESTERN
WISCONSIN.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 350 AM CDT SUN MAY 17 2015

ON MONDAY NIGHT...LOW TEMPERATURES WILL FALL INTO THE MID AND
UPPER 30S ACROSS THE AREA. HOWEVER WITH CLOUDS...NORTHWEST WINDS
AROUND 10 MPH...AND LARGE TEMPERATURE/DEW POINT DEPARTURES...NOT
ANTICIPATING ANY FROST ON THIS NIGHT.

ON TUESDAY NIGHT...HIGH PRESSURE WILL BUILD ACROSS THE AREA. THIS
HIGH WILL KEEP SKIES MOSTLY CLEAR AND THE SURFACE WINDS LESS THAN
5 MPH. THIS WILL ALLOW TEMPERATURES TO FALL INTO THE LOWER AND MID
30S ACROSS MUCH OF WEST-CENTRAL...CENTRAL...AND NORTH-CENTRAL
WISCONSIN. IF THIS TREND CONTINUES...MAY HAVE TO ISSUE A FROST
ADVISORY FOR THIS TIME PERIOD.

ON WEDNESDAY...BOTH THE GFS AND GEM HAVE A SHORT WAVE MOVING
THROUGH THE CENTRAL PLAINS AND MID MISSISSIPPI RIVER VALLEY. WITH
THIS TRACK...ANY PRECIPITATION WOULD REMAIN SOUTH OF OUR AREA.
MEANWHILE THE ECMWF HAS STARTED TO TREND FURTHER NORTH WITH SYSTEM
AND IT NOW HAS PRECIPITATION AS FAR NORTH INTERSTATE 90. WITH THIS
BEING A NEW TREND...JUST KEPT THE FORECAST DRY FOR NOW.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING)
ISSUED AT 618 AM CDT SUN MAY 17 2015

MVFR/LCL IFR CIGS LOOKING TO PERSIST ACROSS THE TAF SITES THRU THE
MORNING AS INCREASING MOISTURE AND A BAND OF SHRA/ISOLATED TSRA
LIFTS NORTH-NORTHEAST ACROSS THE AREA. VSBYS WITH ANY OF THESE SHRA/
TSRA GENERALLY EXPECTED TO REMAIN VFR BUT ANY HEAVIER SHRA OR THE
ISOLATED TSRA ARE LIKELY TO PRODUCE MVFR VSBYS. WITH LIMITED
COVERAGE OF ANY HEAVIER PRECIP CORES...LEFT ANY REDUCED VSBYS OUT OF
THE TAFS FOR THIS MORNING...THOUGH CANNOT RULE OUT ONE OF THESE
PASSING ACROSS EITHER THE KRST/KLSE AIRFIELD. PRESSURE GRADIENT
CONTINUES TO TIGHTEN AS WELL THIS MORNING THEN REMAINS SO THRU THIS
AFTERNOON. SOUTHEAST TO SOUTH WINDS INCREASE TO 15-20KTS G25-30KTS
FOR THE MID MORNING INTO EARLY EVENING HOURS.

CONVECTION/TSRA REMAIN QUESTIONABLE THIS AFTERNOON...BOTH TIMING AND
COVERAGE. CHOSE TO LEAVE MENTION AS VCTS/CB IN THE 20Z-01Z...DUE
MAINLY EXPECTED SCT COVERAGE. IF DETAILS BECOME CLEARER...18Z TAF
CYCLE MAY NEED TO INCREASE THIS TO A SHORT TEMPO PERIOD OF TSRA WITH
LOWER CIGS AND SOME MVFR/IFR VSBYS. CONDITIONS LOOKING TO IMPROVE TO
VFR BY MID EVENING AND THRU THE OVERNIGHT HOURS AS DRIER AIR PUSHES
IN BEHIND ANY LATE AFTERNOON CONVECTION. SOUTH WINDS BECOME WEST TO
NORTHWEST AND REMAIN BRISK/GUSTY AFTER MIDNIGHT...BEHIND A STRONGER
COLD FRONT MOVING ACROSS THE REGION.

&&

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

$$

SHORT TERM...BOYNE
LONG TERM...BOYNE
AVIATION.....RIECK



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