Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 011118
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
618 AM CDT MON SEP 1 2014

.SHORT TERM...(TODAY THROUGH TONIGHT)
ISSUED AT 308 AM CDT MON SEP 1 2014

WATER VAPOR SATELLITE LOOP COUPLED WITH RAP ANALYSIS SHOWS VIGOROUS
MID-LEVEL TROUGH ROTATING THROUGH THE PLAINS TOWARD THE UPPER
MISSISSIPPI RIVER VALLEY. AT THE SURFACE 999MB LOWS WAS OVER WESTERN
ONTARIO WITH A COLD FRONT EXTENDING SOUTHWARD THROUGH MN/NW
IA/CENTRAL NEB. RADAR WAS LIT UP WITH SHOWERS/THUNDERSTORMS ACROSS
EASTERN MN INTO THE FORECAST AREA AHEAD OF THE MID-LEVEL WAVE AND
SURFACE COLD FRONT. OTHERWISE...TEMPERATURES ACROSS THE AREA EARLY
THIS MORNING WERE IN THE 60S.

LOOK FOR THE SURFACE COLD FRONT AND ASSOCIATED CONVECTION TO
CONTINUE PUSHING EAST ACROSS THE AREA THIS MORNING WITH THE BULK OF
THE RAIN EXITING EAST BY LATE MORNING. KEPT LINGERING AND
DIMINISHING CHANCES GOING HOWEVER INTO THE AFTERNOON AS THE MID-
LEVEL TROUGH/COLD AIR ALOFT POSSIBLY POPPING A FEW INSTABILITY
SHOWERS AND THUNDERSTORMS. NOT EXPECTING ANY SEVERE THREAT AS BEST
CAPE AND WIND SHEAR SHIFT EAST/SOUTHEAST OF THE AREA.

FOR TONIGHT...WILL SEE ANOTHER WEAK MID-LEVEL WAVE ROTATE TOWARD THE
AREA FROM THE NORTHERN PLAINS. NAM SHOWING A DECENT SHOT OF 700-
300MB PVA MOVING IN MAINLY WEST OF THE MISSISSIPPI RIVER AFTER
MIDNIGHT WITH BUFKIT SHOWING INSTABILITY/MOISTURE MAINLY CONFINED
ABOVE 800MB. KEPT A SMALL-END CHANCE OF SHOWERS/ISOLATED WEST OF THE
MISSISSIPPI AFTER MIDNIGHT BASED ON THIS SIGNAL. OVERNIGHT LOWS ARE
EXPECTED TO FALL INTO THE 50S.

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 308 AM CDT MON SEP 1 2014

A SMALL CHANCE OF SHOWERS AND THUNDERSTORMS WILL CONTINUE INTO
TUESDAY MAINLY NORTH OF I-94 AS THE WEAK MID-LEVEL TROUGH ROTATES
ACROSS THE FORECAST AREA. PLAN ON HIGHS  RANGING FROM THE MIDDLE 70S
ACROSS NORTH CENTRAL WI...TO THE UPPER 70S/LOWER 80S ELSEWHERE.

SURFACE CYCLOGENESIS OVER THE NORTHERN PLAINS WILL PUSH A WARM FRONT
TOWARD THE AREA WEDNESDAY/WEDNESDAY NIGHT. ALL MODELS SHOW
INCREASING 850MB MOISTURE TRANSPORT/WARM AIR ADVECTION NOSING INTO
THE AREA WITH THE FRONT FOR INCREASING COVERAGE OF THUNDERSTORMS.
PRECIPITABLE WATER VALUES PUSHING 1.9 INCHES BY THURSDAY MORNING WITH
WARM CLOUD DEPTH LAYERS INCREASING INTO THE 4-4.5KM RANGE. BASED ON
THIS SIGNAL...WILL HAVE TO WATCH FOR A HEAVY RAINFALL POTENTIAL
ALONG WITH OTHER SEVERE THREATS AS WELL AS CAPE AND BULK SHEAR
INCREASE ALONG THE WARM FRONT. AT THIS POINT...MODELS SHOWING HIGHER
SEVERE POTENTIAL STAYING WEST OF THE MISSISSIPPI RIVER IN MORE
FAVORABLE CAPE/SHEAR ENVIRONMENT. WILL HAVE TO KEEP A CLOSE ON THIS
OVER THE NEXT COUPLE DAYS. LOOK FOR HIGHS ON WEDNESDAY TO TOP OFF IN
THE UPPER 70S TO MIDDLE 80S WITH DEW POINTS CREEPING UP INTO THE 65-
70 DEGREE RANGE.

THUNDERSTORM CHANCES CONTINUE THURSDAY INTO THURSDAY NIGHT AS THE
LOW PULLS NORTHEAST INTO ONTARIO CANADA...PUSHING A COLD FRONT
THROUGH THE AREA. THURSDAY WILL HAVE TO BE WATCHED CLOSELY AS WELL
FOR SEVERE POTENTIAL AS THE GFS IS SHOWING 0-6KM BULK SHEAR OF 30-
50KT COUPLED WITH MUCAPE POOL OF 2500-4500J/KG. HIGHS ON THURSDAY
AHEAD OF THE COLD FRONT ARE EXPECTED TO TOP OFF WELL INTO THE 80S
WITH DEW POINTS IN THE 70-75 DEGREE RANGE.

DRIER/COOLER AIR FILTERS INTO THE AREA FRIDAY AND INTO THE WEEKEND
AS CANADIAN HIGH PRESSURE BUILD INTO THE REGION. PLAN ON
TEMPERATURES BY THIS WEEKEND TO FEEL A BIT MORE LIKE FALL WITH HIGHS
IN THE 60S/LOWER 70S AND LOWS IN THE 50S.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)
ISSUED AT 618 AM CDT MON SEP 1 2014

SECOND ROUND OF CONVECTION HAS FORMED AHEAD OF THE FRONT AND
EXPECT THIS TO MOVE THROUGH BEFORE 12Z AT KRST AND KLSE BY 14Z.
IFR CONDITIONS WILL BE POSSIBLE IN THIS ACTIVITY. THE FRONT IS
THEN EXPECTED TO PUSH THROUGH SHORTLY BEHIND THE CONVECTION
SWINGING THE WINDS AROUND TO THE WEST AND ALLOWING AN AREA OF MVFR
CEILINGS TO MOVE IN. BOTH THE 01.06Z NAM AND 01.09Z RAP SUGGEST
THESE CEILINGS WILL ONLY LAST THROUGH THE MORNING BEFORE
SCATTERING OUT WITH VFR CONDITIONS THEN EXPECTED THROUGH THE REST
OF THE PERIOD. SOME CONCERN FOR FOG DEVELOPMENT LATE
TONIGHT...ESPECIALLY AT KLSE. FORECAST SOUNDINGS FROM THE NAM
INDICATE SATURATION MAY OCCUR AT THE SURFACE WITH A LIGHT WIND
PROFILE UP THROUGH ABOUT 25OO FEET OR SO. HOWEVER...UNSURE HOW
MUCH MID AND HIGH LEVEL CLOUDS MAY BE AROUND AHEAD OF AN
APPROACHING WEAK SHORT WAVE TROUGH. WILL LET LATER SHIFTS ACCESS
THIS POTENTIAL AND ADD IF NEEDED.

&&

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

$$

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



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