Weather Story NWS La Crosse, WI

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NWS KARX Forecast Discussion

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FXUS63 KARX 100807
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
307 AM CDT FRI SEP 10 2010

.SHORT TERM...TODAY THROUGH SUNDAY NIGHT

MAIN FORECAST CONCERN IS ON RAIN CHANCES TONIGHT INTO SATURDAY AND
THEN AGAIN LATE SUNDAY AFTERNOON/SUNDAY NIGHT.

WATER VAPOR IMAGERY AT 07Z SHOWS SHORTWAVE TROUGH OVER THE NORTHERN
ROCKIES. AT THE SURFACE A COLD FRONT IS PUSHING INTO THE WESTERN
DAKOTAS. SCATTERED CONVECTION IS OCCURRING AHEAD OF THIS SYSTEM FROM
NORTHERN NEBRASKA INTO NORTH DAKOTA. MEANWHILE...FURTHER EAST A
LARGE CLOUD SHIELD EXTENDS ALL THE WAY INTO WESTERN WISCONSIN...WITH
ONLY THE FAR EAST AND NORTHERN FORECAST AREA SEEING ANY BREAKS.

10.00Z MODELS IN GOOD AGREEMENT THROUGH THE FORECAST PERIOD. A
HIGHLY AMPLIFIED FLOW WITH A PROGRESSIVE SHORTWAVE TROUGH NOW OVER
THE NORTHERN ROCKIES WILL PUSH INTO THE NORTHERN PLAINS TODAY AND
THEN INTO NORTHERN MINNESOTA FRIDAY NIGHT. THE ASSOCIATED COLD
FRONT NOW ENTERING THE NORTHERN PLAINS WILL PUSH INTO WESTERN
MINNESOTA BY 06Z TONIGHT AND ACROSS THE FORECAST AREA FROM 09Z
THROUGH 18Z SATURDAY.

EXPECT CLOUDS TO CONTINUE TO THICKEN TODAY ACROSS THE FORECAST AREA.
MOISTURE TRANSPORT INCREASES ACROSS MINNESOTA TODAY AHEAD OF THE
APPROACHING FRONT...WITH MOST OF THE ACTIVITY REMAINING WEST OF THE
AREA AT LEAST THOUGH 21Z. WITH THAT IN MIND DID ADD SOME TIMING TO
THE GRIDS FOR TODAY. BY TONIGHT AS FRONT PUSHES INTO MINNESOTA
MOISTURE TRANSPORT NUDGES INTO THE FORECAST AREA. PRECIPITABLE
WATER VALUES DO INCREASE INTO THE 1.5 INCH RANGE AS THE NIGHT WEARS
ON...BUT THE BULK OF THE MOISTURE GETS SHUNTED INTO THE OHIO
VALLEY AS THE REMNANTS OF HERMINE GETS DRAWN INTO THE WESTERLIES.
NOT MUCH INSTABILITY AHEAD OF THE FRONT...WITH BOTH THE NAM AND GFS
SOWING 300-500 J/KG OF MOIST UNSTABLE CAPES...MAINLY THIS EVENING.
THUS WOULD EXPECT MAINLY SHOWERS WITH ONLY ISOLATED THUNDER. WITH
PROGRESSION OF SYSTEM DID ADD SOME TIMING TO THIS PERIOD AS WELL.

HIGH PRESSURE BEGINS TO DROP THROUGH THE PLAINS ON SATURDAY...WITH
THE COLD FRONT PUSHING EAST OF THE AREA BY LATE IN THE AFTERNOON.
SO EXPECT SHOWERS TO END FROM WEST TO EAST. PRESSURE GRADIENT
TIGHTENS BETWEEN THE DEPARTING FRONT AND THE HIGH OVER THE PLAINS
AND DID RAISE WIND SPEEDS A LITTLE FROM THE PREVIOUS FORECAST...BUT
NOT EXPECTING ANY ADVISORY CRITERIA TO BE MET.

HIGH SETTLES OVER THE PLAINS SATURDAY NIGHT WITH MAINLY CLEAR
SKIES OVER THE UPPER MISSISSIPPI IVER VALLEY REGION. GRADIENT LOOKS
TO REMAIN TIGHT ENOUGH TO PRECLUDE MENTION OF VALLEY FOG A THIS
TIME...AS CENTER OF HIGH REMAINS SOUTH OF THE LOCAL AREA.

AS THE HIGH DRIFTS INTO MISSOURI SUNDAY...ANOTHER SHORTWAVE MOVES
ALONG THE CANADIAN BORDER...PUSHING A WEAK COLD FRONT SOUTHWARD
INTO THE AREA. MOISTURE LOOKS TO BE LACKING A THIS POINT AND LEFT
SUNDAY DRY...AND KEPT LOWER END PROBABILITIES SUNDAY NIGHT.
HOWEVER...NAM INDICATING POTENTIAL FOR SOME LIGHT SHOWERS AS EARLY
AS SUNDAY AFTERNOON SO THIS WILL HAVE TO BE WATCHED WITH LATER
FORECASTS.

TEMPERATURES LOOK TO REMAIN BELOW NORMAL TODAY AND SATURDAY...BUT
REBOUND BACK TO NEAR NORMAL ON SUNDAY WITH MORE SUNSHINE EXPECTED.

.LONG TERM...MONDAY THROUGH THURSDAY

HIGH PRESSURE WILL BE THE MAIN WEATHER INFLUENCE ON MONDAY AND MONDAY
NIGHT...BUT THE 10.00Z GFS AND ECMWF BEGIN TO DIVERGE FOR TUESDAY
AND TUESDAY NIGHT. ECMWF TAKE PUSHES SHORTWAVE ACROSS THE AREA IN
THE NEARLY ZONAL FLOW...WHEREAS GFS KEEPS A RIDGE OF HIGH PRESSURE
OVER THE AREA. A LOOK A THE 10.00Z GFS ENSEMBLE SHOWS SOME LOWER
PROBABILITIES FOR MEASURABLE RAIN FOR TUESDAY AND TUESDAY NIGHT.
WITH THESE DIFFERENCES WILL ALLOW DAY SHIFT TO PERUSE THE FULL SUITE
OF GUIDANCE BEFORE MAKING ANY CHANGES. OTHERWISE REMAINDER OF
FORECAST LOOKS ON TRACK.

&&

.AVIATION...TODAY INTO SATURDAY MORNING

CLOUDS WILL GRADUALLY LOWER TODAY AS THE PATTERN SLOWLY PROGRESSES
AND MOISTURE AHEAD OF THE LOW AND FRONT IN THE PLAINS CONTINUES TO
INCREASE OVER THE AREA. WITH CONTINUED INFLUENCE FROM THE SFC HIGH
OVER MI AND LK SUPERIOR...CLOUDS TODAY WILL REMAIN VFR...MOSTLY
6K-8K FT THIS MORNING THEN 4K-6K FT THIS AFTERNOON. COLD FRONT IN
THE PLAINS PICKS UP SOME SPEED TONIGHT AS THE LOW LIFTS INTO CAN...
MOVING INTO CENTRAL MN/IA BY MIDNIGHT...THEN ACROSS THE TAF SITES
LATER TONIGHT/EARLY SAT MORNING...AROUND 10Z AT KRST...13Z AT KLSE.
AS THE FRONT PUSHES INTO MN/IA THIS EVENING...LOWER LEVEL MOISTURE
INCREASES OVER THE AREA WITH MVFR CLOUDS EXPECTED TO SPREAD WEST TO
EAST ACROSS THE TAF SITES...WELL AHEAD OF THE FRONT. LIFT INCREASES
AS WELL...WITH A BROAD BAND OF -SHRA TO ALSO SPREAD ACROSS THE AREA
AHEAD OF THE FRONT. WILL ADD SOME -SHRA TO THE EVENING/OVERNIGHT
HOURS TONIGHT WITH NEXT SET OF TAFS. INSTABILITY QUITE LIMITED...
WITH ANY TSRA EXPECTED TO BE ISOLATED. WILL LEAVE TSRA/CB MENTION
WITH THIS FRONT OUT OF TAFS FOR NOW. FRONT WILL CONTINUE TO MOVE
EAST OF THE AREA SAT. HOWEVER...APPEARS PLENTY OF LOWER LEVEL
MOISTURE...AND MVFR CLOUDS...WILL LINGER FOR A FEW HOURS BEHIND THE
FRONT INTO SAT MORNING...WITH DECREASING CLOUDS AND RETURN TO VFR
CONDITIONS FROM WEST TO EAST ACROSS THE AREA DURING THE MID/LATE
MORNING HOURS OF SAT.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...

WI...NONE.
MN...NONE.
IA...NONE.

&&

$$

SHORT/LONG TERM...RABERDING
AVIATION..........RRS

NWS arx Office Area Forecast Discussion