Weather Story NWS La Crosse, WI

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NWS KARX Forecast Discussion

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FXUS63 KARX 080821
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
317 AM CDT WED SEP 8 2010

.SHORT TERM...TODAY THROUGH FRIDAY

MAIN CONCERN THROUGH THE PERIOD WILL BE RAIN CHANCES FRIDAY.

SURFACE MAP EARLY THIS MORNING HAS THE STRONG AREA OF LOW PRESSURE
THAT BROUGHT GUSTY WINDS ACROSS THE AREA TUESDAY NOW OVER EASTERN
ONTARIO. BEHIND IT...A RIDGE OF HIGH PRESSURE WAS BUILDING INTO THE
AREA FROM THE PLAINS. IR SATELLITE IMAGERY SHOWING SOME PATCHES OF
STRATOCUMULUS LINGERING ALONG AND EAST OF THE MISSISSIPPI RIVER.
TRENDS THOUGH SHOW THIS STRATOCUMULUS THINNING OUR UNDER THE
INFLUENCE OF INCREASING SUBSIDENCE OF THE INCOMING RIDGE OF HIGH
PRESSURE.

08.00Z NAM/GFS/SREF ALL SHOWING SIMILAR SOLUTIONS WITH REGARD TO
OVERALL MID-LEVEL/SURFACE PATTERN THROUGH THE SHORT TERM. GFS/SREF A
BIT FASTER WITH SYSTEM ON FRIDAY WITH THE NAM TRENDING TOWARD THE
SLOWER 08.00Z ECMWF.

HIGH PRESSURE WILL BE THE DOMINANT WEATHER FEATURE TODAY. STILL SOME
LINGERING STRATOCUMULUS TO BE SEEN MAINLY NORTHEAST OF I-94 THIS
MORNING...BUT MODELS SHOW 925-850MB RH SHOVING EAST OF THE AREA
AFTER 18Z...LENDING TO MOSTLY SUNNY SKIES ACROSS THE AREA TODAY WITH
HIGHS TOPPING OFF IN THE MID 60S TO AROUND 70.

WILL BE WATCHING A MID-LEVEL SHORTWAVE LIFTING ACROSS THE NORTHERN
PLAINS INTO WESTERN MN TONIGHT. CROSS SECTION OF NAM SHOWS AN
INCREASE IN MID-HIGH CLOUD INTO THE AREA AFTER MIDNIGHT IN RESPONSE
TO ISENTROPIC LIFT IN THE 850-700MB LAYER AHEAD OF THIS WAVE. THE
NAM CONTINUES TO SHOW A TREND IN WEAKENING 850-600MB FRONTOGENESIS
AS THE WAVE WASHES OUT IN MEAN RIDGING IN PLACE ACROSS THE AREA. AS
A RESULT...WILL CARRY A DRY FORECAST THROUGH TONIGHT.

STRONG RIDGE OF HIGH PRESSURE REMAINS OVER THE AREA THROUGH THURSDAY
NIGHT AS A VIGOROUS MID-LEVEL TROUGH/SURFACE LOW MOVES OUT OF THE
INTERMOUNTAIN WEST INTO THE NORTHERN PLAINS. MEANWHILE...REMNANTS OF
HERMINE MOVES THROUGH MO. RESULT WILL BE INCREASING CLOUDS IN
ADVANCE OF THESE SYSTEMS...BUT STRENGTH OF THE RIDGE/SUBSIDENCE WILL
KEEP PRECIPITATION SOUTH AND WEST OF THE AREA. MAY BE SOME DELAY ON
THE ONSET OF RAIN ON FRIDAY AS WELL. THE GFS AND SREF SHOW A
SLIGHTLY FASTER EASTWARD PROGRESSION OF A COLD FRONT PUSHING INTO MN
WITH RAIN REACHING INTO THE WESTERN HALF OF WI. MEANWHILE...THE NAM
AND ECMWF HOLD THE FRONT AND RAIN WEST OF THE AREA. WILL SPLIT THE
DIFFERENCE FOR NOW AND CARRY A SLIGHT CHANCE POP MAINLY ALONG AND
WEST OF THE MISSISSIPPI RIVER. CAPE ALSO FAIRLY LIMITED. LOOKING AT
THE NAM 0-3KM MUCAPE ONLY YIELDS GENERALLY LESS THAN 600J/KG
ALONG/WEST OF THE MISSISSIPPI RIVER. BASED ON THIS WILL ONLY CARRY
ISOLATED THUNDER MENTION.

.LONG TERM...FRIDAY NIGHT THROUGH TUESDAY

SHOWERS/THUNDERSTORMS LOOKING MORE LIKELY NOW FOR FRIDAY NIGHT AS
ALL THE MODELS SEEM TO BE LOCKING ON NICELY TO THE MID-LEVEL
TROUGH/SURFACE COLD FRONT MOVING THROUGH THE AREA. KEPT BEST CHANCE
FOR THUNDER ACROSS NORTHEAST IOWA INTO SOUTHWEST WI WHERE 0-3KM
MUCAPE REMAINS IN THE 500-1000J/KG RANGE. THIS SYSTEM REMAINS FAIRLY
PROGRESSIVE...WITH THE COLD FRONT/BULK OF RAIN EXITING EAST OF THE
AREA BY NOON ON SATURDAY. UPPER LEVEL PATTERN TURNS HIGH ZONAL
THROUGH THE REMAINDER OF THE PERIOD WITH ANOTHER MID-LEVEL TROUGH
PRODUCING A CHANCE OF SHRA/TS SUNDAY NIGHT THROUGH MONDAY. SHRA
CHANCES MAY CONTINUE INTO MONDAY NIGHT WITH LINGERING CYCLONIC FLOW
ALOFT. TUESDAY LOOKS DRY FOR NOW AS THE GFS/ECMWF BOTH SHOWING
RIDGING BUILDING INTO THE AREA.

&&

.AVIATION...TODAY AND TONIGHT

A RIDGE OF HIGH PRESSURE BUILDING EAST OVER THE TAF SITES TODAY AND
REMAINING NEARBY TONIGHT WILL HELP MAINTAIN VFR CONDITIONS THROUGH
TONIGHT. IN ADDITION...EXPECT WIND SPEEDS TO STAY AT OR BELOW 10
KNOTS. ONLY ISSUE IF ANY WITH THE FORECAST IS LATE TONIGHT AT KRST
WHERE A HIGH-BASED STRATUS DECK MAY MOVE IN. THERE ARE ALSO A FEW
MODELS PRODUCING LIGHT RAIN FROM THIS STRATUS DECK...BUT THE
PROBABILITY IS TOO LOW TO EVEN MENTION VCSH AT THIS TIME.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

SHORT/LONG TERM...DAS
AVIATION..........AJ

NWS arx Office Area Forecast Discussion