FXUS63 KARX 121352
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
752 AM CST FRI MAR 12 2010

.UPDATE...THIS MORNING

THE DENSE FOG HAS ONCE AGAIN BECOME WIDESPREAD ACROSS SOUTHEAST
MINNESOTA. DUE TO THIS...A DENSE FOG ADVISORY HAS BEEN ISSUED
UNTIL 11 AM THIS MORNING.

&&

.PREV DISCUSSION... /ISSUED 418 AM CST FRI MAR 12 2010/

SHORT TERM...TODAY THROUGH MONDAY

CURRENTLY AS OF 10Z...WATER VAPOR LOOP AND RUC 500MB HEIGHT ANALYSIS
SHOWED RIDGING OVER THE WESTERN U.S. AND ALONG THE EASTERN
SEABOARD...WITH A TROUGH IN-BETWEEN OVER THE CENTRAL PORTION OF THE
COUNTRY. NOTE TOO THAT THE RIDGES ARE ATTEMPTING TO CONNECT ACROSS
SOUTH CENTRAL CANADA...MAKING THE UPPER TROUGH CUTOFF. WITHIN THE
UPPER TROUGH...THE MAIN FEATURES OF NOTE INCLUDE A 535 DAM UPPER LOW
NEAR OMAHA...A SHORTWAVE OVER SOUTHERN WISCONSIN...AND A SHORTWAVE
OVER SOUTHWEST ARKANSAS. THE FORECAST AREA LIES IN A DRY SLOT ALOFT
NORTHEAST OF THE UPPER LOW. DESPITE THE DRYING ALOFT...PLENTY OF LOW
LEVEL MOISTURE EXISTS...ESPECIALLY NORTH OF I-90 WHICH SAW VERY
LITTLE IF ANY CLEARING YESTERDAY AFTERNOON. 00Z MPX AND ESPECIALLY
GRB SOUNDING REFLECTIVE OF THE MOIST LOW LEVELS...AS WELL AS THE DRY
SLOT ALOFT. ISOLATED SHOWERS OR SPRINKLES ARE ALSO OCCURRING WITHIN
THE MOISTURE...MAINLY NORTH AND EAST OF I-94. DENSE FOG EXISTS NORTH
OF I-90...THOUGH DOES APPEAR TO BE DISSIPATING AS WINDS SHIFT FROM
EAST TO SOUTH. ELSEWHERE AND ACROSS MUCH OF THE UPPER MIDWEST...
STRATUS IS SEEN ON 11-3.9UM SATELLITE IMAGERY. AT THE SURFACE...LOW
PRESSURE IS OVER SOUTHWEST IOWA...BUT THE GRADIENT IS VERY WEAK
ACROSS MUCH OF IOWA...WISCONSIN AND ILLINOIS.

TODAY AND TONIGHT...UPPER TROUGH IS PROGGED TO GET PULLED SOUTHEAST
THROUGH TONIGHT...DUE TO A COMBINATION OF TWO FACTORS. THE FIRST IS
RIDGING BUILDING ACROSS THE UPPER GREAT LAKES...AND THE SECOND IS
THE SHORTWAVE IN SOUTHWEST ARKANSAS LIFTING UP INTO ILLINOIS WHICH
PULLS THE UPPER LOW SOUTH. ALSO OF NOTE IS THE SHORTWAVE IN SOUTHERN
WISCONSIN WHICH ROTATES BACK TO THE NORTHWEST INTO WEST-CENTRAL
MINNESOTA. DESPITE ALL OF THE UPPER LEVEL MOTIONS GOING ON...IT
APPEARS THE FORECAST AREA WILL END UP MOSTLY DRY THROUGH TONIGHT. IN
FACT...500MB HEIGHTS ARE FORECAST TO INCREASE...RESULTING IN
SUBSIDENCE AND THEREFORE THE MAINLY DRY MODEL QPF FORECASTS.
HOWEVER...THERE ARE TWO MAIN AREAS OF PRECIPITATION TO CONTEND WITH.
THE FIRST IS THIS MORNING ACROSS CENTRAL WISCONSIN...ASSOCIATED WITH
THE SHORTWAVE IN SOUTHERN WISCONSIN MOVING NORTHWEST. THE SECOND IS
IN SOUTHEAST PORTIONS OF THE FORECAST AREA AFTER MIDNIGHT...WHERE
SOME DEFORMATION PRECIPITATION MAY APPROACH...ON THE NORTHWEST SIDE
OF NEW LOW PRESSURE DEVELOPING OVER THE OHIO RIVER VALLEY. OTHER
CONCERN IS THE ON-GOING DENSE FOG ADVISORY. HAVE CUT THE DENSE FOG
ADVISORY TO AREAS NORTH OF I-90...AS SOUTHERLY WINDS SEEM TO BE
ADVECTING SOME LOWER LEVEL DRY AIR IN OUT OF EASTERN IOWA. THE
ADVISORY COULD GET CANCELLED EARLY ELSEWHERE...IF WINDS TURN
SOUTHERLY ACROSS THE ADVISORY AREA. WIND FORECAST FOR THE MODELS
SHOW A FAIRLY WEAK GRADIENT...SO HARD TO DISCERN WHEN THE TURN COULD
OCCUR. MAY HAVE TO DEAL WITH SOME FOG TONIGHT AGAIN...MOSTLY WITH
LINGERING SURFACE MOISTURE FROM RECENT RAIN AND SNOWMELT.
HOWEVER...WITH A LOT MORE GROUND SHOWING UP...MIGHT BE HARDER TO GET
THAT STEAM FOG OFF THE SNOW PACK. THEREFORE...ONLY WENT WITH PATCHY
FOG AT THIS TIME. CLOUD FORECAST IS A LITTLE TRICKY...WITH THE NAM
SUGGESTIVE OF SOME BREAKING UP OF THE CLOUDS...MAINLY EAST OF THE
MISSISSIPPI RIVER. UNSURE IF THIS IS TRUE...GIVEN THAT IT SUGGESTS
THE CLEARING NOW AND THERE IS NONE. AS A RESULT...WENT MORE
PESSIMISTIC WITH CLOUD COVER. WITH PLENTY OF STRATUS AROUND THE
REGION...IT SHOULD STAY MAINLY CLOUDY THROUGH TONIGHT...LIMITING
HIGH TEMPERATURES SOME TODAY AND KEEPING LOWS MILD AGAIN TONIGHT.

SATURDAY THROUGH MONDAY...THIS ENTIRE PERIOD IS TRICKY FOR
PRECIPITATION FORECASTING...PRIMARILY BECAUSE MODELS SHOW UPPER
LEVEL RIDGING GRADUALLY BUILDING OVER THE FORECAST AREA BUT THERE
REMAINS SOME VERY WEAK ISENTROPIC LIFT. IN THE SYNOPTIC FLOW...THE
UPPER TROUGHING OVER THE SOUTHEASTERN U.S. AT 12Z SATURDAY SLOWLY
PUSHES EAST...REACHING THE MID ATLANTIC COAST BY 00Z MONDAY.
MEANWHILE...THE CURRENT SHORTWAVE OVER SOUTHERN WISCONSIN ENDS UP
BECOMING STATIONARY OVER WESTERN MINNESOTA...SITTING THERE THROUGH
MONDAY. ALTHOUGH UPPER RIDGING IS BUILDING OVER THE AREA TO PROVIDE
MID/UPPER LEVEL SUBSIDENCE...285-290K ISENTROPIC LIFT PLOTS DEPICT
NEUTRAL TO WEAK ISENTROPIC LIFT THROUGH MONDAY...WHICH OCCURS IN A
LAYER THAT IS MOIST. THEREFORE...SOME PRECIPITATION IS POSSIBLE.
HOWEVER...WITH THE MAJORITY OF MODEL QPF FIELDS DRY...PERHAPS THE
MOST THAT WOULD BECOME OF THE LIFT IS SOME SPRINKLES OR DRIZZLE.
ADJUSTMENTS TO THE FORECAST WERE TO BASICALLY REDUCE THE CHANCES OF
PRECIPITATION IN HALF FOR SATURDAY AND SATURDAY NIGHT...AND LEAVE
THE GOING DRY FORECAST FOR SUNDAY INTO MONDAY. COULD SEE GOING DRY
IN LATER FORECASTS FOR SATURDAY AND SATURDAY NIGHT...OR ADDING THE
SPRINKLES/DRIZZLE. CLOUD FORECAST IS ALSO TRICKY DURING THIS TIME
FRAME...AND EVEN MORESO AS THE 12.00Z ECMWF HINTS AT BETTER DRY AIR
ADVECTION FROM THE NORTHEAST SUNDAY INTO MONDAY. ATTEMPTED TO ADJUST
THE CLOUD FORECAST SOME FOR A LITTLE CLEARING EAST OF THE
MISSISSIPPI RIVER. IN THIS SAME AREA...ADJUSTED HIGH TEMPERATURES UP
SOME. MORE CLOUDS ARE LIKELY FOR SOUTHEAST MINNESOTA AND NORTHEAST
IOWA...CLOSER TO THE STATIONARY SHORTWAVE...SO ADJUSTED HIGH
TEMPERATURES DOWN SLIGHTLY. HIGHS OVERALL LOOK MILD...THOUGH...
PROBABLY AROUND 10 DEGREES ABOVE NORMAL. LOWS IN GENERAL SHOULD ALSO
END UP MILD...SINCE DEWPOINTS MAY TAKE A WHILE TO COME DOWN.

LONG TERM...MONDAY NIGHT THROUGH FRIDAY

FEW CHANGES WERE MADE TO THE EXTENDED PORTION OF THE FORECAST. THE
MILD WEATHER LOOKS TO CONTINUE THROUGH FRIDAY...ESPECIALLY TOWARDS
THE END OF THE WEEK WHEN THE 12.00Z ECMWF DEPICTS A PLUME OF 4-6C
850MB TEMPS COMING INTO THE AREA WITH PLENTY OF SUN. ONLY ISSUE IN
THE EXTENDED RIGHT NOW IS THE STATIONARY SHORTWAVE OVER WESTERN
MINNESOTA...AND IF ANY PRECIPITATION ASSOCIATED WITH IT COULD AFFECT
THE FORECAST AREA. THE 12.00Z GFS BROUGHT SOME VERY LIGHT QPF IN
MONDAY NIGHT AND TUESDAY...THOUGH THE 12.00Z ECMWF KEPT IT JUST TO
THE WEST. GIVEN THE DRY FORECAST ALREADY GOING...DECIDED TO LEAVE IT
ALONE.

AVIATION...TODAY THROUGH TONIGHT

THE VISIBILITIES HAVE DRAMATICALLY RISEN AT BOTH KLSE AND KRST. THE
PLANS ARE DROP THE DENSE FOG ADVISORY FOR OLMSTED COUNTY WHICH
INCLUDES KRST. HOWEVER IN LA CROSSE COUNTY...THERE ARE STILL REPORTS
OF DENSE FOG...SO THIS ADVISORY WILL REMAIN IN EFFECT THROUGH
12.17Z. HOWEVER WITH A SOUTH WIND AT KLSE...THE TERMINAL SHOULD STAY
OUT OF THE DENSE FOG...BECAUSE THERE HAS NOT BEEN TOO MANY REPORTS
OF DENSE FOG REPORTED IN THE MISSISSIPPI CHANNEL SOUTH OF THE
TERMINAL.

THE DENSE FOG...ACROSS WINONA AND WABASHA COUNTIES IN SOUTHEAST
MINNESOTA...AND WEST CENTRAL...CENTRAL...AND NORTH CENTRAL
WISCONSIN...SHOULD SLOWLY DISSIPATE DURING THE MID TO LATE MORNING.
ONCE THE FOG BURNS OFF...THE CEILING IN THESE AREAS SHOULD RISE FROM
LIFR TO MVFR.

MEANWHILE THE REMAINDER OF THE AREA SHOULD SEE MVFR CEILINGS THROUGH
THIS TIME PERIOD.

HYDROLOGY...
MODELS CONTINUE TO TREND DRIER WITH QPF THROUGH THE WEEKEND...WITH
THE POTENTIAL OF COMPLETELY DRY FOR MOST OF THE FORECAST AREA IN
QUITE A FEW MODELS. EITHER WAY...QPF AMOUNTS LOOK MAINLY UNDER A
TENTH OF AN INCH. THEREFORE...FOCUS SHOULD SHIFT TO MAINLY RIVERS
EXPERIENCING RUNOFF FROM ONGOING AND/OR PREVIOUS SNOW MELT. MOST
CONCERNING RIVERS ARE THOSE TRIBUTARIES IN MINNESOTA AND IOWA...
SINCE SNOW PACK TO MELT STILL EXISTS. GOING INTO THE WEEKEND AND
EVEN THROUGH MUCH OF NEXT WEEK...TEMPERATURES ARE FORECAST TO REMAIN
ABOVE FREEZING...SO MOST IF NOT ALL OF THE SNOW PACK SHOULD MELT.

FOR LATEST DETAILED INFORMATION CONCERNING RIVER LEVELS AND
POTENTIAL FLOODING...SEE OUR HYDROLOGIC STATEMENTS.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...DENSE FOG ADVISORY UNTIL 11 AM CST THIS MORNING FOR WIZ029-
WIZ032-WIZ033-WIZ034-WIZ042-WIZ043-WIZ044.

MN...DENSE FOG ADVISORY UNTIL 11 AM CST THIS MORNING FOR MNZ079-
MNZ086-MNZ087-MNZ094-MNZ095.

IA...NONE.
&&

$$

SHORT/LONG TERM...AJ
AVIATION..........BOYNE
HYDROLOGY.........AJ
UPDATE............BOYNE


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