892 
FXUS63 KARX 030843
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
342 AM CDT FRI SEP 3 2010

.SHORT TERM...TODAY THROUGH SUNDAY NIGHT

MAIN FORECAST CONCERN IS WINDS TODAY

CURRENTLY AS OF 08Z...WATER VAPOR LOOP AND RUC 500MB HEIGHT ANALYSIS 
SHOWED STRONG RIDGING OVER THE WESTERN U.S INTO SOUTHWEST CANADA... 
TROUGHING FROM NORTHEAST MANITOBA INTO THE MID-MISSISSIPPI VALLEY 
RIVER REGION...AND RIDGING MOSTLY ALONG THE EAST COAST EXCLUDING 
HURRICANE EARL NEAR THE OUTER BANKS OF NORTH CAROLINA. MAIN LINE OF 
SHOWERS AND THUNDERSTORMS AIDED BY HEIGHT FALLS FROM THE UPPER 
TROUGH...AS WELL AS THE PRIMARY SURFACE COLD FRONT...EXTENDS FROM 
EASTERN LOWER MICHIGAN TO SHREVEPORT LOUISIANA. DRY SLOT BEHIND THE 
COLD FRONT OVER THE FORECAST AREA LAST EVENING HAS SHIFTED EAST... 
ALLOWING UPPER LEVEL MOISTURE UNDER THE UPPER TROUGH TO MOVE IN. 
DEEPER MOISTURE...NOTED BY CLOUDS AND SOME SCATTERED SHOWERS... 
EXISTS OVER THE NORTHERN HALVES OF MINNESOTA AND WISCONSIN. 00Z INL 
SOUNDING WAS MIXED UP TO 850MB...BUT THEN SATURATED TO 600MB... 
REFLECTIVE OF THE DEEPER MOISTURE. 850MB TEMPS CERTAINLY COOLER 
UNDER THE UPPER TROUGH COMPARED TO THE PAST FEW DAYS...RANGING FROM 
8-10C PER 00Z RAOBS. THE COOLER AIR HAS BEEN ADVECTING IN ON 35-40 
KNOT WINDS AT 925MB AND 850MB SEEN ON AREA PROFILERS AND VAD WIND 
PROFILES. AT THE SURFACE...1000MB LOW PRESSURE WAS NOTED OVER LAKE 
SUPERIOR WITH A SECONDARY COLD FRONT EXTENDING WESTWARD INTO 
NORTHERN MINNESOTA. IN ADDITION...A 1025MB RIDGE OF HIGH PRESSURE 
WAS LOCATED ALONG THE LEE OF THE ROCKIES. 

TODAY...UPPER TROUGH BASICALLY LOCATED OVER THE FORECAST AREA IS 
PROGGED TO SHIFT EAST INTO THE WESTERN GREAT LAKES REGION. THE COOL 
AND MOIST AIR UNDER THE UPPER TROUGH WILL LIKELY ALLOW CUMULUS TO 
DEVELOP ACROSS MUCH IF NOT ALL THE AREA WITH A LITTLE DAYTIME 
HEATING. THE MOST EXTENSIVE COVERAGE OF THE CUMULUS...AS WELL AS 
OTHER LOW TO MID LEVEL STRATUS...IS EXPECTED ALONG AND NORTH OF I-94 
WHICH IS CLOSER TO THE MAIN CORE OF THE UPPER TROUGH. PLAN ON 
SCATTERED SHOWERS TO DEVELOP AS WELL ALONG AND EAST OF THE 
MISSISSIPPI RIVER...IN PARTICULAR DURING THE AFTERNOON WHEN LOW 
LEVEL LAPSE RATES FROM DAYTIME HEATING ARE GREATEST. IN ADDITION TO 
THE DAYTIME HEATING ALLOWING FOR CLOUDS AND PRECIPITATION 
DEVELOPMENT...THE HEATING WILL HELP RESULT IN BLUSTERY CONDITIONS. 
MODELS ARE IN AGREEMENT THAT THE NEAR 40 KNOT 925MB AND 850MB 
NORTHWEST WINDS WILL HOLD NEARLY STEADY TODAY...SO SOME OF IT LOOKS 
TO MIX DOWN. A TIGHT PRESSURE GRADIENT IN PLACE SHOULD ALSO HELP 
RESULT IN BLUSTERY CONDITIONS. GIVEN THAT BETTER MIXING IS EXPECTED 
OVER THE FAR WESTERN PORTIONS OF THE FORECAST AREA...WHICH SHOULD 
BRING MOST OF THE 40 KT WIND DOWN...ISSUED A WIND ADVISORY FROM 
OLMSTED TO CHICKASAW COUNTIES WEST. ELSEWHERE...THINKING IS PLENTY 
OF CLOUDS AROUND AS WELL AS TERRAIN/TREES SHOULD KEEP WINDS OUT OF 
THE ADVISORY RANGE. HOWEVER...WITH STEEP LOW LEVEL LAPSE RATES...THE 
SHOWERS COULD PRODUCE HIGHER WIND GUSTS AND AS SUCH WILL BE 
MENTIONED IN THE HWO. 850MB TEMPS ARE PROGGED TO COOL FURTHER 
TODAY...DOWN TO 4 TO 6C BY 18Z FROM A SOURCE REGION IN SOUTH CENTRAL 
CANADA. WITH THE CLOUDS AND THESE COOLER TEMPS...TEMPERATURES WILL 
STRUGGLE TO RISE MUCH...PERHAPS 5 DEGREES.

TONIGHT INTO SATURDAY...THE UPPER TROUGH OVER THE WESTERN GREAT 
LAKES REGION IS FORECAST TO LIFT INTO SOUTHEAST CANADA AND THE 
EASTERN GREAT LAKES BY 00Z SUNDAY...BEING PUSHED BY TROUGHING MOVING 
INTO SOUTHWEST CANADA AND THE PACIFIC NORTHWEST. WITH THE UPPER 
TROUGH OVER THE FORECAST AREA MOVING OUT...DRIER AIR AND HIGH 
PRESSURE OVER THE PLAINS WILL BUILD IN. EXPECT ANY PRECIPITATION 
FROM THIS AFTERNOON TO MOSTLY END BY 00Z...WITH CLOUDS DECREASING 
WEST TO EAST THROUGH THE EVENING. CONSIDERED INCLUDING A 20 PERCENT 
CHANCE OF RAIN OVER TAYLOR AND CLARK SAY 00-03Z...BUT NOT CONFIDENT 
THAT MUCH RAIN WILL BE LEFT AT THAT TIME. ALSO THOUGHT ABOUT CLOUDS 
MIGHT TRY TO HOLD ON IN THE TAYLOR COUNTY AREA...DUE TO LAKE EFFECT 
PROCESSES OFF LAKE SUPERIOR...BUT THEY SHOULD STAY OFF TO THE 
NORTHEAST OF TAYLOR COUNTY. NO CONCERN FOR VALLEY FOG TONIGHT WITH 
THE PRESSURE GRADIENT EXPECTED TO STAY FAIRLY TIGHT. IN FACT...THE 
WIND RESULTING FROM THE PRESSURE GRADIENT SHOULD KEEP LOWS FROM 
DROPPING TOO LOW. NONETHELESS...READINGS IN THE 40S SEEM REASONABLE. 
AS THE SURFACE RIDGE MOVES OVERHEAD ON SATURDAY...PLAN ON A MUCH 
LIGHTER WIND DAY. A FEW CUMULUS AND CIRRUS CLOUDS ARE POSSIBLE... 
OTHERWISE PLENTY OF SUNSHINE IS EXPECTED. A COOL DAY IS STILL 
ANTICIPATED...THOUGH...WITH 850MB TEMPS IN THE 3-5C RANGE AT 18Z. 
PLAN ON HIGHS TO END UP SIMILAR OR SLIGHTLY WARMER TO THOSE TODAY.

SATURDAY NIGHT THROUGH SUNDAY NIGHT...MODELS ARE IN DECENT AGREEMENT 
REGARDING HANDLING OF THE NEW UPPER TROUGH IN THE PACIFIC 
NORTHWEST...HAVING IT DEEPEN AND DIG DOWN INTO THE INTERMOUNTAIN 
WEST REGION BY 12Z MONDAY. AS THE TROUGH DIGS...CYCLOGENESIS OCCURS 
OVER WESTERN NEBRASKA AND UPPER RIDGING BUILDS DOWNSTREAM OVER THE 
FORECAST AREA. AS EXPECTED WITH THE UPPER RIDGING BUILDING IN...WARM 
AIR ADVECTION AND ISENTROPIC LIFT ALSO OCCUR OVER THE FORECAST AREA. 
THE QUESTION IS HOW MUCH AVAILABLE MOISTURE WILL THERE BE TO 
GENERATE PRECIPITATION...GIVEN THAT THE CURRENT COLD FRONT THIS 
MORNING HAS CLEARED OUT A LOT OF THE MOISTURE IN THE PLAINS. FEEL 
GOOD THAT SATURDAY NIGHT WILL STAY DRY...WITH CIRRUS AND ALTOSTRATUS 
GRADUALLY ON THE INCREASE WEST TO EAST. TIMING OF THESE CLOUDS ARE 
CRITICAL FOR LOW TEMPERATURES AND VALLEY FOG. FOR NOW GIVEN THE 
CLOUD TIMING UNCERTAINTY...HAVE NOT INCLUDED VALLEY FOG AT THIS 
POINT...BUT CERTAINLY SOMETHING TO WATCH. ALSO HAVE STUCK WITH 
GUIDANCE VALUES FOR LOWS TOO UNTIL THE CLOUDS BECOME MORE CERTAIN. 
FOR SUNDAY...ALTHOUGH THE 03.00Z NAM DEPICTS SOME SHOWERS FORMING 
ACROSS SOUTHERN PORTIONS OF THE FORECAST AREA DURING THE 
AFTERNOON...THE 03.00Z GFS AND 02.21Z SREF ARE DRY. HAVE LEFT THE 
DRY FORECAST GOING UNTIL MORE MODELS SHOW PRECIPITATION. SUNDAY 
SHOULD END UP QUITE A BIT WARMER COMPARED TO SATURDAY...WITH 850MB 
TEMPS CLIMBING TO 10-14C...COOLEST AROUND MEDFORD. FOR SUNDAY 
NIGHT...ISENTROPIC LIFT IS PROGGED TO INCREASE...ESPECIALLY IN THE 
03.00Z ECMWF. WITH THE 03.03Z SREF...03.00Z ECMWF/NAM/GFS ALL 
INDICATING SOME LIGHT PRECIPITATION ASSOCIATED WITH THE LIFT...ADDED 
20 PERCENT CHANCES TO THE FORECAST. ANY PRECIPITATION LOOKS TO COME 
OUT OF AN ALTOCUMULUS CASTELLANOUS DECK...SINCE THE LOW LEVELS ARE 
DRY. WITH A SOUTHERLY WIND AND MORE CLOUDS...A WARMER NIGHT IS 
PLANNED. KEPT LOWS NOT TOO FAR OF MEX GUIDANCE.

.LONG TERM...MONDAY THROUGH FRIDAY

FOR MONDAY AND TUESDAY...MAIN FEATURE TO WATCH IS THE EJECTING UPPER 
TROUGH IN THE INTERMOUNTAIN WEST AND THE ASSOCIATED SURFACE LOW. 
03.00Z GFS/ECMWF HAVE TRENDED A LITTLE FARTHER SOUTH AS IT LIFTS 
INTO MINNESOTA TUESDAY MORNING. AS SUCH...ANOTHER SHOT OF COOL AIR 
IS INDICATED TO COME INTO THE FORECAST AREA...BUT NOT NEARLY AS COOL 
AS THE ONE COMING INTO TODAY. TO ADJUST FOR THE SOUTH TREND... 
LOWERED HIGHS A BIT ON TUESDAY. THE REST OF THE HIGHS...LOWS AS WELL 
AS PRECIPITATION CHANCES DURING THIS PERIOD LOOK REASONABLE. 
OVERALL...THE SYSTEM DOES NOT APPEAR TO BE A BIG PRECIPITATION 
PRODUCER DUE TO THE LACK OF A GOOD MOISTURE FEED.

A BREAK IN PRECIPITATION IS SUGGESTED FOR TUESDAY NIGHT INTO 
WEDNESDAY...ESPECIALLY ALONG AND NORTH OF I-90 AS AN AREA OF HIGH 
PRESSURE BUILDS IN AT THE SURFACE. MEANWHILE...NEW TROUGHING IS 
EXPECTED TO DEVELOP ALONG THE WEST COAST OF THE U.S. THIS TROUGH 
LOOKS TO SLOWLY PUSH EAST INTO THE INTERMOUNTAIN WEST...RESULTING IN 
NEW CYCLOGENESIS OVER THE CENTRAL AND NORTHERN PLAINS. WARM 
ADVECTION DOWNSTREAM COULD PRODUCE SOME SHOWERS AND THUNDERSTORMS 
FROM WEDNESDAY NIGHT RIGHT INTO FRIDAY. THIS SYSTEM MAY HAVE MORE 
MOISTURE TO WORK WITH...SO SOMETHING TO WATCH.

&&

.AVIATION...TODAY THROUGH TONIGHT

WILL BE WATCHING A DEEP LOW PRESSURE SYSTEM MOVING THROUGH SOUTHERN 
ONTARIO AND THE GREAT LAKES REGION TODAY. THIS SYSTEM WILL PRODUCE A 
STRONG PRESSURE GRADIENT ACROSS THE AREA TODAY FOR GUSTY NORTHWEST 
WINDS...ALONG WITH SOME MVFR CLOUD COVER AND ISOLATED TO SCATTERED 
-SHRA ACTIVITY. SUSTAINED NORTHWEST WINDS ACROSS THE AREA ARE 
EXPECTED IN THE 15-25KT RANGE WITH GUSTS AROUND 35KT. THESE WINDS 
WILL DIMINISH THIS EVENING AS THE LOW MOVES FURTHER EAST THROUGH THE 
GREAT LAKES AND A RIDGE OF HIGH PRESSURE BUILDS INTO THE AREA FROM 
THE PLAINS. A STEEP LOW LEVEL LAPSE RATE AND CYCLONIC FLOW 
ASSOCIATED WITH THE LOW IS ALSO EXPECTED TO PRODUCE EXTENSIVE 
CUMULUS/STRATOCUMULUS FIELD TODAY ALONG WITH SCATTERED -SHRA. MOST 
OF THIS ACTIVITY EXPECTED TO HOLD EAST OF THE MISSISSIPPI RIVER 
TODAY. CEILINGS ASSOCIATED WITH THE CLOUD COVER EXPECTED TO BE IN 
MVFR RANGE IN THE 14Z-20Z TIME FRAME. LOOK FOR CLOUDS TO SCATTER OUT 
THIS EVENING WITH THE LOW PUSHING FURTHER EAST OF THE REGION. RIGHT 
NOW...BOTH KRST/KLSE TAF SITES ARE DRY...BUT PLAN TO ADD AT LEAST A 
VCSH AT KLSE FOR LATE THIS MORNING THROUGH THIS AFTERNOON. WILL 
PROVIDE THIS DETAIL WITH 03.12Z TAF ISSUANCE.
&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...NONE.
MN...WIND ADVISORY FROM 10 AM THIS MORNING TO 6 PM CDT THIS EVENING 
     FOR MNZ086-MNZ087-MNZ094-MNZ095.

IA...WIND ADVISORY FROM 10 AM THIS MORNING TO 6 PM CDT THIS EVENING 
     FOR IAZ008-IAZ009-IAZ018-IAZ019.

&&

$$

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