FXUS63 KARX 032149
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
349 PM CST THU DEC 3 2009

.SHORT TERM...TONIGHT THROUGH SUNDAY NIGHT

CONCERNS FOR THIS FORECAST TIME-FRAME DEAL WITH TWO DIFFERENT
PERIODS. FIRST...SNOW ASSOCIATED WITH UPPER LEVEL LOW PASSING
ACROSS THE REGION. SECOND CONCERN COMES TO PLAY FOR SUNDAY/SUNDAY
NIGHT. 

AT 21Z...WATER VAPOR IMAGERY SHOWED THE UPPER LEVEL LOW OVER
SOUTHERN MINNESOTA...WHILE RADAR HAD SNOW SHOWERS EXTENDING SOUTH
AND EAST OF THE LOW.

THE UPPER LOW WILL MOVE EAST ACROSS NORTHERN IOWA AND INTO
SOUTHERN WISCONSIN THROUGH THE EVENING. RUC BUFKIT SOUNDINGS
SHOWING STEEP LAPSE RATES AS WELL AS INSTABILITY OF AROUND 50 J/KG
THIS AFTERNOON AHEAD OF THE LOW...WHICH WILL CONTINUE TO BE SEEN
THROUGH THE EVENING. AS THIS OCCURS...03.18Z NAM DEVELOPS A
700-600MB FRONTOGENESIS BAND ROUGHLY FROM EXTREME NORTHEAST IOWA
INTO CENTRAL WISCONSIN. LARGE SCALE QG FORCING/UPWARD MOTION WAS
SEEN DURING THE AFTERNOON HOURS...AND OMEGA/STRONGEST ISENTROPIC
LIFT ALSO LOOKS TO WANE AS THE EVENING PROGRESSES. DO THINK THERE
WILL BE ENOUGH FORCING...ALONG WITH THE STEEP LAPSE RATES AND
INSTABILITY AS THE LOW PROGRESSES EAST DURING THE EVENING HOURS
TO KEEP SNOW FALLING...WITH ACCUMULATIONS ESPECIALLY ALONG AND
SOUTH OF INTERSTATE 90. WITH THE SNOW SHOWERS BEING QUITE CONVECTIVE
IN NATURE...WOULDN/T BE SURPRISED TO SEE SOME HIGHER SNOWFALL
AMOUNTS UP TO 3 INCHES IN LOCALIZED AREAS...BUT THESE HIGHER
ACCUMULATIONS ARE NOT LIKELY TO BE WIDESPREAD.

ALSO OF CONCERN FOR TONIGHT ARE LOW TEMPERATURES. COLD AIR
ADVECTION WILL BE OCCURRING THROUGH THE NIGHT. HIGHS UPSTREAM OVER
CENTRAL AND NORTHERN MINNESOTA TODAY WERE IN THE MID AND UPPER
TEENS AND THIS COLDER AIRMASS IS PROJECTED TO COME SOUTH. THE
QUESTION IS HOW FAR SOUTH THIS COLDER AIR WILL MAKE IT AND WHAT
THE EFFECTS OF THE CLOUDY SKIES PREVENTING MUCH RADIATIONAL COOLING
WILL DO. THEREFORE...WENT WITH UPPER TEENS IN LOCATIONS WEST OF
THE MISSISSIPPI RIVER WITH MAINLY LOW 20S TO THE EAST.

CONTINUING INTO FRIDAY AND FRIDAY NIGHT...SEVERAL MORE WEAK
IMPULSES OF SHORTWAVE TROUGH ENERGY WILL MOVE THROUGH THE
NORTHWEST FLOW ACROSS THE REGION. THE LOWER LEVELS WILL STAY
SATURATED THROUGH FRIDAY AND INTO FRIDAY NIGHT ACROSS THE EASTERN
PARTS OF THE FORECAST AREA. THERE IS SOME LARGE SCALE UPWARD
MOTION WITH THE PASSING OF THESE SHORTWAVE TROUGHS...HOWEVER IT IS
NOT STRONG AND THERE IS VERY LITTLE IF ANY OMEGA/ISENTROPIC LIFT.
WITH THE WEAK FORCING SIGNALS...KEPT THE FLURRIES IN THE FORECAST
THROUGH THE FRIDAY NIGHT PERIOD.

THEN FOR SATURDAY...POSSIBLY SOME SUN AS WELL AS SOME WARMER
TEMPERATURES UP INTO THE LOWER 30S WITH WEAK RIDGING MOVING IN. 

THE NEXT CONCERN COMES INTO PLAY FOR SUNDAY AND SUNDAY NIGHT AS
A SHORTWAVE TROUGH MOVES ACROSS THE CENTRAL CONUS INTO THE REGION.
DIFFERENCES IN ACTUAL STRENGTH OF THE SHORTWAVE ARE SEEN BETWEEN
MODELS...WHICH LEADS TO DIFFERENCES IN THE POSITION OF THE SURFACE
LOW. ALTHOUGH PRECIPITATION CHANCES LOOK DECENT DURING THE SUNDAY
NIGHT TIME-FRAME ESPECIALLY...TIMING OF WHEN IT WILL MOVE IN AS
WELL AS LOCATION STILL UNCERTAIN DUE TO POSITIONING OF SURFACE
LOW. GFS/GFS ENSEMBLE/CANADIAN WITH THE STRONGER SHORTWAVE TROUGH
SOLUTIONS AND BRING THE SURFACE LOW FURTHER NORTH WHILE THE ECMWF
HAS A MORE SOUTHERLY SOLUTION. IT SHOULD BE NOTED THOUGH THAT THE
ECMWF HAS BEEN QUITE CONSISTENT WITH ITS SOLUTION WITH THIS FEATURE. AS
WAS ALREADY STATED THOUGH...ALL OF THE SOLUTIONS SHOWING PRECIPITATION
ACROSS THE AREA WITH STRONG QG FORCING/ISENTROPIC LIFT THROUGH THE
275K- 295K LAYER. ALSO...TIME/HEIGHT CROSS-SECTIONS FROM THE GFS
SHOWING DEEP SATURATED COLUMN WITH GOOD OMEGA SIGNAL THROUGH THE
COLUMN. AHEAD OF THE SHORTWAVE...A LARGE AREA OF HIGH PRESSURE
WILL BE SITTING OFF TO THE EAST...BRINGING GULF MOISTURE
NORTHWARD...ALLOWING PW VALUES TO APPROACHING 100 PERCENT OF
NORMAL FOR SUNDAY/SUNDAY NIGHT SO ACCUMULATIONS CERTAINLY SEEM
POSSIBLE...AS GFS COBB DATA IS SUGGESTING UPWARDS OF 3-5 INCHES OF
ACCUMULATION.

.LONG TERM...MONDAY THROUGH THURSDAY

MODELS BEGIN THIS PERIOD UNDER GOOD CONSENSUS WITH THE
AFOREMENTIONED SHORTWAVE TROUGH MOVING ACROSS THE UPPER
MISSISSIPPI RIVER VALLEY REGION...THEN TRANSITIONING EAST WITH
WEAK UPPER LEVEL RIDGING FOR LATER MONDAY AND MONDAY NIGHT.

ALSO ON MONDAY...A LARGER TROUGHING FEATURE WILL BE DIGGING
SOUTHWARD ALONG THE WEST COAST. DIFFERENCES BETWEEN MODEL SUITES
BECOME MORE APPARENT WITH THIS FEATURE AS GFS/GFS ENSEMBLE
MEAN/CANADIAN ALL MORE AMPLIFIED WITH THE SHORTWAVE OVER THE WEST
THAN THE ECMWF WHICH IS MUCH FLATTER WITH THE WAVE. AS THIS TROUGH
TRANSITIONS ACROSS THE CONUS...IT LOOKS LIKE IT COULD DEVELOP A
RATHER SIGNIFICANT STORM SYSTEM. 02.00Z MODELS LOOK TO KEEP THE
MAIN THREAT FOR THIS STORM SOUTH OF THE LOCAL AREA...BUT DO BRING
THE NORTHERN FRINGE OF THE SNOW ACROSS THE REGION FOR MID-WEEK.

&&

.AVIATION...

WEATHER SYSTEM WILL BE EXITING THE TAF SITES DURING THE 
BEGINNING PORTION OF THE FORECAST PERIOD. MVFR CONDITIONS IN SW- ARE 
EXPECTED AT THE TAF SITES BUT DUE TO THE INSTABILITY OVER THE 
AREA...THE SNOW SHOWERS COULD BECOME HEAVY AND FORCE PERIODS OF IFR. 
IMPROVING CONDITIONS ARE EXPECTED AFTER 01-03Z. 

&&

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

$$

SHORT/LONG TERM...BROOKS
AVIATION...DB