FXUS63 KARX 272022
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
222 PM CST FRI NOV 27 2009

.SHORT TERM...TONIGHT THROUGH MONDAY

LOOKING AT A SMALL CHANCE FOR SOME LIGHT PRECIPITATION SUNDAY...
OTHERWISE SKY CONDITION AND TEMPERATURES THE MAIN FORECAST FOCUS.

19Z SURFACE ANALYSIS SHOWS HIGH PRESSURE RIDGING FROM THE LOWER OHIO
VALLEY UP ACROSS IL/WI AND INTO WESTERN ONT. WEAK FLOW/PRESSURE
GRADIENT SEEN ACROSS THE PLAINS STATES TO OUR WEST...BUT A WEAK COLD
FRONT TRYING TO TAKE SHAPE ACROSS THE DAKOTAS. THERE IS A FAIR AMOUNT
OF HIGH CLOUD SEEN IN VISIBLE SATELLITE IMAGERY THIS AFTERNOON...BUT
LOOKING OUT THE WINDOW...IT IS PRETTY THIN. WEAK UPPER RIDGING IN
PLACE EAST OF THE ROCKIES...BUT THE NEXT TROUGH WAS MOVING ONTO THE
WEST COAST.

OVERALL...SHORT RANGE MODELS IN RATHER GOOD AGREEMENT WITH NO
SIGNIFICANT DIFFERENCES NOTED WHICH WILL IMPACT THE FORECAST FOR
THE NEXT FEW DAYS. FIRST CONCERN IS TONIGHT...WITH RELATIVELY LIGHT
WINDS AND DEWPOINTS IN THE 30S...WE COULD SEE SOME FOG DEVELOP. MOS
GUIDANCE HAS BEEN INSISTENT ON THIS FOR SEVERAL RUNS NOW...AND SEEMS
REASONABLE. HAVE ADDED THIS TO THE FORECAST. SEE AVIATION DISCUSSION
BELOW FOR MORE DETAIL.

WEST COAST UPPER TROUGH FORECAST TO DEEPEN...WITH A SIGNIFICANT PIECE
CUTTING OFF OVER THE SOUTHWEST ON SATURDAY. ANOTHER PIECE MOVES
ACROSS THE UPPER MIDWEST LATE SATURDAY NIGHT AND SUNDAY. WHILE THERE
WILL BE AMPLE DYNAMIC AND THERMODYNAMIC LIFTING MECHANISMS...MOISTURE
WILL BE QUITE LIMITED.  COLD ADVECTION SHOULD HELP TO LIBERATE THE
LOW LEVEL MOISTURE...BUT DEEPER MOISTURE IS LACKING. AT THIS TIME...
IT IS NOT LOOKING LIKE MUCH MORE THAN FLURRIES...OR PERHAPS A BRIEF
SNOW SHOWER. NO ACCUMULATION IS ANTICIPATED. AND THIS SHOULD BE DONE
BY SUNDAY EVENING AS THE FORCING SHIFTS EAST OF THE REGION. LOOKS TO
BE A BIT BREEZY SUNDAY AS WELL...WITH COLD ADVECTION AND NORTHWEST
WINDS MAKING IT ACTUALLY FEEL LIKE LATE NOVEMBER.

AS UPPER TROUGH SHIFTS EAST...RIDING AGAIN BUILDS IN FOR THE FIRST
PART OF THE WEEK. SUBSIDENCE AND DRY ADVECTION SHOULD ALLOW FOR
CLOUD COVER TO DECREASE SUNDAY NIGHT. ONE EXCEPTION MAY BE PARTS OF
NORTHERN WISCONSIN...WHERE CYCLONIC FLOW AND THE LAST REMNANTS OF
SHORT WAVE ENERGY MAY ALLOW FOR A FEW FLURRIES.

.LONG TERM...MONDAY NIGHT THROUGH FRIDAY

THERE IS CONSIDERABLE UNCERTAINTY IN THE MEDIUM RANGE FORECAST...AS
MODEL SOLUTIONS DIFFER WITH HOW TO HANDLE SHORT WAVE ENERGY CRASHING
THE WEST COAST OF NORTH AMERICA LATE NEXT WEEK. THE ECMWF AND SOME OF
THE GFS ENSEMBLE MEMBERS KEEP A DEEPER CLOSED CIRCULATION OVER THE
NORTHEAST...WITH AN INFLUENCE REACHING FURTHER WEST THAN THE
GFS/GEM. AS SUCH...BY NEXT WEEKEND...ONE GROUPING HAS COLD CYCLONIC
FLOW AND PERHAPS A CHANCE FOR SOME LIGHT SNOW...WHILE THE OTHER
GROUPING INDICATES HIGH PRESSURE.  AT THIS POINT...LEANING MORE
TOWARD THE ECMWF-SUPPORTED CLUSTER OF SOLUTIONS...AS ITS TRACK
RECORD IS USUALLY BETTER. BUT KEPT THE CHANCES ON THE LOW SIDE. ALSO
KEPT TEMPERATURES ON THE COOLER SIDE FOR THIS TIMEFRAME.

OTHER THAN THIS...THE MODELS DO AGREE IN PRINCIPLE IN A SHORT WAVE
MOVING FROM CENTRAL CANADA INTO THE GREAT LAKES FOR WEDNESDAY. THE
MAJORITY OF FORCING FROM THIS SYSTEM LOOKS TO REMAIN NORTH OF THE
FORECAST AREA...AND MOISTURE WILL AGAIN BE SPARSE.  AS SUCH...WILL
LEAVE CHANCES OUT OF THE FORECAST FOR THE TIME BEING.

&&

.AVIATION...TONIGHT AND SATURDAY

MVFR AND IFR RADIATIONAL BR/FG A CONCERN LATE TONIGHT THRU MUCH OF
SAT MORNING. BOUNDARY LAYER AIRMASS ALONG/WEST OF THE MS RIVER
REMAINS RATHER MOIST THIS AFTERNOON...WITH DEW POINTS AROUND 30F AND
19Z RH VALUES STILL IN THE 60-80 PERCENT RANGE. WINDS REMAIN LIGHT
SOUTHEAST INTO THIS EVENING...BECOMING MORE SOUTHERLY THRU THE NIGHT
AS A WEAK TROUGH AXIS APPROACHES FROM THE WEST AND ILL-DEFINED WARM
FRONT APPROACHES FROM THE SOUTH. AIRMASS OVER MUCH OF IA HAS DEW
POINTS IN THE LOWER 30S. WITH ONLY A VEIL OF CIRRUS EXPECTED FOR
CLOUDS TONIGHT...FAVORABLE RADIATIONAL COOLING SET-UP WITH SOME 14+
HRS OF DARKNESS. WINDS BECOME EVEN LIGHTER AS THE TROUGH AXIS
APPROACHES. 925-700MB WARM ADVECTION CONTINUES OVER THE AREA
TONIGHT. MUCH OF THIS GOES INTO WARMING WITH A STRONG SFC-850MB
INVERSION OVER THE AREA...BUT SOME WEAK LIFT INDICATED IN THE
925-700MB LAYER. VSBYS LOWERED INTO THE 7-9SM RANGE 10Z-15Z ALREADY
THIS MORNING. ALL NUMERICAL GUIDANCE BULLETINS DROP VSBYS TO IFR AT
KRST/KLSE AROUND 12Z TO 15Z SAT...BUT CLIMATOLOGY DOES GENERALLY
SUPPORT IFR RADIATIONAL FOG AT THE TAF SITES IN LATE NOV...UNLESS
THERE IS SOME MELTING SNOW ON THE GROUND. BASED ON THIS MORNING AND
EVEN LIGHTER WINDS AND SOME BOUNDARY LAYER CONVERGENCE LATE
TONIGHT...CARRIED MVFR VSBYS IN BR ROUGHLY 08Z THRU 1630Z AT BOTH
KRST/KLSE. PREVIOUS TAF SET HAD ALREADY INCLUDED THIS. ADDED TEMPO
1SM BR SCT IFR STRATUS FOR 10Z-14Z TIME-FRAME FOR NOW WITH LACK OF
SNOWCOVER AND CLIMATOLOGY KIND OF AGAINST PREVAILING IFR/LIFR CIGS/
VSBYS IN FOG.

EVENING CREW WILL HAVE TO KEEP A CLOSE EYE ON DEW POINTS/WINDS/BR
DEVELOPMENT THIS EVENING AND TREND /LIKELY THE 06Z TAF SET/
ACCORDINGLY. IF IFR/LIFR FOG BECOMES PREVAILING...GIVEN TIME OF YEAR
AND LOW SUN ANGLE/SHORT DAYS...FOG/BR /AT LEAST MVFR/ COULD END UP
VERY PERSISTENT THRU MUCH OF SAT...AT LEAST UNTIL THE TROUGH AXIS
PASSES AND WINDS ACROSS THE AREA BECOME NORTHERLY BEHIND IT.

&&

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

$$

SHORT/LONG TERM...MW
AVIATION..........RRS