000 
FXUS63 KARX 130941
AFDLSE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
340 AM CST WED FEB 13 2002

FORECAST CONCERNS THIS PACKAGE...TEMPERATURE...CLOUD AND WIND
TRENDS THRU THU...THEN PRECIPITATION CHANCES LATE THU THRU EARLY
FRI.

SURFACE ANALYSIS AT 08Z SHOWED HIGH PRESSURE CENTERED OVER WESTERN
KS WITH RIDGING TO THE NORTHEAST ACROSS IA/WI. NEXT LEE LOW/TROUGH
WAS ALREADY DEVELOPING INTO CENTRAL CANADA AND NORTHERN PLAINS WITH
DECENT PRESSURE FALLS THIS MORNING. STRONG WARM ADVECTION ALREADY IN
PROGRESS WEST/NORTH OF THE FORECAST AREA...WITH TEMPS STEADY OR
CLIMBING ACROSS MUCH OF MN/WESTERN IA. INCREASING SOUTHWEST WINDS
KEEPING TEMPS RATHER MILD ACROSS THE DAKOTAS...EVEN UNDER MOSTLY
CLEAR SKIES. FURTHER EAST...LIGHT WINDS AND CLEAR SKIES ALLOWING
TEMPS TO DROP PRETTY GOOD OVER MUCH OF NORTHEAST WI. FOG-PRODUCT
IMAGERY SHOWED MID CLOUD DECK BEING GENERATED BY THE WARM ADVECTION
OVER MUCH OF MN. LOWER CLOUD DECK AND EVEN A LITTLE -SN GENERALLY
CONFINED TO NORTHEAST MN...AND MODELS REFLECT THIS QUITE WELL THIS
MORNING. WV IMAGERY SHOWED THE NEXT SHORTWAVE TO IMPACT THE REGION
APPROACHING THE WA/BC COAST. 00Z MODELS LOOK TO HAVE GOOD HANDLE ON
THIS FEATURE AT THIS TIME.

PER PMDHMD...MODEL INITIALIZATIONS ERRORS NOTED WITH UPPER LEVEL
WIND FIELD OVER TX. OF MORE IMPORTANCE ARE INITIALIZATION DIFFERENCES
WITH THE RIDGING OVER THE EASTERN PACIFIC BEHIND THE WA/BC SHORTWAVE.
THIS TRANSLATES INTO SPEED DIFFERENCES WITH THE SYSTEM AS IT MOVES
ACROSS THE REGION IN THE THU NIGHT TIME FRAME. OTHERWISE...00Z MODELS
INITIALIZED REASONABLY WELL WITH FEATURES TO IMPACT THE UPPER MIDWEST
TODAY THRU THU. 00Z ETA IS THE ODD MODEL OUT THIS MORNING WITH
SHORTWAVE PROGRESSING THRU THE NORTH CENTRAL U.S. ABOUT 6HRS FASTER
THAN THE OTHER MODELS. AVN SHOWS BETTER RUN TO RUN CONSISTENCY. 06Z
MESO-ETA BACK IN LINE WITH SPEED OF 00Z AVN/NGM RUNS...SO WILL LEAN
TOWARD AVN FOR SPEED/TIMING THIS CYCLE.

FOR THE SHORT TERM...MODERATE TO STRONG WARM ADVECTION SPREADS ACROSS
THE FORECAST AREA TODAY...ALONG WITH TIGHTENING PRESSURE GRADIENT AS
LOW PRESSURE CONTINUES TO DEEPEN IN CENTRAL CANADA. MODELS INDICATING
SURGES OF MID LEVEL MOISTURE TO PUSH OVER THE AREA TODAY FOR MORE OF
A PARTLY SUNNY DAY. BRISK SOUTHWEST WINDS BY AFTERNOON SHOULD ALLOW
FOR DECENT LOW LEVEL MIXING. FAVORED WARMER NGM-FWC HIGHS...AND EVEN
THESE BUMPED UP A CATEGORY SOME AREAS. 850MB WARM ADVECTION CONTINUES
TONIGHT...ALONG WITH BRISK SOUTHWEST WINDS MOST AREAS. MAINLY HIGH
LEVEL MOISTURE AHEAD OF THE APPROACHING TROUGH OVER THE REGION
TONIGHT. HIGH CLOUDS PLUS THE WINDS SHOULD AGAIN KEEP TEMPS MILD
TONIGHT AND TRENDED LOWS TOWARD MESO-ETA MIN TEMPS...WHICH ARE ABOUT
A CATEGORY ABOVE WARMER OF NGM-AVN LOWS. MESO-ETA MIN TEMP FIELD
ACTUALLY NAILED THE WARM LOWS TUE MORNING...WHICH NGM/AVN GUIDANCE
MISSED BY 8F TO 10F.

MID/UPPER LEVEL Q-G CONVERGENCE AND STRONG PV ADVECTION AHEAD OF THE
SHORTWAVE SPREAD ACROSS THE AREA THU. MUCH OF THIS FORCING/LIFTING
GOES INTO SATURATING THE INITIALLY DRY LOW/MID LEVEL AIRMASS. MODELS
INDICATE SATURATION DOES NOT OCCUR UNTIL LATE IN THE DAY OVER THE
WEST END OF THE FORECAST AREA. AVN GENERATES MUCH MORE WIDESPREAD
PRECIP ACROSS THE REGION BY 00Z FRI...BUT IT HAS ABOUT ABOUT 0.15
INCH MORE PRECIPITABLE WATER WITH THIS SYSTEM THAN THE OTHER MODELS.
THIS LOOKS A BIT OVERDONE GIVEN THE SOURCE REGION OF THE LOW/MID
LEVEL AIRMASS. WILL TRIM BACK PRECIP CHANCES OVER THE EAST/SOUTH
ENDS FOR THU...AND PUSH THOSE OVER THE WEST END TO LATE IN THE DAY.
WITH A WARM START AND CONTINUED BRISK SOUTHWEST WINDS AND GOOD LOW
LEVEL MIXING...RAISED HIGHS A NOTCH ABOVE GUIDANCE MOST AREAS...EVEN
UNDER THICKENING CLOUDS.

STRONG PV ADVECTION AND UPPER LEVEL Q-G CONVERGENCE PUSH ACROSS
THE AREA THU NIGHT. DYNAMIC LIFTING/COOLING ALONG WITH EVAPORATIVE
COOLING ERODE THE 925-850MB WARM LAYER AND CHANGE ANY PRECIP THREAT
RAPIDLY OVER TO SNOW THU EVENING. GUIDANCE POPS IN THE CHANGE RANGE
AND THESE ONLY RAISED A BIT AS MORE REALISTIC LOOKING ETA QPF FIELDS
ONLY PAINT A FEW HUNDRETHS OVER THE FORECAST AREA. WITH PLENTY OF
CLOUDS AND WIND FOR MIXING...FAVORED WARMER AVN-MAV LOWS FOR THU
NIGHT. SYSTEM EXITS QUICKLY FOR FRI WITH BRISK NORTHWEST WINDS AND
COLD ADVECTION OVER THE AREA.

MEDIUM RANGE MODELS POINTING TO ANOTHER SHORTWAVE DIVING SOUTHEAST
AND ACROSS THE GREAT LAKES SAT...WITH A TREND TOWARD MORE OF A
MOSTLY CLOUDY DAY WITH FLURRIES ON SAT. WILL LEAVE THIS ALONE FOR
NOW. REST OF EXTENDED PORTION OF FORECAST IN GOOD SHAPE AS MRF/ECMWF
CONTINUE TO BRING A MAJOR TROUGH INTO THE CENTRAL U.S. FOR THE
MIDDLE OF NEXT WEEK.

.LSE...NONE.

RRS