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000
FXUS63 KARX 031729
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1129 AM CST TUE DEC 3 2013

.UPDATE...
ISSUED AT 1129 AM CST TUE DEC 3 2013

UPDATED TO EXTEND THE DENSE FOG ADVISORY TO NOON WEDNESDAY. LITTLE
IMPROVEMENT NOTED SOUTHWEST OF THE I-94 CORRIDOR WHERE THE DENSE
FOG ADVISORY IS IN EFFECT. VERY LITTLE IF ANY IMPROVEMENT EXPECTED
THIS AFTERNOON AND WITH A BAGGY PRESSURE GRADIENT TONIGHT COMBINED
WITH VERY MOIST FEED OF AIR...EXPECT VISIBILITIES TO DIP NEAR
ZERO AT TIMES AGAIN...LASTING INTO WEDNESDAY MORNING. INCREASING
WINDS SHOULD MIX THE BOUNADRY LAYER UP WEDNESDAY
AFTERNOON...THEREBY IMPROVING VISIBILITIES.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 405 AM CST TUE DEC 3 2013

MAIN FORECAST CONCERNS THIS PACKAGE...PRECIP CHANCES/TYPES MAINLY
THIS AFTERNOON AND TONIGHT...TEMPERATURES.

DATA ANALYSIS AT 06Z HAD A TROUGH OF LOW PRESSURE OVER MN...BACK TO
LOWS IN NEB AND WY. BAND OF -RA/-SN THAT PASSED THRU THE FCST AREA
MON AFTERNOON/EVENING CONTINUED TO SHIFT NORTHEAST OF THE AREA...
ONLY IMPACTING CLARK/TAYLOR COUNTIES INTO THE OVERNIGHT HOURS. IN
ITS WAKE...IN THE AREA OF WEAK LOW LEVEL CONVERGENCE/LIFT AHEAD OF
AND WITH THE SFC-850MB TROUGH...PATCHY TO AREAS OF DRIZZLE AND FOG
WERE COMMON. WITH THE THICK LOW LEVEL CLOUDS AND CONTINUED LOW LEVEL
WARM ADVECTION...EARLY MORNING TEMPERATURES WERE NEAR NORMAL EARLY
DECEMBER HIGHS.

NO PROBLEMS NOTED WITH 03.00Z MODEL INITIALIZATIONS. SOLUTIONS MORE
SIMILAR THAN THEY HAVE BEEN AND CONVERGING ON A COMMON SOLUTION THRU
TONIGHT INTO WED. CAN/ECMWF/UKMET OFFERING UP THE BETTER RUN-TO-RUN
CONSISTENCY WITH THEIR 01.00Z AND 02.00Z RUNS AS A MID LEVEL LOW
DEVELOPS OVER THE NORTHWEST CONUS. TREND FAVORS HOLDING MORE ENERGY
/MID LEVEL LOW/ IN THE WESTERN/SOUTHERN PORTION OF THE WESTERN CONUS
TROUGH WITH A FLATTER LEAD WAVE EJECTING INTO THE UPPER MIDWEST
TONIGHT. STILL SOME DETAIL DIFFERENCES BY LATER TONIGHT WITH GFS
REMAINING STRONGER/FASTER WITH THE LEAD WAVE. CHECK OF OBS VS. MODEL
DATA AT 06Z SHOWED ALL TO BE REASONABLE WITH THE SFC MASS FIELDS
ACROSS THE CENTRAL CONUS. MODELS ALL DOING A DECENT JOB WITH THE
BAND OF WARM ADVECTION/ISENTROPIC LIFT -RA/-SN LIFTING NORTHEAST OF
THE AREA. PER WV IMAGERY...ALL LOOKED RESPECTABLE WITH THE SHORTWAVE
DETAILS OVER NOAM/EASTERN PAC. WITH ECMWF/CAN/UKMET OFFERING THE
BETTER RUN-TO-RUN CONSISTENCY AND NAM/GFS BEGRUDGINGLY TRENDING
TOWARD THEM...LEANED TOWARD THE ECMWF/CAN/UKMET CONSENSUS. GIVEN THE
MODEL DETAIL DIFFERENCES...SHORT-TERM FCST CONFIDENCE IS AVERAGE THIS
CYCLE.

IN THE SHORT TERM...SHORTWAVE LIFTING THRU MN/WI EARLY THIS MORNING
CONTINUES NORTHEAST...TAKING THE LOWER LEVEL THERMO-DYNAMIC FORCING
WITH IT. GENERALLY TRENDED PRECIP CHANCES DOWN THIS MORNING...BUT
CARRIED 20-50 PERCENT CHANCES FOR MUCH OF THE AREA WITH SOME WEAK
LOWER LEVEL LIFT LINGERING ACROSS THE AREA. SOME INDICATIONS AMONG
THE MODELS FOR DEEPENING MOISTURE THIS MORNING...ENOUGH SO FOR
INCREASING PROBABILITIES OF ICE IN THE CLOUDS AND PRECIP TYPE AS
-DZ OR -SN. NEXT SURGE OF INCREASING LOWER LEVEL WARM ADVECTION
SPREADS INTO THE AREA THIS AFTERNOON AND EVENING...THIS WITH
INCREASING DIVERGENCE/LIFT ALOFT AHEAD OF THE MAIN MID LEVEL TROUGH
BEGINNING TO EJECT INTO THE PLAINS. PW VALUES CONTINUE TO INCREASE
AS WELL...AND INCREASE PRECIP CHANCES THRU THE AFTERNOON AND FOR
TONIGHT TO 60-80 PERCENT...ESPECIALLY ACROSS THE NORTHERN 2/3 OF
THE FCST AREA WHERE DEEPER SATURATION IS EXPECTED. WITH SOUNDINGS/
X- SECTIONS SHOWING PLENTY OF ABOVE 0C AIR IN THE SFC- 850MB
LAYER...BULK OF THE PRECIP ACROSS THE FCST AREA THIS AFTERNOON/
TONIGHT WOULD FALL AS RAIN. EXCEPTION IS CLARK/TAYLOR COUNTIES
WHERE TEMPS ALOFT AND AT THE SFC MAY BE COOL ENOUGH FOR A WINTRY
MIX OF PRECIP. GIVEN THE POTENTIAL FOR A LONGER PERIOD OF A
WINTRY MIX OF PRECIP TONIGHT INTO WED NIGHT...WILL ISSUE A WINTER
WEATHER ADVISORY FOR CLARK/TAYLOR COUNTIES FROM 9PM TONIGHT THRU
WED NIGHT. USED A BLEND OF THE GUIDANCE HIGHS/LOWS FOR TODAY/
TONIGHT.

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 405 AM CST TUE DEC 3 2013

MAIN FORECAST CONCERNS FOR WED THRU THU NIGHT...PRECIP TYPE/AMOUNTS
WED INTO WED NIGHT...COLD AIR SPREADING IN WED NIGHT THRU THU
NIGHT.

MODELS COMING INTO BETTER AGREEMENT AS THE MAIN ENERGY FROM THE
WESTERN CONUS TROUGH SWINGS THRU THE REGION WED/WED NIGHT. NAM/GFS
REMAIN STRONGER WITH THE SHORTWAVE TROUGH LIFTING NORTH OF THE
REGION WED NIGHT WHILE ECMWF/CAN/UKMET SHOW RATHER GOOD RUN-TO-RUN
CONSISTENCY WITH THEIR 01.00Z AND 02.00Z RUNS. CONTINUED TO SIDE
WITH THE ECMWF/CAN/UKMET CONSENSUS IN THE WED THRU THU NIGHT
PERIOD. FCST CONFIDENCE FOR THIS PERIOD IS AVERAGE.

SFC-700MB TROUGH/LOW LIFT NORTHEAST INTO THE AREA WED...WITH
CONSIDERABLE DIFFERENCES IN TIMING/TRACK OF THE SFC LOW WHEN
INCLUDING NAM/GFS IN THE MIX. EVEN WITH THE DIFFERENCES ONE COMMON
TREND AMONG THE MODELS IS FOR PLENTY OF SFC-850MB WARM /ABOVE 0C/
AIR TO BE PULLED NORTH ACROSS THE AREA AHEAD OF THE LOW/TROUGH.
DEEPER FORCING/LIFT AND PW VALUES AROUND 0.75 INCH SPREAD ACROSS THE
AREA WED. RAISED PRECIP CHANCES INTO THE 40-80 PERCENT RANGE
WED...AGAIN HIGHEST ACROSS THE NORTH PORTIONS OF THE FCST AREA WHERE
SATURATION IS EXPECTED TO BE DEEPEST. WITH THE TREND TOWARD WARMER
IN THE SFC-850MB LAYER...BULK OF PRECIP ACROSS THE FCST AREA WED
MORNING LOOKS TO FALL AS RAIN...WITH POTENTIAL FOR THE WINTRY MIX
ALONG/NORTH OF HIGHWAY 29. AS THE SFC-850MB TROUGH AXIS PASSES WED
AFTERNOON/EVENING...COLDER AIR SPREADS WEST TO EAST ACROSS THE AREA
CHANGING THE PRECIP TO A MIX THEN SNOW. HOWEVER...PRECIP AMOUNTS
AFTER IT WOULD CHANGE TO SNOW TREND TO THE LIGHT SIDE. GIVEN THE
TIMING AND DETAIL DIFFERENCES AMONG THE MODELS ON THE LOWER LEVEL
THERMAL PROFILES...HELD OFF ON ANY POTENTIAL WINTER WEATHER
ADVISORIES FOR WED INTO WED EVENING. WITH THE SFC-850MB LOW TRENDING
TO TRACK ACROSS THE FCST AREA...BULK OF THE HEAVIER PRECIP AND
ACCUMULATING SNOW LOOKS TO FALL JUST WEST/NORTH OF THE FCST AREA.

SFC-850MB LOW MOVES RATHER QUICKLY NORTHEAST OF THE AREA WED NIGHT/
THU...WITH STRONG LOW LEVEL COLD ADVECTION AND AIR OF ARCTIC ORIGIN
POURING ACROSS THE AREA WED NIGHT. 925MB TEMPS IN THE -8C TO
-16C RANGE...DEPENDING ON MODEL...BY 12Z THU. LOW LEVEL COLD
ADVECTION CONTINUES THU/THU NIGHT WITH 925MB TEMPS IN THE -14C TO
-20C RANGE BY 12Z FRI. USED A BLEND OF THE NUMERICAL TEMP GUIDANCE
FOR HIGHS/LOWS IN THE WED-THU NIGHT PERIOD FOR NOW...WHICH
DEFINITELY TRENDS THE COOLING THIS PERIOD IN THE RIGHT DIRECTION.

FOR FRIDAY THROUGH MONDAY.../DAYS 4 TO 7/...

TREND OF MEDIUM RANGE MODEL RUNS OF 03.00Z IS FOR MORE LONGWAVE
TROUGHING TO REMAIN OVER THE WESTERN CONUS FRI/SAT AND RISING HGTS
OVER THE CENTRAL CONUS. IMPROVING CONSENSUS THEN SWINGS A PORTION OF
THIS TROUGH/SHORTWAVE ENERGY INTO/NORTHEAST THRU THE PLAINS STATE
SUN AND INTO THE UPPER MIDWEST MON. BETTER RUN-TO-RUN CONSISTENCY
RESIDES WITH THE ECMWF. GIVEN THE TRENDS FROM THE 01.00Z AND 02.00Z
RUNS AND POTENTIAL FOR ACCUMULATING SNOW SUN NIGHT/MON...LONG TERM
FCST CONFIDENCE IS A BIT BELOW AVERAGE.

FRI/SAT DOMINATED BY ARCTIC HIGH PRESSURE. 850MB TEMPS SOME 1 TO 2
STANDARD DEVIATIONS BELOW NORMAL...WITH THE COLDEST CORE/GREATEST
ANOMALIES OVER THE ROCKIES/WESTERN PLAINS. TEMPS FRI/SAT TRENDING
SOME 10-20 DEGREES BELOW NORMAL. RISING HGTS OVER THE CENTRAL CONUS
SAT/SUN SEND THE ARCTIC HIGH INTO EASTERN NOAM...WITH SOME LOWER
LEVEL WARM ADVECTION DEVELOPING ACROSS THE MID/UPPER MS VALLEY FOR
SUNDAY. THIS AHEAD OF LOW PRESSURE DEVELOPING IN THE CENTRAL/
SOUTHERN PLAINS. IF MORE CONSISTENT ECMWF SOLUTION IS MORE CORRECT
FOR SUN/SUN NIGHT...A ROUND OF 850-700MB WARM ADVECTION/MOISTURE
INCREASE/LIFT AND SOME ACCUMULATING SNOWFALL WOULD SPREAD ACROSS THE
AREA. SMALL -SN CHANCE FOR SUN/SUN NIGHT REASONABLE FOR NOW UNTIL A
BETTER MODEL CONSENSUS DEVELOPS. ONCE THIS WAVE WOULD PASS...A RE-
ENFORCING SHOT OF ARCTIC AIR WOULD SPREAD INTO THE REGION FOR MON.
THIS EVEN COLDER THAN THE FRI/SAT AIRMASS. MODEL/ENSEMBLE CONSENSUS
HIGHS/LOWS FOR FRI/SAT APPEAR WELL TRENDED AT THIS TIME.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)
ISSUED AT 1129 AM CST TUE DEC 3 2013

LIFR CONDITIONS EXPECTED AT BOTH KRST/KLSE THROUGH THE FORECAST
PERIOD AS A VERY MOIST FEED OF AIR CONTINUES AHEAD OF SURFACE
TROUGH OF LOW PRESSURE AND DEVELOPING AREA OF LOW PRESSURE MOVING
OUT OF MISSOURI INTO EASTERN IA/SOUTHWEST WI. LOOKING AT A SLUG OF
RAIN TO MOVE THROUGH THIS AFTERNOON...THEN TAPERING OFF TO DRIZZLE
BY THIS EVENING AND LASTING THROUGH WEDNESDAY MORNING.
TEMPERATURES WILL BE STAYING ABOVE 32 DEGREES AT THE TAF
SITES...SO NO FREEZING PRECIPITATION ISSUES ARE EXPECTED.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...DENSE FOG ADVISORY UNTIL NOON CST WEDNESDAY FOR WIZ032-033-041-
     053>055-061.

     WINTER WEATHER ADVISORY FROM 9 PM THIS EVENING TO 6 AM CST
     THURSDAY FOR WIZ017-029.

MN...DENSE FOG ADVISORY UNTIL NOON CST WEDNESDAY FOR MNZ079-086>088-
     094>096.

IA...DENSE FOG ADVISORY UNTIL NOON CST WEDNESDAY FOR IAZ008>011-018-
     019-029-030.

&&

$$

UPDATE...DAS
SHORT TERM...RRS
LONG TERM....RRS
AVIATION...DAS