000
FXUS63 KARX 062302
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
500 PM CST FRI DEC 6 2013

.SHORT TERM...(THIS EVENING THROUGH MONDAY)
ISSUED AT 326 PM CST FRI DEC 6 2013

MAIN FORECAST CONCERNS ARE TEMPERATURES AND WIND CHILLS
TONIGHT...THEN ACCUMULATING SNOWS SUNDAY INTO SUNDAY NIGHT.

LATEST WATER VAPOR SATELLITE IMAGERY SHOWS UPPER LEVEL TROUGH OVER
THE ROCKY MOUNTAINS AND UPPER LEVEL LOW OVER HUDSON BAY. REGION
REMAINS UNDER THE INFLUENCE OF THE UPPER LEVEL LOW OVER HUDSON BAY
AND ADVECTING IN AN ARCTIC AIRMASS OVER THE AREA. LATEST 20Z
METARS INDICATE TEMPERATURES RANGING IN THE SINGLE DIGITS ABOVE
ZERO TO THE TEENS OVER FORECAST AREA.

THE LATEST 06.12Z GFS AND NAM ARE IN DECENT AGREEMENT IN DIGGING
UPPER LEVEL TROUGH OVER THE CENTRAL UNITED STATES AND MOVING
SHORTWAVE TROUGH AROUND THE BASE OF THE UPPER LEVEL TROUGH INTO
THE GREAT LAKES REGION SATURDAY NIGHT INTO SUNDAY NIGHT. SUBTLE
DIFFERENCES NOTED BETWEEN THE NAM AND GFS WITH SLIGHT DIFFERENCES
IN TIMING OF SHORTWAVE TROUGH. CONFIDENCE IN FORECAST THROUGH
PERIOD IS INCREASING.

TONIGHT...BOTH THE 06.12Z GFS AND NAM SUGGEST ARCTIC AIRMASS TO
CONTINUE TO ADVECT COLD AIR INTO THE FORECAST AREA...WITH 850MB
TEMPERATURES OF MINUS 16 TO MINUS 20 DEGREES CELSIUS BY 12Z
SATURDAY. THE COMBINATION OF TEMPERATURES FALLING INTO THE TEENS
BELOW ZERO TO AROUND ZERO DEGREES AND WINDS...WILL PRODUCE WIND
CHILL VALUES OF MINUS 10 TO MINUS 30 ACROSS FORECAST AREA. A WIND
CHILL ADVISORY IS IN EFFECT FOR PORTIONS OF WESTERN
WISCONSIN...SOUTHEAST MINNESOTA AND PARTS OF NORTHEAST IOWA
TONIGHT INTO SATURDAY MORNING.

NEXT CONCERN IS SHORTWAVE TROUGH/SURFACE LOW EJECTING OUT INTO THE
CENTRAL PLAINS AND INTO THE GREAT LAKES REGION SATURDAY NIGHT INTO
SUNDAY NIGHT. THE 06.12Z GFS/NAM ARE IN GOOD AGREEMENT WITH THE
ASSOCIATED LIFT AND UPPER LEVEL JET DYNAMICS. BOTH MODELS SUGGEST
ISENTROPIC LIFT AT THE 285K SURFACE TO INCREASE AFTER 06Z SUNDAY
OVER THE FORECAST AREA. HOWEVER...WITH A VERY DRY AIRMASS
ENTRENCHED OVER THE FORECAST AREA...THE ATMOSPHERE WILL TAKE
AWHILE TO SATURATE BETWEEN 06-12Z SUNDAY. SNOW SHOULD BEGIN OVER
THE WESTERN FORECAST AREA AFTER 09Z SUNDAY AND THEN BECOME MORE
WIDESPREAD OVER THE FORECAST AREA DURING THE MORNING AND
AFTERNOON HOURS...AS THE DEEPER LIFT MOVES INTO THE REGION.

THE 06.12Z GFS/NAM INDICATE THE BEST LIFT TO BE ABOVE THE DENDRITIC
GROWTH ZONE...HOWEVER THE MODELS DO SUGGEST A VERY DEEP (200-300MB)
DENDRITIC GROWTH ZONE AND ALLOW FOR FLUFFY SNOW ACROSS THE FORECAST
AREA. SNOWFALL RATIOS OF 20 TO 1 ARE EXPECTED AND THIS WOULD RESULT
IN 2 TO 5 INCHES OF SNOW ACROSS MUCH OF THE FORECAST AREA SUNDAY
MORNING INTO SUNDAY NIGHT.

PRESSURE GRADIENT TIGHTENS AND COLDER AIR ADVECTS IN BEHIND THE
EXITING SHORTWAVE TROUGH/SURFACE LOW MONDAY. SUSTAINED WINDS LOOK
TO BE IN THE 15 TO 25 MPH RANGE ACROSS MUCH OF THE FORECAST AREA.
WITH THE LIGHT FLUFFY SNOW...DRIFTING SNOW CAN BE EXPECTED IN THE
HIGHER TERRAIN AND IN OPEN AREAS. IF THE PRESSURE GRADIENT
TIGHTENS EVEN MORE THAN WHAT THE MODELS SUGGEST...THERE COULD BE
SOME BLOWING SNOW IN THE HIGHER TERRAIN AND OPEN AREAS

.LONG TERM...(MONDAY NIGHT THROUGH FRIDAY)
ISSUED AT 326 PM CST FRI DEC 6 2013

MAIN FORECAST CONCERNS ARE PRECIPITATION CHANCES MONDAY NIGHT INTO
TUESDAY THEN TEMPERATURES FOR MIDDLE OF NEXT WEEK. THE 06.12Z
GFS/ECMWF/GEM ARE IN GOOD AGREEMENT IN DIGGING UPPER LEVEL TROUGH
OVER THE EASTERN HALF OF THE UNITED STATES AND ALLOWING NORTHWEST
FLOW TO DEVELOP OVER THE NORTHERN PLAINS AND GREAT LAKES REGION THROUGH
00Z FRIDAY. THE 06.12Z MODELS ARE IN AGREEMENT IN FLATTENING
UPPER LEVEL TROUGH OVER THE EASTERN UNITED STATES/UPPER LEVEL
RIDGE OVER THE WESTERN UNITED STATES AND DEVELOP WEST TO EAST
ZONAL FLOW OVER THE NORTHERN TIER STATES FRIDAY. THE 06.12Z THE
ECMWF/GFS/GEM ARE IN GOOD AGREEMENT IN MOVING VIGOROUS SHORTWAVE
TROUGH EMBEDDED IN THE NORTHWEST FLOW ALOFT MONDAY NIGHT INTO
TUESDAY. SETTLE DIFFERENCES ARE NOTED IN TIMING OF SHORTWAVE
TROUGH INTO THE UPPER MIDWEST AND GREAT LAKES REGION BETWEEN THE
MODELS. THE MODELS SUGGEST ENOUGH LIFT/FORCING IN ASSOCIATION WITH
SHORTWAVE TROUGH OVER THE NORTHERN HALF OF FORECAST AREA TO
WARRANT SMALL CHANCES OF PRECIPITATION OVER THE EASTERN PARTS OF
THE FORECAST AREA. WITH PASSAGE OF SHORTWAVE TROUGH...COLDER AIR
FILTERS INTO THE FORECAST AREA. THE 06.00Z GEFS INDICATE MINUS 1
TO MINUS 2 STANDARD DEVIATIONS OVER GREAT LAKES REGION TUESDAY
INTO THURSDAY. THE FORECAST AREA WILL REMAIN UNSEASONABLY COLD
INTO MIDDLE OF NEXT WEEK. THE 06.12Z MODELS SHOW UPPER LEVEL RIDGE
AND TROUGH FLATTENING OVER THE NORTHERN TIER STATES LATE IN THE
WEEK. THIS WILL ADVECT WARMER AIR INTO THE FORECAST AREA AND
TEMPERATURES SHOULD CLIMB TO NEAR NORMAL OR SLIGHTLY ABOVE NORMAL
LATE NEXT WEEK.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SATURDAY EVENING)
ISSUED AT 500 PM CST FRI DEC 6 2013

HIGH PRESSURE BUILDS IN FROM THE PLAINS ON SATURDAY...AND SHOULD
BRING VFR CONDITIONS TO THE REGION THROUGH SATURDAY EVENING.

SNOW WILL SPREAD ACROSS THE UPPER MISSISSIPPI RIVER VALLEY ON
SUNDAY...AS AN UPPER LEVEL SHORTWAVE TROUGH SPINS ACROSS THE AREA.
CIGS WILL LOWER TO MVFR/IFR BY SUNDAY MORNING...WITH VSBY
RESTRICTING SNOW FOR MUCH OF SUNDAY/SUNDAY EVENING. SEVERAL INCHES
OF ACCUMULATION ARE EXPECTED...WHICH COULD BLOW AROUND AT KRST IF
WINDS PICK UP A BIT MORE THAN CURRENTLY EXPECTED.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...WIND CHILL ADVISORY FROM 9 PM THIS EVENING TO 9 AM CST SATURDAY
     FOR WIZ032>034.

     WIND CHILL ADVISORY FROM 9 PM THIS EVENING TO NOON CST SATURDAY
     FOR WIZ017-029.

MN...WIND CHILL ADVISORY FROM 9 PM THIS EVENING TO 9 AM CST SATURDAY
     FOR MNZ079-086>088-094-095.

IA...WIND CHILL ADVISORY FROM 9 PM THIS EVENING TO 9 AM CST SATURDAY
     FOR IAZ008-009-018-019.

&&

$$

SHORT TERM...DTJ
LONG TERM....DTJ
AVIATION.....RIECK