FXUS63 KARX 142119
AFDARX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
301 PM CST MON DEC 14 2009
.SHORT TERM...TONIGHT THROUGH THURSDAY
MAIN FORECAST CONCERNS ARE COLD TEMPERATURES TONIGHT INTO TUESDAY.
LATEST WATER VAPOR SATELLITE IMAGERY INDICATING A SERIES OF
SHORTWAVE TROUGHS EMBEDDED IN WEST TO NORTHWEST FLOW ALOFT. FIRST
SHORTWAVE TROUGH OVER SOUTHERN LAKE MICHIGAN IN ASSOCIATION WITH
SURFACE LOW THAT BROUGHT FREEZING DRIZZLE AND SNOW ACROSS FORECAST
AREA OVERNIGHT AND THIS MORNING. NEXT TWO SHORTWAVES UPSTREAM OF
THE AREA OVER CENTRAL MINNESOTA AND THE NORTHERN PLAINS. BOTH OF
THESE ARE PRODUCING VERY LIGHT SNOW OR FLURRIES PER LATEST METARS
OVER THE NORTHERN PLAINS AND SOUTHERN MINNESOTA.
THE 14.12Z GFS AND NAM ARE IN GOOD AGREEMENT IN DIGGING UPPER LEVEL
TROUGH OVER THE NORTHEAST U.S. AND DEVELOPING NORTHWEST FLOW ALOFT
BY 00Z WEDNESDAY OVER THE AREA. BOTH THE MODELS APPEAR TO INITIALIZE
CLOUDS PER RELATIVE HUMIDITY FIELDS AND LATEST VISIBLE SATELLITE
IMAGERY. THE 14.12Z GFS AND NAM ARE IN DECENT AGREEMENT CLEARING
SKIES FROM WEST TO EAST TONIGHT AND ADVECTING COLDER AIR INTO THE
AREA. BIGGEST DIFFERENCE BETWEEN THE MODELS IS TIMING THE VERY WEAK
SHORTWAVES EMBEDDED IN NORTHWEST FLOW INTO THE GREAT LAKES REGION
WEDNESDAY INTO THURSDAY. CONFIDENCE IN FORECAST IS HIGH THROUGH
TUESDAY NIGHT...THEN BEGINS TO DIMINISH SLIGHTLY WEDNESDAY INTO
THURSDAY.
TONIGHT INTO TUESDAY...SECOND SHORTWAVE TROUGH OVER THE NORTHERN
PLAINS MOVES ACROSS NORTHERN MINNESOTA TONIGHT AND SOUTHERN ONTARIO
CANADA BY 00Z WEDNESDAY. BOTH THE 14.12Z GFS AND NAM INDICATING
DEEPER QG FORCING AND ISENTROPIC LIFT OVER THE NORTHERN SECTIONS OF
THE FORECAST AREA AND NORTH OF THE FORECAST AREA. WITH COLDER AIRMASS
AND WEAK ISENTROPIC LIFT PER 14.12Z GFS 285K SURFACE OVER THE AREA
THIS EVENING...HAVE INTRODUCED FLURRIES AND KEPT SMALL CHANCES OVER
NORTHEAST PORTIONS OF THE FORECAST AREA.
BEHIND SHORTWAVE STRONG COLD AIR ADVECTS INTO THE FORECAST AREA
OVERNIGHT...WITH BOTH THE 14.12Z GFS AND NAM INDICATING 850MB
TEMPERATURES FALLING TO MINUS 10 TO MINUS 20 DEGREES CELSIUS BY 12Z
TUESDAY. COMBINED WITH WIND SPEEDS ABOVE FIVE MILES PER HOUR...HAVE
DECIDED TO ISSUE A WIND CHILL ADVISORY FOR PORTIONS OF SOUTHEAST
MINNESOTA AND NORTHEAST IOWA FROM 06Z TO 17Z TUESDAY...WITH APPARENT
TEMPERATURES DROPPING INTO THE MINUS 20 TO MINUS 25 RANGE.
UNDER THE INFLUENCE OF NORTHWEST FLOW ALOFT...TEMPERATURES WILL
REMAIN BELOW NORMAL ACROSS FORECAST AREA THROUGH WEDNESDAY. THEN...
TEMPERATURES WILL BEGIN TO MODERATE FOR THURSDAY...AS 850MB
TEMPERATURES WARM INTO THE SINGLE DIGITS CELSIUS BELOW ZERO BY 00Z
FRIDAY. BOTH THE 14.12Z GFS AND NAM ARE INDICATING A COUPLE OF WEAK
SHORTWAVES TO TRACK ACROSS THE UPPER MIDWEST AND GREAT LAKES REGION
WEDNESDAY INTO THURSDAY. BOTH THE MODELS ARE SHOWING WEAK
ISENTROPIC LIFT...QG FORCING AND VERTICAL MOTION WITH THE WAVES. THE
BUFKIT FORECAST SOUNDINGS AND TIME HEIGHT CROSS SECTIONS INDICATE
ATMOSPHERE HAVING A HARD SATURATING...WILL CONTINUE WITH SMALL
CHANCES OF PRECIPITATION OVER THE EXTREME NORTHERN PARTS OF THE
FORECAST AREA.
.LONG TERM...THURSDAY NIGHT THROUGH MONDAY
MAIN FORECAST CONCERNS ARE PRECIPITATION CHANCES AND
TEMPERATURES THROUGH THE PERIOD. THE 14.00Z GFS AND ECMWF ARE IN
PRETTY GOOD AGREEMENT IN RETROGRADING UPPER LEVEL LOW OVER NOVA
SCOTIA AND NORTHEASTERN U.S. WESTWARD INTO THE GREAT LAKES REGION
THROUGH THE PERIOD. THE BIGGEST ISSUES WILL BE TIMING AND PLACEMENT
OF SHORTWAVES WRAPPING AROUND UPPER LEVEL LOW INTO THE UPPER MIDWEST
AND GREAT LAKES REGION THROUGH THE PERIOD. THE 14.00Z GEFS IS
INDICATING AMPLIFICATION ISSUES WITH THE UPPER LEVEL LOW RETROGRADING
WESTWARD THROUGH THE PERIOD. THIS WILL ALLOW FOR THE UPPER MIDWEST
AND GREAT LAKES REGION TO BE UNDER THE INFLUENCE OF NORTHERLY FLOW
ALOFT AND COLDER AIR TO ADVECT INTO THE REGION THROUGH THE PERIOD.
WITH SHORTWAVES WRAPPING AROUND THE UPPER LEVEL LOW INTO THE AREA...
THIS WILL PROVIDE ENOUGH FORCING AND SATURATION ACROSS FORECAST AREA
THROUGH PERIOD. THOUGH...SNOWFALL AMOUNTS WILL BE LIGHT...MAINLY
FLURRIES AND LIGHT SNOW...WILL CONTINUE WITH SMALL CHANCES OF
PRECIPITATION THROUGH FORECAST PERIOD. BOTH THE 14.00Z GFS AND ECMWF
INDICATING 850MB TEMPERATURES COOLING TO MINUS 10 TO MINUS 20 DEGREES
CELSIUS ACROSS FORECAST AREA BY 00Z MONDAY. THE 14.00Z GEFS 2 METER
SURFACE AND 850MB TEMPERATURES INDICATING STANDARD DEVIATIONS OF
LESS THAN ONE THROUGH FORECAST PERIOD. TEMPERATURES WILL BE
SLIGHTLY BELOW NORMAL ACROSS FORECAST AREA THROUGH FORECAST PERIOD.
&&
.AVIATION...TODAY AND TONIGHT
LOW PRESSURE HAD MOVED INTO LOWER MICHIGAN AT MID AFTERNOON. ONLY
SCATTERED FLURRIES AND PATCHES OF LIGHT SNOW REMAIN AROUND THE LOCAL
AREA. THE FLURRIES WILL CONTINUE INTO THE EVENING HOURS BUT HAVE
LITTLE IMPACT ON THE TAF SITES. MVFR CEILINGS WILL CONTINUE THROUGH
AT LEAST 09Z-10Z. AFTER THAT MODELS DEPICT A CLEARING TREND FROM THE
WEST AND THUS HAVE CEILINGS SCATTERING OUT AT THAT TIME WITH MAINLY
CLEAR SKIES AFTER 12Z TUESDAY.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...NONE.
MN...WIND CHILL ADVISORY FROM MIDNIGHT TONIGHT TO 11 AM CST TUESDAY
FOR MNZ079-MNZ086-MNZ087-MNZ088-MNZ094-MNZ095-MNZ096.
IA...WIND CHILL ADVISORY FROM MIDNIGHT TONIGHT TO 11 AM CST TUESDAY
FOR IAZ008-IAZ009-IAZ010-IAZ011-IAZ018-IAZ019-IAZ029-IAZ030.
&&
$$
SHORT/LONG TERM...DTJ
AVIATION..........RABERDING
