FXUS63 KABR 112108
AFDABR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ABERDEEN SD
308 PM CST FRI DEC 11 2009

.SHORT TERM...TONIGHT THROUGH SUNDAY NIGHT
MAIN FORECAST CHALLENGE IS TEMPERATURES DURING THE WEEKEND...AND
SNOW CHANCES TOWARD THE END OF THE PERIOD. THE GFS AND ECMWF ARE
IN REASONABLE AGREEMENT WITH THE TRACK OF THE PRECIPITATION
PRODUCING SYSTEM SET TO AFFECT THE AREA SUNDAY AND SUNDAY
NIGHT...WHILE THE NAM HAS SIGNIFICANTLY DIFFERENT TRACK. WILL
THEREFORE STICK CLOSER TO A GFS SOLUTION AT THIS TIME.

A WEST TO EAST ELONGATED UPPER LEVEL TROUGH WILL DRIFT FROM THE
NORTHERN PART OF THE COUNTRY OVER CANADA TONIGHT...THEN REMAINS
THERE THROUGH THE END OF THE PERIOD. ZONAL FLOW SETS UP OVER THE
NORTHERN PLAINS TONIGHT...AND REMAINS DOMINANT THROUGH ABOUT MIDDAY
SUNDAY. A SHORTWAVE TROUGH TRACKS FROM THE WEST COAST SUNDAY
MORNING TO THE EASTERN ROCKIES BY SUNDAY EVENING...THEN ACROSS THE
PLAINS SUNDAY NIGHT WITH THE STRONGEST ENERGY FROM SOUTHERN SOUTH
DAKOTA ACROSS EASTERN NEBRASKA.

AT THE SURFACE...A WARM FRONT WILL BE SITUATED OVER THE
DAKOTAS/MINNESOTA BORDER THIS EVENING...WITH THE TRAILING COLD
FRONT PUSHING SOUTHWARD TO REACH THE NORTH DAKOTA/SOUTH DAKOTA
BORDER BY SATURDAY MORNING. THE FRONT DROPS ACROSS ALL BUT THE
SOUTHEASTERN CORNER OF THE STATE BY SATURDAY EVENING...THEN WELL
SOUTH WITH HIGH PRESSURE BEGINNING TO NOSE OVER THE NORTHERN
PLAINS. A LOW PRESSURE SYSTEM OVER THE WEST COAST WILL TRACK
EASTWARD TO THE CENTRAL ROCKIES ON SUNDAY...WITH THE LEADING EDGE
OF PRECIPITATION REACHING WESTERN SOUTH DAKOTA. THE MAIN LOW
CENTER LOOKS TO PUSH ACROSS NEBRASKA SUNDAY NIGHT...WITH A BROAD
AREA OF SNOW TO THE NORTH OF IT ACROSS THE DAKOTAS AND MINNESOTA.
LOOKS AS THOUGH HIGHEST SNOW AMOUNTS WILL BE ACROSS THE NORTHERN
CWA...AND HAVE STUCK CLOSE TO THE GFS FORECAST AMOUNTS OF AROUND
AN INCH ACROSS THE SOUTHERN CWA TO NEAR THREE INCHES ACROSS THE
NORTH.

TEMPERATURES WILL REMAIN BELOW NORMAL THROUGH THE PERIOD...BUT
WITH NO REAL STRONG PUSH OF COLD AIR DIRECTLY BEHIND THE COLD
FRONT...SHOULD SEE HIGHS IN THE TEENS TO LOWER 20S AGAIN ON
SATURDAY. WILL THEN SEE THE COLDER AIR BEGIN TO MOVE IN
SUNDAY...WITH HIGHS BACK DOWN INTO THE SINGLE DIGITS.

.LONG TERM...MONDAY THROUGH FRIDAY
PRECIPITATION CHANCES EARLY IN THE PERIOD...AS WELL AS
TEMPERATURES THROUGHOUT...ARE THE FORECAST CHALLENGES IN THE
EXTENDED.

THE 12Z GFS AND 0Z ECMWF AGREE EXTRAORDINARY WELL WITH REGARDS TO
OVERALL EVOLUTION OF THE LONG WAVE FLOW PATTERN THROUGHOUT THE
EXTENDED. THERE IS EVEN DECENT AGREEMENT IN THE SYNOPTIC
SCALE...IN MINIMAL DIFFERENCES IN TIMING AND PLACEMENT OF FEATURES.

THE PERIOD BEGINS WITH AN AREA OF LOW PRESSURE OVER WESTERN
IOWA...WITH WRAP AROUND PRECIPITATION FALLING IN THE COLD SECTOR
OF THE LOW. THE GFS DOES HINT AT A TROWAL FEATURE POKING INTO THE
EASTERN CWA BY 12Z MONDAY. IN ADDITION...BOTH THE GFS/ECMWF
ADVERTISE A BROAD AREA OF 0.1 INCHES OR GREATER QPF. FOR THESE TWO
REASONS...HAVE INCREASED POPS ON MONDAY TO THE CHC CATEGORY. WOULD
NOT BE SURPRISED IF POPS ARE INCREASED EVEN MORE IN THE COMING
DAYS.

A SECONDARY WAVE DROPS SOUTHEAST ACROSS THE REGION ON MONDAY
NIGHT. THERE MAY BE JUST ENOUGH MOISTURE TO SQUEEZE OUT LIGHT SNOW
OVER PARTS OF THE AREA. WILL MAINTAIN A DRY FORECAST FOR NOW AND
MAINLY FOCUS ON THE BITTER COLD TEMPERATURES. WITH A 1040 MB
CANADIAN HIGH PRESSURE OVER HEAD AND CAA IN THE LOWER
LEVELS...HAVE LOWERED HIGHS A FEW MORE DEGREES ON TUESDAY.
TEMPERATURES AT H85 RANGE FROM -19C IN THE NE...TO -14C IN THE SW
CWA. TEMPS AT H925 GENERALLY RANGE AROUND -20C...WHICH WOULD YIELD
SURFACE TEMPS ON EITHER SIDE OF ZERO.

THE SURFACE HIGH MOVES SOUTHEAST ON WEDNESDAY WITH RETURN FLOW
SETTING UP THROUGH THE CENTRAL AND NORTHERN PLAINS. WHILE WAA WILL
INVADE THE REGION...WILL KEEP HIGH TEMPERATURES ON THURSDAY AND
FRIDAY SOME TEN DEGREES BELOW ADJMEX.

&&

.AVIATION...
A WEAK WAVE WILL MOVE ACROSS THE AREA LATE TONIGHT AND THROUGH DAY
ON SATURDAY. HOWEVER...MOISTURE IS LACKING IN THE LOWER LEVELS SO
ONLY EXPECT INCREASING CLOUDS. EVEN WITH THE INCREASE IN
CLOUDS...FLYING CONDITIONS WILL REMAIN VFR FOR ALL TAF SITES.

&&

.ABR WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
MN...NONE.
&&

$$
SHORT TERM...PARKIN
LONG TERM...SD
AVIATION...SD

WEATHER.GOV/ABERDEEN