FXUS63 KABR 102110
AFDABR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ABERDEEN SD
310 PM CST THU DEC 10 2009

.SHORT TERM...TONIGHT THROUGH SATURDAY NIGHT
MAIN FORECAST CHALLENGE CONTINUES TO BE TEMPERATURES...WITH LITTLE
TO NO SIGNIFICANT WEATHER EXPECTED. A BROAD UPPER TROUGH WILL
EXTEND ACROSS CANADA AND THE FAR NORTHERN PART OF THE UNITED
STATES THIS EVENING...AND WILL CONTINUE TO SLOWLY DRIFT NORTHWARD
THROUGH THE DAY FRIDAY. NORTHWEST FLOW THEN SETS UP OVER THE
NORTHERN PLAINS...BEFORE SHIFTING TO MORE OF A ZONAL FLOW FRIDAY
NIGHT. THIS FLOW WILL CONTINUE INTO THE EARLY PART OF THE WEEKEND
AS A WEAK TROUGH STAYS WELL SOUTH OF THE AREA...SLIDING ACROSS THE
SOUTHERN PLAINS.

AT THE SURFACE...HIGH PRESSURE WILL BE ELONGATED FROM THE PACIFIC
NORTHWEST TO THE SOUTHEASTERN UNITED STATES THIS EVENING. A WEAK
TROUGH WILL SLIDE ACROSS THE NORTHERN PLAINS NORTH OF THE HIGH
PRESSURE SYSTEM THIS EVENING...THEN RIDGING BUILDS BACK UP
OVERNIGHT. THE RIDGE SLIDES EAST OF THE AREA FRIDAY AHEAD OF A
TROUGH DIGGING DOWN THE LEE OF THE ROCKIES. AS THE MAIN LOW CENTER
DROPS OUT OF WESTERN CANADA...THE TROUGH WILL CONTINUE TO DIG...AND
A COLD FRONT WILL REACH SOUTHERN NORTH DAKOTA BY SATURDAY MORNING.
THE FRONT DROPS ACROSS THE CWA EARLY SATURDAY...THEN BECOMES
STATIONARY OVER THE SOUTH DAKOTA/NEBRASKA BORDER SATURDAY NIGHT
WITH THE MAIN AREA OF HIGH PRESSURE AND THE COLDER AIR REMAINING
OVER CANADA. AT THIS TIME...NOT EXPECTING ANY PRECIPITATION DURING
THE PERIOD.

SOME CHANGES IN THE TEMPERATURE FORECAST...WITH SOMEWHAT WARMER
TEMPERATURES NOW EXPECTED THAN PREVIOUSLY THOUGHT. H85 TEMPS WILL
STILL BE IN THE TEENS TO 20S BELOW ZERO THIS EVENING AND INTO
EARLY FRIDAY MORNING...THEN WAA KICKS IN. BY THE END OF THE
PERIOD...BOTH THE NAM AND GFS ARE INDICATING H85 TEMPS BACK UP
AROUND ZERO. HAVE THEREFORE RAISED TEMPERATURES SOME DURING EACH
PERIOD...WITH TEENS TO LOWER 20S LIKELY FOR HIGHS BOTH FRIDAY AND
SATURDAY. WILL SEE ONE MORE NIGHT OF EVERYONE SEEING SUBZERO LOWS
TONIGHT...THEN LOWS FRIDAY NIGHT AND SATURDAY NIGHT WILL BE AROUND
ZERO TO THE MID SINGLE DIGITS ABOVE ZERO.

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

MODELS AGREE OVERALL WITH THE EVOLUTION OF THE LONG WAVE FLOW
PATTERN ACROSS NORTH AMERICA. THE DISAGREEMENT LIES IN THE AMOUNT
OF AMPLITUDE OF A WEST COAST RIDGE AND THE TELECONNECTION TO THE
OHIO RIVER VALLEY/EAST COAST TROF. THE GFS HAS THE HIGHEST DEGREE
OF AMPLITUDE WITH THE WEST COAST RIDGE...WHICH LEADS TO A DEEPER
EAST COAST TROF. IF THE GFS VERIFIES...THEN THERE WOULD BE A
CHANCE OF LIGHT SNOW SUNDAY NIGHT/MONDAY AS A STRONG COLD FRONT
MOVES ACROSS THE REGION. TEMPERATURES AT H925 FALL FROM -5C ON
SUNDAY AFTERNOON...TO -20C BY MONDAY AFTERNOON. THIS POOL OF COLD
AIR PUSHES ACROSS THE OHIO VALLEY ON WEDNESDAY WITH HEIGHTS
INCREASING OVER THE NORTH PLAINS. HEIGHTS CONTINUE TO INCREASE
THROUGHOUT THE REST OF THE EXTENDED...WHICH WOULD MARK THE START
OF A WARMING TREND.

THE 0Z ECMWF ALSO SHOWS A COLD FRONT MOVING ACROSS THE NORTHERN
PLAINS ON SUNDAY NIGHT...WITH LIGHT SNOW BEING POSSIBLE.
HOWEVER...THE ECMWF SHOWS MORE OF A GLANCING BLOW WITH H925 TEMPS
ONLY FALLING TO -15C...WITH -20C ALONG THE US/CANADIAN BORDER.
LIKE THE GFS...THE ECMWF SHOWS THE WEST COAST RIDGE APPROACHING
THE REGION...WITH A WARMING TREND BEGINNING.

FOR THIS FORECAST PACKAGE...USED THE NAEFS FOR THE AMOUNT OF
AMPLITUDE FOR THE RIDGE AND TROF...WHICH MORE OF A BLEND OF THE
12Z GFS AND 0Z ECMWF. AS A SIDE NOTE...THE RMOP IS GENERALLY 50
PERCENT OR LESS ACROSS THE CONUS...AND FOR THE ENTIRE EXTENDED
PORTION OF THE FORECAST. SIMPLY PUT...THERE IS A HIGH DEGREE OF
UNCERTAINTY WITH THE COLD AIR PUSH AT THE BEGINNING OF THE
EXTENDED...AS WELL AS THE WARMING TREND AT TAIL END.

&&

.AVIATION...
PREVAILING VFR CONDITIONS CAN BE EXPECTED AT ALL TAF SITES THROUGH
FRIDAY EVENING. HOWEVER...SOME SCT/BKN CIGS AOA 2K FEET MAY
INVADE THE KABR/KATY TERMINALS THROUGH EARLY THIS EVENING.

&&

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

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

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