Area Forecast Discussion
Issued by NWS Fairbanks, AK

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FXAK69 PAFG 212211
AFDAFG

NORTHERN ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FAIRBANKS AK
111 PM AKST SUN DEC 21 2014

.DISCUSSION...

21/12Z DETERMINISTIC MODEL SUITE IS GENERALLY IN GOOD AGREEMENT
THROUGH 12Z TUESDAY WITH THE OVERALL SYNOPTIC PATTERN.
THEREAFTER...MODEL DIFFERENCES BETWEEN THE GFS AND ECWMF BECOME
APPARENT...WITH THE GFS PAINTING A MORE AMPLIFIED RIDGE ALOFT OVER
MAINLAND ALASKA AND SIGNIFICANT DIFFERENCES WITH THE SURFACE LOW
OVER THE BERING LATE THIS WEEK. USED A BLEND OF THE PREVIOUS
FORECAST AND MODEL BLEND THROUGH 00Z THURSDAY.

MAIN CONCERNS INCLUDE WINDS ALONG THE WEST COAST AND ST LAWRENCE
ISLAND AND FOG/LOW STRATUS DECK OVER THE ARCTIC COAST.
OTHERWISE...FAIRLY QUIET WEATHER PATTERN FOR MOST OF NORTHERN
ALASKA.

1929Z NPP/MODIS MICROPHYSICS RGB SATELLITE IMAGE SHOWS A BAND OF
STRATUS/FOG OVER THE ARCTIC COAST. THINKING THAT LOW STRATUS AND
AREAS OF FOG WILL PERSIST OVER THE NEXT FEW DAYS AS WINDS WILL BE LIGHT.

.ALOFT...

BROAD UPPER LEVEL TROUGH EXTENDS FROM CHUKOTSK PENINSULA SOUTHEAST
OVER THE WESTERN TWO-THIRDS OF AK WITH A RIDGE OVER THE EASTERN
THIRD OF AK AND WESTERN CANADA. THIS TROUGH IS EXPECTED TO WEAKEN
AND LIFTS NORTH THIS EVENING AS A 500 MB VORTEX MAX/TROUGH SWINGS
EAST FROM THE CHUKOTSK PENINSULA. ALL OPERATIONAL MODELS HAVE THIS
TROUGH DEEPENING AS IT PROGRESSES EAST OVER NORTHERN ALASKA.

COINCIDENT WITH THIS TROUGH...WEAK COLD AIR ADVECTION WILL ENSUE
OVER NORTHERN ALASKA. ORIGINATING OVER NORTHERN SIBERIA WITH
CHILLY H850 TEMPERATURES OF -30C...THIS AIRMASS WILL MODIFY AS IT
SPREADS SOUTHEAST AND OVER NORTHERN ALASKA. BY TUESDAY/WEDNESDAY H850
TEMPERATURES OF -15C TO -20C WILL RESIDE OVER THE BROOKS RANGE
NORTH AND -10C TO -15C NORTH OF THE ALASKA RANGE. THESE FORECAST
H850 TEMPERATURES ARE STILL SLIGHTLY ABOVE NORMAL FOR THIS TIME
OF YEAR. THERE ARE SLIGHT DIFFERENCES BETWEEN THE MODELS...ONLY 3C
TO 5C WARMER PER THE ECWMF. AT THE SURFACE...MAY SEE AROUND 10
DEGREES OF COOLING NORTH OF THE BROOKS RANGE BY MIDWEEK...BRINGING
TEMPERATURES BACK TO NEAR NORMAL.

A PROGRESSIVE AND HIGHLY AMPLIFIED RIDGE IS EXPECTED TO BEGIN
BUILDING OVER THE WESTERN BERING SEA MONDAY NIGHT...BY EARLY
WEDNESDAY AFTERNOON...THE RIDGE AXIS WILL EXTEND FROM THE CHUKOTSK
PENINSULA SOUTHEAST OVER SEWARD PENINSULA AND OVER KODIAK ISLAND.
THIS RIDGE WILL GRADUALLY SHIFT NORTHEAST THROUGH THE REMAINDER OF
THE WEEK.

WEAK SHORTWAVES WILL MOVE OVER THE NORTH SLOPE...WEST COAST...AND
WESTERN INTERIOR...BRINGING INCREASED CHANCES FOR SNOW SHOWERS
MONDAY. CHANCES FOR SNOW SHOWERS FOR THE REST OF THE INTERIOR WILL
INCREASE AS THE AFOREMENTIONED H500 TROUGH SWINGS EAST TUESDAY AND
WEDNESDAY.

.SURFACE...

A BROAD LOW PRESSURE/TROUGH EXISTS OVER THE NORTHERN GULF OF
ALASKA AND MAINLAND AK...WITH MULTIPLE LOW CENTERS BEING ANALYZED.
SURFACE HIGH PRESSURE RESIDES OVER SIBERIA AND ARCTIC OCEAN. THE
BROAD LOW PRESSURE/TROUGH WILL EXPAND NORTHWARD OVER THE BEAUFORT
SEA TONIGHT AND MONDAY...ALLOWING THE GRADIENT OVER THE WEST COAST TO
POINT HOPE AND ALONG THE ARCTIC COAST TO RELAX. THIS WILL ALLOW
WINDS TO GRADUALLY DIMINISH OVERNIGHT FOR THE EASTERN BEAUFORT
SEA...POINT HOPE AND THE YUKON DELTA COAST.

CURRENT GFS/NAM/ECWMF ARE DEVELOPING A STRONG LOW NEAR SHEMYA BY
12Z TUESDAY. AFTER 12Z TUESDAY...MODEL SOLUTIONS SIGNIFICANTLY
DIVERGE WITH THE DEVELOPMENT AND PROGRESSION OF THIS LOW AS IT
DEEPENS AND ROTATES AROUND OVER THE BERING SEA. WILL EVALUATE
FUTURE RUNS OF THE GFS/NAM/ECWMF AS DETAILS BECOME CLEARER TO SEE
IF THERE WILL BE IMPACTS FOR THE WEST COAST ASSOCIATED WITH THIS
LOW.


COASTAL HAZARD POTENTIAL DAYS 3 AND 4...NONE

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
HEAVY FREEZING SPRAY WARNING FOR PKZ210.

SMALL CRAFT ADVISORY FOR PKZ210.

GALE WARNING FOR PKZ220.

BRISK WIND ADVISORY FOR PKZ220-PKZ240-PKZ245.
&&

$$

LTH DEC 14



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