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FXAK69 PAFG 211528 AAA
AFDAFG

NORTHERN ALASKA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE FAIRBANKS AK
628 AM AKST SUN DEC 21 2014

UPDATE ADDS PARAGRAPH TO SURFACE SECTION
.DISCUSSION...
CURRENT RUNS OF THE GFS/NAM/ECMWF/CANADA NH MODELS ARE IN
GENERALLY GOOD AGREEMENT OUT THROUGH 12Z WED.

UPPER AIR...
ALL OF THE OPERATIONAL MODELS ARE GRADUALLY DEEPENING AN UPPER
TROUGH SOUTHEASTWARD OUT OF SIBERIA AND THE WESTERN ARCTIC OCEAN
THROUGH MON NIGHT...BRINGING A COLDER AIR MASS TO NORTHWEST ALASKA
AND THE NORTHERN PARTS OF THE WEST COAST. THIS MORNING...THE NAM
AND ECMWF ARE FOLLOWING THE LEAD OF THE GFS IN MOVING THE TROUGH
EASTWARD ACROSS THE NORTHERN HALF OF NORTHERN ALASKA THROUGH WED
EVENING...PULLING THE COLDER AIR MASS EASTWARD ACROSS THE
NORTHERN PARTS OF NORTHERN ALASKA.

A PROGRESSIVE UPPER LEVEL RIDGE IS EXPECTED TO BEGIN BUILDING
OVER THE SOUTHERN BERING SEA AND WESTERN ALEUTIANS MON. BY
TUE AFTERNOON THE RIDGE WILL INCREASE CONSIDERABLY IN AMPLITUDE...
EXTENDING FROM EASTERN INTERIOR SIBERIA TO NUNIVAK ISLAND
AND THE ALASKA PENINSULA. BY WED AFTERNOON...THE RIDGE AXIS
WILL EXTENDING FROM THE NORTH COAST OF EASTERN SIBERIA TO
THE BERING STRAIT AND KODIAK ISLAND. A WEAK SHORT WAVE TROUGH
WILL MOVE THROUGH THE SOUTHERN PART OF THE RIDGE TUE NIGHT AND
WED AND LIKELY DAMPEN OUT ON WED. THIS FEATURE IS EXPECTED TO
HAVE LITTLE IF ANY IMPACT IN OUR FORECAST AREA. THE RIDGE
IS EXPECTED TO CONTINUE TO MOVE ACROSS NORTHERN ALASKA WED
AND THU AS A BROAD TROUGH SWINGS NORTHWARD ACROSS THE SOUTHERN
BERING SEA AND THE WEST COAST.

LATE THIS WEEK AND INTO THE WEEKEND...GEFS/NAEFS AND ECMWF
ENSEMBLE MEANS BUILDING A RIDGE OVER THE GULF OF ALASKA AND THE
ALASKA MAINLAND...BY SAT NIGHT THE MEAN RIDGE AXIS EXTENDS FROM
THE WESTERN ARCTIC OCEAN TO THE CENTRAL ARCTIC COAST THEN
SOUTHEASTWARD INTO THE NORTHERN PANHANDLE. SOUTH TO SOUTHWEST
ALOFT FLOW OVER THE NORTHERN ALASKA MAINLAND ON THE BACK SIDE OF
THE RIDGE WILL BRING IN WARMER AIR ALOFT AND AT THE SURFACE. THIS
TREND IS INDICATED IN GFS EXTENDED MOS TEMPERATURES AT MOST
FORECAST SITES TOWARDS THE END OF THE WEEK.

SURFACE...
THE BIGGEST SHORT TERM ISSUE IS WINDS OVER THE CENTRAL AND EASTERN
ARCTIC COAST AND INTERIOR ARCTIC SLOPE. THE 06Z MANUAL SURFACE
ANALYSIS INDICATED A NARROW TROUGH ALONG THE CENTRAL ARCTIC COAST
THEN TO SOUTH OF BARTER ISLAND...WITH A WEAK RIDGE OVER THE
INLAND ARCTIC COAST. THIS PATTERN IS RESULTING IN EASTERLY GALE
FORCE WINDS AT BARTER ISLAND AND MUCH LIGHTER WINDS FARTHER TO THE
WEST. THESE SURFACE FEATURES ARE GENERALLY NOT WELL HANDLED BY THE
MODELS...AND TEND TO BE MORE PERSISTENT THAN MODEL FORECASTS. AT
THIS TIME...LOOKING FOR THIS PATTERN TO HOLD TOGETHER TODAY THEN
BECOMING GRADUALLY SMOOTHED OUT WHICH SHOULD RESULT IN DECREASING
WINDS ALONG THE EASTERN ARCTIC COAST AND IN MARINE ZONE PKZ245.
WINDS ARE EXPECTED TO SHIFT TO LIGHT WESTERLY IN THIS AREA BY MON
WITH A WEAK SURFACE TROUGH PROGGED TO MOVE EASTWARD. IN ANY
EVENT...CONFIDENCE IN THE WIND FORECASTS IN THIS AREA IS BELOW
AVERAGE.

A TIGHT PINCH IN THE ISOBAR FIELD FROM THE NORTHWEST ALASKA CAPES
TO THE BERING STRAIT AND ST LAWRENCE ISLAND IS PRODUCING BRISK
NORTH TO NORTHEAST WINDS IN THESE AREAS...WITH GALE FORCE WINDS AT
TIN CITY AND GALE GUSTS AT POINT HOPE AND WALES. THIS TIGHT
GRADIENT IS EXPECTED TO GRADUALLY RELAX DURING THE NEXT 24
HOURS...RESULTING IN DECREASING WINDS.

LATE EVENING NASA/SPORT NIGHT MICROPHYSICS RGB IMAGE SHOWS
EXTENSIVE LOW STRATUS OVER THE ARCTIC COAST AND MUCH OF THE INLAND
ARCTIC COAST...WITH ONLY A FEW PATCHES ELSEWHERE IN THE INTERIOR.
PRESENCE OF THE STRATUS IN THESE AREAS IS WELL SUPPORTED BY
AVAILABLE SURFACE OBSERVATIONS.

SCATTERED SNOW SHOWERS OVER THE CENTRAL AND WESTERN ARCTIC
COAST AND OVER THE CHUKCHI AND NORTHERN BERING SEAS ARE
EXPECT TO SPREAD SLOWLY EASTWARD ACROSS THE NORTHERN PARTS
OF NORTHERN ALASKA THROUGH TUE AS THE COLD UPPER TROUGH
MARCHES SLOWLY EASTWARD. SCATTERED SNOW SHOWERS ARE EXPECTED
TO BREAK OUT OVER THE SOUTHERN AND EASTERN INTERIOR MON
NIGHT AND TUE.

BRISK EAST WINDS DEVELOPING OVER ST LAWRENCE ISLAND LATE TUE
AFTERNOON OR TUE EVENING...INCREASING TO GALE LATER TUE NIGHT AS A
WEATHER FRONT APPROACHES FROM THE SOUTH. EASTERLY GALES DEVELOPING
TUE IN THE EXTREME WESTERN PARTS OF MARINE ZONE PKZ210.

CURRENT GFS/ECMWF AND ENSEMBLE MEANS INDICATE THE POSSIBILITY
OF A MODERATELY STRONG LOW MOVING INTO THE SOUTHERN BERING SEA
FRIDAY AFTERNOON OR FRIDAY NIGHT...WITH POTENTIAL FOR GALES OVER
THE NORTHERN BERING SEA.


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-PKZ225-PKZ240-PKZ245.
&&

$$

DEC 14

Alaska Region Headquarters
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Page Modified: 03 Feb 2008 18:00 UTC
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