Area Forecast Discussion
Issued by NWS Fairbanks, AK

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FXAK69 PAFG 202059
AFDAFG

NORTHERN ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FAIRBANKS AK
1159 AM AKST SAT DEC 20 2014

.DISCUSSION...
DETERMINISTIC GUIDANCE ARE GENERALLY IN GOOD AGREEMENT WITH THE
LARGE SCALE PATTERN OUT TO 60-72 HRS. CONCERNS TODAY INCLUDE
MODERATE WINDS ACROSS THE BERING SEA/BERING STRAIT AND
COASTS...WITH GUSTS UP TO 40 MPH BEING OBSERVED AT TIMES AT POINT
HOPE...GAMBELL...AND CAPE ROMANZOFF. THE STRONGEST OF WHICH IS
BEING RECORED NEAR POINT HOPE.

ALSO FOG/STRATUS IS OBSERVED OVER THE NORTH SLOPE AND PORTIONS OF
THE INTERIOR AND WEST COAST THIS MORNING. FOG/STRATUS IS DEPICTED
FAIRLY WELL BY THE NASA SPORT NIGHTTIME MICROPHYSICS IMAGERY THIS
MORNING. IMAGERY SHOWS FOG/STRATUS CONFINED GENERALLY TO THE NORTH
SLOPE...NORTHERN HALF OF THE WEST COAST ZONES...AND OVER SMALL
SECTIONS OF THE AK INTERIOR. OBS INDICATE MAINLY STRATUS IN THE
INTERIOR...WITH FOG MORE PREVALENT OVER THE NORTH SLOPE.

.ALOFT...

BROAD 500 HPA LONGWAVE TROUGH IS POSITIONED OVER THE WESTERN TWO-
THIRDS OF AK WITH A RIDGE OVER NORTHERN AK. RIDGE IS POSITIONED
ACROSS THE NORTHWEST TERRITORIES AND YUKON. TROUGH WILL STAY
RELATIVE STATIONARY IN LOCATION WHILE WEAKENING THE NEXT 48 HRS AS
THE PATTERN ALOFT BECOMES MORE PROGRESSIVE. A RIDGE CURRENTLY JUST
SOUTH OF KAMCHATKA PENINSULA WILL BUILD AND MOVE EAST TOWARD THE
MIDDLE OF THE ALEUTIAN ISLANDS BY EARLY MON. RIDGE THEN MOVES EAST
INTO THE EASTERN ALEUTIAN ISLANDS BY EARLY TUE...THIS IS WHERE
DIFFERENCES START TO BECOME MORE APPARENT IN THE LARGE SCALE
PATTERN.

GFS BECOMES MORE BULLISH WITH THE 500 HPA TROUGH WHILE IT LIFTS
THE TROUGH NORTH ABOUT 60 HRS OUT LATE MON/EARLY TUE.
WHEREIN...THE TROUGH BASE BECOMES TILTED MORE NEGATIVE AT THIS
POINT AS WELL. 500 HPA HEIGHT FALLS OF AROUND 15-25 DAM ARE SEEN
IN THE GFS AND NAM COMPARED TO LESSER HEIGHT FALLS IN THE ECMWF.
THIS TRANSLATES TO A MORE COMPACT SFC LOW ON THE NAM AND GFS LATE
MON...COMPARED TO THE ECMWF...THAT WILL BE MOVING NORTHEAST INTO
SE AK EARLY TUE. GUIDANCE ARE SIMILAR IN MOVING THE TROUGH EAST
ACROSS MUCH OF NORTHERN AK BY THU...WITH THE GFS KEEPING THE
TROUGH STRONGER IN AMPLITUDE AND FARTHER SOUTH COMPARED TO THE
ECMWF.

MEANWHILE...COLDER AIR WILL BEGIN TO PENETRATE THE WEST COAST MON
AS THE TROUGH BEGINS TO LIFT NORTH. GFS IS A BIT COLDER AND MORE
BULLISH WITH HOW FAR THE COLD AIR PENETRATES INTO NORTHERN AK
HOWEVER...DIFFERENCES BETWEEN THE ECMWF ARE NOT THAT
GREAT...GENERALLY 3 TO 5 C.

.SURFACE...

A BROAD SFC LOW EXISTS SOUTH OF MAINLAND ALASKA AND THE ALEUTIAN
ISLANDS WITH MULTIPLE CENTERS ANALYZED...THE STRONGEST ABOUT 927
MB. THIS AREA OF LOW PRESSURE WILL WEAKEN AND BECOME MORE COMPACT
THE NEXT 48 HRS OVER THE GULF OF ALASKA. A NEW SFC LOW DEVELOPS IN
THE NORTHERN PACIFIC AS THE MID-LEVEL TROUGH ALOFT LIFTS NORTH AND
BECOMES MORE NEGATIVELY TILTED AT ITS BASE...BEGINNING ABOUT 54
HRS OUT. AS THE SFC LOW MOVES NORTHEAST INTO SE ALASKA TUE...LOW
PRESSURE WILL BEGIN BUILDING INTO THE INTERIOR.

HIGH PRESSURE CURRENTLY ACROSS THE ARCTIC OCEAN WILL MOVE INTO
THE CANADIAN ARCHIPELAGO BY MON. MEANWHILE...HIGH PRESSURE ACROSS
EASTERN SIBERIA WILL SPREAD INTO BERING AND CHUKCHI SEA AS WELL.

GUIDANCE ARE IN FAIR AGREEMENT WITH LOW PRESSURE DEVELOPING IN
THE WESTERN BERING SEA LATE MON/EARLY TUE. OUTSIDE OF A TROUGH OF
LOW PRESSURE EXTENDING FROM THE SFC LOW MOVING NORTH INTO NORTHERN
ALASKA...ITS CENTER IS NOT EXPECTED TO MOVE EAST MUCH BY WED.

WINDS ARE EXPECTED TO STAY ELEVATED OVER THE BERING SEA-BERING
STRAIT-EXTREME SOUTHERN END OF CHUKCHI SEA THE NEXT 36 HOURS AS
THE GRADIENT STAYS STRONG THERE. LOCAL WINDS...TANANA VALLEY
JET AND WINDS OVER THE NE YUKON FLATS...SHOULD BEGIN TO RELAX THE
NEXT 24 HRS AS LOW PRESSURE IN THE GULF OF ALASKA WEAKENS.

IN REGARD TO PRECIPITATION...DRY CONDITIONS EXPECT OVER THE NEXT
24 HRS OVER INTERIOR AK...WITH FLURRIES OR SNOW SHOWERS EXPECT
OVER THE NORTH SLOPE AND THE WEST COAST. A FEW SHORT-WAVE TROUGHS
WITH MODERATE VORT MAXES WILL TRAVERSE THE NORTH SLOPE...WEST
COAST...AND WESTERN INTERIOR MON AND PROVIDE INCREASE CHANCES FOR
SNOW. INCREASE CHANCES FOR SNOW ARE EXPECTED ON TUE OVER THE REST
OF THE INTERIOR AS THE AFOREMENTIONED 500 HPA TROUGH ALOFT BEGINS
TO LIFT AND MOVE EAST ACROSS NORTHERN AK.

COASTAL HAZARD POTENTIAL DAYS 3 AND 4...NONE

&&

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

SMALL CRAFT ADVISORY FOR PKZ210.

BRISK WIND ADVISORY FOR PKZ220-PKZ225-PKZ240-PKZ245.
&&

$$

ET DEC 14


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