Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 232218
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
218 PM AKDT THU OCT 23 2014

.ANALYSIS AND UPPER LEVELS...

500MB...THE PERSISTENT UPPER TROUGH OVER THE MAINLAND AND GULF
MOVE EAST AS THE BERING SEA RIDGE NOSES IN FROM THE WEST. AN UPPER
LOW OVER EASTERN RUSSIA ACTS AS THE FOCAL POINT FOR TROUGHS MOVING
IN FROM THE WEST THROUGH SAT. THE MORE SIGNIFICANT OF THE TROUGHS
CURRENTLY OVER THE EASTERN BERING SEA MOVES OVER THE CENTRAL
MAINLAND FRI AFTERNOON THEN INTO THE YUKON ON SAT. BROAD ZONAL
WESTERLY FLOW SETS UP ACROSS THE BERING SEA TONIGHT AND HOLDS
THROUGH SAT. A FEW MINOR WAVES ARE EXPECTED TO RIPPLE EAST ACROSS
THE BERING SEA. COLD AIR DROPPING SOUTH BEHIND THE EASTERN RUSSIA
LOW SUN DIGS OUT THE TROUGH OVER THE CENTRAL BERING SETTING UP A
FAIRLY BROAD SW JET. AT THE SAME TIME THE RIDGE BUILDS OVER THE
WESTERN/CENTRAL MAINLAND.

.SURFACE...

A FEW SHOWERS WITH WEAK TROUGHING WAS EVIDENT OVER THE NORTH GULF.
SKIES ELSEWHERE ACROSS SOUTHCENTRAL WERE RELATIVELY CLEAR EXCEPT FOR
PERSISTENT STRATUS OVER THE COPPER RIVER BASIN. OUTFLOW WINDS
CONTINUED INTO THE AFTERNOON HOURS OVER THE NORTH GULF COAST AND
WESTERN KENAI PEN. OUT WEST...OVERRUNNING ASSOCIATED WITH A
FRONTAL TROUGH BROUGHT SNOW TO THE DELTA. THIS AFTERNOON...THE
COAST CAME UNDER THE INFLUENCE OF THE WARM SECTOR OF THE FRONT
AND SNOW RAPIDLY CHANGED OVER TO RAIN.


&&

.MODEL DISCUSSION...
MODELS ARE IN RELATIVELY GOOD AGREEMENT IN THE EAST THROUGH THE
SHORT TERM. OUT WEST...THE MODELS STRUGGLE WITH THE PLACEMENT AND
TIMING OF SURFACE FEATURES UNDER STRONG W TO SW FLOW ALOFT. THE
NAM AND EC ARE THE FASTER OF THE SOLUTIONS WITH THE GFS LAGGING
WELL BEHIND. IT SEEMS REASONABLE TO LEAN TOWARD THE FASTER MODEL
SOLUTIONS IN LIGHT OF THE INITIAL STRONG WESTERLY FLOW THEN
DEEPENING SW FLOW ALOFT OVER THE BERING SEA ON SUN.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...
OUTFLOW WINDS ACROSS THE NORTH/WEST GULF WILL SLOWLY DIMINISH
OVERNIGHT. THE FRONTAL TROUGH MOVING INTO COOK INLET FRI LOOKS
LIKE IT COULD HAVE A GREATER IMPACT THAN ORIGINALLY THOUGHT. THE
UPPER TROUGH ASSOCIATED WITH THIS FEATURE IS SOMEWHAT SHARPER AND
THE LOW AND MID LEVEL(850-700MB) FLOWS WILL LIKELY BE MORE SWLY.
THE RESULT COULD BE MORE WIDESPREAD PRECIPITATION ACROSS THE
REGION ON FRI. CURRENT THINKING IS THAT THE CHUGACH AND TALKEETNA
MOUNTAINS WILL LIKELY SEE MEASURABLE SNOWFALL ON FRI WITH LITTLE
MEASURABLE ACCUMULATIONS AT THE LOWER ELEVATIONS. MINOR
ACCUMULATIONS ARE ALSO POSSIBLE WITH SNOW SHOWERS OVER THE COPPER
RIVER BASIN. THE WARMER TEMPS WILL REMAIN ALONG THE COASTS AND
KENAI PEN...SO MOST OF THE PRECIPITATION IN THOSE AREAS WILL BE
RAIN OR A MIX. SHOWERY WEATHER WILL LIKELY CONTINUE INTO SAT WITH
SW FLOW ALOFT.

SOUTHWEST ALASKA...
A FAST MOVING FRONT WILL RAPIDLY TRACK FROM WEST TO EAST THROUGH
TONIGHT...SPREADING RAIN AND SNOW ACROSS THE REGION. WE WILL BE INCREASING
THE SNOW ACCUMULATIONS OVER THE KUSKOKWIM VALLEY AND INTERIOR
BRISTOL BAY TONIGHT WITH UPSLOPE CONDITIONS. COASTAL AREAS WILL
LIKELY SEE RAIN AND SNOW MIXES. THERE IS STILL SOME CONCERN FOR
POCKETS OF LIGHT FREEZING RAIN OVER INTERIOR BRISTOL BAY THIS
EVENING AS WARM AIR OVERRIDES POCKETS OF SHALLOW COLD SURFACE
AIR. WESTERLY ONSHORE FLOW WILL LINGER BEHIND THE FRONT...WITH
EXTENSIVE CLOUD COVER PERSISTING AFTER THE FRONT CLEARS.

BERING SEA/ALEUTIANS...
A FAST MOVING FRONT TRACKING ACROSS THE BERING WILL CLEAR THE
EASTERN BERING TONIGHT LEAVING LARGELY DRY CONDITIONS ACROSS MOST
OF THE ALEUTIANS AND BERING SEA HEADING INTO THE WEEKEND.

&&

.LONG TERM FORECAST...

MODEL CONSISTENCY...BOTH RUN TO RUN AND BETWEEN MODELS...REMAINS A
PROBLEM. OVERNIGHT OPERATIONAL RUNS RAPIDLY LOST AGREEMENT,
ALTHOUGH THE MORNING RUNS OF THE GFS AND EC WERE MUCH
CLOSER...ESPECIALLY WITH THE LOWS AND FRONTAL SYSTEMS MOVING
ACROSS THE BERING. RELIED HEAVILY ON THE DECISION OF WPC TO BEGIN
WITH A 00Z EC MEAN AS A STARTING POINT. THE GRIDS REPRESENT A
BLEND OF THE WPC GUIDANCE...AND WITH WINDS ENHANCED WITH THE 00Z
EC. THE CONFIDENCE REMAINS FAIRLY LOW...BUT THERE IS SOME HOPE
THAT THE MODELS WILL COME INTO BETTER AGREEMENT IN THE NEXT DAY OR
SO.

THE SOLUTION INVOLVES TWO FRONTAL SYSTEM AFFECTING THE BERING AND
WESTERN AK OVER THE EXTENDED PERIOD. THE INITIAL FRONT...FROM A
BERING STRAIT LOW...MOVES INTO WESTERN AK AND THE EASTERN
ALEUTIANS MON AND DISSIPATES RAPIDLY ON TUE. THE SECOND LOW AND
FRONT AFFECT THE WESTERN BERING TUE NIGHT WITH THE FRONT REACHING
WESTERN AK THU BEFORE DISSIPATING INLAND BY FRI. YET ANOTHER FRONT
MOVES INTO THE WESTERN BERING ON FRI.

WHILE THIS IS HAPPENING THE REMNANTS OF TROPICAL STORM ANA MOVE
INTO SE AK LATER ON MON AND FORM AN ELONGATED TROUGH ALONG THE
NORTHEASTERN GULF COAST THAT PERSISTS THROUGH WED. HIGH PRESSURE
THEN BUILDS OVER THE GULF ON THU.

SHOWERS WILL PERSIST OVER THE BERING AND ALEUTIANS ON MON..AND
THEN RAIN AND SNOW ARE EXPECTED TUE NIGHT BEFORE CHANGING TO SNOW
SHOWERS WED AND THU. MORE RAIN AND SNOW IS EXPECTED FRI. SOME GALES
WILL ACCOMPANY THE FRONTS AS THEY TRANSIT THE BERING.

SOUTHWEST AK WILL HAVE RAIN AND SNOW SHOWERS MON...DRYING ON
TUE...RAIN AND SNOW WED INTO THU...AND SHOWERS LATER ON THU INTO
FRI.

SOUTHCENTRAL WILL BE GENERALLY DRY INLAND THROUGH FRI WITH
SHOWERS ASSOCIATED WITH THE TROUGH ALONG THE COAST TUE AND WED.

&&

AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...MARINE WEATHER STATEMENT 138 150.
         GALE 150.
FIRE WEATHER...NONE.

$$

RMC/DS OCT 14



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