Area Forecast Discussion
Issued by NWS Anchorage, AK

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35
000
FXAK68 PAFC 290134 CCA
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE ANCHORAGE AK
434 PM AKST FRI NOV 28 2014

.ANALYSIS AND UPPER LEVELS...
A LOOK AT THE MORNING WEATHER MAP SHOWS THE REMNANTS OF THE BERING
SEA LOW CONTINUING TO DRIFT NORTHWARD TOWARD FAR EASTERN RUSSIA.
WIDESPREAD INSTABILITY SHOWERS ACROSS MUCH OF THE REST OF THE
BERING SEA ARE GENERATING SCATTERED RAIN SHOWERS ACROSS A WIDE
SWATH OF THE REGION. THE MID LEVEL RIDGING THAT HAS HELPED
REINFORCE STRONG LOW-LEVEL TEMPERATURE INVERSIONS AND GENERATED FOG/STRATUS
PROBLEMS ACROSS SOUTHCENTRAL HAS NOW SHIFTED EASTWARD TOWARD THE
ALCAN BORDER. AS A RESULT...DEEP SOUTHERLY TO SOUTHWESTERLY FLOW
HAS MOVED IN TO ALL OF SOUTHERN ALASKA...WITH MOISTURE STREAMING
NORTHWARD ALONG THE OLD FRONTAL BOUNDARY THAT MADE LANDFALL OVER
THE SOUTHWEST MAINLAND YESTERDAY. A PRECIP SHIELD IS MOVING INTO
EASTERN BRISTOL BAY NOW AND WILL SOON BEGIN TO SPREAD UP COOK
INLET TOWARD ANCHORAGE AND THE MAT-SU TONIGHT. MEANWHILE...INCREASED
CLOUD COVER AHEAD OF THIS FEATURE HAS HELPED UPPER COOK INLET
BREAK OUT OF THE THICK LOW CLOUDINESS. THE ONE EXCEPTION IS LOW
CLOUDINESS THAT WILL PERSIST THROUGHOUT THE DAY AND LIKELY INTO
TONIGHT ACROSS THE COPPER RIVER BASIN.

&&

.MODEL DISCUSSION...
THE MODELS REMAIN IN VERY GOOD OVERALL AGREEMENT THROUGH THE FIRST
SEVERAL DAYS OF THE FORECAST. THE UPPER TROUGH MOVING THROUGH
SOUTHCENTRAL TONIGHT WILL GENERATE A FEW INCHES OF SNOW FOR MOST
PLACES...THOUGH ACCUMULATIONS WILL BE LIMITED BY THE FAST SPEED
WITH WHICH THE DYNAMIC LIFT MOVES THROUGH THE AREA. SOME UPSLOPE
ENHANCEMENT IS LIKELY ACROSS THE ANCHORAGE HILLSIDE AND THE
MATANUSKA VALLEY AS LOW-LEVEL WINDS TURN MORE SOUTHWESTERLY
TOMORROW MORNING. THE NAM CONTINUES TO BE THE MOST AGGRESSIVE WITH
PRECIPITATION AMOUNTS ACROSS THE AREA...AND IS LIKELY ATTEMPTING
TO SIMULATE THE AFOREMENTIONED OROGRAPHIC ENHANCEMENT. THE
AFTERNOON FORECAST WILL REPRESENT A MIDDLE-GROUND SOLUTION BETWEEN
THE NAM (MORE SNOW) AND GFS (LESS SNOW) SOLUTIONS...WITH A
SLIGHTLY HEAVIER WEIGHTING TOWARD THE NAM.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...

AN UPPER LEVEL SHORTWAVE TROUGH WILL MOVE THROUGH SOUTHCENTRAL
ALASKA BY SATURDAY WITH A WEAK SURFACE LOW POSITIONED JUST
OFFSHORE OF THE EASTERN KENAI. SNOWFALL WILL BEGIN TOWARDS EARLY
SATURDAY MORNING BEFORE DIMINISHING BY SATURDAY EVENING AS THE LOW
PRESSURE TRACKS TOWARDS WITH THE TROUGH PASSAGE. THIS WILL BRING
WIDESPREAD SNOWFALL AMOUNTS RANGING FROM 2 TO 4 INCHES THROUGH
THE ANCHORAGE BOWL EXTENDING UP INTO THE MATSU VALLEY. THE
SOUTHERLY FLOW COMBINED WITH UPSLOPE TOPOGRAPHY WILL PRODUCE THE
HEAVIEST SNOWFALL AMOUNTS. GUSTY WESTERLY WINDS WILL COINCIDE WITH THE
PRESSURE GRADIENT INCREASING WITH THE TROUGH PASSAGE THROUGH
WHITTIER...THE BARREN ISLANDS...AND HIGHER ELEVATIONS. AS THE
TROUGH MOVES EASTWARD THE WINDS WILL DIMINISH BY EARLY SUNDAY
MORNING AS AN UPPER LEVEL RIDGE OF HIGH PRESSURE MOVES INTO THE
REGION. BY SUNDAY MORNING...THE PRESSURE GRADIENT WILL STRENGTHEN
THROUGH THOMPSON PASS AND ALONG THE CHUGACH MOUNTAINS RESULTING
IN GUSTY NORTHERLY WINDS BEFORE DIMINISHING BY SUNDAY NIGHT.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
SURFACE RIDGING ACROSS THE SOUTHWEST MAINLAND BREAKS DOWN TODAY
AS A COMBINATION OF WEAK TROUGHING WORKS INLAND FROM THE KUSKOKWIM
DELTA AND ANOTHER SURFACE LOW MOVES A FRONT UP FROM THE NORTH
PACIFIC. ISOLATED TO SCATTERED SNOW SHOWERS WILL BECOME NUMEROUS
IN THE AFTERNOON ACROSS THE KUSKOKWIM AND BRISTOL BAY. A WARMER
AIR MASS ALONG AND SOUTH OF KING SALMON WILL SUPPORT
PRECIPITATION TO FALL AS RAIN...WITH SNOW MIXED AT TIMES.
PRECIPITATION WILL DIMINISH ON SATURDAY FROM WEST TO EAST AS
RIDGING BUILDS BACK INTO THE SOUTHWEST FROM THE BERING.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
LOW PRESSURE OVER THE NORTHERN BERING PUSHES A SHORTWAVE OVER THE
EASTERN BERING TODAY. PRECIPITATION DEVELOPS ALONG THIS WAVE AS RAIN
WITH SNOW MIXED NORTH OF THE PRIBILOF ISLANDS. THE NEXT
SIGNIFICANT FRONT MOVES INTO THE WESTERN ALEUTIANS BY SATURDAY
MORNING BRINGING HEAVY RAIN AND GUSTY GALES WINDS. THE LOW CENTER
DRIVING THE FRONT MOVES ACROSS THE CENTRAL ALEUTIANS LATE SATURDAY
PUSHING THE FRONTAL BOUNDARY THROUGH MUCH OF THE BERING BY
SATURDAY NIGHT.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7...MONDAY THROUGH
FRIDAY)...THIS TIME FRAME WILL START FEATURING A STRENGTHENING LOW
IN THE BERING SEA AND A FAST MOVING SHORTWAVE RIDGE CENTERED OVER
SOUTH CENTRAL. THE BERING SEA LOW WILL BE CENTERED WAY OUT
WEST...CLOSER TO RUSSIA IN FACT...BUT ITS EFFECTS WILL BE FELT
ACROSS THE ENTIRE AREA. FIRST...IT WILL DRIVE A HEALTHY AMOUNT OF
SUB-TROPICAL MOISTURE TOWARDS THE WEST COAST TO START THE WEEK.
THIS MOISTURE WILL COINCIDE WITH A WARM FRONT THAT WILL BRING
850MB TEMPERATURES UP ABOUT 10C FROM SUNDAY INTO MONDAY. THIS
COULD ALSO SPELL A TRANSITION FROM SNOW TO RAIN FOR PLACES FROM
KING SALMON TO BETHEL...POSSIBLY EVEN SOME FREEZING RAIN.

FOR SOUTH CENTRAL...EXPECT SOME PATCHY FOG TO KICK OFF THE WEEK
AS THE SHORTWAVE RIDGE DRIFTS OFF TO THE EAST. THEN A SLOW PATTERN
CHANGE WILL ENSUE. THE WARM FRONT FROM THE WEST COAST WILL FALL
APART SOMEWHAT AS IT MOVES INLAND...BUT IT STILL DOES PUSH PLENTY
OF MOISTURE INTO THE AREA. SEVERAL WEAK UPPER LEVEL WAVES MOVING
FROM THE NORTH PACIFIC WILL TAKE ADVANTAGE OF THIS MOISTURE AND
SHOULD BRING SOME PRECIPITATION FROM KODIAK UP THE COOK INLET. AT
THIS POINT...IT DOES LOOK LIKE THE ATMOSPHERE WILL BE COLD ENOUGH
TO KEEP MOST OF THIS SNOW. BUT AS SOUTH TO SOUTHWEST FLOW PERSISTS
THROUGH THE WEEK...WE WILL NEED TO MONITOR THE CHANCE FOR SOME
MIXED PRECIPITATION.

MODELS HAVE TRENDED SLIGHTLY STRONGER WITH THE PARENT LOW CENTER
OUT WEST. THIS IS LIKELY DUE TO SOME RATHER IMPRESSIVE PHASING
THAT SHOULD OCCUR WITH COLD AIR DIGGING INTO THE BACKSIDE OF THE
TROUGH EARLY MONDAY. THUS...WE HAVE INCREASED THE WINDS OVER SOME
OF THE WESTERN ALEUTIANS AND NOW HAVE A SIZABLE SWATH OF STORM
FORCE WINDS OVER THE MARINE ZONES. THAT SAID...WITH A SLIGHTLY
STRONGER/DEEPER SYSTEM...WE HAVE ALSO PUSHED ITS POSITION SLIGHTLY
FURTHER TOWARDS THE COLDEST AIR (WEST). THE NET DOWNSTREAM-EFFECT
OF THIS IS THAT THE WARM FRONT COULD BE A LITTLE SLOWER TO REACH
THE MAINLAND AND PRECIPITATION MIGHT NOT PENETRATE QUITE AS FAR
INLAND.

MODELS CONTINUE TO STRUGGLE WITH THE EVOLUTION OF THE PATTERN MIDDLE-
END OF THE WEEK...SO CONFIDENCE IS THIS PORTION OF THE FORECAST
REMAINS FAIRLY LOW. THERE IS SOME BETTER AGREEMENT THOUGH THAT THE
LOW PRESSURE FROM THE BERING WILL MOVE SOUTH OF KODIAK ISLAND AND
INTO THE GULF OF AK. THIS SHOULD KEEP OUR PRECIPITATION CHANCES
HIGHER THAN THEY HAVE BEEN FOR THE PAST FEW WEEKS.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALES 130 131 170 172 173 174 175 176 177 178 179 185 411
               412 413 414.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...AD
SOUTHCENTRAL ALASKA...PD
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...ML
LONG TERM...MO


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.