Small Craft Advisory 1034, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
443 PM AKST SUN DEC 27 2015

.ANALYSIS AND UPPER LEVELS...

A PATTERN SHIFT IS UNDERWAY FOR SOUTHERN ALASKA LED IN PART BY AN
UPPER-LEVEL RIDGE BUILDING OVER THE EASTERN PACIFIC OCEAN AND
GULF OF ALASKA. THIS SHIFTS THE STORM TRACK FROM REMAINING SOUTH
OF THE MAINLAND (AS HAS BEEN THE PATTERN RECENTLY) TO A MORE
MERIDIONAL STORM TRACK THAT TAKES STORMS FROM THE NORTHERN PACIFIC
NORTHWARD INTO SOUTHERN ALASKA.

UPSTREAM OF THE BUILDING RIDGE AXIS OVER THE GULF AND EASTERN
PACIFIC...A LONGWAVE TROUGH CONTINUES TO ROTATE THROUGH THE BERING
SEA AND NORTH PACIFIC. AN EMBEDDED VERTICALLY STACKED LOW JUST
NORTH OF ATKA IS BECOMING THE DOMINANT FEATURE OVER THE WESTERN
PORTION OF THE FORECAST AREA AS IT MOVES INTO THE SOUTHERN BERING
SEA. AN UPPER-LEVEL SHORTWAVE STRETCHES FROM THE CENTRAL BERING
OVER THE SOUTHWEST MAINLAND AND THROUGH THE CENTRAL GULF OF
ALASKA. BETWEEN THE LONGWAVE TROUGH AND RIDGE AXES...STRONG
SOUTHERLY FLOW AT THE UPPER AND LOWER LEVELS IS ADVECTING A
MOISTURE RICH SUBTROPICAL AIRMASS NORTHWARD TOWARDS THE ALASKA
PENINSULA AND THE SOUTHWESTERN GULF OF ALASKA. THE STRONG MOISTURE
AND TEMPERATURE ADVECTION IS AIDED BY A NEARLY MERIDIONAL JET
STREAK STRETCHING FROM NEAR 40N TO JUST SOUTH OF THE GULF OF
ALASKA.

AT THE SURFACE...THE UPPER-LOW OVER THE SOUTHERN BERING IS
REFLECTED AS A 967 MB SURFACE LOW JUST NORTH OF ATKA. THE
STRENGTHENING PRESSURE GRADIENT ASSOCIATED WITH THIS LOW IS
SUPPORTING STORM FORCE WINDS OVER AND SOUTH OF THE WESTERN AND
CENTRAL ALEUTIANS. A SURFACE FRONT LAGS SLIGHTLY BEHIND THE
UPPER-LEVEL TROUGH...STRETCHING FROM THE LOW IN THE SOUTHERN
BERING ACROSS THE SOUTHWEST MAINLAND COAST AND INTO THE
SOUTHWESTERN GULF OF ALASKA. SHOWERS OVER THE SOUTHWESTERN
MAINLAND ASSOCIATED WITH THE UPPER TROUGH AND SURFACE FRONT
CONTINUE THROUGH THE EARLY AFTERNOON. MIXED PRECIPITATION FALLING
OVERNIGHT HAS CHANGED OVER TO PRIMARILY RAIN IN DILLINGHAM AND
AREAS FURTHER INLAND. FURTHER NORTHWEST OVER THE KUSKOKWIM
DELTA...OFFSHORE DRAINAGE WINDS ARE KEEPING COOLER SURFACE
TEMPERATURES IN PLACE RESULTING IN A PRIMARY PRECIPITATION TYPE OF
SNOW FROM BETHEL NORTHWARD.

CONVECTIVE SHOWERS OVER THE NORTHERN GULF FORCED BY THE
AFOREMENTIONED UPPER WAVE AND A WEAK SURFACE TROUGH ARE
CONTINUING THROUGH THE LATE MORNING IN A MARGINALLY UNSTABLE
ENVIRONMENT. THESE RAIN AND SNOW SHOWERS ARE MOVING NORTHWESTWARD
WITH THE ONSHORE LOWER-LEVEL FLOW...RESULTING IN ENHANCED
PRECIPITATION AMOUNTS IN UPSLOPE AREAS ALONG THE NORTHERN GULF
COAST AND THE TYPICAL RAIN SHADOW IN THE LEE OF THE CHUGACH
MOUNTAINS. A TIGHTENING SURFACE PRESSURE GRADIENT BETWEEN HIGH
PRESSURE OVER NORTHWESTERN CANADA AND LOW PRESSURE OVER THE BERING
IS SUPPORTING GUSTY SOUTHEASTERLY WINDS THROUGH MUCH OF THE
FORECAST AREA FROM THE EASTERN ALEUTIANS THROUGH SOUTHCENTRAL
ALASKA. THESE CROSS-BARRIER WINDS ARE STRONGEST THROUGH FAVORED
GAPS IN THE ALEUTIAN AND ALASKA RANGES AND ALONG THE TURNAGAIN
ARM.

&&

.MODEL DISCUSSION...

THE SHORT TERM MODEL AGREEMENT REMAINS VERY GOOD BRINGING A TRIPLE
POINT LOW RAPIDLY NORTH ACROSS THE ALASKA PENINSULA TO THE NUNIVAK
ISLAND AREA BY TOMORROW MORNING. THIS RESULTS IN THE FRONT RAPIDLY
MOVING ACROSS KODIAK ISLAND TO THE NORTH GULF COAST MONDAY
MORNING. THE MODELS ARE IN GOOD AGREEMENT WITH RESPECT TO THE PUSH
OF WARM MOIST AIR INTO THE SOUTHERN MAINLAND AND HOLDING THE
SURFACE FREEZING LEVEL TO THE MIDDLE SUSITNA VALLEY SOUTH OF
CHULITNA. THERE IS SOME DISAGREEMENT ON THE EXTENT OF THE PUSH OF
WARMER AIR INTO THE COPPER RIVER BASIN OVERNIGHT TONIGHT AND
MONDAY. WE EXPECT THE WARM AIR TO ERODE THE LOW LEVEL COLD AIR
OVERNIGHT INTO THE MORNING. HOWEVER THE ANTICIPATED PUSH OF
MOISTURE OVER THE BASIN WILL LIKELY RESULT IN SOME ISOLATED AREAS
OF FREEZING RAIN BEFORE THE TEMPERATURES RISE ABOVE FREEZING. THE
MODELS MODELS CONTINUE TO STRUGGLE TO CONVERGE ON A COMMON
SOLUTION FOR THE NEXT INCOMING STORM LATE TUESDAY AND WEDNESDAY.
THE CURRENT MODEL SPREAD HAS A MODERATELY STRONG LOW POTENTIALLY
AS FAR NORTH AS THE PRIBILOF ISLANDS TO NUNIVAK ISLAND TO A STRONG
LOW IN WESTERN BRISTOL BAY TO A MODERATE LOW SOUTH OF THE ALASKA
PENINSULA TUESDAY NIGHT. HOWEVER THE OVERALL LOW COMPLEX IS MOVED
TO THE NORTH TO EAST BERING SEA BY WED AFTERNOON AND THE OVERALL
IMPACT REMAINS SIGNIFICANT WARMING AND AMPLE MOISTURE FLOWING OVER
THE SOUTHERN MAINLAND THROUGH MID WEEK.

&&

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

THE FIRST FRONT MOVING INLAND WILL INDUCE DANGEROUS EAST TO
SOUTHEAST WINDS THROUGH NOON ON MON FOR THE ENTIRE LENGTH OF
TURNAGAIN ARM...PORTAGE VALLEY...CORDOVA...AND HIGHER ELEVATIONS
AROUND ANCHORAGE. THESE STRONG WINDS WILL ALSO DOWNSLOPE AREAS
DOWNWIND OF THE KENAI AND CHUGACH MOUNTAINS...KEEPING THOSE
IMMEDIATE AREAS GENERALLY DRY. ALTHOUGH WARM AIR WILL ACCOMPANY
THIS FRONT AND SPREAD RAIN TO COASTAL LOCATIONS...TEMPERATURES
WILL REMAIN COLD ENOUGH FOR SNOW IN THE SUSITNA VALLEY WEST OF THE
PARKS HIGHWAY. WIND WILL ALSO COMBINE WITH SNOW TO PRODUCE
BLIZZARD CONDITIONS IN THOMPSON PASS. BOTH BLIZZARD AND SNOWFALL
WILL BEGIN LATER TONIGHT AND LAST THROUGH THE DAY ON MONDAY.

AFTER THE FRONT MOVES INLAND THE REGION WILL DRY OUT A BIT THROUGH
TUE BEFORE THE NEXT FRONT ENTERS THE GULF WITH ANOTHER ROUND OF
COASTAL RAIN AND INLAND SNOW FOR THE MIDDLE OF THE WEEK.

&&

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

PRECIPITATION TYPE WILL BE QUITE CHALLENGING OVER THE NEXT SEVERAL
DAYS AS TWO SEPARATE WARM FRONTS (ONE TONIGHT AND ANOTHER MONDAY
MORNING) WILL BRING VERY UNSEASONABLY WARM TEMPERATURES TO THE
REGION. AT THE SAME TIME...PRECIPITATION CHANCES WILL BE ON THE
RISE AS THE FIRST WARM FRONT APPROACHES SOUTHWEST ALASKA. IT LOOKS
LIKE THE BRISTOL BAY ZONE WILL WARM ENOUGH ABOVE FREEZING AND SFC
TO 500 MB HEIGHTS WILL BE INCREASING WHICH FAVORS A RAIN EVENT
ACROSS THIS AREA. FURTHER NORTH INTO THE KUSKOKWIM DELTA AND
LOWER KUSKOKWIM VALLEY...WARMER AIR WILL LAG A TOUCH AS
PRECIPITATION SPREADS NORTHWARD. THIS FAVOR SNOWS ACROSS THE TWO
REGIONS...WITH A TRANSITION TO RAIN FROM BETHEL SOUTH TOWARD
MORNING WHILE THE VALLEY SHOULD REMAIN ALL SNOW AS THE WARMER AIR
HAS A DIFFICULT TIME REPLACING THE COLDER AND MORE DENSE AIR.
MONDAY AND TUESDAY ARE MUCH MORE DIFFICULT IN REGARDS TO
FORECASTING PRECIPITATION TYPE AS THE TEMPERATURES IN THE LOWER
KUSKOKWIM VALLEY WARM ENOUGH TO FAVOR RAIN OVER SNOW (BUT JUST HOW
QUICKLY IS A LITTLE CHALLENGING). THE KUSKOKWIM DELTA WILL LARGELY
BE RAIN BUT OVERNIGHT TEMPERATURES WILL COOL ENOUGH TO FAVOR SNOW
AT TIMES...MAINLY NORTH OF BETHEL...AND PRODUCE SOME MINOR ACCUMULATIONS.

SEVERAL STRONG WIND EVENTS ARE EXPECTED THROUGH GAPS IN THE
ALEUTIAN RANGE NORTH OF KING SALMON OVER THE NEXT SEVERAL DAYS.
THE FIRST EVENT WILL BEGIN TO RAMP UP THIS EVENING AS A POTENT
WARM FRONT ALIGNS THE PRESSURE GRADIENT IN A FAVORABLE EAST TO
WEST ORIENTATION. IN ADDITION...STRONG UPPER LEVEL SUPPORT
ASSOCIATED WITH A NEGATIVELY TILTED TROUGH SHOULD AID IN THE
STRONGER WINDS MIXING DOWN. WIND GUSTS WILL LIKELY PEAK AROUND THE
65 MPH RANGE NORTH OF KING SALMON WHILE THE REST OF THE BRISTOL
BAY ZONE WILL SEE WIND IN THE 20 TO 40 MPH RANGE. THE SECOND EVENT
WILL UNFOLD STARTING TUESDAY MORNING INTO WEDNESDAY AS TWO LOWS IN
THE PROCESS OF PHASING MOVE EASTWARD TOWARD SOUTHWEST ALASKA AND A
RAPIDLY DEVELOPING LOW IN THE NORTH PACIFIC COMES SCREAMING
NORTHWARD TOWARD THE ALASKA PENINSULA. THE STRONG WINDS THIS TIME
WILL NOT BE CONFINED JUST TO THE GAPS OF THE ALASKA RANGE AS
INLAND LOCATIONS AND THE WESTERN CAPES SHOULD ALSO SEE SOME ACTION
FROM THE STRONG WINDS.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...

AN UNSETTLED WEATHER PATTERN IS EXPECTED TO CONTINUE FOR QUITE
SOME TIME AS A SERIES OF LOW PRESSURE SYSTEMS WILL PHASE TOGETHER
OVER THE NEXT 12 TO 18 HOURS. THIS WILL PRODUCE A BROAD AND
COMPLEX LOW THAT WILL ENCOMPASS MUCH OF THE BERING SEA THROUGH AT
LEAST TUESDAY. THIS WILL KEEP PRECIPITATION CHANCES QUITE HIGH AS
THE BROAD SFC AND UPPER LEVEL LOW WILL ENHANCE PRECIPITATION
FORMATION PROCESSES. IN ADDITION...NUMEROUS WEAK WAVES PUSHING
ACROSS THE BROAD TROUGH OVER THE BERING SEA WILL ACT TO ENHANCE
PRECIPITATION AT TIMES. MOSTLY RAIN WILL BE OBSERVED ACROSS THE
BERING SEA WITH THE EXCEPTION OF THE WESTERN ALEUTIANS WHERE COLD
AIR CONTINUES TO FILTER OUT OF SIBERIA AND A FEW INCHES OF SNOW
ACCUMULATION COULD BE SEEN OVER THE NEXT SEVERAL DAYS. SMALL CRAFT
TO GALE FORCE WINDS WILL BE QUITE COMMON THROUGH THE SHORT-TERM
WITH THE POSSIBILITY OF STORM FORCE WINDS LATE TUESDAY NIGHT SOUTH
OF THE ALASKA PENINSULA ASSOCIATED WITH A RAPIDLY DEEPENING LOW.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
WITH MASSIVE RIDGING TO THE EAST OF THE STATE MULTIPLE LOWS WILL
MOVE UP FROM THE NORTH PACIFIC TOWARDS THE WEST COAST. THESE
SYSTEMS ARE EXPECTED TO BE STRONG BRINGING IN LARGE AREAS OF
STRONG WINDS. THE FIRST SYSTEM LOOKS TO MOVE INTO THE EASTERN
BERING WEDNESDAY AND THE SECOND WILL MOVE NEAR THE ALASKA
PENINSULA ON FRIDAY. THIS SETUP WILL ALSO BRING WARM SOUTHERLY
FLOW TO MUCH OF SOUTHERN MAINLAND ALASKA THAT WILL WORK TO KEEP
TEMPERATURES ABOVE NORMALS. SOUTHWEST ALASKA AND THE NORTH GULF
COAST ARE EXPECTED TO SEE PRECIPITATION FOR MUCH OF THE WEEK INTO
THE WEEKEND IN THIS PATTERN BUT THE WARM AIR WILL HELP TO KEEP
IT AS RAIN FOR MANY LOCATIONS.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...HIGH WIND WARNING 101 125 135.
		 BLIZZARD WARNING 131.
		 WINTER WEATHER ADVISORY FOR SNOW 145.
MARINE...GALE 120 128 129 132 136 137 139 141 150-177 179-185.
   		 STORM 119 125 130 131.
		 HEAVY FREEZING SPRAY 185.
&&

SYNOPSIS AND MODEL DISCUSSION...RD
SOUTHCENTRAL ALASKA...DS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MC
LONG TERM...DK