Small Craft Advisory 20, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
518 AM AKST THU JAN 8 2015

.ANALYSIS AND UPPER LEVELS...

A HIGHLY AMPLIFIED PATTERN CONTINUES TO EXERT INCREASING INFLUENCE
ON MAINLAND ALASKA THIS MORNING AS A DEEP SPLIT TROUGH ACROSS THE
NORTHEAST PACIFIC INTERACTS WITH A SHARP NEGATIVE TILT RIDGE
EXTENDING INTO SOUTHERN ALASKA. SATELLITE IMAGERY DEPICTS A
STREAM OF HIGH CLOUD TOPS ASSOCIATED WITH AN ENHANCED ZONE OF WARM
AIR ADVECTION PUSHING INTO NORTHERN ALASKA. THE LOW LEVEL
SUBTROPICAL FRONT IS MOVING TOWARD THE GULF COAST...WITH RADAR
BEGINNING TO SCAN MORE VIGOROUS SHOWERS MOVING NORTHWARD. THE
FRONT IS ALSO RAMPING UP NORTHEAST WINDS ACROSS THE GULF COAST
INTO THE BARREN ISLANDS WITH STORM FORCE WINDS. A SECONDARY
UPPER/SURFACE LOW OVER THE EASTERN BERING HAS ALREADY SPREAD
RAIN...FREEZING RAIN...AND SNOW INTO SOUTHWEST ALASKA. THESE SPLIT
LOWS WILL MERGE AND INTERACT WITH ONE ANOTHER TODAY...WITH THE
SECOND SURGE OF WARM AIR ALOFT TRACKING THROUGH MOST OF
SOUTHCENTRAL. THIS WILL ALLOW FOR WIDESPREAD AREAS OF RAIN ACROSS
COASTAL LOCATIONS...WITH POSSIBLE FREEZING RAIN ACROSS INLAND
AREAS WHERE DEEP POCKETS OF ARCTIC AIR HAVE SETTLED. EVENTUALLY
THE NORTH PACIFIC LOW WILL WEAKEN AND TRACK EAST...THEREBY CUTTING
OFF THE MOISTURE AND WARM AIR CONVEYOR BELT INTO SOUTHERN ALASKA.
CLOUDS AND SHOWERS WILL LINGER ACROSS SOUTHERN ALASKA HEADING INTO
THE WEEKEND AS WEAK RIDGING TAKES HOLD.

THIS BRIEF REPRIEVE WILL BE REPLACED BY A POWERFUL AND LARGE 200
KT COUPLED POLAR/SUBTROPICAL JET STREAM ACROSS THE NORTH
PACIFIC...WHICH WILL EVENTUALLY AMPLIFY NUMEROUS POTENTIAL STRONG
LOWS AS THEY MOVE INTO THE GULF OF ALASKA EARLY NEXT WEEK. THIS
PATTERN WILL YIELD MORE POTENTIAL CHINOOK WARM UPS ACROSS MUCH OF
SOUTHERN ALASKA. THE YEAR WITHOUT A WINTER LOOKS TO CONTINUE AS
SIGNIFICANT WARM ANOMALIES PERSIST ACROSS THE REGION.

&&

.MODEL DISCUSSION...

THE NUMERICAL MODELS ARE IN EXCELLENT AGREEMENT WITH THE GENERAL
SYNOPTIC PATTERN HEADING INTO THE WEEKEND...AND GOOD AGREEMENT
WITH THE LARGE SCALE PATTERN INTO THE MIDDLE OF NEXT WEEK.
HOWEVER...THEY DO VARY IN KEY AREAS SUCH AS PRECIPITATION TIMING
AND DISTRIBUTION. THESE CHALLENGES ARE LEADING TO A LOWER OVERALL
FORECAST CONFIDENCE TODAY AND TONIGHT...WITH INCREASING CONFIDENCE
HEADING INTO THE WEEKEND AS THE WEATHER PATTERN BECOMES MORE
TRANQUIL.

THE BIGGEST CHALLENGES TODAY REVOLVE AROUND THE THERMAL PROFILE
ACROSS VALDEZ AND THE AMOUNT OF PRECIPITATION EXPECTED TO DEVELOP
ACROSS INLAND LOCATIONS OVER SOUTHCENTRAL. THE 12Z UPPER AIR
SOUNDING OVER ANCHORAGE FEATURES TWO WELL DEFINED DRY
LAYERS...WITH THE LOWEST LEVEL DRY LAYER FEATURING A NORTHEAST
WIND DIRECTION. CROSS BARRIER FLOW WILL BE ON THE INCREASE AS THE
FRONT APPROACHES...AND MODELS ARE BOTH TOO FAST AND TOO WET WITH
CURRENT PRECIPITATION TRENDS AS OF 12Z THIS MORNING. JUST HOW MUCH
FREEZING RAIN FALLS FROM ANCHORAGE NORTH IS MORE UNCERTAIN GIVEN
THE DRY AIR ADVECTION FROM THE MAT VALLEY...AND GENERAL DOWNSLOPE
DRYING. THAT SAID...EVEN A BRIEF LIGHT SHOWER MAY BE ENOUGH TO
CREATE SLICK ROADS GIVEN THE RECENT ARCTIC AIR MASS. THERE IS
MORE CONFIDENCE IN SATURATION FROM WASILLA WESTWARD ALONG THE
PARKS HIGHWAY...AS WELL AS ALONG THE WESTERN KENAI PENINSULA.

ELSEWHERE...THERMAL PROFILES AROUND VALDEZ WILL BE QUITE
CHALLENGING AS STRONG WARM AIR ADVECTION PUSHES FREEZING LEVELS
QUITE HIGH. LEFTOVER COLD ARCTIC AIR IN THE LOW LEVELS WOULD
SUGGEST FREEZING RAIN IN TOWN EVEN THOUGH SUCH OCCURRENCES ARE
QUITE RARE. FOR NOW...WILL MENTION THE THREAT FOR SNOW
ACCUMULATIONS CHANGING TO FREEZING RAIN IN TOWN...WITH SNOW
POSSIBLY MIXING WITH RAIN AND FREEZING RAIN LATER TODAY ACROSS
THE PASS.

OUT ACROSS SOUTHWEST ALASKA AND THE BERING...MODEL DISCREPANCIES
ARE SMALL...AND CONFIDENCE IS MODERATE TO HIGH.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (THURSDAY AND FRIDAY)...
A FRONT ASSOCIATED WITH A LOW PRESSURE SYSTEM IN THE SOUTHWEST
GULF WILL PUSH INTO SOUTH CENTRAL ALASKA TODAY. TEMPERATURES AT
THE MID AND UPPER LEVELS ARE QUITE WARM WITH THIS SYSTEM...WHILE
AIR AT THE SURFACE IS QUITE COLD. THIS WILL CREATE WIDESPREAD
CHANCES OF FREEZING RAIN TODAY. THE LOWER LEVELS WILL WARM LATER
IN THE DAY...AND STRONG SOUTHEAST WINDS ALOFT WILL CREATE A DOWN-
SLOPE RAIN SHADOW FOR MOST INLAND AREAS BEGINNING IN THE AFTERNOON
AND CONTINUING INTO FRIDAY. BY FRIDAY NIGHT THE LOW AND THE FRONT
WILL HAVE WEAKEN CONSIDERABLY WITH JUST SOME SCATTERED
SHOWERS...MAINLY COASTAL AREAS.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (THURSDAY AND FRIDAY)...

AS THE LOW OVER THE EASTERN BERING MOVES NORTH...WARMER AIR WILL
CONTINUE TO SPREAD ACROSS THE BRISTOL BAY ZONE...WHERE RAIN WILL
REPLACE RESIDUAL AREAS OF FREEZING RAIN NORTH OF DILLINGHAM. AREAS
OF FREEZING RAIN WILL PERSIST OVER THE EASTERN PORTION OF THE
KUSKOKWIM DELTA AND WILL ENTER THE LOWER KUSKOKWIM FROM SLEETMUTE
WEST. SEVERAL INCHES OF SNOWFALL ARE EXPECTED WEST OF BETHEL IN
THE COLDER AIR...WITH SOME BLOWING SNOW POSSIBLE ALONG THE COAST.
BY FRIDAY FREEZING RAIN WILL BE OVER AS A DEEP LAYER OF COLDER AIR
FROM THE BERING BRINGS SNOW SHOWERS TO THE KUSKOKWIM. THE BRISTOL
BAY ZONE WILL KEEP RAIN SHOWERS IN THE AREA AS WARM AIR PERSISTS
NORTHWEST OF THE ALEUTIAN RANGE.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (THURSDAY AND FRIDAY)...

EXCEPT FOR SNOW OVER THE PRIBILOFS ASSOCIATED WITH THE PASSAGE OF
THE EASTERN BERING LOW...THE REST OF THE BERING AND ALEUTIANS WILL
BE FAIRLY DRY WITH ONLY A FEW RAIN OR SNOW SHOWERS THROUGH THE END
OF THE WORK WEEK.

&&

.LONG TERM FORECAST (SATURDAY THROUGH THURSDAY)...
A WARMER AND MORE UNSETTLED PATTERN IS IN STORE FOR SOUTHCENTRAL
ALASKA FROM THIS WEEKEND INTO THE LATTER HALF OF NEXT WEEK AS A
LONGWAVE RIDGE REMAINS ENTRENCHED OVER THE WEST COAST OF NORTH
AMERICA AND EXTENDS OVER THE INTERIOR MAINLAND TO NEAR THE BERING
STRAIT. THIS WILL ALLOW PERSISTENT SOUTHERLY FLOW TO BECOME
ESTABLISHED OVER THE GULF...YIELDING ABOVE NORMAL TEMPERATURES AS
VARIOUS DISTURBANCES ROTATE NORTHWARD TOWARDS THE MAINLAND. THE
DETAILS OF THESE FEATURES REMAIN DIFFICULT TO NAIL DOWN AT THIS
POINT IN TIME...BUT SHOWER ACTIVITY WILL GENERALLY BE FOCUSED
ALONG THE GULF COAST AND OCCASIONALLY SPREAD INLAND AS
DISTURBANCES MOVE THROUGH. IN BETWEEN THESE DISTURBANCES WILL BE
A SHORT LIVED PERIODS OF CLEARING SKIES WITH CONTINUED WARM
TEMPERATURES AS RIDGING WILL REMAIN IN THE VICINITY OF THE
SOUTHERN MAINLAND THROUGH THE MIDDLE OF NEXT WEEK.

WARM AND UNSETTLED WEATHER WILL ALSO DOMINATE THE BERING SEA AND
ALEUTIANS THIS WEEKEND AS A NORTH PACIFIC LOW BRINGS GALE FORCE
WINDS AND RAIN TO MUCH OF THE AREA. THE BROAD LONGWAVE TROUGH WILL
THEN BECOME NEARLY STATIONARY AND STRETCHING FROM THE NORTH
PACIFIC INTO THE CENTRAL BRING. THIS PATTERN WILL KEEP SHOWERY
CONDITIONS OVER THE REGION THROUGH MUCH OF NEXT WEEK.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...BLIZZARD WARNING 131
         FREEZING RAIN ADVISORY 101 111 121 145 152 155 161.
MARINE...STORM 130 131
         GALE 119 120 127 132 137 138 139.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...JA
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DS
LONG TERM...DEK

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