Small Craft Advisory 23, NWS Anchorage, AK

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

.ANALYSIS AND UPPER LEVELS...
A HIGH AMPLITUDE UPPER LEVEL RIDGE AXIS EXTENDS FROM THE NORTHWEST
U.S. ACROSS BRITISH COLUMBIA AND THE YUKON TO THE NORTHERN MAINLAND
OF ALASKA WITH A CORRESPONDING NEGATIVELY TILTED TROUGH AXIS FROM
THE NORTHEAST PACIFIC THAT EXTENDS NORTHWEST TO A LARGE CLOSED
LOW OVER THE EASTERN BERING SEA. WARM AND MOIST TROPICAL AIR IS
BEING TRANSPORTED NORTHWARD TO THE SOUTHERN MAINLAND. THE INITIAL
ARRIVAL OF WARM AIR ALOFT WITH SUB-FREEZING SURFACE TEMPERATURES
RESULTED IN AREAS OF FREEZING RAIN ACROSS SOUTHCENTRAL ALASKA AND
SOUTHWEST ALASKA LAST NIGHT THROUGH THIS MORNING. FREEZING RAIN
ADVISORIES REMAIN IN EFFECT FOR MANY OF THESE AREAS. THE MOST
SIGNIFICANT ACCUMULATION OF ICE HAS BEEN IN AND NEAR BETHEL WHERE
AROUND ONE QUARTER OF AN INCH OF ICE ACCUMULATION WAS REPORTED.
MOST OTHER AREAS FOR WHICH REPORTS ARE AVAILABLE...ESPECIALLY OVER
SOUTHCENTRAL ALASKA...INDICATE TRACE AMOUNTS OF ICE ACCUMULATION.

A SURFACE LOW WHICH DEVELOPED OVER THE NORTHEAST PACIFIC YESTERDAY
HAS BOTTOMED OUT SOUTH OF KODIAK ISLAND. WINDS ASSOCIATED WITH THE
OCCLUDED FRONT CROSSING THE GULF HAVE PEAKED AND ARE BEGINNING TO
TREND DOWNWARD. RADAR IMAGERY SHOWS THE BULK OF PRECIP ALONG THE
GULF COAST AND PRINCE WILLIAM SOUND. STRONG CROSS BARRIER FLOW IS
LIMITING PRECIP IN THE LEE OF THE KENAI AND CHUGACH MOUNTAINS...BUT
NOT COMPLETELY DRYING THINGS OUT. THE PRESENCE OF A DEEP DOME OF
COLD AIR IS ALLOWING SOME PRECIP TO MAKE IT OVER THE MOUNTAINS...LARGELY
IN THE FROM OF LIGHT FREEZING RAIN OR FREEZING DRIZZLE. SATELLITE
IMAGERY SHOWS

MUCH OF SOUTHWEST ALASKA IS SEEING A DRYING TREND BEHIND ANOTHER
UPPER LEVEL WAVE...BRINGING AN END TO THE FREEZING RAIN THREAT.
MEANWHILE THE LOW OVER THE EASTERN BERING HAS BEGUN TO LIFT
NORTHWARD. THE PRIBILOF ISLANDS REMAIN JUST WEST OF THE LOW CENTER
RIGHT NEAR THE AXIS OF HEAVIEST PRECIP...SO SNOW WILL CONTINUE TO
FALL THROUGH THE DAY. THE ALEUTIANS REMAIN QUIET WITH A WEAK
SHORT-WAVE RIDGE SITTING OVERHEAD.

&&

.MODEL DISCUSSION...
MODELS SEEM TO GENERALLY SHOW THE SAME BASIC IDEA OVER THE NEXT
COUPLE DAYS AS THE ACTIVE WEATHER OF THE PAST COUPLE DAYS BEGINS
TO WIND DOWN OVER THE SOUTHERN MAINLAND. THE BIGGEST CHALLENGE
OVER THE NEXT 12 TO 24 HOURS WILL CONTINUE TO BE THE DETAILS OF
PRECIPITATION PLACEMENT AND PRECIPITATION TYPE. THUS...FORECAST
CONFIDENCE IS AVERAGE TO BELOW AVERAGE.

SIGNIFICANT MODEL SPREAD DEVELOPS ALONG THE ALEUTIANS BEGINNING
SATURDAY A AN UPPER TROUGH ELONGATES EASTWARD SOUTH OF THE CHAIN.
SOME SOLUTIONS INDICATE DEVELOPMENT OF MULTIPLE SURFACE LOWS
ALONG THIS TROUGH WHILE OTHERS INDICATE A SINGLE CONSOLIDATED LOW.
THE ECMWF SHOWS THE BEST RUN-TO-RUN CONSISTENCY WITH ITS DEPICTION
OF ONE LOW...SO WILL GO WITH THAT SOLUTION FOR THE TIME BEING.
FORECAST CONFIDENCE ALONG THE ALEUTIANS THIS WEEKEND IS LOW.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE UPPER LEVEL SHORT-WAVE OVER THE GULF THIS MORNING WILL CROSS
SOUTHCENTRAL ALASKA DURING THE AFTERNOON AND EXIT TO THE NORTH BY
EVENING. THERE DOESN'T APPEAR TO BE ANY SIGNIFICANT WAVES BEHIND
IT. MEANWHILE THE COLD AIRMASS IN PLACE OVER COOK INLET/SUSITNA
VALLEY CORRIDOR WILL CONTINUE TO ERODE...ALLOWING DOWNSLOPE DRYING
TO BECOME MORE EFFECTIVE. THUS...EXPECT THE PRECIP TO COME TO AN
END BY LATE THIS AFTERNOON ENDING THE THREAT OF FREEZING RAIN FOR
MUCH OF THE AREA. THE ONE LOCATION OF CONCERN FOR CONTINUED
FREEZING RAIN IS VALDEZ. ITS IS ALWAYS TOUGH TO SCOUR OUT ALL OF
THE COLD AIR THERE SO SURFACE TEMPERATURES WILL LIKELY REMAIN
BELOW FREEZING UNTIL SOME TIME TOMORROW. WITH LOW LEVEL SOUTHEAST
FLOW A LOT OF THE HEAVIER PRECIP WILL GET CAUGHT UP IN THE
MOUNTAINS SOUTH OF VALDEZ...SO FREEZING RAIN WILL BE LIGHT AND DO
NOT EXPECT MAJOR ICE ACCUMULATION.

AS WE HEAD INTO THE WEEKEND UPPER LEVEL FLOW WILL SPLIT WITH SOME
ENERGY EXITING TO THE NORTH-NORTHWEST UP THE WEST SIDE OF THE
RIDGE AND SOME HEADED EAST ACROSS THE GULF AND SOUTHEAST ALASKA.
THIS WILL RESULT IN A DRYING TREND ACROSS SOUTHCENTRAL AND THE
GULF. AS UPPER LEVEL FLOW BEGINS TO SHIFT ON FRIDAY WARM AIR
ADVECTION FROM THE PACIFIC WILL END...BUT THERE WON'T BE ANY
COLDER AIR MOVING IN. THUS...EXPECT FRIDAY WILL SEE THE WARMEST
SURFACE TEMPERATURES ACROSS THE REGION (ABOVE FREEZING IN A LOT
OF AREAS) AND THEN TEMPERATURES WILL BEGIN TO SLOWLY COOL AS
THROUGH THE WEEKEND AS PRECIP ENDS AND CLOUDS LIFT.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
PRECIP THIS EVENING WILL LARGELY BE CONFINED TO THE IMMEDIATE
COASTLINE...BUT IT WILL SPREAD BACK INLAND LATE TONIGHT THROUGH
FRIDAY AFTERNOON AS THE UPPER TROUGH LIFTS NORTHEASTWARD. WITH
TEMPERATURES NOW ABOVE FREEZING IN ALL OF BRISTOL BAY AND
TEMPERATURES COLD ENOUGH FOR ALL SNOW ALONG THE KUSKOKWIM DELTA
COAST FREEZING RAIN WILL NOT BE A PROBLEM THROUGH THE EVENING
HOURS. HOWEVER...AS PRECIP SPREAD INLAND ACROSS THE KUSKOKWIM
DELTA OVERNIGHT THE AIR MASS WILL STILL BE WARM ENOUGH TO SEE SOME
FREEZING RAIN FROM ABOUT BETHEL EASTWARD. COLDER AIR WILL ADVECT
IN WITH THE TROUGH...SO PRECIP SHOULD CHANGE TO ALL SNOW BEFORE
ENDING. WILL EXTEND THE FREEZING RAIN ADVISORY FOR BETHEL EASTWARD
THROUGH FRIDAY MORNING. THE KUSKOKWIM VALLEY MAY STILL BE WARM
ENOUGH ALOFT FOR FREEZING RAIN AS PRECIP MOVES INLAND FRIDAY...BUT
ITS VERY MARGINAL AND DO NOT EXPECT A WHOLE LOT OF QPF SO DO NOT
PLAN TO ISSUE AN ADVISORY AT THIS TIME.

CONDITIONS WILL DRY OUT ACROSS SOUTHWEST ALASKA FRIDAY NIGHT AND
SATURDAY AS THE UPPER TROUGH EXITS TO THE NORTH AND AN UPPER RIDGE
BUILDS IN BEHIND IT. THE COLD ADVECTION BEHIND THE TROUGH NEVER
REALLY PUSHED VERY FAR INLAND. THEREFORE EXPECT A COOLING TREND IN
TEMPERATURES...BUT MUCH OF THE REGION WILL REMAIN ABOVE NORMAL
THROUGH THE WEEKEND.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE LOW OVER THE EASTERN BERING WILL EXIT TO THE NORTH TONIGHT AND
FRIDAY WITH CONDITIONS DRYING OUT OVER THE PRIBILOF ISLANDS BY
LATE FRIDAY. QUIET CONDITIONS WILL THEN SETTLE IN OVER THE EASTERN
BERING AND ALASKA PENINSULA. MEANWHILE...MORE ACTIVE WEATHER WILL
SET UP ALONG THE ALEUTIANS THIS WEEKEND AS AN UPPER TROUGH SETS UP
OVER THE NORTH PACIFIC.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE WARMER AND MORE UNSETTLED CONDITIONS ASSOCIATED WITH THE
IMMINENT PATTERN CHANGE WILL PERSIST ACROSS MUCH OF THE REGION
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...WHILE A BROAD
UPPER TROUGH REMAINS OVER THE NORTH PACIFIC AND SOUTHERN BERING
SEA. BROAD SOUTHERLY FLOW WILL KEEP ABUNDANT SHOWER ACTIVITY
FOCUSED ALONG THE NORTHERN GULF COAST WITH PRECIPITATION
OCCASIONALLY SPREADING INLAND AS VARIOUS DISTURBANCES ROTATE
NORTHWARD THROUGH THE GULF. SHOWERS WILL ALSO REMAIN IN THE
FORECAST FOR MUCH OF THE BERING BUT WILL BE MOST PREVALENT ALONG
THE ALEUTIANS AS A DEEP NORTH PACIFIC LOW RETROGRADES WESTWARD
ALONG THE CHAIN ACCOMPANIED BY GUSTY EASTERLY WINDS.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...FREEZING RAIN ADVISORY 101 131.
MARINE...GALE 130 132.
FIRE WEATHER...NONE.

&&

JAN 15 SEB