Small Craft Advisory 1020, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
503 AM AKST TUE DEC 22 2015

.ANALYSIS AND UPPER LEVELS...
FOG CONTINUES TO BE THE PRIMARY WEATHER CONCERN ACROSS MUCH OF
SOUTHERN MAINLAND ALASKA THROUGH THE OVERNIGHT PERIOD AND INTO
THE MORNING HOURS. OVER PARTS OF SOUTHCENTRAL...SOME PATCHY FOG
CONTINUES TO LINGER AS THESE AREAS REMAIN SATURATED AND UNDER A
FAIRLY STRONG SURFACE INVERSION. AS THE LOW OVER THE GULF
CONTINUES TO PUSH EASTWARD THIS MORNING...WINDS WILL SHIFT TO THE
NORTHWEST AND BEGIN A COOLING AND DRYING TREND OVER THE AREA. OUT
WEST...PATCHY FOG INITIATED BY THE SAME PHENOMENA DESCRIBED ABOVE
PERSISTS ACROSS THE INTERIOR PORTIONS OF THE KUSKOKWIM DELTA AND
BRISTOL BAY. A WEAK FRONT HAS STARTED TO WORK ITS WAY INTO THE
SOUTHWEST COAST FROM THE EASTERN BERING...WHICH WILL BEGIN TO
SPREAD SNOW INLAND THROUGH THIS MORNING. CURRENT SATELLITE IMAGERY
SHOWS THE STRONG AREA OF INSTABILITY OVER MUCH OF THE ALEUTIANS
AND BERING SEA... WHICH HAS RESULTED IN SOME GUSTY WESTERLY WINDS
AND INSTABILITY SHOWERS. CURRENT IR SATELLITE IMAGERY IS ALSO
SHOWING A LOW PRESSURE CIRCULATION DEVELOPING OVER THE FAR WESTERN
ALEUTIANS.

&&

.MODEL DISCUSSION...
OVERALL THE MODELS REMAIN IN GOOD SYNOPTIC AGREEMENT REGARDING
THE MOVEMENT AND INTENSITY OF THE MAJOR FEATURES IMPACTING THE
AREA OF RESPONSIBILITY. IN THE UPPER LEVELS...THE PRIMARY PACIFIC
JET STREAK REMAINS WELL SOUTH OF THE AREA...KEEPING MOST OF THE
STRONGER STORMS HEADING INTO THE PACIFIC NORTHWEST. A DIGGING
TROUGH OVER THE WESTERN BERING TUESDAY NIGHT HELPS AMPLIFY A RIDGE
OVER THE EASTERN BERING BY WEDNESDAY AFTERNOON...WITH SOME MINOR
DIFFERENCES IN THE INTENSITY OF THE JET STREAK THAT FORMS
DOWNSTREAM OF THE RIDGE OVER SOUTHWEST ALASKA. MODELS HAVE COME
INTO BETTER AGREEMENT REGARDING A NORTH PACIFIC LOW MOVING INTO
THE WESTERN AND CENTRAL ALEUTIANS WEDNESDAY MORNING...HOWEVER...
THEY CONTINUE TO STRUGGLE WITH THE TRACK AND STRENGTH OF THIS
SYSTEM AS IT CROSSES INTO THE BERING SEA WEDNESDAY EVENING. THE
NAM AND EC WERE THE MODELS OF CHOICE CONCERNING THE ABOVE
MENTIONED DIFFERENCES...WITH THE GFS BEING THE SLIGHTLY FASTER AND
WEAKER SOLUTION. CONFIDENCE IN THE FORECAST IS HIGH CONSIDERING
LOW MODEL SPREAD.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE WEAK UPPER TROUGH OVER SOUTH CENTRAL ALASKA WILL MOVE EAST
INTO CANADA THIS AFTERNOON. SOME SHOWERS WILL CONTINUE TODAY FROM
PRINCE WILLIAM SOUND EAST AND OVER THE COPPER RIVER BASIN THEN END
THIS EVENING AS THE TROUGH EXITS THE AREA. FOR MUCH OF SOUTH
CENTRAL ALASKA...SOME LOW/MID CLOUDS WILL CONTINUE THROUGH
WEDNESDAY AS THE UPPER FLOW IS WEAK BEHIND THIS TROUGH. LOW LEVEL
OFFSHORE FLOW WILL STRENGTHEN SLIGHTLY THROUGH WEDNESDAY...KEEPING
THE WINDS GOING AT SEWARD AND WHITTIER. THESE WINDS WILL FURTHER
INCREASE WEDNESDAY NIGHT AS AN UPPER LEVEL RIDGE BUILDS IN FROM
THE WEST AHEAD OF A STRONG STORM OVER THE BERING SEA. THIS RIDGE
WILL ALSO HELP TO CLEAR SKIES OVER INLAND SOUTH CENTRAL.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
A WEAK FRONT WILL PUSH ONSHORE THE MAINLAND TODAY BRINGING AREAS
OF LIGHT SNOW TO THE KUSKOKWIM DELTA AND GREATER BRISTOL BAY. THE
FRONT WILL MOVE INTO THE LOWER KUSKOKWIM VALLEY BRINGING A CHANCE
OF LIGHT SNOW TO THAT AREA AS WELL. BEHIND THE FRONT...A SHOWERY
REGIME WILL MOVE IN WITH THE BEST CHANCE FOR SHOWERS BEING THE
BRISTOL BAY AREA. ANY LINGERING SHOWERS WILL EXIT ON
WEDNESDAY...THEN A FRONT APPROACHES FROM THE SOUTH ON WEDNESDAY
NIGHT WHICH WILL BRING A CHANCE OF SNOW TO MAINLY COASTAL AREAS OF
THE MAINLAND WITH A CHANCE OF BLOWING SNOW AS WELL.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE CONVECTIVE SNOW SHOWER PATTERN WILL CONTINUE THROUGH THE DAY
TODAY BEFORE TAPERING OFF FROM WEST TO EAST DURING THE EVENING AND
OVERNIGHT HOURS. OVERNIGHT...A FRONT ASSOCIATED WITH A DEVELOPING
NORTH PACIFIC LOW PRESSURE WILL SPREAD FIRST SNOW...THEN RAIN OVER
THE CENTRAL ALEUTIANS. WITH A STRONG JET OVERHEAD...AND A DRY SLOT
PUNCHING IN BEHIND THE FRONT THERE IS AMPLE POTENTIAL FOR HIGH
WINDS TO MIX DOWN FROM ABOVE THE SURFACE. A HIGH WIND WATCH HAS
BEEN ISSUED FOR THE CENTRAL ALEUTIANS FOR WEDNESDAY. THE SAME
FRONT WILL SPREAD SNOW CHANGING TO RAIN FOR THE DUTCH HARBOR...THE
PRIBILOF ISLANDS...AND ALASKA PENINSULA. BEFORE SNOW CHANGES TO
RAIN ON THE PRIBILOF ISLANDS...GUSTY EASTERLY WINDS WILL REDUCE
VISIBILITY IN FALLING AND BLOWING SNOW.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...

MODELS ARE COMING INTO SOMEWHAT BETTER AGREEMENT WITH RESPECT TO
THE MIDWEEK BERING STORM...HOWEVER THERE IS STILL SOME
DISAGREEMENT ABOUT HOW FAR NORTH THE SURFACE LOW WILL TRACK
WEDNESDAY NIGHT BEFORE IT STARTS EAST ON THURSDAY. WITH THE VERY
STRONG JET STREAM TO THE SOUTH AM STILL FAVORING THE MORE SOUTHERN
SOLUTIONS WHICH WHICH WOULD BRING THE LOW ROUGHLY 100 TO 150 NM
INTO THE BERING BEFORE IT GETS CAUGHT UP IN THE BROADER WESTERLY
FLOW AND SWINGS EAST.

THE NEXT SIGNIFICANT POINT OF UNCERTAINTY CONCERNS THE FATE OF THE
NEXT ITERATION OF THIS LOW IN THE FRIDAY AND SATURDAY TIME PERIOD.
THE PREFERRED EC CONTINUES TO DEPICT A NORTH PACIFIC TROUGH
SWINGING AROUND THE SOUTH SIDE OF THE LARGE UPPER LOW...WHICH SPINS
UP ANOTHER STRONG SURFACE LOW WHICH LIFTS NORTH INTO THE SOUTHERN
BERING TO THE NORTH OF THE WESTERN TIP OF THE ALASKA PENINSULA
LATE THURSDAY NIGHT/EARLY FRIDAY MORNING. THIS SOLUTION IS CONSISTENT
WITH THE UPPER LEVEL JET LOCATION AND STRENGTH...WITH LAST
EVENING'S GFS AND GEM MODELS NOW TRENDING SIMILAR TO THE EC. ALSO
WITH ALL THE ENERGY AND COLD AIR ASSOCIATED WITH THE TROUGH
SWINGING THROUGH THE NORTH PACIFIC ON THURSDAY AM FAVORING THE
IDEA OF THE WAVE RAPIDLY DEVELOPING INTO A CLOSED LOW THURSDAY
NIGHT.

IMPACT WISE...THE SOLUTION WITH THE STRONG SURFACE LOW SWINGING
ACROSS THE TIP OF THE ALASKA PENINSULA WILL BRING RATHER WINDY
CONDITIONS TO MUCH OF THE BERING REGION...AND MAY RESULT IN FUTURE
HIGH WIND WATCHES AND WARNINGS FOR LATE THURSDAY INTO FRIDAY FOR
THE WESTERN AND CENTRAL ALEUTIANS. THIS WILL ALSO HELP SUSTAIN THE
NORTHERLY OUTFLOW GAP WINDS IN SOUTHCENTRAL ALASKA.
HOWEVER...HEAVIER PRECIPITATION IS LIKELY TO BE LIMITED TO JUST
THE EASTERN BERING AND ADJACENT COASTAL AREAS OF THE SOUTHWEST
MAINLAND. A CONTINUED ACTIVE STORM TRACK WILL BRING ADDITIONAL
STRONG LOWS ACROSS THE ALEUTIANS AND INTO THE BERING THROUGH EARLY
NEXT WEEK...HOWEVER FARTHER EAST THEY WILL TEND TO DROP SOUTH
CROSSING THE GULF CLOSER TO 50N...ONLY MINIMALLY IMPACTING
SOUTHERN SOUTH CENTRAL ALASKA.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...HIGH WIND WATCH...187
MARINE...GALES...127 131 132 150 155 170 172-176 179 185
         STORMS...177 178
         HVY FRZG SPRY...127 180 181 185.

&&

SYNOPSIS AND MODEL DISCUSSION...TP
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MTL
LONG TERM...JR/CC