Small Craft Advisory 909, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
422 PM AKST FRI NOV 14 2014

.ANALYSIS AND UPPER LEVELS...
AN UPPER LEVEL RIDGE THAT STRETCHES FROM THE PANHANDLE AND YUKON
TERRITORY INTO THE CENTRAL INTERIOR CONTINUES TO BRING MOSTLY
CLEAR SKIES TO MUCH OF THE SOUTHERN MAINLAND. SUBSIDENCE UNDER
THIS RIDGE IS PRODUCING AREAS OF FOG AND LOW STRATUS MAINLY ACROSS
INTERIOR VALLEYS. TO THE WEST OF THIS RIDGE...A NORTH PACIFIC LOW
CENTERED SOUTH OF DUTCH HARBOR IS NEARLY STATIONARY. A TIGHT
PRESSURE GRADIENT BETWEEN THIS LOW AND THE SURFACE RIDGE OVER
MAINLAND ALASKA STRETCHES FROM THE CENTRAL GULF OF ALASKA INTO THE
EASTERN BERING SEA...INCLUDING MOST OF BRISTOL BAY. A FRONT
ASSOCIATED WITH A LOW CENTERED OVER THE KAMCHATKA PENINSULA CAN BE
SEEN ENTERING THIS WESTERN ALEUTIANS...BRINGING RAIN AND GUSTY
SOUTHEASTERLY WINDS TO THE SHEMYA AREA. THIS SYSTEM WILL ABSORB
THE LOW NEAR DUTCH HARBOR OVER THE NEXT 2 DAYS...BECOMING THE
PRIMARY WEATHER MAKER IN THE BERING SEA REGION THROUGH THE
WEEKEND.

&&

.MODEL DISCUSSION...
THE MODELS HAVE COME INTO BETTER SYNOPTIC AGREEMENT INTO SUNDAY
WHEN THEY BEGIN TO HAVE SOME FAIRLY MINOR DISAGREEMENTS WITH BOTH
AN ALEUTIAN LOW AND THE LOW IN THE GULF. THE LARGEST MODEL
DISCREPANCIES EXIST IN THE TIMING AND INTENSITY OF A LOW
APPROACHING THE SOUTHERN GULF ON SUNDAY. THE GFS AND NAM ARE
FASTER IN MOVING IT TOWARD KODIAK ISLAND WHILE THE ECMWF IS BOTH
A LITTLE SLOWER AND STRONGER. THE TIMING OF THIS LOW MOVING
THROUGH WILL BE IMPORTANT IN DETERMINING THE DURATION AND
INTENSITY OF THE RAINFALL OVER KODIAK EARLY NEXT WEEK.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
DRY CONDITIONS WILL PERSIST ACROSS MUCH OF THE REGION THROUGH THE
WEEKEND BENEATH HIGH PRESSURE CENTERED OVER WESTERN CANADA...WITH
PRECIPITATION LARGELY CONFINED TO KODIAK ISLAND IN THE VICINITY OF
A WEAK FRONT OVER THE WESTERN GULF. THE MAIN FORECAST CONCERN FOR
THE NEXT SEVERAL NIGHTS WILL CONTINUE TO BE THE POTENTIAL FOR FOG
FORMATION BENEATH CLEAR SKIES AND A STOUT LOW LEVEL INVERSION
WHICH IS BEING ENHANCED BY VERY WARM TEMPERATURES ALOFT. PATCHY
FOG WILL BE POSSIBLE FROM THE ANCHORAGE BOWL INTO THE MATANUSKA
VALLEY BUT WILL BE MOST PERSISTENT ACROSS THE COPPER RIVER BASIN
WHERE THE INVERSION IS SLOWER TO WEAKEN DURING THE AFTERNOON
HOURS. MORE WIDESPREAD PRECIPITATION WILL RETURN TO THE GULF COAST
ON SUNDAY AS A LOW PRESSURE SYSTEM TRACKS NORTHWESTWARD TOWARDS
KODIAK ISLAND...WITH DOWNSLOPING OFF THE CHUGACH MOUNTAINS KEEPING
INLAND AREAS MOSTLY FREE OF PRECIPITATION. THE BEST CHANCE FOR
PRECIPITATION IN THE ANCHORAGE BOWL WILL BE SUNDAY NIGHT AS AS AN
UPPER TROUGH LIFTS THROUGH THE AREA. A BRIEF SHOT OF FREEZING RAIN
APPEARS POSSIBLE AS A WARM LAYER ALOFT PERSISTS OVER THE AREA AND
SURFACE TEMPERATURES LINGER NEAR OR BELOW FREEZING.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
TIMING AND PLACEMENT OF SHORTWAVE TROUGHS AND SMALL SURFACE LOWS
ROTATING AROUND THE LARGE VERTICALLY STACKED NORTH PACIFIC LOW
WILL CONTINUE TO BE THE MAIN FORECAST CHALLENGE OVER THE NEXT FEW
DAYS. THE OFFSHORE PRESSURE GRADIENT ACROSS SOUTHWEST ALASKA HAS
WEAKENED SOMEWHAT...HOWEVER IT WILL TIGHTEN AGAIN AS THE NEXT WAVE
OF LOW PRESSURE ROTATES IN FROM THE WESTERN GULF. YET ANOTHER
SYSTEM ROTATING IN TO THE WESTERN GULF WILL ARRIVE SUNDAY AS MORE
OF A CLOSED CIRCULATION...SPREADING ADDITIONAL PRECIPITATION
ACROSS THE PENINSULA AND INTO SOUTHWEST ALASKA.

WITH EAST TO SOUTHEAST FLOW PERSISTING EXPECT TO SEE OROGRAPHIC
ENHANCEMENT OF PRECIPITATION ALONG THE SOUTHEAST FACING WINDWARD
SIDE OF THE PENINSULA. THE SOUTHEASTERLY FLOW AS WELL AS WARM
CONDITIONS ALOFT FROM THE LARGE BLOCKING RIDGE OVER MUCH OF NW
CANADA AND MAINLAND ALASKA WILL CONTINUE TO KEEP TEMPERATURES WELL
ABOVE NORMAL. STABLE CONDITIONS AND CLEARER SKIES FURTHER INLAND
HOWEVER WILL ALLOW VERY STRONG INVERSIONS TO FORM ALLOWING POCKETS
OF COLD NIGHTTIME TEMPERATURES IN SHELTERED VALLEYS.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE PORTION OF THE BROAD UPPER LEVEL TROUGH OVER THE ALEUTIANS
REMAINS SOMEWHAT COOLER ALOFT...AND CONTINUES TO PRODUCE SCATTERED
SHOWERS ACROSS THE REGION. THE TEMPERATURE PROFILE IN THE
ATMOSPHERE SUPPORTS A MIX OF RAIN AND SNOW...MAINLY WEST OF DUTCH
HARBOR...BUT LITTLE OR NO ACCUMULATION IS EXPECTED.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE BLOCKING PATTERN CONTINUES WITH HIGH PRESSURE OVER THE EASTERN
PART OF THE STATE. HOWEVER...IT WILL MOVE SLIGHTLY MORE TO THE
EAST WHICH WILL ALLOW SOME SHORTWAVES TO MAKE IT OVER MAINLAND
ALASKA. THE MAIN SHORT WAVE TO MOVE THROUGH WILL BE TUESDAY
NIGHT. IT IS EXPECTED TO BRING PRECIPITATION THROUGHOUT MUCH OF
SOUTHCENTRAL ALASKA AS IT PUSHES TO THE NORTH. THERE IS QUITE A
BIT OF DISAGREEMENT AMONG THE MODELS LEADING TO LOWER CONFIDENCE
IN THE EXACT TIMING. OUT WEST VARIOUS COMPLEX LOWS WILL SIT IN THE
BERING THROUGH NEXT WEEK BRINGING RAIN AND SNOW THROUGHOUT THE
BERING AND ALEUTIANS.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING...120 130 131 132 137 138 150 172.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...CB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JR
LONG TERM...DK