Small Craft Advisory 778, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
116 PM AKDT MON OCT 6 2014

.ANALYSIS AND UPPER LEVELS...

A BROAD LONGWAVE TROUGH REMAINS CENTERED OVER MAINLAND ALASKA THIS
MORNING WITH AN EMBEDDED CLOSED UPPER LOW LOCATED OVER THE
COPPER RIVER BASIN...WITH A WEAKENING RESIDUAL LOW OVER THE
NORTH-CENTRAL GULF SLOWLY MOVING SOUTHEAST JUST OFFSHORE. SHOWER
ACTIVITY CONTINUES TO TAPER OFF OVER EASTERN PRINCE WILLIAM SOUND
AND FROM SOUTHWEST TO NORTHEAST ACROSS THE COPPER RIVER BASIN AS
THE TROUGH AXIS BEGINS TO SHIFT EASTWARD. RELATIVELY BENIGN
CONDITIONS PERSIST OTHERWISE ACROSS THE COOK INLET
REGION...SUSITNA VALLEY...AND SOUTHWEST MAINLAND WHERE NORTHWEST
FLOW CONTINUES TO PROMOTE MOSTLY SUNNY TO PARTLY CLOUDY SKIES AND
NORTHERLY WINDS...STRONGEST OVER THE SOUTHWEST MAINLAND. A STRONG
SURFACE LOW IS LOCATED APPROXIMATELY 300 MILES SOUTH OF
SHEMYA...WITH AN ASSOCIATED FRONT DRAPED OVER THE CENTRAL AND
WESTERN ALEUTIANS BRINGING RAIN AND GALE FORCE WINDS TO MUCH OF
THE SOUTHERN BERING SEA. &&

.MODEL DISCUSSION...

MODELS ARE IN GENERALLY GOOD AGREEMENT IN THE SHORT TERM IN
DEPICTING THE UPPER LOW OVER THE COPPER RIVER BASIN MOVING INTO
THE YUKON WHILE A NEW LOW DROPS SOUTH ALONG THE WESTERN ALASKA
RANGE TONIGHT INTO TUESDAY...BRINGING ANOTHER REINFORCING SHOT OF
COLD AIR AND AN INCREASE IN NORTHERLY OFFSHORE WINDS TO SOUTHWEST
AND WESTERN PARTS OF SOUTHCENTRAL.

OUT WEST...MODELS ARE IN GOOD AGREEMENT WITH THE LOW PRESSURE
SYSTEM 300 MILES SOUTH OF SHEMYA MOVING TO ABOUT THE SAME DISTANCE
SOUTH OF AMCHITKA WEDNESDAY MORNING BEFORE BECOMING ABSORBED INTO
A RAPIDLY STRENGTHENING LOW TO ITS SOUTHWEST. THIS NEW LOW MOVES
NORTHEAST WELL SOUTH OF THE ISLANDS...AND PUSHES A STRONG FRONT
INTO THE GULF OF ALASKA BY THURSDAY. THE GREATEST MODEL
DISAGREEMENT OCCURS WITH THE TIMING OF THIS FRONT INTO THE
GULF...ESPECIALLY WITH THE 00Z MODELS FROM LAST EVENING. THE 12Z
MODEL SUITE SHOWED MUCH BETTER AGREEMENT WITH THE FRONT MOVING
INTO THE GULF WEDNESDAY NIGHT AND MOVING TOWARD THE GULF COAST
THURSDAY INTO THURSDAY NIGHT. CONFIDENCE IN THE FORECAST THROUGH
THURSDAY NIGHT IS MODERATE TO HIGH.

 &&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...

AS THE UPPER LEVEL LOW MOVES NORTH AND EAST FROM THE COPPER RIVER
BASIN INTO THE YUKON...SNOW SHOWER ACTIVITY WILL DIMINISH FROM
SOUTHWEST TO NORTHEAST ACROSS THE BASIN THROUGH TONIGHT INTO EARLY
TUESDAY MORNING. OTHERWISE...BENIGN CONDITIONS WITH NORTHERLY FLOW
WILL PERSIST THROUGH MID-WEEK WITH CONTINUED COOL TEMPERATURES.

EASTERLY WINDS WILL INCREASE TO NEAR GALE-FORCE ACROSS THE GULF
LATE WEDNESDAY NIGHT THROUGH THURSDAY AS A STRONG FRONT MOVES
TOWARD THE NORTH GULF COAST...BRINGING INCREASING PROBABILITIES OF
RAIN ALONG THE GULF COAST.

SOUTHWEST ALASKA...

CONDITIONS LOOK TO REMAIN RELATIVELY QUIET ACROSS THE SOUTHWEST
MAINLAND THROUGH THE MIDDLE OF THE WEEK AS OFFSHORE FLOW YIELDS
CLEARING SKIES AND GUSTY NORTHERLY WINDS WITH COLD AIR CONTINUING
TO FILTER IN FROM THE NORTH.

BERING SEA/ALEUTIANS...

RAIN AND GALE FORCE WINDS OVER THE WESTERN AND CENTRAL ALEUTIANS
WILL SPREAD NORTH AND EASTWARD TO THE EASTERN PART OF THE CHAIN
AND THE PRIBILOF ISLANDS BY TONIGHT AND PERSIST THROUGH THE MIDDLE
OF THE WEEK AS THE FRONT PERSISTS IN PLACE OVER THE SOUTHERN
BERING THROUGH TUESDAY NIGHT BEFORE DISSIPATING WEDNESDAY. STRONG
EAST TO NORTHEASTERLY FLOW AND OCCASIONAL SHOWERS WILL THEN
CONTINUE THROUGH THE END OF THE WEEK AS THE STRONG LOW ASSOCIATED
WITH THE REMNANTS OF PHANFONE TRACKS SOUTH OF THE CHAIN.

&&

.LONG TERM FORECAST (FRIDAY THROUGH MONDAY)...

THE EXTENDED PERIOD IS DOMINATED BY AN AMPLIFIED 500 MB TROUGH THAT
CONTINUES TO SLOWLY AMPLIFY THROUGHOUT THE PERIOD. THIS IS DUE IN
LARGE PART TO A SERIES OF UPPER LEVEL DISTURBANCES ORIGINATING
OVER SIBERIA AND THE KAMCHATKA PENINSULA THAT TRAVERSE THE
WESTERN EDGE OF THE TROUGH. AS THESE DISTURBANCES PASS THROUGH THE
APEX OF THE TROUGH...THE TROUGH WILL CONTINUE TO SLOWLY DIG
SOUTHWARD. THIS IS INDICATIVE TO AN ACTIVE WEATHER PATTERN ACROSS
THE BERING SEA AND ALASKA MAINLAND AS THESE DISTURBANCES WILL
PROVIDE ENOUGH UPPER LEVEL ENERGY TO KEEP PRECIPITATION IN THE
FORECAST. WEAK HIGH PRESSURE THAT WAS ONCE LOCATED OVER THE
WESTERN ARCTIC AND BERING STRAIT WILL HAVE BECOME CUT OFF FROM THE
MEAN FLOW BY FRIDAY AND SLOWLY WEAKEN OVER THE NORTHERN AND
WESTERN BERING SEA THROUGH SATURDAY. AT THIS POINT...DETERMINISTIC
GUIDANCE IS PICKING UP ON A CLOSED LOW DROPPING SOUTH FROM
KAMCHATKA INTO THE NORTH PACIFIC ON SATURDAY WHICH RESULTS IN SOME
LONGWAVE RIDGING OVER THE FAR WESTERN BERING SEA THAT FLATTENS OUT
BY MONDAY MORNING. THE SURFACE/UPPER LEVEL REMNANTS OF THE
PHASING FROM PHANFONE AND A NORTH PACIFIC LOW WILL PUSH INTO THE
GULF FRIDAY AFTERNOON AND SLOWLY WEAKEN THROUGH MONDAY AS IT
BECOMES NEARLY STATIONARY OVER THE NORTHERN GULF COAST.

FOR SOUTHWEST ALASKA...PRECIPITATION WILL NOT SPREAD AS FAR INLAND
AS WAS EXPECTED THE PREVIOUS DAYS AS THE RESULTANT LOW FROM THE
PHASING OF PHANFONE AND A NORTH PACIFIC LOW PASSES FURTHER SOUTH
THAN ORIGINALLY EXPECTED. PRECIPITATION WILL LIKELY BE SEEN ALONG
THE ALASKA PENINSULA AND ALASKA RANGE ON FRIDAY AS THE LOW PUSHES
INTO THE GULF...WITH A MORE SHOWERY REGIME BRINGING PRECIPITATION
CHANCES TO THE REST OF SOUTHWEST ALASKA BY SATURDAY AND LINGERING
THROUGH AT LEAST MONDAY. COLDER AIR WILL FILTER IN BEHIND THE LOW
ON FRIDAY...WHICH SHOULD KEEP THE PRECIPITATION TYPE PREDOMINATELY
SNOW...BUT SOME LOCATIONS (ESPECIALLY ALONG THE ALASKA PENINSULA)
COULD SEE SOME OF THE SHOWERS MIXING WITH RAIN IN THE AFTERNOON
HOURS.

FOR SOUTHCENTRAL ALASKA...AS THE AFOREMENTIONED LOW MOVES INTO THE
GULF OF ALASKA ON FRIDAY...THE NORTHERN GULF COAST WILL GET SLAMMED
BY A STRONG WARM FRONT. THIS WILL BRING COPIOUS AMOUNTS OF
RAINFALL TO THE NORTH GULF COAST AS WELL AS A PERIOD OF STRONG
WINDS. THE RAINFALL WILL LIKELY LINGER ALONG THE GULF COAST BEYOND
MONDAY AS THE LOW SLOWLY WEAKENS AND SPINS OVER THE NORTHERN
GULF. FURTHER INLAND WILL BE MUCH DRIER BUT WILL STILL SEE DECENT
CHANCES FOR SNOW AND/OR RAIN. THE LOW IN THE GULF WILL ADVECT
WARMER AIR INTO SOUTHCENTRAL ALASKA...WITH 850 MB TEMPERATURES
REACHING +3 TO +6 BY LATE FRIDAY/EARLY SATURDAY OVER PARTS OF
ANCHORAGE...THE COPPER RIVER BASIN AND PARTS OF THE MAT-SU
VALLEY. WHILE PRECIPITATION MAY START OFF AS SNOW OR A RAIN/SNOW
MIX OVER THESE AREAS...IT WILL LIKELY TRANSITION TO ALL RAIN AS
TEMPERATURES ALOFT WARM. THE EXCEPTION OF COURSE WOULD BE ACROSS
ELEVATED LOCATIONS.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALES...155 170-179 185.
FIRE WEATHER...NONE.

&&

CC OCT 14