Small Craft Advisory 846, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
154 PM AKDT SUN OCT 26 2014

.ANALYSIS AND UPPER LEVELS...
THE UPPER LEVEL PATTERN IS BEGINNING TO CHANGE TODAY AS THE LOW
OVER EASTERN RUSSIA IS DIGGING SOUTHWARD OVER THE BERING SEA AND
THE FLATTENED RIDGE OVER MAINLAND ALASKA IS BEGINNING TO AMPLIFY
AS WELL.
THE BIG WEATHER FEATURE IS THE STRONG SURFACE LOW IN THE
NORTHWEST BERING SEA. THIS LOW IS BEGINNING TO SLOW ITS FORWARD
PROGRESS AND IS NO LONGER STRENGTHENING. IT WILL MOVE VERY LITTLE
BETWEEN THIS EVENING AND MONDAY EVENING AND THEN HEAD TO THE
SOUTHEAST AND CONTINUE TO WEAKEN. THE WEATHER FRONT ASSOCIATED
WITH THIS LOW IS MOVING ONSHORE ALONG SOUTHWEST MAINLAND ALASKA
TODAY AND BRINGING STRONG WINDS AND PRECIPITATION WITH IT. THE
SHORT WAVE THAT BROUGHT SNOW TO THE COPPER RIVER BASIN IS MOVING
ACROSS THE ALCAN BORDER.

&&

.MODEL DISCUSSION...
MODELS ONCE AGAIN HAVE A GOOD HANDLE ON THE LARGE SCALE FEATURES
AND MOVEMENTS OF THE WEATHER SYSTEMS. HOWEVER ONCE AGAIN THEY ARE
HAVING A DIFFICULT TIME WITH THE MOVEMENT OF THE LOW IN THE BERING
SEA AS IT WEAKENS OVER THE NEXT FEW DAYS AND THE DEVELOPMENT OF A
NEW LOW NEAR SAND POINT ON MONDAY. THE ISSUE REALLY HAS TO DO WITH
THE WAY THAT THE JET STREAM INTERACTS WITH THE LOW IN THE BERING
SEA AS THE UPPER LEVEL TROUGH ASSOCIATED WITH THAT LOW DIGS
SOUTHWARD. AS THAT TROUGH DIGS SOUTHWARD OVER THE ALASKA PENINSULA
IT WILL CUT OFF THE SUPPORT FOR THE BERING SEA LOW. AS THIS
HAPPENS CONDITIONS WILL BECOME FAVORABLE FOR THE DEVELOPMENT OF A
NEW LOW OVER THE ALASKA PENINSULA. ALL THE MODELS HAVE THIS
PATTERN AND WEAKEN AND THEN DISSIPATE THE CURRENT BERING SEA LOW.
IT IS THAT THEY DIFFER BY UP TO A FEW HUNDRED MILES WHERE IT WILL
TRACK AS IT HEADS SOUTHEAST MONDAY THROUGH TUESDAY AND HOW FAST IT
WILL DISSIPATE. THEY ALSO ALL HAVE THE DEVELOPMENT OF A NEW LOW
MONDAY AFTERNOON THROUGH MONDAY NIGHT IN THE VICINITY OF THE
ALASKA PENINSULA. ONCE AGAIN THE DEBATE IS HOW FAST IT WILL
DEVELOP AND EXACTLY WHERE. AT THIS TIME IT LOOKS LIKE THE LOW
SHOULD BEGIN TO SPIN UP MONDAY AFTERNOON JUST SOUTH OF THE ALASKA
PENINSULA AND THEN HEAD EASTWARD INTO THE SOUTHERN GULF OF ALASKA
AFTER THAT.
&&

.SHORT TERM FORECAST...
SOUTHCENTRAL ALASKA...
HIGH PRESSURE AND STABLE CONDITIONS ARE OVER SOUTHCENTRAL ALASKA.
THE SHORT WAVE OVER THE COPPER RIVER IS MOVING ACROSS THE ALCAN
BORDER BUT THERE WILL BE SOME FOG AND LOW STRATUS OVERNIGHT INTO
TOMORROW AS THE MOISTURE FROM THE RECENT SNOWFALL GETS TRAPPED
UNDER THE INVERSION.
THE TRICKIEST FORECAST IN SOUTHCENTRAL ALASKA IS THE FOG FORECAST
IN ANCHORAGE AND THE MATANUSKA VALLEY. THIS AREA IN NORTHERN COOK
INLET IS HOLDING IN THE STRATUS REMAINING PUSHED UP ALONG THE
CHUGACH MOUNTAINS AND NOT DISSIPATING VERY FAST. THIS IS A GOOD
INDICATION THAT THERE WILL BE SOME STRATUS AND FOG DEVELOPMENT
AGAIN OVERNIGHT INTO TOMORROW IN THESE AREAS.
THE GUSTY WINDS THAT HAVE BEEN IN SEWARD AND WHITTIER THE PAST FEW
DAYS WILL DIMINISH THIS EVENING AS THE WEAK LOW INT HE NORTHERN
GULF CONTINUES TO MOVE EASTWARD AND THEN DISSIPATES TONIGHT.

SOUTHWEST ALASKA...
THE FRONT ASSOCIATED WITH THE STRONG LOW IN THE NORTHWEST BERING
SEA IS MOVING ON SHORE IN SOUTHWEST ALASKA AND BEGINNING TO
STALL. THIS WILL BRING SOME RAIN AND SNOW INLAND AND RAIN TO THE
COAST. THIS FRONT WILL MAKE IT OVER THE BRISTOL BAY REGION BUT
PRECIPITATION WILL LIKELY BE RELEGATED TO AREAS WEST OF KING
SALMON AS THE NEXT LOW DEVELOPS NEAR SAND POINT TOMORROW WHICH
PULLS THE ENERGY THAT DIRECTION.

BERING SEA/ALEUTIANS...
THE BERING SEA SOUTH OF THE LOW IS IN THE REGION WHERE THE COLD FRONT
HAS PASSED THROUGH. THIS IS BRINGING SOME STRONG WEST TO NORTHWEST
WINDS AND SNOW SHOWERS TO THE BERING SEA. THE FRONT IS PASSING
THROUGH THE PRIBILOF ISLANDS THIS AFTERNOON AND AREAS FROM THE
PRIBILOF'S EASTWARD WILL BE RAIN AHEAD OF THE FRONT AND THEN TURN
TO SNOW SHOWERS AFTERWARDS. MOST OF THE ALEUTIAN CHAIN WILL IS FAR
ENOUGH SOUTH THAT THE PRECIPITATION TYPE NEAR SEA LEVEL WILL BE
MOSTLY RAIN THROUGH LATE TONIGHT WHEN ENOUGH COLDER AIR FINALLY
MAKES IT IN TO BRING IN SOME SNOW SHOWERS AS WELL.

&&

.LONG TERM FORECAST...
WHEN THE LOW THAT IS DEVELOPING NEAR SAND POINT TOMORROW MOVES
SOUTH OF KODIAK EARLY ON WEDNESDAY...THE SOUTHERN MAINLAND WILL
EXPERIENCE A PERIOD OF QUIET WEATHER THAT IS EXPECTED TO CONTINUE
THROUGH THE WEEK. THERE IS NOW MUCH BETTER AGREEMENT WITH THE
TRACK OF THIS LOW THAN YESTERDAY...BUT THE CHALLENGE REMAINS IN
DETERMINING ITS INTENSITY. THE LAST 3 RUNS OF THE EC HAVE BEEN THE
MOST AGGRESSIVE...BRINGING A MID 970 MB LOW TOWARDS THE PANHANDLE
THURSDAY EVENING. SIGNIFICANT SPREAD HOWEVER WAS NOTED BY WPC IN
THE EC ENSEMBLE MEMBERS THIS MORNING (AND A MUCH WEAKER EC
ENSEMBLE MEAN) SO THE FORECAST DOES NOT CAPTURE A LOW THIS DEEP
FOR NOW. THIS SHOULD HAVE A MINIMAL IMPACT ON THE SENSIBLE WEATHER
IN OUR AREA...AS THERE IS STILL CONFIDENCE THAT THIS SYSTEM WILL
STAY SOUTH AND EAST OF THE AOR. THE SOUTHERN MAINLAND IS STILL
EXPECTED TO BE GENERALLY CLEAR AND DRY WITH OFFSHORE FLOW FROM
TUESDAY THROUGH LATE IN THE WEEK.

OVER THE BERING SEA REGION THERE IS MUCH BETTER AGREEMENT THAT THE
ALEUTIAN LOW ENTERING THE AREA ON TUESDAY WILL STRUGGLE TO REACH
THE SOUTHWEST COAST BY THE END OF THE WEEK. THIS SYSTEM WILL BRING
RAIN AND SNOW WITH GUSTY WINDS TO THE BERING SEA AND ALEUTIANS
STARTING TUESDAY AND CONTINUING THROUGH LATE IN THE WORK WEEK.
THIS LOW THEN APPEARS TO BRING THE NEXT CHANCE OF PRECIPITATION TO
THE SOUTHERN MAINLAND BY NEXT WEEKEND.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 170 172-179 181 185.
FIRE WEATHER...NONE.
&&

OCT 14