Small Craft Advisory 778, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
200 PM AKDT SAT OCT 5 2013

.ANALYSIS AND UPPER LEVELS...
A 971 MB LOW PRESSURE SYSTEM IN THE NORTHWEST BERING SEA AND
ASSOCIATED UPPER LEVEL LOW BRINGING A FRONT TO THE WEST COAST OF
ALASKA THIS AFTERNOON. GOOD JET SUPPORT BUT NOT MUCH BAROCLINICITY
WITH THE FRONT. THEREFORE...FRONT IS A BIT WEAK BUT ENOUGH LIFT FOR
RAIN AND SNOW ESPECIALLY IN AREAS FAVORED BY UPSLOPE DUE TO SOUTH AND
SOUTHWEST FLOW. GOOD CONVECTIVE ELEMENTS VISIBLE IN SATELLITE IMAGERY
IN THE CENTRAL AND WESTERN BERING BEHIND THE STRATUS DECK BEHIND THE
FRONT. GOOD WAVE ALONG THE FRONT DIGGING INTO SOUTHWEST GULF OF
ALASKA LOOKS TO SPIN UP LEE SIDE LOW SOUTH OF KODIAK ISLAND TONIGHT.
THIS MAY SPARK SOME GUSTY WINDS ALONG THE APKEN AS WELL AS INCREASE
WIND AND PRECIP OVER KODIAK ISLAND. WEAK WAVE LIFTING ACROSS SOUTH
CENTRAL ALASKA TODAY WITH ISOLATED TO SCATTERED SHOWERS ENDING THIS
AFTERNOON. HOWEVER...WEAK LOW LEVEL FEATURE NEAR CORDOVA CREATING AN
AREA OF CONVERGENCE AND USLOPE FOR SHOWERS PERSISTING TODAY WHILE
WAITING FOR THE FRONT TONIGHT. THE FRONT TO WEAKEN TONIGHT AS IT
CROSSES TOWARD SOUTH CENTRAL BUT REGAIN STRENGTH TOMORROW WITH YET
ANOTHER SHORT WAVE TROUGH ROTATING AROUND THE BERING LOW.

.MODEL DISCUSSION...
THE MODELS ARE ALL ON THE SAME PAGE FOR THE SYNOPTIC SCALE EVOLUTION
THROUGH THE SHORT TERM PERIOD...FIRST 48 HOURS. THE DOMINANT FEATURE
RIGHT NOW IS THE LOW IN THE NORTHWEST BERING SEA WITH AN ASSOCIATED
FRONT PUSHING TO THE COAST. THE FRONT TO WEAKEN AS IT CONTINUES TO
MOVE ONSHORE. HOWEVER...A SECONDARY DISTURBANCE IN THE FLOW TO
RE-INVIGORATE THE FRONT ALONG THE COAST AND INTO SOUTH CENTRAL
TONIGHT AND TOMORROW MORNING. MODELS HAVE FLIPPED ON THE STRENGTH OF
A LOW TO DEVELOP ALONG THE BAROCLINIC ZONE OVER THE NORTH PACIFIC IN
THE DEEPENING TROUGH OVER THE BERING AND NORTH PACIFIC MONDAY. MANY
FACTORS ARE CONTRIBUTING TO THE SLOWING AND AMPLIFICATION OF THE
TROUGH MONDAY. OVERALL...THE TROUGH TO DIG SOUTH TONIGHT INTO SUNDAY
AS A MODERATE DISTURBANCE WITH GOOD COLD AIR ADVECTION. DUE TO THE
RIDGE RESPONSE IN THE GULF...THE BAROCLINICITY INCREASES AND ALLOWS
FOR A STRONGER SURFACE LOW THAN PREVIOUSLY EXPECTED. IN
ADDITION...THIS WILL TEND TO SHIFT THE PROGRESSION OF THE LOW TO THE
WEST OF THE ALASKA/ALEUTIAN RANGE AD SET UP A POTENTIAL WIND STORM
FOR SOUTH CENTRAL ALASKA. THE EXACTNESS OF THIS WIND IS STILL IN
DOUBT. HOWEVER...THE CONFIDENCE IS INCREASING FOR AT LEAST A
TURNAGAIN ARM WIND EVENT AND MAYBE SOME WIND THROUGH THE ANCHORAGE
BOWL AS WELL FOR LATE MONDAY/EARLY TUESDAY. ANY WAY YOU SLICE THE
WIND REGIME WITH THIS SYSTEM...RAIN WILL BE PREVALENT ACROSS
SOUTHWEST AND SOUTH CENTRAL ALASKA. THE LOW WILL LIFT NORTH
TUESDAY BUT RAIN AND WIND WILL CONTINUE ACROSS THE REGION. POTENTIAL
WARNING WINDS WILL DISSIPATE BY AFTERNOON TUESDAY. THE NEXT UPPER LOW
TO MOVE INTO THE WESTERN BERING TUESDAY AS WELL. TIMING OF THIS
FEATURE WILL BRING SOME UNCERTAINTY TO THE FORECAST AFTER TUESDAY.

.SHORT TERM FORECAST...
SOUTHCENTRAL...AN UPPER LEVEL DISTURBANCE IS LIFTING ACROSS THE AREA
THIS AFTERNOON WITH THE ISOLATED SHOWERS ENDING. A SURFACE FEATURE
NEAR CORDOVA ACTING AS AN AREA OF CONVERGENCE FOR SHOWERS THERE.
CLOUDS ARE INCREASING AHEAD OF A FRONT MOVING INTO THE WESTERN GULF
THIS AFTERNOON. THE FRONT IS WEAKENING BUT WILL RE-INTENSIFY AS A
SECONDARY WAVE HELPS THE FRONT ACROSS SOUTHCENTRAL. WIDESPREAD
SHOWERS WILL BE THE RESULT SUNDAY. THE FRONT WILL MOVE OUT OF THE
AREA SUNDAY AS A TRANSITORY RIDGE BUILDS OVER THE MAINLAND. THE
DEVELOPING LOW IN THE NORTH PACIFIC TO RIDE TO BRISTOL BAY MONDAY
NIGHT WITH INCREASING WINDS AND RAIN IN THE GULF AND OVER KODIAK. THE
RIDGE WILL MOVE EAST AND ALLOW FOR DEEP SOUTHWEST MOISTURE. THE LOW
IS BACKED BY STRONG BAROCLINICITY AND JET. THE MAIN FEATURES TO PASS
THROUGH SOUTHCENTRAL MONDAY NIGHT AND LIFT THROUGH THE DAY MONDAY.

SOUTHWEST...A WEAKENING FRONT WILL BE RE-INVIGORATED THIS EVENING BY
AN UPPER LEVEL DISTURBANCE. WINDS HAVE DIED DOWN ACROSS THE COAST AND
INLAND A BIT. AS THE FRONT CROSSES THE AKPEN TONIGHT...EXPECT A FEW
GUSTS THROUGH CHANNELED TERRAIN IN THE EVENING. GOOD CONVECTIVE
SHOWERS TO REIGN SUPREME TONIGHT AND SUNDAY MORNING BEHIND THE FRONT
BEFORE A BIGGER SLUG OF MOISTURE PUSHES INLAND TOMORROW AFTERNOON
WITH THE NORTHWEST BERING LOW GETTING CLOSER. THIS WESTERLY FLOW WILL
BRING UP WATER LEVELS BUT WE ARE NOT EXPECTING ANY COASTAL SURGE AT
THIS TIME. IF ANYTHING RIGHT NOW...A FEW BIGGER WAVES TO CRASH ON THE
BEACH. THE LOW DEVELOPING IN THE NORTH PACIFIC TO RAMP UP MONDAY AND
INTO BRISTOL BAY MONDAY NIGHT. WIND AND RAIN TO DOMINATE MONDAY NIGHT
INTO TUESDAY.

BERING SEA AND ALEUTIANS...THE WESTERN BERING SEA DOMINATES WITH
MODERATE WESTERLY FLOW AND RAINFALL THROUGH SUNDAY. A DEVELOPING LOW
IN THE NORTH PACIFIC TO RAMP UP WINDS MONDAY IN THE BERING AND
ALEUTIANS AS THE PRESSURE GRADIENT PICKS UP. IN ADDITION...THE TAP OF
MOISTURE WILL BE STRONG FOR SIGNIFICANT RAINFALL TO THE CENTRAL AND
EASTERN ALEUTIANS MONDAY. THE LOW LIFTS TO THE MAINLAND MONDAY NIGHT
WITH MODERATE NORTHWEST FLOW OVER THE BERING DEVELOPING. GOOD COLD
AIR IN PLACE BY THEN WITH CONVECTIVE SHOWERS EXPECTED.

.LONG TERM FORECAST...
MODELS DIVERGE A BIT IN THE LONGER TERM...BUT OVERALL THE MEAN FLOW
IS PROGRESSIVE. A FEW STORMS TO MOVE INTO THE BERING SEA BEHIND THE
BIG ONE ON MONDAY NIGHT/TUESDAY. THE LOWS WILL MOVE FRONTS ACROSS THE
MAINLAND THROUGH THE REMAINDER OF WEEK. THE BERING WILL BE COOLER
WHILE THE MAINLAND LOOKS TO BE ABOVE NORMAL IN TEMPS.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...GALE 173 175 177 178 179 180 185
FIRE WEATHER...NONE

JN OCT 13