Small Craft Advisory 54, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
359 PM AKST SUN JAN 18 2015

.ANALYSIS AND UPPER LEVELS...
THERE IS A "DOUBLE BARREL" UPPER LOW TO THE WEST OF ALASKA WITH
ONE CENTER NEAR THE BERING STRAIT AND THE OTHER JUST NORTHWEST OF
THE WESTERN ALEUTIANS. THERE IS ANOTHER LOW OFF THE COAST OF
SOUTHEAST ALASKA. A WEAK NORTH-SOUTH ORIENTED FRONT ASSOCIATED
WITH THE WESTERN LOWS IS DISSIPATING OVER SOUTH CENTRAL AND
EASTERN SOUTHWEST ALASKA. COLDER AIR HAS PUSHED INTO SOUTHWEST
ALASKA WITH TEMPERATURES RUNNING 10 TO 20 DEGREES (F) COLDER THAN
AT THE SAME TIME YESTERDAY. A BIT OF COOLER AIR HAS SEEPED INTO
SOUTH CENTRAL ALASKA AS THE FLOW ALOFT IS NOW FROM THE
SOUTHWEST...BUT WEAK.

&&

.MODEL DISCUSSION...
THE NUMERICAL MODELS QUICKLY BEGIN TO SHOW DIVERGENT SOLUTIONS. BY
42 HOURS INTO THE FORECAST (MONDAY EVENING) THERE IS ALREADY A
DECENT SPREAD DEVELOPING ON A LOW IN THE SOUTHERN GULF...AND THIS
SPREAD WIDENS THROUGH 60 HOURS AS THE LOW PUSHES INTO THE NORTHERN
GULF. AT THIS POINT THE MODELS DIFFER ON TIMING WITH THE ARRIVAL
OF A LARGE FRONT FROM THE SOUTH...WITH THE ECMWF BEING THE SLOWEST
TO BRING IT NORTH. IN FACT BY 84 HOURS (WEDNESDAY AFTERNOON) THE
ECMWF BARELY HAS IT TO THE ALEUTIANS AND SOUTHERN GULF OF ALASKA
WHILE THE OTHER MODELS HAVE IT INTO THE SOUTHERN BERING AND
CENTRAL (OR EVEN NORTHERN) GULF. THE ECMWF HAS BEEN CONSISTENT
WITH THE TIMING FOR THIS FEATURE (AT LEAST THE LAST 3 RUNS). IT IS
HARD TO TOTALLY DISREGARD THE ECMWF WITH ITS GOOD TRACK
RECORD...BUT AT THIS TIME RANGE IT IS PROBABLY BETTER TO GO WITH
A CONSENSUS FORECAST. FORECAST CONFIDENCE IS A LITTLE BELOW NORMAL
TODAY DUE TO THE MODEL DIFFERENCES.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
SHOWERS WILL GRADUALLY WIND DOWN THIS EVENING FROM ANCHORAGE INTO
THE MAT-SU AS BROAD SOUTHWESTERLY FLOW ALOFT BECOMES MORE
SOUTHERLY AND A WEAK SHORTWAVE RIDGE BUILDS OVERHEAD. THIS WILL
ALSO SUPPORT LOW STRATUS AND PATCHY FOG ACROSS THE COPPER RIVER
BASIN THROUGH MONDAY. A SHORTWAVE TROUGH WILL THEN MOVE ACROSS THE
CENTRAL GULF MONDAY NIGHT INTO TUESDAY...WITH MOST OF THE
ASSOCIATED SHOWER ACTIVITY CONFINED TO KODIAK ISLAND AND THE
EASTERN KENAI PENINSULA.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...

WEAK HIGH PRESSURE WILL BUILD OVER THE REGION...WHICH WILL KEEP
MOST LOCATIONS DRY THROUGH TUESDAY. THE EXCEPTION WILL BE SNOW
SHOWERS NEAR THE ALASKA AND ALEUTIAN RANGES THROUGH TUESDAY.
OTHERWISE...THE MAIN STORY WILL BE CONTINUED COLD TEMPERATURES.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...

A WEAK FRONTAL ZONE OVER THE CENTRAL BERING TONIGHT WILL CONTINUE
TO MOVE NORTHEAST...BRINGING SNOW SHOWERS TO THE PRIBILOF ISLANDS
BEFORE WEAKENING MONDAY. OTHERWISE...RATHER QUIESCENT WEATHER FOR
THE BERING SEA WILL BE THE DOMINANT MODE AS WEAK HIGH PRESSURE
ALOFT BUILDS OVER. NEAR GALE FORCE EASTERLY WINDS AND RAIN AND
SNOW SHOWERS WILL DEVELOP ACROSS THE ALEUTIAN CHAIN TUESDAY AS A
NORTH PACIFIC FRONT MOVES UP TOWARD THE AREA.

&&

.LONG TERM FORECAST (TUESDAY NIGHT THROUGH SATURDAY)...

THE MAIN STORM SYSTEM FOR THIS WEEK WILL BE TRAVELING SOUTH OF
THE CENTRAL ALEUTIANS TUESDAY NIGHT. THIS SYSTEM WILL SLOWLY
ADVANCE EAST WITH THE MAIN CENTER SOUTH OF THE ALASKA PENINSULA ON
FRIDAY. THIS SUBTROPICAL STORM SYSTEM ADVECTS WARMER TEMPERATURES
BY MID WEEK INTO THE THE EASTERN BERING AND THE SOUTHWESTERN
MAINLAND AND THEN SPREADING INTO THE GULF AND SOUTHCENTRAL FOR
THE LATTER PART OF THE WEEK. THIS WEATHER PATTERN IS ANOTHER SET
UP FOR MIXED PRECIPITATION CHALLENGES.

AT THE START OF THE LONG TERM FORECAST...UPPER LEVEL RIDGING
PASSES OVER SOUTHERN ALASKA TUESDAY NIGHT KEEPING THE AREA MOSTLY
DRY UNTIL THE NEXT FRONT MOVES UP FROM THE SOUTHERN GULF LATE
WEDNESDAY INTO THURSDAY. PRECIPITATION ACROSS THE SOUTHERN BERING
AND ALEUTIANS INCREASES TUESDAY NIGHT AS A FRONT MOVES UP FROM THE
NORTH PACIFIC. THE STORM SYSTEM WILL PUSH THIS FRONT INTO THE
NORTHERN GULF OF ALASKA LATE WEDNESDAY WITH MULTIPLE REINFORCING
SHORTWAVES KEEPING HIGHER PRECIPITATION CHANCES THROUGH THE END
OF THE WEEK. NORTHERLY FLOW RETURNS LATE WEDNESDAY ACROSS THE
WESTERN BERING ADVECTING COLDER AIR ON THE BACKSIDE OF THE STORM
SYSTEM.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING 172 174 176.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...BL
SOUTHCENTRAL ALASKA...CB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JA
LONG TERM...KH