Small Craft Advisory 759, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
151 PM AKDT TUE SEP 30 2014

.ANALYSIS AND UPPER LEVELS...

SNOW SHOWERS ASSOCIATED WITH AN UPPER WAVE WERE EVIDENT ALONG THE
EASTERN ALASKA RANGE. LOW VFR CONDITIONS WITH STRATUS ASSOCIATED
WITH SUBSIDENCE WAS EVIDENT OVER THE KUSKOKWIM DELTA. THE
REMAINDER OF THE MAINLAND WAS UNDER FAIR SKIES WITH RELATIVELY
COOL AND DRY NORTHERLY FLOW. OUTFLOW WINDS ACROSS
SOUTHCENTRAL...ESPECIALLY THE GULF...PEAKED OVERNIGHT AND ARE ON
THE DECLINE. THE PINCH IN PRESSURE GRADIENT BETWEEN THE EASTERN
BERING RIDGE AND THE LOW COMPLEX OVER THE NORTH PACIFIC CONTINUED BRISK
EASTERLY WINDS ACROSS THE AK PEN...EAST ALEUTIANS/EASTERN BERING
SEA.

&&

.MODEL DISCUSSION...
ALOFT...MODELS HAVE SIMILAR PHASING OF THE TROUGH OVER THE
MAINLAND AND THE CUT-OFF LOW OVER THE NORTH PACIFIC. THIS SOLUTION
SEEMS REASONABLE AS COLD AIR SHOULD DIVE SOUTH ALONG THE FORWARD
SIDE OF AN AMPLIFYING UPPER RIDGE OVER THE EASTERN BERING SEA AND
SHARPEN THE MAINLAND TROUGH. THIS EFFECTIVELY PINCHES OFF THE
BERING SEA RIDGE ON THU AND CREATES A WEAKNESS IN THE HEIGHT
FIELDS WHICH ALLOWS THE NORTH PACIFIC CUT-OFF LOW TO PROGRESS
NORTH.

SURFACE FEATURES HOWEVER ARE MORE PROBLEMATIC WITH RESPECT TO
TIMING...INTENSITY...AND POSITION. OVERALL...THERE SHOULD BE A
FAIRLY STRONG TRIPLE POINT FEATURE SPAWNING OFF THE THE BAROCLINIC
ZONE ASSOCIATED WITH THE CUT-OFF OVER THE NORTH PACIFIC. ALL
MODELS SHOW A FAIRLY GOOD LEFT EXIT JET POSITION OVER THE DEVELOPING
TRIPLE POINT WHICH HEADS INTO THE NORTHERN GULF THU NIGHT/FRI
MORNING. THE 00Z NAM IS THE FASTEST IN MOVING THIS FEATURE NORTH
WITH THE GLOBAL MODELS SOMEWHAT SLOWER. THERE IS A GENERAL
CONSENSUS FOR A FAIRLY STRONG LOW OVER THE NORTHEASTERN GULF FRI.
FOR NOW WILL CONTINUE WITH OFFICIAL GRIDS WITH BLEND OF THE GEM
GLOBAL/GFS IN THE GULF KEEPING GALES WITH THIS FEATURE FOR NOW.
OUT WEST...MODELS HAVE SIMILAR HANDING OF FEATURES...SO IN GENERAL
WILL LEAN TOWARD THE GFS.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...
COOL AND DRY CONDITIONS WITH DIMINISHING WINDS ARE EXPECTED
ACROSS SOUTHCENTRAL OVER THE NEXT COUPLE OF DAYS. STRONG EASTERLY
WINDS AND INCREASED CLOUD COVER IN ADVANCE OF APPROACHING TRIPLE
POINT WILL START PUSHING TOWARD THE SOUTHERN GULF ON THU. GALES
WILL CONTINUE TO SPREAD NORTH WITH THE TRIPLE POINT ON THU NIGHT
AND LOCAL GAP FLOWS WILL DEVELOP ACROSS THE SOUTHERN MAINLAND WITH
INCREASING PRESSURE AND TEMP GRADIENTS. MOISTURE SHOULD SPREAD
INTO THE SOUTHEASTERN COPPER RIVER BASIN AND GULF COAST THU NIGHT
THEN SPREAD WEST ON FRI.  THE WESTWARD EXTENT OF THE MOISTURE
PUSH AND CHARACTER OF PRECIPITATION INLAND ON FRI IS STILL
UNCERTAIN WITH CURRENT MODELS DIFFERENCES. HOWEVER AT THIS
TIME...IT APPEARS THAT THE COAST WILL BE MAINLY RAIN AND THE
COPPER RIVER BASIN LIKELY WILL HAVE SNOW OR A MIX.

SOUTHWEST ALASKA...WHAT LITTLE STRATUS MOVED IN OVER THE DELTA
THIS MORNING SHOULD MOVE SOUTH AS THE NORTHERLY OFFSHORE
STRENGTHEN. EXPECT RELATIVELY DRY AND COOL CONDITIONS TO LAST
OVER THE NEXT COUPLE OF DAYS WITH RIDGING OVER THE MAINLAND AND
LOW PRESSURE IN THE GULF. ALSO EXPECT WINDS CONDITIONS TO PERSIST
AND EVEN STRENGTHEN SOME OVER THE AK PEN THROUGH THU. WILL ALSO
SEE SOME LOCALLY BRISK WINDS OVER BRISTOL BAY.

BERING SEA/ALEUTIANS...RAIN AND WIND WILL CONTINUE TO JUST BARELY
BRUSH THE ALEUTIAN ISLANDS AS THE LOW CONTINUES TO SLOWLY TRACK
TO THE EAST. OTHERWISE HIGH PRESSURE WILL BUILD OVER THE CENTRAL
BERING SEA AND CONTINUE TO STRENGTHEN THROUGH MID
WEEK...CONTINUING THE SPLIT-FLOW BLOCKING PATTERN AND PROVIDING
VERY QUIET CONDITIONS FOR MOST OF THE REGION.

&&

.LONG TERM FORECAST (SAT OCT 4 - TUE OCT 7)...

BEGINNING THE EXTENDED PERIOD SATURDAY...A HIGHLY AMPLIFIED
PATTERN WILL CONTINUE ACROSS THE REGION...WITH A BLOCKING RIDGE
EXTENDING FROM THE BERING NORTHWARD INTO SIBERIA...AND A LONGWAVE
TROUGH OVER THE STATE OF ALASKA. EVENTUALLY THE TROUGH WILL
DEVELOP INTO A CLOSED VORTEX ALOFT OVER SOUTHERN ALASKA AND WILL
REMAIN IN PLACE THROUGH TUESDAY. WHILE THERE WILL NOT BE A
SUBTROPICAL CONNECTION...WEAK DISTURBANCES ROTATING AROUND THE
PERIPHERY OF THE LOW WILL SUPPORT RAIN AND SNOW CHANCES ACROSS
PORTIONS OF SOUTHERN ALASKA MAINLY EAST OF THE ALASKA AND ALEUTIAN
RANGES. THE BEST CHANCES FOR RAIN...THEN SNOW...WILL BE ACROSS THE
COPPER BASIN. ARCTIC AIR WILL CONTINUE TO FILTER INTO SOUTHERN
ALASKA THROUGH THE WEEKEND...WITH GRADUALLY COOLING TEMPERATURES.
RIGHT NOW...THE COLDEST TEMPERATURES WILL LIKELY DEVELOP ON MONDAY
AND TUESDAY AS THE UPPER VORTEX SLOWLY TRANSLATES EAST AND COLDER
AIR AND CLEARER SKIES FORM ACROSS THE STATE.

- AHSENMACHER

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...150 155 172 174.
FIRE WEATHER...NONE.

&&

RMC/AHSENMACHER SEP 14