Small Craft Advisory 741, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
501 AM AKDT TUE SEP 22 2015

.ANALYSIS AND UPPER LEVELS...

UPPER LEVEL TROUGH EXTENDS FROM WESTERN AK TO THE CANADIAN ROCKIES
THIS MORNING. AN EMBEDDED CUT-OFF LOW CURRENTLY HAS DISTINCT
CENTERS SOUTHEAST OF KODIAK ISLAND AND DUE WEST OF HAIDA GWAII...AS
WELL AS A WEAKER LOBE EXTENDING NORTH NEAR MIDDLETON ISLAND. AN
UPPER RIDGE COVERS MOST OF THE BERING. AT THE SURFACE...HIGH
PRESSURE IS CENTERED OVER THE CENTRAL ALEUTIANS...WITH THE MAIN
LOW PRESSURE CENTER JUST OFF SOUTHEAST AK. THIS CONFIGURATION IS
MAINTAINING A TIGHT PRESSURE GRADIENT ACROSS THE AKPEN WITH SMALL
CRAFT WINDS AND SOME GALE FORCE GUSTS MAKING THEIR WAY THROUGH THE
ALEUTIAN RANGE. SHOWERS ARE ROTATING AROUND THE UPPER GULF
LOW...IN PARTICULAR ALONG THE COAST FROM CAPE SAINT ELIAS TO
MONTAGUE ISLAND...AS WELL AS ON THE AKPEN NEAR THE ALEUTIAN RANGE.

&&

.MODEL DISCUSSION...

MODELS ARE IN AGREEMENT THAT LOW PRESSURE IN THE GULF WILL
STEADILY MOVE SOUTHEAST TODAY...AND THEN REMAIN OVER THE EASTERN
HALF OF THE GULF THROUGH WED NIGHT. HIGH PRESSURE OVER THE BERING
BUILDS EAST TODAY...KEEPING THE PRESSURE GRADIENT TIGHT ACROSS THE
AKPEN. THIS GRADIENT BEGINS TO BREAK DOWN LATER TODAY AS THE HIGH
THEN DRIFTS SOUTH. AS THE HIGH DRIFTS SOUTH A FRONT FROM AN
EASTERN RUSSIA LOW WILL MAKE ITS WAY ACROSS THE BERING BEGINNING
LATER TODAY...REACHING THE WEST COAST OF MAINLAND AK WED AFTERNOON
AND THE ALASKA AND ALEUTIAN RANGES WED NIGHT. THE FORECAST
UTILIZES THE NAM FOR ITS BETTER DEPICTION OF GAP WINDS THROUGH THE
AKPEN.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
DRY AND WINDY CONDITIONS ARE IN STORE FOR SOUTHCENTRAL AND THE
GULF AS A STRONG RIDGE BUILDS IN FROM THE BERING SEA THE NEXT
COUPLE DAYS. THIS LOOKS LIKE A WEAK TO MODERATE HYBRID BORA-GAP
WIND EVENT. THE FORCING MECHANISMS FOR STRONG WINDS ARE SPREAD OUT
OVER TIME....WITH LOW LEVEL COLD ADVECTION AT ITS STRONGEST THIS
MORNING AND UPPER LEVEL FORCING (WITH APPROACHING POLAR JET AND
ASSOCIATED DOWNWARD MOMENTUM AND DESCENDING OF STATICALLY STABLE
AIR) NOT ARRIVING UNTIL THIS EVENING. TO COMPLICATE MATTERS A
SHORT-WAVE DROPPING OUT OF THE ARCTIC AND DOWN THE EAST SIDE OF
THE RIDGE NOW APPEARS LIKE IT WILL GREATLY SLOW EASTWARD PROGRESSION
OF THE RIDGE (AND POLAR JET OUT AHEAD OF IT). THIS WILL PROLONG
THE WIND EVENT OVER THE EASTERN PORTION OF SOUTHCENTRAL...NAMELY
THE VALDEZ TO THOMPSON PASS AREA WHERE GUSTY WINDS WILL LIKELY
HOLD ON THROUGH WEDNESDAY NIGHT.

LATEST UPDATES TO THE WIND FORECAST ATTEMPT TO ACCOUNT FOR THE
VARIOUS FORCING MECHANISMS AND ALTERED TIMING OF THEM. RIGHT NOW
IT LOOKS LIKE THE SUSITNA VALLEY TO COOK INLET CORRIDOR WILL SEE
THE STRONGEST WINDS THIS EVENING...THEN WESTERN PRINCE WILLIAM
SOUND LATE TONIGHT...AND EASTERN PRINCE WILLIAM SOUND SOMETIME
ON WEDNESDAY. FORECAST CONFIDENCE IN WINDY CONDITIONS IS HIGH...WHILE
DETAILS OF SPEEDS AND TIMING IS MUCH LOWER. AS WINDS DIE DOWN
WEDNESDAY AND WEDNESDAY NIGHT TEMPS WILL DROP AND THURSDAY MORNING
WILL LIKELY BE ONE OF THE CHILLIEST MORNINGS SO FAR THIS FALL.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
THE UPPER TROUGH EXITS TO THE EAST TODAY WHICH WILL BRING A SLOW
DECLINE IN NORTHERLY WINDS FROM WEST TO EAST ACROSS THE MAINLAND.
LINGERING LOW LEVEL CLOUDS WILL STICK IN MOST AREAS THROUGH THE
MORNING HOURS BEFORE MIXING OUT IN THE AFTERNOON. TEMPERATURES
WILL REMAIN BELOW NORMAL AS COOL AIR FROM THE EXITING SYSTEM
LINGERS OVERHEAD. AN UPPER RIDGE BUILDS IN OVERNIGHT AHEAD OF A
FRONTAL BOUNDARY PUSHING ACROSS THE BERING SEA. THE FRONT WILL BE
WEAKENING AS IT MOVES ASHORE THE KUSKOKWIM DELTA BRINGING STEADY
RAIN TO THAT AREA WHILE PARTS OF THE KUSKOKWIM VALLEY AND INTERIOR
BRISTOL BAY WILL SEE MORE SPOTTY PRECIPITATION OR NONE AT ALL.
DESPITE THE FRONTAL BOUNDARY CHANGING AIR MASSES TEMPERATURES WILL
REMAIN SLIGHTLY BELOW NORMAL WITH LIGHT WESTERLY WINDS ON
THURSDAY.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
HIGH PRESSURE REMAINS ENTRENCHED OVER THE WESTERN ALEUTIANS AND
BERING SEA...HOWEVER AN UPPER JET WILL PUNCH IN FROM THE WEST AND
BRING A FRONTAL BOUNDARY ACROSS THE NORTH SIDE OF THE HIGH. THE
FRONT WILL BRING RAIN MAINLY TO THE NORTHERN BERING SEA AND THEN
EASTERN BERING AS IT SKIRTS THE SURFACE HIGH. GUSTY WESTERLY WINDS
WILL PICK UP BEHIND THE FRONT BEFORE A SERIES OF DISTURBANCES
WEAKENS THE HIGH FROM THE NORTHWEST PACIFIC BY LATE WEEK.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...

BEGINNING THE EXTENDED PERIOD WEDNESDAY EVENING...NORTHERLY AND
DRY OFFSHORE FLOW ACROSS ALASKA WILL BEGIN TO GIVE WAY TO MORE
ZONAL FLOW ALOFT AS A SERIES OF JET STREAKS/WAVE DISTURBANCES
ALOFT ORIGINATING FROM RUSSIA MOVE INTO ALASKA. THIS GENERAL
PATTERN REGIME WILL LEAD TO INCREASED CLOUDINESS AND WET
WEATHER...ESPECIALLY ACROSS THE BERING SEA AND WESTERN ALASKA
WEDNESDAY NIGHT INTO THURSDAY. THE LOW AMPLITUDE NATURE OF THE
UPPER LEVEL FLOW CONTINUES TO RESULT IN A NOISY SIGNAL IN TERMS OF
SPEED AND STRENGTH OF THESE RUSSIAN WAVE DISTURBANCES...WHICH
EVENTUALLY RESULTS IN LARGER UNCERTAINTY HEADING INTO LATE WEEK
WITH RAIN CHANCES...ESPECIALLY ACROSS SOUTHCENTRAL. WITH THAT
SAID...THE UPPER LEVEL FLOW WILL EVENTUALLY BECOME MORE
SOUTHWESTERLY WITH TIME HEADING INTO THE LATE WEEKEND...WHICH
SHOULD BRING IN A MORE WIDESPREAD SWATH OF MOISTURE...WITH RAIN
BECOMING MORE WIDESPREAD SOMETIME LATE SUNDAY INTO EARLY NEXT
WEEK. THEREAFTER...MUCH UNCERTAINTY DEVELOPS WITH THE FLOW PATTERN
AS THE GLOBAL NUMERICAL GUIDANCE CONTINUES TO STRUGGLE WITH HOW
MUCH TROPICAL ENERGY ASSOCIATED WITH THE CURRENTLY DEVELOPING
TROPICAL STORM MALIA MOVES INTO THE NORTHERN LATITUDES. CURRENT
GUIDANCE IS DEPICTING THE POSSIBILITY OF A POWERFUL EXTRATROPICAL
TRANSITION SOMEWHERE NEAR THE FAR WESTERN BERING SEA NEXT
WEEK...BUT THERE IS VERY HIGH UNCERTAINTY AT THIS TIME.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALES...130 131 150.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...DS
SOUTHCENTRAL ALASKA...SB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...ML
LONG TERM...JA