Small Craft Advisory 137, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
511 AM AKST FRI FEB 13 2015

.ANALYSIS AND UPPER LEVELS...
THE FEATURES ALOFT LOOK MUCH THE SAME THIS MORNING AS THE LAST
COUPLE DAYS BUT THINGS ARE CHANGING. THE BROAD AND STACKED LOW
PRESSURE SYSTEM OVER THE EASTERN BERING SEA AND NORTH CENTRAL
PACIFIC CONTINUES TO DRIVE THE FLOW. HOWEVER...THE STRONGER FEATURES
ARE IN THE FLOW TO THE EAST OF THE LONG-WAVE TROUGH MOVING INTO
THE GULF. A COUPLE OF MATURE LOOKING SHORTWAVE TROUGHS ARE
ENTERING THE GULF. OVER THE MAINLAND...WIDESPREAD STRATUS ENGULFS
THE COOK INLET REGION INTO THE SUSITNA VALLEY AND COPPER RIVER
BASIN. SOME OF THIS STRATUS IS ON THE GROUND IN THE FORM OF
QUARTER-MILE VISIBILITY FOG. WINDS ARE GENERALLY LIGHT ACROSS THE
SOUTHCENTRAL EXCEPT FOR GUSTY OUTFLOW WINDS ALONG THE NORTH GULF
COAST.

&&

.MODEL DISCUSSION...
GUIDANCE IS IN GOOD AGREEMENT WITH LARGE SCALE FEATURES. THE
SMALLER FEATURES ARE HANDLED BETTER THAN IN PREVIOUS DAYS
BECAUSE THEY ARE IN FACT...LARGER. THE TWO SHORTWAVES ENTERING
THE GULF ARE PROGGED TO COMBINE FORCES AND DEVELOP A MODERATE
STRENGTH SURFACE LOW THAT WILL LINGER IN THE CENTRAL GULF. NO
MAJOR DIFFERENCES IN THE PRESSURE FIELDS OR PRECIPITATION
FORECASTS. THE EAST AND WEST DOMAINS USED THE 13/00Z NAM AND
13/00Z GEM REGIONAL.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
AREAS OF FOG(SOME DENSE) EVIDENT ALONG KNIK ARM...TURNAGAIN
ARM...AND COOK INLET WILL DIMINISH THROUGH THROUGH THE DAY AS
PRESSURE GRADIENTS INCREASE ACROSS THE AREA. OUTFLOW WINDS OVER
THE EASTERN KENAI AND THE NORTH GULF COAST SHOULD SLOWLY DIMINISH
THROUGH THIS AFTERNOON...THOUGH SEWARD COULD HOLD ON A LITTLE
LONGER. A MODERATELY STRONG LOW AND ASSOCIATED FRONTAL TROUGH
MOVES WEST ACROSS THE GULF TONIGHT THEN LIFTS NORTH ACROSS THE
WESTERN GULF AS IT WEAKENS SAT NIGHT. PRECIPITATION WITH THIS
FEATURE WILL BE NOT LIKELY START IMPACTING THE NORTHERN GULF UNTIL
THIS AFTERNOON THEN MOVES TO THE EASTERN KENAI PEN TONIGHT.
MOISTURE THEN SPREADS WEST OF THE CHUGACH/TALKEETNA MOUNTAINS ON
SAT...BUT CROSS BARRIER FLOW SHOULD KEEP VALUES LOW. PRECIPITATION
TYPE WILL BE GENERALLY RAIN ALONG THE COAST WITH MIXED INLAND. A
BATCH OF BRISK GAP WINDS ARE EXPECTED ACROSS TURNAGAIN ARM SAT/SAT
NIGHT AS THE LOW LIFTS NORTH AND PRESSURE GRADIENTS BECOME
POSITIVE. BRISK SOUTHERLY WINDS ARE EXPECTED ALONG THE COPPER
RIVER ON SAT NIGHT WITH PRESSURE RISES ACROSS THE NORTH GULF.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
A SHORTWAVE TROUGH CURRENTLY ROTATING ACROSS BRISTOL BAY IS
BRINGING SCATTERED SNOW SHOWERS TO COAST THIS MORNING. ONCE THE
TROUGH ROTATES THROUGH DRIER WEATHER WILL PREVAIL OVER MUCH OF
SOUTHWEST ALASKA FROM THIS AFTERNOON THROUGH MIDDAY SATURDAY. THE
EXCEPTION TO THIS WILL BE THE ALASKA PENINSULA WHERE A FRONTAL
SYSTEM IN THE GULF WILL KEEP RAIN LINGERING LONGER.

THE NEXT FAIRLY WEAK TROUGH WILL LIFT THROUGH LATE SATURDAY
AFTERNOON THROUGH SATURDAY NIGHT BRINGING A CHANCE OF RAIN AND
SNOW WITH IT. A SUBSTANTIALLY STRONGER FRONTAL SYSTEM WILL
APPROACH THE ALASKA PENINSULA FROM THE SOUTHEAST SUNDAY MORNING
THEN CROSS OVER TO BRISTOL BAY AND SOUTHWEST ALASKA SUNDAY
AFTERNOON BRINGING STRONG EASTERLY WINDS WITH IT.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
NOT MUCH CHANGE EXPECTED FOR THE ALEUTIANS AND BERING SEA FOR THE
NEXT COUPLE OF DAYS. SHOWERY WEATHER WILL CONTINUE AS TROUGHS
ROTATE AROUND THE BROAD UPPER LOW CENTERED SOUTH OF THE ALEUTIANS
WITH NORTH TO NORTHEAST WINDS PERSISTING. FOR THE PRIBILOF ISLANDS
VISIBILITIES HAVE BEEN IMPROVED TO BETWEEN 1 AND 2 MILES OVERNIGHT
AND EXPECTING THAT TREND TO CONTINUE AS WINDS GRADUALLY DIMINISH
AND SNOW TAPERS OFF THROUGH THE DAY...SO THINKING CURRENT
EXPIRATION TIME FOR THE WINTER WEATHER ADVISORY FOR BLOWING SNOW
AT 5 AM LOOKS GOOD.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE STRONG MERIDIONAL SUBTROPICAL JET STEAK WILL CONTINUE TO TRACK
THROUGH THE GULF BEFORE TRANSITIONING INTO THE YUKON TERRITORY.
THIS WILL STRENGTHEN THE UPPER LEVEL AMPLIFIED RIDGE EXTENDING
FROM THE PACIFIC NORTHWEST THROUGH THE SOUTHEAST ALASKA REGION AND
TOWARDS THE BROOKS RANGE. AS THE RIDGE BUILDS THIS WILL INCREASE
THE PRESSURE GRADIENT AND THE TURNAGAIN ARM WINDS WILL BECOME
GUSTY BY SUNDAY. THIS PATTERN WILL RESULT IN ABOVE AVERAGE
TEMPERATURES THROUGH NEXT WEEK. UPSTREAM THERE IS AN UPPER LEVEL
COMPLEX LOW POSITIONED OVER THE CENTRAL TO EASTERN ALEUTIANS.
THIS SYNOPTIC FEATURE WILL RESULT IN CONTINUED SOUTHERLY FLOW
THROUGH THE GULF. COMBINE THIS WITH THE SEVERAL SHORTWAVES TRACKING
THROUGH THE GULF INTO THE SOUTHCENTRAL ALASKA REGION FOR REST OF
NEXT WEEK. THIS WILL BRING ABUNDANT MOISTURE WITH HEAVY PRECIPITATION
ALONG THE NORTH GULF COAST LINE AND SHOWERS IN THE INLAND AREAS.
THE ANCHORAGE BOWL AND THE WESTERN KENAI PENINSULA WILL HAVE DRIER
CONDITIONS DUE TO THE DOWNSLOPING EFFECT. AS THE NORTH PACIFIC LOW
TRACKS NEAR THE EASTERN ALEUTIANS BY SUNDAY THIS WILL BRING A
LARGE SWATH OF MOISTURE AND WARMER TEMPERATURES TO THE THE BERING
SEA AND SOUTHCENTRAL ALASKA REGION. THE CENTRAL/EASTERN BERING SEA
WILL HAVE STRONG EASTERLY/SOUTHEASTERLY GALE FORCE WINDS AS THE
LOW TRACKS ACROSS THE ALEUTIANS BY MONDAY. THIS LOW WILL BRING
WARMER TEMPERATURES TO SOUTHWEST ALASKA THROUGH THE MAJORITY OF
NEXT WEEK. THE MODELS ARE IN SLIGHTLY BETTER AGREEMENT WITH THE
STORM TRACK OF THE AFOREMENTIONED NORTH PACIFIC LOW.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...DENSE FOG ADVISORY...101.
MARINE...GALE WARNING...119 120 127 130 131 132 173 174 175 176.
         HEAVY FREEZING SPRAY WARNING...179 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...MTL
SOUTHCENTRAL ALASKA...BC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JR
LONG TERM...PLD