Small Craft Advisory 905, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
506 AM AKST SAT NOV 14 2015

.ANALYSIS AND UPPER LEVELS...

LOW PRESSURE CONTINUES TO SLOWLY WEAKEN OVER THE NORTHEASTERN
GULF OF ALASKA...WITH COLD ADVECTION AND ASSOCIATED SCATTERED
SHOWER ACTIVITY CONTINUING TO THE WEST OF THE LOW OVER THE
NORTHERN AND CENTRAL GULF. THE THERMAL AND PRESSURE GRADIENT IS
ALLOWING STRONG WINDS TO CONTINUE THROUGH GAP WIND AREAS OF THE
GULF COAST (SUCH AS VALDEZ...SEWARD AND WHITTIER). AN UPPER LEVEL
TROUGH OVER THE COOK INLET REGION EXTENDING THROUGH THE WESTERN
GULF CONTINUES TO INITIATE A DEFORMATION ZONE OVER THE NORTHERN
GULF AND SOUTHCENTRAL ALASKA. HOWEVER...WITH DRY OFFSHORE FLOW IN
THE LOWER ATMOSPHERE THESE CLOUDS ARE REMAINING HIGH-BASED AND
DEVOID OF PRECIPITATION. THIS TROUGH ALSO SERVES AS THE
DELINEATION...OR EASTERN EDGE...OF THE FAST WEST TO NORTHWESTERLY
UPPER LEVEL FLOW (JET STREAM) THAT HAS BEEN A COMMON FEATURE OVER
THE BERING REGION FOR MANY DAYS NOW. A LOW PRESSURE SYSTEM HAS
MOVED OFF OF THE KAMCHATKA COAST INTO THE NORTHWEST BERING DUE
WEST OF SAINT MATTHEW ISLAND AND CONTINUES TO STRENGTHEN...AND
EXTENDS A WEAK FRONTAL BOUNDARY SOUTH AND EAST THROUGH THE
SOUTHEASTERN BERING BETWEEN THE PRIBILOFS AND SOUTHWEST ALASKA.
BEHIND THIS FRONT AND SOUTH OF THE LOW...A LACK OF LOW-LEVEL
STABILITY IS HELPING TO GENERATE WIDESPREAD SCATTERED TO NUMEROUS
SHOWER ACTIVITY ACROSS MUCH OF THE CENTRAL AND WESTERN BERING SEA.
A FEW ISOLATED LIGHTNING STRIKES HAVE EVEN BEEN DETECTED AHEAD OF
A VORT MAX MOVING WEST TO EAST ACROSS THE SOUTHWESTERN BERING
ACCOMPANIED BY A PRONOUNCED MID-LEVEL DRY SLOT. A WEAK RIDGE OF
HIGH PRESSURE ALOFT BETWEEN THE NORTHWEST BERING LOW AND THE UPPER
LEVEL TROUGH OVER SOUTHCENTRAL ALASKA CONTINUES TO TRACK SLOWLY
EAST ACROSS SOUTHWEST ALASKA.

&&

.MODEL DISCUSSION...
THE MODELS REMAIN IN GOOD AGREEMENT WITH THE DISSIPATION OF THE
GULF LOW INTO A BROAD TROUGH THROUGH SUNDAY OVER THE NORTHEAST
GULF...AND WITH THE DEVELOPMENT OF THE BERING LOW INTO THIS
WEEKEND. IN PARTICULAR THEY HAVE COME INTO BETTER AGREEMENT THAT
ANY SNOWFALL FROM THE GULF LOW AS IT MAKES LANDFALL SATURDAY
AFTERNOON WILL LARGELY STAY CONFINED TO THE EASTERN COPPER RIVER
BASIN...RATHER THAN SPREADING TOWARDS THE VALDEZ/THOMPSON PASS
AREA AS THE MODELS HAD PREVIOUSLY INDICATED. OVER THE BERING SEA
THE MODELS CONTINUE TO BE IN GOOD AGREEMENT WITH THE GENERAL
INTENSITY...BUT STILL HAVE SOME MINOR DIFFERENCES MAINLY IN
POSITIONING AS IT NEARS THE PRIBILOFS TONIGHT. AS A RESULT THERE
IS NOW GOOD CONFIDENCE THAT THIS SYSTEM WILL DEEPEN TO A STORM
FORCE LOW THIS EVENING INTO THE OVERNIGHT PERIOD OVER THE CENTRAL
BERING.

MODEL AGREEMENT ALMOST COMPLETELY DISAPPEARS SUNDAY NIGHT THROUGH
EARLY NEXT WEEK AS MODELS STRUGGLE WITH HOW TO DEPICT INTERACTION
BETWEEN THE JET STREAM OVER THE BERING REGION AND THE NORTHERN
PACIFIC JET STREAM. BECAUSE OF THE COMPLEXITY OF THESE
FEATURES...PREDICTABILITY IS INCREDIBLY LOW AT THIS TIME WITH ANY
SPECIFIC LOW PRESSURE SYSTEM WITH REGARDS TO WINDS AND
PRECIPITATION. HOWEVER...IT DOES APPEAR THAT THE PRIMARY STORM
TRACK FOR ANY LOW PRESSURE SYSTEM(S) WOULD REMAIN SOUTH OF THE
ALASKA MAINLAND AND HEAD IN THE GENERAL DIRECTION OF THE SOUTHEAST
PANHANDLE.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE STRONG WINDS ALONG THE GULF COAST WILL BEGIN A DOWNWARD TREND
TODAY AS THERMAL AND PRESSURE GRADIENTS WEAKEN. THERE MIGHT BE A
BRIEF BUMP BACK UP IN WINDS AS A SHORT-WAVE TROUGH PASSES THROUGH
WESTERN PRINCE WILLIAM SOUND THIS EVENING...BUT NOT NEARLY AS
STRONG AS THEY HAVE BEEN THE PAST COUPLE DAYS.

THE LARGER SCALE TROUGH WHICH HAS BEEN SITTING OVER SOUTHCENTRAL
ALASKA AND THE GULF WILL LIFT NORTHEASTWARD TODAY THROUGH TONIGHT
AND INTERACT WITH THE REMNANT LOW OVER THE NORTHEAST GULF. THIS
WILL CAUSE LIGHT SNOW TO SPREAD INTO THE EASTERN COPPER RIVER
BASIN. LIGHT SNOW OR FLURRIES MAY MAKE IT AS FAR WEST AS
GLENNALLEN. MORE IMPORTANTLY...THE PRESENCE OF CLOUDS WILL KEEP
TEMPERATURES FROM PLUMMETING ACROSS MUCH OF THE BASIN. AREAS NORTH
AND WEST OF GLENNALLEN CAN EXPECT NOTABLY COLDER TEMPERATURES WITH
LESS CLOUD COVER.

MEANWHILE...THE UPPER JET WILL REMAIN ACTIVE FROM THE ALEUTIANS TO
THE SOUTHERN GULF. A SERIES OF SYSTEMS WILL PASS SOUTH OF KODIAK
ISLAND BRINGING QUICK SHOTS OF SNOW SHOWERS...MAINLY ACROSS THE
SOUTH END OF THE ISLAND.

THE REMAINDER OF SOUTHCENTRAL ALASKA WILL SETTLE INTO THE DEEP
FREEZE WITH TEMPERATURES APPROXIMATELY 15 TO 20 DEGREES BELOW
NORMALS FROM THE WESTERN KENAI PENINSULA TO ANCHORAGE AND THE
MAT-SU. SOME VERY LIGHT AND LOCALIZED WINDS THE PAST COUPLE
NIGHTS HAVE KEPT TEMPERATURES FROM DROPPING AS FAR AS THEY COULD
WITH THE AIR MASS IN PLACE. THIS WILL CHANGE THE NEXT COUPLE
NIGHTS AS WINDS GO CALM MOST PLACES.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
INLAND AREAS OF THE SOUTHWEST LOOK TO STAY RELATIVELY DRY THROUGH
THE WEEKEND WITH THE MAJORITY OF THE ACTIVITY HAPPENING FAR ENOUGH
OVER THE WATER TO KEEP ONLY SCATTERED SNOW SHOWERS ALONG THE
COAST. WEAK EASTERLY FLOW WILL ALSO AID IN THIS. ADDITIONALLY...THESE
DRIER CONDITIONS WILL LEAD TO MORE CLEARING IN CLOUD COVER THAT
WILL HELP TO DROP TEMPERATURES OVERNIGHT. AREAS FURTHER INLAND
LOOK TO DROP BELOW ZERO FOR SUNDAY NIGHT WHICH WILL MORE CLEAR AND
COLD THAN TONIGHT.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
NORTHWEST FLOW WILL CONTINUE TO BRING SNOW SHOWERS TO THE BERING
AND RAIN AND SNOW SHOWERS TO THE ALEUTIANS THROUGH SUNDAY. ALSO
ASSOCIATED WITH THIS FLOW IS A LOW OVER THE NORTHERN BERING THAT
IS TRACKING TO THE SOUTHEAST. THE LOW IS SUPPORTED BY A JET STREAK
THAT IS HELPING TO STRENGTHEN WINDS AS IT MOVES ACROSS THE BERING.
HOWEVER...THERE IS ENOUGH DISAGREEMENT AMONGST THE MODELS TO GIVE
UNCERTAINTY WITH THE LOWS POSITION. THIS IMPACTS HOW STRONG THE
NORTHERLY WINDS WILL GET FOR THE PRIBILOF ISLANDS AS THE LOW
PASSES EARLY SUNDAY. IF THE LOW TRACKS OVERHEAD THE WINDS WILL BE
WEAKER THAN IF IT PASSES TO THE EAST. THE HIGHER CONFIDENCE IS
THAT THE LOW WILL PASS JUST TO THE EAST OF THE ISLANDS WHICH WILL
BRING STRONGER NORTHERLY WINDS. THEN SUNDAY EVENING THE LOW MOVES
ACROSS THE ALASKA PENINSULA BRINGING MORE WINDS AND SHOWERS TO THE
AREA.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE BEGINNING OF NEXT WEEK WILL FEATURE WELL BELOW NORMAL
TEMPERATURES ACROSS THE SOUTHERN MAINLAND AS THE LONGWAVE TROUGH
IS REINFORCED BY AN UPPER LOW DIVING SOUTHEAST ACROSS THE BERING
SEA INTO THE GULF OF ALASKA. THIS WILL KEEP ANY PRECIPITATION
CONFINED TO THE GULF AND KODIAK ISLAND THROUGH TUESDAY AS OUTFLOW
WINDS CONTINUE ALONG THE GULF COAST. FORECAST CONFIDENCE DECREASES
BY THE MIDDLE OF THE WEEK AS THE LONGWAVE TROUGH IS DISPLACED
EASTWARD. THE GFS DEPICTS A TRANSITION TO QUASI ZONAL FLOW WITH
SEVERAL UPPER LEVEL WAVES TRACKING THROUGH THE INTERIOR WHEREAS
EUROPEAN GUIDANCE BUILDS A HIGH AMPLITUDE RIDGE OVER THE
MAINLAND. THIS MORE AMPLIFIED SOLUTION WOULD KEEP SOUTHCENTRAL DRY
THROUGH MUCH OF NEXT WEEK AS MOST OF THE ENERGY WOULD BE HELD BACK
OVER THE BERING AND WEST COAST. THE FORECAST REFLECTS SOMEWHAT OF
A MIDDLE GROUND APPROACH...WITH PRECIPITATION CHANCES GRADUALLY
INCREASING FROM WEST TO EAST DURING THE LATTER HALF OF THE WEEK AS
TEMPERATURES SLOWLY MODERATE TO NEAR NORMAL VALUES IN INCREASING
SOUTHWESTERLY FLOW.

OVER THE BERING...A SHOWERY NORTHWEST FLOW REGIME WILL GIVE WAY
TO A MORE PROGRESSIVE PATTERN EARLY IN THE WEEK AS A KAMCHATKA LOW
SWINGS A GALE FORCE FRONT ACROSS THE BERING AND ALEUTIANS. THIS
WILL BE FOLLOWED CLOSELY BY ANOTHER SYSTEM DURING MIDDLE TO LATTER
PORTIONS OF THE WEEK. MODELS ARE STILL STRUGGLING TO PIN DOWN THE
EXACT DETAILS OF THESE FEATURES...BUT IN GENERAL WET AND WINDY
CONDITIONS CAN BE EXPECTED ACROSS THE BERING FOR MUCH OF THE NEXT
WEEK.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...HEAVY FREEZING SPRAY...181.
         GALE...121 127 130 131 132 170 172 173 147 175 176
                179 185

&&

SYNOPSIS AND MODEL DISCUSSION...CC
SOUTHCENTRAL ALASKA...SB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DK
LONG TERM...CB/MMC