Small Craft Advisory 311, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
329 PM AKDT FRI APR 8 2016

.ANALYSIS AND UPPER LEVELS...
LOW PRESSURE ACROSS THE COPPER RIVER BASIN IS LIFTING NORTH
BRINGING AN END TO SNOW ACROSS THE REGION. LIGHT SNOW SHOWERS ARE
MAINLY CONFINED TO THE ALASKA RANGE. ELSEWHERE ACROSS
SOUTHCENTRAL...WEAK RIDGING EXTENDING FROM THE NORTHERN GULF IS
ALLOWING TEMPERATURES TO WARM ACROSS INLAND LOCATIONS WITH A FEW
BREAKS IN THE CLOUDS. TO THE WEST...AN UPPER LEVEL LOW SOUTH OF
THE EASTERN ALEUTIANS PUSHED A FRONT INTO THE SOUTHERN BERING
EARLY THIS AFTERNOON. THE LEADING EDGE OF THE FRONT EXTENDS ALONG
A LINE FROM THE SOUTHERN TIP OF THE KENAI TO DILLINGHAM TO THE
PRIBILOF ISLANDS. RAIN IS DEVELOPING ALONG THE BOUNDARY WITH
SCATTERED SHOWERS ACROSS AREAS OF THE WESTERN GULF WHERE THE FRONT
WRAPS AROUND TO THE SOUTH. THE ASSOCIATED SURFACE LOW HAS A 980 MB
CENTER SOUTH OF NIKOLSKI. GUSTY WINDS ARE MAINLY ALONG A TIGHTER
GRADIENT ACROSS THE SOUTHERN AND CENTRAL BERING BETWEEN 20 TO 35
MPH. A DRIER AIR MASS IS MOVING INTO THE ALASKA PENINSULA BEHIND
THE FRONT WITH ANOTHER SURGE OF MOISTURE ALONG A DEVELOPING
SHORTWAVE

&&

.MODEL DISCUSSION...
MODELS ARE IN GOOD AGREEMENT WITH EACH OTHER...HOWEVER NONE OF
THEM ARE EXCEPTIONAL WITH THE INITIALIZATION OF THE DEVELOPING
SHORTWAVE MOVING AROUND THE BASE OF THE TROUGH CENTERED ALONG THE
EASTERN ALEUTIANS. WATER VAPOR SATELLITE IMAGERY SHOWS A NEW LOW
CENTER AT THE BASE OF THE TROUGH WHICH IS MOVING AT A FAST PACE.
FURTHERMORE...A WEAKER SHORTWAVE NORTHEAST OF THIS FEATURE IS
RACING NORTH TOWARD KODIAK ISLAND. A BLEND OF OPERATIONAL MODELS
WERE USED TO CAPTURE THE NEXT SURGE OF MOISTURE AND TRIPLE POINT
LOW ON SATURDAY ALONG WITH ANOTHER WEAKER FRONT TO FOLLOW ON
SUNDAY. MOST OF THE ADJUSTMENTS WERE MADE ACROSS THE SOUTHWEST
MAINLAND FOR WIND AND PRECIPITATION. WINDS ACROSS BRISTOL BAY WILL
MAINLY GUST ACROSS GAPS...INSTEAD OF WIDESPREAD AS MODELS FIRST
INITIALIZED...AND PRECIPITATION TYPE WILL PRIMARILY BE RAIN.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
A WEAK OCCLUDED FRONT NEAR KODIAK EXTENDING INTO THE CENTRAL GULF
WILL MOVE INTO THE BARREN ISLANDS REGION OVERNIGHT BRINGING RAIN
AND WINDY CONDITIONS. CLOUDS AND MOISTURE WILL CONTINUE TO SPREAD
NORTH ACROSS SOUTHCENTRAL THROUGH TONIGHT AND INTO SAT.
PRECIPITATION...PRIMARILY IN THE FORM OF RAIN...WILL BE HEAVIEST
ALONG THE COAST AND SOUTHEAST EXPOSURES AND GENERALLY SPOTTY
INLAND (LEE OF CHUGACH MOUNTAINS) DUE TO DOWNSLOPE DRYING. BRISK
AND GUSTY GAP FLOWS ARE EXPECTED TO CONTINUE TO STRENGTHEN THROUGH
THIS EVENING IN FAVORED LOCATIONS (TURNAGAIN ARM/KNIK RIVER
VALLEY/COPPER RIVER) IN RESPONSE TO A BUILDING COASTAL RIDGE AND
PRESSURE FALLS OVER THE INTERIOR. GAP FLOWS WILL CONTINUE IN MOST
AREAS THROUGH SAT WITH TURNAGAIN ARM AND PORTAGE VALLEY WINDS
REACHING STRONG WIND CRITERIA BY EVENING AND HOLDING INTO LATE
SAT. GALES WILL GRADUALLY SUBSIDE TO SOLID SMALL CRAFT ADVISORY
LEVELS FROM SATURDAY TO SATURDAY NIGHT AS THE FRONT AND BARRIER
JET SLOWLY WEAKEN AS IT MOVES INLAND LATE SUNDAY.

RAIN WILL INCREASE IN COVERAGE AND INTENSITY OVER THE WESTERN
KENAI SUNDAY AS MODELS DEPICT EXCELLENT CURVATURE VORTICITY IN THE
LEFT EXIT REGION OF A STRONGLY CYCLONIC JET STREAK MOVING NORTH
THROUGH THE AREA.

.FIRE WEATHER DISCUSSION (DAYS 1 AND 2)...
THERE ARE NO SIGNIFICANT FIRE WEATHER CONCERNS OVER THE NEXT
COUPLE OF DAYS.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
THE FRONTAL SYSTEM CURRENTLY OVER BRISTOL BAY AND THE SOUTHERN
BERING WILL CONTINUE TO LIFT NORTH AND PUSH FURTHER INTO TO
SOUTHWEST ALASKA THIS EVENING. A FRONTAL WAVE DEVELOPING TO THE
SOUTH WILL TRACK NORTH TOWARDS THE EASTERN ALASKA PENINSULA
SPREADING ADDITIONAL RAIN INTO THE GREATER BRISTOL BAY AREA LATE
TONIGHT. THE SURFACE LOW ASSOCIATED WITH THIS STRENGTHENING WAVE
WILL CROSS THE ALASKA PENINSULA AND BRISTOL BAY SATURDAY MORNING
THEN CONTINUE NORTH UP THE WEST COAST THROUGH THE REMAINDER OF
SATURDAY. IN ADDITION TO BRINGING WIDESPREAD MODERATE TO
OCCASIONALLY HEAVY RAIN TO SOUTHWEST ALASKA THIS WAVE WILL FURTHER
TIGHTEN THE PRESSURE GRADIENT ACROSS THE MOUNTAINS AND BRING
STRONG EASTERLY WINDS THROUGH THE GAPS AND PASSES IN THE ALEUTIAN
AND ALASKA RANGES TONIGHT AND SATURDAY. RAIN WILL TAPER TO SHOWERS
SATURDAY NIGHT AS THE LOW LIFTS NORTH WITH ANOTHER TROUGH BRUSHING
THROUGH THE AREA SUNDAY AND CONTINUING THE SHOWERS.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE LARGE VERTICALLY STACKED LOW CENTERED NEAR THE EASTERN
ALEUTIANS WILL TRACK SLOWLY TO THE NORTHWEST AND INTO THE CENTRAL
BERING THROUGH THE WEEKEND. INSTABILITY SHOWERS WILL ROTATE ACROSS
THE BERING AND WESTERN THEN CENTRAL ALEUTIANS AS COLD AIR ALOFT
WRAPS AROUND TO THE WEST AND SOUTH OF THIS BROAD LOW. THE NEXT
DEVELOPING FRONTAL SYSTEM WILL TRACK FROM WEST TO EAST SOUTH OF
THE ALEUTIAN CHAIN AROUND 45N THROUGH SATURDAY NIGHT THEN TURN
NORTHEAST AND HEAD TOWARDS THE SOUTHWESTERN GULF AS IT WEAKENS.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE PATTERN THROUGH EARLY NEXT WEEK WILL BE CHARACTERIZED BY A
BROAD NEGATIVELY TILTED LONGWAVE TROUGH ENCOMPASSING THE BERING
SEA. THIS WILL KEEP A GENERALLY SHOWERY REGIME IN PLACE OVER THE
BERING AND GULF REGIONS...WITH ENHANCED CHANCES FOR PRECIPITATION
OVER SOUTHCENTRAL AK IN THE SUNDAY NIGHT TIME FRAME AS A
SHORTWAVE TROUGH ROTATES INLAND FROM THE GULF. ATTENTION THEN
TURNS TO A DEEP NORTH PACIFIC LOW POISED TO APPROACH THE WESTERN
ALEUTIANS MONDAY NIGHT. MODELS ARE IN GENERAL AGREEMENT THAT THIS
LOW WILL DEEPEN INTO THE MID 960 MB RANGE...BUT THEY CONTINUE TO
STRUGGLE GREATLY WITH THE POSITION OF THIS FEATURE AS THE WEEK
PROGRESSES. EUROPEAN AND CANADIAN GUIDANCE HAVE BEEN FAIRLY
CONSISTENT IN TRACKING THE LOW ALONG OR SOUTH OF THE ALEUTIAN
CHAIN THROUGH THURSDAY AND THUS KEEPING MOST OF THE IMPACTS
CONFINED TO THE BERING. RECENT GFS RUNS HAVE BEEN TAKING THE LOW
INTO THE BERING AND STALLING IT NEAR NUNIVAK ISLAND AROUND THE
MIDDLE OF THE WEEK...WHICH WOULD REPRESENT A MORE SIGNIFICANT
THREAT OF STRONG GAP WINDS FOR PORTIONS OF SOUTHCENTRAL AK AS THE
PRESSURE GRADIENT BECOMES MORE FAVORABLE. THE CURRENT EXTENDED
FORECAST REFLECTS A PREFERENCE CLOSER TO THE EC SOLUTION GIVEN THE
BETTER OVERALL CONSISTENCY...HOWEVER THE LARGE MODEL SPREAD LENDS
A LOWER DEGREE OF CONFIDENCE TO THE FORECAST. THE EVOLUTION OF
THIS FEATURE WILL CONTINUE TO BE CLOSELY MONITORED IN THE COMING
DAYS.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING 119 130 131 139 174 179.

&&

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