Small Craft Advisory 390, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
422 PM AKDT THU MAY 5 2016

.ANALYSIS AND UPPER LEVELS...
THE MAIN FEATURE EVIDENT ON SATELLITE THIS AFTERNOON IS A MATURE
LOW PRESSURE SYSTEM BOTH ALOFT AND AT THE SURFACE. A PLUME OF
MOISTURE IS APPROACHING SOUTHCENTRAL ALASKA IN THE SOUTHERLY FLOW
ALOFT BUT IT APPEARS AS IF THE JET STREAM IS LEAVING THE SYSTEM
AND POINTING MORE TOWARD THE NORTHERN PANHANDLE MEANING THE
SYSTEM HAS ENTERED A WEAKENING PHASE. SATELLITE BASED OBSERVATIONS
OF PRECIPITABLE WATER INDICATE THE SAME IN THAT THE PLUME WILL GET
CUT OFF AS THE JET SLIDES EAST. THE GALE FORCE FRONTAL BOUNDARY
ASSOCIATED WITH THIS SYSTEM IS STRETCHING PAST KODIAK ISLAND AND
CURVING ALONG THE NORTH GULF COAST. LATE THIS MORNING THE
MIDDLETON ISLAND RADAR IS INDICATING A CHANGEOVER FROM CONVECTIVE
SHOWERY PRECIPITATION TO MORE STEADY STRATIFORM RAIN AS THE FRONT
APPROACHES.

THE UPPER SYSTEM IS CLOSED OFF TO THE SOUTHWEST OF KODIAK ISLAND
AND VERTICALLY STACKED. IT IS SHUNTING THE UPPER LEVEL RIDGE PAST
THE PANHANDLE THOUGH THERE IS LOCALIZED RIDGING BUILDING OVER
SOUTHCENTRAL WITH THE WARM ADVECTION. THE STACKED SYSTEM IS
POSITIVELY TILTED AS A BIGGER RIDGE BUILDS OVER THE BERING SEA IN
RESPONSE TO A DEEPENING KAMCHATKA LOW. THE SHORT TERM FORECAST
WILL REVOLVE AROUND THE DECAY OF THE UPPER LOW AND THE INCOMING
FRONT OUT WEST.

&&

.MODEL DISCUSSION...
BOTH IN THE UPPER LEVELS AND AT THE SURFACE, MODELS ARE IN GREAT
AGREEMENT WITH THE DEVOLUTION OF THE CURRENT SYSTEM AS IT SLIDES
INTO THE NORTHEASTERN GULF. BOTH DOMAINS PREFERRED THE HIGHER
RESOLUTION NAM WITH ALL ELSE BEING EQUAL.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...

THE FRONT IN THE NORTHERN GULF WILL BRING GUSTY WINDS AND RAIN
ACROSS THE COASTAL AREAS THROUGH LATE EVENING. GUSTY WINDS THAT
DEVELOPED ACROSS CHANNELED TERRAIN ACROSS SOUTHCENTRAL WILL RELAX
AS THE PRESSURE GRADIENT WEAKENS LATE THIS EVENING WHEN THE FRONT
PUSHES INLAND. A STRONG SHORT WAVE ROTATES NORTH FROM THE LOW
NEARING KODIAK AND WILL SPREAD RAIN INLAND OVERNIGHT BRINGING
LIGHT ACCUMULATIONS TO MUCH OF THE AREA. SHOWERS WILL CONTINUE IN
THE FORECAST THROUGH THE BEGINNING OF THE WEEKEND AS THE UPPER LOW
SLOWLY TRACKS ACROSS THE SOUTHERN GULF. DRIER CONDITIONS SET UP SATURDAY
NIGHT AS WEAK SURFACE RIDGING BUILDS INTO GULF.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
AHEAD OF THE MAIN FRONT A SHORTWAVE IS PUSHING THROUGH SOUTHWEST
ALASKA AND WILL MOVE OVER THE KUSKOKWIM DELTA THIS AFTERNOON. THIS
MAY HELP TO INITIATE THUNDERSTORMS WEST OF BETHEL BUT WITH WEAK
INDICES DEVELOPMENT WILL BE LIMITED. BEHIND THE SHORTWAVE...RAIN
WILL COME IN FROM THE SOUTH AS THE MAIN FRONT MOVES IN. THAT FRONT
WILL DISSIPATE LATER ON FRIDAY BUT A NEW FRONT FROM THE WEST WILL
THEN MOVE OVER THE AREA SATURDAY AFTERNOON BRINGING BACK MORE
RAIN.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
RIDGING IS OVER THE CENTRAL ALEUTIANS AND TRACKING EAST WITH A
FRONT RIGHT BEHIND IT OVER THE WESTERN ALEUTIANS. THIS NEW SYSTEM
IS WARM AND BRINGING UP RAIN WITH IT. THE FRONT FOR THIS SYSTEM
WILL MAKE IT TO THE EASTERN ALEUTIANS LATE ON FRIDAY AND THEN TO
THE ALASKA PENINSULA SATURDAY MORNING. BEHIND THE FRONT RAIN
SHOWERS WILL PERSIST UNTIL ANOTHER RIDGE MOVES IN OVER THE WESTERN
ALEUTIANS LATER ON SATURDAY.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
BEGINNING THE EXTENDED PERIOD ON SATURDAY NIGHT...HIGH PRESSURE
WILL BUILD OVER THE SOUTHERN MAINLAND AND BRING CLEARING SKIES AND
WARMER WEATHER TO MUCH OF THE MAINLAND THROUGH SUNDAY MORNING. A
LONGWAVE TROUGH OVER THE CENTRAL BERING WILL BEGIN TO PUSH INTO
THE SOUTHERN MAINLAND SUNDAY AFTERNOON...EVENTUALLY SHIFTING THE
UPPER LEVEL RIDGE AXIS FURTHER EASTWARD AND BRINGING AN END TO
SUNNIER AND PLEASANT WEATHER FOR SOUTHERN ALASKA. ANOTHER UPPER
LEVEL TROUGH WILL BEGIN TO FORM OFF THE EASTERN COAST OF THE
KAMCHATKA PENINSULA...THEN PROGRESS EASTWARD OVER THE WESTERN AND
CENTRAL BERING/ALEUTIANS DURING THE BEGINNING OF NEXT WEEK. THIS
PATTERN OF SOUTHWESTERLY FLOW AT 500 HPA WILL BRING MORE CLOUDS
AND RAIN CHANCES TO MOST OF SOUTHERN ALASKA...AS IT PUSHES FURTHER
EASTWARD THROUGHOUT NEXT WEEK. TEMPERATURES ARE ALSO EXPECTED TO
REMAIN CLOSER TO CLIMATOLOGICAL NORMALS...AS THIS PATTERN CHANGES
AFTER WEEKS OF WELL ABOVE AVERAGE TEMPERATURES.

MODELS AGREEMENT ON THE OVERALL SYNOPTIC PATTERN HAS IMPROVED
THROUGH MUCH OF THE MID-TERM AND LONG-TERM...WITH ONLY MINOR
DIFFERENCES REGARDING SOME OF THE FINER DETAILS FOR NEXT WEEK.
THE VARIOUS MEMBERS OF THE GLOBAL ENSEMBLES AND DETERMINISTIC
MODELS CONTINUE TO HANDLE THE RIDGING OVER THE GULF AND SOUTHERN
ALASKA WELL...AS WELL AS THE UPPER TROUGH AND DECAYING LOW/FRONT
OVER THE BERING THROUGH THE WEEKEND. THEY DO HOWEVER STRUGGLE
SLIGHTLY WITH THE TIMING OF THE FRONT PUSHING EASTWARD...AND HOW
FAR EASTWARD THE PRECIPITATION ASSOCIATED WITH THIS SYSTEM MAKES
IT INTO THE SOUTHERN MAINLAND AND GULF. THE MODELS ALSO CONTINUE
TO STRUGGLE WITH THE TRACK AND TIMING OF THE NEXT LOW AND
ASSOCIATED FRONT PUSHING THROUGH THE BERING DURING THE MIDDLE OF
NEXT WEEK. CURRENTLY THE EC BECOMES A SLIGHT OUTLIER STALLING THE
SURFACE LOW OVER THE WESTERN BERING...AS THE GFS AND CANADIAN
MODELS ARE SHOWING A SLIGHTLY QUICKER AND EASTERLY SOLUTION TO
THESE FEATURES.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING...119 120 130 138 139 155 172 177 178.

&&

SYNOPSIS AND MODEL DISCUSSION...ML
SOUTHCENTRAL ALASKA...KH
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DK
LONG TERM...PEPE