Small Craft Advisory 677, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
241 PM AKDT SAT SEP 6 2014

.ANALYSIS AND UPPER LEVELS...AS ONE SHORT-WAVE EXITS THE COPPER
RIVER BASIN INTO CANADA ANOTHER IS DIGGING SOUTHEASTWARD ACROSS
INTERIOR SOUTHWEST ALASKA TOWARD SOUTHCENTRAL ALASKA. SATELLITE
IMAGERY SHOW SOME CONVECTIVE CUMULUS CLOUDS MOVING INTO THE
SUSITNA VALLEY AHEAD OF THIS. MUCH OF THE REST OF SOUTHCENTRAL
IS STUCK UNDER A BLANKET OF LOW CLOUDS AND/OR FOG THIS
MORNING IN THE WAKE OF THE EXITING SHORT-WAVE - LEAVING BEHIND
STABLE CONDITIONS AND ABUNDANT LOW LEVEL MOISTURE. INCREASED
INSTABILITY AND MID TO UPPER LEVEL LIFT WITH NEXT SHORT-WAVE WILL
HELP BREAK MUCH OF THIS UP AS WE HEAD THROUGH THE DAY. WITH LOW
LEVEL WEST TO NORTHWEST FLOW THE EXCEPTION TO THIS WILL BE ALONG
THE WEST SIDE OF MOUNTAIN RANGES WHICH WILL REMAIN SOCKED IN AS
LOW LEVEL CLOUDS BANK UP AGAINST THE MOUNTAINS. MEANWHILE...AT THE
SURFACE A TROUGH OVER THE NORTHERN GULF COMBINED WITH HIGHER
PRESSURE BUILDING IN FROM THE WEST IS PRODUCING SOME GUSTY GAP
WINDS OVER PORTIONS OF THE WESTERN GULF AND PRINCE WILLIAM SOUND.

THE LARGE DEEP LOW JUST SOUTH OF THE ALEUTIANS BOTTOMED OUT LAST
NIGHT AND HAS BEGUN TO SLOWLY WEAKEN. HOWEVER A LOOK AT WATER
VAPOR IMAGERY SHOWS A STRONG SHORT-WAVE AND JET STREAK MOVING UP
THE EAST SIDE OF THE LOW PRODUCING STRONG UPWARD VERTICAL MOTION
FROM THE EASTERN ALEUTIANS ACROSS MUCH OF THE CENTRAL BERING. THIS
LINES UP PRETTY WELL WITH THE FRONTAL SYSTEM...SO IN WAY THIS IS
HELPING TO ENHANCE RAINFALL ALONG THE FRONT WHICH CONTINUES TO
TRACK NORTH AND EAST ACROSS THE BERING SEA AND ALEUTIANS.

&&

.MODEL DISCUSSION...MODELS CONTINUE TO HAVE A GOOD HANDLE ON
CURRENT SYSTEMS. THERE ARE SOME MINOR DIFFERENCES WITH TRACK OF
THE ALEUTIAN LOW ACROSS THE BERING...PARTICULARLY AS AN UPPER LOW
MOVES OUT OF ASIA TUESDAY ESSENTIALLY REPLACING THE EXISTING LOW
WITH A NEW CENTER FURTHER WEST. MEANWHILE...WITH A PERSISTENTLY
STRONG JET ON THE EAST SIDE OF THE LOW THERE IS A TREND TOWARD
FASTER MOVEMENT OF THE FRONTAL SYSTEM TOWARD MAINLAND ALASKA...SO
WILL ADJUST POP FORECAST TO FOLLOW SUIT. FORECAST CONFIDENCE
STARTS OUT ABOVE AVERAGE BUT DROPS TO AVERAGE TO BELOW AVERAGE
MONDAY NIGHT AND TUESDAY DUE TO UNCERTAINTY IN PLACEMENT OF
SMALLER SCALE FEATURES.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...EXPECT SHOWERS TO REDEVELOP OUT AHEAD OF
APPROACHING SHORT-WAVE THIS AFTERNOON...PRIMARILY WHERE DEEPEST
MOISTURE STILL EXISTS FROM THE TALKEETNA MOUNTAINS EASTWARD ACROSS
THE COPPER RIVER BASIN. ANY CONVECTION THAT FORMS OUTSIDE OF THIS
REGION SHOULD BE MORE ISOLATED IN NATURE. SOUTHCENTRAL WILL THEN
CLEAR OUT TONIGHT INTO SUNDAY MORNING AS THIS SHORT-WAVE QUICKLY
EXITS TO THE EAST AND COOLER AND DRIER AIR MOVES IN. SUBSIDENCE
WITH PASSAGE OF THE WAVE COMBINED WITH WEAK COLD ADVECTION AND
TIGHTENING PRESSURE GRADIENTS WILL CAUSE GAP WINDS TO INCREASE
ALONG PRINCE WILLIAM SOUND AND THE NORTH GULF COAST...PEAKING LATE
TONIGHT THROUGH EARLY SUNDAY MORNING. THE WINDS WILL RAPIDLY COME
DOWN DURING THE DAY SUNDAY AS PRESSURE GRADIENTS SLACKEN AND UPPER
SUPPORT EXITS TO THE EAST.

WITH LIGHT WINDS AND CLEAR SKIES SUNDAY NIGHT LOOKS REALLY GOOD
FOR RADIATIONAL COOLING...WITH TEMPERATURES DROPPING INTO THE 30S
ACROSS MUCH OF THE REGION...SIMILAR TO ONE WEEK AGO. MOST OF THE
SAME AREAS WHICH SAW FREEZING TEMPERATURES LAST WEEKEND CAN EXPECT
TO SEE THEM AGAIN.

WITH FASTER EASTWARD PROGRESSION OF THE BERING FRONTAL SYSTEM
EXPECT INCREASING CLOUDS AND A CHANCE OF SHOWERS AS WE HEAD
THROUGH MONDAY AND MONDAY NIGHT. THERE WON'T BE MUCH STRUCTURE
LEFT TO THE SYSTEM...SO ANY PRECIPITATION THAT DOES FALL WILL BE
MUCH LIGHTER AND SHORT-LIVED THAN THE STORM SYSTEM WHICH MOVED
THROUGH THE PAST COUPLE DAYS.

SOUTHWEST ALASKA...BRISTOL BAY STARTED TODAY OFF WITH AREAS OF LOW
CLOUDS AND FOG. LOW LEVEL OFFSHORE FLOW WILL BEGIN TO INCREASE
OVERNIGHT TONIGHT AHEAD OF APPROACHING FRONTAL SYSTEM. THUS EXPECT
LITTLE IF ANY FOG TO FORM TONIGHT. THE FRONTAL SYSTEM WILL BE
RAPIDLY WEAKENING AS IT ARRIVES ALONG THE SOUTHWEST COAST SUNDAY
AFTERNOON AND EVENING SO EXPECT AREAS OF LIGHT RAIN AND NOT A
WHOLE LOT OF WIND. A SERIES OF UPPER LEVEL WAVES WILL THEN CROSS
THE REGION SUNDAY NIGHT THROUGH TUESDAY BRING OCCASIONAL RAIN OR
SHOWERS. ALL OF THESE FEATURES LOOK WEAK SO PRECIP WILL GENERALLY
BE LIGHT AND INTERMITTENT.

BERING SEA/ALEUTIANS...THE ALEUTIAN SYSTEM WILL BE SLOW TO WEAKEN
AS IT MOVES INTO THE BERING SEA TONIGHT AND SUNDAY. WITH
REINFORCEMENT FROM ANOTHER SYSTEM MOVING OUT OF ASIA TUESDAY A
GENERALLY CLOUDY AND WET PATTERN WILL PERSIST.

&&

.LONG TERM FORECAST...
DESPITE SOME RELATIVELY LARGE CHANGES IN MODEL GUIDANCE OVER THE
PAST 24 HOURS...FORECAST THINKING FOR THE BEGINNING OF THE
EXTENDED TERM REMAINS LARGELY UNCHANGED AS THE SOUTHERN MAINLAND
LOOKS TO TRANSITION BACK TO A MUCH WETTER PATTERN BY EARLY NEXT
WEEK. MODELS HAVE ALL SHIFTED THE LARGE UPPER LOW OVER THE BERING
FARTHER WEST DURING THE FIRST HALF OF NEXT WEEK...WHICH WOULD
FOCUS MOIST SOUTHERLY FLOW OVER THE SOUTHWEST MAINLAND AS OPPOSED
TO SOUTHCENTRAL AK AS HAD BEEN DEPICTED FOR THE PAST SEVERAL DAYS.
HOWEVER...SOUTHCENTRAL WILL STILL SEE PLENTY OF CHANCES FOR
PRECIPITATION THROUGH NEXT WEEK AS A SERIES OF FRONTS MOVE THROUGH
THE GULF.

THE BIGGEST CHANGE TO THE EXTENDED FORECAST INVOLVES THE POTENTIAL
FOR A STRONG STORM TO MOVE INTO THE EASTERN BERING LATE NEXT
WEEK. MODELS HAVE BEEN HINTING AT THIS POSSIBILITY FOR THE PAST
FEW RUNS...WITH BOTH THE EC AND GFS DEPICTING A SUB 960 MB LOW
PASSING EAST OF THE PRIBILOF ISLANDS LATE FRIDAY. FORECAST
CONFIDENCE IN THIS SCENARIO REMAINS LOW GIVEN EXPECTED MODEL
INCONSISTENCIES ASSOCIATED WITH A DAY 7 FORECAST...HOWEVER THIS
POTENTIAL WILL NEED TO BE CLOSELY MONITORED OVER THE COMING DAYS.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING...170 172 173 174 175 176 178 179 185.
FIRE WEATHER...NONE.

&&

SEB/CB SEP 14