Small Craft Advisory 23, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
245 PM AKST MON JAN 7 2013

.ANALYSIS AND UPPER LEVELS...
A BROAD UPPER-LVL TROUGH OVER THE SOUTHERN MAINLAND IS SLOWLY
RETREATING EAST. A SURFACE LOW EMBEDDED IN THIS UPPER TROUGH IS
CENTERED AROUND 120 MILES EAST OF KODIAK CITY...IS FILLING...AND ALSO
DRIFTING TO THE EAST. BANDS OF SNOW AND RAIN SHOWERS WITH THE LOW
BRUSH PRINCE WILLIAM SOUND AND THE SOUTHERN TO EASTERN KENAI
PENINSULA...WITH MAINLY DRY CONDITIONS ASIDE FROM A FEW PASSING
FLURRIES AND CLOUDY SKIES ELSEWHERE ACROSS SOUTHCENTRAL AK. COLD
ADVECTION IS BEGINNING TO WRAP AROUND THE BACKSIDE OF THE LOW WITH
STRENGTHENING N TO W GAP WINDS ACROSS THE NW GULF AND KODIAK ISLAND
PER SURFACE OBSERVATION TRENDS. A SMALL BAROCLINIC ZONE OVER THE
KUSKOKWIM DELTA IS SQUEEZING OUT SOME SNOW OVER THE SW MAINLAND.

FURTHER WEST...AN UPPER-LVL RIDGE BUILDS THROUGH THE EASTERN ALEUTIAN
CHAIN...NESTLED IN BETWEEN THE GULF LOW AND ANOTHER UPPER-LOW THAT IS
NEARLY STATIONARY OFF THE KAMCHATKA PENINSULA. A STRONG FRONT DRAPED
THROUGH THE WEST TO CENTRAL CHAIN EXTENDS BACK TO THE NORTH PACIFIC
OCEAN. A VIGOROUS SURFACE LOW ALONG THE FRONT 350 MILES SOUTH OF
KISKA IS DEEPENING AND TRACKING NORTH WITH AN AREA OF STORM TO
HURRICANE FORCE WINDS.

.MODEL DISCUSSION...
IN THE EAST...THE LOW EAST OF KODIAK CITY IS SHOWN MOVING TO AROUND
250 MILES SOUTHEAST OF MIDDLETON ISLAND TUE AFTERNOON...THEN BECOMING
ABSORBED EARLY ON WED BY A STRONGER LOW MOVING TO SW BRITISH
COLUMBIA. OFF-SHORE FLOW IN IT'S WAKE IS DEPICTED SIMILARLY...
SUGGESTING COOLER AND DRIER CONDITIONS ACROSS SOUTHCENTRAL AK INTO
MID WEEK. MORE SIZABLE DIFFERENCES ARISE LATE WED INTO THU AS A
RESIDUAL SURFACE WAVE FROM THE BERING/ALEUTIANS MIGRATES TOWARDS THE
GULF. FOR NOW HAVE KEPT CLOSE TO THE INHERITED FORECAST WITH SOME
ECMWF BLENDED. OVER SW AK...12Z MODEL QPF INITIALIZATION WAS POOR
OVER THE KUSKOKWIM DELTA BASED ON RADAR...THOUGH THE ECMWF AND UKMET
SEEMED TO HAVE THE CLOSEST PRECIP SOLUTIONS. GFS/NAM DID HAVE SOME
MODEST Q-VECTOR CONVERGENCE IN THIS ZONE OF HEAVIEST PRECIP...WHICH
WEAKENS THIS EVENING.

OUT WEST...CONSIDERABLE DIFFERENCES EXIST WITH THE FRONT AND
DEVELOPING LOW IMPACTING THE WESTERN CHAIN AND BERING. SATELLITE
IMAGERY SUGGESTS THE LOW IS WRAPPING NORTH QUICKLY...GIVING SOME
CREDENCE TO THE GFS SOLUTION WHICH IS FASTEST AND ALSO STRONGEST. THE
ECMWF HAS THE SLOWEST TRACK...BUT THE LAST COUPLE RUNS HAVE BEEN
RATHER CONSISTENT. THERE IS GENERAL AGREEMENT THAT THE LOW TRACKS TO
THE FAR NW BERING SEA TUE AFTERNOON AT PEAK INTENSITY NEAR 970
MB...THEN PINWHEELS WEST TO REINFORCE THE INCREASINGLY COMPLEX
UPPER-LOW THAT DRIFTS CLOSER TOWARDS ATTU IN THE COMING DAYS. AS THE
RESIDUAL FRONT PUSHES THROUGH THE EASTERN BERING...DETAILS ON WHERE
VARIOUS WAVES OF ENERGY TRACK BECOMING INCREASINGLY DIFFICULT TO
RESOLVE. HAVE TENDED TO EMPLOY AN ENSEMBLE APPROACH WITH SOME
GFS/ECWMF BLENDED IN TO THE FORECAST.

.SHORT TERM FORECAST...
SOUTHCENTRAL AND GULF...
SHOWERS ALONG THE NORTHERN GULF COAST TRENDS DRIER AS NORTH TO WEST
OFF-SHORE FLOW ESTABLISHES ITSELF IN THE WAKE OF THE LOW. TYPICAL
AREAS WILL SEE GUSTY GAP WINDS...BUT THE DEGREE AND DURATION OF COLD
ADVECTION IS MARGINALLY WEAK IN THE ABSENCE OF ANY ENTRENCHED ARCTIC
AIR TO BLEED DOWN INTO THE SOUTHERN MAINLAND. AS SUCH...GAP WINDS
SHOULD GENERALLY REMAIN AT GALE FORCE OR WEAKER. INLAND...MID AND LOW
LEVEL DRYING IN THE OFF-SHORE FLOW SHOULD SCOUR OUT CLOUDS AND LEAD
TO MORE SUNSHINE...THE CAVEAT BEING PERHAPS SOME PATCHY MORNING FOG
NEAR THE TURNAGAIN/KNIK ARM INLETS. MOISTURE FROM THE WESTERN
ALEUTIAN SYSTEM TRACKS TOWARDS THE SW GULF AND KODIAK ISLAND ON WED
WITH MORE SNOW/RAIN.

SOUTHWEST AND AKPEN...
BAROCLINIC ZONE OVER SW AK TO SHEAR APART TONIGHT AS ANTI-CYCLONIC
FLOW ALOFT BECOMES PREDOMINANT WITH THE APPROACHING UPPER-RIDGE FROM
THE SOUTHWEST. PRECIPITATION THREAT DECREASES ON TUE WITH LESS
LIFT/FORCING...BUT CHANCES OF FOG/STRATUS INCREASE FROM ACCOMPANYING
SUBSIDENCE AND WEAK WEST FLOW. THE BREAK IN STEADY PRECIPITATION IS
RATHER BRIEF HOWEVER AS ENERGY FROM THE ALEUTIAN SYSTEM FRONT
ADVANCES BY EARLY WED. THERE IS MORE UNCERTAINTY THAN USUAL REGARDING
WIND INTENSITY FORECASTS FOR THE WESTERN CAPES/BRISTOL BAY ON WED DUE
TO POOR MODEL AGREEMENT WITH VARIOUS SURFACE WAVES TRAVERSING THROUGH
THE REGION. A TREND TOWARDS STRENGTHENING WINDS TO GALES MIGHT BE
WARRANTED IF DETAILS CAN BE RESOLVED.

BERING SEA/ALEUTIANS...
HURRICANE FORCE WINDS ARE PROBABLE OVERNIGHT TONIGHT OVER THE WEST
CENTRAL CHAIN AS THE SURFACE LOW DEEPENS SHARPLY AND TRACKS TO JUST
WEST OF ADAK. THE PEAK OF THE WINDS WILL DIMINISH WITH FROPA BUT
REMAIN GUSTY AT SOLID GALES WELL INTO TUE NIGHT DUE TO A SQUEEZED
PRESSURE GRADIENT. THE STRONG FRONT TRACKS THROUGH THE PRIBILOFS AND
EASTERN CHAIN THROUGH TUE. THERE SHOULD BE ENOUGH OF A WARM PUSH IN
THE SOUTHERLY FLOW THAT FALLING SNOW SHOULD BE FAIRLY WET AND LESS
LIKELY TO BLOW AROUND...RETARDING BLOWING SNOW THREATS. RAIN MAY ALSO
MIX IN AT TIMES.

.LONG TERM FORECAST...
AN UPPER-LOW MEANDERS NEAR THE WESTERN TIP OF THE ALEUTIANS THROUGH
LATE WEEK...KEEPING CONDITIONS RATHER UNSETTLED OVER THE
BERING/CHAIN. MODELS SHOW A RATHER STRONG PACIFIC LOW TRACKING TO THE
CHAIN FRI NIGHT TO SAT REINFORCING THIS PATTERN. ACROSS THE SOUTHERN
MAINLAND/GULF...RESIDUAL ENERGY AND MOISTURE FROM TONIGHT'S ALEUTIAN
SYSTEM LOOK TO BE AROUND ON THU AS WEDNESDAY'S UPPER-RIDGE RETREATS
TO THE EAST. GLOBAL MODELS ARE SUGGESTING AN AMPLIFYING FLOW BY THE
WEEKEND AND WHILE DETAILS REMAIN UNCERTAIN...AN ACTIVE PATTERN
APPEARS LIKELY EVEN FOR THE EASTERN AOR.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...HIGH WIND WARNING...187
MARINE...STORM...172 175 412 413
         GALE...130 132 138 140 150 155 170 176 179 185 351 352 411
                414
         HEAVY FREEZING SPRAY...185
FIRE WEATHER...NONE

MALOY