Small Craft Advisory 224, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
441 PM AKDT THU MAR 12 2015

.ANALYSIS AND UPPER LEVELS...
AN UPPER LEVEL LOW IS CENTERED ALONG THE SPINE OF THE WESTERN
ALASKA RANGE BETWEEN THE SUSITNA VALLEY AND KUSKOKWIM VALLEY. A
HIGH AMPLITUDE TROUGH EXTENDS SOUTHWARD ACROSS THE WESTERN GULF
INTO THE NORTH PACIFIC. A SURGE OF ARCTIC AIR BEHIND THE TROUGH IS
LEADING TO SOME FAIRLY STRONG WINDS ALONG THE ALASKA PENINSULA AND
ACROSS THE WESTERN GULF...AS SEEN IN SATELLITE WIND DATA AND WELL
DEFINED CLOUD STREETS IN SATELLITE IMAGERY. SURFACE OBS AND WEB
CAMS ALSO SHOW SOME LOCALLY HEAVY BANDS OF SNOW SHOWERS OVER
SOUTHERN COOK INLET/SOUTH SIDE OF KACHEMAK BAY AND OVER THE FAR
SOUTHERN END OF KODIAK ISLAND. IF THESE BANDS REMAIN STATIONARY
FOR SEVERAL HOURS THESE AREAS COULD PICK UP A QUICK HALF FOOT OF
SNOW. THE SOUTH END OF THE TROUGH IS DIGGING SOUTHEASTWARD
CAUSING THE DOWNSTREAM RIDGE TO AMPLIFY AND HIGH CLOUDS TO SPREAD
WESTWARD ACROSS SOUTHCENTRAL ALASKA.

MEANWHILE OUT WEST A LARGE CYCLONIC CIRCULATION IS CENTERED OVER
THE FAR WESTERN BERING SEA WITH MULTIPLE EMBEDDED WAVES. THE
SUBTROPICAL JET OVER THE NORTHWEST PACIFIC IS HELPING DRIVE THE
TROUGH (AND A SERIES OF SHORT-WAVES) EASTWARD ALONG THE ALEUTIANS.
AT THE SURFACE A GALE FORCE OCCLUDED FRONT IS ELONGATING AS IT
SPREADS NORTH AND EASTWARD ACROSS THE CENTRAL BERING AND CENTRAL
ALEUTIANS. A COUPLE OF WEAK LOWS HAVE FORMED ALONG THE FRONT AND
ANOTHER MARGINALLY STRONGER LOW HAS FORMED JUST UPSTREAM OF THE
WESTERN ALEUTIANS.

&&

.MODEL DISCUSSION...
MODELS REMAIN IN RELATIVELY GOOD AGREEMENT WITH SYNOPTIC SCALE
FEATURES THROUGH SATURDAY. THERE ARE SOME MINOR DIFFERENCES IN
LOW POSITIONS OUT WEST...WHICH IS UNDERSTANDABLE CONSIDERING THE
COMPLEX NATURE OF THE FLOW AND NUMEROUS UPPER LEVEL WAVES
TRANSITING THE REGION. PREFER THE ECMWF WITH THE DEEPENING LOW
SOUTH OF THE ALEUTIAN CHAIN FRIDAY NIGHT AND SATURDAY DUE TO
GOOD RUN-TO-RUN CONSISTENCY. OVER SOUTHCENTRAL ALASKA MODELS HAVE
TRENDED WETTER AND FARTHER WEST WITH PRECIP AS UPPER TROUGH
AMPLIFIES TONIGHT AND FRIDAY. THUS...WILL TREND HIGHER WITH POPS
AND QPF FROM EASTERN PRINCE WILLIAM SOUND TO THE COPPER RIVER
BASIN.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
AS THE UPPER LEVEL TROUGH CONTINUES EASTWARD ACROSS THE GULF IT
WILL BECOME NEGATIVELY TILTED AND INDUCE DEVELOPMENT OF A SURFACE
LOW OVER THE NORTHERN GULF/PRINCE WILLIAM SOUND AREA. THIS ALONG
WITH ARRIVAL OF COLDER AIR WILL HELP STRENGTHEN GAP WINDS..ESPECIALLY
OVER WEST PRINCE WILLIAM SOUND/EASTERN KENAI PENINSULA. MEANWHILE
THE COMBINATION OF INCREASING UPWARD VERTICAL MOTION FROM THE
UPPER TROUGH COMBINED WITH DESTABILIZATION OF THE ATMOSPHERE (AS
COLDER AIR ALOFT MOVES IN) WILL PRODUCE SNOW FROM CORDOVA TO
VALDEZ TO MUCH OF THE COPPER BASIN. SNOWFALL AMOUNTS WILL GENERALLY
BE LIGHT...ALTHOUGH THERE COULD BE SOME HEAVIER CONVECTION FORMING
OVER THE GULF (THANKS TO RELATIVELY WARMER SEA SURFACE
TEMPERATURES) AND MOVING INTO THE CORDOVA AREA...SO WILL TREND
HIGHER WITH AMOUNTS THERE. THERE WILL STILL BE SOME STRONGER
WINDS THROUGH THOMPSON PASS INTO VALDEZ...SO EXPECT LOCALIZED
AREAS OF BLOWING SNOW AND REDUCED VISIBILITIES. THERE ARE HINTS IN
SOME OF THE HIGH-RES GUIDANCE THAT MOISTURE MAY MAKE IT AS FAR
WEST AS ANCHORAGE/PALMER BUT WITH VERY DRY AIR IN PLACE WILL STICK
WITH A DRY FORECAST FOR NOW. THE SNOW AND GAP WINDS WILL ALL
DIMINISH SATURDAY AS THE UPPER TROUGH EXITS TO THE EAST.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
CLEAR AND COLD CONDITIONS WILL CONTINUE TO DOMINATE THE REGION
THROUGH SATURDAY AS A DEEP UPPER TROUGH REMAINS ANCHORED OVER THE
MAINLAND. VERY COLD WIND CHILL VALUES APPROACHING BUT NOT QUITE
REACHING ADVISORY CRITERIA WILL PERSIST THROUGH TONIGHT BEFORE
WINDS BEGIN TO SUBSIDE ON FRIDAY.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
SNOW SHOWERS AND GUSTY NORTHWEST WINDS ALONG THE ALASKA PENINSULA
WILL GRADUALLY DIMINISH THROUGH FRIDAY MORNING AS THE UPPER LEVEL
FLOW WEAKENS AND BACKS AROUND TO THE WEST. ATTENTION THEN TURNS TO
THE WEAKENING FRONT CURRENTLY OVER THE CENTRAL ALEUTIANS. THIS
FRONT WILL SURGE EASTWARD TONIGHT AS A SHORTWAVE TROUGH APPROACHES
FROM THE WEST AND LEADS TO THE RAPID DEVELOPMENT OF A SURFACE WAVE
ALONG THE FRONT. THIS FEATURE WILL SPREAD A MIX OF RAIN AND SNOW
OVER THE EASTERN ALEUTIANS ON FRIDAY AND THEN THE AKPEN ON FRIDAY
NIGHT. WILL ALSO HAVE TO MONITOR THE POTENTIAL FOR BLOWING SNOW
OVER THE PRIBILOF ISLANDS ON FRIDAY NIGHT AS THE FRONT PIVOTS
NORTHWARD...BUT AT THIS TIME IT APPEARS ANY SNOW WOULD BE LIGHT
ENOUGH TO KEEP VISIBILITIES WELL ABOVE ADVISORY CRITERIA. ANOTHER
SURFACE LOW WILL THEN FORM SOUTH OF DUTCH HARBOR EARLY
SATURDAY...KEEPING GUSTY WINDS AND PRECIPITATION OVER THE EASTERN
ALEUTIANS AND AKPEN INTO THE WEEKEND.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
COLDER CONDITIONS WILL COME TO AN END THIS WEEKEND AS A LOW TO THE
SOUTH OF THE ALEUTIANS PUSHES A FRONT OVER MAINLAND ALASKA. AS THE
MODELS FALL IN LINE WITH THIS FEATURE CONFIDENCE IN THE TIMING OF
THE FRONT IS INCREASING. FOR THE MOST PART GUIDANCE IS GOING FOR
SUNDAY MORNING FOR THE FRONT MAKING IT TO THE NORTH GULF COAST.
EVEN THOUGH IT WILL BE BRINGING WARMER AIR FROM THE SOUTH IT IS
EXPECTED TO BE PRIMARILY SNOW AS IT PUSHES INLAND. HOWEVER...AREAS
ALONG THE GULF WILL SEE SOME RAIN. AFTER THIS SYSTEM ANOTHER ONE
IS EXPECTED TO COME UP FROM THE NORTH PACIFIC MID WEEK. THIS
SECOND SYSTEM LOOKS TO BE EVEN WARMER THAN THE FIRST.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALES 121 127 129 130 131 150 155 170 172 173 174 175 176
177 179 185 351 352 411 412 413 414.
FIRE WEATHER...NONE.

&&

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

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1251 AM AKDT FRI MAR 13 2015

AKZ171-132045-
KODIAK ISLAND-
INCLUDING THE CITY OF...KODIAK CITY 1239
1251 AM AKDT FRI MAR 13 2015

...RESUSPENDED ASH FROM KATMAI VOLCANO...

STRONG NORTHWEST WINDS ACROSS BRISTOL BAY ARE RESUSPENDING ASH
FROM KATMAI VOLCANO. THESE STRONG WINDS ARE TRANSPORTING SOME OF
THE ASH AND DUST ACROSS SHELIKOF STRAIT INTO KODIAK ISLAND. THIS
ASH IS VISIBLE ON SATELLITE IMAGERY...MAINLY OVER THE SOUTHERN AND
WESTERN END OF THE ISLAND. WINDS ARE EXPECTED TO PERSIST THROUGH AT
LEAST THIS AFTERNOON. NO ACCUMULATION OF ASH OR DUST IS EXPECTED...
BUT LOWER VISIBILITIES IN VICINITY OF THE ASH WILL BE LIKELY. THIS
ASH IS NOT ASSOCIATED WITH AN ACTIVE ERUPTION.