Small Craft Advisory 951, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
438 PM AKST SAT NOV 29 2014

.ANALYSIS AND UPPER LEVELS...
SNOW HAS BROKEN OUT ACROSS COOK INLET AND THE NORTHERN GULF AHEAD
OF A MID LEVEL TROUGH THAT HAS JUST CROSSED FROM SOUTHWEST ALASKA
INTO WESTERN COOK INLET. WEAK UP-INLET FLOW IS ALLOWING SLIGHTLY
HEAVIER SNOW TO FALL OVER FAVORED UPSLOPE AREAS LIKE THE ANCHORAGE
HILLSIDE AND THE TALKEETNA MOUNTAINS NEAR HATCHER PASS. THE
RAIN/SNOW LINE ON THE KENAI PENINSULA IS HOLDING STEADY NEAR THE
ANCHOR POINT/CLAM GULCH AREA. SNOW HAS ALSO BEGUN FROM CORDOVA TO
VALDEZ AND WILL CONTINUE TO SPREAD NORTH AND EAST INTO THE COPPER
BASIN THROUGHOUT THE REMAINDER OF THE DAY.

WEST OF THE ALASKA RANGE...ANOTHER STORM IS NOW MOVING NORTHWARD
INTO THE WESTERN BERING SEA WITH GALE-FORCE WINDS WIDESPREAD
ACROSS THE WESTERN 2/3 OF THE ALEUTIANS. THIS STORM IS BRINGING
AMPLE WARM AIR AND HEAVY RAIN INTO THE REGION. AN AMPLIFYING
MID LEVEL RIDGE AHEAD/EAST OF THIS FEATURE IS PRODUCING
SUBSIDENCE/SINKING MOTION ACROSS MUCH OF SOUTHWEST ALASKA...WHERE
THE MAIN IMPACT IS WIDESPREAD FOG/STRATUS LINGERING ACROSS BRISTOL
BAY AND THE DELTA. ONSHORE FLOW AND A FEW MIXED RAIN/SNOW SHOWERS
CONTINUE TO PLAGUE THE DELTA...BUT WILL BE DIMINISHING AS THE
AFOREMENTIONED RIDGE CONTINUE TO STRENGTHEN.

&&

.MODEL DISCUSSION...
THE MODELS ARE IN GOOD GENERAL AGREEMENT THROUGH THE FIRST FEW
DAYS OF THE FORECAST AS THE TROUGH OVER SOUTHCENTRAL RACES AWAY TO
THE EAST AND MUCH OF SOUTHERN ALASKA COMES UNDER THE INFLUENCE OF
MID LEVEL RIDGING DOWNSTREAM OF ACTIVE WEATHER ACROSS THE BERING
SEA. THERE DOES REMAIN SOME MODEL UNCERTAINTY WITH HOW FAR WEST
THE CURRENT NORTH PACIFIC LOW CENTER WILL SURGE AS IT REDEVELOPS
IN THE BERING SEA ON SUNDAY. THE GFS HAS PERSISTENTLY BEEN FURTHER
WEST...WITH THE NAM FARTHER EAST AND THE ECMWF IN THE MIDDLE. WE
CONTINUE TO PREFER THE MORE WESTERN SOLUTIONS FOR THIS
FEATURE KNOWING THAT LOWS "PREFER" TO BUILD BACK INTO THE COLD AIR
MOVING OFF THE RUSSIAN LANDMASS INTO THE WESTERN BERING.

&&

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

AN UPPER LEVEL SHORTWAVE TROUGH WILL MOVE THROUGH THE ANCHORAGE
BOWL AND MATSU VALLEY THIS EVENING BEFORE EXITING THE COPPER
RIVER BASIN REGION BY SUNDAY MORNING. SNOW WILL TAPER OFF FROM
WEST TO EAST FOR THE ANCHORAGE BOWL THROUGH THE MATSU VALLEY THIS
EVENING...THEN THE PRINCE WILLIAM SOUND THROUGH THE COPPER RIVER
BASIN BY SUNDAY MORNING. THE SURFACE LOW IS POSITIONED JUST SOUTH
OF PRINCE WILLIAM SOUND ENTRANCE THIS EVENING BEFORE TRACKING
EASTWARD TOWARDS YAKUTAT BY SUNDAY AFTERNOON. THE WHITTIER AREA
WILL HAVE GUSTY WESTERLY WINDS THROUGH SUNDAY MORNING ASSOCIATED
WITH THE TROUGH PASSAGE THIS EVENING. THE COLD AIR ADVECTION WILL
CONTINUE TO FILTER INTO THE REGION THROUGH SUNDAY MORNING. AN
UPSTREAM UPPER LEVEL RIDGE WILL BE BUILDING INTO THE REGION LATE
TONIGHT AND WILL EXTEND THROUGH MONDAY. THIS WILL RESULT IN PATCHY
FOG FORMING UNDER THE RIDGE OF HIGH PRESSURE. BY MONDAY THE
TURNAGAIN ARM AND HIGHER ELEVATIONS WINDS WILL BECOME GUSTY AS THE
PRESSURE GRADIENT INCREASES THROUGHOUT THE AFTERNOON. THIS WILL
COINCIDE WITH A FRONTAL BOUNDARY APPROACHING THE SOUTHERN END OF
KODIAK ISLAND AND MOVING INTO THE NORTHERN GULF BY TUESDAY
MORNING. THIS WILL BRING WIDESPREAD RAIN ALONG THE EASTERN KENAI
PENINSULA EXTENDING INTO THE PRINCE WILLIAM SOUND AREA...INLAND
THE PRECIPITATION WILL BE A MIXTURE OF RAIN AND SNOW.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
SCATTERED SNOW SHOWERS WILL CONTINUE TO FALL OVER THE DELTA AND
LOWER KUSKOKWIM VALLEY THROUGH EARLY THIS EVENING...AS THE TROUGH
OVER THE MAINLAND TRACKS EASTWARD AND INTO THE EASTERN DOMAIN. THE
SCATTERED SNOW SHOWERS OVER THE AREA WILL BRIEFLY LET UP THIS
EVENING...AS A RIDGE OF HIGH PRESSURE BUILDS IN FROM THE WEST
TONIGHT. WIDESPREAD FOG SHOULD REDEVELOP OVERNIGHT OVER A GOOD
PORTION OF THE SOUTHWEST MAINLAND...AS TEMPERATURES DROP
OVERNIGHT AND APPROACH DEWPOINT TEMPERATURES. SNOW WILL BEGIN TO
DEVELOP FROM WEST TO EAST IN THE MORNING AHEAD OF FRONTAL SYSTEM
APPROACHING THE SOUTHWESTERN COAST. AREAS PRONE TO HOLD ONTO THE
COLDER OFFSHORE FLOW (AREAS NORTH AND EAST OF BETHEL...ALONG WITH
THE VALLEYS AND LOW LYING AREAS OF THE LOWER KUSKOKWIM
VALLEY)...WILL LIKELY EXPERIENCE SOME FREEZING RAIN WITH THE
INITIAL FRONTAL PASSAGE. THERE IS ALSO A POSSIBILITY FOR THE
INTERIOR PORTIONS OF BRISTOL BAY (MAINLY NORTH OF KING SALMON) TO
EXPERIENCE SOME AREAS OF FREEZING RAIN WITH THIS SYSTEM...HOWEVER
CONFIDENCE IS NOT HIGH ENOUGH YET TO ISSUE AN ADVISORY.
PRECIPITATION AND GUSTY WINDS ALONG THE ALASKA PENINSULA WILL
PERSIST THROUGH TUESDAY MORNING...CHANGING OVER TO RAIN ON MONDAY
MORNING AS THE WARM SUBTROPICAL AIR MASS IS ADVECTED AHEAD OF THE
LOW THAT ANCHORS OVER BERING.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
A NORTH PACIFIC LOW CONTINUES TO APPROACH THE WESTERN ALEUTIANS
THIS EVENING...WITH AN ASSOCIATED WARM FRONT BRINGING RAIN AND
GUSTY WINDS TO THE CENTRAL AND EASTERN ALEUTIANS THROUGH TOMORROW
NIGHT. GUSTIER WINDS WILL PICK UP OVERNIGHT OVER THE WESTERN
PORTION OF THE BERING/ALEUTIANS...AS AN AREA OF COLD AIR ADVECTION
BEGINS TO SETUP BEHIND THE BERING LOW. STRONGER NORTHWEST WINDS
AND MIXED PRECIPITATION WILL PERSIST ACROSS THE WESTERN
BERING/ALEUTIANS THROUGH TUESDAY MORNING.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...

THE MODELS ARE STARTING TO COME INTO BETTER AGREEMENT MID WEEK AS
AN UPPER TROUGH DESCENDS INTO THE BERING SEA FROM THE ARCTIC
OCEAN INTERACTS WITH A BERING TROUGH MOVING INTO THE NORTH
PACIFIC. AS THIS LOW MOVES INTO THE NORTH PACIFIC...AN WAVE WILL
DEVELOP OVER THE GULF EARLY TUESDAY...AND SPREAD INTO THE NORTH
GULF COAST BY LATE TUESDAY. THIS WILL OCCUR AS THE ARCTIC TROUGH
BRINGS ANOTHER SURGE OF COLD AIR TO THE MAINLAND...WHICH SHOULD BE
SUFFICIENTLY COLD ENOUGH TO KEEP PRECIPITATION AS SNOW IN MOST
AREAS. THE GREATEST CHANCE OF PRECIPITATION EXISTS OVER THE GULF
COAST FROM THIS SYSTEM...WITH DOWNSLOPING ON THE LEE OF THE
CHUGACH RANGE KEEPING THE FORECAST AT JUST A CHANCE OF SNOW FOR
NOW.

BEYOND WEDNESDAY...FORECAST CONFIDENCE THEN QUICKLY DIMINISHES
WITH HOW FAR SOUTH THE ARCTIC TROUGH WILL DIVE INTO THE BERING AND
THIS TROUGH BECOMES NEARLY STATIONARY. FOR THIS REASON WPC WAS
USED HEAVILY FOR THE FORECAST LATE THIS WEEK. CONFIDENCE IS AT ITS
LOWEST WITH THE TRACK OF A POSSIBLE LOW NEAR THE GULF LATE IN THE
WEEK. OUT WEST...THERE IS DECENT AGREEMENT THAT A SERIES OF LOWS
WILL DEVELOP OVER THE BERING MID-LATE NEXT WEEK...BUT WITH LOW
CONFIDENCE AS TO WHERE THESE MAY FORM.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...FREEZING RAIN ADVISORIES 152 AND 155.
MARINE...STORMS 174 411.
 GALES 127 155 165 170 171 172 173 175 176 177 178 179 180 181 185 412
       413 414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...AD
SOUTHCENTRAL ALASKA...PD
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TP
LONG TERM...DK