Small Craft Advisory 933, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
1250 PM AKST TUE NOV 25 2008

.ANALYSIS AND UPPER LEVELS...A STRONG NEAR ZONAL UPPER JET EXTENDS
ACROSS THE NORTH PACIFIC BETWEEN 30N AND 40N AND THEN CURVES
SLIGHTLY NORTHEASTWARD AS IT REACHES THE GULF OF ALASKA. THIS IS
A VERY PROGRESSIVE PATTERN THAT CONTINUES TO DRIVE STORM SYSTEMS
QUICKLY ACROSS THE ALEUTIANS AND THEN NORTHEASTWARD TO MAINLAND
ALASKA. THIS MORNING THERE ARE FIVE LOWS OF NOTE OVER THE NORTH
PACIFIC/ALASKA REGION. A WEAK SURFACE LOW SOUTH OF SEWARD IS
DISSIPATING AS IT MOVES NORTHWARD. RADAR IMAGERY SHOWS SHOWERS
ACROSS PRINCE WILLIAM SOUND AS WELL AS COOK INLET. A WEAK SHORT-WAVE
TRACKING NORTHEASTWARD ALONG THE ALASKA PENINSULA IS HELPING TO
ORGANIZE A LINE OF SHOWERS OVER SOUTHERN COOK INLET. THIS LINE IS
TRANSLATING NORTHWARD EVER SO SLOWLY. COLD AIR BEHIND THE TROUGH
IS ALSO STARTING TO WORK ITS WAY THROUGH THE ALASKA PENINSULA TO
KODIAK ISLAND AND INTO SOUTHERN COOK INLET. WINDS WILL QUICKLY
COME UP IN THIS REGION THROUGH THIS AFTERNOON IN RESPONSE TO THE
COLD ADVECTION. ANOTHER SURFACE LOW HAS MOVED INTO THE SOUTHERN GULF
THIS MORNING AND IS TRACKING VERY QUICKLY TOWARD THE NORTHERN GULF.
LOOKING DOWN TO THE NORTH PACIFIC AROUND 46N 167W IS A MATURE
CYCLONE TRACKING DUE EAST ALONG THE UPPER JET. LOW NUMBER FOUR
IS SOUTH OF ADAK SINKING SLOWLY SOUTHWARD. THERE HAVE BEEN SOME
GALE FORCE WINDS NEAR THE CENTER OF THE LOW...BUT THE LOW IS
WEAKENING AND WINDS ARE DIMINISHING. FINALLY...A RAPIDLY DEEPENING
LOW IS CENTERED NEAR 39N 163E. IT IS WELL POSITIONED BETWEEN TWO
JET STREAKS AND WILL CONTINUE TO DEEPEN.

.MODEL DISCUSSION...MODELS ALL INITIALIZED FAIRLY WELL WITH
POSITIONS OF MAJOR LOWS/TROUGHS THIS MORNING. ALL SOLUTIONS
ARE A LITTLE FAR EAST WITH LOW SOUTH OF ADAK...BUT THIS IS ON
ITS WAY OUT OF THE FORECAST AREA. PREFER THE NAM/UKMET SOLUTION
WITH LOW CURRENTLY OVER THE SOUTHERN GULF. THEY ARE A LITTLE DEEPER
WITH THE CENTRAL PRESSURE WHICH SEEMS TO MATCH UP WITH SATELLITE
IMAGERY AND THEY ARE SLOWER TO WEAKEN THE LOW AS IT MOVES TO THE
NORTHERN GULF. MODELS ARE NOW ALL IN THE SAME GENERAL VICINITY WITH
TRACK OF THE MORE EASTERN LOW OVER THE NORTH PACIFIC TO THE GULF
WEDNESDAY NIGHT...SO WILL GO WITH A BLEND OF THESE SOLUTIONS. THE
ECMWF IS MOST CONSISTENT WITH TRACK OF THE RAPIDLY DEEPENING LOW
OVER THE NORTHWEST PACIFIC. BASED ON RECENT STORM TRACKS PREFER
A TRACK THAT BRINGS LOW JUST EAST OF KODIAK ISLAND.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...THE LOW OVER THE SOUTHERN GULF WILL QUICKLY
HEAD TO THE PRINCE WILLIAM SOUND REGION THIS EVENING. MEANWHILE...A
HIGH AMPLITUDE TROUGH EXTENDING FROM AN UPPER LOW NEAR THE BERING
STRAIT SOUTHWARD ACROSS SOUTHWEST ALASKA WILL PHASE WITH THE
SHORT-WAVE ALONG THE ALASKA PENINSULA AND SWING NORTHEASTWARD
ACROSS SOUTHCENTRAL ALASKA TONIGHT AND INTO INTERIOR ALASKA
WEDNESDAY MORNING. THE COMBINATION OF MOISTURE FROM THE GULF
LOW...LIFT FROM THE UPPER TROUGH...AND LIFT FROM LOW LEVEL COLD
ADVECTION WILL SET UP A DECENT SNOW EVENT ACROSS MUCH OF
SOUTHCENTRAL. IN PARTICULAR...AS LOW LEVEL FLOW SHIFTS TO SOUTHWEST
WITH THE ARRIVAL OF COLD ADVECTION UPSLOPE AREAS OF THE CHUGACH
RANGE...TALKEETNA MOUNTAINS...AND LATER ON ALONG THE ALASKA RANGE
WILL SEE ENHANCED SNOWFALL. EXPECT AN AREAL AVERAGE OF 2 TO 4 INCHES
WITH HIGHER AMOUNTS NEAR THE MOUNTAINS. CONDITIONS WILL GRADUALLY
DRY OUT BEHIND THE TROUGH ON WEDNESDAY...BUT MOISTURE AHEAD OF THE
NEXT LOW MOVING TOWARD THE GULF WILL SPREAD FROM EAST TO WEST ACROSS
SOUTHCENTRAL WEDNESDAY AFTERNOON THROUGH WEDNESDAY NIGHT. THERE IS
ENOUGH WARM AIR ADVECTION TO TURN PRECIPITATION BACK TO RAIN ALONG
THE COAST ON THURSDAY. BY THURSDAY AFTERNOON THE MAJOR PACIFIC
STORM SOUTH OF THE ALEUTIANS WILL BEGIN TO IMPACT SOUTHCENTRAL AS
THE OCCLUSION APPROACHES KODIAK ISLAND. THE EXACT TRACK OF THIS
LOW ACROSS THE GULF IS STILL IN QUESTION. AT THIS POINT A TRACK
ALONG THE FAR WESTERN GULF LOOKS MOST LIKELY...WHICH MEANS LOTS OF
WARM AIR AND MOISTURE WILL BE ADVECTED NORTHWARD ACROSS THE REGION

THURSDAY NIGHT THROUGH SATURDAY.

SOUTHWEST ALASKA...THE UPPER TROUGH CURRENTLY OVER SOUTHWEST ALASKA
IS CURRENTLY ONLY PRODUCING A FEW SNOW SHOWERS. EXPECT SIMILAR
CONDITIONS AS THE TROUGH SWINGS NORTHEAST TONIGHT...WITH THE
EXCEPTION OF ALONG THE ALASKA RANGE WHERE COLD ADVECTION AND
UPSLOPE FLOW WILL RESULT IN AREAS OF LIGHT SNOW. A SURFACE HIGH
WILL BUILD OVER THE REGION WEDNESDAY PROVIDING A COLD AND DRY DAY.
THE PACIFIC SYSTEM WILL SPREAD MOISTURE AND WINDS OVER SOUTHWEST
ALASKA BEGINNING LATE THURSDAY AND CONTINUING INTO THE WEEKEND.
THERE IS POTENTIAL FOR EASTERN PORTIONS OF SOUTHWEST ALASKA TO
WARM UP SIGNIFICANTLY TO THE POINT OF CHANGING PRECIPITATION TO
RAIN...BUT THIS IS HIGHLY DEPENDENT UN TRACK OF STORM WHICH IS
IN QUESTION AT THIS TIME.

BERING SEA/ALEUTIANS...CONDITIONS WILL HEAD QUICKLY DOWNHILL ALONG
THE ALEUTIANS WEDNESDAY AND WEDNESDAY NIGHT AS THE DEEP PACIFIC
SYSTEM PASSES TO THE SOUTH. THERE IS NOW ENOUGH CONFIDENCE IN STORM
TRACK TO SAY THAT ALL OF PRECIPITATION WEST OF THE ALASKA PENINSULA
WILL BE IN THE FORM OF SNOW. COMBINED WITH WIDESPREAD WINDS OF
40 TO 60 MPH LOW VISIBILITIES IN SNOW AND BLOWING SNOW ARE EXPECTED.
FORTUNATELY WATER TEMPERATURES ARE STILL FAIRLY WARM...SO SURFACE
AIR TEMPERATURES SHOULD REMAIN NEAR OR SLIGHTLY ABOVE
FREEZING...ELIMINATING THE THREAT OF BLIZZARD CONDITIONS. THE ALASKA
PENINSULA WILL SEE SOME WARM AIR ADVECTION AS THE OCCLUSION
APPROACHES THURSDAY AFTERNOON...BUT THE FRONT WILL NEVER MOVE
THROUGH. SO IT WILL LIKELY BE MAINLY SNOW WITH A POSSIBLE PERIOD
OF RAIN. AS THE SYSTEM MOVES TO NEAR KODIAK ISLAND FRIDAY BROAD
NORTHERLY FLOW AND COLD ADVECTION WILL DOMINATE THE BERING SEA AND
ALEUTIANS...CONTINUING INTO THE WEEKEND. THUS...EXPECT THE TYPICAL
GUSTY WINDS AND SNOW SHOWERS.

.LONG TERM FORECAST...IT LOOKS LIKE A CHANGE IS IN STORE AS WE
HEAD THROUGH THE EXTENDED FORECAST PERIOD. BOTH THE ECMWF AND GFS
INDICATE FORMATION OF A LARGE UPPER LEVEL CYCLONE SOUTH OF THE
ALEUTIANS EARLY NEXT WEEK WITH A RIDGE BUILDING OVER THE EAST
PACIFIC. THIS MORE AMPLIFIED PATTERN WILL PUT AN END TO THE TRAIN
OF LOWS WE ARE CURRENTLY EXPERIENCING. THEREFORE...EXPECT GENERALLY
DRIER AND CALMER CONDITIONS ACROSS THE REGION...AT LEAST TEMPORARILY.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...STORM WARNING...155 170 172.
         GALE WARNING...120 130 160 165 171 175 176.
         HEAVY FREEZING SPRAY WARNING...130.
FIRE WEATHER...NONE.

SEB NOV 08