Small Craft Advisory 109, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
421 PM AKST TUE FEB 3 2015

.ANALYSIS AND UPPER LEVELS...

THE UPPER LEVEL RIDGE REMAIN THE DOMINANT FEATURE OVER THE
FORECAST AREA TODAY EXTENDING FROM THE NORTHERN BERING SEA TO THE
ALCAN BORDER IN THE COPPER RIVER BASIN. THIS RIDGE WILL REMAIN
ANCHORED OVER THE NORTHERN BERING SEA THROUGH THE REST OF THE
WEEK. HOWEVER AN UPPER LEVEL LOW IN THE CANADIAN ARCTIC WILL CROSS
THE YUKON AND MOVE INTO THE NORTHEAST GULF OF ALASKA THURSDAY
NIGHT.
THE SURFACE PATTERN IS SIMILAR TO THE UPPER LEVELS WITH HIGH
PRESSURE OVER THE NORTHERN BERING SEA AND MOST OF MAINLAND
ALASKA. THE ONLY SIGNIFICANT LOW NEARBY IS WELL SOUTH OF THE
ALASKA PENINSULA AND WILL REMAIN SOUTH OF THE AREA. HOWEVER THIS
PATTERN IS KEEPING A TIGHT PRESSURE GRADIENT OVER THE
ALEUTIANS...BERING SEA...AND INTO SOUTHWEST MAINLAND ALASKA.

&&

.MODEL DISCUSSION...
MODELS ARE IN BETTER AGREEMENT IN THE UPPER LEVEL PATTERN THAN
THEY WERE YESTERDAY. THE GFS HAS NOW SHIFTED ITS SOLUTION TO BRING
THE 500 MB LOW OUT OF THE YUKON THURSDAY NIGHT AND OVER YAKUTAT
INTO THE NORTHEAST GULF FRIDAY MORNING. GETTING A CONSISTENT
PATTERN BETWEEN THE MODELS IS IMPORTANT IN TIMING THE SHORT WAVES
LATE THIS WEEK WHICH WILL INCREASE WINDS IN THE SOUTHCENTRAL AND
SOUTHWEST ALASKA.

&&

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

FOG HAS LINGERED ACROSS ANCHORAGE AND VICINITY THROUGH THIS
AFTERNOON...AND WITH LITTLE CHANGE IN THE AIR MASS FOG IS LIKELY
TO LINGER THROUGH MOST OF WEDNESDAY. THE FOG WILL LIKELY BE QUITE
SHALLOW...YET LOCALLY DENSE AT TIMES. FOG WILL LIKELY ALSO BE
PREVALENT ACROSS PARTS OF THE COPPER RIVER VALLEY THROUGH MUCH OF
WEDNESDAY.

OTHERWISE...CONDITIONS WILL BE CLEAR...DRY...AND COLD. HIGH
PRESSURE BUILDING OVER THE INTERIOR OF ALASKA AND LOW PRESSURE
OVER THE SOUTHEAST GULF WILL COMBINE TO INDUCE AN INCREASING
PRESSURE GRADIENT ACROSS SOUTHCENTRAL THROUGH THURSDAY. WINDS WILL
BEGIN TO APPROACH STRONG WIND CRITERIA THROUGH THE TYPICAL
CHANNELED AREAS ESPECIALLY TOWARD EASTERN PRINCE WILLIAM SOUND
DURING THE DAY ON THURSDAY AS SOME UPPER LEVEL JET SUPPORT BEGINS
TO APPROACH OVERHEAD.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (TONIGHT THROUGH FRI)...

OFFSHORE FLOW WILL CONTINUE THROUGH THE END OF THE WORK WEEK WHICH
WILL KEEP SKIES ON THE CLEAR SIDE ACROSS THE SOUTHWEST MAINLAND.
COLDER AIR WILL BEGIN TO FILTER ACROSS THE REGION THURSDAY
AFTERNOON AS AN ARCTIC TROUGH SLIDES TOWARD THE YUKON...WITH MUCH
OF THE COLD AIR REMAINING WELL TO THE EAST OF SOUTHWEST ALASKA.
THE FORECAST HAS BEEN UPDATED TO SHUNT THE COLDER AIR EASTWARD AND
KEEP SLIGHTLY WARMER TEMPERATURES ACROSS THE AREA. ONCE CONCERN
THAT COULD DEVELOP BY THE END OF THE WEEK WILL BE THE POTENTIAL
FOR HAZARDOUS WIND CHILLS AS TEMPERATURES DROP BELOW FREEZING AND
WINDS OF 20 TO 30 MPH WILL BE POSSIBLE ACROSS THE KUSKOKWIM DELTA.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (TONIGHT THROUGH FRI)...

AN UPPER LEVEL WAVE BEING ABSORBED BY A LOW IN THE NORTH PACIFIC
WILL ACCOMPANY A PIECE OF COLD AIR ROTATING AROUND THE HIGH
PRESSURE IN THE BERING SEA. THE COMBINATION OF THESE TWO FEATURES
WILL ALLOW FOR RAIN AND SNOW CHANCES TO INCREASE ACROSS THE ALASKA
PENINSULA TONIGHT AND SPREAD WESTWARD THROUGH THE END OF THE WORK
WEEK. WARMER AIR ROTATING AROUND THE BACK SIDE OF THE LOW IN THE
NORTH PACIFIC WILL CREATE A BRIEF WARM UP ACROSS THE ALASKA
PENINSULA AND ALEUTAINS THROUGH THE WEEK BEFORE COLDER TEMPERATURES
RETURN BY FRIDAY.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7...FRI THROUGH TUE)...WELL
OUR LONG-WAVE FLOW IS SET TO CHANGE FROM ONE TYPE OF BLOCKING
PATTERN TO ANOTHER. EARLY IN THIS PERIOD...THE REX BLOCK OVER THE
BERING WILL START TO LOOSE ITS STRUCTURE AS ARCTIC AIR DIVES DOWN
OVER THE MAINLAND. THIS COLD AIR WILL DIG A NEW TROUGH OVER THE
EXTREME NE GULF OF ALASKA AND START TO FORM A CLOSED UPPER LEVEL
LOW THERE. MEANWHILE...HIGH PRESSURE REMAINS DOMINANT OVER THE
BERING WITH A WEAK CLOSED AREA OF LOW PRESSURE SOUTH OF WESTERN
ALEUTIANS. THIS LOW-HIGH-LOW COUPLET WILL FORM A NON-STANDARD
OMEGA BLOCK. WHILE THE OMEGA BLOCK WILL NOT REMAIN INTACT FOR A
TERRIBLY LONG TIME...IT WILL CONTROL MUCH OF THE WEATHER THROUGH
THE WEEKEND.

WINDS WILL INCREASE DURING THIS PERIOD...ESPECIALLY FOR AREAS FROM
BRISTOL BAY BACK THROUGH THE COPPER RIVER DELTA THAT FAVOR
NORTHERLY FLOW. A DRY BUT RATHER STRONG SHORTWAVE WILL BRING A
BLAST OF ARCTIC AIR THROUGH MUCH OF SOUTH CENTRAL ON SATURDAY.
OVER THE PAST 24 HOURS...THE MODELS HAVE DONE SOME COMPROMISING.
THE EC HAS LED THE WAY IN TERMS OF SYNOPTICS ASSOCIATED WITH HAVE
AN UPPER-LEVEL CLOSED LOW NEAR YAKUTAT. BUT THE GFS SEEMS TO BE
TRACKING A LITTLE BIT BETTER ON THE 850MB TEMPERATURE DROP THAT
WILL OCCUR WITH THIS SYSTEM. THE NET EFFECT OF ALL THIS IS THAT
THE STRONGEST WINDS NOW LOOK LIKE THEY WILL OCCUR A BIT FURTHER
WEST...FROM THE COOK INLET BACK THROUGH BRISTOL BAY. PLACES LIKE
THE MATANUSKA VALLEY...THOMPSON PASS AND SEWARD WILL STILL SEE
STRONG WINDS...BUT NOT QUITE AS STRONG AS IF THE UPPER LEVEL
SUPPORT HAD PUSHED RIGHT THROUGH THOSE AREAS. WITH COLD AIR IN
PLACE AND A REINFORCING SHOT DUE IN FOR THE WEEKEND...WIND CHILLS
COULD REACH THEIR COLDEST OF THE SEASON DROPPING TO THE -20 TO -30
RANGE.

THE PATTERN THEN BEGINS TO SHIFT INTO NEXT WEEK AS THE COLD AIR
DIGS DEEP ENOUGH INTO THE NORTH PACIFIC THAT IT RE-ESTABLISHES THE
LONG-WAVE TROUGH. THIS WILL ALLOW MOISTURE AND WARMER TEMPERATURES
TO CLIMB BACK TOWARDS THE MAINLAND BY THE EARLY TO MIDDLE PART OF
NEXT WEEK.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALES 127 128 155 170 172 173 174.
         HEAVY FREEZING 126 127 139 414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...CC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MC
LONG TERM...MO