Small Craft Advisory 729, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
157 PM AKDT SUN SEP 21 2014

.ANALYSIS AND UPPER LEVELS...
THE UPPER LEVEL PATTERN THAT HAS BEEN IS PLACE THE PAST NUMBER OF
DAYS IS SHIFTING EASTWARD TODAY. THE HIGH OVER THE EASTERN BERING
SEA IS BUILDING OVER THE SOUTHWEST AND WESTERN COAST OF THE STATE
WHICH IS PUSHING THE LONGWAVE TROUGH EASTWARD. THIS UPPER LEVEL
TROUGH HAS DEVELOPED A CUT OFF LOW OVER THE GULF OF ALASKA. THE
250 MB JET STREAM IS RUNNING SOUTH OF THE ALEUTIANS BETWEEN 40N
AND 45N AND THEN CURVES AROUND THE CUT OFF LOW IN THE GULF AND IS
RUNNING DUE NORTH TO SOUTH OVER THE PANHANDLE BEFORE TURNING
SHARPLY TO THE EAST OVER THE YUKON. THE JET STREAM IS IMPORTANT
TODAY AS IT IS WHAT IS RAPIDLY INTENSIFYING A SURFACE LOW RUNNING
NORTHWARD OVER THE EASTERN GULF OF ALASKA. DUE TO THE JET CURVING BACK
TO THE EAST THIS LOW WILL LOSE ITS UPPER LEVEL SUPPORT TONIGHT AND
THEN RAPIDLY WEAKEN AS THE MAIN SURFACE LOW MOVES TOWARD MONTAGUE
ISLAND AS A LEE SIDE SURFACE LOW DEVELOPS IN THE YUKON WITH THE
UPPER LEVEL SUPPORT.
IN THE WESTERN BERING SEA THERE IS ANOTHER LOW THAT WILL REMAIN IN
THE AREA FOR THE NEXT FEW DAYS BUT NOT MAKING MUCH EASTWARD
PROGRESS DUE TO THE RIDGE IN THE EASTERN BERING SEA.

&&

.MODEL DISCUSSION...
COMPUTER MODELS CONTINUE TO STRUGGLE WITH THE LOW MOVING THROUGH
THE EASTERN GULF OF ALASKA. THE ECMWF AND GEM SEEM TO HAVE PICKED
UP ON THE WAY THE LOW IS RAPIDLY STRENGTHENING THIS
AFTERNOON...AND THEN WILL RAPIDLY WEAKEN OVERNIGHT AS ITS ENERGY
SPLITS WITH SOME OF THE UPPER LEVEL SUPPORT MOVING INTO THE YUKON
AND THE MAIN SURFACE LOW HEADS TOWARD MONTAGUE ISLAND OVERNIGHT.
THE GFS AND NAM DO HAVE A SIMILAR TRACK BUT THEY AND NOT DETECTING
THE INITIAL STRENGTH OF THIS LOW AS THE NEARBY OBSERVATIONS ARE
ALREADY 10 PLUS MB LOWER THAN THE GFS INDICATES AND WELL BELOW THE
NAM SOLUTION AS WELL. AFTER THIS LOW MOVES THROUGH THE MODELS ARE
ALL VERY MUCH IN AGREEMENT WITH THE RIDGE IN THE BERING SEA MOVING
EASTWARD SO IT STRETCHES FROM SOUTH OF THE ALASKA PENINSULA INTO
SOUTHWEST ALASKA AND THEN CURVES OVER THE INTERIOR AND SOUTH
CENTRAL ALASKA. THERE WILL ALSO BE THE DEVELOPMENT OF A TROUGH OF
LOW PRESSURE ALONG THE NORTH GULF COAST.

&&

.SHORT TERM FORECAST...
SOUTHCENTRAL ALASKA...
TWO WEATHER FEATURES WILL BE IMPACTING THE AREA OVER THE NEXT DAY.
THE FIRST IS A COLD FRONT MOVING THROUGH THE SUSITNA VALLEY AND
UPPER COOK INLET THIS AFTERNOON WHICH WILL MOVE TO THE ALCAN
BORDER BY MONDAY AFTERNOON. THERE ARE SOME SHOWERS THAT HAVE
DEVELOPED AHEAD OF THIS FRONT AND THE FREEZING LEVEL IS LOW
ENOUGH THAT THE MORE INTENSE SHOWERS COULD HAVE SOME SMALL HAIL IN
THEM. BEHIND THIS COLD FRONT THE WINDS WILL TURN TO THE NORTHWEST
AND GET BREEZY WITH THE COLDER AND DRIER AIR MOVING IN. GAPS IN
THE ALASKA RANGE WILL BE ESPECIALLY GUSTY OVERNIGHT INTO TOMORROW.
THE SECOND FEATURE IS THE LOW IN THE EASTERN GULF THAT IS MOVING
TO THE NORTH WHICH WILL TURN NORTHWEST IN ITS MOTION THIS
EVENING. MOST OF THE RAINFALL WITH THIS SYSTEM WILL BE RELEGATED
TO THE GULF COAST FROM PRINCE WILLIAM SOUND EASTWARD.

SOUTHWEST ALASKA...
THE RIDGE BUILDING INTO THE AREA IS KEEPING NORTHERLY WINDS AND
MOSTLY CLEAR SKIES INTO TOMORROW. SOME CLOUDS WILL MOVE THROUGH
THE KUSKOKWIM VALLEY AND DELTA MONDAY NIGHT INTO TUESDAY DUE TO A
SHORT WAVE MOVING ACROSS THE AREA BUT NOTHING MORE THAN A FEW
PASSING SHOWERS IS EXPECTED AS FAR AS PRECIPITATION.

BERING SEA/ALEUTIANS...
THE EASTERN BERING SEA IS SEEING A DECREASE INT CLOUDS DUE TO THE
CIRCULATION OF THE RIDGE BRINGING DRIER AIR FROM THE MAINLAND
OVER THE AREA. THE WESTERN BERING SEA AND WEST AND CENTRAL
ALEUTIANS WILL SEE SOME PERIODS OF LIGHT RAINFALL WITH THE LOW
PRESSURE IN THAT AREA.
EASTERN ALEUTIANS WILL REMAIN UNDER NORTHERLY FLOW WHICH WILL
KEEP SOME SHOWERS AROUND THROUGH THE NIGHT.
THE ALASKA PENINSULA WILL SEE SOME PARTIAL CLEARING FROM
NORTHEAST TO SOUTHWEST AS THE DRIER AIR FROM THE MAINLAND FILTERS
INTO THE AREA.

&&

.LONG TERM FORECAST...
THERE IS NO CHANGE TO THE GENERAL PATTERN EXPECTED WITH AN
UNSEASONALY DRY AND PLEASANT AUTUMN PATTERN DOMINATING THE STATE
AS A SPLIT UPPER LEVEL JET PATTERN CONTINUES. SOME UNCERTAINTY
STILL EXISTS WITH THE DEVELOPMENT OF A TROUGH ACROSS THE NORTH
CENTRAL PACIFIC...AND ITS EVENTUAL TRACK INTO THE GULF OF ALASKA.
THE ECMWF REMAINS THE MOST BULLISH IN TRACKING THE FRONT INTO THE
NORTH GULF COAST...BUT IT HAS DRAMATICALLY BACKED OFF ITS PREVIOUS
SOLUTIONS. THE GENERAL THINKING IS THE LOW WILL MAINLY IMPACT
COASTAL LOCATIONS...ALTHOUGH SOME CLOUDS AND PRECIP WILL
POTENTIALLY MOVE INTO THE COPPER BASIN OVER THE WEEKEND. AS A
WHOLE...HOWEVER...LARGELY DRY AND QUIESCENT WEATHER FOR ALASKA
WILL LIKELY CONTINUE THROUGH THE WEEKEND.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.
&&

SEP 14