Small Craft Advisory 737, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
200 PM AKDT TUE SEP 24 2013

.ANALYSIS AND UPPER LEVELS...
THE DOMINANT FEATURE ON THE MORNING WEATHER MAP IS A MATURE
VERTICALLY STACKED LOW OVER THE SOUTHERN BERING SEA. THE LOW HAS NOW
OCCLUDED AND THE ASSOCIATED FRONT HAS MOVED WELL AHEAD OF THE LOW
CENTER ITSELF AND IS CURRENTLY MOVING INLAND ALONG THE SOUTHWEST
MAINLAND COAST. THE STRONGEST WINDS ARE ASSOCIATED WITH THE
PRESSURE GRADIENT AROUND THE LOW CENTER ITSELF (RATHER THAN THE
ASSOCIATED FRONT) AND ARE CURRENTLY AFFECTING THE DUTCH HARBOR
AREA...WHERE A HIGH WIND WARNING REMAINS IN EFFECT AT THIS TIME. BACK
FURTHER WEST...VISIBLE SATELLITE IMAGERY CONFIRMS THE PRESENCE OF TWO
CIRCULATION CENTERS. THIS IS DEFORMING THE PRESSURE FIELD ENOUGH TO
PREVENT HIGH WINDS FROM AFFECTING THE CENTRAL ALEUTIAN ISLANDS.

AHEAD OF THIS LARGE STORM...HIGH PRESSURE IS MAKING FOR A MOSTLY
SUNNY DAY ACROSS MOST OF SOUTHCENTRAL...THOUGH A STRONG 150 KT JET
OVER THE EASTERN BERING IS RAPIDLY SPREADING CLOUDINESS INTO THE COOK
INLET REGION. LOCALIZED AREAS OF LOW CLOUDS AND FOG ARE PERSISTING
OVER THE COPPER RIVER BASIN AND PARTS OF THE MAT-SU VALLEY...BUT WILL
DISSIPATE BY LATER THIS AFTERNOON. MEANWHILE...NORTHWEST GAP FLOWS
ACROSS THE GULF COAST HAVE FINALLY DIMINISHED AS THE INFLUENCE OF
YESTERDAYS LOW HAS ALL BUT DISSIPATED NEAR THE PANHANDLE.

.MODEL DISCUSSION...
THE MODELS ARE IN GOOD AGREEMENT WITH THE BASIC EVOLUTION OF THE
STORM CURRENTLY IN THE BERING. THE STORM IS CURRENTLY AT MAX
INTENSITY AND WILL BE WEAKENING RAPIDLY AS IT MOVES INTO THE WESTERN
GULF BY LATE WED AFTERNOON. WHILE THE LARGER-PICTURE DETAILS ARE IN
GOOD AGREEMENT...THERE ARE SOME TRICKY DETAILS WITH TIMING AND
INTENSITY OF WINDS THROUGH SOME OF THE FAVORED TERRAIN GAPS LIKE
TURNAGAIN ARM. SINCE THE NAM HAS SUPERIOR MODEL RESOLUTION IT WAS
UTILIZED FOR MANY OF THESE FEATURES OVER THE EASTERN FORECAST DOMAIN.
MEANWHILE...OUT WEST...THE LARGEST MODEL ISSUES REVOLVE AROUND THE
NEXT LOW IN THE SERIES THAT WILL DEVELOP RAPIDLY ON THURSDAY
AFTERNOON OVER THE NORTHERN BERING. ALL MODELS HAVE SPED UP THIS
FEATURE DESPITE THE RAPID INTENSIFICATION OF THE STORM (WHICH OFTEN
WOULD SLOW DOWN A STORMS FORWARD PROGRESS) BUT IS VERY BELIEVABLE IN
THIS CASE DUE TO THE UNUSUALLY STRONG 210 KT JET OVERHEAD FUELING
DEVELOPMENT. THE GFS WAS CHOSEN AS THE MODEL OF CHOICE FOR THIS
STORM...THOUGH THE NAM AND EC ARE NOT FAR BEHIND AND ALL DEPICT THE
SAME GENERAL EVOLUTION.

.SHORT TERM FORECAST...
SOUTHCENTRAL...CLOUDS AND PRECIPITATION WILL MOVE BACK INTO THE
REGION IN A HURRY THIS EVENING. SIGNIFICANT WARMING ALOFT WILL ALLOW
PRECIP TO FALL AS RAIN AT MOST LOCATIONS...WITH THE EXCEPTION OF SOME
HIGHER ELEVATION MOUNTAIN PASSES AND THE FAR NORTHERN SUSITNA VALLEY
WHERE PRECIP MAY REMAIN A HEAVY WET SNOW DURING THIS EVENT. THIS IS
PRIMARILY DUE TO THE RAPID WEAKENING OF THE STORM THAT IN TURN IS
ENDING THE STRONG NORTHWARD PUSH OF WARM AIR EXPERIENCED EARLIER IN
THE STORMS LIFECYCLE. WITH DUE SOUTH-SOUTHWESTERLY FLOW ALOFT EXPECT
EVEN THE USUAL DOWNSLOPE AREAS WILL SEE RAIN ON WEDNESDAY...EVEN AS
STRONG WINDS BLOW THROUGH THE FAVORED TERRAIN GAPS.

SOUTHWEST...THE FRONT MOVING THROUGH THE AREA TODAY HAS BEEN
RELATIVELY UNIMPRESSIVE AS WINDS AND PRECIP HAVE BOTH BEEN WEAKENING
AS THE FRONT RACES AHEAD OF THE LOW. PRECIPITATION WILL MOVE BACK IN
BY WEDNESDAY MORNING AS THE LOW CENTER APPROACHES BRISTOL BAY...BUT
THE AFOREMENTIONED SIGNIFICANT WEAKENING TREND WILL LIKELY ENSURE
PRECIP IS MORE SHOWERY IN NATURE THAN A STEADY AND PERSISTENT RAIN.

BERING SEA AND ALEUTIANS...STRONG SOUTHWEST WINDS ARE STILL EXPECTED
OVER THE EASTERN ALEUTIANS AND ALASKA PENINSULA TONIGHT AS THE STRONG
LOW WEAKENS AND MOVES TO THE EAST. AS MENTIONED ABOVE...WIND SPEEDS
HAVE BEEN LESS THAN EXPECTED AT THE FEW OBSERVATION POINTS ALONG THE
ALEUTIANS...LIKELY DUE TO MULTIPLE SURFACE LOWS FRAGMENTING THE
STORMS ENERGY. WEAK HIGH PRESSURE WILL BUILD IN FROM THE WEST ACROSS
MUCH OF THE REGION MAKING WEDNESDAY A FAIRLY BENIGN WEATHER DAY. BY
THURSDAY THE STRONG JET ALOFT WILL START A RAPID INTENSIFICATION OF A
LOW OVER THE NORTHWEST BERING SEA. THIS LOW WILL FOLLOW A SIMILAR
TRACK TO PREVIOUS LOWS (THROUGH BRISTOL BAY AND INTO THE WESTERN
GULF) BUT FORWARD SPEED WILL BE SIGNIFICANTLY FASTER THAN THE CURRENT
STORM. THIS MEANS WIND SPEEDS WILL LIKELY BE MUCH STRONGER AND MORE
WIDESPREAD THAN THE CURRENT LOW (MUCH MORE LIKE THE STORM OF LAST
WEEKEND) AND WILL RESULT IN HIGH WINDS ESPECIALLY ACROSS THE EASTERN
HALF OF THE BERING SEA REGION.

.LONG TERM FORECAST...
EXTENDED MODELS SUGGEST THE LONGWAVE TROUGH OVER THE MAINLAND WILL
LARGELY REMAIN INTACT THROUGH EARLY NEXT WEEK. THE NORTH PACIFIC
RIDGE MAY FLATTEN A BIT...ALLOWING THE STORM TRACK THROUGH THE BERING
TO SAG SOUTHWARD...THOUGH STORMS STILL CONTINUE TO MOVE INTO THE
SOUTHERN GULF. THIS WILL ALSO ALLOW NEAR OR SLIGHT BELOW-NORMAL
TEMPERATURES TO PERSIST ACROSS MUCH OF THE MAINLAND.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...HIGH WIND WARNING 185
MARINE...STORM 155 170
         GALE 120 125 130 132 150 160 165 171 172 175 176 179
FIRE WEATHER...NONE

AMD SEP 13