Small Craft Advisory 597, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
200 PM AKDT TUE AUG 23 2011

.MODEL DISCUSSION...MODELS INITIALIZED REASONABLY THIS MORNING.
FORECAST TRENDS ARE IN GENERAL AGREEMENT. HOWEVER...THE NAM IS
SOMEWHAT OF AN OUTLIER WITH THE LOW MOVING SE OF KODIAK THU AND A LOW
SKIRTING SOUTH OF THE ALEUTIANS. THE GFS/ECMWF SOLUTIONS APPEAR TO BE
THE MOST REASONABLE AND WILL USED IN GENERAL THIS FORECAST PACKAGE.

.UPPER LEVELS...
.500MB...PROGRESSIVE PATTERN IN PLACE. THE LOW CENTER NEAR ST.
LAWRENCE ISLAND CONTINUES TO ACT AS THE FULCRUM FOR WAVES MOVING
ACROSS THE BERING SEA AND MAINLAND. SHORT WAVE EXTENDING FROM THIS
CENTER TO A LOW OVER THE NORTH GULF SPLITS AS THE LOW IN THE GULF
MOVES EAST AND CARRIES A BULK OF THE ENERGY. THE NORTHERN HALF MOVES
INTO THE INTERIOR WED. A SECONDARY AND DYNAMICALLY MORE INTENSE
TROUGH MOVED SOUTH OF THE EASTERN RUSSIA COAST THIS MORNING. THIS
TROUGH SHARPENS AS IT MOVES TO ALONG 160W WED AFTERNOON. A CENTER
DEVELOPS NEAR THE BASE AT 50N 155W WED EVENING AND INTENSIFIES AS IT
MOVES INTO THE SOUTHERN GULF. THE CENTER THEN WEAKENS...SLOWS...AND
BECOMES NEARLY CUT-OFF AS THE RIDGE BUILDS FROM WESTERN CANADA TO
OVER THE MAINLAND THU NIGHT AND FRI. YET ANOTHER WAVE MOVES ACROSS
THE BERING SEA TO THE EASTERN ALEUTIANS FRI AFTERNOON AS THE ST.
LAWRENCE CENTER RETROGRADES W.

.SHORT TERM FORECAST...
SOUTHCENTRAL
AS THE MAJORITY OF THE UPPER LEVEL ENERGY SPLITS OFF AND SOUTH OF THE
KENAI PENINSULA THIS AFTERNOON...WILL LIKELY BEGIN WEAKENING THE AREA
OF RAIN ALONG THE BAROCLINIC ZONE. HOWEVER...THE SUPPORTING WEAK
SHORTWAVE ALOFT DOES IS SLOW TO CLEAR THE REGION TONIGHT...SO
EXPECT AT LEAST SOME PERIODS OF RAIN OR SHOWERS UNTIL IT DOES SO.
ALSO A FEW THUNDERSTORMS ARE POSSIBLE LATE THIS AFTERNOON AND EVENING
OVER THE COPPER RIVER BASIN. RESIDUAL LOW LEVEL MOISTURE IN THE WAKE
OF THE PRECIPITATION COUPLED WITH SUBSIDENCE BEHIND THE EXITING
SYSTEM WILL PRODUCE AREAS OF FOG AND STRATUS OVERNIGHT INTO WEDNESDAY
MORNING. A FEW SUNNY BREAKS POSSIBLE ON WEDNESDAY...BUT SOUTHCENTRAL
AK REMAINS DOWNSTREAM OF THE UPPER LOW NEAR THE SW MAINLAND...SO
SUBTLE DISTURBANCES MAY STILL ROTATE THROUGH FLOW BRINGING SOME
SPOTTY SHOWERS. THE NEXT SIGNIFICANT CENTER TO IMPACT SOUTHCENTRAL
DEVELOPS OVER THE NE EASTERN PACIFIC AHEAD OF A SHARPENING UPPER
TROUGH AND UNDER A STRONG JET CORE. THE FASTER FORECAST MOVEMENT OF
THIS CENTER FROM THE 12Z GFS/ECMWF MODEL RUNS SEEMS REASONABLE IN
LIGHT OF STRONG UPPER JET. CENTER DEEPENS INTO THE 980S AS IT MOVES
INTO THE SOUTHERN GULF OF ALASKA THU. THE LOW THEN SLOWS AND WEAKENS
AS IT BECOMES STACKED WITH UPPER CENTER OVER THE GULF FRI. EXPECT
GALES WITH THIS SYSTEM AS IT ENTERS THE GULF. THE COASTAL RIDGE WILL
BUILD IN ADVANCE OF THIS SYSTEM WED AND PRODUCE STRONG GAP WINDS
ACROSS TURNAGAIN ARM AND PORTAGE VALLEY.

SOUTHWEST AK...
THE LOW CENTER APPROACHING THE PRIBILOF ISLANDS THIS AFTERNOON MAKES
LANDFALL OVER THE DELTA THIS EVENING...THEN MOVES NORTH AND WEST TO
NEAR THE GULF OF ANADYR THU. THE WARM ADVECTION WITH ADVANCING
FRONTAL TROUGH WILL SPREAD RAIN TO MUCH OF SW ALASKA THROUGH TONIGHT.
COLD ADVECTION BEHIND COLD PORTION OF FRONT BRINGS SHOWERY WEATHER TO
THE DELTA EARLY WED. THE GENERAL FRONTAL TROUGH STALLS AND WEAKENS
OVER THE EASTERN PORTION OF THE REGION AS THE RIDGE BUILDS TO THE
EAST. SO GENERALLY CLOUDY UNSETTLED WEATHER WILL HOLD OVER THE REGION
THROUGH THU.

BERING SEA/ALEUTIANS...
ONGOING GALES ACROSS THE BERING SEA...WITH THE LOW PUSHING TO THE
PRIBILOFS THIS AFTERNOON AND TO THE SW MAINLAND TONIGHT. AN
ASSOCIATED FRONT WILL DRAG RAIN THROUGH THE CENTRAL AND EASTERN CHAIN
THROUGH WEDNESDAY AS WELL. ANOTHER LOW PRESSURE SYSTEM DROPS DOWN
FROM EASTERN RUSSIA AND MOVES TO THE EASTERN BERING SEA WEST OF THE
PRIBILOFS ON THURSDAY. YET ANOTHER CENTER SKIRTS SOUTH OF THE
ALEUTIANS WED AND RECURVES TO NEAR UNALASKA EARLY FRI MORNING. THIS
CENTER INTENSIFIES AS IT TRACKS SOUTH OF THE ALEUTIANS AND BRING A
ROUND OF WINDY AND WET CONDITIONS.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE...172 175 411 412 413
FIRE WEATHER...NONE.

RMC AUG 11