Small Craft Advisory 946, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
1220 PM AKST TUE DEC 27 2011

.ANALYSIS AND UPPER LEVELS...LONG-WAVE TROUGH IS FIRMLY ENTRENCHED
OVER ALASKA AND THE NORTH PACIFIC. THE UPPER JET AND STORM TRACK
IS PRIMARILY SOUTH OF THE ALASKA REGION...ALTHOUGH THE JET DOES
CURVE NORTHEASTWARD AS IT REACHES THE NORTHEAST PACIFIC WHICH WILL
CONTINUE TO GUIDE STORMS TOWARD SOUTHEAST ALASKA. THE COLD CORE
UPPER LOW WHICH HAS BEEN MEANDERING AROUND SOUTHWEST ALASKA THE
PAST COUPLE DAYS IS MAKING ITS WAY NORTHWARD ALONG THE ALASKA
RANGE/SUSITNA VALLEY CORRIDOR LED BY A SHARP SHORT-WAVE TROUGH.
A MODERATELY INTENSE BAND OF SNOW AHEAD OF THIS TROUGH MOVED THROUGH
ANCHORAGE AND VICINITY THIS MORNING BRINGING AN INCH OR TWO OF SNOW.
AREAS OF LIGHTER SNOW CONTINUE BEHIND THE TROUGH WITH WEAK LIFT
SUPPLIED BY THE UPPER LOW. ARCTIC AIR IS FLOWING OVER THE RELATIVELY
WARM WATERS OF THE GULF OF ALASKA PRODUCING FAIRLY IMPRESSIVE LOW
LEVEL INSTABILITY. A STEADY STREAM OF SNOW SHOWERS IS MOVING ONSHORE
ACROSS EASTERN PRINCE WILLIAM SOUND AS WELL AS ALONG KACHEMAK BAY.
WEST OF THE UPPER CENTER IS CHARACTERIZED BY GENERALLY WEAK UPPER
FEATURES AND BROAD NORTHERLY FLOW WITH WEAK COLD ADVECTION AND
INSTABILITY. THUS...NUMEROUS SNOW SHOWERS AND LOCALLY GUSTY WINDS
DOMINATE THE BERING SEA AND ALEUTIANS.

.MODEL DISCUSSION...MODELS ARE ALL IN GOOD AGREEMENT WITH SYNOPTIC
SCALE FEATURES. THERE ARE MINOR DIFFERENCES ON THE MESOSCALE BUT
THESE ARE ALL WEAK FEATURES THAT HAVE MINIMAL AFFECT ON THE
RESULTANT FORECAST. ONLY MINOR ADJUSTMENTS WILL BE MADE TO
CURRENT FORECAST.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...UPPER LOW WILL EXIT TO INTERIOR ALASKA TONIGHT.
HOWEVER...CYCLONIC UPPER LEVEL FLOW WILL PERSIST ACROSS SOUTHCENTRAL.
A DISTINCT SHORT-WAVE TROUGH ON THE SOUTH SIDE OF THE UPPER LOW WILL
SLOWLY ROTATE ACROSS SOUTHCENTRAL TONIGHT THROUGH WEDNESDAY NIGHT.
THIS WILL MAINTAIN AREAS OF LIGHT SNOW WITH LITTLE OR NO
ACCUMULATION. AREAS OF MORE INTENSE INTENSE SNOW WILL CONTINUE
OVER THE GULF AND PRINCE WILLIAM SOUND DUE TO GREATER INSTABILITY.
AS A STRONG LOW OVER THE NORTHEAST PACIFIC TRACKS TO SOUTHEAST
ALASKA WEDNESDAY AFTERNOON THE PRESSURE GRADIENT WILL TIGHTEN BACK
UP ALONG THE GULF COAST AND STRONG GAP WINDS WILL RESUME. THIS WILL
ONCE AGAIN PRODUCE REDUCED VISIBILITIES IN SNOW AND BLOWING SNOW
THROUGH THOMPSON PASS. IT LOOKS LIKE THE SNOWFALL WILL GENERALLY
BE LIGHT IN THAT AREA SO THINK REALLY LOW VISIBILITIES WILL BE
ISOLATED. AS WE HEAD TO THE END OF THE WEAK SOUTHCENTRAL WILL SETTLE
UNDER A BROAD TROUGH WITH A WEAK SURFACE LOW IN THE PRINCE WILLIAM
SOUND AREA. THIS WILL RESULT IN MAINLY DRY AND COLD CONDITIONS
INLAND WITH AREAS OF SNOW OR SNOW SHOWERS ALONG THE COAST.

SOUTHWEST ALASKA...AS UPPER LOW MOVES TO INTERIOR ALASKA A FEW WEAK
WAVES WILL ROTATE SOUTHWARD BEHIND IT. THE MAIN IMPACT WILL TO
REINFORCE THE ARCTIC AIR. OTHER THAN THAT LOOK FOR A CONTINUATION
OF CURRENT WEATHER WITH A FEW CLOUDS AND SHOWERS MAINLY ALONG THE
IMMEDIATE COAST.

BERING SEA/ALEUTIANS...VERY LITTLE WILL CHANGE THIS WEEK SO EXPECT
CONTINUES SNOW SHOWERS AND LOCALLY GUSTY WINDS. A LOW WILL FORM
OVER THE FAR WESTERN BERING MID WEEK AND MOVE TO THE CENTRAL BERING
AT THE END OF THE WEEK...BUT WILL REMAIN WEAK.

.LONG TERM FORECAST...LONG-WAVE PATTERN WILL REMAIN IN PLACE THROUGH
NEXT WEEKEND WITH MODELS HINTING AT SOME CHANGES IN FLOW AS WE HEAD
INTO NEXT WEEK. HOWEVER...THERE IS POOR AGREEMENT AND CONSISTENCY
IN WHAT THE CHANGES WILL BE.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...HEAVY FREEZING SPRAY WARNING 130 132 138 185.
FIRE WEATHER...NONE.

SEB DEC 11