Small Craft Advisory 133, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
200 PM AKST SUN FEB 10 2013

.ANALYSIS AND UPPER LEVELS...
THE OVERALL WEATHER PATTERN HAS SHIFTED INTO A STABLE PATTERN THAT
WILL GENERALLY MAINTAIN FOR MUCH OF THE NEXT WEEK. THIS PATTERN IS
COMPOSED OF A LONGWAVE TROUGH OVER THE BERING SEA WITH AN ANCHORING
UPPER LOW CENTER NEAR SAINT MATTHEW ISLAND. FURTHER TO THE EAST...THE
HIGH AMPLITUDE RIDGE OF THE LAST FEW DAYS HAS MOVED EASTWARD AND
FLATTENED A BIT...SETTING THE SOUTHERN MAINLAND UP UNDER BROAD
SOUTHWESTERLY FLOW. AN AREA OF PRESSURE RISES BEHIND YESTERDAYS LOW
IS RESULTING IN GUSTY SOUTHERLY WINDS ACROSS THE COOK INLET REGION
AND EVEN INTO THE MAT-SU VALLEY AND COPPER RIVER BASIN. SNOW IS
FALLING AT MANY HIGHER ELEVATIONS...WITH A MIX OF RAIN AND SNOW AT
LOWER ELEVATIONS. MEANWHILE...THE FIRST IN A PARADE OF RELATIVELY
WEAK DISTURBANCES IS MOVING SOUTH OF THE AKPEN TOWARD THE NORTH GULF
COAST.

.MODEL DISCUSSION...
THE MODELS ARE IN GOOD SYNOPTIC AGREEMENT THROUGH THE FIRST 48
HOURS...WITH AGREEMENT AND FORECAST CONFIDENCE DIMINISHING BEYOND THE
FIRST FEW DAYS OF THE FORECAST. IN THE FIRST 48 HOURS...THE ONLY
DISCREPANCY OF NOTE INVOLVES THE TRACK OF THE SURFACE LOW CURRENTLY
SOUTH OF KODIAK MOVING TOWARD PRINCE WILLIAM SOUND. THE NAM HAS BEEN
AN OUTLIER WITH A MORE EASTERLY TRACK FOR SEVERAL DAYS...WHILE THE
EC/GFS/GEM HAVE BEEN CONSISTENT WITH A MORE WESTERLY TRACK INTO
WESTERN PRINCE WILLIAM SOUND BY LATE TONIGHT. THE FURTHER WEST TRACK
WOULD SUGGEST AN AREA OF SNOW WOULD AGAIN RETURN TO THE ANCHORAGE AND
MAT VALLEY AREAS TONIGHT...WHILE THE NAM WOULD KEEP THE COOK INLET
REGION MOSTLY DRY. AT THIS TIME THE PREFERENCE IS FOR THIS FURTHER
WEST TRACK BASED ON MODEL CONSENSUS AS WELL AS RADAR RETURNS OVER
BRISTOL BAY SUGGESTING DEEPER MOISTURE WILL PERSIST FARTHER TO THE
WEST THAN THE NAM DEPICTS. FURTHER OUT IN TIME...A STRONG NORTH
PACIFIC LOW WILL DEVELOP BY MIDWEEK AND FOLLOW A SIMILAR TRACK TOWARD
KODIAK ISLAND. THE EC IS THE OUTLIER WITH THIS FEATURE...BEING BOTH
SLOWER AND WEAKER. NEARLY ALL OTHER AVAILABLE MODELS SUGGEST A FASTER
AND STRONGER SOLUTION...WHICH IS PREFERRED AND WILL BE INCORPORATED
INTO THIS FORECAST PACKAGE.

.SHORT TERM FORECAST...
SOUTHCENTRAL...WIDESPREAD SOUTHERLY WINDS ACROSS THE REGION WILL
CONTINUE TO DIMINISH THROUGH THE REMAINDER OF THE AFTERNOON AS
PRESSURE RISES BEHIND THE DEPARTING LOW ARE REPLACED BY PRESSURE
FALLS AHEAD OF THE LOW NEAR KODIAK ISLAND. PRECIPITATION IS ALREADY
BEGINNING TO INCREASE AGAIN OVER THE SOUTHERN KENAI AND CENTRAL GULF
IN ADVANCE OF THIS LOW. AS MENTIONED ABOVE...THE MAIN CHALLENGE WILL
BE PINPOINTING THE PLACEMENT OF THE LOW...AND BY EXTENSION FIGURING
OUT HOW FAR WEST INTO COOK INLET THE PRECIPITATION WILL DEVELOP THIS
EVENING. BASED ON MODEL...SATELLITE...AND RADAR TRENDS THIS AFTERNOON
IT SEEMS LIKELY THAT AFTER A SHORT BREAK THIS EVENING PRECIP WILL BE
WORKING BACK INTO THE ANCHORAGE AND MAT VALLEY LATER TOWARD MIDNIGHT.
TEMPERATURES SHOULD HAVE COOLED ENOUGH TO ALLOW ALL-SNOW BY THIS
POINT...AND FAIRLY MINOR ACCUMULATIONS OF SNOW ARE LIKELY BY MONDAY
MORNING. THE HIGHEST AMOUNTS WILL LIKELY BE THE HILLSIDE AND OTHER
HIGHER ELEVATIONS AS THEY WILL NOT ONLY BE FURTHER EAST AND CLOSER TO
THE LOW...BUT ALSO WILL HAVE A WEAK UPSLOPE COMPONENT TO THE WINDS.

SOUTHWEST...SIMILAR TO SOUTHCENTRAL...BROAD SOUTHWESTERLY FLOW WILL
KEEP PERIODS OF SNOW MOVING ONSHORE THROUGH THE FIRST HALF OF THE
WEEK. NO MAJOR ACCUMULATIONS ARE EXPECTED...BUT OVER TIME THE SMALL
AMOUNTS WILL LIKELY ADD UP...ESPECIALLY IN AREAS WHERE SOUTH FACING
MOUNTAINS ENHANCE THE ATMOSPHERIC LIFT.

BERING SEA AND ALEUTIANS...NUMEROUS WEAK EMBEDDED SHORTWAVE TROUGHS
ROTATING AROUND THE COLD UPPER LOW NEAR SAINT MATTHEW WILL KEEP
INTERMITTENT PERIODS OF SNOW/SNOW SHOWERS ACROSS MUCH OF THE REGION
THROUGH MIDWEEK. THE RAIN/SNOW LINE WILL REMAIN GENERALLY STATIONARY
OVER THE EASTERN HALF OF THE ALEUTIANS. THE NEXT MAJOR STORM MOVES IN
MIDWEEK AND HAS THE POTENTIAL TO BRING BLIZZARD CONDITIONS TO THE
CENTRAL AND/OR EASTERN ALEUTIANS DEPENDING ON THE EXACT TRACK. STAY
TUNED TO THE CURRENT FORECAST FOR THE LATEST INFORMATION.

.LONG TERM FORECAST...
THE UPPER LOW OVER THE BERING WILL RETREAT NORTHWARD BY
MIDWEEK...PAVING THE WAY FOR A RETURN OF A MORE PROGRESSIVE WEATHER
PATTERN WITH ALTERNATING WARM-UPS AND COOL-DOWNS OVER MUCH OF THE
STATE BY NEXT WEEKEND. IN GENERAL...TEMPERATURES WILL REMAIN NEAR OR
SLIGHTLY ABOVE NORMAL FOR MOST OF THE MAINLAND...AND NEAR OR BELOW
NORMAL OVER THE BERING SEA/ALEUTIAN REGION.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...SNOW ADVISORY 145
MARINE...GALE 120
         HEAVY FREEZING SPRAY 160 179
FIRE WEATHER...NONE

AMD FEB 13