Small Craft Advisory 15, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
100 PM AKST FRI JAN 3 2014

.ANALYSIS AND UPPER LEVELS...THE UPPER LEVEL FLOW IS HIGHLY AMPLIFIED
AND PROGRESSIVE LEADING TO AN ACTIVE STORM TRACK ACROSS THE ALASKA
REGION. A SHORT-WAVE TROUGH OVER SOUTHWEST ALASKA IS TRACKING QUICKLY
NORTHEASTWARD TOWARD SOUTHCENTRAL AND ULTIMATELY INTERIOR ALASKA.
THIS IS PRODUCING AREAS OF GENERALLY LIGHT PRECIPITATION. A WARM
NOSE IN THE LOW LEVELS HAS RESULTED IN RAIN MIXING IN AT TIMES IN
ANCHORAGE...BUT AREAS FURTHER NORTH ARE ALL SNOW.

THE FOCUS FOR THE NEXT COUPLE DAYS IS ON A STORM SYSTEM CURRENTLY
OVER THE NORTH CENTRAL PACIFIC. WATER VAPOR IMAGERY SHOWS A LONG
FETCH OF TROPICAL MOISTURE STREAMING NORTHWARD TOWARD KODIAK ISLAND
AND THE ALASKA PENINSULA...WHICH WILL LEAD TO WARMING TEMPERATURES
AND HEAVY PRECIPITATION AS THIS SYSTEM TRACKS NORTHWARD THE NEXT
COUPLE DAYS. SATELLITE SCATTEROMETER DATA INDICATES STORM FORCE
WINDS ON THE FRONT EDGE OF THIS SYSTEM.

ANOTHER POWERFUL SYSTEM IS JUST NORTH OF SHEMYA IS BRINGING STRONG
WINDS TO THE WESTERN TO CENTRAL BERING AND ALEUTIANS. THE CENTRAL
PRESSURE IS LOWER THAN WHAT FORECAST MODELS HAD INDICATED...SITTING
SOMEWHERE AROUND 960 MB THIS MORNING. THUS...INSTEAD OF WIDESPREAD
GALE FORCE WINDS THAT WERE EXPECTED...SURFACE OBSERVATIONS INDICATE
AREAS OF STORM FORCE WINDS (ESPECIALLY IN THE VICINITY OF THE LOW
CENTER). THIS LOW IS TRACKING TO THE WEST NORTHWEST TOWARD THE
KAMCHATKA PENINSULA SO EXPECT IMPROVING CONDITIONS ACROSS THE
ALEUTIANS AND CENTRAL BERING SEA.

.MODEL DISCUSSION...MODELS ARE IN GOOD AGREEMENT WITH HANDLING OF
THE STORM SYSTEM OVER THE NORTH-CENTRAL PACIFIC. THE FIRST NOTABLE
DIFFERENCES SHOW UP WITH TRACK OF A TRIPLE POINT LOW SOUTH OF THE
CENTRAL ALEUTIANS ON SUNDAY. PREFER THE 12Z GFS WHICH IS A NICE
MIDDLE GROUND AMONG ALL THE SOLUTIONS AND WHICH IS VERY CLOSE TO
THE CURRENT FORECAST.

.SHORT TERM FORECAST...

SOUTHCENTRAL/SOUTHWEST ALASKA...THE UPPER LEVEL TROUGH CROSSING
THE REGION TODAY WILL QUICKLY EXIT TO THE NORTH TONIGHT BRINGING
A VERY BRIEF BREAK OUT AHEAD OF THE PACIFIC STORM. WHILE THE UPPER
LEVELS WILL DRY OUT BEHIND THIS SHIRT-WAVE THE LOW LEVEL AIR MASS
WILL SEE VERY LITTLE CHANGE...SO EXPECT AREAS OF LOW CLOUDS AND
FOG TO HANG AROUND.

UNLIKE MANY OF THE WARM-UPS THIS WINTER WHICH HAVE PRODUCED
SIGNIFICANT FREEZING RAIN...LOW LEVEL TEMPERATURES WILL START OUT
RELATIVELY WARM AS THIS SYSTEM ARRIVES. THEREFORE...DO NOT EXPECT
FREEZING RAIN TO BE A MAJOR PROBLEM ANYWHERE. THERE MIGHT BE A
TRANSITION FROM SNOW TO FREEZING RAIN TO RAIN IN SOME AREAS...BUT
THE PERIOD OF FREEZING RAIN WOULD BE BRIEF AS SURFACE TEMPERATURES
QUICKLY RISE ABOVE FREEZING. THE GREATEST IMPACTS FROM THIS SYSTEM
WILL BE STRONG WINDS (PRIMARILY OVER MARINE AREAS) AND HEAVY
PRECIPITATION.

THE SURFACE LOW WILL TRACK NORTHWESTWARD TOWARD THE EASTERN BERING
WHILE THE FRONTAL SYSTEM ELONGATES SPREADS OUT OVER THE GULF AND
BRISTOL BAY. THIS ELONGATION WILL SLOW THE NORTHWARD PROGRESSION OF
THE FRONT SATURDAY AND SATURDAY NIGHT KEEPING THE WARMEST AIR FROM
HEADING INLAND. ONCE THE REMNANTS OF THE FRONT FINALLY DO PUSH
INLAND ON SUNDAY THE AIR MASS WILL HAVE MODIFIED ENOUGH TO PREVENT
A HUGE WARM-UP. EVEN SO...EXPECT TEMPERATURES TO RISE ABOVE FREEZING
FRO MUCH OF THE REGION ON SUNDAY. AS FAR AS PRECIPITATION...STRONG
EASTERLY FLOW AHEAD OF THE SYSTEM WILL PRODUCE DOWNSLOP DRYING ON
THE WEST SIDE OF MOUNTAIN RANGES FROM THE CHUGACH AND KENAI
MOUNTAINS TO THE ALASKA RANGE TO THE KUSKOKWIM AND AHKLUN MOUNTAINS.
THERE WILL STILL BE A CHANCE OF BRIEF PERIODS OF PRECIP AS UPPER
LEVEL WAVES MOVE THROUGH...BUT EXPECT VERY LITTLE QPF. TEH HEAVIEST
PRECIP CAN BE EXPECTED ALONG THE GULF COAST FROM KODIAK ISLAND TO
PRINCE WILLIAM SOUND. TEMPERATURES WILL WARM QUICKLY ENOUGH NEAR
SEA LEVEL THAT PRECIPITATION WILL BE MAINLY IN THE FORM OF RAIN.
THE ONE EXCEPTION IS VALDEZ WHERE THE COLD AIR USUALLY HANGS IN
UNTIL FRONTAL PASSAGE...WHICH IN THIS CASE WON'T OCCUR UNTIL SUNDAY.
THEREFORE...EXPECT HEAVY WET SNOW SATURDAY NIGHT INTO SUNDAY FROM
VALDEZ ON UP TO THOMPSON PASS. A BLIZZARD WATCH IS IN EFFECT FOR
THOMPSON PASS...BUT WITH THE FRONT STALLING ALONG THE NORTH GULF
COAST THERE MAY NOT BE ENOUGH WIND TO CAUSE BLIZZARD CONDITIONS
UNTIL SUNDAY MORNING. BY THIS TIME TEMPERATURES MAY WARM ENOUGH
TO LIMIT BLOWING SNOW. WITH A DEEPER LAYER OF COLD AIR SITTING IN
THE COPPER RIVER BASIN EXPECT THE MOIST SOUTHERLY FLOW TO BRING
ACCUMULATING SNOW TO THE COPPER RIVER BASIN...ESPECIALLY SOUTH OF
GLENNALLEN DOWN TO THOMPSON PASS. WILL ISSUE A WINTER WEATHER
ADVISORY SPECIFICALLY FOR THIS AREA.

THE LOW CENTER WILL EXIT TO THE WEST ACROSS THE CENTRAL BERING ON
SUNDAY BUT ANOTHER STORM WILL ALREADY APPROACHING FROM THE NORTH
CENTRAL PACIFIC. EXPECT ANOTHER ROUND OF PRECIP MONDAY AND
TUESDAY...ALTHOUGH THIS SECOND STORM LOOKS MUCH LESS IMPRESSIVE
BOTH WIND WISE AND PRECIP WISE. TEMPERATURES WILL REMAIN ABOVE
NORMAL AS A REINFORCING SHOT OF WARM AIR ARRIVES WITH THIS SYSTEM.

BERING SEA/ALEUTIANS...THE LONG-WAVE TROUGH WILL SIT OVER THE BERING
SEA AND NORTH PACIFIC WITH A STRONG SUBTROPICAL JET AIDING
DEVELOPMENT OF SURFACE LOWS. THE GENERAL TRACK OF THESE SYSTEMS
WILL BE EASTWARD ACROSS THE NORTH PACIFIC AND THEN CURVING NORTHWARD
TO THE EASTERN BERING AND EXITING BACK TO THE WEST. EXPECT GENERALLY
MODERATE STRENGTH LOWS...VERY TYPICAL FOR THIS TIME OF YEAR.

.LONG TERM FORECAST...MEDIUM RANGE MODELS ARE IN DECENT AGREEMENT
ON WEAKENING/BREAKDOWN OF THE DOWNSTREAM RIDGE OVER WESTERN NORTH
AMERICA. THIS WILL LEAD TO NEAR ZONAL FLOW ACROSS THE NORTH PACIFIC
NEXT WEEK WITH FAST MOVING STORMS TRACKING ALONG THE SOUTHERN TIER
OF THE FORECAST AREA FROM THE ALEUTIANS TO THE GULF. THIS MORE
SOUTHERLY STORM TRACK WILL ALLOW TEMPERATURES TO GRADUALLY COOL
ACROSS SOUTHCENTRAL AND SOUTHWEST ALASKA TO NEAR NORMAL BY THE
END OF NEXT WEEK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WATCH 131.
         WINTER WEATHER ADVISORY 141.
MARINE...STORM WARNING...119 120 130 131 132 138 150 155.
         GALE WARNING...125 136 137 139 141 160 165 170 172 174 178
                        179 180 181 185.
         HEAVY FREEZING SPRAY WARNING...185.
FIRE WEATHER...NONE.

SEB JAN 14