Small Craft Advisory 1127, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
500 AM AST WED DEC 6 2006

.DISCUSSION...

..ANALYSIS..
THE UPPER LEVEL LONGWAVE PATTERN REMAINS RELATIVELY STATIONARY THIS
MORNING WITH THE LONGWAVE TROUGH LOCATED OVER THE BERING
SEA...PLACING MUCH OF SOUTHCENTRAL AND EASTERN ALASKA UNDER SOUTHERLY
FLOW. THIS HAS LED TO THE WARMER AND WETTER PATTERN THAT HAS BEEN
SEEN OVER THE LAST FEW DAYS ACROSS SOUTHCENTRAL WHILE THE
CENTRAL/WESTERN ALEUTIANS HAVE BEEN COOLER THAN AVERAGE...WITH SNOW
BEING REPORTED AT STATIONS INCLUDING SHEMYA AND ADAK OVERNIGHT. A
POWERFUL 250MB JET STREAM HAS BEEN SPANNING MUCH OF THE NORTH PACIFIC
ALONG 40N...HELPING TO SPAWN NEW STORM SYSTEMS AS JET MAXES THAT MAKE
THEIR WAY ALONG THE JET STREAM. THE SURFACE PATTERN IS DOMINATED BY
TWO MAIN SYSTEMS. THE FIRST IS THE REMNANTS OF A POWERFUL LOW SOUTH
OF KODIAK ISLAND. RAIN  BANDS FROM THIS SYSTEM ARE MAKING THEIR WAY
ONSHORE ALONG THE NORTHERN GULF COAST. MOST OF THE PRECIP IS LIMITED
TO WINDWARD SLOPES OF THE COASTAL MOUNTAIN RANGES AND THE ALASKA
RANGE WITH SNOW FALLING OVER HIGHER ELEVATIONS AS WELL AS AROUND
VALDEZ WHERE ENOUGH COLD AIR IS TRAPPED IN THE LOW LEVELS TO KEEP
PRECIP FROZEN. A LOW JUST NORTH OF THE PRIBILOFS WITH A SURFACE
TROUGH EXTENDING WEST OF THE LOW CENTER IS GENERATING A LARGE SWATH
OF OVERRUNNING INDUCED SNOWFALL ACROSS THE NORTHERN AND WESTERN
BERING SEA PER IR IMAGERY/SFC OBS. IR IMAGERY ALSO REVEALS A
DEVELOPING LOW SOUTH OF UNALASKA ISLAND WHICH IS PROGGED TO BE THE
NEXT MAJOR SYSTEM TO AFFECT THE FORECAST AREA.

..MODELS..
MODELS ARE IN GOOD AGREEMENT OVERALL WITH THE MAIN FEATURE BEING THE
DEVELOPING LOW OF UNALASKA ISLAND. THE NAM/WRF IS FAVORED THIS
MORNING AS IT INITIALIZES THE DEVELOPING LOW AS WELL AS THE SEPARATE
LOW NORTH OF THE PRIBILOFS A LITTLE BETTER THAN THE GFS/ECMWF. GFS
AND NAM/WRF MATCH UP WELL WITH BOTH MODELS DRIVING THIS LOW EAST AND
THEN NORTH ACROSS KODIAK ISLAND AND INTO THE MAINLAND AROUND KAMISHAK
BAY SATURDAY NIGHT WHILE ANOTHER SERIES OF LOWS FORM AND MOVE RAPIDLY
EAST WELL SOUTH OF THE ALEUTIANS...CLOSER TO THE 250MB JET AXIS. IN
THE EXTENDED...THE GFS ENSEMBLE SHOWS A SIGNIFICANT DEGREE OF
VARIANCE WITH REGARDS TO THE EXACT POSITIONING OF THE LOW AFTER
SATURDAY WITH SOME ENSEMBLE MEMBERS POSITIONING THE MAIN LOW OVER
BRISTOL BAY AND OTHERS SUGGESTING A LOW FARTHER EAST OVER KODIAK
ISLAND. THIS DIFFERENCE IS ALSO REFLECTED IN THE COMPARISON OF THE
CURRENT GFS WHICH HAS THE LOW FARTHER EAST WHEREAS THE OLD RUN HAS
THE LOW OVER BRISTOL BAY. THE TWO RUNS...ALONG WITH THE THE ENSEMBLE
MEMBERS...COME BACK INTO LINE BY SUNDAY NIGHT WITH THE REDEVELOPMENT
OF THE LOW IN THE NORTHEASTERN GULF. THE TIMING OF THE NEXT LOW TO
MOVE INTO THE GULF EARLY NEXT WEEK VARIES WIDELY BETWEEN ENSEMBLE
MEMBERS AND THE ECMWF. AS A RESULT...JUST NUDGING EXTENDED GRIDS
SLIGHTLY TOWARDS NEW GFS RUN DUE TO LOW MODEL CONFIDENCE.

..FORECAST EAST AND SOUTH OF THE ALASKA RANGE..
THE RAIN SHOWER ACTIVITY ALONG THE NORTHERN GULF COAST WILL REMAIN
WIDESPREAD THROUGH TODAY AND FRIDAY AS THE FLOW THROUGH THE LOW AND
MID LEVELS REMAINS CYCLONIC AND ONSHORE. SHOWER ACTIVITY ACROSS THE
INLAND ZONES WILL BE MORE SCATTERED IN NATURE AS THE MAJORITY OF THE
MOISTURE WILL BE SCOURED OUT BY THE COASTAL MOUNTAINS. ANOTHER
SIGNIFICANT SHOT OF PRECIP MOVES IN ALONG THE COAST FRIDAY EVENING AS
A FRONT MOVES OUT AHEAD OF THE LOW SOUTH OF KODIAK ISLAND. ONCE AGAIN
THOUGH...THE MAJORITY OF THE MOISTURE SHOULD BE SCOURED OUT BY THE
MOUNTAINS...LEAVING JUST SCATTERED SHOWERS INLAND. WITH THE MAIN
UPPER LOW SHIFTING TO THE EAST AND OVER SOUTHCENTRAL DURING THE
WEEKEND...EXPECT THE UNSETTLED WEATHER TO CONTINUE WELL INTO NEXT
WEEK WITH CHANCE POPS ACROSS MOST OF THE ZONES THROUGH WEDNESDAY.
LOOK FOR TEMPERATURES TO REMAIN AT OR ABOVE NORMAL INTO NEXT WEEK AS
SOUTHERLY FLOW REMAINS OVER THE REGION.

..SOUTHWEST MAINLAND FORECAST..
LOOK FOR ISOLATED SNOW SHOWERS ACROSS THE SOUTHWEST MAINLAND ZONES
TODAY...MAINLY FROM WHAT LIMITED MOISTURE MANAGES TO SPILL OVER THE
ALASKA AND ALEUTIAN RANGES. LOOK FOR SHOWER ACTIVITY TO DIMINISH
TONIGHT AS THE LOW LEVEL FLOW BECOMES MORE EASTERLY. THE EXCEPTION IS
THE AK PEN WHICH WILL SEE A MIXTURE OF RAIN AND SNOW TONIGHT AS THE
MATURING LOW PULLS CLOSER AND THE WARM FRONT BRUSHES BY. A SERIES OF
SHORTWAVES ROTATES ACROSS THE REGION KEEPS CHANCE POPS UP THROUGH THE
WEEKEND WHILE COLD ADVECTION BEHIND THE LOW KEEPS SHOWERS LIKELY
ALONG THE AKPEN. THE MOVEMENT OF AN UPPER LOW INTO SW AK FROM THE
NORTHWEST WILL ALSO KEEP AT LEAST A CHANCE OF SHOWERS IN THE FORECAST
INTO THE MIDDLE OF NEXT WEEK AS COLDER AIR (850MB TEMPS AROUND -14 AS
COMPARED TO -4 CURRENTLY) FINALLY BEGINS TO ADVECT INTO THE AREA
STARTING EARLY MONDAY MORNING.

..ALEUTIAN/BERING SEA FORECAST..
SNOW SHOWERS WILL CONTINUE TO ABOUND ACROSS MUCH OF THE ALEUTIANS AS
A SURFACE TROUGH DROPS INTO PLACE JUST NORTH OF THE ALEUTIANS BEHIND
THE ADVANCING LOW TO THE EAST. THIS TROUGH REMAINS IN PLACE INTO
SUNDAY...ALLOWING FOR SNOW ACCUMULATIONS OF 3 TO 6 INCHES ACROSS THE
CENTRAL AND WESTERN ALEUTIANS. AFTER THE TROUGH PUSHES SOUTH OF THE
ISLANDS...WIDESPREAD COLD ADVECTION TAKES OVER...ALLOWING FOR SNOW
SHOWERS AND COOLER THAN AVERAGE TEMPERATURES TO CONTINUE ACROSS MUCH
OF THE BERING SEA INTO THE MIDDLE OF NEXT WEEK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...GALES 120 130 132 170 172 175 185

WOOD DEC 06