Small Craft Advisory 966, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
434 PM AKST THU DEC 4 2014

.ANALYSIS AND UPPER LEVELS...
THERE IS AN UPPER LEVEL LOW CENTERED JUST SOUTH OF THE CENTRAL
ALEUTIANS. THERE IS AN ELONGATED TROUGH STRETCHING FROM THE
ALASKA PENINSULA WITH MOISTURE STREAMING ALONG A FRONT THAT IS
OVER THE WESTERN GULF AND INTO KODIAK ISLAND. THERE IS A DEVELOPING
LOW JUST OFF THE EAST COAST OF JAPAN MOVING RAPIDLY TOWARDS THE
NORTHWEST. THERE IS A RIDGE OVER THE ALASKA PANHANDLE PUSHING INTO
THE EASTERN CORNER OF SOUTH CENTRAL ALASKA.

&&

.MODEL DISCUSSION...
THE NUMERICAL MODELS ARE IN FAIRLY GOOD AGREEMENT ON THE OVER-ALL
PATTERN BUT NOT SO MUCH IN AGREEMENT ON THE SMALLER SCALE DETAILS.
THERE IS FAIRLY LARGE SPREAD IN THE SURFACE PRESSURE PATTERNS ASSOCIATED
WITH THE ALASKA PENINSULA TROUGH. MOSTLY THIS AFFECTS THE TIMING OF
"SURGES" ALONG THE GULF/KODIAK FRONT. PREFER THE HI- RES MODELS (NAM
AND REGIONAL GEM) FOR THESE FEATURES. THERE ARE ALSO SOME DIFFERENCES
WITH A LOW (ORIGINALLY THE LOW OFF THE COAST OF JAPAN) SLIDING SOUTH
OF THE ALEUTIANS FRIDAY AFTERNOON THROUGH SATURDAY AFTERNOON THEN A
LARGE AMOUNT OF SPREAD WITH VARIOUS SURFACE LOWS OVER THE NORTH PACIFIC
AND GULF OF ALASKA ON SUNDAY. PREFER THE GLOBAL MODELS (GFS AND ECMWF)
FOR THIS TIME FRAME BUT WITH LOWER CONFIDENCE.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
WITH THE FRONT WEAKENING THIS EVENING MOST OF THE AREA SHOULD SEE
A RELATIVE BREAK IN THE WET WEATHER AS WE HEAD INTO FRIDAY. RADAR
IS SHOWING PRECIPITATION WINDING DOWN ACROSS THE AREA WITH THE
HEAVIEST SNOW CONFINED NOW TO MAINLY THE SKWENTNA AREA AND ALONG
THE EASTERN FLANK OF THE AK RANGE. SOME RAIN SHOWERS CONTINUE TO
MOVE FROM PRINCE WILLIAM SOUND INTO PORTAGE VALLEY BUT EVEN THOSE
SHOULD TAPER OFF LATER THIS EVENING. FOR FRIDAY MOST PLACES WILL
WILL REMAIN DRY THROUGH MUCH OF THE DAY AS THE NORTH AMERICAN
RIDGE PUSHES UP FROM THE PANHANDLE BRIEFLY. THE BIGGEST EXCEPTION
TO THIS IS KODIAK WHERE RAIN WILL CONTINUE WITH MOIST FLOW FROM
THE SOUTHEAST. BY LATE IN THE DAY FRIDAY THE NEXT FRONT WILL BE
TAKING SHAPE ACROSS THE NORTHERN GULF AND PRECIPITATION WILL
IMPACT THE GULF COAST RIGHT AROUND SUNSET. THIS SYSTEM DOES NOT
HAVE A TON OF THERMAL ADVECTION WITH IT SO TEMPERATURES SHOULD
HOVER NEAR WHERE THEY ARE NOW MAKING FOR SNOW FOR INLAND AND
HIGHER ELEVATIONS WITH RAIN CONTINUING AT MANY COASTAL LOCALES.
THIS FRONT WILL STRUGGLE TO BRING PRECIPITATION INLAND VERY FAR
WITH ALMOST NO UPPER LEVEL SUPPORT. BY SATURDAY THE UPPER LEVEL
NORTH AMERICAN RIDGE MAKES ANOTHER PUSH TOWARDS THE ANCHORAGE
AREA. THIS WILL KEEP WARM MOIST AIR EMBEDDED IN VARIOUS WEAK WAVES
HEADING TOWARDS THE COAST. THIS SHOULD ALSO SERVE TO TIGHTEN UP
THE SOUTHEASTERLY GRADIENT GOING INTO SUNDAY. SO WINDS THROUGH THE
TYPICAL AREAS ARE LIKELY TO INCREASE OVER THE WEEKEND WITH MILD
AND DRY CONDITIONS EXPECTED ON THE LEE SIDE OF THE CHUGACH AND
KENAI MOUNTAINS.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...

CLOUD COVER WILL BE ON THE INCREASE ACROSS THE WESTERN LOWER
KUSKOKWIM VALLEY AND KUSKOKWIM DELTA THIS EVENING AS A WEAK FRONT
FRONT LIFTS NORTH OVER THE BRISTOL BAY AREA. IN ADDITION RAIN AND
SNOW CHANCES WILL BE ON THE RISE AS THE FRONT AND AN ASSOCIATED
UPPER LEVEL DISTURBANCE PUSH ACROSS THE BRISTOL BAY AREA. CROSS
BARRIER FLOW ALONG THE ALASKA RANGE WILL CREATE A SMALL DOWNSLOPE
HOLE OVER NEAR KING SALMON LEADING TO MORE SHOWERY PRECIPITATION
WHILE THE ALASKA RANGE AND WESTERN CAPES WILL SEE A STEADY DOSE OF
RAIN AND SNOW. OVERNIGHT TEMPERATURES WILL BE A BIT WARMER THAN
THOSE OBSERVED LAST NIGHT DUE TO THE INCREASING CLOUD COVER AND
ASSOCIATED INSULATION PREVENTING THE GROUND FROM COOLING OFF AS
MUCH. BY FRIDAY NIGHT INTO SATURDAY MORNING MUCH COOLER TEMPERATURES
(SOME PLACES NEAR 0 DEGREES IN THE LOWER KUSKOKWIM VALLEY) WILL BE
SEEN AS SKIES CLEAR A LITTLE BIT AND NORTHEASTERLY WINDS BEGIN TO
USHER IN A MUCH COLDER AIR MASS ACROSS SOUTHWEST ALASKA.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...

AN AREA OF LOW PRESSURE SITUATED JUST TO THE SOUTHWEST OF NIKOLSKI
WILL CONTINUE TO PUSH SOUTH INTO THE NORTH PACIFIC THIS EVENING.
WHILE THE LOW PUSHES SOUTH RAIN CHANCES OVER THE CENTRAL ALEUTIANS
AND MAJORITY OF THE BERING SEA WILL BEGIN TO TAPER OFF TONIGHT.
HOWEVER RAIN AND SNOW CHANCES WILL BE ON THE RISE AGAIN ON FRIDAY
AS A SECOND AREA OF LOW PRESSURE PUSHES JUST SOUTH OF THE ALEUTIAN
ISLANDS THROUGH LATE FRIDAY. MODELS HAVE GOTTEN INTO MUCH BETTER
AGREEMENT WITH THE SYSTEM OVER THE PAST 24 HOURS. THEY ARE NOW
SHOWING THAT THE LOW PRESSURE SYSTEM WILL CONTINUE TO STRENGTHEN
AS IT SKIRTS THE WESTERN ALEUTIANS. ALSO THE LOW WILL HAVE BECOME
COLD CORE PRIOR TO ENTERING THE COASTAL WATERS OF SHEMYA WHICH
WILL LEAD TO A MORE NEUTRAL ADVECTION PATTERN INSTEAD OF A WEAK
WARM AIR ADVECTION PATTERN. THIS SHOULD LEAD TO A 12 TO 18 HOUR
PERIOD OF STORM FORCE WINDS NEAR SHEMYA. THE STRONGEST WINDS AND
WAVES WILL REMAIN SOUTH OF THE ALEUTIANS IN THE NORTH PACIFIC.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE STORM FORCE LOW SOUTHWEST OF ADAK WILL CONTINUE TO TRACK
EASTWARD TRANSITIONING INTO A COMPLEX SYSTEM BY SUNDAY OVER THE
NORTH PACIFIC. THIS WILL BRING GUSTY WINDS WITH WIDESPREAD
PRECIPITATION OVER THE ALEUTIANS SPREADING INTO THE LOWER BERING
SEA. THERE IS AN UPPER LEVEL OMEGA BLOCK LOCATED OVER SIBERIA
WHICH WILL PRODUCE NORTHERLY FLOW THROUGH THE BERING SEA/ALEUTIANS
BY MONDAY. THIS PATTERN WILL CONTINUE WITH COLD AIR FILTERING INTO
THE REGION. BY WEDNESDAY THE HIGH TEMPERATURES WILL BE IN THE
SINGLE DIGITS AND LOWS RANGING FROM ZERO TO MINUS FIVE BELOW OVER
THE KUSKOKWIM DELTA AND LOWER KUSKOKWIM VALLEY THROUGH THURSDAY.
THE MODELS STRUGGLED WITH PLACEMENT OF THIS STORM FORCE LOW. THE
GFS/ECMWF WERE THE PREFERRED MODELS OF CHOICE WITH THE NAM BEING
THE OUTLIER WITH THIS SYSTEM.

THE SOUTHCENTRAL ALASKA REGION WILL HAVE AN UPPER LEVEL RIDGE OF
HIGH PRESSURE OVER THE NORTHERN GULF COASTLINE EXTENDING INTO THE
MATSU VALLEY WESTWARD THROUGH THE YUKON DELTA BY SATURDAY. THIS
WILL BRING GUSTY WINDS THROUGH TURNAGAIN ARM AND  THE SOUTHWEST
MAINLAND THROUGH SUNDAY BEFORE DIMINISHING AS THE PRESSURE
GRADIENT WEAKENS. THE TEMPERATURES WILL CONTINUE TO WARM DUE TO THE
HIGH PRESSURE RIDGE AND THE SOUTHEASTERLY FLOW THROUGH THE GULF.
THERE WILL BE SEVERAL SHORTWAVES TRACKING THROUGH THE WESTERN/NORTHERN
GULF BRINGING WIDESPREAD RAIN AND WARMER TEMPERATURES HEADING INTO
THE WEEKEND THROUGH THE EARLY PART OF NEXT WEEK. THE AREAS OF
CONCERN WILL BE THE CHANCE FOR FREEZING RAIN FOR THE INTERIOR OF
SOUTHCENTRAL ALASKA AND SOUTHWEST MAINLAND BY THIS WEEKEND. ANY
PRECIPITATION FALLING THROUGH THE WARM LAYER ALOFT WILL TURN INTO
FREEZING PRECIPITATION AS IT TRANSITIONS THROUGH THE COLDER LAYER
AT THE SURFACE. THE MODELS ARE STILL HAVING DIFFICULTY WITH THE
TIMING AND STRENGTH OF THE SHORTWAVES AS THEY TRACK THROUGH GULF.
THE FORECAST CONFIDENCE REMAINS BELOW AVERAGE DUE TO THE UNCERTAINTY
OF THE AFOREMENTIONED SYNOPTIC FEATURES.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...STORM 178. GALE 130 131 138 172 174 175 176 177 411.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...BL/SAM
SOUTHCENTRAL ALASKA...MO
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MC
LONG TERM...PD