Small Craft Advisory 1029, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
521 AM AKST SAT DEC 26 2015

.ANALYSIS AND UPPER LEVELS...
THE REMNANTS OF A ONCE POWERFUL STORM CONTINUES TO DOMINATE THE
REGIONAL SYNOPTIC PATTERN THIS MORNING...WITH A DEEP 964 HPA LOW
OVER THE EASTERN BERING SEA...AND ITS ASSOCIATED STORM FORCE FRONT
MOVING THROUGH THE NORTHERN GULF COAST. WINDS REMAIN QUITE STRONG
ACROSS MOST OF SOUTHWEST ALASKA...AS WELL AS ACROSS COASTAL
INTERIOR LOCATIONS ALONG THE KENAI PENINSULA WHERE BOTH GAP WINDS
AND DOWN INLET WINDS ARE RATHER STRONG. OBSERVATIONS AND RADAR NOW
DEPICT THE FRONT WEAKENING AS IT MOVES INTO PRINCE WILLIAM SOUND.
A MESOSCALE CIRCULATION ALONG THE FRONT...AS SEEN ON WATER VAPOR
SATELLITE IMAGERY...HAS STALLED THE NORTHWARD PROGRESSION OF THE
FRONT ACROSS THE KENAI PENINSULA...WITH A NARROW BUT CONCENTRATED
BAND OF SNOWFALL IMPACTING THE AREA NORTH OF KACHEMAK BAY AND
SOUTH OF KENAI AS OF 2 AM THIS MORNING. HEAVY SNOW ALSO IMPACTED
PORTIONS OF TURNAGAIN PASS...WITH WEBCAMS SUGGESTING OVER A FOOT
OF SNOWFALL OVERNIGHT AS THE FRONT MOVED INLAND. HOWEVER...WITH A
TYPICAL STRONG DOWNSLOPE SHADOW...MOST OF INTERIOR SOUTHCENTRAL
HAS REMAINED QUIET WITH ONLY A FEW INLAND FLURRIES. WITH THE MAIN
BELT OF SUBTROPICAL MOISTURE NOW MOVING EAST AND NORTH OF
SOUTHCENTRAL...A MORE SHOWERY REGIME ALONG THE COASTS OF SOUTHWEST
AND SOUTHCENTRAL WILL FOLLOW BEHIND THIS FRONT (AND THE BERING
LOW) AS COOLER AIR WRAPS IN FROM THE WEST.

FARTHER WEST...AN ELONGATED WARM FRONT IS MOVING INTO THE FAR
SOUTHWESTERN BERING SEA...BUT WILL BEGIN TO INTERACT WITH THE
STILL LARGE UPPER LOW OVER THE EASTERN BERING...SHEARING IT OUT
AND KEEPING IT FROM LIFTING TOO FAR NORTH OVER THE ALEUTIAN CHAIN.

WITH TIME...THE REMNANTS OF THE LARGE BERING LOW WILL SLOWLY
WEAKEN AND DRIFT INTO THE NORTHERN GULF COAST...KEEPING STEADY
PRECIPITATION ALONG THE COASTS OF BOTH SOUTHWEST ALASKA AND THE
NORTHERN GULF.

&&

.MODEL DISCUSSION...
THE MODELS ARE IN EXCELLENT AGREEMENT WITH THE LARGE SCALE
SYNOPTIC PATTERN FOR THE NEXT THREE DAYS. AS THE PATTERN BECOMES
DRIVEN BY ANOTHER STRONG PACIFIC JET STREAM MOVING SOUTH OF THE
BERING SEA MONDAY...SMALLER SCALE DETAILS BEGIN TO BECOME MUCH
LESS CERTAIN...ALTHOUGH MOST OF THESE DISCREPANCIES ARE OVER THE
BERING SEA...AND ARE NOT OF LARGE CONSEQUENCE. OVER SOUTHERN
ALASKA AND THE GULF...THERE ARE DIFFERENCES IN THE DEVELOPMENT OF
AN ELONGATED WARM FRONT AND ASSOCIATED UPPER TROUGH MOVING INTO
SOUTHERN ALASKA LATE SUNDAY AND MONDAY. MOST NOTABLY...THE NAM AND
GFS DEPICT A MORE NEGATIVE TILTED TROUGH...WHICH WOULD BRING RAIN
INTO SOUTHWEST ALASKA BEFORE A TURNOVER TO SNOW. THESE DIFFERENCES
ALSO YIELD SLIGHT TRACK AND STRENGTH DIFFERENCES OF THE LOW AS IT
TRACKS THROUGH THE GULF (SEE EXTENDED DISCUSSION FOR MORE
INFORMATION). AS A WHOLE...A MORE MIDDLE GROUND APPROACH FAVORING
THE ECMWF WAS UTILIZED IN THIS FORECAST. FORECAST CONFIDENCE
IMPACT WISE IS MODERATELY HIGH THROUGH SUNDAY NIGHT.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
SOME LOCALLY GUSTY WINDS PERSIST ACROSS SOUTHCENTRAL EARLY THIS
MORNING AS AN ELONGATED FRONT PUSHES ONSHORE AND DISSIPATES.
THESE WINDS WILL RAPIDLY DIMINISH AS THE UPPER TROUGH PROGRESSES
INLAND. THE STEADY PRECIPITATION IS PRETTY MUCH OVER ALONG THE
COAST. A COOLER UNSTABLE AIR MASS BEHIND THE FRONT WILL CONTINUE
TO PRODUCE SHOWERS TODAY...MAINLY ALONG THE GULF COAST. THE AIR
MASS WILL BE JUST COOL ENOUGH ALOFT TO CHANGE PRECIP BACK TO
MOSTLY SNOW IN THE PRINCE WILLIAM SOUND.

THE NEXT FEATURE OF INTEREST IS THE VERTICALLY STACKED LOW SPINNING
OVER THE EASTERN BERING SEA. A SHORT-WAVE TROUGH AND SURFACE FRONT
ORIGINATING FROM THIS SYSTEM WILL SWING NORTHEASTWARD ACROSS
KODIAK ISLAND AND THE GULF BRINGING ANOTHER ROUND OF STRONG WINDS
AND STEADY PRECIP TO THE GULF COAST TONIGHT THROUGH SUNDAY. WITH
PERSISTENT STRONG SOUTHEASTERLY LOW LEVEL FLOW AREAS IN THE LEE
OF THE COASTAL MOUNTAINS WILL REMAIN MOSTLY DRY. AN ACTIVE
PACIFIC JET WILL THEN BRING ANOTHER MUCH STRONGER FRONT INTO THE
GULF SUNDAY AND SUNDAY NIGHT...RESULTING IN MORE INTENSE WINDS AND
PRECIP. TEMPERATURES WILL WARM A LITTLE MORE AS EACH OF THESE
FRONTS MOVES THROUGH...SO THAT BY SUNDAY NIGHT PRECIP ALONG THE
GULF COASTAL ZONES WILL BE ALL RAIN.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
THE UPPER LEVEL CLOSED LOW REMAINS OVER THE EASTERN BERING SEA
THROUGH THE WEEKEND. SHORTWAVES FROM THIS SYNOPTIC FEATURE WILL
SWEEP THROUGH THE SOUTHWEST REGION. THIS WILL PRODUCE SOME
SCATTERED SNOW SHOWERS ON SATURDAY BEFORE THE SECONDARY STRONGER
SHORTWAVE MOVES THROUGH THE BRISTOL BAY REGION ON SUNDAY. THIS
SHORTWAVE WILL BECOME NEGATIVELY TILTED ALONG THE ALASKA PENINSULA
BEFORE MOVING NORTHWARD. THIS SYNOPTIC FEATURE COMBINED WITH THE
WEATHER FRONT IN THE REGION WILL SEE INCREASED PRESSURE GRADIENTS
RESULTING IN STRONG GUSTY EASTERLY TO SOUTHEASTERLY WINDS THROUGH
THE BRISTOL BAY INLAND AREAS. THERE WILL BE A MIXTURE OF RAIN AND
SNOW ALONG THE COAST EXCEPT FOR ALL SNOW INLAND WITH THE COOLER
TEMPERATURES. LOOK FOR HEAVIER SNOW FALL AMOUNTS NORTH AND WEST OF
DILLINGHAM EXTENDING INTO THE LOWER KUSKOKWIM REGION SUNDAY
AFTERNOON EXTENDING INTO THE LATE EVENING HOURS.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE REMNANTS OF THE STORM FORCE LOW REMAINS OVER THE LOWER
EASTERN BERING SEA WITH GALE FORCE EASTERLY WINDS IN THE BRISTOL
BAY REGION EXTENDING INTO THE KUSKOKWIM BAY AREA. WHILE ON THE
BACKSIDE OF THIS SYSTEM THE CENTRAL ALEUTIANS ARE RECEIVING GUSTY
NORTHWESTERLY WINDS BEFORE SHIFTING MORE NORTHERLY THROUGH THE
CENTRAL TO NORTHERN BERING SEA. THIS WILL RESULT IN A SHOWERY
WEATHER REGIME THROUGH SUNDAY MORNING. THE WESTERN ALEUTIANS WILL
HAVE A STORM FORCE LOW APPROACH JUST SOUTH OF THE CHAIN ON SUNDAY
MORNING WITH GALE FORCE SOUTHEASTERLY WINDS ENTERING THE WESTERN
CHAIN. THIS IS SETTING UP A DEFORMATION ZONE OVER SHEMYA WHICH
WILL RESULT IN A DECENT AMOUNT OF SNOW ACCUMULATION AS THE
TEMPERATURES REMAIN BELOW FREEZING THROUGH THE WEEKEND. BY SUNDAY
THIS LOW WILL BE LOCATED OVER THE CENTRAL ALEUTIANS WITH STORM
FORCE WESTERLY WINDS ON THE PACIFIC SIDE. THE ASSOCIATED WEATHER
FRONT WITH THIS SYSTEM WILL BE ENTERING THE BRISTOL BAY AREA. THE
MODELS ARE STRUGGLING WITH THE POSSIBILITY OF A TRIPLE POINT LOW
FORMING JUST SOUTHWEST OF KODIAK ISLAND BY LATE SUNDAY EVENING.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
BEGINNING THE EXTENDED PERIOD ON MONDAY...AN ELONGATED UPPER
LEVEL TROUGH WILL BE MOVING ACROSS SOUTHWEST ALASKA INTO
SOUTHCENTRAL. SPREADING RAIN ALONG THE NORTHERN GULF COAST...AND
RAIN AND SNOW ACROSS MUCH OF SOUTHWEST ALASKA. AS THIS LOW MOVES
INLAND LATE MONDAY AFTERNOON INTO TUESDAY EVENING...THERE IS A
POTENTIAL FOR A QUICK SHOT OF RAIN AND SNOW ACROSS PORTIONS OF
INTERIOR SOUTHCENTRAL...BUT THERE IS STILL ENOUGH UNCERTAINTY WITH
THE ORIENTATION OF THE UPPER TROUGH AND THE TRACK OF THE SURFACE
LOW TO BE CONFIDENT WITH RESPECT TO THAT FEATURE AT THIS TIME.
HOWEVER...SHOULD THE LOW TRACK MOVE UP COOK INLET AND INTO THE
SUSITNA VALLEY LIKE THE NAM AND GFS DEPICT...WINDS UP THE INLET
AND OFF TURNAGAIN ARM COULD RESULT IN TEMPERATURES RISING TO WELL
ABOVE FREEZING ACROSS PARTS OF COOK INLET INCLUDING ANCHORAGE.

IN THE BERING...A GALE FORCE LOW AND ASSOCIATED UPPER TROUGH WILL
BECOME A SEMI-PERMANENT FIXTURE ACROSS THE REGION...SETTING THE
STAGE FOR WHAT IS GOING TO BE A RATHER ACTIVE AND DRAMATIC WARM UP
ACROSS MUCH OF SOUTHERN ALASKA AS THE NORTHEAST PACIFIC RIDGE RAMPS
UP. A SERIES OF POTENTIALLY POWERFUL LOWS WILL BEGIN EJECTING OFF
THE EASTERN PACIFIC JET STREAM...MOVING INTO THE BERING AND GULF
OF ALASKA BEGINNING LATE TUESDAY AND CONTINUING INTO THE WEEKEND.

THE FIRST OF THESE POWERFUL STORMS LOOKS TO IMPACT THE REGION
TUESDAY EVENING INTO WEDNESDAY...WHICH WILL HAVE THE GREATEST
IMPACTS ACROSS SOUTHWEST ALASKA AND PORTIONS OF THE CENTRAL AND
EASTERN BERING. THIS LOW...WHICH WILL BE DEVELOPING ALONG THE BASE
OF THE BERING TROUGH...WILL BE TAPPING SUBTROPICAL MOISTURE IN THE
NORTH PACIFIC...AND WILL BE DEAMPLIFYING AS IT EJECTS NORTHWARD.
THIS WILL RESULT IN THE POSSIBILITY OF A POWERFUL AND FAST MOVING
STORM FORCE LOW TO TRACK THROUGH THE ALASKA PENINSULA. SUCH A
STORM COULD BE A DRAMATIC WIND EVENT FOR PORTIONS OF SOUTHWEST
ALASKA AND THE ALASKA PENINSULA. THERE IS...AS USUAL...SOME
DIFFERENCES AMONG THE GLOBAL NUMERICAL GUIDANCE AT THIS
RANGE...BUT THEY ARE ALL DEPICTING SIMILAR SOLUTIONS...AND HAVE
BEEN SHOWING SUCH DEVELOPMENT FOR A FEW DAYS. STAY TUNED.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING...119 130 131 132 138 150 155 160 170 172
                        173 178 180 185.
         STORM WARNING...174 176 177.
         HEAVY FREEZING SPRAY WARNING...181 185.

&&

SYNOPSIS AND MODEL DISCUSSION...JA
SOUTHCENTRAL ALASKA...SB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PD
LONG TERM...JA

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1000 AM AKST SAT DEC 26 2015

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0944 AM     SNOW             3 NNW MOOSE PASS        60.50N 149.42W
12/26/2015  M2.0 INCH                           AK   PUBLIC

            LIGHT FLURRIES ONGOING. OVERNIGHT SNOWFALL TOTAL

0944 AM     SNOW             10 S GIRDWOOD           60.80N 149.17W
12/26/2015  E12.0 INCH                          AK   DEPT OF HIGHWAYS

            ESTIMATED FROM SNOW STAKE AT TURNAGAIN PASS

0944 AM     SNOW             3 ENE GIRDWOOD          60.96N 149.09W
12/26/2015  M14.0 INCH                          AK   PUBLIC

            ALYESKA RESORT REPORTS 1-2 INCHES NEAR THE BOTTOM OF THE
            MOUNTAIN AND 14 NEAR THE TOP OVERNIGHT.

0944 AM     SNOW             GIRDWOOD                60.94N 149.18W
12/26/2015  M0.5 INCH                           AK   OTHER FEDERAL

            OVERNIGHT SNOW TOTAL IN TOWN

0944 AM     SNOW             5 WNW PORTAGE           60.82N 148.98W
12/26/2015  E7.0 INCH                           AK   DEPT OF HIGHWAYS

            6 TO 7 INCHES ESTIMATED OVERNIGHT SNOWFALL TOTAL

&&

JPW