Small Craft Advisory 861, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
421 PM AKDT FRI OCT 30 2015

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

AN UPPER LEVEL TROUGH CONTINUES OVER THE STATE WITH A CLOSED
CENTER SPINNING IN THE WESTERN GULF. TO THE WEST...A RIDGE IS OVER
THE BERING WITH A PROGRESSIVELY EASTWARD MOVING TROUGH OVER THE
KAMCHATKA PENINSULA. AT THE SURFACE...THE PATTERN IS REFLECTIVE
WITH A LOW OVER THE GULF AND RIDGE CENTERED IN THE BERING. THE
FRONT THAT MOVED ACROSS THE WESTERN AREAS OF THE STATE ON
THURSDAY...HAS MADE LITTLE PROGRESS THROUGH TODAY WITH THE
BOUNDARY NOW STRETCHING FROM THE SUSITNA VALLEY TO THE WESTERN
GULF. SNOW SHOWERS ARE DEVELOPING ALONG THE BOUNDARY FROM KENAI
NORTH. SHOWERS CONTINUE TO DEVELOP ALONG A CONVECTIVELY UNSTABLE
AIR MASS OVER PRINCE WILLIAM SOUND AND THE NORTHERN GULF WITH
PROPAGATION TO THE NORTH AND WEST. EASTERLY FLOW ON THE NORTH SIDE
OF THE LOW IS CARRYING THIS MOISTURE ACROSS THE SOUND TO THE
ANCHORAGE BOWL WHERE IT TRANSITIONS TO SNOW ALONG A COOLER
ISOTHERMAL LAYER JUST OFF THE SURFACE. AS FOR WINDS...NORTHERLY
FLOW REMAINS STRONG OVER THE SOUTHWEST MAINLAND...ALASKA PENINSULA
AND EASTERN ALEUTIANS. AN INCREASE OF STRONGER NORTHERLY FLOW
ACROSS THE WESTERN ALASKA RANGE EARLY THIS AFTERNOON IS A GOOD
INDICATION THAT THE FRONT IS BEGINNING TO ADVANCE.

MODEL DISCUSSION...
MODELS CONTINUE TO BE IN GOOD SYNOPTIC AGREEMENT THROUGH THE SHORT
TERM THIS WEEKEND. A TRANSITION IN THE UPPER LEVEL PATTERN IS
ANTICIPATED WITH THE UPPER LEVEL LOW OVER THE MAINLAND GAINING
EASTWARD MOMENTUM TONIGHT. FOR THE WEEKEND...THE UPPER RIDGE WILL
DEAMPLIFY AS IT PASSES OVER THE MAINLAND AND THE UPPER LOW OVER
KAMCHATKA MOVES A FRONT ACROSS THE BERING/ALEUTIANS.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
WIDESPREAD SNOW AND RAIN SHOWERS WILL GRADUALLY DIMINISH IN
COVERAGE OVERNIGHT AND THEN END FROM WEST TO EAST ON SATURDAY AS
THE UPPER TROUGH PUSHES THROUGH SOUTHCENTRAL. THIS LEAVES OUTFLOW
WINDS AS THE PRIMARY FORECAST CHALLENGE FOR THE WEEKEND AS COLD
ADVECTION CONTINUES ACROSS THE AREA. NORTHERLY WINDS WILL CONTINUE
TO INCREASE TONIGHT THROUGH FAVORED GAPS ALONG THE NORTH GULF
COAST AND THEN PEAK IN INTENSITY LATE SATURDAY AFTERNOON INTO
SATURDAY NIGHT AS THE TROUGH AXIS PUSHES EAST ACROSS PRINCE
WILLIAM SOUND AND A 100 KT JET STREAK MOVES OVERHEAD. THEREFORE
INTRODUCED STRONG WIND HEADLINES FOR WHITTIER/VALDEZ AND THE
COPPER RIVER DELTA WITH THE AFTERNOON FORECAST PACKAGE. WINDS WILL
THEN DIMINISH THROUGH SUNDAY AFTERNOON AS AN UPPER LEVEL RIDGE
MOVES OVERHEAD...BRINGING A SLIGHT MODERATING TREND IN
TEMPERATURES AND INCREASING CHANCES OF PRECIPITATION FROM THE WEST
BY LATE SUNDAY.

&&

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

THE MAINLAND WILL CONTINUE TO DRY OUT BEHIND THE DIGGING TROUGH
AND FRONT THROUGH THIS EVENING. THE BEST CHANCES FOR SNOW WILL BE
ALONG/OVER THE ALASKA/ALEUTIAN RANGES BUT ANY PRECIPITATION SHOULD
BE VERY LIGHT. THE BIGGER IMPACT ON SENSIBLE WEATHER WILL BE THE
SEASONABLY COLD AIR MASS CONTINUING TO MOVE IN FROM THE NORTH
ALONG WITH THE GUSTY NORTHERLY WINDS ACCOMPANYING IT...HOWEVER
MOST AREAS FROM BRISTOL BAY NORTH WILL BEGIN TO SEE A GRADUAL
DOWNTURN IN THE STRONGEST WINDS THROUGH TONIGHT AND EARLY
SATURDAY. THIS AIR MASS WILL BRING SOME OF THE COLDER MINIMUMS OF
THE SEASON LATE TONIGHT...HOWEVER THIS WILL BE SHORT-LIVED AS A
FRONT FROM THE BERING SEA BRINGS A PATTERN CHANGE.

TEMPERATURES AND MOISTURE WILL RISE SUBSTANTIALLY LATE SATURDAY
NIGHT THROUGH SUNDAY WITH A STRONG BUT WEAKENING WEATHER FRONT
BARRELING INLAND. TEMPERATURES WILL ONLY BE COLD ENOUGH FOR
PRECIPITATION TO BEGIN AS SNOW JUST AT ONSET OF PRECIPITATION
BEFORE A CHANGEOVER TO RAIN. NO SIGNIFICANT ACCUMULATIONS OF SNOW
ARE EXPECTED AT THIS TIME.

&&

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

WINDS WILL CONTINUE TO ROAR OUT OF THE BAYS AND PASSES OF THE
ALASKA PENINSULA AND WELL OUT INTO THE NORTH PACIFIC THROUGH
SATURDAY...THOUGH ON A DOWNWARD TREND AFTER TONIGHT. CONDITIONS
WILL RAPIDLY CHANGE FROM WEST TO EAST AS A STRONG GALE-FORCE
WEATHER FRONT RACES EAST FROM THE WESTERN ALEUTIANS TONIGHT TO THE
BRISTOL BAY AND ALASKA PENINSULA REGION LATE SATURDAY NIGHT INTO
SUNDAY NIGHT. A WIDESPREAD AREA OF RAIN ALONG WITH WARMER
TEMPERATURES CAN BE EXPECTED WITH THE GALE-FORCE WINDS AHEAD OF
THE FRONT...WITH SCATTERED TO NUMEROUS RAIN SHOWERS AND CONTINUED
WINDY CONDITIONS BEHIND THE FRONT.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...

THE EXPECTED WARM-UP EARLY NEXT WEEK LOOKS LESS PROMISING TODAY
AS A DEEP UPPER LEVEL TROUGH OVER THE BERING SEA LOOKS TO KEEP
HIGH PRESSURE FURTHER SOUTH AND EAST. A QUICK SHORTWAVE RIDGE
LOOKS TO QUICKLY SLIDE ACROSS SOUTHWEST AND SOUTHCENTRAL ALASKA
THROUGHOUT THE DAY MONDAY WHICH WILL BE THE TURNING POINT
TEMPERATURE WISE. AS MENTIONED EARLIER...THE WARM-UP LOOKS LESS
PROMISING BUT IS STILL EXPECTED TO OCCUR (JUST TO A LESSER
MAGNITUDE).

LOOKING AT THE BIG PICTURE...THE AFOREMENTIONED SHORTWAVE RIDGE
WILL BE QUICK TO MOVE ACROSS THE AREA ON MONDAY AS A POTENT
SHORTWAVE IS EXPECTED TO DIG OUT OF THE UPPER LEVEL TROUGH AND
AMPLIFY THE LONGWAVE PATTERN. THIS WAVE WILL SPIN UP A WEAK SFC
BASED LOW WHICH WILL MOVE INLAND NEAR BRISTOL BAY TUESDAY MORNING.
THIS SHOULD KEEP INCREASE RAIN CHANCES AS WELL AS BRING GALE FORCE
WINDS TO THE ALEUTIAN ISLANDS AND ALASKA PENINSULA LATE MONDAY AND
EARLY TUESDAY. THIS LOW WILL MOVE INTO SOUTHCENTRAL ALASKA EARLY
TUESDAY AND LIKELY PRODUCE PERIODS OF RAIN AND SNOW. CURRENTLY IT
APPEARS ANYTHING NORTH OF KENAI WOULD BE IN THE SNOW ZONE WITH
JUST COASTAL AREAS REMAINING RAIN. MODELS ARE STRUGGLING A TOUCH
WITH THE POSITION OF THE UPPER LEVEL WAVE AND SFC LOW...WHICH WILL
HAVE A LOT TO DO WITH HOW MUCH PRECIPITATION WILL BE OBSERVED.

THE MOST SIGNIFICANT (POSSIBLY) YET THE MOST INCONSISTENT FEATURE
WILL BE THE POSSIBILITY OF A SIGNIFICANT LOW DEVELOPING SOUTH OF
THE CENTRAL ALEUTIANS ON WEDNESDAY AND THURSDAY. THE REASON FOR
THE INCONSISTENCY IS THAT THE ARCTIC JET AND NORTH PACIFIC JET
APPEAR TO PHASE TOGETHER BRIEFLY WHICH CREATES A VERY POTENT JET
STREAK. THIS JET STREAK COULD QUICKLY DEVELOP AN UPPER LEVEL AND
SFC LOW THAT COULD EXCEED 24 MB STRENGTHENING IN 24 HOURS.
HOWEVER...THE JET STREAMS COULD ALSO HAVE LITTLE PHASING AND THE TWO
SEPARATE JET STREAKS COULD CLASH AND CREATE A WEAKER SFC LOW. THE
ONE THING OF NOTE IS THAT MODELS ARE TRENDING FURTHER NORTH WITH
LOW DEVELOPMENT POSSIBLY IN THE SOUTHERN BERING SEA. SHOULD THIS
SOLUTION PAN OUT...A PERIOD OF HEAVY RAIN FOR THE ALEUTIANS AND
ALASKA PENINSULA COULD BE SEEN AS WELL AS A LARGE AREA OF STORM
FORCE WINDS ACROSS THE ALEUTIANS AND BERING SEA.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING 127 130 131 132 150 155 160 165 170 172 173
 174 175 176 177 178 179 180.

&&

SYNOPSIS AND MODEL DISCUSSION...KH
SOUTHCENTRAL ALASKA...CB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CC
LONG TERM...MC

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1032 PM AKDT FRI OCT 30 2015

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

1020 PM     SNOW             3 NW GLEN ALPS          61.13N 149.76W
10/30/2015  M3.0 INCH                           AK   PUBLIC

&&

RDUELL