Small Craft Advisory 1011, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
434 AM AKST SUN DEC 20 2015

.ANALYSIS AND UPPER LEVELS...

CUT-OFF UPPER LOWS ARE OVER THE GULF AND EAST OF KAMCHATKA...WITH A
WEAKENING UPPER LOW OVER WESTERN AK THIS MORNING. A RIDGE HAS
ALSO DEVELOPED OVER THE CENTRAL BERING. A STRONG TRANSPACIFIC JET
IS SHOWING ONLY A SLIGHT ANTICYCLONIC BULGE SOUTH OF THE EASTERN
ALEUTIANS IN WHAT IS OTHERWISE A NEAR ZONAL PATTERN. AT THE
SURFACE...LOWS ARE OVER THE CENTRAL GULF...THE WESTERN AK
COAST...NEAR KAMCHATKA AND OVER THE WESTERN ALEUTIANS. A SURFACE RIDGE
IS OVER THE CENTRAL BERING WHILE A SURFACE FRONT EXTENDS FROM THE
KAMCHATKA LOW ACROSS THE WESTERN ALEUTIANS. SNOW SHOWERS HAVE
MOVED INLAND ACROSS THE KUSKOKWIM DELTA...AND PERSIST OVER THE
NORTHWEST GULF AND KENAI PENINSULA AS WELL AS THE WESTERN
ALEUTIANS.

&&

.MODEL DISCUSSION...

AS IS OFTEN THE CASE WITH A STRONG ZONAL JET SOUTH OF THE FORECAST
AREA...THERE IS SIGNIFICANT VARIABILITY WITH HOW MODELS ARE
HANDLING LOW DEVELOPMENT AND MOVEMENT NORTH OF THE JET. STRETCHING
OF THE LOWS WITH CENTERS IN DIFFERENT LOCATIONS SEEMS TO BE THE
NORM. THIS IS ESPECIALLY TRUE OVER THE BERING WHERE THE WESTERN
ALEUTIAN AND KAMCHATKA LOWS MERGE...STRETCH...AND REDEVELOP
DISTINCT LOWS. WHEN SEVERAL MODELS ARE VIEWED TOGETHER...THESE
REDEVELOPED LOWS FORM IN A LINE EXTENDING FROM THE KAMCHATKA
PENINSULA TO SOUTHEAST AK BY MON NIGHT. SINCE THERE MUST BE ONLY
ONE SOLUTION...THE FORECAST UTILIZES THE EC IN THE EAST...WHICH
HAS BEEN FAIRLY CONSISTENT OVER THE LAST FEW RUNS. WITH THIS
SOLUTION THE GULF LOW DISSIPATES OVER SE AK MON MORNING AND
ANOTHER LOW FORMS NEAR THE AKPEN AND DRIFTS INTO THE CENTRAL GULF
BY MON NIGHT. IN THE WEST THE GFS WAS PREFERRED...ALTHOUGH ALSO SIMILAR
TO THE EC. WITH THIS CHOICE THE WESTERN AK LOW MOVES INLAND AND
DISSIPATES THIS AFTERNOON. THE WESTERN ALEUTIAN AND KAMCHATKA LOWS
MERGE AND ELONGATE DIAGONALLY ACROSS THE BERING TONIGHT BEFORE
AGAIN DEVELOPING DISTINCT CENTERS OVER THE WESTERN AND EASTERN
BERING MON NIGHT. CONFIDENCE WITH DETAILS OUT WEST IS LOW...BUT
SLIGHTLY HIGHER OVER THE EASTERN DOMAIN.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE VERTICALLY STACKED LOW IN THE CENTRAL GULF WILL MOVE EAST
TODAY AND BECOME A NON-FACTOR IN THE WEATHER FOR SOUTH CENTRAL
TONIGHT. THIS HAS INCREASED THE OFFSHORE GRADIENT AND THE WINDS IN
SUCH FAVORED AREAS NEAR GAPS (SUCH AS SEWARD AND WHITTIER) WILL
CONTINUE TODAY THEN WEAKEN TONIGHT AND MONDAY. THE WEAK
DEFORMATION ZONE STRETCHING FROM THE GULF LOW THROUGH THE KENAI
PENINSULA AND INTO SOUTHWEST ALASKA WILL BRING SOME ISOLATED
SHOWERS TO THE KENAI...THEN BREAK APART LATER TODAY. THE SOUTH
CENTRAL INTERIOR WILL REMAIN UNDER WEAK HIGH PRESSURE THROUGH
TONIGHT. ON MONDAY AND MONDAY NIGHT THE THE UPPER LOW OVER THAT
HAS BEEN OVER SOUTHWEST ALASKA WILL PUSH EASTWARD INTO SOUTH
CENTRAL ALASKA...BRINGING A CHANCE OF SNOW SHOWERS TO MUCH OF
THE AREA.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
THE FORECAST FOR TODAY WILL REVOLVE AROUND A WEAKENING STACKED LOW
PRESSURE SYSTEM DRIFTING OVER THE MAINLAND THROUGH THE DAY.
NUMEROUS TO SCATTERED SNOW SHOWERS WILL PERSIST THROUGH THE
DAY...DECREASING IN COVERAGE THROUGH THE OVERNIGHT HOURS. WINDS
WILL CONTINUE TO DECREASE AS THE SYSTEM WEAKENS AND TEMPERATURES
WILL REMAIN MODERATED BY CLOUD COVER. ON MONDAY...A COLDER AIR
MASS FILTERS IN FROM THE INTERIOR WITHIN A WEAK OUTFLOW PATTERN.
LIGHT NORTHERLY WINDS...CLEARING CLOUDS...AND COLDER TEMPERATURES
WILL TAKE HOLD THROUGH TUESDAY.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
A VERY COMPLEX FORECAST SHAPING UP OVER THE WESTERN/CENTRAL
ALEUTIANS. A STALLED FRONTAL BOUNDARY WILL SEE CYCLOGENESIS AS A
SHORTWAVE TROUGH INVIGORATES IT. GUIDANCE HAS BEEN ALL OVER THE
PLACE WITH THIS FEATURE BUT THE LATEST PICTURE IS THAT THE ENERGY
WILL SPREAD OUT INTO AN ELONGATED CIRCULATION WITH ONE
CONSOLIDATED SURFACE LOW IN THE WESTERN BERING...THEN A SEPARATE
DEVELOPMENT FURTHER TOWARD THE EASTERN ALEUTIANS LATER TONIGHT.
THE SECONDARY DEVELOPMENT COULD BE A STRONGER COMPACT SYSTEM WITH
A SMALL AREA OF VERY STRONG WINDS BUT LIKELY IT WILL BE A FAST
MOVING SYSTEM AS IT GETS CAUGHT UP IN THE LARGELY ZONAL FLOW. A
FRONTAL BOUNDARY WILL CONNECT THESE TWO CIRCULATIONS...STRETCHING
ACROSS THE BERING SEA. AS THIS SYSTEM DEVELOPS THERE WILL BE A
BRIEF SHOT OF STRONG WINDS IN THE ADAK AREA EARLY THIS EVENING BUT
IT WILL BE SHORT LIVED. BEHIND THE FRONT ANOTHER SHOWERY REGIME
WILL STAY IN PLACE WITH WEAKER WINDS.

&&

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

THE JET STREAM WILL KEEP THE ACTIVE STORM TRACK SUPPRESSED SOUTH
OF THE ALASKA MAINLAND FOR MUCH OF NEXT WEEK...AND WILL ALLOW FOR
COLD AIR TO SPILL SOUTH INTO SOUTHERN ALASKA BRINGING TEMPERATURES
WELL BELOW NORMAL BY THE MIDDLE TO LATER PART OF CHRISTMAS
WEEK...ESPECIALLY FOR SOUTHCENTRAL. MODEL AGREEMENT WITH
INDIVIDUAL SYSTEMS AND FEATURES IS POOR AT BEST...YIELDING LOW
CONFIDENCE IN THE FORECAST OUTSIDE OF THE FACT THAT BELOW NORMAL
TEMPERATURES AND OUTFLOW WINDS WILL IMPACT THE REGION...HOWEVER
THERE IS HIGH CONFIDENCE THAT THERE WILL BE A PERIOD OF BELOW
NORMAL TEMPERATURES OVER THE MAINLAND...ESPECIALLY SOUTHCENTRAL
ALASKA...AND OUTFLOW WINDS WILL BE ONE OF THE MAIN IMPACTS FROM
THE COLD AIR FILTERING THROUGH THE TERRAIN GAPS INTO THE NORTHERN
GULF AND PRINCE WILLIAM SOUND.

ACROSS THE BERING REGION...THE MAIN FEATURE THAT WILL BEAR
WATCHING WILL BE THE DEPARTING STRONG LOW HEADING TOWARD THE GULF
MONDAY INTO TUESDAY...THEN THE POSSIBILITY OF ANOTHER STRONG LOW
ENTERING THE SOUTHWEST BERING FROM THE NORTH PACIFIC MID- TO LATE
WEEK THAT MAY BRING ANOTHER ROUND OF STRONG WINDS TO THE REGION AT
SOME POINT DURING THIS TIMEFRAME.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...HEAVY FREEZING SPRAY 181 185
         GALES 155 165 170 172 173 174 175 176 177
         178 180 181 185 352 411 412 413 414

&&

SYNOPSIS AND MODEL DISCUSSION...DS
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...ML
LONG TERM...CC