Small Craft Advisory 131, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
405 PM AKST WED FEB 11 2015

.ANALYSIS AND UPPER LEVELS...

THE UPPER LEVEL PATTERN IS VERY SIMILAR TO YESTERDAY WITH A
LONGWAVE TROUGH EXTENDING THROUGH THE BERING STRAIT TO SOUTH OF
THE ALASKA PENINSULA. THIS TROUGH IS FLANKED BY HIGH AMPLITUDE
RIDGES IN THE WESTERN BERING SEA AND WESTERN CANADA. THIS IS
PRODUCING SOUTHERLY FLOW ALOFT OVER MAINLAND ALASKA. THE 250 MB
JET IS WELL SOUTH OF THE AREA AS IT FLOWS SOUTH OF THE TROUGH AND
GULF OF ALASKA.

THE SURFACE LOW THAT WAS SOUTH OF THE GULF OF ALASKA YESTERDAY
MOVED INTO EASTERN PRINCE WILLIAM SOUND EARLY THIS MORNING AND IS
NOW OVER THE COPPER RIVER BASIN. THIS LOW WILL CONTINUE TO TRACK
TO THE NORTHEAST AND OUT OF THE AREA OVERNIGHT.
THE SURFACE LOW SOUTH OF THE ALASKA PENINSULA REMAINS IN PLACE AND
IS MOVING SLOWLY TO THE NORTHWEST. A FRONT THAT IS ASSOCIATED WITH
THIS LOW CONTINUES TO MOVE THROUGH SOUTHWEST ALASKA BRINGING
WARMER AIR IN BEHIND IT.

&&

.MODEL DISCUSSION...

MODELS FROM YESTERDAY WERE ALL A BIT TOO FAR WEST WITH THE LOW
THAT IS TRACKING INTO THE COPPER RIVER BASIN THIS AFTERNOON. THEY
ALL BROUGHT THE LOW INTO WESTERN PRINCE WILLIAM SOUND BUT THE LOW
WENT INTO THE EASTERN SOUND. THE RESULT IS THE SNOW ADVISORY FOR
THE COPPER RIVER BASIN AS THE LOW TRACKS OVER THE TOP OF THEM.

FOR TODAY THE MODELS ARE HOLDING TOGETHER WELL WITH THE ANCHOR LOW
SOUTH OF THE ALASKA PENINSULA. THE MORE DYNAMICALLY ACTIVE AREA IS
OVER THE GULF OF ALASKA AND MODELS ARE STRUGGLING TO RESOLVE THE
DISTURBANCES MOVING THROUGH THE GULF AND INTO SOUTHCENTRAL THE
NEXT FEW DAYS. AN EXAMPLE OF THESE DIFFERENCES IS WITH A WEAK WAVE
MOVING UP COOK INLET TOMORROW. THE ECMWF IS BRINGING ACCUMULATING
SNOWFALL AROUND COOK INLET TOMORROW WHILE THE GFS AND NAM ARE
SHOWING THIS POSSIBILITY BUT THEIR SOLUTIONS WOULD BRING LITTLE TO
NO SNOWFALL.

&&

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

LOW PRESSURE CONTINUES TO DISSIPATE OVER THE CHUGACH RANGE WHILE
THE UPPER LEVEL SYSTEM CONTINUES TO MOVE INLAND. SNOW WILL
DIMINISH THROUGH THE EVENING IN THE COPPER RIVER BASIN...ENDING
LATE THIS EVENING FOR AREAS NORTH OF GLENNALLEN TOWARD THE ALASKA
RANGE.

OTHERWISE...THE MAJOR FORECAST HEADACHE THE NEXT 36 HOURS OR SO
WILL BE CLOSELY WATCHING EACH DISTURBANCE MOVING NORTH ACROSS THE
GULF INTO SOUTHCENTRAL ALASKA. WITH A LESS STABLE REGIME AND
RELATIVELY LITTLE CROSS-BARRIER FLOW...THERE IS A HIGHER THAN
NORMAL CHANCE THAT A TIMELY-POSITIONED DISTURBANCE COULD CREATE
SOME ACCUMULATING SNOW ALONG THE WESTERN SLOPES OF THE CHUGACH AND
KENAI MOUNTAIN RANGES TOMORROW.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
SNOW SHOWERS OVER THE BRISTOL BAY AREA HAVE STARTED TO PUSH INTO
THE LOWER KUSKOKWIM VALLEY AND KUSKOKWIM DELTA...AS THE
FRONT/INVERTED TROUGH OVER THE EASTERN BERING LIFTS INTO THE
CENTRAL BERING. A SERIES OF WEAK UPPER LEVEL WAVES WILL CONTINUE
TO TRAVERSE PARTS OF THE SOUTHWEST MAINLAND THROUGH THE END OF THE
WEEK...KEEPING SOME RAIN AND SNOW SHOWERS IN THE FORECAST FOR
PARTS OF THE SOUTHWEST MAINLAND. WITH CONTINUED GUSTY OFFSHORE
FLOW THERE IS POTENTIAL FOR SOME BLOWING SNOW ISSUES TONIGHT INTO
TOMORROW MORNING...MAINLY ALONG THE DELTA COAST WHERE THE WINDS
WILL BE STRONGEST. ACTUAL ACCUMULATIONS WILL REMAIN ON THE LIGHT
SIDE OVER THE AREA...ESPECIALLY WITH WARMER TEMPERATURES
CONTINUING TO MOVE IN FROM THE SOUTHEAST. LOCATIONS ALONG THE
ALEUTIAN RANGE AND ALASKA PENINSULA ARE LIKELY TO SEE RAIN MIXING
IN WITH SNOW THROUGH THE END OF THE WEEK.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE PRECIPITATION ASSOCIATED WITH THE FRONT OVER THE EASTERN
BERING WILL CONTINUE TO SPREAD NORTH AND WESTWARD THROUGH THURSDAY
NIGHT. SNOW WILL PERSIST OVER THE PRIBILOF ISLANDS ALONG WITH MIXED
PRECIPITATION OVER THE EASTERN HALF OF THE ALEUTIAN CHAIN THROUGH
THE END OF THE WEEK...AS THE NORTH PACIFIC LOW SLOWLY DRIFTS OVER
DUTCH HARBOR BY FRIDAY. WITH THIS SYSTEM STILL OFF TO THE
SOUTHEAST OF THE PRIBILOF ISLANDS...PERSISTENT NORTHEASTERLY GALE
FORCE WINDS WILL PRODUCE AREAS OF BLOWING SNOW OVER THE PRIBILOF
ISLANDS THROUGH THE END OF THE WEEK. A BLOWING SNOW ADVISORY IS IN
EFFECT THROUGH TOMORROW (THURSDAY) MORNING.

&&

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

BEGINNING SATURDAY...WEAK DISTURBANCES AND SOUTHERLY FLOW ALOFT
WILL SUPPORT A WEAK TROUGH AXIS FROM THE CENTRAL ALEUTIAN CHAIN
TO THE EASTERN GULF OF ALASKA. MOISTURE AND CLOUDS WILL SPREAD
FROM THE COAST TO INLAND LOCATIONS THROUGH SUNDAY AS THE TROUGHING
ALOFT LIFTS NORTH AND WEAKENS. PRECIPITATION TYPE WILL GENERALLY
BE SNOW INLAND...ALTHOUGH SOME SPOTTY RAIN SHOWERS WILL OCCUR NEAR
COASTAL LOCATIONS. HOWEVER...INLAND PRECIP WILL GENERALLY BE
LIGHT AND SHOWERY.

BY MONDAY...A DRAMATIC SHIFT IN THE OVERALL PATTERN WILL
BEGIN TO UNFOLD AS A HIGHLY AMPLIFIED NORTH AMERICAN RIDGE BUILDS
INTO SOUTHERN ALASKA. THERE IS MUCH BETTER AGREEMENT AMONG THE
GLOBAL NUMERICAL GUIDANCE THAT A STRONG NORTH PACIFIC LOW WILL
SHIFT INTO THE CENTRAL BERING...SPREADING WARM SUBTROPICAL AIR
INTO SOUTHERN ALASKA. BESIDES HEAVY COASTAL RAIN...THE GENERAL
WAVE PATTERN ALOFT AND ASSOCIATED STRONG PRESSURE GRADIENT WILL
LIKELY BE SUCCESSFUL IN ERODING ANY COLD AIR IN THE LOWER
ELEVATIONS...EVENTUALLY RESULTING IN ANOMALOUSLY WARM TEMPERATURES
BY MIDWEEK. THIS PATTERN WILL ALSO IMPACT THE BERING SEA WITH A
PERIOD OF STRONG EASTERLY WINDS OFF THE ICE EDGE...EVENTUALLY
TURNING SOUTHEAST AS THE FRONT TRACKS TOWARD THE BERING STRAIGHT
MONDAY AND TUESDAY.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...SNOW ADVISORY 141
         BLOWING SNOW ADVISORY 195
MARINE...GALE 173 174 175 176 179 181
         HEAVY FREEZING SPRAY 179 185
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...CC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TP
LONG TERM...JA