Small Craft Advisory 915, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
140 PM AKST THU DEC 15 2011

.ANALYSIS AND UPPER LEVELS...
THE LONG WAVE PATTERN REMAINS UNCHANGED WITH A DEEP TROUGH OVER
WESTERN ALASKA EXTENDING ALL THE WAY SOUTH TO THE TROPICS. THE
UPSTREAM RIDGE THAT IS BLOCKING THIS TROUGH IS CENTERED OFF THE
CALIFORNIA COAST. THESE TWO FEATURES THAT ARE DRIVING OUR WEATHER
PATTERN WILL GO THROUGH CYCLES BUT OVERALL WILL NOT BE DISPLACED
THROUGH NEXT WEEK. THE RESULT WILL BE A CONTINUED ACTIVE PATTERN WITH
A SERIES OF STRONG LOWS DEVELOPING SOUTH OF THE ALEUTIANS AND THEN
BENDING NORTH TOWARD THE ALASKA PENINSULA.

THE EARLY AFTERNOON SATELLITE IMAGES CLEARLY DEPICT FOUR AREAS OF LOW
PRESSURE ACROSS OUR DOMAIN. THE ANCHOR LOW FOR THE BROAD CYCLONIC
CIRCULATION IS A 972 MB LOW NEAR CAPE NEWENHAM. THE FIRST WAVE
ROTATING AROUND ITS PERIPHERY IS A WEAKENING 992 MB LOW APPROACHING
THE NORTHEAST GULF COAST WHERE IT WILL DISSIPATE AS IT MOVES INLAND
TONIGHT. THE SECOND LOW IS ASSOCIATED WITH A WAVE MOVING AROUND THE
BASE OF THE LARGE SCALE CYCLONIC CIRCULATION WHICH WILL HAVE NO
IMPACT ON OUR DOMAIN. A THIRD LOW IS DEVELOPING NEAR THE WESTERN
ALEUTIANS. THIS LOW WILL WILL MOVE INTO THE EASTERN BERING SEA LATER
THIS WEEKEND...REPLACING THE CURRENT ANCHOR LOW. IF WE ZOOM OUT A
LITTLE MORE...WE CAN SEE EVIDENCE OF THE NEXT WAVE LINED UP OVER THE
NORTHWEST PACIFIC. THIS LAST WAVE WILL BECOME A VERY STRONG LOW NEAR
THE ALASKA PENINSULA BY THE END OF THE WEEKEND.

.MODEL DISCUSSION...THE FORECAST MODELS CONTINUE TO STRUGGLE ON THE
FAST PACED PATTERN WITH LOW AFTER LOW DEVELOPING. THIS MORNING...THE
NAM INITIALIZES VERY POORLY ON TWO OF THE AFOREMENTIONED LOWS. NOT
SURPRISINGLY...THE NAM IS AN OUTLIER LATER THIS WEEKEND WITH SEVERAL
OF THE DEVELOPING FEATURES. THERE IS MUCH MORE CONFIDENCE WITH THE
ECMWF WHICH HAS SHOWN SOME RUN TO RUN CONSISTENCY AND INITIALIZES
WELL THIS MORNING ON ALL MAJOR FEATURES. THE MOST CRITICAL MODEL
DIFFERENCE APPEARS TO BE RESOLVED WITH THE LATEST RUN. EARLIER THERE
WAS MUCH UNCERTAINTY WITH A DEVELOPING LOW ON SUNDAY...AND WHICH
TRACK IT WAS GOING TO TAKE. THE GFS AND ECMWF SEEMED TO HAVE LOCKED
IN ON A SIMILAR SOLUTION...TAKING THE LOW INLAND NEAR THE ALASKA
PENINSULA AND THEN WEAKENING IT SUNDAY NIGHT.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...THE CHALLENGE FOR THE SOUTHCENTRAL FORECAST
WILL BE CENTERED AROUND THE POTENTIAL FOR MORE CHINOOK WINDS BY THE
END OF THE WEEKEND. UNTIL THEN...A SERIES OF WEAKER UPPER LEVEL WAVES
WILL IMPACT MAINLY THE COASTAL SECTIONS WITH RAIN AND SNOW WHILE THE
INTERIOR ONLY SEES SCATTERED PRECIPITATION. THE PRESSURE GRADIENT
ACROSS THE CHUGACH RANGE WILL REMAIN ELEVATED THROUGH THE WEEKEND
WHICH WILL FUNNEL WINDS THROUGH TURNAGAIN ARM. TYPICALLY...THESE
WINDS ONLY EFFECT THE HIGHER ELEVATIONS BUT SINCE OUR COLD AIR HAS
BEEN SCOURED OUT...IT WILL BE MUCH EASIER FOR THE STRONGER WINDS TO
MIX DOWN TO THE SURFACE. THIS CAN BE SEEN RIGHT NOW WITH PARTS OF THE
LOWER HILLSIDE EXPERIENCING EAST WINDS TO 20 MPH AND TEMPERATURES IN
THE UPPER 30S.

SO WITH EACH WAVE AND FRONTAL BOUNDARY THAT DEVELOPS OVER THE
WEEKEND...WE WILL HAVE TO WATCH CLOSELY FOR SIGNS THAT WINDS WILL
AGAIN INCREASE THROUGHOUT ANCHORAGE. THE BIGGEST THREAT WILL BE ON
SUNDAY AS A LOW DEEPENS TO APPROXIMATELY 960 MB AS IT MOVES OVER THE
ALASKA PENINSULA.

COLD AIR ON THE BACKSIDE OF THIS LOW WILL QUICKLY FILTER ACROSS THE
REGION SUNDAY EVENING...BRINGING ANOTHER CHANCE OF SNOWFALL BEFORE A
SHORTWAVE RIDGE BUILDS ON MONDAY.

SOUTHWEST ALASKA...THE NEXT 48 HOURS OVER SOUTHWEST ALASKA WILL
REMAIN UNCHANGED WITH SCATTERED TO NUMEROUS RAIN AND SNOW SHOWERS AND
LOCALLY GUSTY WINDS FROM THE EAST. TEMPERATURES ACROSS MOST OF THE
AREA REMAIN WELL ABOVE NORMAL...HOVERING JUST ABOVE FREEZING. THE
POTENTIAL FOR MORE SIGNIFICANT PRECIPITATION AROUND BRISTOL BAY IS ON
SUNDAY ASSOCIATED WITH THE LARGE 960 MB LOW. LIKEWISE...LOCALLY VERY
WINDY CONDITIONS ARE LIKELY WITH THIS SYSTEM. UNLIKE LAST WEEK...THE
POTENTIAL FOR BLIZZARD CONDITIONS DOES NOT LOOK VERY GOOD AS PLENTY
OF WARM AIR SPILLS ACROSS THE ALEUTIAN AND ALASKA RANGES INTO THE
SOUTHWEST INTERIOR. BY MONDAY...SOUTHWEST FLOW WILL RESUME WITH
WIDESPREAD SNOW SHOWERS PREVAILING THROUGH EARLY NEXT WEEK.

BERING SEA/ALEUTIANS...
THE CHALLENGE FOR THE BERING SEA AND ALEUTIANS WILL CONTINUE TO BE
TRYING TO CAPTURE THE MULTIPLE LOWS DEVELOPING AND THEN WEAKENING.
WINDS AROUND THESE LOWS ARE GENERALLY GALE FORCE OR WEAKER. AT THIS
TIME...THERE ARE NO THREATS FOR WATCHES OR WARNINGS THROUGH THE
WEEKEND.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING...120 130 132 138 150 155 160 170
FIRE WEATHER...NONE.

AB DEC 11