Gale Warning 315, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
506 AM AKDT WED APR 15 2015

.ANALYSIS AND UPPER LEVELS...THE VERTICALLY STACKED LOW IS NOW
DRIFTING SLOWLY NORTHEAST THROUGH THE GULF OF ALASKA. THE FRONT
ASSOCIATED WITH THIS SYSTEM HAS PUSHED THROUGH MIDDLETON ISLAND
AND IS NOW BEARING DOWN ON THE COAST. THERE IS A CONVECTIVE
ELEMENT IN THE CORRIDOR OF STRONGEST LIFT ASSOCIATED WITH THE WARM
MOIST GULF AIR...SO SOME HEAVIER SHOWERS ARE JUST APPROACHING PRINCE
WILLIAM SOUND. GUSTY NORTH TO NORTHEAST AGEOSTROPHIC WINDS ARE
COMMON ACROSS SOUTHCENTRAL PULLING INTO THIS LOW. OVER THE
SOUTHWEST...CONDITIONS ARE QUIET. SOME MID AND HIGH CLOUDS HAVE
WRAPPED OVER THE BRISTOL BAY REGION FROM THE EAST. SO FAR
THOUGH...NONE OF THE RETURNS FROM THE RADAR HAVE PRODUCED ANY
PRECIPITATION AT THE SURFACE. OVER THE EASTERN ALEUTIANS AND
ALASKA PENINSULA...BROAD NORTHWEST FLOW CONTINUES TO PRODUCE SOME
COLD AIR ADVECTION SHOWERS...ESPECIALLY ON THE BERING SIDE.
FURTHER WEST...WE FINALLY SEE SOME JET ACTIVITY APPROACHING THE
REGION...WITH A CONFLUENT JET AXIS AT 180-190 KT AS THE SOUTHERN
STREAM AND NORTHERN STREAM COMBINE THEIR ENERGY. THIS WILL HELP TO
FERRY A DEVELOPING SURFACE LOW QUICKLY TO THE EAST JUST SOUTH OF
THE CHAIN.

&&

.MODEL DISCUSSION...MODELS CONTINUE TO HANDLE THE GENERAL IDEA OF
THE PATTERN WELL AND ARE IN GOOD SYNOPTIC AGREEMENT. HOWEVER...THE
DETAILS ARE STILL QUITE DIFFERENT FROM MODEL TO MODEL AND OFTEN
TIMES EVEN RUN TO RUN. THE END RESULT...HIGH CONFIDENCE IN THE
OVERALL PATTERN BUT LOWER CONFIDENCE IN THE EXACT TIMING AND
AMOUNTS OF PRECIPITATION...ESPECIALLY THROUGH THE POPULATED AREAS
OF SOUTHCENTRAL. OUT WEST...THE ECMWF WAS PREFERRED AS IT HAS HAD
THE BEST HANDLE ON THE DEVELOPING LOW AND ITS TRACK FOR THE PAST
COUPLE OF DAYS. THE MOST NOTABLE DIFFERENCES THERE ARE LATE THU
INTO FRIDAY AS ANOTHER PIECE OF JET ENERGY PUSHES A WEAK SURFACE
FEATURE UNDER THE PRIMARY LOW. THE INTERACTION OF THESE FEATURES
DIFFERS SIGNIFICANTLY AMONG THE MODELS AND THUS...THERE IS LOW
CONFIDENCE IN THIS TIME-FRAME. THIS SPREAD AND LOWER CONFIDENCE
EXTRAPOLATES DOWNSTREAM AS THE ENTIRE SYSTEM PUSHES A FRONT INTO
KODIAK AND THE WESTERN GULF ON FRIDAY. THE NAM WAS CONSIDER A
FAIRLY SIGNIFICANT OUTLIER AS IT IS CONSIDERABLY SLOWER THAN THE
GLOBAL MODELS IN BRINGING PRECIPITATION TO THE GULF COAST BY LATE
FRIDAY.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2...WEDNESDAY
AND THURSDAY)...GUSTY NORTH TO NORTHEAST WINDS WILL SLOWLY
DIMINISH TODAY AS THE LOW NEARS THE GULF COAST AND RIDGING MOVES
EAST OF THE ALCAN BORDER. AS THE FRONT MOVES INLAND...THE AIRMASS
BEHIND IT IS QUITE UNSTABLE. THIS WILL KEEP THE POTENTIAL FOR
SOME HEAVIER SHOWERS ALONG THE COAST...ESPECIALLY AS YOU START TO
ADD IN SOME DAY-TIME HEATING. AS THE LOW DRIFTS CLOSER TO THE
COASTLINE...THE CROSS BARRIER FLOW WILL ALSO SUBSIDE. THIS WILL
ALLOW PRECIPITATION TO NOT ONLY IMPACT COASTAL AREAS BUT ALSO
SPREAD TO THE LEE SIDE OF THE MOUNTAINS. IT LOOKS LIKELY THAT MOST
PLACES WILL SEE SOME PRECIPITATION...BUT AMOUNTS WILL GENERALLY BE
LIGHT FOR INLAND LOCATIONS. THE LOW LIFTS INLAND THROUGHOUT
THURSDAY FROM THE KENAI PENINSULA INTO THE ANCHORAGE BOWL AND
EVENTUALLY THE SUSITNA VALLEY. THIS SHOULD BRING THE BEST CHANCE
FOR STEADY PRECIPITATION FOR THESE AREAS. WITH THAT LOW
TRACK...THERE WILL BE LIMITED COLD AIR FOR THE SYSTEM TO TAKE
ADVANTAGE OF. THUS...PRECIPITATION COULD BE A RAIN SNOW MIX DURING
THE OVERNIGHT HOURS...BUT WILL GENERALLY BE JUST RAIN. THE
EXCEPTION TO THIS WILL BE THE HIGHER ELEVATIONS OF THE PARKS
HIGHWAY WHERE SEVERAL INCHES OF SNOW COULD ACCUMULATE BY THE TIME
THE LOW FINALLY EXITS TO THE NORTH FRIDAY MORNING. WITH
SUBSTANTIAL RIDGING MOVING IN BEHIND THE LOW...EXPECT TYPICAL
SOUTHEAST GAP WINDS TO INCREASE THURSDAY AFTERNOON TO INCLUDE THE
KNIK VALLEY AND COPPER RIVER BASIN.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
THROUGH THURSDAY THE SOUTHWEST ALASKAN MAINLAND WILL STAY UNDER
THE INFLUENCE OF THE WEAKENING LOW MOVING NORTHWARD INTO THE KENAI
PENINSULA. THIS WILL KEEP THE REGION IN A FAIRLY QUIET PATTERN
UNDER DRY NORTHERLY FLOW. PRECIPITATION WILL BE LIMITED TO THE
MOUNTAINS ALONG THE ALEUTIAN RANGE/ALASKA PENINSULA AND THE
EASTERN INTERIOR OF THE KUSKOKWIM VALLEY. MODEST COLD AIR
ADVECTION AND CLEARING SKIES WILL BRING COOLER TEMPERATURES TO THE
REGION. THE COLDEST TEMPERATURES WILL BE IN THE KUSKOKWIM DELTA
WITH LOW TEMPERATURES INTO THE SINGLE DIGITS FOR MANY LOCATIONS
WHICH IS ROUGHLY 5 TO 10 DEGREES BELOW NORMAL FOR MID-APRIL.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE EASTERN HALF OF THE BERING SEA AND THE ALEUTIAN CHAIN WILL
REMAIN UNDER NORTHERLY FLOW TODAY AS THE WEAK RIDGE TRAVELS
TRAVELS EASTWARD OVER THE NEXT 24 HOURS. COLD AIR ADVECTION WILL
CONTINUE AND BRING AREAS OF FREEZING SPRAY AS FAR SOUTH AS THE
ALASKA PENINSULA COAST THIS AFTERNOON AND TONIGHT. AS THE LOW
CURRENTLY DEVELOPING SOUTHWEST OF SHEMYA MOVES EASTWARD ALONG THE
SOUTH SIDE OF THE ALEUTIAN CHAIN...STRONG EASTERLY WINDS TO GALE
FORCE WILL DEVELOP OVER THE CHAIN AND THE SOUTHERN BERING SEA BY
TOMORROW. PRECIPITATION WILL BE MAINLY A MIX OF RAIN AND SNOW AS
THE FRONTAL BOUNDARY RUNS PARALLEL TO THE ALEUTIANS THROUGH THE
PERIOD.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
A DEEP LOW SOUTH OF THE ALEUTIANS IS THE MAJOR FEATURE IN THE MID
TERM. FOR THE MOST PART THERE IS GOOD AGREEMENT WITH THE TRACK OF
THIS LOW NORTH INTO THE EASTERN BERING BUT THERE ARE SOME
DISCREPANCIES WITH THE TIMING. THE GEM IS THE FASTEST PROGRESSING
THE LOW ACROSS THE ALEUTIANS WHILE BOTH THE EC AND GFS ARE SLOWER.
THE ENSEMBLES ALSO FAVORED THE SLOWER SOLUTION SO THAT WAS THE
PREFERRED TRACK.

DESPITE SOME TIMING DIFFERENCES WITH THE MAIN LOW CENTER THE
MODELS ARE IN DECENT AGREEMENT WITH THE PROGRESSION OF ITS
ASSOCIATED FRONT. THE CONSENSUS IS THAT THE FRONT WILL MAKE IT TO
KODIAK ISLAND BY FRIDAY AFTERNOON AND TO THE NORTH GULF COAST
FRIDAY NIGHT. THIS WILL BE A WARMER SYSTEM WITH THE MAJORITY OF
THE PRECIPITATION EXPECTED TO BE RAIN. MEANWHILE...FLOW OVER THE
BERING AND ALEUTIANS WILL BE NORTHERLY WITH RAIN AND SNOW SHOWERS.
THROUGH THE WEEKEND THE LOW ITSELF WILL SLOWLY TRACK NORTH ALONG
THE WEST COAST KEEPING SOUTHERLY FLOW FOR THE GULF AND NORTHERLY
FLOW OVER THE BERING.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALES 172-174 176
         HEAVY FREEZING SPRAY 160 180.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...MO
SOUTHCENTRAL ALASKA...MO
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...RF
LONG TERM...DK