Small Craft Advisory 231, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
524 AM AKDT SUN MAR 15 2015

.ANALYSIS AND UPPER LEVELS...

A VERY STRONG ZONAL JET STREAM REMAINS CENTERED JUST SOUTH OF 40N
THROUGH AROUND 155W BEFORE A SMALLER PIECE CURVES NORTH ALONG
150N AND INTO THE WESTERN GULF. THE RESULTS OF THESE UPPER LEVEL
FEATURES AND THE STRONG BAROCLINIC ZONE IN PLACE ARE A 970 MB
SURFACE LOW ROUGHLY 100 NM SOUTH OF THE TIP OF THE ALASKA
PENINSULA AND A STRONG SURFACE FRONT PUSHING INTO BRISTOL BAY AND
THE SOUTHWESTERN GULF OF ALASKA THIS MORNING.

WHILE THE VERTICALLY STACKED LOW WILL REMAIN CENTERED OVER THE
UNIMAK PASS AND THE EASTERN ALEUTIANS A 60 TO 80 KT 500 MB SOUTH-
SOUTHEASTERLY JET ACCOMPANYING THE SURFACE FRONT WILL KEEP IT
STRONG AS IT CROSSES THE GULF TONIGHT AND MONDAY. A SHORTWAVE
ROTATING AROUND THE LOW WILL SPIN UP AN ADDITIONAL SURFACE LOW AND
TIGHT PRESSURE GRADIENT SOUTH OF THE ALASKA PENINSULA MONDAY
AFTERNOON THAT WILL CONTINUE TO STRENGTHEN AS IT TRACKS INTO
BRISTOL BAY MONDAY NIGHT WHILE A SECOND SURFACE LOW TRACKS THROUGH
THE EASTERN GULF.

&&

.MODEL DISCUSSION...

IN GENERAL MODELS ARE INITIALIZED FAIRLY WELL THIS MORNING AND IN
GOOD AGREEMENT REGARDING THE POSITION OF THE BIG LOW AND PERTINENT
SHORTWAVES ROTATING AROUND IT. ONE AREA OF DIFFERENCE HOWEVER
INVOLVES THE SPEED AT WHICH THEY ARE ADVECTING WARM AIR NORTH WITH
THE FRONTAL SYSTEM AS IT CROSSES THE ALASKA PENINSULA AND
ALEUTIANS...WITH THE NAM AND EC LAGGING BEHIND THE GFS (WARM
ADVECTION WISE) AS THE FRONT LIFTS NORTH INTO THE BERING. SURFACE
OBSERVATIONS AND THE RATE AT WHICH SNOW IS CHANGING OVER TO RAIN
SUPPORTS THE MORE QUICKLY WARMING GFS SOLUTION.

WHILE THE LARGE SCALE PATTERN AND TREND OF WARMING AND MOISTENING
WITH SOUTH TO SOUTHEASTERLY FLOW REMAINS CONSISTENT...MODEL
DIFFERENCES DO START TO INCREASE WITH THE TIMING OF THE TWO WAVES
LIFTING NORTH MONDAY AND MONDAY NIGHT AND MORE SO WITH THE
FOLLOWING SYSTEMS THROUGH THE WEEK.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
A WEATHER PATTERN CHANGE IS IN STORE FOR THE AREA TODAY. THE UPPER
LOW THAT HAS BEEN SITTING OVER SOUTHERN ALASKA IS MOVING NORTH AND
EAST. AN UPPER LOW IS SETTLING INTO THE ALASKA PENINSULA AND
EASTERN ALEUTIANS. THE LEADING WARM FRONT FROM THIS LOW THAT IS
OVER KODIAK EARLY THIS MORNING WILL REACH THE GULF COAST LATER
THIS MORNING THEN SLOWLY WORK ITS WAY INLAND LATER TODAY AND
TONIGHT. THIS WILL OPEN UP WARM SOUTHERLY FLOW FOR THE NEXT
SEVERAL DAYS. SURFACE HIGH TEMPERATURES ON MONDAY WILL WARM 15 TO
20 DEGREES COMPARED TO TODAYS HIGHS. PLENTY OF MOISTURE WILL
ACCOMPANY THIS SOUTHERLY FLOW AND PRECIPITATION SHOULD BE
SIGNIFICANT FOR COASTAL AREAS...ESPECIALLY THE EASTERN KENAI
PENINSULA. MUCH OF THIS WILL FALL AS SNOW IN THE EASTERN KENAI...AND
COULD ALSO MIX WITH WINDS IN PORTAGE VALLEY AND EASTERN TURNAGAIN
ARM FOR SOME NASTY WINTER CONDITIONS. FURTHER INLAND MUCH LESS
PRECIPITATION IS EXPECTED AS SOUTHEASTERLY FLOW AT THE LOWER AND
MID LEVELS WILL "DOWN-SLOPE" MOST AREAS. THE BEST CHANCE FOR
PRECIPITATION INLAND WILL BE WITH AN UPPER LEVEL SYSTEM PASSAGE ON
MONDAY.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
THE FRONT OVER THE SOUTHEASTERN BERING SEA IS BEGINNING TO MAKE
LANDFALL OVER COASTAL BRISTOL BAY WITH SNOW SHOWERS STARTING TO
MOVE INTO WESTERN BRISTOL BAY. SNOW WILL CONTINUE TO SPREAD
THROUGHOUT NORTHERN AND WESTERN BRISTOL BAY THIS MORNING...AND
CONTINUE TO SPREAD INTO KUSKOKWIM DELTA BY THIS AFTERNOON. WINDS
ALONG THE FRONT WILL INCREASE THROUGHOUT THE MORNING...WHICH WILL
CREATE ISOLATED AREAS OF BLOWING SNOW THIS AFTERNOON ONCE
ENOUGH SNOW FALLS TO CREATE VISIBILITY ISSUES. SNOW AND WIND WILL
BEGIN TO DIMINISH IN MOST AREAS LATE THIS EVENING AS THE FRONT
CONTINUES TO WEAKEN AND A SHORTWAVE LIFTS OUT OF THE AREA. SNOW
ACCUMULATION FROM THIS EVENT IS EXPECTED TO REMAIN ON THE LIGHT
SIDE...WITH JUST AN INCH OR TWO OF SNOW EXPECTED BY THIS EVENING.
BY MONDAY NIGHT INTO TUESDAY...ANOTHER ROUND OF SNOW AND RAIN WILL
APPROACH THE SOUTHWEST MAINLAND AS THE NEXT SHORTWAVE FROM THE
ALEUTIAN LOW MOVES OVERHEAD WITH MOIST SOUTHERLY FLOW.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE PRIMARY FOCUS OVER THIS AREA CONTINUES TO BE WITH CONTINUED
BLIZZARD CONDITIONS FOR THE PRIBILOF ISLANDS. THE AREA IS
CURRENTLY IN A SMALL BREAK IN THE SNOW SHOWERS...BUT THE WINDS
ALONE ARE CONTINUING TO REDUCE VISIBILITY TO AROUND A MILE. AS
SNOW REDEVELOPS OVER THE NEXT FEW HOURS...BLIZZARD CONDITIONS ARE
EXPECTED TO RETURN TO THE AREA AND PERSIST INTO THE LATE MORNING.
SNOW SHOWERS WILL THEN REMAIN IN THE AREA INTO EARLY THIS EVENING
WITH CONTINUED STRONG NORTHERLY WINDS...WHICH MAY CREATE BRIEF
PERIODS OF NEAR BLIZZARD CONDITIONS...BUT THESE ARE NOT EXPECTED
TO BE COMMON OR LONG LASTING ENOUGH TO WARRANT EXTENDING THE
BLIZZARD WARNING THAT WILL REMAIN IN EFFECT UNTIL 10AM THIS
MORNING. THE LOW WILL MAKE VERY LITTLE MOVEMENT INTO EARLY NEXT
WEEK AND BRING PERIODS OF SNOW BACK INTO THE AREA AS A SERIES OF
SHORTWAVES PASS OVERHEAD. THIS WILL KEEP THE POSSIBILITY OF
BLIZZARD CONDITIONS IN THE AREA INTO TUESDAY AS STRONG NORTHERLY
WINDS WILL ALSO BE VERY SLOW TO DIMINISH.

THIS PERSISTENT AND VERY SLOW MOVING LOW CENTERED NEAR THE EASTERN
ALEUTIANS WILL CONTINUE TO BRING SNOW SHOWER TO THE CENTRAL
ALEUTIANS...BECOMING RAIN AND SNOW AS YOU MOVE FURTHER EAST
TOWARDS THE AKPEN. WINDS LOOK TO REMAIN GUSTY IN MOST AREAS
AROUND THIS LOW...BUT ALL AREAS OUTSIDE OF THE PRIBILOFS ARE
EXPECTED TO REMAIN UNDER STRONG WINDS THROUGH EARLY NEXT WEEK.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
MODELS CONTINUE TO STRUGGLE WITH A CLOSED UPPER LOW THAT REMAINS
STATIONARY OVER THE EASTERN BERING AND AKPEN THROUGH MID
WEEK...WITH THE MOST RECENT RUNS OF THE AMERICAN MODELS BEGINNING
TO CONVERGE CLOSER ONTO A COMMON SOLUTION. MODELS ARE SHOWING THE
MAIN SURFACE LOW REMAINING STATIONARY NEAR THE EASTERN
ALEUTIANS...WITH A EQUALLY STRONG SURFACE LOW SPLITTING OFF THE
MAIN SYSTEM AND PROGRESSING NORTHWARD INTO THE NORTHEASTERN BERING
BY WEDNESDAY MORNING. AS THE PRIMARY SYSTEM OVER THE EASTERN
ALEUTIANS WEAKENS...ANOTHER SURFACE LOW QUICKLY DEVELOPS TO THE
SOUTHEAST AND TRACK UP TOWARD THE AKPEN BY WEDNESDAY AFTERNOON.
THIS NEW SYSTEM WILL ABSORB THE PRIMARY LOW AND QUICKLY BECOME
THE MAIN WEATHER PRODUCING SYSTEM OVER THE AREA BY WEDNESDAY
AFTERNOON. MODELS THEN SHOW THIS SYSTEM EITHER TRACKING INTO THE
NORTHERN BERING BEFORE DISSIPATING BY THE WEEKEND (EC)...OR
TRACKING OVER THE CENTRAL BERING THEN CENTRAL/EASTERN ALEUTIANS
INTO THE WEEKEND (GFS). HOWEVER WITH THE CONTINUED MODEL
DISCREPANCIES IN BOTH THE MID AND LONG TERM...THE TIMING AND
STRENGTH OF MOST OF THESE FEATURES REMAIN OF LOW CONFIDENCE.

THE OVERALL EFFECT OF THESE SYSTEMS WILL BE CONTINUED UNSETTLED
WEATHER THROUGHOUT THE SOUTHERN MAINLAND AND ALEUTIANS/BERING.
SNOW SHOWERS WILL PERSIST OVER MUCH OF THE BERING...WHILE WARMER
AIR PUSHES INTO SOUTHWEST ALASKA WITH RAIN AND SNOW. AS THE GULF
LOWS MOVE NORTH DURING THE WEEK...THEY WILL BRING RAIN TO THE GULF
COAST WITH SOME SNOW CROSSING COASTAL RANGES AND REACHING INLAND
ZONES.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WINTER STORM WATCH 125. BLIZZARD WARNING 195.
MARINE...STORM WARNING 119 130 138 180 414.
         GALE WARNING 120 125 131 132 139 150 155 160 165 170
                      173 174 175 179 181 185 351 352 412 413.
         HEAVY FREEZING SPRAY 130 139 140 179 185 412 414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...JER
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DEK
LONG TERM...TP