Small Craft Advisory 879, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
501 AM AKST THU NOV 5 2015

.ANALYSIS AND UPPER LEVELS...
THE ALL-ENCOMPASSING FEATURE ALOFT TODAY IS A BEAST OF AN UPPER
LOW PRESSURE SYSTEM OVER THE BERING SEA...WHICH HAS EFFECTIVELY
BECOME THE LONGWAVE TROUGH. A PRETTY CONTINUOUS JET STREAM PEAKING
OUT AT 120 KTS RUNS FROM KAMCHATKA DROPPING SOUTHWARD AROUND THE
TROUGH AND CURVING BACK UP INTO THE GULF. THE AFOREMENTIONED
SYSTEM IS FULLY MATURED AND WRAPPED UP IN THE EASTERN BERING SEA
AS THE JET STREAM BEGINS TO OUT-PACE IT AND SHIFT EASTWARD OVER
SOUTHCENTRAL ALASKA. THE MAIN OCCLUDED FRONT IS CURRENTLY MAKING
LANDFALL EARLY THIS MORNING OVER THE SOUTHWEST MAINLAND AND MOVING
INTO THE GULF...WHICH IS WHERE THE STEADIEST
PRECIPITATION...MOSTLY RAIN NEAR SEA LEVEL...EXISTS WITH THIS
SYSTEM. DESPITE ENTERING A WEAKENING PHASE OF ITS LIFE CYCLE...THE
SYSTEM STILL PACKS A PUNCH IN THE WIND FIELD WITH CENTRAL PRESSURE
IN THE MID 960 MB RANGE. THE STRONGEST WINDS ARE ON THE BACKSIDE
OF THE LOW...AIDED BY MODIFIED ARCTIC AIR IN COLD
ADVECTION...WHICH IS WRAPPING AROUND THE SOUTH-SIDE OF THE SYSTEM.

&&

.MODEL DISCUSSION...
AS THE CURRENT SYSTEM IS PAST DEVELOPMENT AND INTO A
MATURE/WEAKENING STAGE...GUIDANCE IS IN REALLY GREAT AGREEMENT
WITH THE TRACK AND STRENGTH OF FEATURES BOTH ALOFT AND AT THE
SURFACE. THE ONLY DIFFERENCES ARISE FROM SPATIAL RESOLUTION AND
TERRAIN HANDLING.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE LARGE LOW OVER THE EASTERN BERING SEA WILL CONTINUE TO MOVE
EAST OVER THE NEXT COUPLE OF DAYS AS THE PATTERN REMAINS
PROGRESSIVE. THE LOW CENTER WILL CROSS KODIAK LATE TONIGHT AND BE
JUST TO THE SOUTHWEST OF YAKUTAT LATE FRIDAY NIGHT. A STRONG FRONT
ASSOCIATED WITH THIS LOW WILL MOVE INTO THE NORTHERN GULF BY THIS
AFTERNOON AND MOVE ASHORE TONIGHT. THIS FRONT WILL BRING STRONG
WINDS AND HEAVY PRECIPITATION TO COASTAL AREAS WITH LESSER AMOUNTS
INLAND. SOME INLAND AREAS THAT WILL SEE SIGNIFICANT WEATHER
INCLUDE THE WESTERN SUSITNA VALLEY AND SOUTHERN COPPER RIVER
VALLEY WHERE SIGNIFICANT SNOWFALL IS EXPECTED. WINDS WILL BE
FAIRLY STRONG ALONG TURNAGAIN ARM THROUGH THIS AFTERNOON AHEAD OF
THE FRONT AND WITH THE SURFACE LOW TO THE WEST. PRECIPITATION TYPE
IS A CHALLENGE FOR AREAS NEAR COOK INLET THROUGH FRIDAY AS THE
UPPER LOW PUSHES WARM AIR NORTHWARD. AFTER THE FRONT MOVES INLAND
TONIGHT CYCLONIC FLOW WILL BE OVER SOUTH CENTRAL ALASKA FOR
CONTINUED SHOWERS...DIMINISHING THROUGH FRIDAY NIGHT. COOLER AIR
WILL ALSO BEGIN TO SEEP INTO THE AREA FRIDAY AS THE FLOW BECOMES
NORTHWESTERLY.

&&

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

AS THE ALEUTIAN LOW MOVES ACROSS THE AKPEN TODAY AND
TONIGHT...WIND AND RAIN WILL AFFECT THE REGION DURING THE
DAY...WITH SOME SNOW FOR THE KUSKOKWIM DELTA AND VALLEY OVERNIGHT
INTO FRIDAY. AS THE LOW CONTINUES MOVING EAST COLDER AIR WILL FILTER
ACROSS THE SOUTHWEST THROUGH FRIDAY NIGHT. ADDITIONAL LIGHT SNOW
WILL END ON SAT.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...

LOW PRESSURE MOVING ACROSS BRISTOL BAY TODAY WILL KEEP
RAIN...ALONG WITH GALES AND STORM FORCE WINDS...ACROSS THE EASTERN
HALF OF THE ALEUTIANS. AS THE LOW CROSSES INTO THE GULF THROUGH
SATURDAY...WINDS ARE EXPECTED TO SLOWLY DIMINISH THROUGH FRIDAY
NIGHT. THE WESTERN ALEUTIANS WILL BE ON THE BACK SIDE OF THE LOW.
THIS AREA WILL CONTINUE TO EXPERIENCE RAIN SHOWERS AND SMALL
CRAFT LEVEL WINDS THROUGH FRIDAY NIGHT.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
EVEN THOUGH THE MODELS HAVE THE SAME GENERAL IDEA WITH THE MAIN
PRESSURE CENTERS FOR THE EXTENDED FORECAST THERE IS STILL QUITE A
BIT OF UNCERTAINTY IN TERMS OF IMPACTS. THE LOW THAT WILL BE IN
THE GULF BY FRIDAY HAS THE MOST AGREEMENT WITH IT MOVING OFF TO
THE EAST AS IT WEAKENS THROUGH THE WEEKEND DIMINISHING
PRECIPITATION FOR THE SOUTHCENTRAL. THE OTHER PROBLEM IS THE LOW
MOVING INTO THE NORTHERN BERING OVER THE WEEKEND. THERE IS A LOT
OF DIFFERENCE WITH THE TIMING OF THE FRONT ASSOCIATED WITH THIS
LOW. SOME OF THE MODELS BRING IT INTO THE SOUTHWEST EARLY ON
SUNDAY WHILE SOME OF THE ENSEMBLES ARE MUCH SLOWER RESULTING IN AN
ALMOST 24-HOUR TIME DIFFERENCE. THERE IS ALSO DISAGREEMENT AS TO
WHETHER THE PRECIPITATION WILL FALL AS RAIN OR SNOW DEPENDING ON
THE STRENGTH OF THE SYSTEM AND HOW MUCH WARM AIR IT BRINGS UP FROM
THE SOUTH. THIS RESULTS IN A LOW CONFIDENCE FORECAST BY LATE
WEEKEND.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WINTER WEATHER ADVISORIES...141 145.
MARINE...GALES...120 131 132 139 150 160 165 171 176-181
 STORMS....119 125 130 155 170 172-175

&&

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