Small Craft Advisory 146, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
504 AM AKST MON FEB 16 2015

.ANALYSIS AND UPPER LEVELS...

THE UPPER AIR PATTERN IS CHARACTERIZED BY A SEASONABLY STRONG NORTH
PACIFIC TROUGH DEAMPLIFYING INTO A COMPACT SHORTWAVE TROUGH AS IT
MOVES TOWARD THE ALASKA PENINSULA. THE SURFACE LOW IS CURRENTLY
CENTERED APPROXIMATELY 120 NM SOUTHWEST OF COLD BAY...WITH AN
ASSOCIATED SPRAWLING STORM FORCE LOW ACROSS THE NORTHERN GULF OF
ALASKA. THE WARM FRONT ALOFT CAN BE SEEN LIFTING NORTHWESTWARD
ACROSS THE KUSKOKWIM DELTA ON BOTH RADAR AND SATELLITE...WITH A
SECOND SURGE OF MOISTURE ALONG THE LEFT EXIT OF THE UPPER LEVEL
JET STREAM LIFTING TOWARD KODIAK ISLAND. THIS SECOND SURGE OF
MOISTURE WILL BRING THE HEAVIEST PRECIPITATION OF THE EVENT TO
SOUTHWEST ALASKA...AND THE BEST CHANCE OF PRECIPITATION ACROSS
SOUTHCENTRAL ALASKA MIDDAY THROUGH TONIGHT. WITH THE PASSAGE OF
THE OCCLUDED FRONT ACROSS SOUTHERN ALASKA LATE THIS AFTERNOON
THROUGH TONIGHT...WARMER MARITIME AIR WILL OVERSPREAD MANY
LOCATIONS...WITH A CORRESPONDING RISE IN LOCAL TEMPERATURES.

&&

.MODEL DISCUSSION...

THE SUITE OF NUMERICAL MODELS ARE ALL IN VERY GOOD AGREEMENT WITH
THE GENERAL SYNOPTIC PATTERN HEADING INTO MIDWEEK. EVEN WITH
SMALLER SCALE DISCREPANCIES DEVELOPING MIDWEEK WITH RESPECT TO A
COMPACT WAVE DISTURBANCE TRACKING OVER SOUTHERN ALASKA...THE
OVERALL REGIONAL UPPER AIR PATTERN IS FAIRLY SIMILAR ACROSS ALL
THE MAJOR GLOBAL MODELING PLATFORMS INTO THE WEEKEND. AS A
RESULT...OVERALL FORECAST CONFIDENCE IS MODERATE TO HIGH.

&&

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

A STRONG NORTH PACIFIC STORM WILL CONTINUE TO IMPACT SOUTHCENTRAL
ALASKA TODAY. THE FIRST FRONT THAT CAME THROUGH OVERNIGHT DROPPED
BETWEEN AN 1 AND 1 1/2 INCHES OF RAIN ON THE PACIFIC SIDE OF THE
KENAI PENINSULA. MEANWHILE...THE WESTWARD/PRECIP-SHADOWED AREAS
FROM THE EASTERN KENAI UP TO THE MAT-SU RECEIVED NOTHING. A STRONG
TRAILING SHORTWAVE TROUGH IS LOCATED SOUTHEAST OF KODIAK ISLAND
AND IS DRIVING NORTHWARD ON A 140KT DUE SOUTHERLY JET. THIS
FEATURE WILL BRING A SECOND AND HEAVIER ROUND OF RAIN TO THE
COASTAL AREAS TODAY. TEMPERATURES ARE WARM ENOUGH FOR RAIN EVEN
THROUGH TURNAGAIN PASS...BUT THOMPSON PASS AND THE COPPER RIVER
BASIN WILL LIKELY STAY COLD ENOUGH FOR SNOW AT LEAST DURING THE
DAYTIME TODAY. MEANWHILE...THE TYPICAL DOWNSLOPE AREAS AROUND COOK
INLET WILL REMAIN MOSTLY OR COMPLETELY DRY ONCE AGAIN.

THE SECOND PHASE OF THE STORM WILL BEGIN AS THE UPPER WAVE DRIVES
UP COOK INLET THIS AFTERNOON AND REVERSES THE NORTHERLY PRESSURE
GRADIENT IN COOK INLET. THIS WILL ALLOW A BRIEF PERIOD OF GUSTY
SOUTHEASTERLY WINDS TO AFFECT PORTIONS OF ANCHORAGE AND THE
MATANUSKA VALLEY AS THE FRONT FINALLY CLEARS THE AREA...AND WILL
ALSO LIKELY BE ACCOMPANIED BY A BRIEF PERIOD OF RAIN OR RAIN
SHOWERS. BY LATE EVENING...COOLER AIR ALOFT BEGINS TO FILTER INTO
THE AREA ALOFT AND WILL DROP SNOW LEVELS AS THE PRECIP WINDS
DOWN. HOWEVER...CONTINUED SOUTHERLY WINDS UP COOK INLET SHOULD
KEEP OVERNIGHT SURFACE TEMPERATURES ABOVE FREEZING...SO ANY
PRECIP THAT FALLS WILL NOT ACCUMULATE MUCH AND MAY ACTUALLY FALL
AS RAIN. THIS GENERALLY LIGHT SOUTHERLY WIND REGIME WITH A FEW
RAIN OR SNOW SHOWERS WILL CONTINUE THROUGH TUESDAY...WITH ABOVE
FREEZING TEMPERATURES AGAIN EXPECTED AT MOST OF THE POPULATION
CENTERS.

&&

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

THE MAIN STORY ACROSS THE REGION WILL BE NUMEROUS WAVES OF
MOISTURE TRACKING OVER THE AREA...THE MOST SIGNIFICANT COMING
TODAY AND TONIGHT. A CURRENT BAND OF SNOW TRACKING OVER THE
KUSKOKWIM DELTA WILL MOVE OFFSHORE LATER TODAY...WITH A SECONDARY
SURGE OF MOISTURE TRACKING OVER THE ENTIRE REGION BY THIS
AFTERNOON...SPREADING RAIN...POCKETS OF SNOW AND LOCALIZED AREAS
OF FREEZING RAIN. THE BEST CHANCE OF FREEZING RAIN WILL BE ACROSS
THE KUSKOKWIM DELTA LATE THIS MORNING THROUGH EARLY AFTERNOON
BEFORE PRECIPITATION GRADUALLY CHANGES BACK OVER TO RAIN AND SNOW.
ELSEWHERE...STRONG SOUTHEAST FLOW OFF THE ALASKA RANGE WILL KEEP
PRECIP TYPE AS ALL RAIN. STRONG SOUTHEAST SURFACE WINDS...ESPECIALLY
ACROSS THE BRISTOL BAY REGION...WILL GRADUALLY DIMINISH THIS
AFTERNOON. ON TUESDAY...ONSHORE FLOW BEHIND THE FRONT WILL RESULT
IN SLOWLY COOLING TEMPERATURES AND MORE SHOWERY CONDITIONS.

&&

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

A SEASONABLY STRONG LOW CENTERED NEAR COLD BAY WILL SLOWLY WEAKEN
AND DRIFT NORTH TOWARD THE BERING STRAIT THROUGH TUESDAY. MODERATE
TO HEAVY BANDS OF PRECIPITATION WILL MOSTLY IMPACT THE EASTERN
ALEUTIANS AND PRIBILOF ISLANDS...WITH MORE SHOWERY CONDITIONS
ACROSS THE WESTERN CHAIN. NORTHERLY WINDS ACROSS THE PRIBILOF
ISLANDS WILL KEEP TEMPERATURES COOL ENOUGH FOR SNOW AND AREAS OF
BLOWING SNOW AS THE LOW LIFTS NORTH THROUGH TODAY. WEAK HIGH
PRESSURE SETTLES IN TUESDAY NIGHT...WITH DIMINISHING WINDS AND
PRECIPITATION TRENDS REGION WIDE.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
AN UPPER LEVEL AMPLIFIED RIDGE BUILDS INTO THE GULF AND WILL
EXTEND THROUGH THE MAINLAND NORTHWARD INTO THE BARROW REGION
BY THURSDAY. THIS RIDGE WILL GRADUALLY MOVE TO THE EAST WITH
CONTINUED SOUTHERLY FLOW THROUGH THE GULF EXTENDING INTO THE
INTERIOR OF SOUTHCENTRAL ALASKA REGION. SOUTH OF THE CENTRAL
ALEUTIANS IN THE NORTH PACIFIC OCEAN THERE IS AN UPPER LEVEL
CLOSED LOW NEAR 42N 172W. THIS LOW WILL SLOWLY MOVE TOWARD
DUTCH HARBOR BY SATURDAY AND CROSS OVER THE ALEUTIAN CHAIN INTO
THE EASTERN BERING SEA BY SUNDAY. REFLECTED AT THE SURFACE IS A
NORTH PACIFIC LOW AND AN INVERTED TROUGH EXTENDING THROUGH DUTCH
HARBOR AREA. THE MODELS ARE STRUGGLING WITH THE STRENGTH AND
POSITIONING OF THIS LOW AS IT TRACKS NORTHWARD HEADING INTO THE
WEEKEND. THE SOUTHWEST/SOUTHCENTRAL ALASKA REGIONS WILL CONTINUE
TO HAVE WARM AIR ADVECTION WITH ABOVE AVERAGE TEMPERATURES WITH A
CONTINUED WET PATTERN. THE GFS MODEL IS MORE AGGRESSIVE WITH AN
UPPER LEVEL SHORTWAVE POSITIONED OVER THE BRISTOL BAY AREA
EXTENDING INTO THE NORTHERN GULF...WHILE THE OTHER MODELS HAVE A
VERY WEAK SHORTWAVE FARTHER UPSTREAM OVER THE EASTERN ALEUTIANS.
IF THE GFS MODEL TRACK WORKS OUT THIS WILL BRING PRECIPITATION TO
SOUTHWEST/SOUTHCENTRAL REGION BY FRIDAY. THE CENTRAL AND EASTERN
BERING SEA WILL HAVE WARMER TEMPERATURES HEADING INTO THE WEEKEND
AS THE NORTH PACIFIC LOW TRACKS TOWARDS DUTCH HARBOR BY SATURDAY.
THE WESTERN BERING SEA AND THE WESTERN ALEUTIANS WILL HAVE
NORTHEASTERLY WINDS AND SHOWERY PRECIPITATION AS THE SIBERIAN HIGH
REMAINS IN PLACE THROUGH SUNDAY.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...FREEZING RAIN ADVISORY...155.
MARINE...STORM WARNING...119 120 130 131.
         GALE WARNING...125 138 139 150 155 160 165 170 172 173
                        174 179 180 181 185.
         HEAVY FREEZING SPRAY WARNING...185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...JA
SOUTHCENTRAL ALASKA...AD
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JA
LONG TERM...PLD