Small Craft Advisory 375, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
508 AM AKDT FRI MAY 1 2015

.ANALYSIS AND UPPER LEVELS...
THERE IS AN UPPER LOW OVER THE CENTRAL BERING SEA...WITH AN
EXTENSION TO THE ALASKA PENINSULA. THIS LOW AND ITS EXTENSION EACH
HAVE A WEAK REFLECTION AT THE SURFACE. ZONAL FLOW CONTINUES OVER
THE NORTHERN PACIFIC TO THE SOUTH OF THE ABOVE MENTIONED SYSTEM.
THE FLOW ALOFT OVER SOUTHERN ALASKA IS STILL WEAKLY
CYCLONIC...WHICH IS COMBINED WITH SOME MOISTURE TO CREATE
UNSTABLE CONDITIONS. OVER THE SOUTHWEST...THE ONSHORE FLOW HAS
HELPED PUSH MORE STABLE AIR AND FOG INLAND OVER THE KUSKOKWIM
DELTA AND BRISTOL BAY AREAS. THIS STABLE AIR WILL LIKELY HINDER
THUNDERSTORM FORMATION OVER THESE AREAS TODAY...WITH THE
EXCEPTION OF SOME POSSIBLE ISOLATED THUNDERSTORMS OVER THE LOWER
KUSKOKWIM VALLEY.

&&

.MODEL DISCUSSION...
THE NUMERICAL MODELS CONTINUE TO BE IN VERY GOOD AGREEMENT IN THE
SHORT TERM. THERE ARE OF COURSE SOME MINOR DIFFERENCES IN THE
MOISTURE/STABILITY FIELDS BUT THESE ARE FAIRLY EASILY HANDLED IN
THE FORECAST. THEREFORE FORECAST CONFIDENCE IS HIGHER THAN NORMAL.

&&

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

MOSTLY SUNNY CONDITIONS FOR MANY AREAS THIS MORNING WILL GIVE WAY
TO INCREASING CLOUDS AND DIURNAL SHOWER ACTIVITY ONCE AGAIN THIS
AFTERNOON...MAINLY FROM ANCHORAGE NORTHWARD. AS WAS THE CASE YESTERDAY
WINDS ALOFT REMAIN QUITE WEAK...SO MOST OF THE ACTIVITY SHOULD
DEVELOP AND REMAIN OVER AREA MOUNTAIN RANGES THROUGH THE
AFTERNOON. A WEAK UPPER LEVEL DISTURBANCE MOVING NORTHWARD THROUGH
COOK INLET THIS EVENING MAY HELP KICK OFF A FEW MORE SHOWERS THIS
EVENING OVER INTERIOR AREAS OF THE KENAI PENINSULA AND ANCHORAGE.

FOR THE WEEKEND...HIGH PRESSURE BUILDING IN FROM THE SOUTH WILL
MAKE FOR A VERY NICE WEEKEND ACROSS THE MAJOR POPULATION
CENTERS...WITH TEMPERATURES WARMING INTO THE UPPER 50S. WINDS
WILL REMAIN QUITE LIGHT...SO GENERALLY WEAK AFTERNOON/EVENING SEA
BREEZES CAN AND SHOULD BE ANTICIPATED. A RELATIVELY WEAK LOW AND
ASSOCIATED WEATHER FRONT WILL MOVE INTO THE SOUTHERN GULF SATURDAY
MORNING...THOUGH ONLY SOUTHERN PORTIONS OF KODIAK ISLAND ARE
LIKELY TO SEE STEADY RAIN BEFORE THE SYSTEM MOVES EASTWARD TOWARD
THE PANHANDLE ON SUNDAY.

&&

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

SCATTERED RAIN SHOWERS...BEGINNING AS SNOW IN THE MORNING FOR SOME
PARTS OF SOUTHWEST ALASKA...WILL GRADUALLY SHIFT NORTH THROUGH THE
DAY TODAY AS A WEST-EAST ORIENTED TROUGH AXIS DRIFTS NORTH ACROSS
THE SOUTHWEST MAINLAND. MODELS SUGGEST A SMALL PATCH OF MID-LEVEL
DRY AIR OVER THE KUSKOKWIM VALLEY ZONE THIS AFTERNOON...SO A
SLIGHT CHANCE OF THUNDERSTORMS WAS KEPT IN THE FORECAST FOR THIS
AFTERNOON AND EARLY EVENING. HOWEVER...ANY LIGHTNING SHOULD IMPACT
ONLY HIGHER ELEVATIONS MAINLY JUST NORTH AND WEST OF
SLEETMUTE...AND WEAK SOUTHERLY STORM MOTIONS SHOULD PUSH ANY
LIGHTNING ACTIVITY TO THE NORTH.

OTHERWISE FOR TODAY...SOUTHWEST FLOW WILL CONTINUE TO PUSH A DEEP
MARINE LAYER ONSHORE...WITH DENSE FOG EXPECTED DURING THE MORNING
HOURS THIS MORNING NEAR BETHEL AND ALONG THE COAST.

THROUGH THE DAY ON SATURDAY INTO SATURDAY NIGHT...AN UPPER LEVEL
LOW WILL DEEPEN OVER THE EASTERN BERING...WITH AN UPPER LEVEL
SOUTHERLY JET STREAK STRENGTHENING OVER THE SOUTHWEST MAINLAND.
THIS WILL PROVIDE THE MECHANISM FOR DEEP MOISTURE FROM THE PACIFIC
MOVING NORTH AND OVER THE REGION LATE SATURDAY THROUGH SATURDAY
NIGHT...WITH AT LEAST NUMEROUS RAIN SHOWERS IF NOT STRATIFORM RAIN
ACROSS MOST OF THE SOUTHWEST MAINLAND DURING THIS TIME.

&&

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

UPPER LEVEL LOW OVER THE CENTRAL BERING MOVES TO THE EASTERN
BERING SATURDAY AND THEN INLAND FOR SUNDAY. AN AMPLIFYING RIDGE OF
HIGH PRESSURE BUILDS OVER THE CENTRAL AND EASTERN BERING BEHIND
THIS FEATURE LIKELY RESULTING IN WEAK WINDS AND LOW LEVEL STRATUS
DEVELOPING OR CONTINUING. UPSTREAM OVER THE WESTERN
ALEUTIANS...UPPER LEVEL LOW WILL PUSH A LOW-END GALE-FORCE FRONT
SLOWLY ACROSS THE REGION THROUGH SATURDAY NIGHT. MODELS ARE REALLY
STRUGGLING WITH PLACEMENT OF A NEW LOW THAT ARRIVES FROM THE SOUTH
OVER THE PACIFIC TOWARD SUNDAY MORNING...BUT WILL STICK WITH THE
EUROPEAN SOLUTION WHICH IS MORE CONSISTENT AND KEEPS THE NEW LOW
WELL SOUTH OF THE ISLANDS.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
A NARROW RIDGE WILL BUILD OVER THE EASTERN HALF OF THE MAINLAND BY THIS
WEEKEND WHICH LOOKS TO KEEP RELATIVELY BENIGN CONDITIONS CHARACTERIZED
BY DIURNAL SHOWER ACTIVITY OVER SOUTHCENTRAL AK THROUGH EARLY NEXT WEEK.
THE COMPLICATING FACTOR WILL BE A WEAK UPPER TROUGH THAT EVOLVES INTO
A CUTOFF LOW OVER THE SOUTHWEST MAINLAND BY MONDAY. THE GFS IS MORE
AGGRESSIVE IN MOVING THIS FEATURE EASTWARD AND BRINGING ADDITIONAL
PRECIPITATION INTO SOUTHCENTRAL AK WHEREAS MOST OF THE GUIDANCE KEEPS
THE LOW FARTHER BACK TO THE WEST AS IT GRADUALLY WEAKENS. THE FORECAST
REFLECTS THE LATTER SCENARIO FOR NOW WHICH WOULD KEEP MORE WIDESPREAD
SHOWER ACTIVITY CONFINED TO SOUTHWEST AK AND LIMIT IMPACTS FOR SOUTHCENTRAL
AK PRIMARILY TO INCREASED CLOUD COVER.

MEANWHILE A BROAD UPPER LOW WHICH WILL BE LOCATED OVER THE WESTERN
ALEUTIANS THIS WEEKEND WILL MOVE TO NEAR THE ALASKA PENINSULA BY THE
MIDDLE OF NEXT WEEK. THIS WILL RESULT IN WINDY AND RAINY CONDITIONS
ACROSS MUCH OF THE ALEUTIAN CHAIN WITH A PERIOD OF WETTER CONDITIONS
ALSO RETURNING TO SOUTHCENTRAL AK AND ESPECIALLY THE GULF COAST BY
THE MIDDLE OF THE WEEK AS A FRONT PUSHES INTO THE GULF.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING...177 178.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...TP
SOUTHCENTRAL ALASKA...AMD
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CC
LONG TERM...CB