Small Craft Advisory 376, NWS Anchorage, AK

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

.ANALYSIS AND UPPER LEVELS...
THERE IS AN UPPER LEVEL LOW OVER THE EAST-CENTRAL BERING THAT IS
WEAKENING AND MOVING SLOWLY EAST. A WEAK UPPER TROUGH EXTENDS FROM
THIS LOW EASTWARD INTO THE NORTHERN GULF JUST NORTH OF KODIAK
ISLAND...BUT IS PRODUCING VERY LITTLE WEATHER. THERE IS ANOTHER
LOW OVER THE NORTH PACIFIC SOUTH OF THE ALASKA PENINSULA THAT IS
MOVING TO THE EAST-NORTHEAST AND STRENGTHENING. YET ANOTHER LOW
IS TO THE SOUTHEAST OF KAMCHATKA...WITH THE WARM FRONT JUST MOVING
INTO THE WESTERN ALEUTIANS. WEAK RIDGING IS OVER THE GULF OF
ALASKA AND THE CENTRAL ALEUTIANS. WEAK FLOW ALOFT IS OVER THE
SOUTHERN ALASKA MAINLAND WITH ISOLATED AND DIURNALLY ENHANCED
SHOWERS CONTINUING...BUT WEAKER THAN HAS BEEN THE CASE THE LAST
FEW DAYS.

&&

.MODEL DISCUSSION...
THE NUMERICAL MODELS CONTINUE TO BE IN VERY GOOD AGREEMENT THROUGH
THE SHORT TERM. THERE ARE SOME MINOR DIFFERENCES ON HOW THEY
HANDLE THE MOISTURE/SHOWERS OVER THE SOUTHERN ALASKA MAINLAND BUT
THIS IS ONLY OF MINOR CONCERN. THERE IS ALSO A QUESTION WITH THE
DEVELOPMENT AND MOVEMENT OF A LOW IN THE ALEUTIANS ON SUNDAY BUT
THE ECMWF SEEMS TO BE THE BEST SOLUTION AT THIS TIME.

&&

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

ISOLATED TO SCATTERED RAIN SHOWERS ARE ONCE AGAIN IMPACTING MOST
OF SOUTHCENTRAL...ALTHOUGH SEA BREEZES NEAR COASTAL
LOCATIONS...INCLUDING ANCHORAGE...ARE DAMPING THOSE SHOWERS. A FEW
ROGUE THUNDERSTORMS HAVE BEEN DETECTED ACROSS THE KENAI PENINSULA.
A ROGUE THUNDERSTORM IS ALSO POSSIBLE OVER THE SUSITNA VALLEY
THIS EVENING BEFORE SHOWERS TAPER OFF AFTER DARK.

AS WEAK HIGH PRESSURE SLOWLY BUILDS ALOFT OVER SOUTHCENTRAL...SLOW
DRYING ACROSS THE REGION WILL DEVELOP THROUGH SUNDAY. DIURNAL
SHOWERS WILL ONCE AGAIN DEVELOP ON SATURDAY...BUT THEY WILL BE
LESS WIDESPREAD AND INTENSE. BY SUNDAY...HIGH PRESSURE WILL
LARGELY CAP THE ATMOSPHERE OFF...KEEPING ONLY A FEW ISOLATED
THUNDERSTORMS OVER THE HIGHEST MOUNTAINS ARE THE TALKEETNA
MOUNTAINS AND THE ALASKA RANGE. AN OTHERWISE WARM AND DRY DAY IS
IN STORE FOR SUNDAY.

&&

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

SCATTERED RAIN SHOWERS...BEGINNING AS SNOW IN THE MORNING SOME
PARTS OF SOUTHWEST ALASKA...WILL GRADUALLY SHIFT NORTH THROUGH THE
DAY TODAY AS 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 THIS 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)...
CONDITIONS START OFF DRY ACROSS SOUTHCENTRAL AT THE BEGINNING OF NEXT
WEEK AS UPPER LEVEL RIDGING DOMINATES EAST ALASKA. A LOW PRESSURE
SYSTEM ACROSS THE CENTRAL ALEUTIANS ON SUNDAY NIGHT BRINGS
SCATTERED RAIN AND SNOW SHOWERS ACROSS THE CHAIN AND THEN TO THE
SOUTHWESTERN MAINLAND AND WESTERN GULF AS IT MOVES A TROUGH
NORTHWARD ON MONDAY AND TUESDAY. THE FRONT DIMINISHES TUESDAY
NIGHT AS A FINAL PUSH MAKES IT TO THE NORTHEASTERN GULF.

RIDGING BUILDS ACROSS THE BERING FROM THE NORTH AS THE LOW
PRESSURE SYSTEM ALONG THE CHAIN EXITS TO THE EAST. THIS PATTERN
IS A SET UP FOR A TEMPERATURE INVERSION OVER THE BERING WHICH WILL
TRAP LOW LEVEL MOISTURE NEAR THE SURFACE. THIS RESULTS IN A
PATTERN THAT SHIFTS FROM AREAS OF FOG AT NIGHT IMPROVING TO LOW
CLOUDS DURING THE AFTERNOONS. AT THE MIDDLE OF NEXT WEEK...ANOTHER
SURFACE LOW MOVES A FRONT INTO THE SOUTHERN THE GULF WEDNESDAY
NIGHT AND TO THE COAST BY THURSDAY NIGHT. RAIN ALONG THE FRONT CAN
BE EXPECTED WITH THIS SYSTEM WITH ISOLATED TO SCATTERED SHOWERS
INLAND AS THE SYSTEM WEAKENS AS IT APPROACHES THE COAST AND
DOWNSLOPING OVER THE MOUNTAINS LIMITS PRECIPITATION.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 176 177 178.
FIRE WEATHER...NONE.
&&

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