Small Craft Advisory 377, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
512 AM AKDT SAT MAY 2 2015

.ANALYSIS AND UPPER LEVELS...

THE OVERALL WEATHER PATTERN IS DOMINATED MAINLY BY TWO AREAS OF
LOW PRESSURE AT THIS TIME. THE FIRST BEING AN AREA OF LOW PRESSURE
PUSHING ACROSS THE FAR NORTHERN PACIFIC WHICH HAS BEGUN TO PUSH A
FRONT INTO THE SOUTHWESTERN GULF OF ALASKA. THE SECOND OF THESE
LOWS IS PUSHING TOWARD THE WESTERN ALEUTIANS EARLY THIS MORNING
AFTER PUSHING OFF THE KAMCHATKA PENINSULA FRIDAY MORNING. HIGH
PRESSURE BOTH AT THE SURFACE AND ALOFT HAS BEGUN TO SITUATE OVER
SOUTHCENTRAL ALASKA WHICH WILL HELP STABILIZE THE ATMOSPHERE AFTER
MULTIPLE THUNDERSTORMS OBSERVED OVER THE KENAI PENINSULA ON
FRIDAY.

THERE IS A WEAK SHORTWAVE CURRENTLY NEAR THE PRIBILOF ISLANDS
THAT IS PUSHING EASTWARD SLOWLY AS IT GETS CUT OFF THE FROM THE
MEAN FLOW. ONE FEATURE OF NOTE THAT IS SMALL AND IMPACTLESS
PRESENTLY BUT WILL BECOME A POTENT AREA OF LOW PRESSURE IN THE
COMING DAYS IS A WEAK SHORTWAVE SITUATED NEAR 39N 178E. A
DEVELOPING MID LEVEL JET HAS AIDED IN THE DEVELOPMENT OF A WEAK
SURFACE REFLECTION WHICH LOOKS PRIMED FOR RAPID DEVELOPMENT IN THE
COMING DAYS.

&&

.MODEL DISCUSSION...

THE 00Z RUN OF THE SYNOPTIC AND AMERICAN MODELS INITIALIZED VERY
WELL AND ARE IN GREAT AGREEMENT THROUGH SUNDAY MORNING BEFORE THE
ECMWF BECOMES A SLIGHT OUTLIER WITH THE RAPID DEVELOPMENT OF AN
AREA OF LOW PRESSURE SOUTH OF ADAK. IT IS QUITE SURPRISING TO HAVE
SUPERB MODEL AGREEMENT WITH THE AFOREMENTIONED LOW AS MULTIPLE
PIECES OF ENERGY PHASE TOGETHER. WITH A RAPIDLY DEVELOPING LOW
ABSORBING AN ELONGATED AREA OF LOW PRESSURE OVER THE WESTERN
BERING SEA AND A DEVELOPING MID LEVEL AND UPPER LEVEL JET...ONE
WOULD THINK A LARGE MODEL SPREAD WOULD BE LIKELY. WITH THE MODELS
NOW TRENDING STRONGER AND AN EXPANSION OF THE SURFACE RIDGE OVER
THE NORTHERN BERING...A PERIOD OF STRONG WINDS NOW LOOKS LIKELY
ALONG THE FRONT AS IT PUSHES ACROSS THE CENTRAL ALEUTIANS. A BLEND
OF THE AMERICAN MODELS (NAM AND GFS) WAS USED THROUGH THE SHORT-
TERM DUE IN LARGE PART TO MODEL AGREEMENT WITH THE DEVELOPMENT OF
THIS LOW. SOUTHCENTRAL ALASKA LOOKS HIGH AND DRY SO REALLY NO
DISCREPANCIES TO BE SEEN.

&&

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

HIGH PRESSURE IS BUILDING IN FROM THE SOUTH TODAY AND HAS SET THE
STAGE FOR A WARM AND SUNNY WEEKEND ACROSS THE SOUTHERN MAINLAND.
THE PRESSURE GRADIENTS REMAIN VERY LIGHT ACROSS THE AREA...SO
WEAK TO MODERATE DAILY SEA BREEZES WILL BE THE OVERALL WIND
PATTERN FOR THE NEXT FEW DAYS. AT THE SAME TIME...THE AIRMASS IS
GROWING MORE AND MORE STABLE AS TEMPERATURES ALOFT WARM AND LAPSE
RATES DECREASE. SHOWER ACTIVITY TODAY WILL BE CONFINED TO THE
NORTHERN TIER OF ZONES INCLUDING THE COPPER RIVER BASIN AND MAT-SU
VALLEY. HOWEVER...WITH STORM MOTION REMAINING WEAK MOST CONVECTIVE
DEVELOPMENT IS LIKELY TO BEGIN AND REMAIN OVER MOUNTAINOUS
TERRAIN.

THE NEAREST SIGNIFICANT WEATHER IS FOUND WELL TO THE SOUTH WHERE
A WEATHER FRONT WILL STALL TODAY OVER KODIAK ISLAND AND THE
SOUTHERN GULF OF ALASKA. WHILE THIS WILL KEEP CLOUDINESS ACROSS
MOST OF KODIAK ISLAND...THE STEADY RAINFALL WILL BE LIMITED TO THE
SOUTHERN END OF THE ISLAND THROUGH SUNDAY.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
UPPER LEVEL LOW JUST OFF THE COAST OF SOUTHWEST ALASKA IS
BEGINNING TO APPROACH THE SOUTHWEST COAST...WHERE IT WILL BECOME
NEARLY STATIONARY THROUGH SUNDAY. UPPER LEVEL JET ENERGY ON THE
DOWNSTREAM SIDE OF THIS LOW WILL ALLOW FOR GOOD MOISTURE TRANSPORT
NORTH OVER THE REGION. WIDESPREAD RAIN IS EXPECTED THROUGHOUT THE
REGION...ESPECIALLY FROM THIS AFTERNOON INTO MOST OF THE DAY
SUNDAY.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
MAIN FOCUS OF THE NEXT COUPLE OF DAYS IS THE MODELS' DEPICTION OF
AN INTENSIFYING LOW THAT WILL MOVE FROM THE NORTH PACIFIC TO NEAR
OR OVER THE CENTRAL ALEUTIANS BY LATE SUNDAY AFTERNOON. MODELS
DEPICT A REGION OF STRONG STORM-FORCE WINDS JUST ABOVE THE SURFACE
WITH NEAR ZERO THETA-E LAPSE RATE FOR THE ADAK (PADK) BUFKIT
PROFILE INDICATING THE POTENTIAL FOR GOOD MOMENTUM TRANSPORT
DOWNWARD OF THOSE STRONGER WINDS ALOFT. THUS...HAVE SIGNIFICANTLY
UPPED WINDS AND WAVEHEIGHTS FOR SUNDAY INTO SUNDAY NIGHT AROUND
THE CENTRAL ALEUTIANS...AND INDICATED MAXIMUM WIND GUSTS TO 70 MPH
LATE IN THE AFTERNOON AND EARLY EVENING FOR ADAK AND ATKA. SINCE
THESE WINDS ARE STRONG BUT NOT IMPACTFUL TO THE AREA WE HAVE
DECIDED NOT TO ISSUE A WATCH FOR HIGH WINDS AT THIS TIME...BUT
THIS WILL BEAR CLOSE WATCHING.

MEANWHILE OVER THE REMAINDER OF THE BERING REGION...HIGH PRESSURE
RIDGING OVER THE REMAINING ICE PACK AND LIGHT NORTH TO NORTHEAST
WINDS WILL ALLOW FOR THE DEVELOPMENT OF AT LEAST SOME PATCHY FOG
WHICH SHOULD DRIFT SOUTH INTO THE CENTRAL AND EASTERN
BERING...ESPECIALLY AS WEAK WARM ADVECTION BEGINS BY TONIGHT
ACROSS THE AREA.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
CONDITIONS START OFF DRY ACROSS THE SOUTHCENTRAL AT THE BEGINNING
OF NEXT WEEK AS UPPER LEVEL RIDGING DOMINATES EASTERN 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 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...STORMS...175 176.
		 GALES...172 173 174 177.
FIRE WEATHER...NONE.

&&

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