Small Craft Advisory 365, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
424 PM AKDT SUN APR 26 2015

.ANALYSIS AND UPPER LEVELS...
THE MAIN WEATHER FEATURE OVER THE EASTERN HALF OF SOUTHERN ALASKA
IS THE LOW IN THE GULF AND THE FRONT ASSOCIATED WITH IT. SOUTHWEST
MAINLAND ALASKA IS UNDER HIGH PRESSURE WITH ANOTHER LOW IN THE
WESTERN BERING SEA THAT HAS A FRONT PUSHING EASTWARD TOWARD THE
PRIBILOF ISLANDS AND AND ACROSS THE ALEUTIANS. THE JET STREAM IS
RUNNING WEST TO EAST OVER THE ALEUTIANS AND THEN DIPPING SOUTH
AROUND THE LOW IN THE GULF BEFORE HEADING BACK TO THE NORTHEAST
OVER PARTS OF THE PANHANDLE.

&&

.MODEL DISCUSSION...
MODELS ARE HANDLING THE SYNOPTIC PATTERN VERY WELL AND ARE
ESPECIALLY GOOD IN THE GULF OF ALASKA REGION. ALL THE MODELS STILL
DISPLAY THE LOW IN THE BERING SEA GETTING ABSORBED BY A STRONGER
ONE TO THE WEST TOMORROW. THE DEVELOPMENT AND MOVEMENT OF THIS
SECOND LOW AFTER IT ABSORBS THE FIRST ONE IS THE AREA WHERE THE
NAM IS STRUGGLING MORE THAN THE OTHER MODELS. THE GFS ECMWF AND
GEM ALL SHOW THIS LOW ELONGATING WITH THE MAIN LOW NEAR DUTCH
HARBOR ON TUESDAY...WITH A TROUGH AND POSSIBLE SECONDARY LOW
TRAILING 500 TO 600 MILES NORTHWEST OF THE MAIN LOW. THE NAM DOES
NOT SEEM TO RECOGNIZE THIS STRUCTURE WHICH IS LIKELY TO OCCUR AND
IS SEEKING A MEAN POSITION BETWEEN THE LOWS. THEREFORE THE NAM WAS
NOT USED IN THIS REGION WITH THE GFS BEING THE PREFERRED SOLUTION.
ANOTHER FEATURE OF INTEREST IS AN EASTERLY WAVE DEVELOPING OVER
THE YUKON ALONG THE FRONT. THE NAM REMAINS MUCH MORE AGGRESSIVE
WITH THIS WAVE BRINGING PRECIPITATION ALL THE WAY TO THE ANCHORAGE
AREA AND SUSITNA VALLEY MONDAY. THE GFS SHOWS THIS FEATURE BUT IS
NOT TREATING IT AS STRONGLY. THE GFS WAS PREFERRED IN THIS AREA AS
WELL WITH THE SHORT WAVE MOVING INTO THE AREA BUT NOT BRINGING
MUCH PRECIPITATION EXCEPT FOR A FEW RAIN SHOWERS.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
MUCH OF THE COOK INLET REGION IS ON THE PERIPHERY OF THICKER
CLOUD COVER TO THE SOUTH AND EAST. THESE CLOUDS ARE ASSOCIATED
WITH THE LOW SPINNING WELL SOUTH IN THE GULF. THE WARMEST LOW-
LEVEL AIRMASS OF THE SPRING SO FAR HAS SURGED IN FROM CANADA AHEAD
OF THE WEAK FRONT ALONG THE GULF COAST. DESPITE THE HIGH CLOUDINESS
AND FILTERED SUNSHINE IN UPPER COOK INLET THE TEMPERATURES FOR
MANY AREAS HAVE REACHED THE WARMEST OF THE SEASON SO FAR WITH
MULTIPLE READINGS AROUND 60 FROM EAST ANCHORAGE UP TO THE MAT-SU
VALLEY. THE AIRMASS REMAINS VERY DRY...THOUGH THE GUSTY NORTHEAST
WINDS EXPECTED THIS MORNING HAVE FAILED TO DEVELOP. AS A RESULT...ALL
FIRE WEATHER (RED FLAG) WARNINGS HAVE BEEN CANCELLED.

STEADIER PERIODS OF RAIN REMAIN JUST OFFSHORE MOST OF THE COASTAL
AREAS AT THIS TIME...BUT AS MID- AND UPPER- LEVEL EASTERLY FLOW
CONTINUES ACROSS THE AREA TONIGHT THIS PRECIP SHOULD SLOWLY MAKE
PROGRESS ONSHORE. INCREASED SHOWER ACTIVITY IS ALSO EXPECTED
OVERNIGHT ACROSS THE EASTERN COPPER RIVER BASIN AS A WEAK EASTERLY
SHORTWAVE MOVES IN AND TAKES ADVANTAGE OF SOME OF THE EXISTING
INSTABILITY OF THE AIRMASS. MODEL GUIDANCE IS GENERALLY TRYING TO
SPREAD THIS SHOWER ACTIVITY ALL THE WAY TO THE MAT-SU AND ANCHORAGE
AREAS BY TOMORROW AFTERNOON...THOUGH THE CHALLENGE WITH THIS BEING
REALIZED IS GOING TO BE THE VERY DRY AIRMASS CURRENTLY IN PLACE.
CURRENT THINKING IS THAT THE FORCING WILL NOT BE STRONG ENOUGH TO
BE A BIG/WIDESPREAD RAINMAKER...THUS WILL HEDGE TO THE LOWER/DRIER
END OF THE GUIDANCE ENVELOPE WITH GENERALLY ISOLATED TO SCATTERED
SHOWER ACTIVITY ACROSS THE REGION THROUGH TUESDAY.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (TONIGHT THROUGH)...
NORTHERLY FLOW TONIGHT BECOMES LIGHT ON MONDAY AS WEAK RIDGING
SLIDES ACROSS THE SOUTHWEST FROM THE EASTERN BERING. OTHER THAN
PATCHY FOG ALONG THE COAST...RELATIVELY DRY CONDITIONS ARE EXPECTED
THROUGH MID WEEK. A FEW SHOWERS ARE POSSIBLE MONDAY NIGHT AS A
WEAK SHORT WAVE MOVES FROM THE EAST AROUND THE GULF LOW. SHOWERS
WILL BE LIMITED WITH LITTLE MOISTURE AVAILABLE.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (TODAY AND MONDAY)...
THE STORM SYSTEM ACROSS THE WESTERN BERING WEAKENS BY MONDAY AND
IS FOLLOWED BY A SECOND SYSTEM ON TUESDAY. THIS SYSTEM TAKES A
SOUTHERLY PATH ALONG THE ALEUTIAN CHAIN BRINGING BRIEF GUSTY WINDS
AND PRECIPITATION AS THE SYSTEM TRACKS QUICKLY TO THE ALASKA
PENINSULA BEFORE DIVING SOUTHWARD BY WEDNESDAY MORNING.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE 130 KNOT ZONAL JET STREAM OVER THE ALEUTIANS WILL CONTINUE TO
TRACK TO THE EAST HEADING INTO THE WEEKEND. THIS WILL BRING SEVERAL
LOWS FROM THE BERING SEA INTO THE LOWER GULF THROUGH WEDNESDAY.
THESE SYSTEMS WILL BE ACCOMPANIED BY SHOWERS IN THE GULF AND ALONG
THE COASTAL AREAS. BY THURSDAY AN UPPER LEVEL RIDGE WILL BUILD
INTO THE WESTERN GULF. THIS RIDGE WILL BECOME AMPLIFIED WITH A
SOUTHEAST TO NORTHWEST PLACEMENT BY SATURDAY. THIS SYNOPTIC
FEATURE WILL BRING WARMER TEMPERATURES AND DRIER CONDITIONS TO
THE SOUTHCENTRAL REGION. THIS WILL INCREASE THE CHANCES FOR
AFTERNOON TO EVENING SHOWERY ACTIVITY FOR THE INLAND AREAS.

THE BERING SEA AND THE ALEUTIAN CHAIN WILL HAVE A LOW OVER THE
WESTERN ALEUTIANS TUESDAY MORNING BEFORE TRACKING TO THE EASTERN
ALEUTIANS BY LATE TUESDAY NIGHT. THIS SYSTEM WILL BRING RAIN OUT
AHEAD OF THIS SYSTEM AND RAIN SHOWERS ON THE BACKSIDE OF THE LOW
AS IT MOVES ALONG THE CHAIN. BY WEDNESDAY ANOTHER WEAK LOW FORMS
IN THE WESTERN BERING SEA BEFORE DIMINISHING INTO A TROUGH OVER
THE REGION THROUGH FRIDAY. THEN ANOTHER NORTH PACIFIC APPROACHES
THE WESTERN ALEUTIANS BY SATURDAY. THIS WILL CONTINUE TO BRING
WARMER TEMPERATURES AND RAIN SHOWERS FOR THE BERING SEA AND THE
ALEUTIAN CHAIN HEADING INTO THE WEEKEND. THE MODELS WERE
STRUGGLING WITH THE TIMING AND PLACEMENT OF THESE LOWS AS THEY
TRACK THROUGH THE BERING SEA. THIS RESULTED IN WPC USING A BLEND
OF THE ECMWF/GFS ENSEMBLE MEANS THROUGH THE NEXT SEVERAL DAYS.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING 132 177 178.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...AD
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KH
LONG TERM...PD