Small Craft Advisory 526, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
457 AM AKDT FRI JUN 26 2015

.ANALYSIS AND UPPER LEVELS...

THE BEGINNING OF A PATTERN CHANGE IN UPON ALASKA AS TWO SYSTEMS
(ONE THAT ORIGINATED OVER THE ARCTIC AND ANOTHER IN THE GULF OF
ALASKA) BEGIN TO INTERACT AND USHER IN A NEW AIR MASS. THE FIRST
SYSTEM WE TALK ABOUT THIS MORNING THE ARCTIC TROUGH THAT IS
DESCENDING UPON THE WEST COAST OF ALASKA. THIS TROUGH IS THE MAIN
DRIVER BEHIND THE PATTERN CHANGE BECAUSE IT TOOK A FEATURE OF THIS
MAGNITUDE TO FINALLY FLATTEN OUT AND SHUNT THE RIDGE THAT HAD BEEN
SO PERSISTENT OVER MUCH OF ALASKA EASTWARD. WHILE IT APPEARS NOT
ALL OF ALASKA WILL FEEL THE FULL EFFECTS OF THE PATTERN
CHANGE...IT LOOKS TO USHER IN SOME MUCH NEEDED COOLER TEMPERATURES
AND MOISTURE TO HELP COMBAT THE ONGOING FIRE WEATHER CONCERNS
ACROSS ALASKA. THIS TROUGH HAS A TRUE SURFACE COLD FRONT
ASSOCIATED WITH IT THAT IS CURRENTLY PUSHING ACROSS THE KUSKOKWIM
DELTA (AS SEEN BY MULTIPLE OBSERVATION SITES). THIS WILL BRING
COOLER TEMPERATURES AND HIGHER RH VALUES OVER THE NEXT SEVERAL
DAYS WHICH WILL HELP KEEP FIRE WEATHER CONCERNS IN CHECK. THE
ARCTIC TROUGH HAS FLATTENED UP THE UPPER LEVELS AND A BROAD UPPER
LEVEL TROUGH IS MOVING OVER SOUTHWEST ALASKA...WHICH HAS AIDED IN
A DAILY WEAKENING OF THE THERMAL TROUGH. WITH THE THERMAL TROUGH
WEAKENING...CONVECTION HAS BEEN LESS AND LESS EACH AFTERNOON WHICH
HAS HELPED LOWER ADDITIONAL WILDFIRE STARTS DUE TO LIGHTNING.

THE OTHER MAIN FEATURE ASSOCIATED WITH THE PATTERN SHIFT IS LARGE
UPPER LEVEL LOW IN THE SOUTHERN GULF OF ALASKA THAT HAS BEGUN TO
INTERACT WITH THE ARCTIC TROUGH DIVING SOUTH. THE UPPER LEVEL LOW
HAS SITUATED ON TOP OF THE SURFACE BASED LOW IN THE GULF OF ALASKA
AND SLOWLY PUSHING NORTH THIS MORNING WHILE DRIVING A WEAK UPPER
LEVEL WAVE ALONG THE NORTHERN GULF COAST. THIS LOW WILL CONTINUE
TO INTRODUCE CLOUDS AND MOISTURE ACROSS SOUTHCENTRAL ALASKA WHICH
WILL KEEP TEMPERATURES COOLER THAN THE PAST FEW DAYS AS WELL AS
BRING SOME MUCH NEEDED RAINFALL OVER THE NEXT SEVERAL DAYS TO
AREAS IMPACTED BY WILDFIRES.

AND OF COURSE...THE BERING SEA IS ENCOMPASSED BY A LARGE LONGWAVE
RIDGE (VERY TYPICAL THIS TIME OF THE YEAR) AND HAS BROUGHT PLENTY
OF LOW STRATUS AND FOG TO THE BERING SEA AND ALEUTIAN ISLANDS.
WITH SOME NORTHERLY FLOW UPSLOPING ALONG THE MOUNTAINS TERRAIN OF
THE ALEUTIANS...SOME SCATTERED RAIN SHOWERS AND LIGHT DRIZZLE HAS
BEEN OBSERVED INTERMITTENTLY.

&&

.MODEL DISCUSSION...

MODELS CONTINUE TO HANDLE THE PATTERN CHANGE VERY WELL AS THE
MODELS HAVE SOME LARGE SCALE FEATURES TO LATCH ONTO. THEY HAVE
ALSO BEEN DOING A SURPRISINGLY GOOD JOB HANDING THE STRENGTH AND
PLACEMENT OF THE THERMAL TROUGH AS IT RECEDES EASTWARD AND WEAKENS.
OF COURSE THE SHORTWAVES IMPACTING THE NORTHERN GULF COAST OF
ALASKA ARE MODELED SLIGHTLY DIFFERENT BY ALL DETERMINISTIC
GUIDANCE...HOWEVER THEY ALL PAINT A SIMILAR PICTURE WITH RAINFALL
ACROSS THE NORTHERN GULF COAST AND TRYING TO SPREAD INLAND THIS
AFTERNOON. IT WILL BE INTERESTING TO SEE HOW THE ARCTIC TROUGH AND
THE LOW IN THE GULF OF ALASKA PHASE ON SATURDAY AS A DEFORMATION
ZONE APPEARS TO DEVELOP BETWEEN THE TWO SYSTEMS AS THEY BEGIN TO
INTERACT. THIS WILL MAINLY IMPACT SOUTHWEST ALASKA BUT DUE TO SOME
LARGE ONGOING FIRES IT COULD REALLY BE SOME MUCH NEEDED RELIEF.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
RAIN OUT AHEAD OF AN UPPER LEVEL WAVE WILL PUSH ONSHORE THIS MORNING.
THE HEAVIEST QPF WILL BE AROUND PRINCE WILLIAM SOUND...BUT WITH
WEAK CROSS BARRIER FLOW ALSO EXPECT STEADY LIGHT RAIN TO MOVE OVER
THE COASTAL MOUNTAINS TO THE WESTERN KENAI...ANCHORAGE...AS WELL
AS PORTIONS OF THE MAT-SU AND COPPER BASIN. AS THE MOISTURE
CONTINUES TO INTERIOR SOUTHCENTRAL THIS AFTERNOON PRECIP FARTHER
SOUTH WILL DIMINISH AND BECOME MORE SHOWERY. THERE MAY EVEN BE
A FEW BREAKS OF SUN THIS AFTERNOON...BUT OVERALL IT WILL BE A
NOTABLY COOLER DAY ACROSS THE ENTIRE REGION. THE SURFACE RIDGE
BUILDING IN BEHIND THE UPPER WAVE LOOKS STRONGER THAN THE PAST
COUPLE DAYS. THUS EXPECT STRONGER WINDS ACROSS MUCH OF THE REGION
COMPARED TO THE LAST COUPLE DAYS...ESPECIALLY THROUGH MOUNTAIN
GAPS AND ACROSS THE COPPER BASIN.

AN UPPER LEVEL LOW OVER THE PACIFIC WILL LIFT NORTHWARD INTO THE
WESTERN GULF SATURDAY BRINGING ANOTHER ROUND OF RAIN TO THE GULF
COAST AND KODIAK ISLAND. COOL TEMPERATURES ALOFT COMBINED WITH LOW
LEVEL RIDGING OVER THE REST OF SOUTHCENTRAL ALASKA WILL LEAD TO
DECREASING STABILITY AND A RETURN TO A MORE SHOWERY REGIME. THERE
MAY EVEN BE A FEW THUNDERSTORMS ESPECIALLY OVER THE MOUNTAINS.
WINDS WILL AGAIN KICK UP DURING THE AFTERNOON AND EVENING AS THE
SURFACE RIDGE BUILDS OUT AHEAD OF THE GULF LOW.

&&

.FIRE WEATHER...
COOLER AND MOISTER AIR MOVING IN FROM THE GULF WILL MAKE IT ALL
THE WAY TO THE ALASKA RANGE BY LATER TODAY. THUS...DO NOT EXPECT
ANY THUNDERSTORMS...THOUGH THERE IS THE POSSIBILITY OF A FEW
ISOLATED STRIKES RIGHT ALONG THE ALASKA RANGE. MUCH OF THE AREA
WILL SEE A PERIOD OF LIGHT RAIN TODAY...BUT WETTING RAINS WILL BE
CONFINED MAINLY TO THE GULF COASTAL ZONE AND OVER THE MOUNTAINS.
WINDS WILL BE STRONGER AND MORE WIDESPREAD THIS AFTERNOON INTO
EVENING...ESPECIALLY ACROSS THE COPPER RIVER BASIN. SATURDAY WILL
SEE A RETURN TO A BIT OF SUNSHINE WITH MARGINALLY WARMER AND DRIER
CONDITIONS. DIURNAL CONVECTION WILL PROVIDE THE BEST CHANCE OF
RAIN...BUT WILL BE FOCUSED PRIMARILY ALONG AND NEAR THE MOUNTAINS.
WINDS WILL KICK UP AGAIN SATURDAY AFTERNOON AND EVENING THOUGH IT
DOES NOT APPEAR THEY WILL BE AS STRONG AS TODAY.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
THE MAIN FORECAST CONCERN THROUGH THE SHORT TERM WILL CONTINUE TO
BE THE LOCATION OF THUNDERSTORM DEVELOPMENT OVER SOUTHWEST ALASKA.
THE BEST DYNAMICS TODAY LOOK TO BE ALONG THE ALASKA RANGE AND THE
AHKLUN MOUNTAINS NORTHEASTWARD THROUGH THE MIDDLE KUSKOKWIM
VALLEY AS THE UPPER TROUGH APPROACHES THE AREA. AS THE UPPER
TROUGH STALLS ON SATURDAY...THE AREA FOR POTENTIAL THUNDERSTORM
DEVELOPMENT WILL EXPAND TO MOST OF THE REGION EAST OF THE
KILBUCK/AHKLUN MOUNTAINS...HOWEVER THUNDERSTORM COVERAGE IS
EXPECTED TO REMAIN ISOLATED.

THE SECOND WEATHER CONCERN AGAIN IS WIDESPREAD SMOKE FROM THE
NUMEROUS FIRES IN THE REGION...ESPECIALLY OVER THE LOWER/MIDDLE
KUSKOKWIM VALLEY. MORNING INVERSIONS WILL CONTINUE TO ALLOW
SMOKE TO BECOME LOCALLY DENSE IN SOME AREAS...ESPECIALLY VALLEY
LOCATIONS. CONDITIONS WILL IMPROVE SOMEWHAT IN THE AFTERNOON TODAY
AS THE INVERSIONS LIFT BEFORE DETERIORATING AGAIN THIS EVENING.
ON SATURDAY...CONDITIONS SHOULD IMPROVE AREA WIDE AS THE COOLER
AND MORE MOIST AIR MASS ENTERS THE REGION.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
WINDS WILL BEGIN TO INCREASE TODAY TO NEAR GALE FORCE OVER THE
EASTERN HALF OF THE BERING SEA AS THE LOW PUSHES SOUTH INTO THE
ALASKA PENINSULA. EXPECT RAIN SHOWERS TO INCREASE FROM UNALASKA
EASTWARD AS THIS LOW MIGRATES SOUTHWARD. RAIN CHANCES WILL
INCREASE ALONG THE WESTERN ALEUTIANS ON SATURDAY AS THE FRONT
ASSOCIATED WITH THE WESTERN LOW BEGINS TO IMPACT THE REGION.
PATCHY FOG AND STATUS ARE EXPECTED TO CONTINUE OVER MUCH OF THE
BERING SEA.

&&

.FIRE WEATHER...
A SHIFT TO A COOLER AND WETTER PATTERN IS UNDERWAY FOR SOUTHWEST
ALASKA AS A FRONT WILL ENTER THE REGION TODAY AND STALL OVER THE
REGION WHILE AN AREA OF LOW PRESSURE REMAINS SOUTH OF THE ALASKA
PENINSULA. ISOLATED WET THUNDERSTORMS ARE EXPECTED AGAIN TODAY
OVER THE MIDDLE KUSKOKWIM VALLEY AND ALONG THE AHKLUN MOUNTAINS.
THE AREA FOR THUNDERSTORM DEVELOPMENT ON SATURDAY WILL BE MORE
WIDESPREAD WITH DEVELOPMENT POSSIBLE OVER MUCH OF THE REGION EAST
OF THE KILBUCK/AHKLUN MOUNTAINS...HOWEVER OVERALL THUNDERSTORM
COVERAGE IS EXPECTED TO BE ISOLATED. MINIMUM RH VALUES TODAY WILL
IN THE MID TO UPPER 30S ALONG AND WEST OF THE KILBUCK MOUNTAINS
AND LONG THE KUSKOKWIM MOUNTAINS. RH RECOVERIES OVERNIGHT ARE
EXPECTED TO BE GOOD. RH VALUES ARE EXPECTED TO BE HIGHER ON
SATURDAY WITH WIDESPREAD PRECIPITATION OVER THE REGION.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...

LARGE AND EXPANSIVE UPPER LOW CENTERED SOUTH OF THE AKPEN THIS
WEEKEND WILL BE ACCOMPANIED BY A DIGGING TROUGH FROM THE NORTH
DROPPING SOUTH INTO THE BERING SEA EARLY TO MIDDLE NEXT WEEK. AS
THIS NEW LOW MOVES SOUTH AND EXPANDS...THE AKPEN LOW WILL MEANDER
AND SLOWLY DISSIPATE NEAR OR OVER SOUTHERN ALASKA WHILE AN UPPER
RIDGE BUILDS ACROSS THE PARTS OF THE STATE BY THE END OF NEXT
WEEK.

THE MAIN IMPACTS WILL BE A CONTINUED CLOUDIER AND COOLER WEATHER
PATTERN FOR MUCH OF THE SOUTHERN MAINLAND THROUGH MUCH OF NEXT
WEEK...WHICH SHOULD AID IN FIREFIGHTING EFFORTS ACROSS THE
ANCHORAGE AREA OF RESPONSIBILITY. PERIODS OF RAIN ALONG THE
COAST...WITH ISOLATED TO NUMEROUS SHOWER ACTIVITY INLAND...WILL
BE PREVALENT FOR MUCH OF THE PERIOD.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...MMC
SOUTHCENTRAL ALASKA...SB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...RF
LONG TERM...CC