Small Craft Advisory 417, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
527 AM AKDT FRI MAY 15 2015

.ANALYSIS AND UPPER LEVELS...
THE UPPER LEVEL LOW THAT BROUGHT WIDESPREAD WETTING RAINS
THROUGHOUT THE SOUTHWEST MAINLAND YESTERDAY IS NOW LOCATED JUST
SOUTH OF THE AKPENN...WITH RAIN CONTINUING FROM NORTHERN BRISTOL
BAY INTO THE KUSKOKWIM DELTA. OVER SOUTHERN BRISTOL BAY...AREAS OF
PATCHY FOG ARE DEVELOPING AS CLOUDS BEGIN TO CLEAR WITH A VERY
MOIST BOUNDARY LAYER AND LIGHT WINDS. TO THE EAST OF THIS
LOW...RIDGING CONTINUES TO HOLD FROM THE PANHANDLE INTO THE
EASTERN MAINLAND...WHICH IS KEEPING A MAJORITY OF THE RAINFALL
ASSOCIATED WITH THE AKPENN LOW CONFINED TO THE WESTERN GULF AND
THE KENAI PENINSULA...WITH ONLY ISOLATED LIGHT SHOWERS FALLING
OVER THE ANCHORAGE BOWL. OVER THE WESTERN ALEUTIANS THE NEXT LOW
TO IMPACT THE REGION IS BEGINNING TO ENTER THE PICTURE...WHICH
WILL CONTINUE ON ITS EASTERLY TRACK AS IT SLOWLY WEAKENS TODAY.
BETWEEN THESE TWO SYSTEMS...A NARROW AREA OF WEAK HIGH PRESSURE IS
SUPPLYING JUST ENOUGH STABILITY TO BRING AREAS OF FOG AND LOW
STRATUS INTO THE PRIBILOF ISLANDS.

&&

.MODEL DISCUSSION...
THE MODELS REMAIN IN VERY GOOD SYNOPTIC AGREEMENT THROUGH THIS
WEEKEND...AND HAVE ESPECIALLY COME INTO BETTER AGREEMENT WITH THE
TRACK AND INTENSITY OF THE LOW CURRENTLY ENTERING THE WESTERN
ALEUTIANS. BECAUSE OF THIS THE HIGHER RESOLUTION NAM WAS
PREFERRED...WITH ONLY MINOR FORECAST CHANGES NEEDED. THE LONE EXCEPTION
TO THIS WAS THE NEXT LOW PUSHING TOWARDS THE CENTRAL ALEUTIANS BY
EARLY NEXT WEEK. THE EC WAS PREFERRED WITH THAT FEATURE. THERE
REMAINS SOME UNCERTAINTY WITH HOW THE MODELS HANDLE INDIVIDUAL
SHORTWAVES AND RAINFALL FROM THE AKPENN LOW...BUT OVERALL FORECAST
CONFIDENCE IS STILL HIGHER THAN NORMAL.

&&

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

A WEATHER FRONT OVER THE WESTERN GULF THIS MORNING WILL MOVE NORTH
ACROSS SOUTHCENTRAL TONIGHT AND WEAKEN. THE MAJORITY OF THE RAIN
ASSOCIATED WITH THIS FEATURE WILL FALL ALONG THE COASTS AND EAST
EXPOSURES OF THE SUSITNA VALLEY. THE CROSS BARRIER FLOW WILL LIMIT
PRECIPITATION TO SPRINKLES OR SHOWERS WEST OF THE KENAI
AND CHUGACH MOUNTAINS...THOUGH THERE COULD BE A BRIEF PERIOD OF
RAIN WITH THE FRONTAL PASSAGE TONIGHT. THE COPPER RIVER BASIN
OVERALL WILL REMAIN DRY AS THE FRONT BREAKS UP BEFORE GETTING THAT
FAR. WINDY CONDITIONS WILL ACCOMPANY THE FRONT AS IT HEADS NORTH
TODAY/TONIGHT...WITH FAIRLY SIGNIFICANT GAP FLOWS...MOST NOTABLY
TURNAGAIN ARM...KNIK RIVER...AND ALONG THE COPPER RIVER. MODERATE
PRESSURE RISES ON THE BACKSIDE OF THE FRONT WILL PROLONG GAP FLOWS
INTO EARLY SAT MORNING. GENERALLY LIGHT PRESSURE GRADIENTS ON SAT
AFTERNOON WILL ALLOW FOR A RETURN TO TYPICAL DIURNAL WINDS/SEA
BREEZES UNDER INCREASING SUNSHINE.

.FIRE WEATHER...THE MAIN FIRE WEATHER THREAT AREA WILL BE THE
COPPER RIVER BASIN FOR THIS AFTERNOON AND EVENING. PRESSURE RISES
ALONG THE COAST IN ADVANCE OF APPROACHING FRONTAL SYSTEM COUPLED
WITH LOWER PRESSURES INLAND AND ABUNDANT SUNSHINE WILL CREATE VERY
GUSTY SOUTH WINDS THIS AFTERNOON AND CONTINUING INTO EARLY SAT. RH
VALUES THIS AFTERNOON AND EVENING WILL HOLD IN THE 20S. HUMIDITIES
WILL BE SLOW TO RECOVER BUT SHOULD RISE ABOVE CRITICAL VALUES LATE
IN THE EVENING AND END THE RED FLAG THREAT. RH VALUES OVER THE
COPPER RIVER WILL DROP AGAIN INTO THE 20S SAT AFTERNOON...BUT THE
LACK OF ACCOMPANYING WINDS SHOULD NEGATE ANY RED FLAG THREAT.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
A WEAK LOW AND ITS ASSOCIATED FRONT WILL MOVE THROUGH THE
REGION OVER THE NEXT 24 HOURS BRINGING WITH IT WIDESPREAD
SHOWERS AND GUSTY WINDS TO THE SOUTHWEST MAINLAND. WINDS TODAY
WILL BE THE STRONGEST ALONG THE ALASKA/ALEUTIAN RANGE AS THE
FRONT PUSHES NORTHWARD. THERE SHOULD BE ENOUGH MIXING DOWN TO THE
SURFACE AS WELL AS LOCAL TERRAIN EFFECTS TO PRODUCE GUSTS TO 45
MPH.

AS THE SYSTEM MOVES THROUGH THIS AFTERNOON...THERE IS ENOUGH
UPPER LEVEL FORCING FOR THE POSSIBILITY OF ISOLATED WET
THUNDERSTORMS FOR AREAS WEST AND NORTH OF KING SALMON THROUGH THE
KUSKOKWIM DELTA THIS AFTERNOON THROUGH EARLY THIS EVENING. THE 06Z
NAM IS INDICATING CAPE VALUES OF NEAR 500 J/KG AND SOME LI VALUES
OF -2...SO SOME ISOLATED THUNDERSTORMS SHOULD FIRE OFF THIS
AFTERNOON INTO THIS EVENING WITH THE BEST LOCATIONS ALONG BOTH
SIDES OF THE AHKLUN/KILBUCK MOUNTAINS.

AS THE FIRST FRONT MOVES THROUGH THE REGION TONIGHT...A SECOND
FRONT ASSOCIATED WITH A LOW IN THE CENTRAL ALEUTIANS WILL BEGIN
IMPACT THE COASTAL AREAS...BRINGING WITH IT A SECOND ROUND OF
RAIN AND GUSTY WINDS WITH THE HIGHEST WINDS ALONG THE COAST.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
A LOW SOUTH LOCATED SOUTH OF SHEMYA THIS MORNING AND ITS
ASSOCIATED FRONT WILL BEGIN TO IMPACT THE WESTERN ALEUTIANS THIS
MORNING AS THE LOW MOVES INTO THE CENTRAL BERING SEA THROUGH
TOMORROW NIGHT. IN THE SHORT TERM...AREAS OF FOG ARE EXPECTED OVER
THE EASTERN BERING SEA AND THE PRIBILOF ISLANDS THIS MORNING WITH
VISIBILITIES AS LOW AS ONE QUARTER MILE AT TIMES.
AS THE LOW MOVES THROUGH THE CENTRAL ALEUTIANS TONIGHT...EXPECT
STEADY RAIN ALONG THE CENTRAL ALEUTIANS TO THE ALASKA PENINSULA
WITH THE HEAVIEST TOTALS AGAIN FROM DUTCH HARBOR EASTWARD TO NEAR
SAND POINT. THIS SYSTEM DOES NOT HAVE THE DEEP MOISTURE TAP THAT
THE PREVIOUS TWO SYSTEMS DID...SO RAINFALL TOTALS SHOULD BE MORE
MODERATE. WINDS WILL INCREASE LATER TONIGHT AND INTO TOMORROW
ALONG THE EASTERN AND WESTERN PERIPHERY OF THE LOW...BUT SHOULD
REMAIN BELOW GALE FORCE.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7...SUNDAY THROUGH THURSDAY)...
ON SUNDAY...THE NORTH AMERICAN RIDGE WILL CONTINUE TO EXERT
INCREASING INFLUENCE OVER SOUTHCENTRAL ALASKA AS A LARGE TROUGH
REMAINS OVER THE BERING SEA. THERE IS INCREASING CONFIDENCE THE
RIDGE AXIS WILL SLOWLY BUILD WITH TIME...KEEPING PRECIPITATION AND
MOISTURE ACROSS SOUTHWEST ALASKA AND KODIAK ISLAND...WITH DRIER
AND WARMER WEATHER OVER THE REMAINDER OF SOUTHCENTRAL. THE ECMWF
HAS BEEN LEADING THE WAY WITH THIS SCENARIO...AND THE FORECAST
HEAVILY FAVORS THAT. THE GFS HAS BEEN SLOWLY TRENDING AWAY FROM
WIDESPREAD WET WEATHER OVER THE LAST TWO DAYS. THIS GENERAL
PATTERN WILL PERSIST THROUGH NEXT WEEK...WITH THE POTENTIAL FOR
SOME OF THE WARMEST WEATHER OF THE YEAR ACROSS SOUTHCENTRAL. THIS
SCENARIO WOULD ALSO MAKE FOR LESS GUSTY LOCAL SOUTHEAST GAPS
WINDS THAN WE HAVE SEEN OVER THE PAST FEW DAYS. THE BERING AND
ALEUTIANS WILL REMAIN STORMIER AND WETTER AS THE PACIFIC STORM
TRACK REMAINS WEST OF THE BLOCKING HIGH.

.FIRE WEATHER...DRY AND WARM WEATHER WILL CONTINUE OVER MUCH OF
SOUTHCENTRAL...PARTICULARLY OVER THE COPPER RIVER BASIN. WITH HIGH
PRESSURE BUILDING OVERHEAD...WINDS SHOULD NOT BE QUITE AS GUSTY AS
THEY HAVE BEEN THIS WEEK. BUT AT THE SAME TIME...RELATIVE
HUMIDITIES WILL CONTINUE TO FALL AND COULD CAUSE MORE FIRE WEATHER
CONCERNS. ANOTHER ELEMENT IS THE POTENTIAL FOR SOME CONVECTION
SUNDAY AFTERNOON...MAINLY IN THE EASTERN COPPER RIVER BASIN.
SEVERAL MODELS ARE SHOWING A WEAK WAVE PASSING THROUGH THE AREA
RIGHT DURING PEAK HEATING ON SUNDAY AFTERNOON. WITH TEMPERATURES
NEAR 70 DEGREES...THERE WILL BE SOME INSTABILITY...SO THIS BEARS
WATCHING.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING 130 131.
FIRE WEATHER...RED FLAG WARNING 141.

&&

SYNOPSIS AND MODEL DISCUSSION...DEK
SOUTHCENTRAL ALASKA...RMC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...RF
LONG TERM...MSO