Small Craft Advisory 595, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE ANCHORAGE AK
118 PM AKDT THU AUG 7 2014

.ANALYSIS AND UPPER LEVELS...A LARGE VERTICALLY STACKED LOW IS
DRIFTING WESTWARD OVER THE CENTRAL BERING SEA WHILE A STRONG
SUBTROPICAL JET ALONG THE ALEUTIANS CONTINUES TO DRIVE THE
OCCLUDED FRONT EASTWARD TOWARD THE GULF OF ALASKA. THE PORTION
OF THE FRONT OVER THE EASTERN BERING AND SOUTHWEST ALASKA IS
BEGINNING TO ELONGATE...ALTHOUGH RADAR SHOWS A SOLID BAND OF
LIGHT TO MODERATE RAIN OVER THE KUSKOKWIM DELTA AND BRISTOL BAY.
THERE ARE STRONG EAST TO SOUTHEAST WINDS OUT AHEAD OF THE FRONT
WHICH OFTEN INDICATES THE POTENTIAL FOR DOWNSLOPING ON THE WEST
SIDE OF THE ALEUTIAN AND ALASKA RANGES. FURTHER INVESTIGATION
SHOWS THE DEPTH OF SOUTHEASTERLIES IS RELATIVELY SHALLOW AND WINDS
VEER TO SOUTHERLY AS YOU GO UP IN HEIGHT FROM 850 MB TO 500 MB.
THUS...THERE IS LIKELY SOME DOWNSLOPE DRYING OCCURRING IN THE LOW
LEVELS BUT RAIN IS FALLING ALOFT FROM FAIRLY HIGH CEILINGS. OUT
AHEAD OF THE FRONT A SERIES OF WEAK UPPER WAVES ARE PRODUCING
SHOWERS FROM PRINCE WILLIAM SOUND ACROSS THE KENAI PENINSULA INTO
NORTHERN COOK INLET.

&&

.MODEL DISCUSSION...MODELS ARE GENERALLY IN GOOD AGREEMENT. THE
LARGEST DIFFERENCES ARE CENTERED SOUTH OF THE ALASKA PENINSULA
AND KODIAK ISLAND AS THE LOW OVER THE BERING SEA CROSSES THE
ALASKA PENINSULA AND MERGES WITH A NEWLY FORMING LOW ON THE EAST
SIDE OF THE DIGGING UPPER TROUGH. THE GFS IS MOST AGGRESSIVE WITH
DEVELOPMENT OF THIS NEW LOW (AS WELL AS FARTHER EAST THAN ANY
OTHER SOLUTION)...BUT GOOD UPPER SUPPORT LENDS SOME CREDENCE TO
THIS SOLUTION. NOT READY TO BUY COMPLETELY INTO IT YET...BUT WILL
TREND TOWARD IT. REGARDLESS OF LOW STRENGTH ALL MODELS ARE
STRONGER WITH THE SECOND OCCLUDED FRONT SPREADING ACROSS THE GULF
SATURDAY AND REINFORCING THE BARRIER JET ALONG THE NORTH GULF
COAST. ANOTHER FORECAST CHALLENGE IS DECIDING HOW FAR NORTHWARD
THE FRONTS WILL PUSH. UPPER LEVEL STEERING FLOW IS SOUTHERLY
BEHIND THE FIRST FRONT BUT FAIRLY WEAK...SO EXPECT SOME OF THE
STRONGEST WINDS TO MAKE IT INTO SOUTHERN PRINCE WILLIAM
SOUND...BUT NOT PUSH ALL THE WAY ONSHORE. UPPER FLOW IS
SOUTHEASTERLY BEHIND THE SECOND FRONT SO THINK IT WILL LIKELY
STALL A LITTLE BIT FURTHER SOUTH. THE HIGHER RESOLUTION MODELS
(NAM/GEM-REG) HAVE A MUCH BETTER DEPICTION OF STRONGER WINDS
MAKING IT INTO PRINCE WILLIAM SOUND. LASTLY...MODELS ALL DIFFER
WITH STRENGTH/LOCATION OF THE MANY WAVES EMBEDDED IN THE UPPER
LEVEL FLOW. WITH STRONGER DOWNSLOPING EXPECTED OVER SOUTHCENTRAL
THAN OVER SOUTHWEST ALASKA THESE WAVES WOULD BE THE ONE THING THAT
COULD DISTURB THE FLOW (OR OVERCOME THE DOWNSLOPING) AND PRODUCE
RAIN ON THE LEE SIDE OF THE MOUNTAINS. BECAUSE OF THE MODEL
DIFFERENCES MENTIONED ABOVE ALONG WITH THE CHALLENGE ASSOCIATED
WITH FORECASTING SMALLER SCALE FEATURES FORECAST CONFIDENCE IS
AVERAGE TO SLIGHTLY BELOW AVERAGE OVER THE NEXT FEW DAYS.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...THE CHARACTER OF THE STORM SYSTEMS IS
BEGINNING TO CHANGE AS WE HEAD THROUGH EARLY AUGUST...WITH
A STRONGER JET STREAM LEADING TO MORE WELL DEFINED STORM SYSTEMS
AND DEEPER MOISTURE. THE GULF COASTAL REGION WILL CERTAINLY TAKE
THE BRUNT OF THE WEATHER THE NEXT COUPLE OF DAYS WITH PERIODS OF
STRONG WINDS AND MODERATE RAIN. WITH A SERIES OF FEATURES MOVING
THROUGH COMBINED WITH SOMEWHAT VARIABLE LOW LEVEL FLOW (LOCATION
OF HEAVIEST RAIN WILL CHANGE WITH TIME) FLOODING POTENTIAL LOOKS
TO BE LOW.

IT LOOKS LIKE A FAIRLY CLASSIC EXAMPLE OF DOWNSLOPE DRYING IN THE
LEE OF THE CHUGACH AND KENAI MOUNTAINS...BUT THE POTENTIAL FOR
STRONGER UPPER WAVES TO MOVE OVERHEAD COULD LEAD TO A BRIEF PERIOD
OF LIGHT RAIN. RIGHT NOW THERE SEEMS TO BE SOME MODEL AGREEMENT IN
ONE OF THESE UPPER WAVE MOVING THROUGH FRIDAY AFTERNOON AND
EVENING. THE UPPER LOW WILL SET UP SHOP IN THE VICINITY OF KODIAK
ISLAND FOR THE WEEKEND...SO EXPECT CONTINUED COOL AND WET
CONDITIONS ALONG THE GULF COAST AS WAVES CONTINUE TO ROTATE
AROUND THE UPPER CENTER. INLAND AREAS WILL DEFINITELY BE
DRIER...BUT CLOUD COVER WILL BE EXTENSIVE AND ONCE DOWNSLOPE WINDS
WEAKEN AN INCREASED CHANCE OF SHOWERS.

SOUTHWEST ALASKA...THE FRONT CURRENTLY OVER SOUTHWEST ALASKA WILL
CONTINUE TO ELONGATE AND WEAKEN AS IT MOVES INLAND...SO EXPECT
MUCH LOWER QPF OVER THE KUSKOKWIM VALLEY. A SERIES OF UPPER LEVEL
WAVES WILL CONTINUE TO TRANSIT THE REGION THROUGH FRIDAY NIGHT
PRODUCING MORE SHOWERY TYPE PRECIPITATION. WITH ABUNDANT LOW LEVEL
MOISTURE AND FAIRLY LIGHT SURFACE WINDS ALONG THE COAST...EXPECT
LOW CLOUDS TO BECOME WIDESPREAD TONIGHT ALONG WITH SOME AREAS OF
FOG. AS THE BERING LOW SETS UP SHOP SOUTH OF KODIAK ISLAND
SATURDAY LOW LEVEL WINDS WILL BACK TO OFFSHORE...PROVIDING SOME
MARGINAL IMPROVEMENT IN CLOUD CEILINGS AND VISIBILITIES. THE
THREAT FOR SHOWERS WILL PERSIST THROUGH THE WEEKEND AS UPPER WAVES
MOVE IN FROM THE EAST. FORECAST CONFIDENCE IN LOCATION AND TIMING
OF INDIVIDUAL WAVES IS LOW...MAKING FOR A CHALLENGING
PRECIPITATION FORECAST.

BERING SEA/ALEUTIANS...EXPECT IMPROVING CONDITIONS AS THE BERING
LOW TRACKS TO SOUTH OF KODIAK ISLAND SATURDAY AND A SHORT-WAVE
RIDGE BUILDS IN FROM THE WEST. UPPER LEVEL FLOW WILL REMAIN
PROGRESSIVE HOWEVER...WITH ANOTHER TROUGH MOVING OUT OF ASIA INTO
THE WESTERN BERING OVER THE WEEKEND.

&&

.LONG TERM FORECAST...

INITIALLY THERE WILL BE AN OLD COMPLEX UPPER-LOW MEANDERING IN THE
GULF EARLY NEXT WEEK BUT THE INCREASINGLY DOMINANT FEATURE IN THE
AOR WILL BE THE BERING SEA/ALEUTIAN SYSTEM SWEEPING EASTWARD.
MODELS HAVE REASONABLY GOOD AGREEMENT ON A DEEPER AND SLOWER
MOVING SYSTEM ON MON COMPARED TO PREVIOUS DAYS AS IT TAPS INTO
STRONG JET STREAM ENERGY ALOFT. THIS FEATURE EVENTUALLY ABSORBS
THE COMPLEX LOW IN THE GULF. THERE IS THE TYPICAL INCREASED MODEL
SOLUTION DIVERGENCE BY MID WEEK REGARDING HOW FAR EAST THE PARENT
ALEUTIAN UPPER-LOW WILL TRACK...WITH THE GFS NOSING IT TOWARDS
KODIAK ISLAND AND THE ECMWF HANGING IT BACK NEAR THE PRIBILOF
ISLANDS NEXT WED. THE SENSIBLE WEATHER IMPACTS FROM A GFS SOLUTION
WOULD BE STRONGER FRONTS SWEEPING THROUGH THE GULF THE MIDDLE PART
OF NEXT WEEK WITH HEAVIER QPF. HAVE TRENDED TO AN ENSEMBLE LEANING
WPC SOLUTION FOR MID NEXT WEEK WHICH TEMPERS THE DIFFERENCES IN
POSITIONS AND ORIENTATIONS OF THE MAIN FEATURES. THE BRUNT OF
PRECIPITATION WOULD LIKELY BE ACROSS KODIAK ISLAND TO PRINCE
WILLIAM SOUND AS EAST TO SOUTHEAST ONSHORE FLOW PREVAILS. THE
REMAINDER OF THE SOUTHERN MAINLAND LOOKS TO REMAIN MORE ON THE
CLOUDY SIDE WITH AT LEAST SOME CHANCES FOR RAIN AS SPOKES OF
MOISTURE AND ENERGY PERIODICALLY MOVE INLAND FROM THE GULF.
FURTHER WEST BEHIND THE ALEUTIAN SYSTEM...EXPECTING CONDITIONS TO
BE SHOWERY WITH DIMINISHING WINDS AS THE BRUNT OF THE ENERGY
PROGRESSES EASTWARD.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING 119 125.
FIRE WEATHER...NONE.

&&

SEB/JAM AUG 14