Small Craft Advisory 394, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
200 PM AKDT TUE MAY 7 2013

.ANALYSIS AND UPPER LEVELS...
THE MAIN FEATURES ACROSS THE AOR ARE A COMPLEX PACIFIC LOW SOUTH OF
THE EASTERN CHAIN/AKPEN...FLANKED BY AN AMPLIFYING UPPER-RIDGE IN THE
SOUTHERN GULF OF AK AND A RIDGE IN THE NW PACIFIC. THE COMPLEX SYSTEM
FEATURES A STATIONARY SURFACE LOW AROUND 400 MILES SOUTHEAST OF ATKA
WHICH IS FILLING...AND A DEVELOPING SURFACE LOW AROUND 700 MILES
SOUTH OF SAND POINT WHICH IS MOVING NORTH. PROXIMITY TO THE DYING LOW
SOUTHEAST OF ATKA IS ALLOWING RAIN TO PERSIST OVER THE EASTERN AND
CENTRAL CHAIN WITH BRISK EAST TO NORTHEAST WINDS. THE SOUTHERN
MAINLAND IS CHARACTERIZED BY NEUTRAL/FLAT FLOW ALOFT WITH A SERIES OF
VORTICITY SHEAR LOBES DRAGGING MID AND HIGH CLOUDS ACROSS THE REGION.
THERE IS A SHORTWAVE TROUGH ROTATING PAST GAMBELL ISLAND TOWARDS SW
AK...BUT IT IS MOVING INTO A VERY DRY AIRMASS COURTESY OF HIGH
PRESSURE STAMPED OVER THE KUSKOKWIM VALLEY. THERE ARE SOME WEAK RADAR
ECHOES OVER BRISTOL BAY BUT WITH THE MID AND LOW LAYERS OF THE
ATMOSPHERE FAIRLY DRY...THIS MAY BE VIRGA. ACROSS SOUTHCENTRAL...SOME
SPOTTY DIURNAL SHOWERS/SPRINKLES EXIST NEAR THE CHUGACH/TALKEETNA
MOUNTAINS...WHILE THE GULF IS LACKING ANY SUBSTANTIAL PRECIPITATION
ASIDE FROM A FEW SPRINKLES NEAR THE SOUTHERN COAST OF KODIAK ISLAND
IN WEAK ONSHORE FLOW.

.MODEL DISCUSSION...
MODELS SATISFACTORILY CAPTURE THE MAIN WEATHER PICTURE AND ASSOCIATED
TRENDS. THE SURFACE LOW DEVELOPING SOUTH OF SAND POINT THIS EVENING
TRACKS TO AROUND 450 MILES SOUTHEAST OF UNALASKA AT 995 MB WED
AFTERNOON THEN PINWHEELS TO 500 MILES SOUTH OF UNALASKA AT 1001 MB ON
THU. THIS FEATURE THEN DRIFTS SOUTH TOWARDS THE PARENT UPPER-LOW ON
FRI WHILE NEW DEVELOPMENT ALONG THE SOUTHERN FLANK OF THE OVERALL
COMPLEX/TROUGH WRAPS YET ANOTHER LOW UP TO AROUND 500 MILES SOUTHEAST
OF KODIAK ISLAND ON FRI. THERE ARE SOME POSITION AND ORIENTATION
DIFFERENCES OF VARIOUS LOBES OF ENERGY INTERACTING WITH EACH OTHER IN
THIS COMPLEX PATTERN...BUT THE SPIRIT OF THE DEPICTIONS ARE VERY
SIMILAR AMONG THE MODELS. WITH THE SURFACE FEATURES NOT DRIFTING MUCH
FURTHER NORTH THAN 50N LATITUDE...THESE DIFFERENCES ARE NOT TOO
SIGNIFICANT. MEANWHILE...THE UPPER-RIDGE OVER THE NW PACIFIC SHIFTS
EAST AHEAD OF ANOTHER POWERFUL LOW PUSHING OFF NORTHERN JAPAN. THE
UPPER RIDGE AXIS MOVES FROM ROUGHLY 170E LONGITUDE TO NEAR ADAK ON
FRI. FURTHER EAST...THE UPPER RIDGE IN THE GULF BUILDS NORTH AND
EAST...WITH THE AMPLIFIED NEGATIVELY TILTED AXIS ALIGNED ROUGHLY FROM
KETCHIKAN TO THE KUSKOKWIM VALLEY EARLY THU AND HANGING STEADY INTO
FRI. RESPECTABLE WARMING OF THE ATMOSPHERE ESPECIALLY AT LOWER LEVELS
HAS BEEN CONSISTENT IN THE MODELS GIVING FAIRLY GOOD CONFIDENCE TO
TEMPERATURE FORECASTS.

.SHORT TERM FORECAST...
SOUTHCENTRAL/GULF...
MID AND HIGH CLOUDS WITH THE EMBEDDED SHEAR LOBES ALOFT WILL LARGELY
HAVE MOVED THROUGH THE SOUTHERN MAINLAND BY WED ALLOWING FOR MORE
SUNSHINE. EXPECT TYPICAL DIURNAL SEABREEZES NEAR THE COASTS AND
SHOWERS NEAR MOUNTAINS. SHOWER COVERAGE SHOULD BE LESS EACH DAY
BECAUSE EVEN AS TEMPERATURES WARM NEAR GROUND LEVEL...THERE SHOULD BE
NEARLY COMPARABLE WARMING ALOFT ALONG WITH ADDED SUBSIDENCE FROM THE
UPPER-RIDGE. ACROSS THE GULF...CONDITIONS SHOULD CONTINUE TO REMAIN
BENIGN WITH HIGH PRESSURE DOMINANT. THE FAR SW GULF WILL SEE A
SLIGHTLY SQUEEZED PRESSURE GRADIENT AND AN UPTICK IN WINDS IN THE
COMING DAYS DUE TO PERIPHERAL EFFECTS FROM THE COMPLEX PACIFIC LOW.
ORGANIZED AREAS OF PRECIPITATION ARE NOT EXPECTED...THOUGH SOME
PASSING SPRINKLES OR PERIODS OF VERY LIGHT RAIN COULD BRUSH KODIAK
ISLAND IN ONSHORE FLOW AND WEAK DYNAMIC LIFT. A REINFORCING SHOT OF
MID AND HIGH CLOUDS FROM THE COMPLEX LOW TO REACH SOUTHCENTRAL ON
THU...BUT THERE SHOULD STILL BE SUNNY BREAKS AND SEASONABLY WARM
TEMPERATURES.

SOUTHWEST/AKPEN...
A BAND OF NARROW BUT RATHER DENSE FOG DEVELOPED TUE OVER INLAND AREAS
OF THE KUSKOKWIM DELTA AS VERY STRONG SUBSIDENCE TRAPPED ALL OF THE
AVAILABLE LOW LVL MOISTURE NEAR BETHEL. FLOW HAS NOT GONE OFF-SHORE
AT ALL (STILL ONSHORE). THE LONGER THIS TAKES TO DEVELOP...THE LONGER
THE WINDOW FOR ANOTHER POTENTIAL BAND TO DEVELOP OVERNIGHT
TONIGHT...BUT ONCE IT DOES...THE WINDS SHOULD QUICKLY SCOUR OUT FOG
AND EVEN MAY LEAD TO A FEW SUNNY BREAKS FROM THE LOW CLOUDS ALONG THE
KUSKOKWIM DELTA COAST. FURTHER INLAND...HIGH PRESSURE SUPPORTS AMPLE
SUNSHINE OVER THE KUSKOKWIM VALLEY AND INTERIOR BRISTOL BAY WHICH
LOOKS TO CONTINUE IN EARNEST MID-WEEK. SOUTHERN REACHES OF BRISTOL
BAY DOWN THROUGH THE AKPEN SHOULD BEAR THE BRUNT OF CLOUDS...WITH
HIGHEST RAIN CHANCES ALONG THE AKPEN. WINDS WILL TREND TOWARDS GALES
IN A STRONGER PRESSURE GRADIENT ON THE PACIFIC SIDE OF THE AKPEN.

BERING SEA/ALEUTIANS...
BENIGN WEATHER PERSISTS FOR THE MUCH OF THE BERING SEA AND WESTERN
ALEUTIAN CHAIN UNDER THE INFLUENCE OF SLOW MOVING HIGH PRESSURE. THE
STRONGEST WINDS WILL BE OVER THE CENTRAL TO EASTERN CHAIN ASSOCIATED
WITH THE COMPLEX PACIFIC LOW. THE PRESSURE GRADIENT DOES WEAKEN
SLOWLY WITH TIME AS THE OVERALL COMPLEX RETREATS EAST.

.LONG TERM FORECAST...
THE COMPLEX PACIFIC LOW MOVES FROM ROUGHLY 160W LONGITUDE SOUTH OF
THE EASTERN CHAIN TONIGHT TO 145W LONGITUDE SOUTH OF THE GULF OF AK
ON SAT. MODELS STILL SHOW A CHUNK OF ENERGY DIPPING SOUTH OUT OF
EASTERN SIBERIA THROUGH WEST AND SW AK DURING THE WEEKEND AND EARLY
NEXT WEEK. THERE IS CONSIDERABLE UNCERTAINTY IN THE DETAILS...BUT A
TREND TO COOLER AND WETTER STILL SEEMS APPROPRIATE FOR THE SOUTHERN
MAINLAND. OUT WEST...THE RESIDUAL ENERGY FROM THE LOW PUSHING OFF
NORTHERN JAPAN WORKS TOWARDS THE WESTERN CHAIN...THOUGH WITH THE CORE
OF THE JET STREAM NEAR 40N...THE STEERING TRACK SHOULD BE SOUTH OF
THE CHAIN. THE UPPER-RIDGE DOWNSTREAM OF THIS SYSTEM GETS SHOVED INTO
THE CENTRAL BERING...LEADING TO DIMINISHING WINDS OVER THE EASTERN
HALF OF THE CHAIN. JUST THE OPPOSITE WILL OCCUR OVER THE WESTERN HALF
OF THE CHAIN IN A STRENGTHENING PRESSURE GRADIENT BETWEEN THE RIDGE
AND AFOREMENTIONED RESIDUAL LOW.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...GALE...155 170 172
FIRE WEATHER...NONE

MALOY