Small Craft Advisory 464, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE ANCHORAGE AK
738 PM AKDT WED JUN 11 2014

.UPDATE...
ZONES 101/111/121
THE SUBTLEST OF LIFT ALONG FAR SOUTHERN PERIPHERY OF SHORTWAVE
TROUGH IS LIFTING THROUGH UPPER COOK INLET AND THE SUSITNA VALLEY
THIS EVENING. A COUPLE PASSING SHOWERS THAT HAVE FORMED NEAR THE
CHUGACH/KENAI RANGES SHOULD DIMINISH FAIRLY QUICKLY AS THE
EVENING WEARS ON.

JAM

&&

.PREV DISCUSSION... /ISSUED 401 PM AKDT WED JUN 11 2014/

ANALYSIS AND UPPER LEVELS...
THE PERSISTENT COLD UPPER LOW OF RECENT DAYS IS NOW LOCATED OVER
THE INTERIOR OF THE STATE AND CONTINUING TO MOVE AWAY TO THE
NORTH. THE LAST VESTIGES OF THIS FEATURE ARE SOME LINGERING
INSTABILITY CLOUDS/SHOWERS OVER INTERIOR PORTIONS OF THE SUSITNA
VALLEY AND COPPER RIVER BASIN...BUT THESE WILL NOT REACH THE
INTENSITY OF YESTERDAY AS INSTABILITY CONTINUES TO DIMINISH
THROUGHOUT THE DAY. MEANWHILE...WEAK HIGH PRESSURE IS BUILDING INTO
SOUTHCENTRAL ALASKA. THIS REPRESENTS A BRIEF BREAK IN THE PARADE
OF LOW PRESSURE SYSTEMS MOVING INTO AND THROUGH THE PERSISTENT
LONGWAVE TROUGH THAT ENCOMPASSES THE ENTIRE REGION. THIS AMPLE
SUNSHINE COMBINED WITH A MODERATING/WARMING AIRMASS ARE HELPING
BOOST TEMPERATURES CLOSER TO NORMAL VALUES FOR THIS TIME OF YEAR.

OUT WEST...A VERTICALLY STACKED LOW IS CHURNING SLOWLY EASTWARD
THROUGH THE BERING SEA. A RAPIDLY WEAKENING ASSOCIATED FRONT IS
MOVING ONSHORE THE SOUTHWEST MAINLAND COAST...WITH LIGHT RAIN
BEING REPORTED FROM NUNIVAK ISLAND DOWN TO THE ALASKA PENINSULA.
WINDS IN ALL QUADRANTS AROUND THIS LOW AS WELL AS ALONG THE FRONT
ITSELF ARE GENERALLY UNDER 25-30 MPH...WITH THE GUSTIEST
CONDITIONS OCCURRING THROUGH THE CHANNELED TERRAIN OF THE EASTERN
ALEUTIANS AND ALASKA PENINSULA.

MODEL DISCUSSION...
THE MODELS ARE IN GOOD SYNOPTIC AGREEMENT THROUGHOUT THE SHORT
TERM (84 HOURS) FORECAST PERIOD. THE BREAKDOWN OF THE DOWNSTREAM
RIDGE OVER WESTERN NORTH AMERICA WILL ALLOW THE JET STREAM OVER
THE GULF OF ALASKA TO BECOME MORE ZONAL. THIS WILL ALLOW THE UPPER
LOW CURRENTLY IN THE BERING TO MOVE EAST INTO THE GULF OF ALASKA
BY FRIDAY NIGHT...WITH THE ASSOCIATED SURFACE LOW
REFORMING/REDEVELOPING OVER THE WESTERN GULF AT THE SAME TIME. THE
ECMWF WAS THE FIRST MODEL TO DEPICT THIS SCENARIO...AND ALL THE
MODELS ARE NOW DEPICTING A SIMILAR ATMOSPHERIC EVOLUTION. THE
CHALLENGE WILL BE IN HOW QUICKLY AND HOW FAR SOUTH THIS LOW
DEVELOPS. THE SLIGHTLY FURTHER SOUTH SOLUTION SHOWN BY THE GFS
WOULD END WIDESPREAD RAINFALL ACROSS INTERIOR AREAS SOONER ON
FRIDAY...WHILE A DELAYED DEVELOPMENT WOULD PROLONG STEADY RAIN
OVER COOK INLET AND INLAND AREAS DURING THE DAY FRIDAY. AT THIS
TIME...A CONSENSUS-BASED APPROACH THAT HAPPENS TO BE FAIRLY CLOSE
TO THE INHERITED FORECAST IS PREFERRED...AND SHOULD SEE STEADY
RAINS BECOME CONFINED LARGELY TO THE GULF COASTAL AREAS BY FRIDAY
AFTERNOON. OUT WEST...A SECONDARY LOW PRESSURE CENTER WILL DROP
INTO THE LONGWAVE TROUGH FROM EASTERN RUSSIA ON FRIDAY. THE NAM
SEEMS TO BE LAGGING THE GLOBAL MODELS WITH THE SPEED OF THIS
SOUTHWARD MOVEMENT...SO THE GFS/ECMWF ARE THE PREFERRED SOLUTIONS
TODAY.

SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...ABUNDANT SUNSHINE IS DOMINATING MUCH OF THE
AREA TODAY COURTESY OF A SHORTWAVE RIDGE PASSING THROUGH. THE BLUE
SKIES PROVIDE STARK CONTRAST TO THE FRESH SNOW THAT FELL DOWN TO
NEARLY 3500 FT OVER THE FRONT RANGE ON TUESDAY. AFTER THE
WIDESPREAD WETTING RAIN YESTERDAY...THE SUN IS WELCOME NEWS FOR
THOSE WITH AGRICULTURAL INTERESTS. THE RIDGE WILL NOT LAST LONG
THOUGH. THURSDAY WILL BRING INCREASING CLOUDS THROUGHOUT THE DAY
WITH PRECIPITATION SPREADING FROM KODIAK IN THE LATE AFTERNOON UP
THE COOK INLET JUST AFTER MIDNIGHT. FRIDAY WILL SEE THE TRIPLE
POINT LOW STRENGTHENING IN THE WESTERN GULF. THIS WILL BRING
ANOTHER ROUND OF MODERATE TO STRONG SOUTHEAST WINDS AND A BROAD
SWATH OF PRECIPITATION. THESE SOUTHEAST WINDS WILL BRING
DOWNSLOPING CONDITIONS TO THE TYPICAL AREAS DOWNSTREAM OF THE
KENAI AND CHUGACH MOUNTAINS. THIS MEANS LIMITED PRECIPITATION FOR
KENAI...THE ANCHORAGE BOWL..AND THE MAT- SU VALLEY. IT WILL ALSO
BRING GUSTY WINDS TO THE TURNAGAIN ARM AND OTHER FAVORED AREAS.
THE HEAVIEST PRECIPITATION WILL IMPACT THE GULF COAST EARLY FRIDAY
AND SPREAD INTO THE PRINCE WILLIAM SOUND BY THE AFTERNOON. THE LOW
CENTER KEEPS TRACKING INTO THE NORTHEASTERN GULF BY SATURDAY. THAT
WILL PUSH MOST OF THE STEADIER PRECIPITATION INTO THE PANHANDLE
WHILE LEAVING MUCH OF SOUTHCENTRAL IN LINGERING SHOWERS BUT LIKELY
A FEW BREAKS IN THE CLOUDS LATER IN THE DAY.

SOUTHWEST ALASKA...A WEAKENING WARM FRONT TRYING TO MAKE ITS WAY
INTO BRISTOL BAY IS BUTTING UP AGAINST A SHORTWAVE RIDGE THAT IS
HOLDING STRONG ACROSS THE SOUTHWEST. SO WHILE THERE IS SOME LIGHT
RAIN AND FOG ALONG THE COAST...MAINLY INLAND LOCATIONS ARE STILL
SEEING MOSTLY SUNNY SKIES. THIS FIRST FRONT WILL FALL APART AS IT
SLIDES NORTH TOWARDS THE KUSKOKWIM DELTA...BUT IT WILL QUICKLY BE
REPLACED BY A STRONGER SYSTEM THAT WILL MOVE INTO BRISTOL BAY ON
THURSDAY. THIS SYSTEM WILL BRING ANOTHER ROUND OF MODERATE
PRECIPITATION THAT SHOULD BE ABLE TO PENETRATE MOST OF THE WAY TO
THE ALASKA RANGE BY THURSDAY NIGHT. AS THE ENERGY FROM THIS SYSTEM
TRANSFERS INTO THE GULF...RAIN WILL TURN MORE SHOWERY IN NATURE ON
FRIDAY. BY SATURDAY...MODELS AGREE THAT THE ATMOSPHERE SHOULD
BEGIN TO DRY OUT. BUT UNDER WEAK NORTHWESTERLY FLOW...AFTERNOON
SHOWERS ARE LIKELY TO FIRE ALONG THE HIGHER TERRAIN.

BERING SEA/ALEUTIANS...IT IS QUITE REMARKABLE HOW LITTLE CHANGE
THERE HAS BEEN IN THE LONGWAVE PATTER OVER THE REGION. AND THIS
WILL CONTINUE AT LEAST THROUGH THE WEEKEND. OVER THE WESTERN
EXTENT OF THE BERING...COLDER AIR CONTINUES TO PLUNGE SOUTH OFF OF
RUSSIA. THIS THEN IN TURN GETS PICKED UP BY A FAST MOVING ZONAL
JET ON THE SOUTH SIDE OF THE ALEUTIAN CHAIN. THE COLDER AIR HELPS
REINFORCE THE TROUGH OVER THE REGION AND EVENTUALLY TURNS INTO
SOME TYPE OF WEAK BAROCLINIC ZONE OVER THE WARMER TEMPS NEAR THE
EASTERN ALEUTIANS. THAT SAID...TYPICAL JUNE WEATHER WILL PERSIST
THROUGH THE SHORT TERM WITH SHOWERS AND LIGHT WINDS.

LONG TERM FORECAST (SUN THROUGH THU)...THE ENSEMBLE MEANS SEEM
TO BE TRENDING TOWARDS SHIFTING THE LONGWAVE TROUGH SLIGHTLY TO
THE EAST. SO INSTEAD OF BEING ALIGNED THROUGH THE EASTERN
BERING...IT WOULD BE STRETCH OUT INTO THE NORTHERN GULF. THERE
CONTINUES TO BE CONSIDERABLE UNCERTAINTY ON THE EASTERN SIDE OF
THE TROUGH...PRIMARILY CONCERNING THE N PAC RIDGE. HOW STRONG THE
RIDGE WILL BE WILL DICTATE WHERE THE TROUGH WILL SET UP SHOP. THE
11/00Z EC ENSEMBLE MEAN SHOWED A DEEP MERIDIONAL TROUGH FAR
ENOUGH WEST IN THE GULF THAT IT WOULD PUMP SIGNIFICANT WARM AIR
AND HIGH PRECIPITABLE WATER VALUES DIRECTLY INTO SOUTH CENTRAL.
BUT THE 11/12Z RUN SHIFTED THE TROUGH SEVERAL HUNDRED MILES TO
THE EAST BRINGING THE SOUTHERLY FLOW MOSTLY INTO THE WRANGELL ST
ELIAS AREA. SO A VERY BROAD BRUSH APPROACH CONTINUES TO BE USED IN
THIS TIME FRAME UNTIL MODELS SHOW MORE CERTAINTY WITH THE DETAILS.

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

AMD/MSO JUN 14