Small Craft Advisory 494, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
424 PM AKDT WED JUN 10 2015

.ANALYSIS AND UPPER LEVELS...

THE UPPER LEVEL LOW REMAINS ANCHORED IN THE ARCTIC NORTHWEST OF
ALASKA. THE LONGWAVE TROUGH EXTENDING OUT OF THIS LOW STRETCHES
FROM THE NORTHWEST COAST THROUGH SOUTHCENTRAL ALASKA AND INTO THE
CENTRAL GULF OF ALASKA. A FRONT MOVING WITH THIS UPPER LEVEL
TROUGH IS PRODUCING LIFT IN THE KUSKOKWIM VALLEY THIS AFTERNOON
AND EVENING WHICH WILL BRING THE POSSIBILITY OF THUNDERSTORMS.

THE SUSITNA VALLEY AND NORTHERN COPPER RIVER BASIN ARE UNSTABLE
THIS AFTERNOON AND BREAKS IN THE CLOUDS MAY BE ENOUGH TO PRODUCE
THUNDERSTORMS THIS AFTERNOON AND EVENING. THERE IS ALSO SOME
INSTABILITY OVER THE KENAI PENINSULA THAT MAY BE ENOUGH TO
PRODUCE A THUNDERSTORM OR TWO THOUGH THE KENAI IS NOT AS UNSTABLE
AS AREAS TO THE NORTH.

&&

.MODEL DISCUSSION...

MODELS REMAIN IN GOOD AGREEMENT WITH THE UPPER LEVEL SHORT WAVES
MOVING THROUGH THE AREA THE NEXT TWO DAYS AND THEN THEN RIDGE
BUILDING INTO THE AREA FOR THE WEEKEND AND AT LEAST THE FIRST HALF
OF NEXT WEEK. MODELS ARE HOLDING ONTO DEVELOPING THE UPPER LEVEL BLOCKING
RIDGE OVER THE STATE FOR EARLY NEXT WEEK. TEMPERATURES FROM THE
EXTENDED MOS GUIDANCE INDICATES A GOOD AREA OF SOUTHERN ALASKA
RUNNING 10 TO 15 DEGREES ABOVE CLIMATOLOGY. THERE ARE SOME SUBTLE
DIFFERENCES BETWEEN THE ECMWF AND GFS MODELS IN THE SURFACE RIDGE.
THEY BOTH HAVE IT SET UP OVER THE INTERIOR OF THE STATE AND
SOUTHWEST ALASKA WITH PART OF IT PUSHING INTO SOUTHCENTRAL ALASKA.
WHAT IS A MORE SIGNIFICANT FEATURE IS THE DEVELOPMENT SATURDAY
THROUGH MONDAY OF A SURFACE TROUGH ALONG THE NORTH GULF COAST.
WHILE THESE MODELS WAVER SOME ON THE EXACT PLACEMENT THE FACT THAT
IT IS A LEE SIDE TROUGH FAVORS IT DEVELOPING JUST OFFSHORE OF THE
NORTH GULF COAST WHERE IT TYPICALLY DOES IN NORTHERLY SUMMER FLOW.
WHAT THIS MEANS IS THAT THERE WILL BE OUTFLOW WINDS ALONG THE
COAST AND IN SOME INTERIOR AREAS AS WELL. THIS WILL INCREASE THE
TEMPERATURES DUE TO DOWNSLOPING AND LOWER RELATIVE HUMIDITY VALUES
AS WELL.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
A SHOWERY PATTERN WILL CONTINUE INTO FRIDAY AS SEVERAL
DISTURBANCES TRAVERSE THE REGION. THE FIRST OF THESE FEATURES
WILL MOVE THROUGH THIS EVENING...WITH ISOLATED THUNDERSTORMS
POSSIBLE ACROSS THE SUSITNA VALLEY AND COPPER RIVER BASIN AND ALSO
THE WESTERN KENAI PENINSULA AS A FEW BREAKS OF SUNSHINE WILL ALLOW
FOR ENHANCED INSTABILITY. THUNDERSTORM POTENTIAL WILL LARGELY BE
CONFINED TO THE COPPER RIVER BASIN ON THURSDAY AS THE MEAN TROUGH
AXIS SHIFTS EAST OF THE COOK INLET REGION AND THEN AGAIN ON FRIDAY
AS ANOTHER SHORTWAVE DIVES SOUTHWARD TOWARDS THE EASTERN GULF.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
SOUTHWEST ALASKA WILL CONTINUE TO BE IN A SHOWERY PATTERN
THROUGH FRIDAY AS A SERIES OF UPPER LEVEL SHORT WAVES MOVE
THROUGH THE REGION. ISOLATED WET THUNDERSTORMS ARE EXPECTED
TONIGHT FROM SLEETMUTE EAST...MAINLY ALONG THE ALASKA RANGE.
COASTAL FOG...MAINLY DURING THE OVERNIGHT HOURS..WILL CONTINUE
THROUGH FRIDAY.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
WINDS OVER THE REGION WILL GENERALLY STAY BRISK THROUGH FRIDAY AS
HIGH PRESSURE BUILDS OVER THE REGION. THE FRONT ASSOCIATED WITH
THE LOW MOVING ALONG THE EASTERN RUSSIAN COAST WILL BEGIN TO
IMPACT THE WESTERN ALEUTIANS THURSDAY AFTERNOON BRINGING WITH IT
AREAS OF GALE FORCE WINDS AND RAIN. ELSEWHERE...AREAS OF
FOG...DENSE AT TIMES...WILL CONTINUE OVER MOST OF THE BERING SEA
AND ADJACENT COASTAL WATERS.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
AN UPPER LEVEL CLOSED HIGH PRESSURE IS POSITIONED OVER THE
SHUMAGIN ISLANDS WITH AN AMPLIFIED RIDGE EXTENDING NORTHWARD
THROUGH THE ALASKA INTERIOR INTO THE NORTH SLOPE BY SATURDAY.
THIS CLOSED HIGH PRESSURE WILL MOVE OVER THE LOWER KUSKOKWIM
VALLEY INTO THE MATSU VALLEY BY SUNDAY. THIS SYSTEM WILL
STRENGTHEN AND BECOME STATIONARY OVER THE SOUTHCENTRAL THROUGH
WEDNESDAY. WEAK SHORTWAVE TROUGHS WILL TRACK NORTHWARD ON THE
BACKSIDE OF THE RIDGE BUT WILL FALL APART AS IT CONTINUES TO
RUN INTO THE AMPLIFIED RIDGE. ANY PRECIPITATION WILL BE ALONG THE
KUSKOKWIM DELTA REGION NORTHWARD ALONG THE COAST THROUGH THE NEXT
SEVERAL DAYS. THE MAIN CONCERN WILL BE THE SIGNIFICANTLY WARMER
TEMPERATURES THROUGHOUT THE ALASKA REGION AS WE HEAD INTO THE
MIDDLE OF NEXT WEEK. THESE WARMER TEMPERATURES WILL BE
ACCOMPANIED BY DRIER CONDITIONS AND LOWER RELATIVE HUMIDITIES
THROUGH THE COPPER RIVER BASIN...MATSU VALLEY AND INTERIOR
PORTIONS OF SOUTHWEST ALASKA. THE COPPER RIVER BASIN AND ALONG
THE NORTHERN GULF WILL HAVE NORTHERLY OFFSHORE WINDS AND WILL
LIKELY SEE CLOSE TO RECORD SETTING TEMPERATURES FOR THE SEWARD AND
THE COPPER RIVER BASIN REGION. THERE WILL LIKELY BE FIRE WEATHER
CONCERNS AS RELATIVE HUMIDITIES LOWER FOR THE MATSU VALLEY AND
THE COPPER RIVER BASIN REGIONS THROUGH THE WEEKEND AND INTO THE
MIDWEEK. MEANWHILE...THE WESTERN ALEUTIANS WILL HAVE THE REMNANTS
OF THE KAMCHATKA LOW AND WILL CONTINUE TO BRING SOUTHERLY GALE
FORCE WINDS ACCOMPANIED BY RAIN/FOG INTO THE WESTERN/CENTRAL
BERING SEA THROUGH THIS WEEKEND BEFORE DIMINISHING BY MONDAY. THEN
HIGH PRESSURE WILL BEGIN TO BUILD OVER THE BERING SEA THROUGH MIDWEEK.
THIS WILL BRING LOW STRATUS AND FOG THROUGHOUT THE BERING AND
ALONG THE SOUTHWEST COASTLINE HEADING INTO NEXT WEEK.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALES 178.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...CB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...RF
LONG TERM...PD