Small Craft Advisory 546, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
112 PM AKDT MON JUL 15 2013

.ANALYSIS AND UPPER LEVELS...A LARGE UPPER LEVEL CLOSED LOW IS
ANCHORED OVER EASTERN SIBERIA WITH A HIGH AMPLITUDE TROUGH EXITING
SOUTHWARD ACROSS THE WESTERN BERING SEA. A CORRESPONDINGLY HIGH
AMPLITUDE RIDGE IS CENTERED OVER EASTERN MAINLAND ALASKA NORTHWARD
TO THE BEAUFORT SEA. WATER VAPOR IMAGERY SHOWS A SERIES OF
SHORT-WAVES MOVING INTO THE BASE OF THE TROUGH FROM RUSSIA AND
FROM THE NORTHWEST PACIFIC...THEN TRACKING NORTHEASTWARD ACROSS
THE BERING SEA AND THEN NORTHWARD (UP THE WEST SIDE OF THE RIDGE)
ACROSS WESTERN ALASKA. THE LATEST SHORT-WAVE IS PUSHING RIGHT INTO
THE RIDGE HELPING TO WEAKEN AND NUDGE IT EASTWARD WHICH WILL ALLOW
FOR MORE EASTWARD PROGRESSION OF SUCCESSIVE WAVES. RAINFALL WITH
THESE UPPER WAVES IS FOCUSED FROM THE EASTERN ALEUTIANS TO SOUTHWEST
ALASKA THIS MORNING. ELSEWHERE ACROSS THE BERING SEA...GULF OF
ALASKA...AND COASTAL SOUTHCENTRAL A VERY STABLE AIRMASS IS RESULTING
IN WIDESPREAD STRATUS AND FOG.

.MODEL DISCUSSION...AS WOULD BE EXPECTED WITH A MULTITUDE OF
SHORT-WAVES IN FAST FLOW THERE ARE SOME DIFFERENCES IN STRENGTH
AND TIMING OF THESE WAVES AMONG THE MODELS. HOWEVER...CONSIDERING
THE FORECAST DIFFICULTY THE DIFFERENCES ARE MINOR. THERE ISN'T MUCH
SPACE BETWEEN WAVES SO PERIODS OF RAIN WILL CONTINUE ALONG THE MAIN
TRACK FROM THE EASTERN BERING TO SOUTHWEST ALASKA. THE MAIN FORECAST
CHALLENGE IS FIGURING OUT HOW FAR THESE WAVES WILL PENETRATE INTO
SOUTHCENTRAL ALASKA AS THE RIDGE WEAKENS. THE NAM IS MORE AGGRESSIVE
AND A BIT FURTHER SOUTH WITH WAVES THAN OTHER MODELS. HOWEVER...ALL
MODELS INDICATE SOME CHANCE OF SHOWERS AS THESE WAVES TRACK ACROSS
THE NORTHERN TIER OF SOUTHCENTRAL FORECAST THE NEXT FEW DAYS.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...THE 12Z ANCHORAGE SOUNDING SHOWS THE MARINE
LAYER IS MUCH THICKER THAN YESTERDAY WITH A NEARLY SATURATED PROFILE
UP THROUGH 6000 FEET. WITH PERSISTENT SOUTHWEST LOW LEVEL FLOW AND
HIGH CLOUDS MOVING OVERHEAD AND BLOCKING A BIT OF THE SOLAR RADIATION
IT WILL BE VERY DIFFICULT TO BURN OFF THIS MARINE LAYER ALONG THE
IMMEDIATE COASTAL AREAS. THUS EXPECT CLOUDS TO HOLD IN...WITH PERHAPS
A FEW BREAKS LATE THIS AFTERNOON AND EVENING. THE UPPER LEVEL RIDGE
WILL CONTINUE TO WEAKEN TONIGHT AND WEDNESDAY WHICH WILL ALLOW UPPER
LEVEL SHORT-WAVES TRACKING ACROSS SOUTHWEST ALASKA TO CLIP PART OF
SOUTHCENTRAL. THE INCREASE IN CLOUDS WITH THESE WAVES WILL REDUCE
RADIATIVE COOLING AT THE TOP OF THE MARINE LAYER AND HELP DISSIPATE
SOME OF IT. ALSO EXPECT AT LEAST A FEW SHOWERS TO DEVELOP AHEAD OF
ONE WAVE MOVING THROUGH TUESDAY...MAINLY OVER INTERIOR SOUTHCENTRAL.
MODELS ARE HINTING TOWARD A FURTHER SOUTH TRACK WITH A WAVE ON
WEDNESDAY NIGHT AND THURSDAY...WHICH COULD BRING SHOWER ACTIVITY AS
FAR SOUTH AS THE ANCHORAGE AREA. EVEN THOUGH THE MARINE LAYER WILL
BREAK UP IN SOME AREAS EXPECT SIGNIFICANT MID TO HIGH LEVEL CLOUDS
TO PERSIST OVER THE NEXT FEW DAYS.

SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...EXPECT PERIODS OF RAIN OVER
THE NEXT FEW DAYS FROM THE EASTERN ALEUTIANS NORTHEASTWARD ACROSS
SOUTHWEST ALASKA AS FAIRLY STRONG UPPER LEVEL SHORT-WAVES CONTINUE
TO TRACK RIGHT OVER THE REGION. THE KUSKOKWIM DELTA COAST AND
PRIBILOF ISLANDS WILL BE RIGHT ON THE WESTERN EDGE OF THESE WAVES
AND WILL BE ON THE DRIER SIDE COMPARED WITH THE REST OF THE REGION.
VERY MOIST LOW LEVELS WILL LEAD TO FOG AND STRATUS AND PERHAPS SOME
DRIZZLE DURING THE BRIEF BREAKS IN RAIN.

.LONG TERM FORECAST...CHANCES OF RAIN/SHOWERS WILL INCREASE OVER
SOUTHCENTRAL MID TO LATE WEEK AS THE UPPER RIDGE FLATTENS OUT AND
ALLOWS BETTER ACCESS TO SHORT-WAVES TRACKING OUT OF THE BERING SEA
TROUGH. THIS PATTERN LOOKS LIKE IT WILL HOLD THROUGH NEXT WEEKEND.
SO THE CHALLENGE WILL REMAIN THE TRACK AND STRENGTH OF SHORT-WAVES
ACROSS THE REGION.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

SEB JUL 13