Small Craft Advisory 394, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
130 PM ADT SUN MAY 4 2008

.ANALYSIS AND UPPER LEVELS...TWO COMPLEX LOWS ARE EMBEDDED WITHIN
LONG-WAVE TROUGH CENTERED OVER THE ALASKA/BERING SEA REGION. ONE
EXTENDS FROM THE EASTERN BERING TO THE GULF WITH A 995 MB SURFACE
REFLECTION OVER THE SOUTHCENTRAL GULF. RADAR IMAGERY SHOWS RAIN IS
CONFINED TO THE IMMEDIATE COAST WITH A FEW SHOWERS MAKING IT INTO
COOK INLET AND ISOLATED TO SCATTERED SHOWERS ALONG THE SOUTHWEST
ALASKA COAST. EXTENSIVE CLOUD COVER OVER INTERIOR SOUTHCENTRAL THIS
MORNING IS SLOWLY DEVELOPING A FEW SUN BREAKS AS THE SURFACE HEATS
AND BREAKS THE SHALLOW STABLE LAYER SEEN IN THE 12Z ANCHORAGE AND
MCGRATH SOUNDINGS. VISIBLE SATELLITE IMAGERY SHOWS A VERY SOLID
LAYER OF CLOUDS OVER THE BERING SEA AND ALEUTIANS UNDER WEAK
NORTHWEST COLD ADVECTION FLOW. A LOW THAT MOVED OFF OF KAMCHATKA
HAS PUSHED A FRONT TO THE WESTERN ALEUTIANS THIS MORNING AND UPPER
LEVEL DIVERGENCE JUST AHEAD OF THE LOW HAS CONTRIBUTED TO THE
FORMATION OF A TRIPLE POINT LOW. MEANWHILE A RIDGE IS BUILDING JUST
WEST OF THIS SYSTEM AHEAD OF ANOTHER SYSTEM DROPPING SOUTHEASTWARD
OUT OF RUSSIA.

.MODEL DISCUSSION...MODELS REMAIN IN FAIRLY GOOD AGREEMENT THROUGH
ABOUT TUESDAY AND THEN LARGE DIFFERENCES AND RUN-TO-RUN
CONSISTENCIES DEVELOP. THERE ARE SOME DIFFERENCES IN THE DETAILS
OF ALEUTIAN SYSTEM AS IT REACHES THE CENTRAL ALEUTIANS MONDAY NIGHT
AND MOVES NORTHWARD INTO THE BERING TUESDAY. THIS IS LARGELY DUE TO
THE COMPLEX NATURE OF THE UPPER LOW WITH MULTIPLE WAVES ROTATING
AROUND THE MAIN CENTER AND COLD AIR FEEDING INTO THE BACK SIDE OF
THE SYSTEM AS HIGH AMPLITUDE RIDGE DEVELOPS UPSTREAM. SECONDARY LOW
FORMATION IS LIKELY...BUT IT IS TOO SOON FOR MODELS TO RESOLVE TIMING
AND LOCATION. WILL STICK CLOSE TO CURRENT FORECAST...WHICH IS CLOSEST
TO THE 12Z GFS SOLUTION. FOR THE MORE UNCERTAIN EXTENDED PERIOD
COORDINATED WITH JUNEAU/HPC TO TREND TOWARD THE 12Z GFS...WHICH IS
PREFERRED OVER THE ECMWF WHICH HAS FLIP-FLOPPED ITS SOLUTION THE
PAST FEW RUNS.

.SHORT TERM FORECAST...

SOUTHERN MAINLAND...UPPER WAVES EMBEDDED IN COMPLEX UPPER CIRCULATION
WILL ROTATE ACROSS THE SOUTHERN MAINLAND TONIGHT AND MONDAY
GENERATING A FEW SHOWERS...MAINLY ALONG THE MOUNTAINS. THE MORE
DOMINANT GULF CIRCULATION WILL HELP TO CONSOLIDATE THE UPPER LOW
TONIGHT AND UPSTREAM SYSTEM WILL HELP PUSH THIS LOW EASTWARD MONDAY
AND TUESDAY. AS THE SURFACE LOW BEGINS TO MOVE EASTWARD ON MONDAY
RIDGE WILL BUILD FROM SOUTHEAST ALASKA TO THE NORTHERN GULF COAST
ONCE AGAIN. AFTER A RESPITE FROM WINDS TODAY GUSTY WINDS WILL DEVELOP
MONDAY AFTERNOON AND EVENING ALONG SOUTHERN PORTIONS OF SOUTHCENTRAL.

FAIRLY EXTENSIVE CLOUD COVER WILL HELP KEEP TEMPERATURES DOWN AND SO
RELATIVE HUMIDITIES WILL REMAIN ABOVE KEY FIRE WEATHER THRESHOLDS.
THE SOUTHERN MAINLAND WILL DRY OUT TUESDAY AS THE SYSTEM MOVES
AWAY...ALTHOUGH THE BERING SEA FRONT WILL APPROACH THE SOUTHWEST
COAST BY LATE TUESDAY. THIS FRONT WILL SLOWLY MOVE ONSHORE AND TO
KODIAK ISLAND ON WEDNESDAY WHILE THE REST OF THE SOUTHERN MAINLAND
SHOULD SEE SOME SUN.

BERING SEA/ALEUTIANS/ALASKA PENINSULA...RIDGE WILL QUICKLY AMPLIFY
OVER KAMCHATKA/EASTERN RUSSIA THE NEXT COUPLE DAYS. THIS WILL RESULT
IN A STRENGTHENING JET WHICH WILL TRANSPORT COLDER AIR SOUTHWARD
ACROSS THE WESTERN BERING INTO THE NORTH PACIFIC. SOME OF THIS COLD
AIR WILL ALSO FEED INTO THE ALEUTIAN LOW AND HELP TO DEEPEN IT.
THIS COMBINED WITH UPPER WAVES ROTATING AROUND UPPER LOW CENTER
WILL LIKELY RESULT IN NEW LOWS CONTINUOUSLY FORMING DOWNSTREAM.
THE AMPLIFICATION OF THE PATTERN WILL HELP STALL THE EASTWARD
PROGRESSION OF THE SYSTEM ON TUESDAY. THE LOW WILL THEN DRIFT
NORTHWARD AND SET UP SHOP IN THE BERING SEA WHILE THE FRONT SLOWLY
CONTINUES TO TRACK OUTWARD FROM THE LOW AND WEAKEN.

.LONG TERM FORECAST...ALTHOUGH DETAILS ARE IN QUESTION...THERE IS
SOME CONFIDENCE IN THE GENERAL SET-UP FOR THE EXTENDED PERIOD. MEAN
LONG-WAVE TROUGH WILL REMAIN CENTERED OVER THE BERING SEA. THE LOW
THAT MOVES INTO THE BERING MID WEEK WILL REMAIN THERE THROUGH THE
END OF THE WEEK. SOUTHCENTRAL AND INTERIOR SOUTHWEST WILL REMAIN DRY
THROUGH MID WEEK AND THEN A LOW WILL FORM SOMEWHERE IN THE VICINITY
OF THE GULF AND BE FORCED NORTHWARD TOWARD MAINLAND ALASKA LATE IN
THE WEEK BRINGING A SHOT OF PRECIPITATION...ESPECIALLY ALONG THE
COAST.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING 120 172 175 176.
FIRE WEATHER...NONE.

SEB MAY 08