Small Craft Advisory 627, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
230 PM AKDT MON AUG 10 2009

.ANALYSIS AND UPPER LEVELS...

A 1001 MB LOW IS FORMING CURRENTLY IN THE WRANGELL-ST. ELIAS NATIONAL
PARK REGION TO THE SOUTH OF A CUT-OFF UPPER LEVEL LOW OVER THE
NORTHEASTERN PART OF THE STATE. THIS FLOW OUT OF THE NORTH OVER
SOUTHCENTRAL AND OFFSHORE INTO THE GULF IS TRANSPORTING RATHER DRY
AND CLEAR WEATHER FROM THE INTERIOR OVER THE REGION. THE ONE DOWNSIDE
TO THIS PATTERN IS THAT THE SMOKE FROM THE MASSIVE FIRES IN THE
INTERIOR IS MAKING ITS WAY SOUTHWESTWARD TO THE WEST OF THE ANCHORAGE
AND MAT-SU AREAS...BUT THEN CURVING BACK SOUTHEASTWARD SO AS TO
AFFECT THE HOMER AND KODIAK REGIONS.

IN THE BERING SEA REGION...A HIGHLY AMPLIFIED YET NARROW UPPER RIDGE
CONTINUES TO RESIDE ACROSS THE CENTRAL AND EASTERN BERING SEA. THE
SUBSIDENCE INVERSION BELOW THIS FEATURE IS TRAPPING MOISTURE NEAR THE
SURFACE AND IS RESULTING IN WIDESPREAD FOG ACROSS THE REGION. OVER
MOST OF ZONE 155 AND THE BERING SIDE OF THE ALASKA
PENINSULA...ONSHORE FLOW FROM THE NORTH AND NORTHWEST IS RESULTING IN
VERY LOW STRATUS WITH BASES BELOW 1000 FEET. MEANWHILE...A LARGE
UPPER LOW BETWEEN SHEMYA AND THE KAMCHATKA PENINSULA CONTINUES TO
MOVE LITTLE BUT IS ROTATING DISTURBANCES INTO THE NORTH PACIFIC WHICH
WILL PLAY A LARGE ROLE IN OUR WEATHER REGIME OVER THE COMING DAYS.

.MODEL DISCUSSION...

NAM/GFS/EURO MODELS SEEM TO BE IN REASONABLE AGREEMENT ON THE TRACK
OF THE NORTH PACIFIC LOW THAT WILL MOVE NORTHEAST ACROSS THE CENTRAL
ALEUTIANS TUESDAY AFTERNOON AND THEN INTO THE BRISTOL BAY REGION BY
LATE WEDNESDAY AFTERNOON. THERE IS NOT...HOWEVER...GOOD AGREEMENT ON
THE STRENGTH OF THIS LOW...AS THE NAM IS STRENGTHENING THIS LOW INTO
THE MID 990S WHILE THE EURO AND GFS ARE MUCH WEAKER. USING THE NAM
SOLUTION RESULTS IN WIND SPEEDS THAT ARE UP TO 20 KNOTS STRONGER THAN
THE GFS...WHICH SEEMS LESS LIKELY TO OCCUR AT THIS TIME.
THEREFORE...WENT WITH THE GFS WITH A SLIGHT INCREASE IN WINDS IN THE
GRIDS TO ACCOUNT FOR SOME POSSIBILITY THAT THE NAM COULD BE ONTO
SOMETHING. USING THE GFS...WE WILL ALSO NEED TO WATCH FOR POSSIBLE
TRIPLE POINT LOW DEVELOPMENT NEAR KODIAK IN THE 72-84 HOUR
TIMEFRAME...WHICH IS ALSO HINTED AT BY THE EURO AND TO A LESSER
EXTENT BY THE NAM...WHICH KEEPS THAT DEVELOPMENT MORE NORTH OR ALONG
THE AKPEN THAN IN THE GULF (BUT WHICH IS DISCARDED AT THIS TIME).
CONFIDENCE IN THE MODEL SOLUTIONS IS RELATIVELY HIGH OUT TO 48 HOURS
AND THEN LOW TO MEDIUM OUT TO 84 HOURS AND BEYOND.

.SHORT TERM FORECAST...

SOUTH AND EAST OF THE ALASKA RANGE...

EXPECT TO SEE CONTINUED NORTHERLY TO NORTHWESTERLY FLOW ALOFT OVER
SOUTHCENTRAL...RESULTING IN MOSTLY CLEAR AND PLEASANT WEATHER THROUGH
TUESDAY. WIND FLOW OVER THE NEXT 24 TO 36 HOURS SHOULD KEEP THE SMOKE
AND HAZE FROM FIRES IN THE INTERIOR TO THE WEST OF ANCHORAGE...BUT
MAY CONTINUE TO AFFECT AREAS SUCH AS THE SOUTHWESTERN KENAI PENINSULA
AND KODIAK. AS THE NEXT SYSTEM APPROACHES FROM THE WEST ON
WEDNESDAY...EXPECT TO SEE THE FLOW SWITCH BACK TO THE SOUTH AND
WEST...RESULTING IN ONSHORE FLOW...MOISTURE ADVECTION...CLOUDS...AND
THE INCREASED LIKELIHOOD OF RAIN MOVING ACROSS THE REGION FROM
SOUTHWEST TO NORTHEAST FROM LATE WEDNESDAY NIGHT THROUGH THURSDAY.

SOUTHWEST ALASKA MAINLAND...

A WEAK THERMAL TROUGH WILL RESIDE JUST NORTH OF THE REGION...WITH
WEAK LOW PRESSURE OVER THE YUKON DELTA REGION THROUGH TUESDAY NIGHT.
BY THAT TIME...THE NEXT DISTURBANCE WILL BE APPROACHING FROM THE
SOUTH AND WEST...AND WILL BRING A GOOD CHANCE OF RAIN TO THE REGION
FROM THE SECOND HALF OF WEDNESDAY THROUGH A GOOD PART OF THURSDAY.

AKPEN/ALEUTIANS/BERING SEA...

THE UPPER RIDGE CURRENTLY OVER THE CENTRAL AND EASTERN BERING SEA
WILL BEGIN BREAKING DOWN AND MOVING OVER SOUTHWEST ALASKA TONIGHT
THROUGH EARLY WEDNESDAY...GIVING WAY TO AN APPROACHING UPPER LEVEL
LOW WHICH WILL USHER ACROSS A SERIES OF DISTURBANCES AND BRING
UNSETTLED WEATHER BACK TO MOST OF THE BERING SEA THROUGH THE MEDIUM
RANGE.

.LONG TERM FORECAST...

AN ACTIVE PERIOD OF WEATHER APPEARS ON TAP FOR THE MEDIUM TO LONG
RANGE PERIODS...WITH THE APPROACHING UPPER LOW SETTING UP SHOP OVER
THE BERING SEA NEAR SOUTHWEST ALASKA. THIS WILL BRING MOSTLY ONSHORE
FLOW...WITH NUMEROUS DISTURBANCES ROTATING AROUND THIS FEATURE
BRINGING RAINY CONDITIONS AND AN AUTUMN-LIKE FEEL TO MOST OF THE
REGION.

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

CASSELL AUG 09