Small Craft Advisory 443, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
500 AM ADT WED MAY 21 2008

.ANALYSIS AND UPPER LEVELS...
THIS MORNING...A VERY DEEP SEMI-CLOSED UPPER LEVEL TROUGH EXTENDS
FROM THE BERING SEA SOUTH TO AROUND 25N LATITUDE WITH A STRONG JET
STREAM ROUNDING THE BASE OF THE TROUGH. AT THE SURFACE IS A WEAK
SURFACE LOW PRESSURE NEAR DUTCH HARBOR DRIFTING AROUND AND WEAKENING
SINCE IT LACKS UPPER LEVEL JET SUPPORT IN THE MIDDLE OF THE TROUGH.
A WEAK...DISSIPATING FRONT EXTENDS EAST FROM THE LOW INTO THE WEST
CENTRAL GULF. A THERMAL TROUGH PERSISTS FROM THE KUSKOKWIM VALLEY
EAST TO THE COPPER RIVER BASIN AND WILL BE THE FOCUS FOR AFTERNOON
SHOWERS AND STORMS AGAIN TODAY.

THE MAIN FORECAST ISSUE IS A STRONG LOW PRESSURE WHICH IS FORMING IN
THE NORTH CENTRAL PACIFIC ALONG THE UPPER LEVEL JET STREAM ON THE
EAST SIDE OF THE TROUGH. THIS LOW IS EXPECTED TO STRENGTHEN RAPIDLY
AS IT MOVES NORTH TO THE ALASKA PENINSULA THURSDAY NIGHT AND FRIDAY.

.MODEL DISCUSSION...
MODELS ARE HAVING SOME ISSUES WITH THE UPCOMING MAJOR LOW PRESSURE
SYSTEM...WITH DISAGREEMENTS ON BOTH THE SPEED AND TRACK OF THE
LOW...AND MINOR DISAGREEMENTS ON ITS STRENGTH. WE ARE FAVORING THE
SLOWER/MORE WESTERLY TRACK OF THE 0Z MODEL SUITE...WHICH TAKES THE
LOW ACROSS THE ALASKA PENINSULA NEAR KING COVE FRIDAY MORNING AND
MOVES IT ACROSS THE EASTERN BERING BETWEEN THE PRIBILOFS AND NUNIVAK
ISLAND ON FRIDAY AND SATURDAY. OZ GFS SEEMS TO BE THE OUTLIER IN ITS
FAR EAST/FAST TRACK AND OUR FORECAST GENERALLY GOES AWAY FROM ITS
SOLUTION.

.SHORT TERM FORECAST...
SOUTHCENTRAL...
ANOTHER DAY OF CONVECTION IS EXPECTED OVER INLAND SOUTHCENTRAL TODAY
ALONG THE THERMAL TROUGH...WITH SOME THUNDERSTORMS POSSIBLE.
TEMPERATURES WILL ALSO BE RELATIVELY WARM AGAIN AWAY FROM THE
WATER...WITH A REASONABLE AMOUNT OF SUNSHINE. A FRONT OVER THE GULF
OF ALASKA IS WEAKENING RAPIDLY THIS MORNING AS IT MOVES
NORTH...PERHAPS EVEN DIEING OUT EARLY ENOUGH TO KEEP KODIAK DRY
TODAY. OF IMPORTANCE...MARINE STRATUS IS FILLING IN OVER THE GULF
VERY FAST WITH MIDDLETON ISLAND AND CORDOVA ALREADY AFFECTED...AND
THE MARINE STRATUS SHOULD STICK AROUND IN THESE AREAS.

THE THERMAL TROUGH LIFTS NORTHWARD TOMORROW AS HIGH PRESSURE
STRENGTHENS OVER THE GULF...LEADING TO SOMEWHAT LESS CONVECTION OVER
SOUTHCENTRAL ALONG WITH A STRONGER PRESSURE GRADIENT AND LOCALLY
GUSTY WINDS. ON THURSDAY NIGHT AND FRIDAY...HIGH PRESSURE OVER THE
NORTHERN GULF GIVES WAY TO A STRONG WEATHER FRONT FOR THIS TIME OF
THE YEAR...WITH GUSTY WINDS AND FAIRLY SIGNIFICANT RAINFALL FOR THE
USUAL COASTAL UPSLOPE AREAS.

SOUTHWEST MAINLAND...
THUNDERSTORMS ARE POSSIBLE TODAY ALONG THE THERMAL TROUGH FROM
BETHEL TO MCGRATH. CONVECTION IS EXPECTED TO BE LESS WIDESPREAD
ACROSS THE SOUTHWEST MAINLAND THURSDAY AS THE THERMAL TROUGH MOVES
NORTH AND A WEAK FRONT MOVES ONSHORE WITH A MORE MARITIME AIRMASS. A
STRONG LOW PRESSURE MOVES NORTH TO KING COVE FRIDAY
MORNING...BRINGING WIDESPREAD PRECIPITATION AND STRONG WINDS TO THE
SOUTHWEST MAINLAND.

BERING SEA/ALEUTIANS...
VERY ACTIVE WEATHER PATTERN TO PERSIST FOR THE EASTERN HALF OF THE
BERING/ALEUTIAN/AKPEN REGION. A WEAK SLOW MOVING LOW PRESSURE NEAR
DUTCH HARBOR THIS MORNING IS BRINGING WIDESPREAD RAIN SHOWERS AND
SOME SNOW FROM THE CENTRAL BERING/ALEUTIANS EASTWARD. THIS LOW
DRIFTS AROUND JUST NORTH OF DUTCH HARBOR THROUGH TOMORROW THEN
DISSIPATES AS A STRONG LOW PRESSURE MOVES NORTH TOWARD THE AKPEN.
THIS LOW CROSSES THE AKPEN NEAR KING COVE FRIDAY MORNING AND MOVES
NORTH THROUGH THE EASTERN BERING FRIDAY AFTERNOON AND
NIGHT...BRINGING WIDESPREAD GALES AND SIGNIFICANT PRECIPITATION
THANKS TO ITS STRONG DYNAMICS AND TAP OF MOISTURE FROM THE TROPICS.

.LONG TERM FORECAST...
ONCE THE STRONG LOW IN THE EASTERN BERING MOVES NORTH AND CLEARS THE
REGION AROUND SUNDAY...A FAIRLY BENIGN WEATHER PATTERN IS EXPECTED
TO SET UP WITH ZONAL WEST TO EAST FLOW AND HIGH PRESSURE SOMEWHERE
OVER THE GULF OF ALASKA OR NORTH PACIFIC SOUTH OF THE AKPEN.

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

FOISY MAY 08