Small Craft Advisory 704, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
400 AM ADT SAT SEP 1 2007

.ANALYSIS AND UPPER LEVELS...
AT UPPER LEVELS...FLOW IS VERY LIGHT FROM THE EASTERN BERING EAST
INTO THE YUKON. HOWEVER...A STRONG JET STREAM IS PRESENT FROM JUST
OFF KAMCHATKA EAST TO THE SOUTHWEST BERING AND SOUTHEAST FROM THERE
INTO THE NORTH PACIFIC. BECAUSE THIS JET IS CURVED
ANTICYCLONICALLY...THERE CURRENTLY IS NOT ANY STRONG SURFACE LOW
PRESSURE ASSOCIATED WITH THIS JET. AT THE SURFACE THIS MORNING WEAK
HIGH PRESSURE RESIDES IN THE BERING...WITH A WEAK SURFACE TROUGH
FROM THE COPPER RIVER BASIN WEST AND SOUTH ALONG THE ALASKA RANGE.

THE PATTERN WILL BE CHANGING SIGNIFICANTLY. AN UPPER LEVEL TROUGH
DIGS SOUTHEAST OUT OF RUSSIA TODAY AND A SURFACE LOW PRESSURE WILL
INTENSIFY RAPIDLY TONIGHT ALONG THE RESIDING STRONG UPPER LEVEL JET
AROUND ADAK. THIS LOW WILL THEN MOVE EAST ALONG THE ALEUTIANS OVER
THE NEXT FEW DAYS...CONTINUING TO STRENGTHEN. THE WEAK SURFACE
TROUGH ALONG THE ALASKA RANGE THIS MORNING WILL DRIFT NORTH AND
WEAKEN THROUGH SUNDAY AS MORE STABLE BUT WEAK SOUTHERLY FLOW MOVES
INTO THE SOUTHERN MAINLAND.

.MODEL DISCUSSION...
MORE CONFIDENCE IS DEVELOPING IN THE FORECAST FOR BOTH THE SHORT
TERM AND EXTENDED. NAM/WRF IS STILL THE OUTLIER FOR THE UPCOMING
ALEUTIAN LOW WITH ITS TRACK BEING TOO SLOW AND NORTHERLY.
OPERATIONAL GFS STILL APPEARS TO TRACK THE LOW A BIT TOO FAST...BUT
OPERATIONAL GFS IS IN BETTER AGREEMENT THAN IT HAD BEEN WITH GFS
ENSEMBLE MEAN AS WELL AS SREF MEAN AND UKMET. FAVORING THE SLIGHTLY
SLOWER TRACK OF THE LOW THAN THE OPERATIONAL GFS HAS...BUT CERTAINLY
NOT GOING WITH THE SLOWEST AND FURTHER NORTH NAM/WRF TRACK. GOOD
CONFIDENCE IN THIS LOW EVENTUALLY TRACKING THROUGH THE NORTHERN GULF
OF ALASKA TUESDAY AND WEDNESDAY...WITH ANOTHER DEEP BERING LOW
DEVELOPING AROUND THURSDAY.

.SHORT TERM FORECAST...
SOUTHCENTRAL/SOUTHWEST MAINLAND...
FOG AGAIN A PROBLEM THIS MORNING THANKS TO LIGHT FLOW AT ALL LEVELS.
EXPECT THUNDERSTORM ACTIVITY AGAIN THIS AFTERNOON FROM BRISTOL BAY
NORTH INTO THE KUSKOKWIM VALLEY. THE ACTIVITY OVER SOUTHCENTRAL WILL
BEGIN TO SHIFT NORTH A BIT...WITH THE MAIN FOCUS LIKELY BEING NORTH
OF ANCHORAGE. MORE STABLE SOUTHERLY FLOW TO CONTINUE TO WORK INTO
THE SOUTHERN MAINLAND ON SUNDAY AHEAD OF THE LARGE ALEUTIAN LOW
PRESSURE. RAIN CHANCES WILL STILL EXIST SUNDAY...BUT THUNDERSTORM
ACTIVITY WILL BE KEPT AT A MINIMUM.

BERING/ALEUTIAN FORECAST...
RAPID CYCLOGENESIS TO OCCUR LATE TODAY INTO TONIGHT AROUND THE
CENTRAL ALEUTIANS. THE LOW PRESSURE WILL CONTINUE TO STRENGTHEN AS IT
MOVES EAST TO THE ALASKA PENINSULA MONDAY. GALES CAN BE EXPECTED
WITH THIS LOW. A SHORTWAVE RIDGE WILL BUILD IN BEHIND THIS LOW.

.LONG TERM FORECAST...
THE BIG ALEUTIAN LOW WILL MOVE INTO THE GULF OF ALASKA ON
TUESDAY...WITH ITS EFFECTS BEING FELT MONDAY THROUGH WEDNESDAY FROM
BRISTOL BAY OVER TO SOUTHCENTRAL. SIGNIFICANT RAIN CAN BE EXPECTED
ESPECIALLY NEAR THE GULF COAST. A LARGE BERING/ALEUTIAN LOW COMPLEX
WILL PROBABLY FORM SOMETIME AROUND WEDNESDAY OR THURSDAY AND
PERSIST. IT CERTAINLY LOOKS LIKE THE WEATHER PATTERN IS BEGINNING TO
CRANK UP FOR FALL.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING ZONES 170 171 172.
FIRE WEATHER...NONE.

FOISY SEP 07