Small Craft Advisory 536, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
200 PM AKDT MON JUL 7 2008

.ANALYSIS AND UPPER LEVELS...A CLOSED LOW NEAR 53N 151W IS EMBEDDED
WITHIN A POSITIVELY TILTED TROUGH THAT EXTENDS FROM MAINLAND ALASKA
AND THE YUKON SOUTHWESTWARD TO AROUND 35N 170W. THE LOW IS TRACKING
SLOWLY OFF TO THE NORTHEAST. WATER VAPOR IMAGERY SHOWS MULTIPLE
SHORT-WAVES ROTATING AROUND THE LOW CENTER. THE MOST SIGNIFICANT OF
THESE IS ROTATING WESTWARD ACROSS SOUTHCENTRAL. RADAR IMAGERY SHOWS
A BAND OF RAIN FROM COOK INLET SOUTHWESTWARD TO THE ALASKA PENINSULA.

ANOTHER STRONG SHORT-WAVE OVER THE SOUTHERN YUKON IS ROTATING
WESTWARD TOWARD THE COPPER RIVER BASIN.

THE THERMAL TROUGH EXTENDS FROM INTERIOR ALASKA SOUTHWESTWARD TO THE
KUSKOKWIM DELTA. BETHEL AND MCGRATH SOUNDINGS SHOW FAIRLY STEEP LOW
LEVEL INVERSIONS TO ABOUT 900 MB AND THEN DRY ADIABATIC LAPSE RATES
UP TO 700 MB. THIS LAYER OF INSTABILITY IS PRODUCING ISOLATED
THUNDERSTORMS FROM THE KUSKOKWIM VALLY ACROSS THE KILBUCK MOUNTAINS
AND INTO THE BERING SEA THIS MORNING.

A SHORT-WAVE RIDGE OVER THE NORTHWEST PACIFIC EXTENDS UP INTO THE
WESTERN BERING SEA...BUT A STRONG SHORT-WAVE OVER FAR EASTERN RUSSIA
IS PUSHING THE RIDGE BACK SOUTHWARD AS IT SWINGS TOWARD THE NORTHERN
BERING. CLEAR SKIES DOMINATE JUST AHEAD OF THE RIDGE OVER THE CENTRAL
TO EASTERN BERING INCLUDING THE PRIBILOF ISLANDS.

.MODEL DISCUSSION...GFS IS VERIFYING BETTER THAN NAM WITH THE UPPER
WAVE AND ASSOCIATED PRECIPITATION OVER THE SOUTHERN MAINLAND THIS
MORNING. NAM ALSO DIFFERS SLIGHTLY FROM GFS/UKMET/ECMWF IN
ORIENTATION OF UPPER LOW/RIDGE COUPLET OVER SOUTHEAST ALASKA AND
SOUTHCENTRAL TUESDAY. THEREFORE...PREFER GFS TIMING AND PLACEMENT
OF THE NEXT SHORT-WAVE. OUT WEST THE GFS HAS TRENDED TOWARD
YESTERDAYS 00Z ECMWF SOLUTION IN HANDLING OF THE NEXT LOW DROPPING
SOUTHWARD ACROSS THE BERING. MEANWHILE THE NEW 12Z ECMWF HAS JUMPED
BACK TO A PREVIOUS SOLUTION WHICH STALLED THE LOW WEST OF NUNIVAK
ISLAND. WILL STICK WITH THE 00Z ECMWF/12Z GFS SOLUTION FOR NOW.

.SHORT TERM FORECAST...

SOUTHCENTRAL...EXTENSIVE CLOUD COVER ALONG WITH A FEW SHOWERS WILL
REMAIN IN PLACE TODAY BETWEEN THE TWO UPPER WAVES. THE UPPER WAVE
OVER THE YUKON WILL TRACK WESTWARD INTO THE COPPER RIVER BASIN LATE
THIS AFTERNOON AND THEN TAKE A MORE SOUTHERLY TRACK AS THE UPPER
FLOW SHIFTS TO THE NORTH TONIGHT AND TUESDAY. MEANWHILE ANOTHER WAVE
WILL DROP SOUTH FROM THE INTERIOR ACROSS THE SUSITNA VALLEY. THESE
UPPER WAVES WILL PRODUCE ANOTHER ROUND OF RAIN ACROSS SOUTHCENTRAL
TONIGHT THROUGH TUESDAY NIGHT. THERE IS SOME UNCERTAINTY IN THE
EXACT TRACK OF THESE FEATURES. RIGHT NOW IT LOOKS LIKE THE STEADIEST
RAIN WILL FALL OVER THE WESTERN COPPER BASIN/TALKEETNA MOUNTAINS
TONIGHT AND THEN SPREAD DOWN ACROSS ANCHORAGE AND THE KENAI PENINSULA
ON TUESDAY. A RIDGE WILL GRADUALLY BUILD OVER MAINLAND ALASKA TUESDAY
NIGHT AND WEDNESDAY...BUT IT LOOKS LIKE IT WILL BE A DIRTY
RIDGE...WITH WEAK UPPER WAVES HELPING TO MAINTAIN QUITE A FEW CLOUDS
AS WELL AS SCATTERED CONVECTION. THE RIDGE WILL STRENGTHEN A BIT
WEDNESDAY NIGHT AND THURSDAY WHILE THE THERMAL TROUGH DROPS SOUTH OF
THE ALASKA RANGE. EXPECT TYPICAL SUMMERTIME CONDITIONS OF A BIT OF
SUN ACCOMPANIED BY AFTERNOON AND EVENING CONVECTION...MAINLY ALONG
THE MOUNTAINS.

SOUTHWEST ALASKA...DO NOT EXPECT TO COMPLETELY REALIZE ALL OF THE
CONVECTIVE AVAILABLE POTENTIAL ENERGY OVER SOUTHWEST ALASKA TODAY.
THE LOW LEVEL CAP IS A BIT MUCH TO OVERCOME. SURFACE TEMPERATURES
ARE RUNNING 4 TO 9 DEGREES LOWER THAN 24 HOURS AGO ACROSS THE
KUSKOKWIM VALLEY AND DELTA AND MORE STABLE AIR IS GRADUALLY WORKING
ITS WAY INTO THE REGION FROM THE SOUTHEAST. HOWEVER...WITH THERMAL
TROUGH JUST TO THE NORTH AND WEST AND UNSTABLE CONDITIONS ABOVE NEAR
SURFACE LAYER EXPECT SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS TO
FORM...ESPECIALLY ALONG THE MOUNTAINS. PRIME AREA LOOKS TO BE ALONG
THE KUSKOKWIM AND KILBUCK MOUNTAINS. THE THERMAL TROUGH WILL  BE
PUSHED NORTHWARD TONIGHT AND TUESDAY AS MORE STABLE AIR APPROACHES
FROM EAST AND WEST. THIS WILL BRING A TEMPORARY END TO THE THREAT
OF THUNDERSTORMS. WEAK HIGH PRESSURE WILL BUILD OVERHEAD TUESDAY AND
WEDNESDAY. EXPECT ONLY A FEW SHOWERS...MAINLY ALONG THE MOUNTAINS
DURING THE AFTERNOON AND EVENING HOURS.

BERING SEA/ALEUTIANS/ALASKA PENINSULA...THE LOW OVER THE RUSSIAN FAR
EAST WILL DROP SOUTHWARD INTO THE NORTHERN BERING TONIGHT AND TUESDAY
PUSHING A DECENT SUMMERTIME FRONT SOUTHWARD TO THE WESTERN ALEUTIANS.
EXPECT SMALL CRAFT TO MIN GALES AHEAD OF THE FRONT AS WELL AS ON THE
BACK SIDE OF THE LOW WHERE THERE WILL BE A JET OVERHEAD. MODELS HAVE
BEEN VERY INCONSISTENT IN EVOLUTION OF THIS LOW SO CONFIDENCE BEYOND
WEDNESDAY IS QUITE LOW. WITH RIDGING TO THE EAST OVER MAINLAND ALASKA
EXPECT THE LOW WILL STALL SOMEWHERE FROM THE EASTERN BERING TO ALASKA
PENINSULA.

.LONG TERM FORECAST...LOOKS LIKE RIDGE WILL BRIEFLY HOLD OVER
MAINLAND ALASKA LATE THIS WEEK...BUT TROUGH WILL TRANSITION BACK
TO THE GULF NEXT WEEKEND AS RIDGE BUILDS OVER THE WESTERN BERING
SEA.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING 185.
FIRE WEATHER...NONE.

SEB JUL 08