Small Craft Advisory 590, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
200 PM AKDT SUN AUG 21 2011

.MODEL DISCUSSION...THE GFS/NAM/ECMWF ADEQUATELY HANDLE THE UPPER
LEVEL PATTERN WITH A SHORT WAVE LIFTING ACROSS THE EASTERN MAINLAND
MON AND A DIGGING LONG WAVE OVER THE EASTERN BERING SEA. DIFFERENCES
ARISE IN THE SURFACE AND QPF FIELDS. THE NAM SEEMS TO BE THE MORE
PROGRESSIVE OF THE SOLUTIONS BY MOVING A SURFACE LOW TO THE EASTERN
BERING SEA WELL AHEAD OF THE GFS/NAM SOLUTIONS AND ALSO BRINGS
CONSIDERABLY MORE QPF INTO COOK INLET/SUSITNA VALLEY WED. THE DIGGING
UPPER TROUGH OVER THE EASTERN BERING WILL LIKELY BUILD A RIDGE OVER
BRISTOL BAY AND TEND TO SLOW THE SURFACE CENTER DOWN. THIS WOULD
FAVOR THE GFS AND TO A LESSER EXTENT THE ECMWF SOLUTION. SO THE GFS
IS OVERALL PREFERRED FOR THIS FORECAST PACKAGE.

.ANALYSIS AND UPPER LEVELS...
.500MB...LOW CENTER OVER THE NORTHERN GULF LIFTS NORTH AND WEAKENS
MON NIGHT/TUE AS SHORT WAVE ROTATING AROUND LOW NEAR SAINT LAWRENCE
ISLAND DIGS ACROSS SW AK AND KODIAK. A LOW DEVELOPS NEAR THE BASE OF
THE TROUGH OVER THE GULF TUE AND MOVES SE WHILE THE NORTHERN PORTION
MOVES OVER INTERIOR ALASKA. THE LOW THAT MOVES TOWARD SAINT LAWRENCE
ISLAND MON RETROGRADES WEST TUE AS A SECONDARY LOW DEVELOPS IN
DIGGING TROUGH OVER THE EASTERN BERING SEA TUE AFTERNOON AND WED. BY
WED AFTERNOON...THE TROUGH EXTENDS FROM EASTERN SIBERIA TO SE OF THE
AK PEN. THE RIDGE WHICH BUILDS OVER BRISTOL BAY TUE MOVES TO THE
EASTERN MAINLAND/EAST GULF WED AFTERNOON.

.SURFACE...WEAK LOW PRESSURE CONTINUES ACROSS THE NORTHERN GULF OF AK
THROUGH WED. A SERIES OF WEAK LOW CENTERS OVER THE EASTERN AND
SOUTHERN GULF OF AK HOLDS LOW PRESSURE OVER THE REGION THROUGH WED.
MOISTURE ASSOCIATED WITH A TROUGH EXTENDING OVER WESTERN AK MOVES
INTO SOUTHERN COOK INLET MON MORNING THEN CONTINUES NORTH AND EAST TO
THE SOUTHERN SUSITNA VALLEY AND WESTERN GULF MON NIGHT/TUE. LOW NEAR
THE GULF OF ANADYR MOVES TO SOUTHERN NORTON SOUND TONIGHT AND WEAKENS
WITH WEAK RIDGING OVER BRISTOL BAY. DEVELOPING LOW CENTER MOVING
ACROSS EASTERN RUSSIA MOVES TO NEAR NUNIVAK ISLAND TUE WITH A
PRESSURE IN THE UPPER 980S.

.SHORT TERM FORECAST...
BREAKS IN THE CLOUD COVER AND A STRENGTHENING THERMAL TROUGH WILL
ALLOW FOR ISOLATED AFTERNOON AND EVENING THUNDERSTORMS OVER THE
COPPER RIVER BASIN TODAY. CONDITIONS LOOK A LITTLE MORE STABLE
MON...HOWEVER STILL COULD SEE A FEW THUNDERSTORMS ALONG THE AK RANGE.
SHOWERS ARE GENERALLY EXPECTED ACROSS THE AREA THROUGH THIS EVENING.
INCREASING MOISTURE WITH THE TROUGH MOVING INTO SOUTHERN COOK INLET
MON MORNING WILL BRING INCREASING CHANCES FOR RAIN...WHICH WILL
SPREAD TO MUCH OF THE KENAI/ANCHORAGE BOWL MON NIGHT THEN BECOME MORE
SHOWERY TUE AFTERNOON.

SOUTHWEST...
SHOWERS OVER BRISTOL BAY THIS EVENING WILL BE REPLACED BY STRATUS AND
FOG AS RIDING BUILDS OVERNIGHT. EXTENSIVE LOW CLOUDS OVER WESTERN
COASTS WILL CONTINUE THROUGH TONIGHT WITH SHOWERS OR RAIN INCREASING
ACROSS THE AREA MON WITH APPROACH OF UPPER TROUGH AND WEAKENING
SURFACE LOW. DEVELOPING LOW AND ASSOCIATED FRONTAL TROUGH WILL BRING
WARMING TEMPS AND RAIN TO MUCH OF SW AK TUE AFTERNOON/NIGHT.

BERING SEA/ALEUTIANS...
BRISK NORTHWEST FLOW YIELDING GALE-FORCE GUSTS ACROSS THE SOUTHERN
AKPEN AND ADJACENT WATERS...WEAKENING AS THE PRESSURE GRADIENT
RELAXES TONIGHT. THE SYSTEM DROPPING OUT OF SIBERIA TO BRING A LARGER
SWATH OF GALES TO THE BERING SEA MONDAY NIGHT THROUGH MID-WEEK.
LION'S SHARE OF THE PRECIPITATION LOOKS TO HIT THE PRIBILOF ISLANDS
AND CENTRAL/EASTERN ALEUTIANS AS THE SYSTEM WORKS EAST.

.LONG TERM FORECAST...
THE AOR LARGELY REMAINS IN THE LONG-WAVE TROUGH THROUGH LATE WEEK
KEEPING THINGS UNSETTLED. JET STREAM SUPPORTING STRONG SYSTEMS IN THE
BERING/ALEUTIAN REGION EVENTUALLY MIGRATES EAST...ALLOWING STORM
TRACK TOWARDS THE GULF OF AK...WITH POSSIBLE INCREASING SENSIBLE
WEATHER IMPACTS TO SOUTHCENTRAL AK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALES 180 AND 185.
FIRE WEATHER...NONE.

RMC AUG 11