Small Craft Advisory 528, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
115 PM AKDT FRI JUL 3 2009

.MODEL DISCUSSION...

MODELS ARE IN EXCELLENT AGREEMENT IN THE SHORT TERM....WHILE LEANED
TOWARDS THE EUROPEAN MODEL FOR THE VERY END OF THE SHORT TERM THROUGH
THE MEDIUM RANGE FOR ITS MORE CONSISTENT HANDLING OF THE NEXT SYSTEM
TO AFFECT THE BERING SEA AND NORTH PACIFIC REGION.

.ANALYSIS AND UPPER LEVELS...

ALOFT...A WEAK UPPER LEVEL LOW IS CONTINUING TO MOVE SOUTH AND EAST
THROUGH THE OFFSHORE WATERS OF THE GULF OF ALASKA TOWARDS THE
NORTHEAST PACIFIC...WHILE A HIGHLY AMPLIFIED BUT NARROW RIDGE BUILDS
OVER THE REGION FROM THE NORTHERN AK PENINSULA TO THE MIDDLE AND
UPPER KUSKOKWIM VALLEY. WEAK NORTH-NORTHEAST TO SOUTH-SOUTHWEST
OFFSHORE FLOW IS LOCATED OVER MOST OF SOUTHCENTRAL AND THIS IS
TRANSPORTING SMOKE FROM A LARGE 19000+ ACRE FIRE OVER THE
SOUTHCENTRAL REGION RESULTING IN HAZY CONDITIONS.  MEANWHILE...A
STRONG UPPER LOW IS LIFTING NORTHWARDS OVER THE NORTHWESTERN BERING
SEA AND IS RESPONSIBLE FOR DECENT ONSHORE FLOW OVER THE DELTA REGION
AND WINDY CONDITIONS OVER MOST OF THE BERING SEA.

AT THE SURFACE...WEAK HIGH PRESSURE IS LOCATED OVER ALL OF
SOUTHCENTRAL AND THE COASTAL WATERS EARLY THIS AFTERNOON...AND THIS
IS HELPING TO CONTRIBUTE TO MARINE STRATUS AND SOME FOG ALONG THE
COASTLINES TO PLACES LIKE HOMER AND KODIAK.  SOME FOG HAS ALSO BEEN
NOTED IN THE SOUTHERN SUSITNA VALLEY THIS MORNING...BUT THIS SHOULD
BURN OFF WITH ABUNDANT SUNSHINE AND A FAIRLY HIGH SUN ANGLE AT THIS
TIME OF YEAR.  OUT WEST...ONSHORE FLOW FROM THE AK PENINSULA
WESTWARDS AND INCREASING TOWARDS THE DELTA REGION IS RESPONSIBLE FOR
BRINGING LIGHT RAIN AND MOSTLY CLOUDY TO OVERCAST CONDITIONS.  THIS
IS ALL ASSOCIATED WITH A RAPIDLY WEAKENING AND ELONGATING FRONT THAT
IS RUNNING INTO THE AMPLIFIED RIDGE AND HIGH PRESSURE SYSTEM JUST TO
ITS EAST.  NEAR GALE TO GALE FORCE WINDS ARE AFFECTING THE DELTA
COASTLINE AND NUNIVAK ISLAND WITH THE TIGHTENED PRESSURE GRADIENT
BETWEEN A 985 MB LOW PRESSURE CENTER MOVING NORTH IN THE NORTHERN
BERING SEA AND WEAK HIGH PRESSURE OVER THE INTERIOR AND SOUTHCENTRAL.

.SHORT TERM FORECAST...

SOUTH AND EAST OF THE ALASKA RANGE...

PRECIPITATION SHOULD BE LIMITED TO AFTERNOON AND EVENING CONVECTION
WHICH FORMS OVER THE HIGHEST ELEVATIONS OF THE TALKEETNA MOUNTAINS
AND THOSE SURROUNDING THE COPPER RIVER BASIN...LIKELY DECREASING IN
COVERAGE THROUGH THE WEEKEND AS MID-LEVEL TEMPERATURES ASSOCIATED
WITH THE BUILDING UPPER RIDGE CONTINUE TO RISE AND TRY TO CAP THE
CONVECTION.  MEANWHILE...CALM WINDS AND THE SUBSIDENCE INVERSION
SHOULD ALLOW FOR MARINE STRATUS TO CONTINUE IN THE GULF.

SOUTHWEST ALASKA...

WINDS WILL WEAKEN GRADUALLY AND PRECIPITATION DIMINISH AS UPPER LEVEL
SUPPORT LIFTS RAPIDLY NORTHWARD AND THE FRONT WASHES OUT AS IT
CONTINUES RUNNING INTO THE BLOCKING RIDGE.  A WEAK SHORTWAVE APPEARS
TO MOVE JUST NORTH AND WEST OF THE DELTA REGION ON SATURDAY
AFTERNOON...BUT THIS WILL LIKELY ONLY PRODUCE SOME HIGH CLOUDS
NORTHWEST OF BETHEL FOR THE FOURTH OF JULY WHILE SURFACE HIGH IS
LOCATED OVER THE REGION.  THE NEXT SYSTEM TO AFFECT THE AREA LATE
SUNDAY THROUGH MONDAY WILL BRING GREATEST CHANCE OF PRECIPITATION
ONCE AGAIN TO THE DELTA REGION AND THE SOUTHERN HALF OF THE AK
PENINSULA AS IT TAKES A TRACK NORTHWARDS THROUGH THE BERING THANKS TO
THE BLOCKING HIGH PRESSURE OVER MOST OF THE STATE PERSISTING INTO
MIDWEEK.

ALEUTIANS/BERING SEA...

RAIN CHANCES CONTINUE FOR THE CENTRAL ALEUTIANS THROUGH THE SHORT
TERM AS THE NEXT SYSTEM...BETTER HANDLED BY THE EUROPEAN
MODEL...TAKES A TRACK SIMILAR TO THE ONE CURRENTLY MOVING NORTH
THROUGH THE REGION. THEREFORE...SHOULD SEE A PERIOD OF INCREASED
WINDS TO NEAR OR AT GALE FORCE AND RAIN OVER MOST OF THE REGION
EXCEPT THE WESTERN ALEUTIANS FROM SATURDAY NIGHT THROUGH MONDAY.

.LONG TERM FORECAST...

THE EUROPEAN MODEL AND HPC GUIDANCE WERE RELIED UPON FOR THE MEDIUM
RANGE AS IT HAS REMAINED MORE CONSISTENT WITH ITS HANDLING OF THE
NEXT LOW IN THE BERING SEA.  THIS SOLUTION KEEPS THE RIDGE OVER THE
ANCHORAGE AOR THROUGH THE MEDIUM RANGE...WITH PERHAPS SOME FLATTENING
TO ZONAL FLOW FROM WEDNESDAY ONWARD AS A SYSTEM CLIPS THE
NORTHEASTERN PART OF THE STATE INTO THE YUKON TERRITORY.  AN UPPER
LEVEL LOW AND ASSOCIATED UNSETTLED WEATHER WILL REMAIN OVER THE
WESTERN AND CENTRAL BERING SEA.

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

CC JUL 09