Small Craft Advisory 132, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
515 AM AKST THU FEB 17 2011

CORRECTION TO BERING SEA/ALEUTIANS DISCUSSION

.ANALYSIS AND UPPER LEVELS...
AN UPPER-RIDGE OVER SOUTHCENTRAL ALASKA THIS MORNING IS PROGRESSING
EAST TOWARDS THE ALCAN BORDER. TO THE WEST...A LARGE TROUGH IS OVER
THE BERING SEA AND ADVANCING EAST TOWARDS THE MAINLAND. AT THE
SURFACE A TROUGH OF LOW PRESSURE IS DRAPED ALONG THE NORTHERN GULF
COAST AND IS WEAKENING. OUT WEST A STRONG LOW PRESSURE SYSTEM AROUND
250 NM NORTH OF SAINT MATTHEW ISLAND IS EJECTING NORTHEAST TOWARDS
THE CHUKCHI SEA. AN ASSOCIATED FRONT IS MOVING ASHORE THE KUSKOKWIM
DELTA SPREADING STEADY SNOW.

.MODEL DISCUSSION...
IN THE EAST...MODELS DEPICT THE FRONT APPROACHING THE SW ALASKA
MOVING TOWARDS SOUTHCENTRAL WITH A WAVE OF LOW PRESSURE DEVELOPING
ALONG NEAR THE EASTERN KENAI PENINSULA FRIDAY MORNING...THEN MOVING
THIS LOW TO SOUTHEAST OF JUST SOUTHEAST OF CORDOVA SATURDAY MORNING.
THE GFS AND ECMWF SOLUTION SEEM TO HAVE CAPTURED THIS FEATURE AND
ASSOCIATED MOISTURE BEST. HOWEVER...THE NAM SUGGESTS THE HEAVIEST QPF
OVER THE NEXT 24 HOURS PARTICULARLY ACROSS THE MAT-SU VALLEYS...AND
THIS IS FEASIBLE AS IR AND WATER VAPOR SATELLITE IMAGERY DEPICT A
MODEST FETCH OF MOISTURE FROM THE NORTH PACIFIC ADVANCING.

IN THE WEST...MODELS SIMILARLY CAPTURE THE AFOREMENTIONED FRONT OVER
THE SW MAINLAND...THE BROAD SHOWERY REGIME IN IT'S WAKE...AND THE
APPROACH OF ANOTHER FRONT INTO THE WESTERN BERING ON SATURDAY.

.SHORT TERM FORECAST...
SOUTHCENTRAL...
TRANSITORY RIDGE WILL MOVE TO THE ALCAN BORDER THIS EVENING AND ALLOW
THE FLOW ALOFT TO SHIFT MORE TO THE SOUTHWEST USHERING IN A MORE
FAVORABLE DIRECTION FOR DEEPER MOISTURE TRANSPORT. LOOK FOR LIGHT
SNOW TO OVERSPREAD THE SUSITNA VALLEY DOWN TO THE KENAI PENINSULA
LATE THIS EVENING...AND BECOME HEAVIER OVERNIGHT AS THE RESIDUAL
FRONT APPROACHES FROM THE SOUTHWEST MAINLAND AND A WAVE OF LOW
PRESSURE DEVELOPS NEAR THE KENAI PENINSULA. PERIODS OF MODERATE TO
HEAVY SNOW ARE EXPECTED THROUGH EARLY FRIDAY AFTERNOON...BEFORE THE
LOW MOVES TOWARDS THE NORTH CENTRAL GULF. WINTER WEATHER ADVISORIES
FOR SNOW HAVE BEEN POSTED FOR THE ANCHORAGE BOWL AND MAT-SU VALLEYS
TO COVER THIS THREAT. THE PASSAGE OF AN UPPER-LVL SHORTWAVE LOOKS TO
TAPER PRECIPITATION TO SHOWERS BY FRIDAY EVENING ACROSS MOST AREAS
EXCEPT EASTERN PRINCE WILLIAM SOUND.

SOUTHWEST...
SNOW WILL TAPER TO SHOWERS THROUGH TONIGHT AS THE AFOREMENTIONED
FRONT MOVES TO THE EAST. SNOW MAY BE MIXED AT TIMES WITH RAIN OVER
BRISTOL BAY AS A SMALL WARM NOSE POKES IN FROM THE SOUTH. A SERIES OF
UPPER-LVL DISTURBANCES KEEPS THE THREAT OF SNOW OR SNOW SHOWERS
AROUND INTO EARLY SATURDAY.

BERING SEA/ALEUTIANS...
CYCLONIC FLOW IN THE TROUGH WILL KEEP ABUNDANT SNOW SHOWERS AROUND
THROUGH FRIDAY OVER THE BERING/PRIBILOFS. A BRIEF RESPITE OVER THE
ALEUTIAN CHAIN AS WEAK RIDGING BUILDS IN FRIDAY...AND THEN ANOTHER
FRONT LOOKS TO ADVANCE TO THE WESTERN ALEUTIANS/BERING EARLY
SATURDAY...WITH ANOTHER ROUND OF STRONG WINDS AND RAIN/SNOW.

.LONG TERM FORECAST...
FORECAST CONFIDENCE IN THE EXTENDED PORTION OF THE FORECAST REMAINS
BELOW AVERAGE...AS MODELS STILL ARE STRUGGLING WITH THE PATTERN.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...WINTER WEATHER ADVISORY...101 111 145
MARINE...STORM...185
         GALE...150 165 170 172 175 176 180 411 412 413 414
         HEAVY FREEZING SPRAY...185 411

JAM FEB 11