Dense Fog Advisory 4, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE ANCHORAGE AK
220 PM AKDT MON OCT 8 2012

.ANALYSIS AND UPPER LEVELS...
AN UPPER-LVL RIDGE OVER THE GULF OF AK IS SUPPORTING SURFACE HIGH
PRESSURE THAT IS BUILDING ACROSS THE SOUTHERN MAINLAND. A FRONT WHICH
BROUGHT WIDESPREAD RAIN TO SOUTHCENTRAL AK YESTERDAY HAS MOVED WELL
INLAND TOWARDS THE ALASKA RANGE AND IS WEAKENING...THOUGH A FEW
SPOTTY SHOWERS REMAIN OVER THE NORTHERN REACHES OF THE SUSITNA
VALLEY. WITH THE LOSS OF STEADY PRECIPITATION AND WATER LEVELS
FALLING ACROSS AREA STREAMS AND RIVERS...THE FLOOD ADVISORIES ARE
EXPIRING THIS AFTERNOON. THE PASSAGE OF THE FRONT HAS USHERED IN
ANOMALOUSLY HIGH TEMPERATURES ALOFT...WITH FREEZING LEVELS OF 8000 TO
10000 FEET POKING THROUGH SOUTHCENTRAL AK CORROBORATED BY SOUNDINGS.
SUBSIDENCE FROM THE GULF HIGH PRESSURE COUPLED WITH RESIDUAL LOW LVL
MOISTURE AND STRONG INVERSIONS HAVE SUPPORTED WIDESPREAD FOG AND
STRATUS THROUGH KODIAK ISLAND...PRINCE WILLIAM SOUND...AND HAVE
ENVELOPED COOK INLET UP THROUGH THE MAT-SU VALLEYS. SOME MOISTURE HAS
POKED THROUGH GAPS IN THE ALEUTIAN RANGE AND SPILLED OVER INTO
BRISTOL BAY AS WELL.

THE AFOREMENTIONED FRONT'S WESTERN PORTION EXTENDS THROUGH THE
KUSKOKWIM VALLEY AND DELTA AND POINTS WEST INTO THE NORTHCENTRAL
BERING...AND CONTINUES MOVING WEST SPREADING RAIN ALONG WITH IT. A
RIDGE OF HIGH PRESSURE IS CENTERED OVER EASTERN SIBERIA AND THE
CHUKCHI SEA...WITH A SQUEEZED PRESSURE GRADIENT BETWEEN ITSELF AND
THE FRONT SUPPORTING GALE FORCE WINDS OVER THE NORTHERN BERING SEA.
ALSO OF NOTE IS A LOW PRESSURE SYSTEM DEVELOPING AROUND 350 MILES
SOUTHWEST OF SHEMYA DRIFTING NORTHEAST.

.MODEL DISCUSSION...
MODELS IN GENERAL HAVE A GOOD HANDLE ON THE OVERALL PICTURE. IN THE
EAST...THE UPPER-LVL RIDGE OVER THE GULF IS DEPICTED WEAKENING MID
WEEK AS A VIGOROUS UPPER TROUGH MOVES DOWN ALONG IT'S EASTERN FLANK
WHILE A LOW IN THE CENTRAL PACIFIC PUSHES AGAINST IT FROM THE
SOUTHWEST. THE FRONT ASSOCIATED WITH THE CENTRAL PACIFIC SYSTEM
TRACKS TO THE SOUTHERN AND SOUTHWESTERN FRINGES OF THE GULF OF AK ON
WED...IT'S NORTHWARD PROGRESSION THEREAFTER SHUNTED BY THE RESIDUAL
AND WEAKENED UPPER-RIDGE. SHORTWAVE ENERGY DROPPING SOUTH OUT OF
NORTHEASTERN AK IS DEPICTED SWINGING ALONG THE FAR NORTHERN COPPER
RIVER BASIN TUESDAY AND WEDNESDAY. MEANWHILE...MODELS SHOW THE
UNUSUALLY WARM TEMPERATURES ALOFT COOLING OFF CONSIDERABLY. AT 850
MB...TEMPERATURES PEAK AROUND 6 TO 9 CELSIUS TONIGHT AND DROP TO NEAR
0 CELSIUS AT A COMMENSURATE TIME WED NIGHT. THE NAM APPEARS SLIGHTLY
FASTER WITH THIS DEVELOPMENT...THOUGH ALL MODELS ARE IN THE BALLPARK.
HAVE KEPT THE FORECAST PACKAGE CLOSE TO THE NAM/GFS SOLUTIONS FOR
SOUTHCENTRAL AK AND THE GULF OF AK.

OUT WEST...THE FRONT OVER THE NORTH CENTRAL BERING TRACKS TO THE
NORTHWESTERN BERING TUE AFTERNOON. THE LOW SOUTHWEST OF THE WESTERN
CHAIN IS DEPICTED REACHING PEAK INTENSITY TUE NIGHT...AND SHOWN
MEANDERING IN THE GENERAL VICINITY 150 TO 300 MILES SOUTHWEST OF
SHEMYA THROUGH WED NIGHT. ON THU...THE GFS AND ECWMF DEPICT ANOTHER
PACIFIC SYSTEM TRACKING TO AROUND 300 MILES SOUTH OF NIKOLSKI. THE
NAM ALSO SHOWS THIS SYSTEM...BUT POSITIONS IT 350 MILES SOUTHEAST OF
THE GFS/ECMWF CONSENSUS. HAVE GENERALLY STAYED CLOSE TO THE GFS/ECMWF
IN THE AFTERNOON FORECAST PACKAGE FOR THE BERING/CHAIN.

.SHORT TERM FORECAST...
SOUTHCENTRAL...
FOG AND STRATUS LOOKS TO KEEP A FOOTHOLD OVER THE GULF ON UP THROUGH
COOK INLET/MAT-SU VALLEYS INTO EARLY TUESDAY. HOWEVER THE STRENGTH OF
THE ACCOMPANYING SUBSIDENCE PEAKS TONIGHT WITH THE RIDGE ITSELF
BEGINNING TO FLATTEN OUT AND WEAKEN WITH TIME. THE UP INLET LOW LVL
FLOW BECOMES MORE DOWN INLET AND THE ACCOMPANYING INVERSIONS ERODE AS
COOLER AND DRIER AIR BEGINS TO BLEED DOWN FROM THE INTERIOR. THIS
WILL ALSO RESULT IN OFF-SHORE FLOW GAP WINDS FOR PRINCE WILLIAM SOUND
AND KENAI PENINSULA...HELPING TO SCOUR OUT THE LOW CLOUDS. AS SUCH
EXPECTING FAIR AMOUNTS OF SUNSHINE TO BECOME PREDOMINANT ACROSS MUCH
OF SOUTHCENTRAL ALASKA IN THE COMING DAYS. A CAVEAT WILL BE ALONG
NORTHERN PORTIONS OF THE COPPER RIVER BASIN WHERE ENERGY FROM THE
UPPER TROUGH MAY SQUEEZE OUT SOME RAIN OR SNOW SHOWERS TUE INTO WED.
ACROSS KODIAK ISLAND...WEAK ONSHORE FLOW LIKELY TO KEEP MORE CLOUDS
THAN SUN FOR THE MAJORITY OF THE WEEK.

SOUTHWEST...
WITH THE FRONT MOVING OFFSHORE...PRECIPITATION SHOULD BEGIN TAPERING
OFF TONIGHT OVER THE KUSKOKWIM DELTA AND VALLEY. RESIDUAL LOW LVL
MOISTURE TO STILL SUPPORT SOME AREAS OF FOG INTO TUE. AS THE RIDGE IN
THE GULF WEAKENS...A SMALL CUT-OFF UPPER HIGH SETS UP OVER NW BRISTOL
BAY...WITH DRIER OFF-SHORE FLOW DEVELOPING. THIS SHOULD ENABLE AREAS
OF THE SOUTHWEST MAINLAND TO ALSO SEE MARKEDLY IMPROVED CONDITIONS AS
WELL IN THE COMING DAYS.

BERING SEA/ALEUTIANS...
INITIAL GALES IN THE BERING LOOK TO WEAKEN AS THE PRESSURE GRADIENT
RELAXES A BIT WITH FRONTAL PASSAGE. BROAD LOW PRESSURE HOWEVER
KEEPING THE BERING SEA/ALEUTIANS IN THE THICK OF HIGH RAIN AND GUSTY
WINDS CHANCES.

.LONG TERM FORECAST...
LONGER RANGE MODELS SHOW CONSIDERABLY COLDER AIR FILTERING DOWN FROM
NORTHERN ALASKA AND THE BERING STRAIT LATE WEEK INTO THE WEEKEND.
THIS WOULD TEND TO KEEP A COOL AND GENERALLY DRY REGIME ACROSS THE
SOUTHERN MAINLAND AND A COOL SHOWERY REGIME OVER THE CHAIN/BERING.
STORM TRACK INITIALLY IS SOUTH OF THE CHAIN...BUT BY LATE WEEKEND AND
EARLY NEXT WEEK MAY TREND MORE TOWARDS THE GULF OF AK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...GALE...180 185 411 412
FIRE WEATHER...NONE

MALOY