FXAK68 PAFC 111408
AFDAFC
AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
500 AM AKST FRI DEC 11 2009
.ANALYSIS AND UPPER LEVELS...
LARGE OMEGA BLOCKING PATTERN CONTINUES TO DOMINATE THE UPPER LEVELS
OVER ALASKA. AS THE DAYS PASS...THE HIGH WILL CONTINUE TO ELONGATE
AND EVENTUALLY WEAKEN AS IT SHIFTS OVER THE NORTHERN BERING AS A DEEP
UPPER LEVEL LOW OVER THE ARCTIC SHIFTS SOUTH. ON THE WESTERN FLANK OF
THE RIDGE...AN UPPER LEVEL LOW OVER THE BERING IS MOVING NORTH WITH A
MODERATELY STRONG LOW REFLECTED AT THE SURFACE.
.MODEL DISCUSSION...
ACROSS THE FORECAST AREAS IN THE EAST AND WEST...THERE ARE NO ISSUES
TO BE HAD WITH THE MODELS THROUGH THE WEEKEND. ALL MODELS ARE
STRUGGLING TO HANDLE THE EVOLUTION OF ANOTHER LOW THAT WILL STAY
SOUTH OF OUR AREA. ISSUES FOR THE EAST DON'T GET PROBLEMATIC UNTIL
EARLY INTO NEXT WEEK WITH THE DEVELOPMENT OF A WEAK SURFACE LOW ON
THE BACKSIDE OF THE PARENT LOW THAT WILL MOVE OVER JUNEAU. THE MODELS
CONTINUE TO TREND THAT WEAK LOW FURTHER EAST...AND BEING OUT OVER 114
HOURS...THERE IS PLENTY OF TIME TO RESOLVE THESE DIFFERENCES. THE
FORECAST THIS MORNING WAS BASED OFF OF THE NAM WITH A TRANSITION INTO
THE GFS. CONFIDENCE REMAINS MODERATELY HIGH...WITH THE BIGGEST
CONCERNS OVER THE LONGEVITY OF THE FOG ALONG THE INLET.
.SHORT TERM FORECAST...
IN THE EAST...THE LATEST GUIDANCE IS SHOWING THAT THE INVERSION THAT
HAS LOCKED CLOUDS AT THE LOWEST LEVELS ACROSS MUCH OF THE COOK INLET
REGION...IS CONTINUING TO WEAKEN AND WILL LIKELY BE BROKEN BY THIS
WEEKEND. AREAS IN AND ALONG COOK INLET WILL CONTINUE TO SEE FREEZING
FOG THROUGHOUT THE DAY TODAY...TONIGHT AND INTO TOMORROW.
VISIBILITIES WILL TEND TO IMPROVE AND DECREASE AT VARIOUS THROUGHOUT
THE DAY AS THE WEAK FLOW AND STRONG INVERSION EXIST. THE DENSE FOG
ADVISORY WILL CONTINUE FOR ANCHORAGE...AND WILL BE KEPT THROUGH THIS
AFTERNOON. A WEAK NORTHERLY FLOW AT THE SURFACE SHOULD HELP TO KEEP
THE DENSEST AREAS OF FOG TO THE SOUTH...AND CONDITIONS WILL GRADUALLY
IMPROVE. THE MAJORITY OF THE AREA WILL CONTINUE TO SEE CLEAR AND
SUNNY SKIES THROUGHOUT THE DAY...WITH THE EXCEPTION BEING MANY
COASTAL AREAS. PRECIPITATION WILL BEGIN TO CREEP INTO THE EASTERN
COASTALS AND INTO PRINCE WILLIAM SOUND LATE SUNDAY. OUTSIDE OF RIMING
FROM ICE CRYSTALS IN THE FOG...NO PRECIPITATION WILL IS EXPECTED
ANYWHERE UNTIL THE UPPER LEVEL RIDGE RETROGRADES TO THE WEST...THE
EXCEPTION BEING HOMER...WHERE LIGHT SNOW IS FALLING OUT OF THE
STRATUS.
OUT WEST...
SURFACE LOW SOUTH OF SHEMYA WILL SLIDE TO THE NORTHWEST BEFORE
DISSIPATING SATURDAY EVENING. INTERMITTENT RAIN AND SNOW SHOWERS WILL
BE EXPECTED ACROSS THE CHAIN THROUGH THE WEEKEND...MAINLY WEST OF
COLD BAY. FOGGY CONDITIONS WILL PERSIST FOR THE DAY ACROSS PARTS OF
THE MAINLAND.
.LONG TERM FORECAST...
THE LONG TERM TREND IS FOR TEMPERATURES TO BEGIN TO DROP INTO THE
MIDDLE OF NEXT WEEK. THE UPPER LEVEL RIDGE WILL RETROGRADE INTO THE
BERING AND A COLD UPPER LEVEL LOW OVER THE ARCTIC WILL SLOWLY DROP
SOUTH ACROSS THE NORTHERN CANADIAN AND ALASKAN BORDER. TEMPERATURES
WILL STEADILY FALL AS THERE WILL BE A SURGE OF COLD AIR BEING EJECTED
OUT OF THE NORTH. LONGWAVE TROUGH OVER CANADA AND LONGWAVE RIDGE OVER
THE EASTERN BERING WILL BOTH SHIFT TO THE WEST...LEAVING A LONGWAVE
TROUGH ALONG THE WESTERN MAINLAND. THIS PATTERN CHANGE COULD BRING
ABOUT A MORE ACTIVE WEATHER PATTERN FOR THE LONG RANGE FORECASTS. THE
CURRENT LONG RANGE FORECAST WAS BASED OFF A COMBINATION OF NATIONAL
HPC GUIDANCE AND THE ECMWF WITH MODERATE CONFIDENCE.
.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...DENSE FOG ADVISORY 101
MARINE...GALE 172 180
FIRE WEATHER...NONE
SHEA DEC 09
