FXAK68 PAFC 102206 AFDAFC AREA FORECAST DISCUSSION SOUTHCENTRAL AND SOUTHWEST ALASKA 105 PM AST WED JAN 10 2007 .DISCUSSION... UPPER LEVELS...A MAJOR HEMISPHERIC LOW IS NEARLY STATIONARY AT 55N 169E. LONG-WAVE TROUGH EXTENDS FROM EASTERN EUROPE ALL THE WAY ACROSS ASIA AND THE NORTH PACIFIC. AN EAST-WEST 250 MB JET IS RIDING OUT OF EASTERN ASIA BETWEEN 35N AND 40N OVER TO ABOUT 170W. THERE IS A SHORT-WAVE RIDGE OVER THE EAST PACIFIC CENTERED BETWEEN 140W AND 150E AND NOSING UP INTO MAINLAND ALASKA. THIS PATTERN WILL DRIVE STORM SYSTEMS EASTWARD WELL SOUTH OF THE ALEUTIANS AND THEN NORTHWARD ACROSS THE AKPENN OR GULF OF ALASKA INTO MAINLAND ALASKA. THE BERING SEA/ALEUTIANS/SOUTHWEST ALASKA EXPERIENCED SIGNIFICANT WARNING THE PAST FEW DAYS AS SYSTEMS MOVED NORTHWARD ACROSS THE BERING SEA. SOUTHCENTRAL ALASKA WILL UNDERGO SIMILAR WARMING THE NEXT FEW DAYS AND BEYOND AS SYSTEMS BRING PROGRESSIVELY WARMER AIR NORTHWARD. FOR THE SHORT-TERM FORECAST AIR WILL REMAIN COLD ENOUGH THAT WITH THE EXCEPTION OF KODIAK ISLAND PRECIPITATION WILL REMAIN IN THE FORM OF SNOW. SURFACE...THE SURFACE REFLECTION OF UPPER LOW OVER THE WESTERN BERING HAS AN ESTIMATED CENTRAL PRESSURE OF 968 MB. SOMEWHAT COLDER AIR IS BEING TRANSPORTED OUT OF EASTERN RUSSIA SOUTH OF THE LOW CENTER AND THEN NORTHWARD INTO THE BERING SEA. AS INDICATED BY THE 12Z SHEMYA SOUNDING THIS HAS CREATED A MODERATELY UNSTABLE ATMOSPHERE. SATELLITE IMAGERY SHOWS THE RESULT OF THIS WHICH IS A LARGE AREA OF SHOWERS ROTATING NORTHWARD ACROSS THE ALEUTIANS INTO THE CENTRAL BERING SEA. AS THE UPPER LEVELS CONTINUE TO COOL PRECIPITATION TYPE IS SWITCHING TO SNOW. FARTHER EAST IS A SURFACE LOW CENTERED JUST WEST OF NUNIVAK ISLAND WITH COLD FRONT EXTENDING SOUTHWARD ACROSS THE EASTERN BERING SEA AND AKPENN. THE LOW IS TRACKING NORTHWARD AND WITH A RIDGE OVER THE GULF THE COLD FRONT IS MAKING VERY LITTLE EASTWARD PROGRESS. RADAR IMAGERY SHOWS THE BACK EDGE OF PRECIPITATION RIGHT ALONG THE SOUTHWEST COAST. STRONG WINDS ALONG THIS FRONT PRODUCED BLIZZARD CONDITIONS EARLIER ACROSS THE KUSKOKWIM DELTA. WINDS REMAIN STRONG BUT SNOW HAS DIMINISHED AND TEMPERATURE HAVE RISEN TO NEAR FREEZING SO THE BLIZZARD WARNING WAS ALLOWED TO EXPIRE AT NOON. LIGHT SNOW IS SLOWLY MAKING ITS WAY UP COOK INLET. THIS SNOW IS MAINLY DUE TO WARMER AIR OVERRIDING ARCTIC AIR MASS CURRENTLY SITTING OVER SOUTHCENTRAL. AIR TEMPERATURES ARE SLOWLY RISING...BUT REMAIN BELOW ZERO ACROSS MUCH OF INTERIOR SOUTHCENTRAL. MODEL ANALYSIS...MODELS INITIALIZED WELL AND DEPICT A SIMILAR SOLUTION THROUGH 48 HOURS. BEYOND THAT POINT MODEL SOLUTIONS DIVERGE AND MODELS DISPLAY POOR RUN-TO-RUN CONSISTENCY. FOR NOW WILL TREND TOWARD THE NEW GFS SOLUTION BEYOND 48 HOURS. SOUTHCENTRAL FORECAST...THE COLD FRONT OFF THE SOUTHWEST ALASKA COAST WILL BECOME STATIONARY OVER SOUTHWEST ALASKA TONIGHT AND REMAIN THERE THROUGH THURSDAY. THIS WILL PROVIDE A PROLONGED PERIOD OF SOUTHERLY FLOW AND MOISTURE TRANSPORT AHEAD OF THE FRONT OVER SOUTHCENTRAL ALASKA. THIS WILL PRODUCE SIGNIFICANT SNOWFALL FOR MUCH OF THE SUSITNA VALLEY WITH ENHANCED SNOW ALONG THE UPSLOPE OF THE ALASKA RANGE. THE EAST-WEST PRESSURE GRADIENT ACROSS SOUTHCENTRAL WILL INCREASE TONIGHT AS GULF OF ALASKA RIDGE SLIDES EASTWARD. THIS WILL PROVIDE SOME STRONG LOW LEVEL WINDS OUT OF THE SOUTHEAST ACROSS THE KENAI MOUNTAINS. HOWEVER...WITH SOUTH TO SOUTHWEST FLOW ALOFT SNOW IS STILL EXPECTED TO FALL ALONG THE LEE SIDE OF THE MOUNTAINS...BUT SHOULD REMAIN LIGHTER CLOSER TO THE MOUNTAINS DOE TO THESE WINDS. ASIDE FROM THE SUSITNA VALLEY THE HEAVIEST SNOWFALL IS EXPECTED ALONG THE SOUTH SIDE OF KACHEMAK BAY WHICH IS RIGHT IN THE PATH OF THE DEEPEST MOISTURE AND UNAFFECTED BY THE LOW LEVEL WINDS EXPECTED TO DEVELOP ACROSS THE KENAI MOUNTAINS. SNOW WILL ALSO DEVELOP THIS AFTERNOON AND EVENING ACROSS THE PRINCE WILLIAM SOUND REGION AND LIGHT SNOW SHOULD SPREAD INLAND TO THE COPPER RIVER BASIN OVERNIGHT AS WARMER AIR CONTINUES TO OVERRIDE THE ARCTIC AIR IN PLACE. AS THE PRESSURE GRADIENT TIGHTENS WINDS MAY REACH ABOUT 25 MPH THROUGH PORTAGE VALLEY AND PORTAGE ARM AND RESULT IN BLOWING SNOW. A BLOWING SNOW ADVISORY HAS BEEN ISSUED FOR TONIGHT...EXPECT THIS TO BE A MARGINAL EVENT SINCE WINDS ARE EXPECTED TO BARELY REACH HIGH ENOUGH TO PRODUCE LOW VISIBILITIES. AS WE HEAD TO THE END OF THE WEEK AN UPPER LEVEL SHORT-WAVE WILL TRACK NORTHWARD TO SOUTHCENTRAL. THIS WILL CAUSE THE FLOW TO SHIFT TO EASTERLY THURSDAY NIGHT AND FRIDAY AND HELP CUT OFF SNOW IN MANY PLACES...ESPECIALLY INLAND WHILE THE COASTAL AREAS WILL REMAIN SNOWY. LOOK FOR PATTERN TO REMAIN WET (OR SNOWY) AS WE HEAD INTO THE EXTENDED PERIOD WITH THE STORM TRACK BRING SYSTEMS UP TO THE SOUTHERN MAINLAND. EACH SYSTEM WILL PROVIDE A LITTLE MORE WARMING AND WE MAY EVENTUALLY HAVE TO START DEALING WITH PRECIPITATION TYPE PROBLEMS AGAIN. SOUTHWEST ALASKA FORECAST...AS THE COLD FRONT BECOMES STATIONARY OVER SOUTHWEST ALASKA TONIGHT AREAS JUST NORTH EAST OF THE FRONT...MAINLY ALONG THE ALASKA AND ALEUTIAN RANGES...WILL CONTINUE TO SEE PERIODS OF SNOW WHILE AREAS WEST OF THE FRONT WILL DRY OUT. AS THE UPPER SHORT-WAVE MOVES ACROSS THE REGION THURSDAY NIGHT AND FRIDAY ANOTHER ROUND OF SNOW IS LIKELY. AS MENTIONED ABOVE PATTERN WILL REMAIN ACTIVE FOR THIS REGION AS WE HEAD INTO THE EXTENDED PERIOD. BERING SEA/ALEUTIANS FORECAST...FAR AWAY FROM THE STORM TRACK MOST OF THE BERING SEA AND ALEUTIANS WILL REMAIN UNDER A SHOWERY REGIME THROUGH THE WEEKEND. .AER/ALU...WATCH/WARNING SUMMARY PUBLIC...NONE. MARINE...GALE WARNING 132 150 155. HEAVY FREEZING SPRAY 140. SEB JAN 07