Snow Advisory 10, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
1210 PM AST SAT JAN 27 2007

.DISCUSSION...

UPPER LEVELS...BLOCKING RIDGE IS CENTERED JUST OFF THE BRITISH
COLUMBIA COAST WITH A HIGH AMPLITUDE TROUGH TO THE WEST FROM THE
BERING SEA ALL THE WAY DOWN TO 20N LATITUDE. THE UPPER JET EXTENDS
EASTWARD OUT OF ASIA BETWEEN 30N AND 40N ALL THE WAY TO ABOUT 160W.
IT THEN MAKE A LEFT TURN AND HEADS DUE NORTH UP TO SOUTHCENTRAL
ALASKA. ONLY CHANGE TO THIS PATTERN EXPECTED OVER THE NEXT SEVEN
DAYS IS FOR RIDGE TO BUILD NORTH AND WESTWARD UP INTO MAINLAND
ALASKA. THIS WILL CURVE THE JET BACK TOWARD THE BERING SEA AND
FORCE THE STORM TRACK FARTHER WEST. SO FOR THE SHORT-TERM THE
PARADE OF STORMS ALONG WITH IMPRESSIVE MOISTURE TRANSPORT AND
WARM AIR ADVECTION WILL CONTINUE TO TRACK FROM THE EAST PACIFIC
NORTHWESTWARD INTO THE BERING SEA. AS WE HEAD TO NEXT WEEK EXPECT
THE STORMS TO TRACK FARTHER SOUTH AND WEST ALONG OR SOUTH OF THE
ALEUTIANS RESULTING IN DRIER WEATHER FOR THE SOUTHERN MAINLAND.

ANALYSIS...WATER VAPOR IMAGERY SHOWS TWO STREAMS OF MOISTURE FROM
THE TROPICS...ONE ALONG 140W AND THEN NORTHEASTWARD TO SOUTHEAST
ALASKA WHICH HAS LOST BEST UPPER SUPPORT FOR CONTINUED MOISTURE
TRANSPORT...AND ANOTHER ALONG 150W UP TO THE GULF OF ALASKA AND
THE SOUTHERN MAINLAND WHICH WILL CONTINUE TO PUMP MOISTURE
NORTHWARD AS UPPER JET STRENGTHENS. A MATURE VERTICALLY STACKED
LOW IS LOCATED JUST SOUTH OF DUTCH HARBOR TRACKING TOWARD THE
PRIBILOF ISLANDS. THE OCCLUDED FRONT WRAPS AROUND THE LOW FROM THE
EASTERN ALEUTIANS UP TO THE EASTERN BERING AND THEN SOUTHEASTWARD
ACROSS THE ALASKA PENINSULA AND WILL CONTINUE TO SPREAD OUT TO THE
NORTH AND EAST. IMPRESSIVE COLD ADVECTION JUST TO THE WEST OF THIS
FRONT ACROSS THE CENTRAL BERING WITH BLIZZARD CONDITIONS NOTED FROM
THE PRIBILOFS TO THE CENTRAL ALEUTIANS. COLD ADVECTION SNOW SHOWERS
ACROSS MUCH OF THE WESTERN BERING AND WESTERN ALEUTIANS. VISIBILITIES
ARE ALSO LOWERING ALONG THE KUSKOKWIM COAST IN SNOW AND BLOWING
SNOW AND BLIZZARD CONDITIONS ARE EXPECTED TO DEVELOP BY AFTERNOON
AS THE HEAVIER PRECIP AND STRONGER WINDS ASSOCIATED WITH THE FRONT
MOVES IN. TEMPS ARE RISING THROUGH THE 20S SO WILL HAVE TO WATCH
THEM CLOSELY TO SEE IF THEY GET UP TO FREEZING BECAUSE THIS WOULD
LIKELY KEEP VISIBILITIES ABOVE BLIZZARD LEVELS. FAIRLY QUIET
CONDITIONS ACROSS SOUTHCENTRAL THIS MORNING WITH JUST A FEW SHOWERS.
PRECIP WILL INCREASE ALONG THE GULF COAST LATER TODAY AS THE OCCLUDED
FRONT APPROACHES. OF SIGNIFICANCE TO THE FORECAST...SURFACE TEMPS
ARE ABOVE FREEZING FROM THE CENTRAL ALEUTIANS TO THE AKPENN TO MUCH
OF THE GULF COASTAL REGION.

MODEL DISCUSSION...MODELS INITIALIZED WELL AND SOLUTIONS ARE VERY
SIMILAR WITH HANDLING OF THE CURRENT SYSTEM AS IT TRACKS ACROSS
THE CENTRAL BERING. THERE CONTINUES TO BE SIGNIFICANT DIFFERENCES
IN HANDLING OF NEXT SYSTEM(S). ALL MODELS PICK UP ON LOW CURRENTLY
DEVELOPING NEAR 38N 167W. ALL MODELS ALSO DEVELOP ANOTHER LOW
THIS EVENING FARTHER EAST NEAR THE LEFT EXIT REGION OF THE UPPER
JET. THE GFS IS THE OUTLIER IN DEVELOPING THIS LOW FARTHER EAST
THAN THE NAM/UKMET/ECMWF AND MAINTAINING TWO DISTINCT LOWS. THE
PREFERRED SOLUTION IS THE MODEL CONSENSUS WHICH DEVELOPS THIS
NEW LOW INTO THE DOMINANT LOW AND ABSORBING THE LOW CURRENTLY
AT 38N 167W.

BERING SEA/ALEUTIANS/SOUTHWEST ALASKA FORECAST...OCCLUDED FRONT WILL
MOVE THROUGH THE PRIBILOFS LATE THIS AFTERNOON OR EVENING AND WINDS
WILL DIMINISH. HOWEVER...EXPECT WINDS TO REMAIN GUSTY OUT OF THE
NORTHEAST AHEAD OF THE LOW CENTER SO BLIZZARD CONDITIONS SHOULD
CONTINUE. THE LOW WILL REACH THE PRIBILOFS LATE TONIGHT AND WINDS
WILL COME WAY DOWN...ENDING THE BLIZZARD CONDITIONS AND CHANGING
PRECIP TO SHOWERS. WINDS WILL ALSO DIMINISH BY LATE TONIGHT ACROSS
THE CENTRAL ALEUTIANS AS THE LOW WEAKENS AND PRESSURE GRADIENT
RELAXES...SO BLIZZARD CONDITIONS SHOULD END THERE BY MORNING AS WELL.
HOWEVER...COLD ADVECTION AND SNOW SHOWERS WILL CONTINUE SO WINDS
WILL REMAIN GUSTY AND THERE MAY BE OCCASIONALLY LOW VISIBILITIES IN
SNOW SHOWERS. THE KUSKOKWIM DELTA IS A TOUGHER CALL SINCE THERE IS
SOME QUESTION AS TO HOW WARM TEMPERATURES WILL GET ALONG THE COAST
AND WHETHER BLIZZARD CONDITIONS WILL DEVELOP THIS AFTERNOON.
THEREFORE...WILL WAIT UNTIL LATER THIS AFTERNOON TO MAKE A DECISION
ON THIS WARNING. STRONG SOUTHEASTERLY FLOW ACROSS AHEAD OF FRONT
WILL RESULT IN DOWNSLOPE DRYING ACROSS PORTIONS OF SOUTHWEST ALASKA.
THEREFORE...DO NOT EXPECT SIGNIFICANT PRECIP ACROSS THIS REGION.
THE NEXT SYSTEM WILL APPROACH THE AKPENN AND EASTERN ALEUTIANS
SUNDAY NIGHT AND MOVE ACROSS THE BERING SEA MONDAY AND TUESDAY.
THIS SYSTEM WILL BRING EVEN WARMER AIR THAN THE CURRENT SYSTEM DID
AND PRECIP TYPE FROM THE EASTERN ALEUTIANS TO SOUTHWEST ALASKA WILL
BE PREDOMINANTLY RAIN. LOOKS LIKE WARM AIR MAY EVEN MAKE IT FAR
ENOUGH NORTH AND WEST TO CHANGE PRECIP TO RAIN ON THE PRIBILOFS.
THEREFORE...DO NOT EXPECT ANY PUBLIC WARNINGS WILL NEED TO BE ISSUED.

STRONGEST WINDS WILL OCCUR ON THE EAST SIDE OF THE STORM WHERE MAX
GALES TO MIN STORMS ARE EXPECTED FOR THE SOUTHWEST ALASKA COASTAL
WATERS AND AKPENN COASTAL WATERS. YET ANOTHER SYSTEM WILL START TO
IMPACT THE REGION BY TUESDAY...WITH THE EFFECTS BEING FELT FARTHER
WEST AS THE STORM TRACK SHIFTS SOUTH AND WEST.

SOUTHCENTRAL FORECAST...THE OCCLUDED FRONT ASSOCIATED WITH THE LOW
NEAR THE EASTERN ALEUTIANS WILL WEAKEN AS IT TRACK ACROSS KODIAK
ISLAND TONIGHT AND TO SOUTHCENTRAL SUNDAY. HOWEVER...THE SURFACE
PRESSURE GRADIENT AND UPPER LEVEL HEIGHT GRADIENT WILL REMAIN
TIGHT AND STRONG SOUTHEAST FLOW WILL CONTINUE. THEREFORE...EXPECT
THE TYPICAL LEE SIDE DOWNSLOPE DRYING. WITH AN ABUNDANT SUPPLY OF
MOISTURE THE GULF COAST AND PRINCE WILLIAM SOUND WILL SEE
SIGNIFICANT PRECIP TOTALS TONIGHT SUNDAY. HOWEVER...UNLIKE THE
LAST STORM WHICH RESULTED IN SNOW AMOUNTS MEASURED IN FEET...THERE
IS ENOUGH WARM AIR IN PLACE AND MORE MOVING INTO THE AREA SO THAT
MOST OF THE PRECIP ALONG THE COAST AT SEA LEVEL WILL BE IN THE FORM
OF RAIN. ONE AREA THAT WILL LIKELY REMAIN ALL SNOW IS THOMPSON PASS.
THEY WILL ALSO SEE GUSTY WINDS LATER TONIGHT AS THE GRADIENT
TIGHTENS UP CAUSING BLOWING SNOW. TEMPS WILL RISE INTO THE UPPER 20S
TO NEAR FREEZING SO SNOW WILL BE WET WHICH SHOULD MINIMIZE THE
EXTENT OF BLOWING SNOW AND KEEP VISIBILITIES FROM GETTING TO LOW.
HOWEVER...THERE IS A CHANCE THAT THEY MAY SEE A BRIEF PERIOD OF LOW
VISIBILITIES BEFORE TEMPS WARM UP. SO FOR NOW DO NOT PLAN ON ISSUING
ANY ADVISORIES OR WARNINGS...BUT WILL MONITOR TRENDS CLOSELY AND
ISSUE A BLOWING SNOW ADVISORY IF NECESSARY. ELSEWHERE...WILL ISSUE
A SNOW ADVISORY FOR THE WESTERN SUSITNA VALLEY WHICH WILL RECEIVE
ENHANCED SNOWFALL FROM THE SOUTHEAST UPSLOPE FLOW. SOUTHCENTRAL WILL
DRY OUT SUNDAY NIGHT EXCEPT FOR SOME SHOWERS ALONG THE COAST. SINCE
THE NEXT STORM SYSTEM IS EXPECTED TO TRACK FARTHER WEST EXPECT
LIGHTER AMOUNTS OF PRECIP...MAINLY ALONG THE COAST...SUNDAY
NIGHT THROUGH MONDAY NIGHT...AND EVEN WARMER AIR. BY MID WEEK THE
RIDGE WILL BUILD OVERHEAD AND SOUTHCENTRAL WILL DRY OUT WITH TEMPS
NEAR TO A BIT ABOVE AVERAGE. ONLY CHANCE OF PRECIP FOR MID TO LATE
WEEK WILL BE KODIAK ISLAND WHICH WILL BE ON THE OUTER FRINGE OF
ALEUTIAN STORMS.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING 155 187 195.
MARINE...GALE WARNING 120 130 132 138 150 155 160
                      165 172 179 180 185.
         HEAVY FREEZING SPRAY WARNING 179 185.

SEB JAN 07