Small Craft Advisory 128, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
1245 PM AST WED FEB 13 2008

.ANALYSIS AND UPPER LEVELS...SATELLITE IMAGERY SHOWS A LARGE DEEP
MATURE LOW AFFECTING MUCH OF ALASKA TODAY. THE LOW IS CENTERED ABOUT
300 MILES SOUTH OF COLD BAY. CENTRAL PRESSURE BOTTOMED OUT AROUND
950 MB AND THE LOW HAS BEGUN TO WEAKEN WITH CURRENT PRESSURE AROUND
960 MB. THE LOW IS TRACKING VERY SLOWLY NORTHEASTWARD. THE OCCLUDED
FRONT EXTENDS NORTHEASTWARD FROM THE LOW TO JUST EAST  OF COLD BAY
UP ACROSS EASTERN BRISTOL BAY AND THEN EASTWARD ACROSS THE NORTHERN
GULF. STRONG NORTHERLY COLD ADVECTION WINDS WEST OF THIS FRONT
COMBINED WITH SNOW AND SNOW SHOWERS ARE RESULTING IN BLIZZARD
CONDITIONS FROM THE PRIBILOFS TO THE EASTERN ALEUTIANS AND SOUTHERN
ALASKA PENINSULA TO THE SOUTHWEST COAST. WIDESPREAD GALES WITH STORM
FORCE GUSTS ARE BEING OBSERVED ACROSS THE EASTERN BERING REGION.
EASTERLY CHINOOK WINDS DOMINATE EAST OF THE FRONT ALONG THE ALASKA
PENINSULA AND AHEAD OF THE FRONT OVER SOUTHCENTRAL ALASKA.
COMBINATION OF WINDS AND WARM ADVECTION BEHIND THE FRONT ARE CAUSING
SIGNIFICANT WARM-UPS BEHIND THE FRONT. LOCATIONS ALONG THE NORTHERN
ALASKA PENINSULA HAVE WARMED FROM SINGLE DIGITS TO TEENS EARLY THIS
MORNING TO THE 30S LATE THIS MORNING. PRECIPITATION OVER SOUTHCENTRAL
IS STILL MAINLY SNOW AS OF LATE MORNING...BUT AS THE FRONT MAKES
NORTHWARD PROGRESS TEMPERATURES WILL WARM AND CHANGE MUCH OF
PRECIPITATION OVER TO RAIN. DOWNSLOPE AREAS ARE SEEING THE TYPICAL
DRYING AFFECT WITH ONLY A FEW FLURRIES MAKING IT TO THE SURFACE.

.MODEL DISCUSSION...MODELS CONTINUE TO HAVE A GOOD HANDLE ON CURRENT
SYSTEM AND ARE VERY CONSISTENT IN TRACKING THE LOW OVER KODIAK ISLAND
AND THEN INLAND ACROSS THE COOK INLET/SUSITNA VALLEY CORRIDOR.
THEREFORE...WILL NOT MAKE ANY SIGNIFICANT CHANGES TO SHORT-TERM
FORECAST. WILL FOCUS ON FINE-TUNING THE DETAILS AND WARNING TIMES.
MODEL SOLUTIONS CONTINUE TO DIVERGE WITH DETAILS OF THE NEXT COUPLE
SYSTEMS SOUTH OF THE ALEUTIANS...THOUGH THEY ARE AT LEAST NOW IN THE
SAME GENERAL REGION WITH LOW POSITIONS. CURRENT FORECAST WAS BASED
HEAVILY ON BLEND OF PRIOR GFS SOLUTIONS AND PLAN TO STICK CLOSE TO
THIS FOR NOW.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...THE OCCLUDED FRONT WILL MOVE ONSHORE LATE THIS
AFTERNOON THROUGH THIS EVENING. THIS WILL TURN PRECIPITATION TO ALL
RAIN ALONG AND NEAR THE COAST. THOMPSON PASS IS HIGH ENOUGH THAT
THEY WILL REMAIN ALL SNOW...SO THERE IS A BLIZZARD WARNING IN EFFECT
BEGINNING 6 PM THIS EVENING AS WINDS INCREASE AHEAD OF THE FRONT
THROUGH THURSDAY MORNING. WINDS WILL DIMINISH BY THURSDAY MORNING
BEHIND THE FRONT AND TEMPERATURES SHOULD WARM ENOUGH TO CREATE WETTER
SNOW SO THAT VISIBILITIES SHOULD IMPROVE. HOWEVER...WINDS WILL
INCREASE AGAIN THURSDAY NIGHT AS GRADIENT TIGHTENS UP AND COLD AIR
ADVECTION BEHIND THE LOW KICKS IN...SO THOMPSON PASS COULD GET BACK
INTO BLIZZARD CONDITIONS. WILL WAIT UNTIL FIRST WARNING UNFOLDS
BEFORE MOVING ON TO THE NEXT. CHINOOK WINDS WILL REMAIN STRONG AHEAD
OF THE FRONT TODAY...KEEPING DOWNSLOPE AREAS MOSTLY DRY. LOW LEVEL
FLOW DOWN COOK INLET WILL MAINTAIN A THIN LAYER OF BELOW FREEZING
AIR AT THE SURFACE WHILE WARM AIR OVERRUNS IT. THIS WILL RESULT IN
AREAS OF RAIN AT HIGHER ELEVATIONS INCLUDING THE ANCHORAGE
HILLSIDE...WHILE LOW ELEVATIONS MAY SEE SOME LIGHT FREEZING RAIN.
CHINOOK WINDS WILL LIKELY DIMINISH TONIGHT AS THE FRONT MOVES INLAND
AND FALL APART. HOWEVER WINDS WILL INCREASE AGAIN THURSDAY AS THE
LOW MOVES TO COOK INLET AND THE COLD AIR WILL CONTINUE TO ERODE FROM
THE TOP DOWN. AS THE LOW PASSES WEST OF ANCHORAGE EARLY THURSDAY
EVENING THERE MAY BE A BRIEF PERIOD WHERE TEMPERATURES RISE ABOVE
FREEZING EVERYWHERE AND PLAIN RAIN FALLS. THE COLD AIR WILL BE MOVING
IN FAST...SO BY LATE EVENING ALL PRECIPITATION WOULD BE BACK TO SNOW.
THE ONE AREA THAT WILL SEE STEADY SNOWFALL TODAY THROUGH THURSDAY IS
THE WESTERN SUSITNA VALLEY WHERE UPSLOPE FLOW WILL ENHANCE SNOW
AMOUNTS. A SNOW ADVISORY IS IN EFFECT THROUGH THURSDAY AFTERNOON
FOR THIS AREA. SNOW SHOULD LIGHTEN UP THURSDAY AFTERNOON FOR SKWENTA
AND NORTHWARD AS THE LOW LEVEL FLOW BACKS TO THE EAST WITH THE LOW
MOVING INTO THE INLET. THE COLD ADVECTION BEHIND THE SYSTEM WILL BE
STRONG SO PRECIPITATION WILL CHANGE OVER TO SNOW EVERYWHERE THURSDAY
NIGHT AND MOST PLACES SHOULD SEE SOME SNOW ACCUMULATION AS A SHARP
UPPER SHORT-WAVE SWINGS THROUGH. THE STRONG COLD ADVECTION WILL ALSO
RESULT IN THE NORMAL STORM FORCE GUSTS THROUGH THE KODIAK ISLAND
MARINE AREAS AND POSSIBLY INTO THE SOUTHERN PORTION OF COOK INLET. IF
THERE IS PRECIPITATION LEFT IN KACHEMAK BAY WHEN THE WINDS GET IN
THERE HOMER AND VICINITY COULD SEE BLIZZARD CONDITIONS AT SOME POINT
THURSDAY NIGHT. WILL WAIT ANOTHER MODEL RUN BEFORE DECIDING WHETHER
TO ISSUE A BLIZZARD WATCH. SOUTHCENTRAL WILL DRY OUT FRIDAY AS A
SHORT-WAVE RIDGE MOVES OVERHEAD. THERE IS NOT A WHOLE LOT OF
CONFIDENCE IN DETAILS OF THE NEXT SYSTEM...BUT AT THIS POINT IT LOOKS
LIKE SOUTHCENTRAL WILL BE IMPACTED BY SATURDAY WITH ANOTHER ROUND OF
WINDS AND PRECIPITATION.

SOUTHWEST ALASKA...THE WESTWARD PROGRESSION OF THE FRONT WILL
CONTINUE THROUGH THIS EVENING AND THEN STALL APPROXIMATELY ALONG A
LINE FROM MCGRATH TO DILLINGHAM LATE TONIGHT AS THE UPPER TROUGH
BEGINS TO BECOME NEGATIVELY TILTED. AREAS JUST WEST OF THE ALASKA
AND ALEUTIAN RANGES WILL CONTINUE TO SEE THA FFECTS OF DOWNSLOPE
DRYING...BUT THE LITTLE PRECIPITATION THAT DOES FALL WILL BE MAINLY
IN THE FORM OF RAIN. FARTHER AWAY FROM THE MOUNTAINS LOW LEVEL COLD
AIR WILL STAY FIRMLY ENTRENCHED SUCH THAT THERE WILL BE AN AREA WITH
GOOD POTENTIAL FOR FREEZING RAIN. WEST OF THE FRONT PRECIPITATION
WILL REMAIN ALL SNOW. STRONG WINDS ALONG THE SOUTHWEST COAST WILL
MAINTAIN BLIZZARD CONDITIONS. THE BLIZZARD WARNINGS HAVE BEEN
EXTENDED UNTIL MIDNIGHT...BUT THESE WILL MOST LIKELY BE EXTENDED TO
THURSDAY AFTERNOON BECAUSE THE COLD ADVECTION WILL KICK IN LATE
TONIGHT INTO THURSDAY MAINTAINING THE STRONG WINDS ALONG THE COAST.
THE COLD ADVECTION WILL SPREAD INLAND THURSDAY AFTERNOON AND EVENING
CHANGING ALL PRECIPITATION BACK TO SNOW. EXPECT VERY STRONG WESTERLY
GUSTS ALONG THE NORTHERN ALASKA PENINSULA THURSDAY DUE TO STRONG
COLD ADVECTION. SOUTHWEST WILL DRY OUT FRIDAY AS A RIDGE MOVES
OVERHEAD...BUT THE NEXT SYSTEM WILL BRING MORE WINDS AND
PRECIPITATION TO THE REGION FRIDAY NIGHT INTO SATURDAY.

BERING SEA/ALEUTIANS/ALASKA PENINSULA...VERY STRONG COLD ADVECTION
ACROSS THE EASTERN BERING WILL MAINTAIN BLIZZARD CONDITIONS ACROSS
MANY AREAS THROUGH TONIGHT. THE ACTUAL SNOWFALL WILL LIGHTEN UP...BUT
THE WINDS WILL CONTINUE TO BLOW A FAIRLY DRY SNOW AROUND AND MAINTAIN
THE BLIZZARD CONDITIONS. WINDS WILL GRADUALLY DIMINISH FROM THE
PRIBILOFS AND EASTERN ALEUTIANS EARLY THURSDAY TO THE SOUTHWEST
ALASKA COAST LATE THURSDAY...SO EXPECT IMPROVING VISIBILITIES THROUGH
THE DAY. THE NEXT PACIFIC SYSTEM WILL MOVE TO SOUTH OF THE WESTERN
ALEUTIANS THURSDAY AFTERNOON AND INITIALLY WILL BE BLOCKED FROM
MOVING NORTHWARD BY A RIDGE CENTERED UP OVER EASTERN RUSSIA...SO THE
ALEUTIANS WILL SEE THE INITIAL IMPACT OF STRONG EASTERLIES AND SNOW.
BULK OF PRECIPITATION LOOKS LIKE IT WILL STAY SOUTH OF
ALEUTIANS...BUT IF IT DOES MAKE IT TO THE ALEUTIANS COULD SEE
BLIZZARD CONDITIONS. UNCERTAINTY IN FORECAST GROWS BY FRIDAY...BUT
EXPECT A TRIPLE POINT LOW TO FORM TO THE EAST AND THEN TRACK
NORTHWARD TOWARD THE ALASKA PENINSULA.

.LONG TERM FORECAST...LONG-WAVE PATTERN OF TROUGH CENTERED OVER THE
BERING AND RIDGE CENTERED OVER WESTERN NORTH AMERICA LOOKS LIKE IT
WILL BECOME MORE AMPLIFIED THROUGH THE EXTENDED PERIOD. THIS WILL
MAINTAIN AN ACTIVE STORM TRACK THAT TAKES STORMS FROM SOUTH OF THE
ALEUTIANS NORTHWARD OVER MAINLAND ALASKA. THERE ARE HINTS OF A
PATTERN CHANGE LATE NEXT WEEK...BUT IT IT TOO EARLY TO HAVE ANY
CONFIDENCE IN THAT.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING ZONE 131 155 161 181 185 195.
MARINE...STORM WARNING 170 171.
         GALE WARNING 120 125 130 132 138 140 141 150 155 160 165
                      172 175 176 179 180.
         HEAVY FREEZING SPRAY WARNING 130 132 138 140 141 165 179
                                      185.
FIRE WEATHER...NONE.

SEB FEB 08