Gale Warning 392, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
400 AM ADT MON APR 24 2006

.DISCUSSION...

ANALYSIS...A MAJOR LOW PRESSURE SYSTEM IS LOCATED AT ABOUT 57.5N 146W
AT 08Z AND IS TRACKING NORTHWEST TOWARD SEWARD AT ABOUT 30 KT. BASED
ON SATELLITE IMAGERY AND NEARBY SHIP OBS/BUOYS WE HAVE ESTIMATED THE
CENTRAL PRESSURE AT 985 MB. PRECIP HAS SPREAD OVER PRINCE WILLIAM
SOUND AND OVER THE MOUNTAINS INTO COOK INLET. WITH NORTHERLY FLOW
IN THE LOW LEVELS IN THE COOK INLET CORRIDOR LOW LEVELS ARE DRY AND
THEREFORE THERE HAVE BEEN SEVERAL HOURS OF VIRGA. PRECIPITATION IS
JUST NOW STARTING TO REACH THE GROUND OVER THIS REGION. SURFACE TEMPS
ARE ABOVE FREEZING BUT WILL FALL TO NEAR FREEZING AS THE LOW LEVELS
COOL IN RESPONSE TO MELTING AND EVAPORATION. EXPECT LITTLE PRECIP
OVER ANCHORAGE AND MAT VALLEY TONIGHT IN OVERRUNNING PRECIP. DRY SLOT
IS ALREADY APPROACHING WESTERN PRINCE WILLIAM SOUND. RADAR SHOWS A
MODERATE BAND OF SNOW SETTING UP FROM NORTH OF COOK INLET
SOUTHEASTWARD ACROSS THE WESTERN KENAI. THIS LINES UP WITH THE LOW
LEVEL TROUGH AXIS WHICH WILL SLOWLY SHIFT SOUTHWESTWARD AS LOW
APPROACHES THIS MORNING. WINDS ALONG THE NORTHERN GULF ARE NOW
APPROACHING STORM FORCE AND WILL MAX OUT EARLY THIS MORNING BEFORE
DIMINISHING BEHIND THE LOW THIS AFTERNOON.

IT IS VERY CALM OUT WEST TONIGHT UNDER BROAD NORTHERLY FLOW AND A
RIDGE OF HIGH PRESSURE OVER THE WESTERN BERING. A WEAK SURFACE LOW
IS OVER THE NORTHERN BERING JUST AHEAD OF A VERY COLD UPPER LOW OVER
EASTERN SIBERIA.

MODEL ANALYSIS...MODELS HAVE FINALLY COME TO A CONSENSUS ON THE GULF
LOW. UNFORTUNATELY THEY ARE ALL TOO WEAK. THE GFS IS CLOSEST AT 989
MB AT 06Z. THE GFS HAS ALSO BEEN THE MOST CONSISTENT AND ACCURATE
THE PAST FEW RUNS SO IT IS STILL THE PREFERRED MODEL. WILL INCREASE
WINDS DUE TO THE STRONGER LOW. OUT WEST THE MODELS ARE FAIRLY
CONSISTENT IN EVOLUTION LOW MOVING OUT OF SIBERIA. THE NAM AND
PARALLEL NAM DEVELOP MULTIPLE SURFACE LOWS WHILE THE GFS MAINTAINS
ONE STRONGER LOW. WITH STRONG COLD ADVECTION OVER THE WARMER BERING
SEA WATERS AND UPPER LEVEL JET DEVELOPING FROM EASTERN SIBERIA
SOUTHEASTWARD INTO THE CENTRAL BERING...PREFER THE MULTIPLE LOW
SOLUTION. THERE WILL LIKELY BE MULTIPLE POLAR LOWS DEVELOPING AS
THE COLD AIR MOVES OVER WATER. HOWEVER DO PREFER THE DEEPER MAIN
LOW AS PER THE GFS. SO WILL USE A MODEL BLEND OUT WEST.

AER SHORT-TERM FORECASTS...STRONG GULF LOW WILL QUICKLY WEAKEN AS
IT MOVES INLAND NEAR SEWARD LATE MONDAY MORNING AND TRACKS TO THE
NORTHERN SUSITNA MONDAY AFTERNOON. MODERATE TO HEAVY PRECIP WILL
CONTINUE OVER PRINCE WILLIAM SOUND THIS MORNING WITH SNOW SHOWERS
TO FOLLOW THIS AFTERNOON AS COLD AIR ALOFT MOVES IN BEHIND THE
SYSTEM. THERE IS CURRENTLY A BLOWING ADVISORY IN EFFECT FOR PORTAGE
VALLEY AND TURNAGAIN ARM. THEY SHOULD SEE EASTERLIES PICK UP SOON AS
THE LOW GETS CLOSER. SURFACE TEMPS ARE SLIGHTLY ABOVE FREEZING AT
PORTAGE BUT MAY FALL AS OCCLUDED FRONT GOES THROUGH AND COLDER AIR
MOVES BACK IN. WILL KEEP AN EYE ON OBS AND MAKE A LAST MINUTE
DECISION ON WHETHER TO KEEP THIS ADVISORY UP. EXPECT STRONG GUSTY
WINDS BEHIND THE LOW DUE TO GRADIENT AND RAPIDLY RISING SURFACE
PRESSURES. WILL PAY SPECIAL ATTENTION TO HOMER WHERE SOUTHWEST WINDS
WILL DEVELOP AS THE LOW REACHES SEWARD. COMBINED WITH SNOW THIS
MAY PRODUCE SOME VERY LOW VISIBILITIES. THEREFORE...WILL ISSUE A
BLOWING SNOW ADVISORY FOR HOMER AND VICINITY. ANCHORAGE/MAT
VALLEY/AND ALL BUT THE WESTERN SUSITNA WILL STAY MAINLY DRY THROUGH
MUCH OF THE DAY AS THE LOW MOVES OVERHEAD. SNOW WILL BEGIN BY LATE
AFTERNOON AS COLD ADVECTION MOVES UP COOK INLET. FOR ANCHORAGE TO
WASILLA LOOKS LIKE WILL RECEIVE A COUPLE INCHES OF SNOW MONDAY
AFTERNOON THROUGH EVENING BEFORE FLOW TURNS SOUTHEAST AND RIDGE
BEGINS TO BUILD ALONG NORTH GULF COAST. SNOW WILL LAST AT LEAST
THROUGH TUESDAY MORNING FOR THE NORTHERN SUSITNA UNDER STRONG
SOUTHERLY FLOW. MAY GET UP TO A FOOT NORTH OF TALKEETNA BY THE TIME
THIS EVENT IS OVER. SNOW SHOWERS WILL LINGER ON TUESDAY AHEAD OF
UPPER TROUGH AXIS. DRYING WILL OCCUR TUESDAY NIGHT AND WEDNESDAY
AS A SHORTWAVE RIDGE BUILDS OVERHEAD AND FLOW SHIFTS TO OFFSHORE.

ALU SHORT-TERM FORECASTS...LOOK FOR SNOW AS LOW TRACKS SOUTHWARD
ACROSS BERING SEA MONDAY AND TUESDAY AND INTO THE NORTH PACIFIC
TUESDAY NIGHT. THE PRESSURE GRADIENT WEST OF THE LOW WILL BE VERY
TIGHT DUE TO HIGH PRESSURE OVER THE FAR WESTERN BERING SEA. COLD
ADVECTION WILL BE MODERATE TO STRONG WITH 850 TEMPS DOWN TO -18
DEGREES CELSIUS. THIS WILL PRODUCE MAX GALES TO MIN STORMS OVER
THE CENTRAL BERING MONDAY NIGHT AND TUESDAY SPREADING TO THE CENTRAL
AND EASTERN ALEUTIANS TUESDAY NIGHT AND WEDNESDAY. WITH IMPRESSIVE
DYNAMICS AND INSTABILITY CREATED BY EXTREMELY COLD AIR ALOFT WILL
PRODUCE AREAS OF MODERATE TO HEAVY SNOW AND SNOW SHOWERS. WILL NEED
TO CONSIDER PUTTING OUT A BLIZZARD WATCH FOR EASTERN AND CENTRAL
ALEUTIANS FOR TUESDAY TO TUESDAY NIGHT TIME FRAME. WILL LEAVE FOR
ONE MORE MODEL RUN SINCE THAT WOULD BE A 4TH PERIOD WATCH.

EXTENDED FORECASTS...CONSISTENT WITH GFS MODEL RUN FROM 24 HOURS AGO
COLD CORE LOW SOUTH OF THE AKPENN WEDNESDAY WILL MOVE INTO THE GULF
THURSDAY BRINGING RAIN AND SNOW TO COASTAL REGIONS. IT WILL THEN SET
UP SHOP SOUTH OF KENAI PENINSULA THROUGH THE WEEKEND. WITH VERY COLD
AIR ALOFT EXPECT A SHOWERY PATTERN ACROSS THE SOUTHERN MAINLAND
THURSDAY THROUGH MONDAY. WILL LIKELY SEE OCCASIONAL SUN INLAND WHICH
WILL PRODUCE CBS IN THE AFTERNOON/EVENING. FOR THE BERING COLD
NORTHERLY FLOW WILL BEGIN TO ABATE AS WE HEAD INTO THE END OF THE
WEEK AND HIGH PRESSURE SLIDES EASTWARD OVER THE CENTRAL BERING. LOOK
FOR A WARM-UP STARTING IN THE WEST ON THE WEEKEND AS A NEW STORM
APPROACHES FROM THE SOUTHWEST.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...STORMS 120 172 185. GALES 125 130 132 170 171 175 179.
         HEAVY FREEZING SPRAY 185.
FIRE WEATHER...NONE.

SEB APR 06