Small Craft Advisory 142, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
1250 PM AST MON FEB 18 2008

.ANALYSIS AND UPPER LEVELS...A HIGH AMPLITUDE PATTERN IS RESULTING
IN EXTREMES IN TEMPERATURE ACROSS ALASKA. A LONG-WAVE TROUGH IS
CENTERED OVER THE BERING SEA WITH AN ANCHOR LOW EAST OF ATKA. A
RIDGE IS CENTERED OVER THE WESTERN UNITED STATES AND WESTERN CANADA.
A 180 TO 200 KT UPPER JET RUNS NEARLY ZONAL ACROSS THE NORTH PACIFIC
BETWEEN 30N AND 40N LATITUDE. A MUCH WEAKER JET(AROUND 80KT) EXTENDS
NORTHWARD ALONG THE WEST SIDE OF THE RIDGE ACROSS THE GULF OF ALASKA.
THIS PATTERN HAS RESULTED IN AN ACTIVE STORM TRACK WITH LOWS RAPIDLY
DEVELOPING OVER THE NORTH PACIFIC AND TRACKING NORTHWARD ACROSS THE
GULF AND THEN NORTHWESTWARD ACROSS SOUTHWEST ALASKA. THE REMNANTS OF
A LOW THAT MOVED ACROSS KODIAK ISLAND SUNDAY ARE OVER WESTERN ALASKA
THIS MORNING WITH NUMEROUS SNOW SHOWERS MOVING ACROSS THE SOUTHERN
KUSKOKWIM VALLEY AND THE KUSKOKWIM DELTA. SHOWERS ALSO CONTINUE IN
MAINLY UPSLOPE REGIONS OF SOUTHCENTRAL AS WELL AS AROUND THE CENTRAL
ALEUTIANS LOW. WIDESPREAD CHINOOK WINDS WERE OBSERVED SUNDAY
AFTERNOON AND NIGHT HELPING TO WARM TEMPERATURES ACROSS SOUTHCENTRAL
AND EASTERN PORTIONS OF SOUTHWEST INTO THE 30S AND 40S AND CHANGE
PRECIPITATION TO RAIN. GUSTY WINDS CONTINUE THIS MORNING BUT HAVE
BEGUN TO DIMINISH. TEMPERATURES HAVE DROPPED A FEW DEGREES AND WILL
CONTINUE TO VERY SLOWLY FALL AS THE WINDS DECREASE.

THE NEXT STORM IN LINE TO MOVE ACROSS THE FORECAST AREA IS
APPROACHING 50N 143W LATE THIS MORNING WITH AN ESTIMATED CENTRAL
PRESSURE AROUND 975 MB. BASED ON SATELLITE IMAGERY THE MODELS ARE
ABOUT 4 TO 6 HOURS SLOW WITH THE TRACK OF THIS LOW. THERE ARE TWO
MORE SURFACE LOWS IN LINE TO THE WEST ALONG THE UPPER JET.

.MODEL DISCUSSION...THE NAM IS MUCH TOO FAR SOUTH WITH THE LOW
APPROACHING THE GULF. THE OTHER MODELS 00Z POSITION IS CLOSE TO
THE POSITION AT 20Z. THEREFORE...WILL NEED TO SPEED UP THE MOVEMENT
OF WINDS AND PRECIPITATION INTO SOUTHCENTRAL TONIGHT. MODELS ARE
IN AGREEMENT ON THE TRACK OF THE LOW TO THE BARREN ISLANDS AND THEN
INLAND OVER SOUTHWEST ALASKA. THIS IS CONSISTENT WITH CURRENT
FORECAST SO DO NOT EXPECT ANY MAJOR CHANGES OTHER THAN WHAT IS
REQUIRED TO ACCOUNT FOR CHANGE IN TIMING. MODEL SOLUTIONS DIVERGE
WITH TRACK OF NEXT LOW INTO THE GULF LATE WEDNESDAY...BUT ARE ALL
GROUPED IN THE SAME REGION.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...FLOW WILL SHIFT AROUND TOWARD THE NORTH THIS
AFTERNOON AND EVENING WHICH WILL DIMINISH OR END THE PRECIPITATION
CURRENTLY FALLING IN THE SOUTHEAST FLOW UPSLOPE AREAS. THE SNOW
ADVISORY FOR ALONG THE ALASKA RANGE HAS BEEN CANCELLED DUE TO THE
LIGHTENING UP OF SNOW AND WARMING OF TEMPERATURES TO AROUND FREEZING.
PRECIPITATION AHEAD OF THE  NEXT LOW WILL MOVE INTO COASTAL AREAS
THIS EVENING AND THEN SPREAD OVER THE REST OF SOUTHCENTRAL
OVERNIGHT...WITH HEAVIEST PRECIPITATION ALONG THE COAST/KODIAK ISLAND
AS WELL AS THE KENAI PENINSULA. MORE WARM AIR WILL ACCOMPANY THIS
LOW SO PRECIPITATION WILL BE RAIN ALONG THE COAST AND RAIN AND SNOW
INLAND. EXPECT GALES OVER THE COASTAL MARINE AREAS...MAINLY NORTH AND
EAST OF THE LOW. STORM FORCE WINDS CAN BE EXPECTED ALONG THE NORTHERN
GULF. ALSO OF NOTE...IT LOOKS LIKE A DYNAMIC FETCH IS SETTING UP EAST
OF THE LOW CENTER SO EXPECT WAVE HEIGHTS TO EASILY REACH 30 FEET OVER
THE EASTERN TO NORTHERN GULF. EASTERLY CHINOOKS WILL DEVELOP ONCE
AGAIN WHEN THE LOW REACHES THE BARREN ISLANDS REGION TUESDAY AND
PEAK TUESDAY NIGHT AS THE LOW MOVES INLAND OVER THE KUSKOKWIM VALLEY.
AS IN THE PAST EVENT EXPECT THE GUSTY WINDS TO BE WIDESPREAD...SO
TEMPERATURES WILL ONCE AGAIN REACH INTO THE 30S AND 40S. THE NEXT
STORM WILL NOT BE TOO FAR OFF...SO THERE WILL BE A BRIEF LULL IN
SOME PLACES WEDNESDAY...BUT MORE PRECIPITATION WILL MOVE BACK INTO
COASTAL AREAS BY LATE WEDNESDAY.

SOUTHWEST ALASKA...AS ONE BATCH OF SHOWERS EXITS SOUTHWEST ALASKA
THIS AFTERNOON MORE WILL MOVE IN FROM THE EAST AHEAD OF THE NEXT
LOW. STEADY PRECIPITATION WILL OVERSPREAD MUCH OF SOUTHWEST ALASKA
TUESDAY AS THE LOW MOVES INLAND WITH RAIN AND SNOW NEAR THE ALASKA
AND ALEUTIAN RANGES AND ALL SNOW AS YOU HEAD WESTWARD. PRECIPITATION
WILL DIMINISH TO SHOWERS BY WEDNESDAY AND COLDER AIR WILL START
ADVECTING IN FROM THE WEST AS A RIDGE BEGINS TO BUILD OVER THE
WESTERN BERING AND THE UPPER TROUGH SLIDES EASTWARD.

BERING SEA/ALEUTIANS/ALASKA PENINSULA...SHOWERS WILL CONTINUE TO
SWIRL AROUND THE LOW SITTING OVER THE CENTRAL ALEUTIANS. THIS LOW
WILL MOVE EASTWARD AND WEAKEN THROUGH WEDNESDAY. COLD ADVECTION WILL
PROGRESS EASTWARD ACROSS THE BERING AS THE LOW MOVES EASTWARD. A
RIDGE WILL ALSO BEGIN TO BUILD OVER THE WESTERN BERING BY MID WEEK
HELPING TO INTENSIFY THE COLD ADVECTION. THIS WILL LEAD TO THE NORMAL
GUSTY NORTHERLIES AND SNOW SHOWERS.

.LONG TERM FORECAST...PATTERN CHANGE WILL BEGIN MID WEEK AND BE IN
PLACE BY NEXT WEEKEND. A RIDGE WILL SET BACK UP OVER THE BERING WITH
A TROUGH OVER THE MAINLAND AND GULF. SO EXPECT AN END TO THE ACTIVE
STORM TRACK ACROSS MAINLAND ALASKA AND COLDER AIR TO MOVE BACK INTO
THE REGION.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...STORM WARNING 120.
         GALE WARNING 125 129 130 140 175.
         HEAVY FREEZING SPRAY 185.
FIRE WEATHER...NONE.

SEB FEB 08