Gale Warning 339, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
245 PM AKDT THU APR 8 2010

.ANALYSIS AND UPPER LEVELS...
A BROAD UPPER LEVEL TROUGH CONTINUES TO SLOWLY MIGRATE EASTWARD
TOWARDS NORTHWESTERN CANADA...BUT STILL COVERS MUCH OF THE EASTERN
HALF OF ALASKA. A FILLING UPPER LEVEL LOW ALSO EXISTS AT THE BASE OF
THE TROUGH OVER THE NORTHERN ALASKA PANHANDLE. A SMALL SHORTWAVE
SOUTH OF KODIAK IS DIVING SOUTH WITH THE JET STREAM AND PROGRESSING
OUT OF THE FORECAST AREA. FURTHER WEST...THE JET TAKES ON A
MERIDIONAL APPEARANCE AS A STRONG RIDGE BUILDS OVER THE CENTRAL
ALEUTIANS/BERING SEA...PUSHING THE JET STREAM AS FAR NORTH AS THE
BERING STRAIT. A NEGATIVELY TILTED LOW PRESSURE TROUGH ORIGINATING
FROM A LOW IN THE NORTHERN SEA OF OKHOTSK IS QUICKLY WRAPPING NORTH
AND EAST INTO THE SOUTHWESTERN BERING SEA.

AT THE SURFACE...A BROAD REGION OF LOW PRESSURE STILL COVERS MUCH OF
EASTERN ALASKA...BUT IS SLOWLY ERODING AS AN INVERTED HIGH PRESSURE
RIDGE ORIGINATING FROM NORTH CENTRAL SIBERIA DIGS ACROSS THE EASTERN
BERING AND WESTERN ALASKA. CLOUDS AND SNOW SHOWERS CONTINUE OVER THE
WRANGELL MOUNTAINS AND EASTERN ALASKA RANGE COURTESY OF A SHARP
SURFACE TROUGH EXTENDING ACROSS EAST CENTRAL ALASKA. AREAS OF LOW
CLOUDS AND FLURRIES ALSO EXIST AROUND THE KUSKOKWIM DELTA...BUT IN
GENERAL THE SKIES OVER SOUTHERN ALASKA ARE MOSTLY SUNNY TO CLEAR. A
LOW PRESSURE SYSTEM TIED TO THE SHORTWAVE SOUTH OF KODIAK IS
WEAKENING AND DIPPING SOUTHEASTWARD OUT INTO THE NORTHEASTERN
PACIFIC. THE WEATHER OVER THE WESTERN HALF OF THE ALEUTIANS HAS
DETERIORATED THROUGHOUT THE DAY DUE TO A WARM FRONT LIFTING NORTH
TOWARDS THE WESTERN ISLANDS. THIS FRONT IS ASSOCIATED WITH A RAPIDLY
DEEPENING 972 MB LOW 200 MILES SOUTH OF SHEYMA THAT IS TRACKING
NORTHEASTWARD AT 40 KTS.

.MODEL DISCUSSION...
MODELS ARE IN EXCELLENT AGREEMENT OVERALL THROUGH THE FORECAST
PERIOD...WITH ONLY A FEW BLEMISHES WORTH MENTIONING. THE ECMWF HAS
COME BACK INTO AGREEMENT WITH THE NAM AND GFS OVER THE TRACK OF THE
BERING LOW THROUGH SATURDAY...THOUGH IT IS STILL SOMEWHAT STRONGER
THAN THE OTHER MODELS (BUT NOT AS MUCH AS YESTERDAY). THE NAM
SOLUTION OUT PAST 36 HOURS LAGS APPROXIMATELY THREE TO SIX HOURS
BEHIND THE OTHER MODELS...AND THUS DELAYS THE ARRIVAL OF THE BERING
FRONT AND ASSOCIATED PRECIPITATION TO SOUTHWEST ALASKA ON SATURDAY
MORNING. THIS IS POSSIBLY DUE TO THE MODEL DEPICTING A SLIGHTLY
WEAKER UPPER LEVEL JET THAN THE OTHER MODELS...THUS RESULTING IN A
SLOWER WEATHER PATTERN. THE MODELS DIVERGE WITH RESPECT TO THE TIMING
AND STRUCTURE OF THE OCCLUDED FRONT AS IT WRAPS NORTHWARD INTO THE
NORTHERN GULF LATE IN THE WEEKEND.

.SHORT TERM FORECAST...
.SOUTH CENTRAL ALASKA...SOUTH CENTRAL ALASKA WILL BATHE IN SUN TODAY
AND TOMORROW AS AN UPPER LEVEL RIDGE BUILDING OUT OF THE ALEUTIANS
ASSUMES CONTROL OF THE REGION'S WEATHER. CLOUD COVER WILL BUILD FROM
WEST TO EAST ON SATURDAY AS A FRONTAL SYSTEM MOVES ACROSS SOUTHWEST
ALASKA. WINDS WILL ALSO INCREASE THROUGH THE TURNAGAIN ARM REGION AND
OTHER MOUNTAIN GAPS DUE TO INCREASING PRESSURE DIFFERENCES BETWEEN
EASTERN AND WESTERN SIDES OF THE REGION. SNOW SHOWERS MAY IMPACT
PORTIONS OF SOUTH CENTRAL ALASKA ON SATURDAY AND SUNDAY AS THE
REMNANTS OF THE FRONTAL SYSTEM PUSH THROUGH.

.SOUTHWEST ALASKA...UPPER LEVEL RIDGING BUILDS EASTWARD OUT OF THE
ALEUTIANS TODAY AND WILL PAMPER RESIDENTS OF SOUTHWESTERN ALASKA WITH
CLEAR SKIES AND LIGHT WINDS. LIGHT NORTHERLY WINDS WILL MODERATE
TEMPERATURES...BUT THE WEATHER WILL REMAIN BEAUTIFUL NONETHELESS. THE
PLACID WEATHER WILL BECOME A DISTANT MEMORY BY FRIDAY AFTERNOON AS
CLOUDS AND STRONG WINDS SMOTHER THE REGION IN ADVANCE OF A FRONTAL
SYSTEM MOVING ONSHORE FROM THE BERING. SNOW SETS IN ON SATURDAY
MORNING OVER COASTAL SOUTHWEST ALASKA AND PUSHES INLAND TO THE ALASKA
RANGE BY SATURDAY AFTERNOON. NEAR BLIZZARD CONDITIONS WILL PLAGUE THE
KUSKOKWIM DELTA AND THE WESTERN CAPES ON SATURDAY MORNING...HOWEVER
EXPECT WIDESPREAD BLOWING SNOW ACROSS ALMOST ALL OF SOUTHWEST ALASKA
THROUGHOUT THE WEEKEND.

.ALEUTIANS AND BERING SEA...STORM FORCE WINDS ARE CURRENTLY
APPROACHING THE WESTERN ALEUTIANS AS THE LOW SOUTH OF SHEMYA
CONTINUES TO DEEPEN AND MOVE TOWARDS THE WESTERN ISLANDS. THE LOW
TRACKS DIRECTLY OVER THE NEAR ISLANDS TONIGHT AND MOVES INTO THE WEST
CENTRAL BERING SEA TOMORROW. THE SYSTEM BOTTOMS OUT AT 956 MB ON
FRIDAY NIGHT AND SLOWS DOWN ON SATURDAY AFTERNOON 600 MILES WEST OF
NUNIVAK ISLAND. OCCLUDED AND WEAKENING...THE LOW MEANDERS EASTWARD
OVER THE OPEN BERING SEA THROUGH THE REST OF THE WEEKEND. A RAIN AND
SNOW MIXTURE HAS BEEN REPORTED AT SHEYMA OVER THE PAST FEW
HOURS...AND THIS WINTERY MIXTURE WILL LIKELY CONTINUE BEFORE CHANGING
OVER TO SNOW TONIGHT AS THE ISLAND BECOMES ENVELOPED IN THE WRAP
AROUND COLD AIR ADVECTION BEHIND THE LOW.

THE REST OF THE ALEUTIANS REMAIN IN THE WARM AIR ADVECTION AND START
OUT AS RAIN EITHER TODAY (WEST OF DUTCH HARBOR) OR TOMORROW MORNING
BEFORE CHANGING OVER TO SNOW ON FRIDAY OVER THE CENTRAL ALEUTIANS AND
ON SATURDAY OVER THE EASTERN ALEUTIANS AND THE AKEPN. WHILE THE
HEAVIEST PRECIPITATION PUSHES OUT OF THE EASTERN ALEUTIANS BY
SATURDAY MORNING...EXPECT SNOW SHOWERS TO PERSIST THROUGH THE
WEEKEND. WIDESPREAD GALES WITH AREAS OF STORM FORCE WINDS RAPIDLY
DEVELOP ACROSS THE WESTERN BERING SEA AND THE WESTERN HALF OF THE
ALEUTIANS TONIGHT AND SPREAD EASTWARD THROUGHOUT THE DAY TOMORROW.
WINDS OF 50 TO 60 KTS CAN BE EXPECTED NEAR THE FRONTAL BOUNDARY AS IT
PUSHES ACROSS THE CENTRAL BERING OVER THE NEXT 24 HOURS AND OVER THE
WESTERN ALEUTIANS TOMORROW DUE TO STRONG COLD AIR ADVECTION. NEAR
BLIZZARD CONDITIONS ARE POSSIBLE FOR THE PRIBILOF ISLANDS ON FRIDAY
MORNING BEFORE THE SNOW MIXES WITH RAIN AND WINDS DECREASE DURING THE
AFTERNOON.

.LONG TERM FORECAST...
AN AMPLIFIED AND PROGRESSIVE UPPER LEVEL JET WILL REMAIN OVER THE
REGION THROUGH AT LEAST THE NEXT WEEK...BRINGING WITH IT A PARADE OF
STORMS INTO THE CENTRAL BERING. THERE ARE SIGNIFICANT DIFFERENCES
AMONG THE MODELS AS TO THE TRACKS OF THESE LOWS (ESPECIALLY THE LOW
SLATED TO AFFECT THE BERING DURING THE BEGINNING OF NEXT WEEK)...BUT
IN GENERAL THEY WILL BE SPACED IN TWO TO THREE DAY INTERVALS. THESE
STORMS WILL HAVE THE GREATEST IMPACT ON THE BERING SEA AND
SOUTHWESTERN ALASKA...BUT COULD ALSO IMPACT SOUTH CENTRAL ALASKA AS
WELL...THOUGH IN A WEAKER STATE.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WATCH...155 161 195.
MARINE...GALE WARNING...150 155 160 165 170 171 172 179 180.
         STORM WARNING...175 176 185.
FIRE WEATHER...NONE.

KS APR 10