Gale Warning 242, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
350 PM AKDT SAT MAR 23 2013

.ANALYSIS AND UPPER LEVELS...
MUCH OF THE AOR IS DOMINATED BY A LONGWAVE TROUGH ALOFT. A NEARLY
STATIONARY LOW CENTERED OVER THE SEA OF OKHOTSK IS BEGINNING TO DRIFT
NORTH...WHILE AN ASSOCIATED FRONT IS MOVING EAST TOWARDS THE FAR
WESTERN CHAIN. UPPER-LVL RIDGING BUILDS DOWNSTREAM OF IT OVER THE
BERING SEA SUPPORTING SURFACE HIGH PRESSURE AND GENERALLY BENIGN
WEATHER. AN UPPER LOW SWINGS THROUGH THE AKPEN AND IS TRACKING
TOWARDS THE WESTERN GULF WITH A SHIELD OF SNOW...WITH IT'S NORTHERN
PERIPHERAL MOISTURE BRUSHING SOUTHERN BRISTOL BAY AS THIS OCCURS. AN
ARCTIC HIGH PRESSURE SYSTEM JUST NORTH OF THE ALASKA RANGE IN CENTRAL
AK SUPPORTS A COLD AND DRY AIRMASS WHICH BLEEDS DOWN INTO SW AK. THE
PRESSURE GRADIENT REMAINS SQUEEZED ENOUGH TO SUPPORT BRISK WINDS AND
ADVISORY LEVEL WIND CHILLS NEAR 40 BELOW ZERO OVER THE KUSKOKWIM
DELTA. A STRONG VORTEX ALOFT NEAR TIN CITY, AK IS SWINGING SOUTH
THROUGH THE CHUCKHI SEA TOWARDS SW AK.

ACROSS SOUTHCENTRAL AK...A FRONTAL ZONE WAS SLOW TO CLEAR UPPER COOK
INLET EARLIER TODAY ALLOWING SNOW/FLURRIES TO LINGER A BIT LONGER
ACROSS THE REGION. THE TRAILING EDGE OF THE FRONT IS DISSIPATING NOW
OVER THE FAR NORTHERN GULF...AND THOUGH IT'S ASSOCIATED LIFT IS
WEAKENING...MODESTLY STRONG ONSHORE FLOW CONTINUES TO ALLOW FOR AREAS
OF SNOW BACK THROUGH PRINCE WILLIAM SOUND AND COPPER RIVER BASIN.
WEAK TRANSITORY UPPER RIDGING POKES THROUGH KODIAK ISLAND TO THE
SOUTHERN TO WESTERN GULF OF AK AHEAD OF THE NW AK VORTEX AND AKPEN
LOW.

.MODEL DISCUSSION...
OUT WEST...MODELS SHOW A WAVE OF LOW PRESSURE FORMING TONIGHT ALONG
THE FRONT WHICH IS NEARING THE FAR WESTERN CHAIN. THIS LOW CENTERED
AROUND 500 MILES SOUTH OF KISKA AT 1008 MB EARLY SUN MORNING WILL
THEN TRACK TO NEAR ADAK AT PEAK INTENSITY AROUND 1000 MB MON
AFTERNOON. MODELS AGREE THAT THE LOW THEN FILLS AS IT SKIMS THE
EASTERN CHAIN...DISSIPATING AROUND 250 MILES SOUTHEAST OF UNALASKA ON
TUE. A STRONGER 970 MB LOW PRESSURE SYSTEM IS DEPICTED MOVING TO
AROUND 600 MILES SOUTHWEST OF ATTU ON TUE...WITH AN ASSOCIATED FRONT
PUSHING INTO THE WESTERN CHAIN. THE ECMWF/GEM ARE DEEPEST WITH
CENTRAL PRESSURE FOR THIS FEATURE (LOW 960S MB)...BUT OVERALL
POSITION AND TREND IS SIMILAR AMONG THE SOLUTIONS. MODELS SHOW THAT
THE HIGH PRESSURE OVER THE CENTRAL BERING SEA IS WEAKENED SOME AS
THESE SERIES OF LOWS PUSH INTO THE HIGH'S SUPPORTING UPPER-LVL RIDGE.
THE RIDGE IS FURTHER ERODED AND BROKEN FROM THE NORTHEAST BY THE
VORTEX SWINGING OUT OF THE CHUCKHI SEA.

IN THE EAST...THE LOW EJECTING OFF THE AKPEN MOVES TO AROUND 100
MILES SOUTHEAST OF KODIAK CITY AT 999 MB SUN MORNING...MOVES TO
PRINCE WILLIAM SOUND AT 991 MB ON MON AND THEN REMAINS STATIONARY
WHILE WEAKENING THROUGH TUE. ALOFT...THE ECMWF AND GEM SHOW PHASING
OF THIS LOW WITH THE STRONG VORTEX SWINGING DOWN SW AK LATE SUN NIGHT
OVER WESTERN PRINCE WILLIAM SOUND. THE GFS AND NAM SHOW SOME PHASING
AS WELL...BUT LATER ON (MON) AND FURTHER EAST IN THE SOUND. HAVE
TENDED TO LEAN ON THE ECMWF WHICH HAS BEEN RATHER CONSISTENT THE LAST
FEW RUNS. THE DEGREE OF COLD ADVECTION DEPICTED AS THESE DYNAMICS
PLAY OUT IS RATHER SIMILAR HOWEVER. 850 MB TEMPERATURES OVER UPPER
COOK INLET DROP FROM -7 C SUN AFTERNOON TO -17 C BY MON AFTERNOON...
WITH EVEN FURTHER COOLING TO A TOUCH UNDER -20 C ON TUE. THIS ALL
OCCURING AS STRONG LIFT FROM THE SUPPORTING WAVES ALOFT SLOWLY
TRAVERSE THROUGH GIVES FAIRLY GOOD CONFIDENCE OF A RESPECTABLE SNOW
EVENT FOR MAINLAND SOUTHCENTRAL AK.

.SHORT TERM FORECAST...
SOUTHCENTRAL/GULF...
WITH THE TRANSITORY RIDGE PUSHING THROUGH KODIAK ISLAND BY EARLY THIS
EVENING...ONSHORE FLOW QUICKLY ESTABLISHES ITSELF AHEAD OF THE WAVE
PUSHING OFF THE AKPEN LEADING TO A RETURN OF SNOW OR SNOW/RAIN MIX.
WINDS WILL STRENGTHEN AS WELL...THOUGH BELIEVE WIND INTENSITY WILL
NOT BE STRONG ENOUGH TO PRODUCE SIGNIFICANT BLOWING SNOW CONCERNS
WHILE PRECIP IS ONGOING. THE STRONGEST WINDS WILL BEGIN TO ARRIVE
LATE SUN NIGHT AFTER THE FLOW GOES OFF-SHORE AND SNOW WITH THE
SURFACE WAVE HAS MOVED TOWARDS THE SOUTHERN MAINLAND. WINDS DO TREND
TO GALES AND EVEN STORM FORCE WITH TIME AS THE COLD-ADVECTION BEGINS
BLEEDING THROUGH FAVORED GAPS OUT OF SHELIKOF STRAIT AND KAMISHAK
BAY.

ACROSS THE SOUTHERN MAINLAND...SNOW INTENSITY LIGHTENS UP WITH THE
DISSIPATION OF THE FRONT...BUT DOES NOT GO AWAY COMPLETELY ACROSS
PRINCE WILLIAM SOUND AS THE FLOW REMAINS SOMEWHAT ONSHORE...WITH SOME
LINGERING LIFT ALSO PESTERING THE COPPER RIVER BASIN. TEMPS
MEANDERING AROUND OR A HAIR ABOVE FREEZING AT THE SURFACE MAY ALLOW
SOME LOCALIZED AREAS TO SEE SOME RAIN MIXED IN OVER THE EASTERN
SOUND...BUT PREDOMINATELY SNOW IS EXPECTED. ELSEWHERE...ISENTROPIC
LIFT WILL BE ON THE INCREASE OVER THE KENAI PENINSULA AND UP COOK
INLET OVERNIGHT INTO SUN...WHICH MAY ALLOW FOR SOME LIGHT SNOW. THE
STRONGER REINFORCING SHOT LOOKS TO BE SUN NIGHT AND MON ASSOCIATED
WITH THE AFOREMENTIONED SURFACE WAVE MOVING UP THE GULF TO THE SOUND.

SOUTHWEST/AKPEN...
COLD AND DRY CHARACTERIZES MUCH OF INTERIOR SW ALASKA. ACROSS THE
KUSKOKWIM DELTA...BITING WIND CHILLS ARE PERSISTING IN THE COLD/DRY
AIRMASS. WINDS SHOULD SLACKEN A TOUCH ON SUN REDUCING THE THREAT OF
THE LOWEST CHILLS...BUT DO NOT LOOK TO GO CALM...SO REGARDLESS
CONDITIONS WILL REMAIN BRISK THE REMAINDER OF THE WEEKEND. SNOW WITH
THE WAVE OVER THE AKPEN WILL BRUSH AREAS OF BRISTOL BAY...BUT WITH
THE PRE EXISTING AIRMASS RATHER DRY COUPLED WITH NORTH/DRY FLOW...THE
PRECIP SHIELD SHOULD HAVE TROUBLE PUSHING MUCH FURTHER WEST THAN KING
SALMON/NAKNEK. THUS AREAS SOUTH AND EAST OF DILLINGHAM HAVE THE BEST
CHANCES OF OVERNIGHT PRECIP. THE STRONGEST WINDS THE NEXT 24 HOURS
APPEAR TO BE AROUND THE AKPEN AND ADJACENT WATERS FROM CAPE SARICHEF
TO SITKINAK AS THE PRESSURE GRADIENT REMAINS A BIT SQUEEZED IN THE
WAKE OF THE SURFACE WAVE WITH A SMALL PUSH OF COLD ADVECTION. PENDING
ON HOW MUCH TRANSPORTABLE SNOW EXISTS...THERE IS A CHANCE OF SOME
LOCALLY REDUCED VISIBILITY IN BLOWING SNOW THROUGH THE AKPEN. AS THE
NW AK VORTEX SWINGS DOWN...IT HELPS FLATTEN THE BERING SEA RIDGE...
SUCH THAT HIGH PRESSURE OVER THE CENTRAL BERING SEA MIGRATES TO THE
WESTERN AKPEN BY LATE MON AND NEAR SW AK BY TUE. THIS SHOULD FINALLY
HELP TO RELAX THE PRESSURE GRADIENT LEADING TO WEAKER WINDS.

BERING SEA/ALEUTIANS...
THERE ARE SOME LINGERING SNOW SHOWERS OVER THE EASTERN CHAIN BUT
THESE SHOULD EBB AS SUBSIDENCE FROM HIGH PRESSURE SPREADS OVER THE
REGION. A DEEP LAYER OF COLD DRY AIR EVIDENT ON SATELLITE IMAGERY IS
POKING DOWN THROUGH THE PRIBILOF ISLANDS LEADING TO DECREASED CLOUDS
HERE WITH SOME OF THIS PUSHING TOWARDS THE EASTERN CHAIN ON SUN.
FURTHER WEST...BENIGN CONDITIONS OVERNIGHT TREND WETTER AND WINDIER
SUN TO MON AS THE PACIFIC WAVE APPROACHES. SLIGHTLY WARMING
TEMPERATURES SHOULD ALLOW PRECIP TO BE A MIX OF SNOW AND RAIN AS IT
OVERSPREADS THE CHAIN.

.LONG TERM FORECAST...
THE COLD VORTEX/UPPER LOW MEANDERING THROUGH THE SOUTHERN MAINLAND
EARLY IN THE WEEK BEGINS TO RETREAT BACK TOWARDS CENTRAL AK MID WEEK.
THIS SHOULD LOOSEN THE ARCTIC GRIP AND ALLOW FOR SOME MODERATION OF
TEMPERATURES...ESPECIALLY OVER SW AK. CYCLONIC FLOW ALOFT WEAKENS A
BIT AS WELL...SO CHANCES OF PRECIP MAY DROP A BIT AS WELL. THE
PRESSURE GRADIENT ALSO SHOULD RELAX AND HELP WEAKEN WINDS THROUGH THE
GULF OF AK. OUT WEST...FORECAST CHALLENGES WILL SURROUND WHAT'S LEFT
OF THE 970 MB LOW...THOUGH IT SHOULD HAVE WEAKENED BY THE TIME IT
MOVES INTO THE ALEUTIAN CHAIN.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...WIND CHILL ADVISORY...155
MARINE...STORM...130
         GALE...120 132 136 137 138 150 155 165 176 351 352
         HEAVY FREEZING SPRAY...130 138 140 150 179 411 412 414
FIRE WEATHER...NONE

MALOY