High Wind in Alaska, December 14, 2011

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
520 AM AKST TUE DEC 13 2011

.ANALYSIS AND UPPER LEVELS...
A COMPLEX PATTERN PERSISTS ACROSS THE AOR. IN THE EAST...A WEAK LOW
OVER KODIAK ISLAND IS FILLING AS IT DRIFTS EAST TOWARDS THE NORTHERN
GULF. AN ASSOCIATED FRONT IS SPREADING SNOW ACROSS PRINCE WILLIAM
SOUND...BUT IT IS WEAKENING NEAR THE COAST. ACROSS THE SW
MAINLAND...AN UPPER-RIDGE IS POKING NORTH...WITH SURFACE HIGH
PRESSURE ALLOWING FOR SOME SUNSHINE. OUT WEST...A LOW AROUND 300
MILES NORTH OF SHEMYA IS RETROGRADING WEST TOWARDS THE KAMCHATKA
PENINSULA. IN IT'S WAKE A REX BLOCK IS DEVELOPING AS ANOTHER DEEP LOW
APPROACHES THE CENTRAL/EASTERN ALEUTIANS...AND THE CREST OF THE
AFOREMENTIONED WESTERN MAINLAND RIDGE PINCHES OFF INTO AN UPPER HIGH
ADJACENT TO THE LOW.

.MODEL DISCUSSION...
MODELS ACCEPTABLY CAPTURE THE WEATHER PICTURE. IN THE EAST...MODELS
SHOW THE SYSTEM IN THE GULF WASHING OUT LATER THIS AFTERNOON WITH
IT'S MOISTURE LARGELY REMAINING AROUND COASTAL AREAS WITH REASONABLE
AGREEMENT. THE FRONT ASSOCIATED WITH THE LOW NEARING THE CENTRAL
ALEUTIAN CHAIN APPROACHES THE SOUTHERN GULF TONIGHT AND MOVES TO
SOUTHCENTRAL ON THURSDAY. MODELS ALSO CAPTURE THIS SIMILARLY...THOUGH
THE NAM WAS GENERALLY PREFERRED FOR IT'S BETTER DEPICTION OF LOCAL
EFFECTS. FORECASTS THEREAFTER BEGIN TRENDING TOWARDS THE ECMWF
SOLUTION DUE TO BETTER CONTINUITY.

OUT WEST...MODELS HANDLE THE LOW NORTH OF ATTU SIMILARLY AS IT
DEPARTS THE AOR. THE SYSTEM APPROACHING THE CENTRAL AND EASTERN CHAIN
HOWEVER SEEMS TO BE BEST HANDLED BY THE ECMWF. SATELLITE IMAGERY THIS
MORNING SHOWS TWO LOW CENTERS...ONE 300 MILES SOUTH OF NIKOLSKI AND A
SECONDARY LOW 500 MILES SOUTHEAST OF THAT. THE ECMWF HAS BEEN MOST
CONSISTENT IN DEVELOPING THIS SECONDARY LOW INTO THE PREDOMINANT ONE
THE NEXT 24 TO 36 HOURS. PREVIOUS RUNS OF THE NAM HAD BEEN SLOW TO
COME AROUND TO THIS DEVELOPMENT. AND THOUGH THE 00Z RUN DID TREND A
BIT TOWARDS THE ECMWF...THE 06Z RUN HAS INITIALIZED POORLY. THE GFS
DOES NOT SHOW THIS SECONDARY DEVELOPMENT IN IT'S INITIALIZATION
EITHER...AND INSTEAD DEEPENS THE NORTHERN MOST LOW. AS SUCH...THE
ECMWF WAS EMPLOYED FOR THE LION'S SHARE OF THE FORECAST PERIOD.

.SHORT TERM FORECAST...
SOUTHCENTRAL...
FORECAST CHALLENGES ACROSS SOUTHCENTRAL AK WILL REVOLVE AROUND THE
SERIES OF FRONTS THAT TRAVERSE THE GULF. THE CURRENT ONE OVER THE
NORTHERN GULF IS WEAKENING IN PLACE WITH LITTLE NORTHWARD THRUST. THE
NEXT ONE THAT ADVANCES ON THURSDAY WILL BE A BIT STRONGER BRINGING A
REINFORCING SHOT OF GALES TO MARINE AREAS. ALSO LOOK FOR INCREASING
TURNAGAIN ARM/PORTAGE VALLEY WINDS WITH THIS NEXT FRONT...THOUGH AT
THIS JUNCTURE IT IS BELIEVED THAT THEY WILL REMAIN BELOW WARNING
LEVELS BECAUSE THE FRONT WILL BE ELONGATED AND WEAKENING SOMEWHAT AS
IT APPROACHES. THE NORTHWARD PUSH WILL HOWEVER ALLOW MOISTURE TO
ADVANCE FURTHER INLAND...BRINGING BETTER CHANCES OF STEADY SNOW TO
THE ANCHORAGE BOWL AND MAT-SU VALLEYS THURSDAY NIGHT INTO EARLY
FRIDAY. SNOW AND BLOWING SNOW THROUGH PORTAGE VALLEY IS A
THREAT...BUT BELIEVE TEMPERATURES WILL PROBABLY BE MARGINALLY
WARM...ALLOWING SOME RAIN  TO MIX IN AND TEMPER THE BLIZZARD THREAT.

SOUTHWEST....
FAIR AND DRY CONDITIONS WILL GIVE WAY TO INCREASING CLOUDS AND
STRENGTHENING WINDS AHEAD OF THE FRONT ASSOCIATED WITH THE ALEUTIAN
SYSTEM. THE BRUNT OF THE UPPER-LVL SUPPORT WILL BE DEFLECTED EAST OF
THE ALASKA RANGE...AND AS SUCH QPF SHOULD BE ON THE LOW SIDE. STRONG
WINDS WILL PRODUCE LOCAL AREAS OF REDUCED VISIBILITY IN BLOWING
SNOW...BUT NOT SUFFICIENT TO PRODUCE BLIZZARD OR ADVISORY CONDITIONS.
SHOWERS TO PERSIST INTO FRIDAY AS THE LOW PARENT LOW PRESSURE SYSTEM
MEANDERS JUST TO THE WEST OF THE WESTERN CAPES.

BERING SEA/ALEUTIANS...
THE LOW PRESSURE SYSTEM IN THE NORTH PACIFIC WILL TRACK NORTH THROUGH
TONIGHT TO AROUND 100 MILES EAST OF DUTCH HARBOR EARLY THURSDAY
MORNING...THEN DRIFT SLOWLY NORTHEAST TO FRIDAY...PROGRESSION
SOMEWHAT SHUNTED BY THE UPPER-HIGH TO THE NORTH. HIGH WIND WARNINGS
PERSIST FOR THE EASTERN ALEUTIAN AND AKPEN. THE AKPEN WARNING END
TIME WAS EXTENDED FROM LATE TONIGHT TO EARLY THURSDAY MORNING...AS IT
APPEARS A STRONG CORE OF WINDS BEHIND THE FRONT WILL WRAP AROUND THE
LOW AND PERSIST A BIT LONGER THAN ORIGINALLY THOUGHT. STRONG WINDS
WILL BE ACCOMPANIED BY WEAK WARM ADVECTION...BUT THE LION'S SHARE OF
PRECIPITATION TO FALL AS RAIN. THROUGH THE PRIBILOF ISLANDS...FLOW
WILL BE MORE NORTHEASTERLY...ALLOWING SOME COLD AIR TO REMAIN WITH
WET SNOW MIXED IN. IN THE FAR WESTERN CHAIN...SNOW SHOWERS TO PERSIST
IN THE WAKE OF THE RETROGRADING LOW.

.LONG TERM FORECAST...
SEMI BLOCKED PATTERN TO GIVE WAY TO A MORE PROGRESSIVE ONE LATE IN
THE WEEK. STORM TRACK ALLOWING SYSTEMS TO MOVE FROM THE PACIFIC
THROUGH THE EASTERN CHAIN AND UP TO THE SOUTHWEST MAINLAND WITH
INCREASED MOISTURE AND CHANCES OF PRECIPITATION.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...HIGH WIND WARNING...181 185
MARINE...HURRICANE FORCE WIND...155
         STORM...130 150 160 165 170 171 172 176 179 180 351 352 411
                 414
         GALE...120 125 129 132 138 140 141 175 412 413
         HEAVY FREEZING SPRAY...140 180 185
FIRE WEATHER...NONE

JAM DEC 11