Brisk Wind Advisory 27, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
535 AM AKST FRI MAR 1 2013

.ANALYSIS AND UPPER LEVELS...
THERE ARE SEVERAL WEATHER FEATURES ACROSS THE AOR THIS MORNING. A
COLD UPPER-LOW IS CENTERED OVER EASTERN SIBERIA AND SLOWLY DRIFTING
NORTH. AN OLD UPPER-LOW NEAR PRINCE WILLIAM SOUND OPENED INTO A
TROUGH OVERNIGHT AND IS FILLING AS IT MOVES NORTHWEST INTO THE KENAI
PENINSULA. SNOW/RAIN ASSOCIATED WITH IT STILL FALLS ACROSS PRINCE
WILLIAM SOUND WITH ONLY A TOUCH OF PRECIP MAKING IT ACROSS THE
CHUGACH/KENAI RANGES. A WEAK SURFACE LOW 450 MILES SOUTH OF MIDDLETON
ISLAND IS MOVING NORTHEAST AND ALSO FILLING AS THE CORE OF THE
UPPER-JET IS DISPLACED FURTHER TO THE SOUTHEAST. BEHIND THE GULF
LOWS...UPPER-LVL RIDGING SUPPORTS SURFACE HIGH PRESSURE OVER THE SW
MAINLAND. A COUPLE OF WEAK UPPER DISTURBANCES STILL ALLOWS FOR A FEW
PASSING FLURRIES NEAR THE ALASKA/ALEUTIAN RANGES. BUT OVERALL
OFF-SHORE FLOW IS HELPING TO SCOUR OUT MUCH OF THE CLOUDINESS (SAVE
FOR THE AKPEN AND WESTERN CAPES)...LEADING TO A PARTICULARLY
COOL/CRISP MORNING OVER THE KUSKOKWIM DELTA. THE MOST SIGNIFICANT
WEATHER FEATURE OVER THE AOR IS A POWERFUL 967 MB SURFACE LOW 250 NM
SOUTHWEST OF ATKA WHICH IS MOVING EAST. MODERATE SNOW AND STORM TO
HURRICANE FORCE WINDS ENVELOP THE WESTERN TO CENTRAL ALEUTIAN
CHAIN...WITH BLIZZARD CONDITIONS LIKELY ONGOING BETWEEN ADAK AND
KISKA. ALSO OF NOTE IS A STRONG LOW OVER NORTHERN JAPAN WHICH IS
QUICKLY MOVING EAST.

.MODEL DISCUSSION...
MODELS ADEQUATELY CAPTURE THE MAIN WEATHER FEATURES AND HAVE
REASONABLY GOOD AGREEMENT. THE LOW NEAR PRINCE WILLIAM SOUND IS
DEPICTED DISSIPATING THIS EVENING AS IT MOVES INTO THE KENAI
PENINSULA. THE LOW 450 MILES SOUTH OF MIDDLETON ISLAND MOVES TO
AROUND 220 MILES SOUTHEAST OF MIDDLETON ISLAND SAT AFTERNOON AND
DISSIPATES AHEAD OF THE ALEUTIAN SYSTEM'S FRONT WHICH TRACKS TO THE
SW GULF SAT EVENING. THE FRONT THEN STALLS IN PLACE THROUGH
SUN...LIKELY BECAUSE THE RIDGE BUILDING AHEAD OF THE FRONT BECOMES
FAIRLY NEGATIVELY TILTED AS THE PARENT PACIFIC LOW CONTINUES TO MOVE
EAST AND THEN SOUTHEAST IN RESPONSE TO THE SUPPORTING 150 KT UPPER
JET CONTINUING TO DIG SOUTH OF THE GULF OF AK. THE PACIFIC LOW
REACHES PEAK INTENSITY AROUND 965 MB THIS AFTERNOON 100 MILES SOUTH
OF ATKA...FILLS AS IT PASSES 150 MILES SOUTH OF UNALASKA ON
SAT...THEN MOVES TO AROUND 400 MILES SOUTH OF CHIGNIK AT 990 MB ON
SUN. THE SYSTEM MOVING OFF JAPAN MEANWHILE TRACKS TO AROUND 400 MILES
WEST OF ATTU ON SUN...WITH IT'S ASSOCIATED FRONT APPROACHING THE FAR
WESTERN CHAIN/BERING LATE SAT NIGHT. THE MORNING FORECAST PACKAGE
GENERALLY LEANED ON THE GFS SOLUTION THROUGH THE WEEKEND...TOWARDS
GFS/ECMWF INTO MID NEXT WEEK.

.SHORT TERM FORECAST...
SOUTHCENTRAL/GULF...
THE BIGGEST FORECAST CHALLENGE APPEARS TO BE SCOPE OF PRECIPITATION
SPILLING OVER THE CHUGACH/KENAI RANGES TODAY AND TONIGHT. LITTLE TO
NO DOWNSLOPING IS ANTICIPATED AS THE FLOW ALOFT REMAINS SOUTHERLY...
BUT DYNAMIC LIFT IS ALSO FAIRLY WEAK. ALL IN ALL...SOME PERIODS OF
SNOW CANNOT BE RULED OUT AS WHAT'S LEFT OF THE LOW CONTINUE TO MOVE
INLAND...BUT ACCUMULATIONS SHOULD REMAIN RATHER LIGHT...WITH THE
STEADIEST PRECIP ALONG COASTAL AREAS. A WEAK SHORTWAVE STARVED OF
MOISTURE ROTATES THROUGH SOUTHCENTRAL EARLY SAT AND WITH IT'S PASSAGE
EVEN DRIER CONDITIONS APPEAR ON THE HORIZON...ALLOWING FOR
RESPECTABLE AMOUNTS OF SUNSHINE FOR THE SOUTHERN MAINLAND THIS
WEEKEND.

ACROSS KODIAK ISLAND...THE UPPER RIDGE SHOULD PROVIDE FAIR/DRY
WEATHER THROUGH TONIGHT. DEEP CLOUDS FROM THE ALEUTIAN SYSTEM BEGIN
MOVING IN EARLY SAT WHILE THE FLOW AT LOW LEVELS BECOMES MORE ONSHORE
AND MOIST AHEAD OF THE FRONT LEADING TO PRECIPITATION BY SAT EVENING.
AS MENTIONED EARLIER...THE FRONT LOOKS TO STALL OVER THE SW GULF AND
KODIAK ISLAND...SO CONDITIONS SHOULD REMAIN PERSISTENTLY SNOWY/RAINY
FOR MUCH OF THE REMAINING WEEKEND. THE FRONT DOES BEGIN TO DISSIPATE
AS THE PARENT LOW RETREATS SOUTH OF THE GULF...ALLOWING PRECIP TO
BECOME MORE SHOWERY WITH TIME.

SOUTHWEST/AKPEN...
NESTLED IN BETWEEN SYSTEMS INITIALLY...SW AK GENERALLY REMAINS DRY
THROUGH TONIGHT. FRONTAL MOISTURE OVERSPREADS BRISTOL BAY AND THE
KUSKOKWIM DELTA DURING THE WEEKEND...FOCUSED MAINLY ON THE
COASTS/WESTERN CAPES. THERE WILL BE SOME BLOWING SNOW CONSIDERATIONS
AS WELL...THOUGH WITH QPF ON THE LIGHT SIDE HAVE NOT INTRODUCED ANY
WATCHES/WARNINGS. SOUTH TO EAST WINDS WILL BE ESPECIALLY GUSTY
THROUGH FAVORED CHANNELED TERRAIN. THE FRONT WILL BE NOSING TOWARDS
THE AKPEN AT THE TAIL END OF IT'S PEAK INTENSITY THIS EVENING...BUT
IT'S ASSOCIATED SQUEEZED PRESSURE GRADIENT MAY LEAD TO A PERIOD OF
WINDS IN EXCESS OF 75 MPH AND HAVE ISSUED A HIGH WIND WATCH FOR THE
AREA WEST OF SAND POINT. PRECIPITATION IS GENERALLY EXPECTED TO BE
SNOW...THOUGH IT MAY MIX WITH RAIN AT TIMES SOUTH OF BRISTOL BAY WITH
925 TEMPS NEARING 0 CELSIUS. ALL PRECIP CHANGES BACK TO SNOW BUT WILL
LIKELY BE MUCH MORE SHOWERY SAT NIGHT INTO SUN AS THE LOW SLIPS AWAY
AND SOME COLD ADVECTION FILLS IN.

BERING SEA/ALEUTIANS...
BLIZZARD THREATS FOR THE ALEUTIAN CHAIN AND THE PRIBILOF ISLANDS OVER
THE NEXT 24 TO 36 HRS. SNOW AND STRONG WINDS AHEAD OF THE FRONT ARE
LEADING TO REDUCED VISIBILITY OVER THE CENTRAL CHAIN THIS MORNING AND
THIS WILL SPREAD TO THE EASTERN CHAIN THIS AFTERNOON...THOUGH IT
SHOULD BE BLUNTED SOMEWHAT BY WARMING TEMPERATURES TO NEAR OR
SLIGHTLY ABOVE FREEZING AND ALLOW SOME RAIN TO BE MIXED IN AT TIMES.
THE EAST WINDS SHIFT MORE NORTH OVER THE CENTRAL CHAIN BY THIS
EVENING TURNING ALL PRECIP BACK TO SNOW IN THE DEFORMATION AREA.
WINDS WILL BE CONSIDERABLY STRONGER AT THIS JUNCTURE AS WELL...AND
VISIBILITY SHOULD BECOME SUBSTANTIALLY WORSE THAN ANYTHING
EXPERIENCED EARLIER IN THE DAY. THE EASTERN CHAIN WILL SEE THE FRONT
TRAVERSING AT PEAK INTENSITY THIS AFTERNOON/EVENING WITH SOME LOW TO
MID-LVL INSTABILITY. THIS COUPLED WITH FUNNELING FROM TERRAIN SHOULD
ALLOW WINDS TO QUICKLY RAMP UP TO WARNING LEVELS. COLD AIR WILL BE
SLOWER TO MIGRATE TO THE EASTERN PART OF THE CHAIN...AND WITH LESS
LIFT AS TIME WEARS ON...PRECIP INTENSITY EVEN WITH GUSTY WINDS SHOULD
NOT LEAD TO A BLIZZARD ON THE BACKSIDE OF THE SYSTEM. THE PRIBILOF
ISLANDS SHOULD STAY ON THE COLD SIDE OF THE SYSTEM (AIDED BY ICE
PACK) AND WITH WINDS RAMPING UP QUICKLY WITH THE ARRIVAL OF SNOW...A
BLIZZARD WARNING HAS BEEN POSTED HERE AS WELL.

.LONG TERM FORECAST...
OPERATIONAL MODELS HAVE SOME ORIENTATION DIFFERENCES WITH THE
FEATURES...BUT OVERALL PRETTY GOOD AGREEMENT WITH REGARDS TO THE
TRENDS. THE BERING/ALEUTIAN CHAIN STILL LOOKS TO BE DOMINATED BY AN
UPPER-TROUGH. THE RESIDUAL FRONT THAT IMPACTS THE WESTERN BERING ON
SUN TRACKS TO THE AKPEN AND SW AK MID NEXT WEEK. THE GULF AND
SOUTHERN MAINLAND LOOK TO INITIALLY BE DRY UNDER UPPER-RIDGING...BUT
ENERGY FROM THE BERING SEA MOVING UP AGAINST IT HELPS TO BREAK IT
DOWN MID NEXT WEEK...LEADING TO SLIGHTLY MORE UNSETTLED WEATHER.
ANOTHER POWERFUL PACIFIC LOW IS DEPICTED MOVING UP TOWARDS THE
AKPEN/KODIAK MID TO LATE NEXT WEEK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING...187 191 195
         HIGH WIND WARNING...185
         HIGH WIND WATCH...181
MARINE...HURRICANE FORCE WIND...172 175
         STORM...155 170 171 176 413 414
         GALE...132 150 160 165 179 180 185 411 412
         HEAVY FREEZING SPRAY...175 176 411 412 413
FIRE WEATHER...NONE

MALOY