Gale Warning 246, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
200 PM AKDT FRI MAR 14 2014

.ANALYSIS AND UPPER LEVELS...
A NEGATIVELY TILTED LONGWAVE TROUGH IS LOCATED OVER THE EASTERN
BERING SEA...WITH ASSOCIATED DEEP-LAYER SOUTHEAST FLOW OVER MOST OF
THE ALASKA MAINLAND. AS EXPECTED...A STRONG SHORTWAVE AHEAD OF THE
MAIN TROUGH AXIS SPUN UP A FAST BUT HARD-HITTING SURFACE LOW OVER THE
WESTERN GULF OVERNIGHT THAT BROUGHT HEAVY PRECIPITATION TO THE
EASTERN KENAI MOUNTAINS AND KODIAK ISLAND. THIS LOW BOTTOMED OUT
AROUND 967 MB EARLY THIS MORNING AND IS NOW WEAKENING RAPIDLY AS IT
CROSSES INTO LOWER COOK INLET. AN IMPRESSIVELY COLD ARCTIC AIRMASS IS
ENTRENCHED OVER SOUTHWEST ALASKA...AND IS NOW ON THE MOVE AROUND THE
SOUTH SIDE OF THE LOW CENTER AND BEGINNING TO MOVE UP COOK INLET. THE
EVOLUTION OF THE AFOREMENTIONED LOW AND COLD AIRMASS IS THE PRIMARY
FORECAST CHALLENGE TODAY. MEANWHILE OUT WEST...GUSTY NORTH WINDS AND
INSTABILITY SNOW SHOWERS CONTINUE OVER MOST OF THE BERING SEA AND
ALEUTIAN REGION WITH THE EXCEPTION OF THE FAR WESTERN ALEUTIANS WHERE
WINDS HAVE SHIFTED TO THE SOUTH AHEAD OF AN APPROACHING PACIFIC
WEATHER FRONT.

.MODEL DISCUSSION...
ALL AVAILABLE MODELS ARE IN REASONABLE SYNOPTIC AGREEMENT WITH THE
MOVEMENT OF THE BASIC FEATURES. CONFIDENCE IS HIGH IN AN AIRMASS
REPLACEMENT OVER MUCH OF THE MAINLAND AS THE ARCTIC AIR CURRENTLY
OVER THE EASTERN BERING AND SOUTHWEST MAINLAND SPREADS NORTHWARD
THROUGH TOMORROW. THERE IS SOME DISAGREEMENT ABOUT HOW QUICKLY THE
WEAKENING LOW AND ACCOMPANYING COLD AIR SURGE WILL MOVE UP COOK INLET
TONIGHT. FOR SEVERAL DAYS THE ECMWF HAS BEEN THE SLOWEST MODEL TO
BRING IN THIS NEW AIRMASS..AND BASED ON CURRENT OBS AND SATELLITE
DATA IT SEEMS THAT PERHAPS EVEN THE ECMWF IS A BIT TOO SLOW. THIS
DELAYED THE ONSET OF BLOWING SNOW AND BLIZZARD CONDITIONS OVER THE
SOUTHERN KENAI PENINSULA TODAY...AND MAY ALSO DELAY THE ONSET OF
STEADY SNOW ACROSS THE ANCHORAGE AND MAT-SU AREAS TONIGHT.
MEANWHILE...OUT WEST THERE IS SOME MOVEMENT AMONG THE OTHER GLOBAL
MODELS TOWARD THE ECMWF SOLUTION OF A CLOSED UPPER LOW (AND
ASSOCIATED CONSOLIDATED SURFACE ENERGY) OVER THE CENTRAL BERING ON
SUNDAY. THUS THE ECMWF REMAINS THE PREFERRED MODEL FOR BOTH DOMAINS
FOR THE AFTERNOON FORECAST PACKAGE.

.SHORT TERM FORECAST...
SOUTHCENTRAL...AN ABRUPT TRANSITION LINE FROM WARM AND WET SOUTHEAST
WINDS TO COLD AND SNOWY SOUTHWEST WINDS WILL MOVE UP COOK INLET LATE
THIS AFTERNOON AND EVENING. STEADY SNOW WILL BECOME MORE SHOWERY
AROUND KACHEMAK BAY...THOUGH STRONG SOUTHWEST WINDS AND DROPPING
TEMPERATURES WILL CONTINUE THROUGH MIDNIGHT AND CONTINUE THE BLIZZARD
THREAT THROUGH THE EVENING HOURS. MEANWHILE...AS THE COLD AIR REACHES
ANCHORAGE LATE THIS AFTERNOON A MIX OF RAIN AND SNOW WILL DEVELOP AND
QUICKLY CHANGE OVER TO ALL SNOW AS THE ENTIRE COLUMN COOLS
DRAMATICALLY. THE TOTAL SNOWFALL AMOUNTS FOR ANCHORAGE AND THE MAT-SU
REMAIN LOWER CONFIDENCE THAN USUAL AS THERE ARE SOME KEY DIFFERENCES
FROM TYPICAL SNOW EVENTS. STRONG COLD AIR ADVECTION FAVORS HIGHEST
AMOUNTS ON THE HILLSIDE...SO WILL TREND THAT DIRECTION WITH THE
AFTERNOON FORECAST AND KEEP AMOUNTS BELOW ADVISORY LEVEL.

SOUTHWEST MAINLAND...A FAIRLY NARROW DEFORMATION BAND IS BRINGING
STEADY SNOW ALONG A LINE FROM ANIAK TO ILIAMNA. THIS SNOW BAND WILL
CONTINUE TO WEAKEN QUICKLY DURING THE EVENING HOURS...WITH MINIMAL
ADDITIONAL ACCUMULATIONS. GENERAL ONSHORE FLOW WILL CONTINUE THROUGH
THE FIRST HALF OF THE WEEKEND...WHICH WILL KEEP CLOUDS AND SNOW
SHOWERS AROUND (ESPECIALLY OVER COASTAL LOCATIONS). BY SUNDAY A
BERING FRONT WILL MOVE ONSHORE AND BRING ANOTHER ROUND OF SNOW AND
GUSTY WINDS.

BERING SEA AND ALEUTIANS...NORTHERLY WINDS AND SNOW SHOWERS WILL
CONTINUE THROUGH THE MORNING ACROSS THE EASTERN HALF OF THE AREA. A
FRONT ASSOCIATED WITH A LOW SOUTH OF THE KAMCHATKA PENINSULA IS
GETTING READY TO ENTER THE WESTERN BERING THIS EVENING. THIS
GALE-FORCE FRONT WILL GRADUALLY ELONGATE AND CROSS THE ENTIRE BERING
DURING THE FIRST HALF OF THE WEEKEND. MOST PLACES ON THE ALEUTIAN
CHAIN WILL WARM UP ENOUGH TO CHANGE TO RAIN AS THE FRONT
PASSES...EXCEPT THE PRIBILOFS WHERE A WET SNOW MAY PERSIST EVEN AS
THE FRONT APPROACHES.

.LONG TERM FORECAST...
THE LONGWAVE TROUGH IS CURRENTLY OVER THE EASTERN BERING WHICH IS
STEERING THE STORM TRACK INTO THE SOUTHERN MAINLAND. OVER THE COURSE
OF THE NEXT WEEK THIS LONGWAVE APPEARS AS IF IT WILL SLOWLY
RETROGRADE WESTWARD...EVENTUALLY ALLOWING SOME SHORTWAVE RIDGING TO
BUILD INTO THE EASTERN BERING AND WEST COAST OF ALASKA AND SHIFTING
THE STORM TRACK TO THE WEST AS WELL. TEMPERATURES ACROSS MOST OF THE
REGION SHOULD RETURN TO NEAR SEASONAL NORMS BY EARLY NEXT WEEK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING 121
MARINE...GALE 150 155 160 165 170 172 173 174 175 176 177 178 179 180
              181 185
         HEAVY FREEZING SPRAY 130 131 132 136 137 138 139 140 141 160
                              165 179 180
FIRE WEATHER...NONE

AMD MAR 14