Blizzard Watch 16, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
1140 AM AKST THU FEB 28 2013

.ANALYSIS AND UPPER LEVELS...A DEEP COMPACT LOW IS TRACKING
NORTHWARD ACROSS THE EASTERN GULF THIS MORNING. THE STRONGEST
WINDS (GALE FORCE) ARE BEING OBSERVED ON THE NORTH TO EAST SIDE
OF THE LOW. A SHORT-WAVE TROUGH WHICH CROSSED SOUTHCENTRAL ALASKA
EARLY THIS MORNING IS HEADING ACROSS THE ALASKA RANGE TO SOUTHWEST
ALASKA. THERE ARE A FEW SHOWERS LINGERING BEHIND THE TROUGH IN AN
UNSTABLE AIR MASS. THESE SHOWERS WILL DIMINISH THIS AFTERNOON AS
THE APPROACHING LOW CAUSES WIND TO BACK TOWARD THE NORTH. MIDDLETON
ISLAND RADAR SHOWS THE PRECIP MOVING IN OUT AHEAD OF THE LOW IS
REMAINING OFFSHORE. THIS IS DUE TO THE FACT FLOW HAS ALREADY
BACKED TO NORTHEASTERLY OVER SOUTHEAST PRINCE WILLIAM SOUND.

CONDITIONS ARE FAIRLY CALM ACROSS THE REST OF THE FORECAST AREA
THIS MORNING. FLOW OVER SOUTHWEST ALASKA IS VERY WEAK AND DIFFUSE
WITH MULTIPLE FEATURES PASSING BY...RESULTING IN AREAS OF LIGHT
SNOW. COLD ADVECTION BEHIND AN EXITING LOW SOUTH OF THE ALASKA
PENINSULA IS PRODUCING SNOW SHOWERS AND BLOWING SNOW FROM THE
EASTERN ALEUTIANS TO SOUTHERN ALASKA PENINSULA.

THE NEXT MAJOR STORM TO AFFECT THE AREA IS NOW INTENSIFYING OVER
THE NORTHWEST PACIFIC AND HEADED NORTHEAST TOWARD THE ALEUTIANS.

.MODEL DISCUSSION...GFS SOLUTION IS VERIFYING BEST WITH EASTERN
GULF LOW AND OBSERVED WINDS FROM THE NORTHERN TO EASTERN GULF.
HOWEVER...DON'T PARTICULARLY LIKE THE GFS SOLUTION OF TRACKING
THIS LOW TO WESTERN PRINCE WILLIAM SOUND. WITH A TROUGH EXTENDING
FROM THE LOW BACK TO SOUTHCENTRAL WOULD EXPECT A SOLUTION MORE
LIKE THE GEMGLB WHICH WEAKENS THE MAIN LOW SOUTH OF CAPE SUCKLING
AND DEVELOPS A SECONDARY LOW OVER WEST PRINCE WILLIAM SOUND.

CONTINUE TO FAVOR THE ECMWF/GEMGLB SOLUTIONS WITH TRACK OF MAJOR
STORM SYSTEM ALONG THE ALEUTIANS THE NEXT COUPLE DAYS. FOR THE MOST
PART THEY HAVE SHOWN VERY GOOD RUN-TO-RUN CONSISTENCY. THE GFS MODEL
HAS BEEN FAIRLY CONSISTENT AS WELL BUT HAS BEEN FASTER AND FARTHER
NORTH COMPARED TO THE CLUSTER OF OTHER MODEL SOLUTIONS.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...AS LOW WEAKENS OVER THE NORTHERN GULF TONIGHT
OFFSHORE FLOW WILL WEAKEN WHICH WILL ALLOW STEADY PRECIP TO MOVE
BACK INTO THE PRINCE WILLIAM SOUND REGION. A REMNANT LOW IS EXPECTED
TO SET UP OVER PRINCE WILLIAM SOUND BY EARLY TOMORROW MORNING...WITH
LOW LEVEL MOISTURE FROM THE MAIN SYSTEM ADVECTING WESTWARD ACROSS
THE KENAI AND CHUGACH MOUNTAINS. THERE WON'T BE A LOT OF UPPER LEVEL
FORCING AS THE UPPER CENTER HEADS INLAND. HOWEVER THIS IS A FAVORABLE
SET-UP FOR LIGHT SNOW FROM THE WESTERN KENAI TO ANCHORAGE AND THE
MAT-SU. THE LARGER UPPER TROUGH OVER THE REGION WILL EVENTUALLY LIFT
NORTHEASTWARD FRIDAY NIGHT AND SATURDAY. HOWEVER...BUILDING RIDGE
RIGHT BEHIND IT MEANS IT WILL RAPIDLY BE WEAKENING AND SURFACE LOW
OVER WESTERN PRINCE WILLIAM SOUND WILL BE DISSIPATING BY THAT POINT.
SO SNOW POTENTIAL DOES NOT LOOK AS FAVORABLE. IN ANY CASE
SOUTHCENTRAL WILL DRY OUT AND COOL DOWN A BIT SATURDAY AS UPPER
RIDGE MOVES OVERHEAD.

SOUTHWEST ALASKA...SNOW WILL GRADUALLY END OVER SOUTHWEST ALASKA
TONIGHT AS UPPER TROUGH BEGINS TO LIFT NORTHEASTWARD. SKIES WILL
THEN CLEAR OUT FRIDAY AND FRIDAY NIGHT AS UPPER RIDGE BUILDING OUT
AHEAD OF ALEUTIAN SYSTEM ARRIVES. THIS RIDGE WILL BUILD OVER MAINLAND
ALASKA OVER THE WEEKEND AND HELP BLOCK THE ALEUTIANS SYSTEM FROM
MAKING IT VERY FAR EASTWARD. AT THIS POINT IT LOOKS LIKE THE
SOUTHWEST COAST WILL BE RIGHT ON THE OUTER PERIPHERY OF THE SYSTEM
SATURDAY AFTERNOON AND SATURDAY NIGHT...MEANING THERE IS POTENTIAL
FOR SNOW AND BLOWING SNOW. THERE IS STILL A CHANCE THIS COULD REMAIN
JUST OFFSHORE. AT THIS POINT THERE IS NOT ENOUGH CONFIDENCE IN THE
STORM TRACK TO LEAN ONE WAY OR THE OTHER.

BERING SEA/ALEUTIANS...CONTINUE TO FAVOR STORM TRACK AS DEPICTED BY
THE ECMWF AND GEMGLB MODELS. NO MATTER WHICH STORM TRACK YOU GO WITH
CONDITIONS LOOK FAVORABLE FOR BLIZZARD CONDITIONS NORTH AND WEST OF
THE LOW CENTER. PLAN TO UPGRADE THE CURRENT BLIZZARD WATCHES FOR THE
CENTRAL AND WESTERN ALEUTIANS TO WARNINGS WITH THE AFTERNOON PACKAGE.
IN ADDITION...EXPECT THE STRONGEST WINDS ON THE BACK SIDE OF THE LOW
AS COLD AIR QUICKLY WRAPS INTO THE SYSTEM. FOR NOW WILL STICK WITH
STORM FORCE WINDS...BUT IF THE LOW IS A LITTLE DEEPER THAN FORECAST
WILL LIKELY SEE AN AREA OF HURRICANE FORCE WINDS ALONG THE CENTRAL
TO WESTERN ALEUTIANS. BLIZZARD CONDITIONS ALSO LOOK FAVORABLE ON
THE PRIBILOF ISLANDS AS THE OCCLUDED FRONT ARRIVES ON FRIDAY
EVENING...ESPECIALLY FOR SAINT PAUL ISLAND WHICH IS SURROUNDED BY
SEA ICE. THE PRESENCE OF THE SEA ICE MAKES IT MORE OF A CONTINENTAL
TYPE CLIMATE...MAINTAINING COLDER TEMPERATURES AS AIR MOVES OVER
ICE INSTEAD OF WATER. AREAS FURTHER SOUTH AND AHEAD OF THE LOW WILL
WARM ENOUGH TO SEE A MIX WITH OR CHANGE TO RAIN. WINDS ALONG THE
OCCLUDED FRONT WILL ALSO BE QUITE STRONG...BUT AT THIS POINT IT
DOES NOT LOOK STRONG ENOUGH TO REACH THE HIGH WIND WARNING THRESHOLD.
THIS SYSTEM WILL EXIT TO THE SOUTHEAST SATURDAY NIGHT AND SUNDAY AS
ANOTHER SYSTEM MOVES INTO THE WESTERN BERING SEA.

.LONG TERM FORECAST...THE RIDGE WHICH BUILDS OVER MAINLAND ALASKA
THIS WEEKEND WILL CUT-OFF AND LIFT NORTHWARD TOWARD THE POLE EARLY
NEXT WEEK. THIS WILL LEAVE A MUCH WEAKER RIDGE IN PLACE SO THAT THE
NEXT TROUGH CROSSING THE BERING WILL LIKELY BE ABLE TO MAKE INROADS
ACROSS MAINLAND ALASKA BY THE MIDDLE OF NEXT WEEK. THAT STILL LEAVES
SEVERAL DAYS OF DRY CONDITIONS ACROSS MOST OF THE MAINLAND. THE
STORM WHICH TRACKS INTO THE WESTERN BERING ON SUNDAY WILL BRING
WIDESPREAD SOUTHERLIES INTO THE BERING SEA RESULTING IN MUCH WARMER
TEMPERATURES AS WE HEAD INTO EARLY NEXT WEEK. LOOKING THROUGH THE
END OF NEXT WEEK MODELS ARE KEYING ON A MAJOR SYSTEM TRACKING SOUTH
OF THE ALASKA PENINSULA AND THEN INTO THE GULF.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WATCH 187 191.
MARINE...STORM WARNING...170 172 175 176.
         GALE WARNING...155 165 171 179 180 185.
         HEAVY FREEZING SPRAY WARNING...165 176 179.
FIRE WEATHER...NONE.

SEB FEB 13