Blizzard Watch 15, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
1220 PM AKST WED FEB 27 2013

.ANALYSIS AND UPPER LEVELS...AN UPPER LEVEL TROUGH EXTENDS FROM
THE CENTRAL ALEUTIANS TO SOUTHCENTRAL ALASKA AND THE GULF OF ALASKA
WITH RIDGING OVER INTERIOR ALASKA AND OVER THE WESTERN BERING AND
ALEUTIANS. SEVERAL FEATURES ARE MOVING THROUGH THE TROUGH AND AROUND
A FAIRLY LARGE AND DIFFUSE UPPER LEVEL CLOSED LOW ALONG THE ALASKA
PENINSULA. A SMALL BUT SHARP SHORT-WAVE TROUGH OVER THE NORTHERN
GULF IS ROTATING NORTHWESTWARD ACROSS THE KENAI PENINSULA. STRONGER
WINDS OUT AHEAD OF THE TROUGH ARE WEAKENING AS IT MOVES ONSHORE.
HOWEVER...PRESSURE RISES AND A MORE UNSTABLE AIR MASS BEHIND THE
TROUGH ARE LEADING TO GUSTY WINDS AND SHOWERS. A MODERATE STRENGTH
LOW IS TRACKING NORTHWARD ACROSS THE EASTERN GULF BUT THIS IS
EXPECTED TO WEAKEN OVER THE NORTHEAST GULF WITH LITTLE IMPACT TO
SOUTHCENTRAL ALASKA. A VORT-MAX EAST OF THE PRIBILOF ISLANDS IS
ROTATING SOUTHWESTWARD AROUND THE UPPER CENTER AND PRODUCING AREAS
OF LIGHT SNOW. A MATURE LOW SOUTH OF THE EASTERN ALEUTIANS IS
WEAKENING AS IT TRACKS EASTWARD. A NARROW BAND OF STRONGER WINDS
ON THE BACK SIDE OF THIS LOW IS PRODUCING AREAS OF BLOWING SNOW
FROM THE PRIBILOF ISLANDS TO THE CENTRAL ALEUTIANS.

.MODEL DISCUSSION...MODELS ALL INITIALIZED FAIRLY WELL WITH MAJOR
FEATURES BUT SOLUTIONS QUICKLY DIVERGE. ECMWF AND UMKET SEEM TO
HAVE A BETTER TRACK (FURTHER EAST) ON THE EASTERN GULF LOW BASED
ON LATEST SATELLITE TRENDS. THE NAM IS AN OUTLIER WITH THE UPPER
LEVEL SHORT-WAVE ASSOCIATED WITH THIS SURFACE LOW AS IT MOVES TO
SOUTHCENTRAL EARLY THURSDAY. MODELS ARE ALL OVER THE PLACE WITH
TRACK AND STRENGTH OF A LOW FORMING EAST OF SHEMYA TONIGHT AND
MOVING INTO THE CENTRAL BERING THURSDAY. THE ONLY TREND SEEMS TO
BE TOWARD A DEEPER LOW. WILL TREND TOWARD THE GFS TO DEPICT A SMALL
AREA OF SMALLER WINDS AROUND THE LOW CENTER RECOGNIZING THAT THERE
IS LOW CONFIDENCE IN THE TRACK. FOR NEXT MAJOR STORM SYSTEM MOVING
TO THE ALEUTIANS FRIDAY THERE CONTINUES TO BE SOME SPEED AND TRACK
DIFFERENCES. THERE IS A TREND TOWARD FASTER AND FURTHER NORTH.
CURRENT FORECAST WAS BASED ON THE SLOWER AND FURTHER SOUTH ECMWF
SO WILL BLEND TOWARD THE LATEST ECMWF TO REFLECT THE OVERALL TREND.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...AS TROUGH MOVES ACROSS THE KENAI PENINSULA
AND OVER COOK INLET THIS AFTERNOON WINDS WILL RAPIDLY INCREASE
ALONG TURNAGAIN ARM THANKS TO AN INCREASED PRESSURE GRADIENT AND
PRESSURE RISES BEHIND THE TROUGH. WINDS WILL COME DOWN ACROSS THE
REGION OVERNIGHT AS TROUGH AND AREA OF PRESSURE RISES EXITS TO THE
NORTHWEST. THERE WILL BE A BIT OF A REPEAT AS ANOTHER TROUGH MOVES
THROUGH IN A SIMILAR FASHION EARLY THURSDAY. HOWEVER THE SECOND
TROUGH WILL BE WEAKER SO DON'T EXPECT WINDS TO BE AS STRONG. THE
BULK OF PRECIP THIS AFTERNOON AND TONIGHT WILL REMAIN ALONG THE
COAST PARTLY DUE TO THE STRONG WINDS ACROSS THE MOUNTAINS. WITH
WEAKER WINDS TOMORROW AND A SLIGHTLY MORE FAVORABLE ORIENTATION OF
THE UPPER TROUGH EXPECT TO SEE MORE PRECIP MAKE IT ACROSS THE KENAI
MOUNTAINS...ALTHOUGH MOST OF IT SHOULD REMAIN SOUTH OF ANCHORAGE.
ANOTHER LOW WILL TRACK INTO THE EASTERN GULF THURSDAY BUT EXPECT
IT TO REMAIN IN THE EAST AND ONLY AFFECT THE COPPER BASIN AND
EASTERN PRINCE WILLIAM SOUND AREAS.

SOUTHWEST ALASKA...SOUTHWEST ALASKA WILL BE ON THE PERIPHERY OF
FEATURES MOVING THROUGH THE REGION. HIGH PRESSURE WILL THEN BUILD
ON THURSDAY NIGHT AND FRIDAY AND HOLD IN UNTIL ARRIVAL OF A FRONT
FROM THE BERING SEA SOMETIME THIS WEEKEND. THUS...EXPECT GENERALLY
BENIGN WEATHER FOR THE NEXT FEW DAYS.

BERING SEA/ALEUTIANS...THE BERING SEA WILL REMAIN RELATIVELY QUIET
UNTIL ARRIVAL OF A MAJOR PACIFIC STORM THURSDAY NIGHT AND FRIDAY.
THERE IS STILL UNCERTAINTY IN THE EXACT TRACK AND SPEED OF THIS LOW.
HOWEVER BASED ON THE STRENGTH THERE IS POTENTIAL FOR HIGH WIND
AND/OR BLIZZARD CONDITIONS FROM THE PRIBILOFS TO THE ALEUTIANS.

.LONG TERM FORECAST...CONFIDENCE IS GAINING IN DEVELOPMENT OF A
BLOCKING RIDGE FROM THE ARCTIC SOUTHWARD ACROSS MAINLAND ALASKA
THIS WEEKEND...ALTHOUGH UNCERTAINTY REMAINS IN HOW STRONG IT WILL
BE AND HOW LONG IT WILL HOLD OVER THE AREA. INITIALLY THIS WILL
CAUSE THE MAJOR SYSTEM ALONG THE ALEUTIANS AT THE END OF THE WEEK
TO DIVE SOUTHEASTWARD TOWARD THE NORTHEAST PACIFIC...KEEPING
SOUTHCENTRAL ALASKA DRY. ANOTHER SYSTEM MOVING INTO THE BERING
LATER THIS WEEKEND WILL TRY TO MOVE EASTWARD INTO THIS RIDGE AND
BRING PRECIP BACK TO SOUTHCENTRAL EARLY TO MID WEEK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...STORM WARNING...175 176.
         GALE WARNING...120 170 172.
         HEAVY FREEZING SPRAY WARNING...165 179.
FIRE WEATHER...NONE.

SEB FEB 13