Blizzard in Alaska, February 20, 2014

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
400 PM AKST WED FEB 19 2014

.ANALYSIS AND UPPER LEVELS...
THE LONGWAVE PATTERN IS IN THE MIDST OF A TRANSITION. THE UPPER LOW
THAT HAS LINGERED AROUND SOUTHWEST ALASKA FOR THE PAST WEEK IS NOW
WEAKENING QUICKLY AND DRIFTING SLOWLY TO THE NORTHEAST. AN IMPRESSIVE
UPPER LEVEL TROUGH THAT ACTED AS A FOCUSING MECHANISM FOR HEAVY SNOW
ACROSS THE ANCHORAGE BOWL OVERNIGHT HAS WEAKENED AND MOVED NORTHWARD.
CONVECTIVE SNOW SHOWERS ACROSS THE GULF CONTINUE TO IMPACT PRIMARILY
COASTAL LOCATIONS WITH OCCASIONAL MODERATE SNOWFALL RATES.
MEANWHILE...WIDESPREAD BUT MUCH LESS INTENSE SNOWFALL ASSOCIATED WITH
THE UPPER LEVEL LOW CENTER ITSELF IS LINGERING AROUND COOK INLET. OUT
WEST...AN UPPER TROUGH IS BEGINNING TO AMPLIFY ACROSS THE WESTERN
BERING SEA. THIS IS GIVING A BOOST TO SEVERAL WEAK SURFACE LOWS IN
THE AREA. IN PARTICULAR...A COMPACT SYSTEM NEAR THE WESTERN ALEUTIANS
IS RAPIDLY DEEPENING...AND WILL BRING A ROUND OF SNOW AND BLOWING
SNOW TO THE WESTERN ALEUTIANS BEGINNING THIS EVENING.

.MODEL DISCUSSION...
THE MODELS ARE IN GOOD SYNOPTIC AGREEMENT. THE AMPLIFYING TROUGH IN
THE BERING WILL SEE MULTIPLE LOWS PINWHEELING AROUND THE OVERALL
UPPER LOW POSITION OVER THE COMING DAYS...AND NOT SURPRISINGLY THE
MODELS ARE STRUGGLING A BIT WITH SOME OF THE FINER DETAILS OF TIMING
AND PLACEMENT OF THESE FEATURES. OVERALL THE ECMWF HAS BEEN THE MOST
CONSISTENT...BUT A COMPOSITE BLEND OF THE CURRENT MODEL RUNS WILL BE
USED TO TWEAK THE FORECAST TODAY IN MOSTLY MINOR WAYS.

.SHORT TERM FORECAST...
SOUTHCENTRAL...THE PRESENCE OF THE WEAKENING UPPER LOW CENTER OVER
COOK INLET WILL KEEP THE COASTLINES UNDER A SHOWERY PATTERN THROUGH
THURSDAY MORNING. MULTIPLE WEAK UPPER TROUGHS ROTATING AROUND THE LOW
CENTER WILL ALSO LIKELY CONTINUE TO PRODUCE PERIODS OF LIGHT SNOW
AROUND COOK INLET THROUGH THURSDAY MORNING...THOUGH ANY ACCUMULATIONS
WILL BE MINOR. BY THURSDAY AFTERNOON THE UNSETTLED WEATHER WILL
CONTINUE TO SLIDE OFF TO THE EAST AS WARM AIR ADVECTION AND HIGH
PRESSURE BEGIN TO MOVE INTO THE AREA. THIS WILL ALSO LIKELY LEAD TO
THE DEVELOPMENT OF AREAS OF FOG BY THE END OF THE WEEK...ESPECIALLY
ACROSS INTERIOR LOCATIONS WHERE WINDS WILL BE THE LIGHTEST.

SOUTHWEST...PARTLY CLOUDY AND MOSTLY DRY CONDITIONS WILL CONTINUE
TONIGHT AS THE UPPER LOW WEAKENS AND MOVES AWAY. AS PRESSURE DROPS IN
THE BERING SEA FLOW WILL BECOME INCREASINGLY OFFSHORE AT THE SURFACE
BY THURSDAY MORNING. MEANWHILE...SOUTHERLY FLOW ALOFT WILL ALLOW
WARMER AIR TO BEGIN TO MOVE INTO THE AREA WITH A LONGWAVE RIDGE
DEVELOPING IN EARNEST ACROSS THE REGION BY SATURDAY. THE COAST WILL
SEE SEVERAL CHANCES FOR PRECIP THROUGH THE WEEKEND AS MULTIPLE FRONTS
STALL AND WEAKEN JUST OFFSHORE. INTERIOR AREAS WILL REMAIN DRY WITH
TEMPERATURES MODERATING DRAMATICALLY BY THE START OF THE WEEKEND.

BERING SEA AND ALEUTIANS...A SMALL BUT SURPRISINGLY POTENT LOW IS
BEGINNING TO TAKE SHAPE NEAR THE WESTERN ALEUTIANS. WITH COLD AIR IN
PLACE THERE WILL BE A PERIOD OVERNIGHT OF STRONG WINDS AND BLOWING
SNOW OVER THE FAR END OF THE CHAIN...WHERE A WINTER WEATHER ADVISORY
REMAINS IN EFFECT THROUGH THURSDAY MORNING. FURTHER EAST...ANOTHER
SHORT-LIVED BUT SURPRISINGLY STRONG LOW WILL CROSS INTO THE BERING
SEA TONIGHT AND DEVELOP SOUTHWEST OF THE PRIBILOF ISLANDS ON
THURSDAY. THIS WILL LIKELY BRING A PERIOD OF SNOW AND BLOWING SNOW TO
THIS AREA AS WELL DURING THE DAY THURSDAY. BASED ON MARGINALLY
IMPRESSIVE UPPER LEVEL SUPPORT FOR THIS SYSTEM...AND AN EASTERLY
(RATHER THAN A NORTHERLY) WIND DIRECTION...THINK THE AREA WILL BE
ABLE TO AVOID BLIZZARD CONDITIONS. THUS WILL PLAN TO CHANGE THE
BLIZZARD WATCH TO A BLOWING SNOW ADVISORY WITH THE AFTERNOON PACKAGE.

.LONG TERM FORECAST FROM PREVIOUS DISCUSSION...
CONFIDENCE CONTINUES TO INCREASE IN A HIGH AMPLITUDE PATTERN
RETURNING TO ALASKA SIMILAR BY THIS WEEKEND. A DEEP COMPLEX LOW WILL
SET UP IN THE BERING SEA WITH RIDGING FURTHER EAST OVER THE MAINLAND.
GUIDANCE IS HINTING AT RIDGING STAYING ENTRENCHED OVER THE PANHANDLE
THROUGH MUCH OF THE STATE WHILE A NEGATIVELY TILTED LARGE
TROUGH/COMPLEX LOW STRETCHES FROM THE BERING SEA THROUGH THE EASTERN
PACIFIC.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING 195 AND WINTER WEATHER ADVISORY 191
MARINE...GALE 178 179
         HEAVY FREEZING SPRAY 130 136 137 139 141 160 165
FIRE WEATHER...NONE

AMD/MTL FEB 14