Heavy Freezing Spray Warning 21, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
200 PM AKST TUE FEB 11 2014

.ANALYSIS AND UPPER LEVELS...
THE LONGWAVE PATTERN IS STABLE AND FEATURES A STRONG RIDGE OVER THE
BERING SEA AND A LONGWAVE TROUGH OVER THE GULF OF ALASKA AND
NORTHEAST PACIFIC. MAINLAND ALASKA REMAINS UNDER COLD AND DRY
NORTHERLY FLOW...WITH A WEAKENING UPPER-LEVEL SHORTWAVE CURRENTLY
BRINGING A THIN BAND OF HIGH CLOUDS FROM THE SUSITNA VALLEY
STRETCHING BACK THROUGH BRISTOL BAY. A LINGERING SURFACE LOW IN THE
GULF CONTINUES TO PULL RELATIVELY WEAK WINDS THROUGH THE FAVORED GAPS
ALONG THE COASTLINE. MEANWHILE...HIGH PRESSURE ALL THE WAY DOWN TO
THE SURFACE OVER MUCH OF THE BERING IS BRINGING UNSEASONABLY BENIGN
CONDITIONS TO MANY LOCATIONS.

.MODEL DISCUSSION...
MODELS ARE IN OUTSTANDING OVERALL AGREEMENT. ALL MODELS BRING THE
VIGOROUS UPPER LOW CURRENTLY APPROACHING THE NORTH SLOPE DOWN THROUGH
SOUTHWEST ALASKA THROUGH THE END OF THE WEEK. ACCOMPANYING THIS LOW
WILL BE ONE OF THE COLDEST AIRMASSES OF THE SEASON SO FAR. THERE ARE
SOME DIFFERENCES WITH THE EXACT POSITION OF THE SURFACE LOW THAT
DEVELOPS BENEATH THE UPPER LOW IN THE WESTERN GULF FOR THE 2ND HALF
OF THE WEEK. GIVEN THE FACT THAT THE UPPER LOW WILL BE HARDLY
MOVING...IT MAKES SENSE THAT THERE WILL BE MULTIPLE SURFACE LOWS
SPINNING UNDERNEATH THE PARENT UPPER LOW. THE EXACT POSITION OF THESE
CIRCULATION CENTERS WILL CONTROL WHETHER THE COOK INLET REGION GETS
ANY SNOW. AT THIS TIME THE NAM LOOKS TO BE A BIT FURTHER EAST WITH
THE UPPER CENTER THAN THE GEM/ECMWF/GFS CONSENSUS...AND WILL LEAN
SLIGHTLY AWAY FROM THE NAM FOR THIS REASON WITH PREPARATION OF THE
AFTERNOON FORECASTS.

.SHORT TERM FORECAST...
SOUTHCENTRAL...A FEW PASSING CLOUDS WILL BE THE ONLY IMPACT FROM THE
LEADING UPPER TROUGH CURRENTLY MOVING THROUGH THE REGION FROM NORTH
TO SOUTH. AS THE UPPER TROUGH DIGS SOUTHWARD ON WEDNESDAY FLOW WILL
BECOME MORE SOUTHERLY ACROSS MUCH OF THE AREA...LEADING TO INCREASING
CLOUDS AND SNOW DEVELOPING ALONG THE COAST BY WEDNESDAY AFTERNOON.
CONFIDENCE IS HIGH THAT COASTAL AREAS WILL SEE MULTIPLE PERIODS OF
GENERALLY LIGHT SNOWFALL BEGINNING WEDNESDAY NIGHT AND CONTINUING
THROUGH THE START OF THE WEEKEND. THE MORE UNCERTAIN FORECAST IS
WHETHER ANCHORAGE AND THE REST OF THE COOK INLET REGION WILL SEE MUCH
(IF ANY) SNOW AS THIS UPPER LOW REMAINS PARKED NEAR KODIAK ISLAND
DURING THE 2ND HALF OF THE WEEK. BASED ON CURRENT
GUIDANCE...SOUTHEASTERLY FLOW AROUND THE DEVELOPING LOW SHOULD BRING
SOME OVERRUNNING/WARM ADVECTION TO THE REGION BEGINNING WEDNESDAY
EVENING...WITH SURFACE LOW POSITION LIKELY MINIMIZING DOWNSLOPING AND
LEADING TO THE BEST CHANCE OF SNOW LATE WEDNESDAY NIGHT THROUGH
THURSDAY MORNING. WHILE ANY ACCUMULATION SHOULD BE MINOR...CONFIDENCE
IS NOW HIGH ENOUGH TO INCREASE POPS TO LIKELY LATE WEDNESDAY NIGHT
INTO THURSDAY. A TIGHTENING GRADIENT WILL ONCE AGAIN INCREASE WINDS
THROUGH THE GAPS AS THE SURFACE LOW DEVELOPS...WHICH MAY COMBINE WITH
LOW-DENSITY LIGHT TO MODERATE SNOWFALL TO CREATE SOME BLOWING SNOW
CONCERNS LATER THIS WEEK. WILL NEED TO MONITOR CLOSELY FOR POSSIBLE
HAZARD ISSUANCE IN SUBSEQUENT FORECAST PACKAGES...ESPECIALLY AROUND
THOMPSON PASS.

SOUTHWEST...THE BIGGEST IMPACT FROM THE UPPER LOW DROPPING INTO THE
REGION WILL BE THE ACCOMPANYING SURGE OF ARCTIC AIR. AS MENTIONED
ABOVE...THIS LOOKS TO RIVAL THE COLDEST TEMPERATURES OF THE SEASON SO
FAR WITH MANY AREAS SEEING TEMPERATURES IN THE DOUBLE DIGITS BELOW
ZERO. COMBINING WITH THESE TEMPERATURES WILL BE GUSTY NORTH
WINDS...WHICH WILL LIKELY DROP WIND CHILLS ACROSS THE MAINLAND TO
ADVISORY LEVELS. THUS WILL BE ISSUING WIND CHILL ADVISORIES FOR THE
WEDNESDAY NIGHT TO THURSDAY NIGHT PERIODS...WITH SLOW IMPROVEMENT
BEGINNING FRIDAY.

BERING SEA AND ALEUTIANS...HIGH PRESSURE WILL REMAIN GENERALLY IN
CONTROL THROUGH THE WEEKEND. A WEAK LOW PRESSURE CENTER WILL ELONGATE
AND SLIDE THROUGH THE CENTRAL BERING/ALEUTIANS ON
WEDNESDAY...BRINGING A BRIEF UPTICK TO WINDS AND SHOWER ACTIVITY.
ELSEWHERE...CONVECTIVE SNOW SHOWERS WILL DEVELOP OVER BRISTOL
BAY/EASTERN BERING SEA AS COLD AIR BEGINS A MASS MOVEMENT SOUTHWARD.
THIS WILL KEEP AREAS FROM DUTCH HARBOR EASTWARD IN STEADY SNOW
SHOWERS AND GUSTY WINDS BEGINNING THURSDAY AND CONTINUING THROUGH THE
WEEKEND.

.LONG TERM FORECAST FROM PREVIOUS DISCUSSION...
FORECAST CONFIDENCE REMAINS RELATIVELY HIGH INTO THE EXTENDED TERM AS
THE DEEP UPPER LOW DROPPING SOUTHWARD FROM THE ARCTIC LOOKS TO REMAIN
ENTRENCHED OVER THE WESTERN GULF OF ALASKA THROUGH THE MIDDLE OF NEXT
WEEK. THIS WOULD GENERALLY RESULT IN CONTINUED COLD TEMPERATURES AND
GUSTY OUTFLOW WINDS OVER THE SOUTHERN HALF OF THE MAINLAND...WITH THE
BEST CHANCE FOR PRECIPITATION REMAINING ALONG THE NORTHERN GULF
COAST. PRECIPITATION WILL ALSO BE POSSIBLE FOR INLAND PORTIONS OF
SOUTHCENTRAL AK DEPENDING ON THE EXACT POSITION OF THE LOW.
MEANWHILE...A MORE ACTIVE PATTERN LOOKS TO BE IN STORE FOR THE BERING
AS SEVERAL SYSTEMS MOVE THROUGH AND PROVIDE OCCASIONAL CHANCES FOR
PRECIPITATION.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...WIND CHILL ADVISORY 152 155 161
MARINE...GALE 127 130 131 132 150 160 165 175 176 177 180
         HEAVY FREEZING SPRAY 121 126 127 128 129 130 138 150 160 165
                              180 185
FIRE WEATHER...NONE

AMD/CC/CB FEB 14