Heavy Freezing Spray Warning 2, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
428 PM AKST SUN JAN 17 2016

.ANALYSIS AND UPPER LEVELS...

A WEAKENING VERTICALLY STACKED LOW SITS OVER THE NORTH PACIFIC
APPROXIMATELY 500 MILES SOUTH OF THE ALASKA PENINSULA. THIS
RELATIVELY STATIONARY LOW CONTINUES TO BE THE MAIN FEATURE OVER
THE AOR AS IT CONTINUES TO SLOWLY FILL. THE UPPER JET IS WRAPPING
AROUND THE BASE OF THE LOW...SUPPORTING DEVELOPMENT OF WAVES IN
THE PACIFIC OCEAN THAT ARE TRACKING AROUND THE BASE OF THE LOW AND
NORTHWARD INTO THE EASTERN GULF. ONE SUCH LOW...WHICH WILL IMPACT
SOUTHCENTRAL ALASKA TOMORROW...IS CURRENTLY OFF THE COAST OF HAIDA
GWAII AND MOVING NORTHEASTWARD INTO THE EASTERN GULF OF ALASKA.
THIS LOW HAS BEGUN TO SLOWLY WEAKEN AS IT TRACKS AWAY FROM ITS
UPPER LEVEL SUPPORT TO THE SOUTH. OVER THE MAINLAND...SHOWERS ARE
PERSISTING OVER SOUTHCENTRAL IN BROAD CYCLONIC ONSHORE FLOW. A
WAVE PUSHING THROUGH SOUTHWESTERN ALASKA IS SUPPORTING LIGHT SNOW
SHOWERS OVER THE BRISTOL BAY REGION. AN UPPER LEVEL INVERTED
TROUGH IS MOVING EASTWARD OVER THE BERING SEA AND PRODUCING RAIN
AND SNOW SHOWERS OVER THE BERING AND EASTERN ALEUTIANS.

&&

.MODEL DISCUSSION...

THE MODELS ARE IN GOOD AGREEMENT ON THE KEY SYNOPTIC FEATURES.
MODELS ALL INITIALIZED WELL WITH THE LOWER 960S LOW WEST OF HAIDA
GWAII THIS AFTERNOON. FORECAST SOLUTIONS AS IS IT MOVES INTO THE
NORTHERN GULF MON ARE REASONABLE WITH THE GFS20/NAM12 THE
PREFERRED CHOICE. THE NEXT WAVE WHICH MOVES INTO THE NORTHERN
GULF TUE LOOKS TO BE MUCH WEAKER THEN THE MON LOW. SO WILL LEAN
MORE WITH A NAM/ECMWF BLEND WITH THIS CENTER.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
SOME LINGERING RAIN SHOWERS BEGIN TO TAPER OFF OVER THE SOUTHERN
KENAI PENINSULA AND KODIAK ISLAND EARLY THIS EVENING...AS THE
WEAK WAVE ASSOCIATED WITH THESE SHOWERS SHIFTS FURTHER WEST AND
DISSIPATES OVER THE ALASKA RANGE. THE GENERAL FLOW ACROSS THE AREA
REMAINS A NORTHERLY/OFFSHORE FLOW AS RIDGING SLOWLY BUILDS TOWARD
THE CENTRAL INTERIOR...RESULTING IN TYPICAL GUSTY CONDITIONS
ALONG THE COOK INLET AND THROUGH CHANNELED TERRAIN ALONG THE
NORTHEAST GULF COAST. A LOW TRACKING THROUGH THE SOUTHEAST GULF
TONIGHT WILL BE THE NEXT STORM SYSTEM TO WATCH...AS IT ORGANIZES
AND MOVES INTO THE NORTHERN GULF MONDAY MORNING. THIS SYSTEM WILL
BRING GUSTY GALE TO STORM FORCE WINDS TO THE NORTHERN GULF...ALONG
WITH RAIN AS IT MOVES THROUGH THE AREA. AS THIS SYSTEM SETS UP
SOUTH OF PRINCE WILLIAM SOUND...IT WILL ACT TO TIGHTEN THE
GRADIENT ALONG THE NORTHERN GULF COAST AND SURROUNDING AREAS. THIS
WILL RESULT IN INCREASED GAP WINDS SURROUNDING PRINCE WILLIAM
SOUND THROUGH TUESDAY...AND A STRONG BARRIER JET FORMING ALONG THE
NORTHERN GULF COAST MONDAY. THE LOW CENTER APPROACHES THE SOUTHERN
TIP OF THE KENAI BY MONDAY AFTERNOON...AND THEN DIMINISHES AS IT
TRACKS ACROSS ALEUTIAN RANGE EARLY TUESDAY MORNING.

A SECOND LOW FOLLOWS CLOSELY BEHIND THE INITIAL SYSTEM MENTIONED
ABOVE...TRACKING UP FROM THE SOUTHEAST GULF AND ALONG THE NORTHERN
GULF COAST TUESDAY AFTERNOON. MODELS ARE CURRENTLY SHOWING THIS
SYSTEM TO BE WEAKER THAN THE INITIAL LOW ON TRACKING INTO THE AREA
MONDAY...AND ARE ALSO STRUGGLING WITH THE TIMING AND STRENGTH OF
THIS SYSTEM AS IT APPROACHES THE NORTHERN GULF COAST.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...

CLOUD COVER WILL BE ON THE INCREASE THIS EVENING AS A WEAK
SHORTWAVE PROPAGATES WESTWARD ACROSS SOUTHWEST ALASKA. THIS SHORT
WAVE (CURRENTLY NEAR KODIAK ISLAND) WILL SLIGHTLY INCREASE SNOW
CHANCES ACROSS THE REGION BEFORE MOVING OFFSHORE MONDAY MORNING.
WHILE THE ATMOSPHERE REMAINS FAIRLY STABLE AT THE LOW LEVEL...MID-
LEVEL LAPSE RATES WILL BE BETWEEN 7.5 TO 8.5 DEGREE C/KM LEADING
TO SOME INSTABILITY. HOWEVER...THE STOUT INVERSION AT THE SURFACE
WILL MAKE TAPPING INTO ANY OF THIS INSTABILITY QUITE DIFFICULT.
HOWEVER...HIGHER ELEVATIONS OF THE AHKLUN AND KILBUCK MOUNTAINS
WILL BE ABOVE THE INVERSION AND MORE PRONE TO CONVECTIVE SNOW
SHOWERS DUE TO THE STEEP MID-LEVEL LAPSE RATES. A FEW SNOW SHOWERS
WILL LIKELY BE SEEN ACROSS THE BRISTOL BAY AREA AND KUSKOKWIM
DELTA BUT SNOW ACCUMULATION SHOULD BE PRETTY TOUGH TO COME BY WITH
LIGHT SNOWFALL AND A QUICKLY PROPAGATING SHORTWAVE. LOCATIONS IN
THE VICINITY OF THE KILBUCK AND AHKLUN MOUNTAINS COULD SEE
SNOWFALL UP TO 1 INCH IN ACCUMULATION. FOLLOWING THE
SHORTWAVE...CONDITIONS APPEAR DRY ACROSS MUCH OF SOUTHWEST ALASKA
THROUGH TUESDAY MORNING BEFORE ANOTHER WEAK SHORTWAVE PROPAGATES
ACROSS THE REGION.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...

AN UPPER LEVEL DISTURBANCE WEST OF THE PRIBILOF ISLANDS CONTINUES
TO SPARK SNOW SHOWERS ACROSS THE BERING SEA THIS AFTERNOON. THIS
UPPER LOW WILL AID IN THE DEVELOPMENT OF A SFC LOW OVERNIGHT
TONIGHT AND ALLOW FOR A TIGHTENING OF THE PRESSURE GRADIENT TO
SUPPORT GALE FORCE WINDS FOR THE NORTHERN AND WESTERN BERING SEA.
A DECENT FEED OF WARM AIR WILL BE ADVECTED NORTHWARD ACROSS THE
BERING SEA TONIGHT IN RESPONSE TO THE NEWLY FORMING LOW WHICH
WILL AID IN SNOWFALL TRANSITIONING TO RAIN OVERNIGHT ACROSS THE
EASTERN BERING SEA INCLUDING THE PRIBILOF ISLANDS. SOME OF THIS
WARMER AIR WILL GET TRAPPED UNDER THE INVERSION IN THE EASTERN
BERING SEA WHERE THE ATMOSPHERE WILL BE MUCH MORE STABLE...LEADING
TO THE DEVELOPMENT OF FOG FROM THE PRIBILOF ISLANDS EASTWARD
TONIGHT. THE PRIBILOF ISLANDS COULD SEE UP TO AN ADDITIONAL INCH
OF SNOW THIS EVENING AND EARLY TONIGHT BEFORE THE SHORTWAVE PUSHES
WESTWARD AND PRECIPITATION TAPERS OFF/CHANGES TO RAIN.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...

BY TUESDAY EVENING...A FAST-MOVING AND WELL-DEVELOPED WEST-MOVING
FRONT MOVES WEST ACROSS THE NORTHERN GULF COASTLINE AND THEN
ACROSS SOUTHWEST ALASKA. SUSTAINED PRECIPITATION CHANCES WILL BE
ALMOST EXCLUSIVELY LIMITED TO THE EASTERN SLOPES OF THE MOUNTAIN
RANGES...WITH LITTLE OPPORTUNITY FOR ACCUMULATING PRECIPITATION ON
THE LEEWARD SIDES THAT INCLUDE THE LARGE POPULATION CENTERS.
AS THE FRONT MOVES THROUGH...PRESSURE RISES IMMEDIATELY BEHIND THE
PASSING TROUGH WILL ALLOW FOR A BRIEF PERIOD OF GUSTY WINDS
THROUGH WEST-EAST TERRAIN GAPS...BUT THESE SHOULD BE TERRIBLY
IMPACTFUL.

BEYOND THIS FEATURE...SYNOPTICALLY...A LARGE LOW PRESSURE CENTER
OF ACTION WILL CONTINUE TUESDAY AND WEDNESDAY OVER THE SOUTHERN
BERING AND NORTH PACIFIC...WITH MANY EMBEDDED DISTURBANCES
ROTATING WITHIN ITS SPHERE OF INFLUENCE RESPONSIBLE FOR MUCH OF
THE CLOUDINESS AND SNOW/RAIN CHANCES TO THE REGION. BY WEDNESDAY
NIGHT INTO THURSDAY A SLIGHT PATTERN CHANGE WILL OCCUR AS A GALE-
FORCE LOW MOVES TO THE SOUTH OF THE WESTERN ALEUTIANS AND A LOW
FROM THE NORTHEAST PACIFIC MOVES NORTH INTO THE SOUTHERN
GULF...WITH A WEAK UPPER LEVEL RIDGE REPLACING AFOREMENTIONED
EXPANSIVE LOW PRESSURE CENTER OF ACTION. THIS SLIGHT PATTERN
CHANGE WILL BE SHORT-LIVED...HOWEVER...AS A RETURN TO THE
EXPANSIVE CENTER OF ACTION OVER THE SOUTHERN BERING AND NORTH
PACIFIC RETURNS BY LATE NEXT WEEKEND.

THE MAIN IMPACTS WITH THIS PATTERN WILL BE LITTLE CHANGE IN
TEMPERATURES...WITH NEAR NORMAL TO ABOVE NORMAL TEMPERATURES OVER
MUCH OF THE REGION...AND PRECIPITATION CHANCES REMAINING NEAR
NORMAL TO ABOVE NORMAL. STRONGER WINDS TO GALE-FORCE WILL BE
CONFINED TO STRONGER EMBEDDED LOWS WITHIN THE BROAD CYCLONIC
PATTERN.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...STORM 119.
		 GALE 120 125 139 178.
		 HEAVY FREEZING SPRAY 160 180-185.

&&

SYNOPSIS AND MODEL DISCUSSION...RMC
SOUTHCENTRAL ALASKA...TP
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MC
LONG TERM...CC