Heavy Freezing Spray Warning 69, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
529 PM AKDT SUN MAR 27 2016

.ANALYSIS AND UPPER LEVELS...

AS THE EASTERN PACIFIC UPPER-LEVEL RIDGE FURTHER BUILDS JUST TO
THE EAST OF THE AOR...THE TRANSITION TO A MORE ACTIVE (AND WET)
WEATHER PATTERN CONTINUES UPSTREAM OF THE RIDGE AXIS. A VERTICALLY
STACKED LOW SITS JUST SOUTH OF THE CENTRAL ALEUTIAN ISLANDS WITH
AN ASSOCIATED DECAYING FRONT STRETCHING ZONALLY ACROSS THE
SOUTHERN BERING. THE UPPER-LEVEL SUBTROPICAL JET IS HIGHLY
AMPLIFIED OVER THE NORTHEASTERN PACIFIC WITH A JET STREAK
EXTENDING MERIDIONALLY ALONG THE 160W MERIDIAN FROM 40N THROUGH
KODIAK ISLAND. THIS UPPER-LEVEL FEATURE ALONG WITH DEEP SOUTHERLY
LOW AND MID-LEVEL FLOW IN THE WARM SECTOR OF THE NORTH PACIFIC
CYCLONE IS SUPPORTING DEEP MOISTURE ADVECTION INTO SOUTHCENTRAL
ALASKA TODAY. THE MOISTURE ADVECTION IS BEST SEEN ON SATELLITE
IMAGERY THIS AFTERNOON AS A LARGE PLUME OF FAST MOVING SUBTROPICAL
MOISTURE EXTENDING FROM THE NORTH CENTRAL PACIFIC TO THE
SOUTHCENTRAL ALASKA COAST. THIS MOISTURE WAS FOCUSED THIS MORNING
ON THE ALASKA PENINSULA...WHERE THE MORNING COLD BAY SOUNDING
SHOWED A PRECIPITABLE WATER (PW) VALUE OF 0.71"...WHICH IS 259%
NORMAL FOR THIS TIME OF YEAR. IN THE PAST FEW HOURS THE FOCUS OF
THE MOISTURE PLUME HAS PROGRESSED NORTHEASTWARD...SHIFTING THE
AREA OF HIGHEST PW VALUES TO ALONG THE COOK INLET AND WESTERN GULF
COAST REGION THIS AFTERNOON. THIS IS SETTING THE STAGE FOR A VERY
WET BEGINNING TO THE WEEK FOR MUCH OF THE SOUTHERN MAINLAND.

A WARM FRONT AND UPPER LEVEL DEFORMATION OVER THE BRISTOL BAY
REGION IS SUPPORTING SUBSTANTIAL LIFT ACROSS THE AREA...WHERE
STEADY PRECIPITATION CAN BE SEEN ON RADAR IMAGERY THROUGH THE
MORNING. SURFACE TEMPERATURES OVER THE SOUTHWEST ARE WARMING AS
THE SUBTROPICAL AIRMASS APPROACHES FROM THE SOUTH...BUT CURRENTLY
REMAIN JUST COLD ENOUGH TO SUPPORT SOME SNOW MIXED IN WITH THE
RAIN NORTH OF BRISTOL BAY FOR NOW. MEANWHILE TEMPERATURES OVER THE
WESTERN GULF COAST AND COOK INLET REGION HAVE WARMED TO ABOVE
FREEZING. THE WARMER AIR IS SUPPORTING RAIN AS THE PRIMARY
PRECIPITATION TYPE OVER THE KENAI PENINSULA AND KODIAK ISLAND AS
THE PRECIPITATION ATTRIBUTED TO THE DEEP-LAYER MOISTURE PUSH AND
SURFACE FRONT ADVANCES NORTHWARD UP THE GULF COAST THIS
AFTERNOON. FURTHER NORTH... SHOWERS ACROSS THE SUSITNA VALLEY AND
COPPER RIVER BASIN ARE ATTRIBUTED TO AN UPPER LEVEL DISTURBANCE
LIFTING NORTHEAST THROUGH THE CENTRAL INTERIOR.

.MODEL DISCUSSION...

MODELS REMAIN IN GENERALLY GOOD AGREEMENT ON THE OVERALL SYNOPTIC
PATTERN IN THE SHORT TERM...WITH AN IMPRESSIVE JET POISED TO PUMP
SIGNIFICANT MOISTURE TOWARDS THE GULF OF ALASKA FROM THE NORTH
PACIFIC. HOWEVER...WHILE A RAINY PATTERN IS ANTICIPATED FOR MUCH
OF SOUTHCENTRAL FOR MUCH OF THE WEEK, MODELS DIFFER SIGNIFICANTLY
ON HOW MUCH WILL FALL. THE LATEST NAM MODEL INDICATES THAT THE
COASTAL JET AND DOWNSLOPING WILL BE MORE INTENSE ACROSS
ANCHORAGE...THE MATANUSKA VALLEY AND WESTERN KENAI PENINSULA.
MEANWHILE...THE GFS MODEL INDICATES HEAVIER AND MORE WIDESPREAD
PRECIPITATION. AS A RESULT...A BLEND OF MODELS WAS PREFERRED.

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

THE FRONT HAS MADE ITS WAY OVER SOUTHCENTRAL ALASKA BRINGING THE
BEGINNINGS OF RAIN AND WARM AIR TO THE AREA. WITH RIDGING OFF TO
THE EAST AND THE JET CONTINUING TO BRING MORE WARM AIR AND
MOISTURE UP FROM THE SOUTH...RAIN LOOKS TO REMAIN WIDESPREAD INTO
TUESDAY. HOWEVER...THE HEAVIEST RAIN LOOKS TO BE MONDAY WHERE HIGH
FREEZING LEVELS WILL ALLOW FOR RAIN EVEN IN MANY HIGHER
ELEVATIONS LIKE THOMPSON PASS. ANOTHER IMPACT FROM THIS SYSTEM IS
STRONGER WINDS THROUGH THE EAST TO WEST ORIENTED GAPS LIKE
TURNAGAIN ARM. WINDS WILL INCREASE TONIGHT AS THE PRESSURE
GRADIENT INCREASES AND BE THE STRONGEST DURING THE DAY MONDAY
UNTIL DIMINISHING MONDAY NIGHT.

&&

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

THE FRONTAL SYSTEM MOVING THROUGH THE SOUTHWEST COAST WILL
CONTINUE TO BRING RAIN AND SNOW TO BRISTOL BAY THROUGH THIS
EVENING. MOST OF THE ACCUMULATING SNOW SHOULD REMAIN WEST OF KING
SALMON WHERE NORTHERLY FLOW WILL KEEP TEMPERATURES COOL ENOUGH FOR
SNOW. OVER EASTERN BRISTOL BAY...EASTERLY FLOW ALONG THE
ALEUTIAN/ALASKAN RANGES HAVE SWITCHED THE SNOW OVER TO
RAIN...WHICH SHOULD PERSIST THROUGH THE OVERNIGHT. TO THE
NORTH...SNOW WILL DEVELOP FROM SOUTH TO NORTH OVER THE KUSKOKWIM
DELTA THIS EVENING...WHICH ALONG WITH GUSTY OFFSHORE WINDS WILL
BRING AREAS OF BLOWING SNOW INTO MONDAY MORNING. THE WORST
CONDITIONS ARE EXPECTED ALONG THE COAST...ESPECIALLY TO THE SOUTH
OF BETHEL WHERE THE HEAVIEST SNOWFALL IS EXPECTED. WITH NO CURRENT
TRANSPORTABLE SNOW ON THE GROUND ANY BLOWING SNOW WILL BE FROM NEW
SNOWFALL...AND WITH ONLY A FEW INCHES EXPECTED BLIZZARD CONDITIONS
ARE NOT EXPECTED. THIS FRONT WILL DEPART THE SOUTHWEST MAINLAND
BY MONDAY AFTERNOON...BUT AN UPPER LEVEL TROUGH APPROACHING THE
DELTA COAST WILL KEEP RAIN AND SNOW IN THE AREA INTO
TUESDAY...ESPECIALLY ALONG THE ALASKAN/ALEUTIAN RANGES.

&&

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

CONFIDENCE REMAINS GOOD THAT THE BLIZZARD CONDITIONS THAT
DEVELOPED THIS AFTERNOON AT SAINT GEORGE ALONG THE FRONT WILL
LARGELY REMAIN SOUTH OF SAINT PAUL ISLAND...SO THE BLIZZARD
WARNING REMAINS JUST FOR SAINT GEORGE ISLAND THIS EVENING.
OTHERWISE THE GALE FORCE FRONT WILL CONTINUE TO IMPACT MAINLY THE
PRIBILOF ISLANDS...SOUTHERN BERING SEA...AND WESTERN ALEUTIANS.
THIS FRONT WILL THEN DISSIPATE OVER THE CENTRAL BERING LATE
TONIGHT...AND BRING A PERIOD OF QUIET WEATHER TO REGION WITH LOW
PRECIPITATION CHANCES AND WINDS FALLING BELOW SMALL CRAFT.

&&

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

AN UNSEASONABLY WARM AND WET PATTERN IS EXPECTED TO TAKE HOLD
ACROSS THE REGION THROUGH MUCH OF THE NEXT WEEK AS A STOUT
NORTHEAST PACIFIC RIDGE KEEPS WARM AND MOIST AIR FROM THE
SUBTROPICAL PACIFIC FOCUSED ON THE SOUTHERN MAINLAND IN DEEP
SOUTHERLY FLOW. THIS WILL RESULT IN TEMPERATURES RUNNING WELL
ABOVE SEASONAL NORMAL VALUES ACROSS SOUTHCENTRAL AND SOUTHWEST
ALASKA...ALONG WITH ABUNDANT RAINFALL AS SEVERAL EMBEDDED WAVES
MOVE INTO THE REGION. RECENT MODEL RUNS HAVE BEEN HINTING AT A
BRIEF RESPITE FROM THE WET CONDITIONS FOR SOUTHCENTRAL AK
BEGINNING ON THURSDAY AS THE RIDGE EXTENDS WESTWARD OVER THE AREA
AND THE PRECIPITATION SHIFTS TO THE SOUTHWEST MAINLAND AND EASTERN
BERING. HOWEVER...THE WET PATTERN WILL THEN QUICKLY RETURN BY THE
WEEKEND AS THE RIDGE IS NUDGED BACK TO THE EAST BY ANOTHER LOW
APPROACHING THE ALASKA PENINSULA. THIS LOW WILL THEN MOVE OVER THE
EASTERN BERING...WITH PRECIPITATION CHANCES INCREASING FROM EAST
TO WEST ACROSS THE BERING AS THE WEEK PROGRESSES.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...BLIZZARD WARNING 195 AND BLOWING SNOW ADVISORY 155
MARINE...GALES 119 125 177 178 179 180 181 411 412 413 414

&&

SYNOPSIS AND MODEL DISCUSSION...RD/EN
SOUTHCENTRAL ALASKA...DK
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DEK
LONG TERM...CB