683
FXAK68 PAFC 260141
AFDAFC
SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
541 PM AKDT MON MAR 25 2019
ANALYSIS AND UPPER LEVELS
THE UPPER-LEVEL WIND PATTERN IS SHOWING ANOTHER HIGH-AMPLITUDE
WAVE OVER ALASKA. A SKINNY RIDGE HAS FORMED OVER THE REGION. THIS
SETUP IS ALLOWING HIGH CLOUDS OVER PORTIONS OF SOUTHCENTRAL AND IS
STEERING STRONG BERING SEA LOWS FROM SOUTH TO NORTH TOWARD THE
ARCTIC. THE NET EFFECT HAS BEEN AND IS ABOVE- NORMAL TEMPERATURES
FOR THE MAINLAND AND CONTINUED UNSETTLED WEATHER FOR SOUTHWEST AND
THE ALEUTIAN CHAIN.
STORM TO HURRICANE FORCE WINDS OVER THE SOUTHERN BERING BEGAN THE
MORNING, BUT AS THE LOW MOVED NORTH BY NEARLY 10-DEGREES LATITUDE
IN 12 HOURS, WINDS HAVE BEEN SUBSIDING AND A HIGH WIND WARNING
WAS ALLOWED TO EXPIRE EARLY THIS MORNING OVER THE CENTRAL
ALEUTIANS. GUSTY WINDS CONTINUED THERE, AND WERE ALSO NOTABLE ON
THE WRAP- AROUND NORTH FLOW MOVING THROUGH THE WESTERN CHAIN.
RAIN AND SNOW CONTINUED FOR THE KUSKOKWIM DELTA, ESPECIALLY IN THE
NORTH, WHERE HOOPER BAY AND COASTAL POINTS SOUTH TO KIPNUK TRUDGED
THROUGH THE MORNING UNDER IFR CONDITIONS. INLAND AREAS WERE MILDER
AND WETTER. GUSTY CONDITIONS WERE AN ADDED BONUS.
CONCERN FOR MINOR RISES IN COASTAL AREAS OF THE NORTHERN KUSKOKWIM
BAY HAVE THE ATTENTION OF FORECAST TEAM. THERE ARE TOO MANY
UNKNOWNS WITH SHOREFAST ICE, FEW TIDE GAUGES, AND MINIMAL
REPORTS.
MODEL DISCUSSION
PRESSURE AND MOISTURE FIELDS INITIALIZED WELL IN ALL THE MAIN
MODELS THIS MORNING. THERE WERE NO SIGNIFICANT DIFFERENCES OUTSIDE
OF NORMAL MODEL BIASES, THOUGH THE ECMWF DID SEE TO BE SLIGHTLY
SLOWER WITH THE SOUTHERLY SURGE OF WARMTH INTO SOUTHWEST ALASKA
EARLY THIS WEEK.
GFS IS A WETTER SOLUTION IN THE MID-RANGE, WHILE THE NAM IS DRIER
SOLUTION IN THIS TIMEFRAME. FORECASTER CHOICE LEANED TOWARD A GFS
PREFERENCE TO KEEP SOME PRECIPITATION IN THE OUTCOME INTO THE
WEEK.
THE FORECAST CHALLENGES FOR THE WEEK WILL BE CONSIDERING SKY
COVER VERSUS TEMPERATURE VERSUS INCREASING LENGTH OF DAYLIGHT
HOURS, ALL WITH RESPECT TO FOG FORMATION OVER THE MAINLAND.
FOR SOUTHWEST, ESPECIALLY INLAND AREAS, A CHALLENGE WILL BE TO
DETERMINE HOW MUCH THE DEVELOPING GULF OF ALASKA RIDGE EATS AWAY
AT PRECIPITATION CHANCES WHILE BERING SEA TROUGHS ATTEMPT TO PLOW
THROUGH THE STABILITY.
AVIATION
PANC... VFR CONDITIONS ARE EXPECTED THROUGH THE PERIOD. THE ONLY
UNKNOWN AT THIS TIME IS ANY POTENTIAL FOR VICINITY FOG DUE TO
RECENT SNOWMELT AND POTENTIAL FOR BREAKS IN CLOUD COVER. TURNAGAIN
ARM WINDS ARE NOT EXPECTED TO PLAY A ROLE IN THE FORECAST GOING
FORWARD.
SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)
A HIGH AMPLITUDE UPPER RIDGE IS BUILDING OVER SOUTHCENTRAL, AND
THIS WILL PROMOTE DRY WEATHER ACROSS THE MAINLAND. THE POSITION OF
THE UPPER RIDGE WITH SOUTHCENTRAL ALONG THE WESTERN SIDE WILL KEEP
QUITE A BIT OF HIGH CLOUDS OVER THE AREA, SO THIS WILL LIMIT FOG
AND KEEP LOW TEMPERATURES ABOVE AVERAGE. THAT SAID, SOME FOG WILL
BE POSSIBLE OVERNIGHT ESPECIALLY ALONG AND NEAR COOK INLET AND
KNIK ARM. OFFSHORE WINDS WILL BECOME A LITTLE GUSTY THROUGH
FAVORED GAPS THIS EVENING AS A SHORTWAVE TROUGH ROUNDS THE TOP OF
THE RIDGE, BUT THESE WINDS WILL NOT BE STRONG AND THEY WILL END
TOMORROW AFTERNOON.
SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)
(TONIGHT
THROUGH WEDNESDAY AFTERNOON)
THE FRONTAL BOUNDARY ASSOCIATED WITH THE DEPARTING STORM FORCE LOW
IN THE BERING CONTINUES TO MOVE EASTWARD ACROSS SOUTHWEST ALASKA.
GUSTY SOUTHERLY WINDS WILL CONTINUE ALONG THE NORTHERN KUSKOKWIM
DELTA COAST OVERNIGHT ALLOWING FOR THE POSSIBILITY OF ELEVATED
WATER LEVELS AROUND THE HAZEN BAY AREA NORTHWARD.
PRECIPITATION WILL GRADUALLY DIMINISH THIS EVENING FROM WEST TO
EAST. AN UPPER LEVEL RIDGE POSITIONED OVER THE MAINLAND WEAKENS
THIS FRONT SIGNIFICANTLY ALLOWING FOR GENERALLY DRIER CONDITIONS
ACROSS SOUTHWEST FOR TUESDAY. A SURFACE RIDGE OVER THE EASTERN
BERING WILL PROVIDE ONSHORE FLOW ALONG THE BRISTOL BAY COAST
TUESDAY EVENING INTO WEDNESDAY MORNING. WITH WEAK ONSHORE FLOW AND
AMPLE MOISTURE, AREAS OF FOG ARE LIKELY ALONG THE SOUTHWEST COAST
WEDNESDAY MORNING, ESPECIALLY AROUND THE BRISTOL BAY AREA.
MEANWHILE, A WEAK UPPER LEVEL SHORTWAVE THAT DEVELOPS OVER THE
PRIBILOFS TUESDAY EVENING QUICKLY MOVES NORTHWARD OVER NUNIVAK
ISLAND AND HOOPER BAY FOR WEDNESDAY MORNING. THIS FEATURE MAY
PRODUCE A PERIOD OF GUSTY SOUTHERLY WINDS AND SNOW SHOWERS OVER
THE NORTHERN KUSKOKWIM DELTA COAST WEDNESDAY MORNING BEFORE
QUICKLY LIFTING NORTH.
SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)
(TONIGHT THROUGH WEDNESDAY AFTERNOON)
THE STORM FORCE LOW THAT HAS BROUGHT UNSETTLED CONDITIONS ACROSS
THE BERING SEA OVER THE LAST FEW DAYS CONTINUES TO EXIT THE
BERING TO THE NORTH THIS AFTERNOON. STORM FORCE WINDS OVER THE
NORTHERN BERING WILL DIMINISH TO GALES TONIGHT. BEHIND THE LOW, A
SHOWERY REGIME WILL MOVE OVER THE BERING WITH WIDESPREAD SOUTHWESTERLY
FLOW PERSISTING THROUGH TUESDAY. ONE FEATURE TO NOTE IS A WEAK
UPPER LEVEL SHORTWAVE THAT MOVES OVER THE PRIBILOFS TUESDAY NIGHT
INTO EARLY WEDNESDAY MORNING. THIS WILL LIKELY BRING A FEW SNOW
SHOWERS TO THE PRIBILOF ISLANDS, THOUGH NO ACCUMULATION IS
EXPECTED. BY WEDNESDAY AFTERNOON, A WARM FRONT ASSOCIATED WITH A
KAMCHATKA LOW MOVES OVER THE WESTERN ALEUTIANS, BRINING ANOTHER
ROUND OF WARM SOUTHERLY FLOW TO THE SOUTHERN BERING.
MARINE (DAYS 3 THROUGH 5)
GULF OF ALASKA...CONFIDENCE IS HIGH THAT THAT HIGH PRESSURE WILL
BE ESTABLISHED OVER THE GULF THURSDAY THROUGH SATURDAY.
BERING SEA...THE LOW TRACK IS EXPECTED TO REMAIN IN THE WESTERN
BERING SEA THURSDAY THROUGH SATURDAY. THIS SHOULD KEEP PERSISTENT
SOUTHERLY WINDS OVER THE MAJORITY OF THE BERING SEA WITH SOME GALES
LIKELY AT TIMES.
LONG TERM FORECAST (DAYS 3 THROUGH 7)
A DISSIPATING SHORT WAVE OVER SOUTHWEST MAINLAND ALASKA WILL BRING
IN A CHANCE OF PRECIPITATION LATE THURSDAY INTO THURSDAY NIGHT AND
THAT WILL BE THE LAST SHOT OF PRECIPITATION FOR SOUTHERN MAINLAND
ALASKA FOR THE WEEK. BY FRIDAY THE OVERALL PATTERN WILL BECOME
MUCH MORE SETTLED OVER THE REGION THAN IT HAS BEEN FOR AWHILE.
THIS IS DUE TO THE UPPER LEVEL RIDGE BUILDING IN STRONG OVER THE
MAINLAND PART OF ALASKA AND THEN PERSISTING INTO EARLY NEXT WEEK
AT LEAST. THE LOW TRACK WILL BE OVER THE WESTERN BERING SEA
THROUGH THE WEEKEND AND THEN SOME UNCERTAINTY INCREASES AS THE LOW
TRACK BEGINS TO EDGE EASTWARD ACROSS THE BERING SEA.
SOUTHCENTRAL AND SOUTHWEST MAINLAND ALASKA WILL THEREFORE BE UNDER
A WARM CORE HIGH PRESSURE DOME THROUGH THE WEEKEND. WHILE THIS IS
A COMMON PATTERN FOR THIS TIME OF YEAR IT WILL BRING IN ABOVE
NORMAL TEMPERATURES FOR THE REGION. THE BIGGEST QUESTION WILL BE
WHETHER FOG AND/OR LOW STRATUS DEVELOPS IN LOW LYING AREAS
INCLUDING COOK INLET DURING THE PERIOD. SHOULD THE FOG OR STRATUS
DEVELOP, IT WILL KEEP THE TEMPERATURE SPREAD LESS, BUT STILL
ABOVE NORMAL. SHOULD CLEAR SKIES DOMINATE, THE LOWS WILL STILL BE
ABOVE NORMAL DUE TO THE WARMTH ALOFT OF THE RIDGE. HOWEVER THE
DAYTIME HIGHS WILL THEN BE WELL ABOVE NORMAL WITH SOME AREAS
PUSHING INTO THE 50S.
AFC WATCHES/WARNINGS/ADVISORIES
PUBLIC...NONE.
MARINE...STORM 185 412. GALES 177-179 411 413 414.
SYNOPSIS AND MODEL DISCUSSION...DS
SOUTHCENTRAL ALASKA...JA
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KO
MARINE/LONG TERM...EZ
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