531
FXAK68 PAFC 290121
AFDAFC
SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
521 PM AKDT FRI AUG 28 2026
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 THROUGH 3: THIS
AFTERNOON THROUGH MONDAY AFTERNOON)...
KEY MESSAGES:
- GENERALLY IMPROVING CONDITIONS TONIGHT, FOLLOWED BY DRY BUT
LOCALIZED WINDY WEATHER THIS WEEKEND. THEN, AN INCOMING LOW
WILL BRING WETTER, COOLER, AND WINDIER CONDITIONS AS WE HEAD
INTO NEXT WEEK.
- WHILE RAIN WILL BE TAPERING OFF THROUGH SATURDAY MORNING, RIVERS
IN SUSITNA VALLEY MAY STILL BE HIGH THIS WEEKEND AS WATER LEVEL
TRENDS LAG BEHIND RAINFALL.
- THIS WEEKEND'S GUSTY NORTHERLY TO WESTERLY OFFSHORE WINDS WILL
BE STRONGEST ALONG THE COAST AND IN MARINE WATERS. AREAS TO
WATCH INCLUDE RESURRECTION BAY, PRINCE WILLIAM SOUND, AND
KACHEMAK BAY.
- COLDER CONDITIONS SATURDAY NIGHT THROUGH EARLY NEXT WEEK,
INCLUDING THE POTENTIAL FOR SNOW IN MOUNTAIN PASSES EARLY MONDAY
MORNING.
DISCUSSION:
WINDS PEAK OVER THE NEXT FEW HOURS AS THE PRESSURE GRADIENT
TIGHTENS BETWEEN A SURFACE LOW NEAR SEWARD AND ANOTHER SURFACE LOW
MOVING INTO COOK INLET. OBSERVED WINDS HAVE BEEN ABOUT WHAT WAS
EXPECTED, ALBEIT A BIT WEAKER THAN FORECAST IN ALL BUT FAR
WESTERN AND FAR SOUTHERN ANCHORAGE BOWL, AND A BIT STRONGER
THROUGH PALMER. THE LATEST OBSERVED MAX WIND GUSTS HAVE BEEN 49
MPH IN GULKANA, 49 MPH IN THE ANCHORAGE HILLSIDE, 47 MPH AT TED
STEVENS AIRPORT, 45 MPH IN PALMER, AND 44 MPH IN KENAI.
THOUGH MOST AREAS WILL HAVE SEEN THEIR HEAVIEST RAIN EARLIER
TODAY, ANOTHER ROUND OF RAIN SHOWERS IS ON THE WAY THIS EVENING
THROUGH TOMORROW AFTERNOON AS A TROUGH CURRENTLY OVER WESTERN
ALASKA PIVOTS EASTWARD INTO SOUTHCENTRAL. THE HEAVIEST RAIN WILL
REMAIN OVER HIGHER ELEVATION MOUNTAINS, THOUGH MUCH OF THE
SOUTHCENTRAL MAINLAND (EXCEPT FOR PERHAPS WESTERN KENAI PENINSULA)
WILL LIKELY SEE SOME ADDITIONAL LIGHT ACCUMULATIONS. FOR SUSITNA
VALLEY, RISING RIVER LEVELS REMAIN A CONCERN THROUGH THE WEEKEND.
RIVER GAUGES ARE ALREADY SHOWING RISING WATER LEVELS FROM OUR
FIRST ROUND OF RAIN EARLIER THIS MORNING, AND WATER LEVELS WILL
LIKELY CONTINUE TO CLIMB WITH THE SECOND ROUND THIS EVENING.
CURRENT THINKING IS THAT WATER LEVELS WILL GENERALLY REMAIN LOWER
THAN WHAT WAS OBSERVED EARLIER THIS WEEK, THOUGH WE WILL BE
CLOSELY MONITORING RIVER GAUGES OVER THE NEXT FEW DAYS.
FROM SATURDAY THROUGH ABOUT SUNDAY EVENING, THE DEPARTING SURFACE
LOW IN THE GULF, IN CONJUNCTION WITH RIDGING OVER THE BERING SEA,
WILL LEAD TO GUSTY OFFSHORE WINDS, MOSTLY ALONG THE COAST AND
EXTENDING INTO THE GULF. AWAY FROM THE COAST, GENERALLY EXPECT
CLEARER SKIES, A LARGER DIURNAL TEMPERATURE RANGE, LIGHT WINDS,
AND MOSTLY DRY CONDITIONS EXCEPT FOR UP TO 30% CHANCE OF RAIN
SHOWERS IN HIGHER TERRAIN. WITH THESE CLEARER SKIES, OVERNIGHT
LOWS SATURDAY NIGHT INTO EARLY MONDAY MORNING COULD LEAD TO
TEMPERATURES APPROACHING FREEZING.
THE BIGGER COOL-DOWN WILL ARRIVE SUNDAY EVENING INTO MONDAY, AS A
LOW CUTTING ACROSS ALASKA FROM SEWARD PENINSULA SOUTHEASTWARDS
TOWARDS PRINCE WILLIAM SOUND BRINGS A MUCH COOLER AIR MASS. THIS
WILL LIKELY LEAD TO HIGHER ELEVATION SNOW/TERMINATION DUST, AND
PERHAPS EVEN SNOW AT HIGHER ELEVATION MOUNTAIN PASSES, LIKE BROAD,
TAHNETA, AND THOMPSON PASSES. WHETHER THE SNOW WILL STICK WILL
DEPEND ON ROAD SURFACE TEMPERATURES - THIS EARLY IN THE SEASON,
PROBABLY NOT. FOR LOWER ELEVATIONS, EXPECT WIDESPREAD RAIN AND A
RESURGENCE OF GUSTY OFFSHORE WINDS.
-KC
.SHORT TERM FORECAST SOUTHWEST ALASKA/BERING SEA/ALEUTIANS (DAYS
1 THROUGH 3: TONIGHT THROUGH MONDAY MORNING)...
CONDITIONS ACROSS SOUTHWEST ALASKA HAVE IMPROVED THIS AFTERNOON
AS THE UPPER LEVEL TROUGH AXIS CLEARS THE INTERIOR SOUTHWEST AND
SHIFTS EAST INTO SOUTHCENTRAL. THE TRAILING COLD FRONT EXTENDING
OFF OF THE SURFACE LOW OVER NORTHERN ALASKA SIMILARLY SHIFTS TO
THE EAST, ALLOWING FOR THE RAINFALL THAT HAS LINGERED ACROSS THE
ALASKA PENINSULA THIS AFTERNOON TO TAPER OFF. ELSEWHERE, SATELLITE
AND RADAR IMAGERY CONTINUE TO SHOW A SHOWERY REGIME ACROSS THE
REST OF SOUTHWEST ALASKA AS WEAK UPPER LEVEL PERTURBATIONS MOVE
ACROSS THE REGION. THE REMAINING SHOWER ACTIVITY IS EXPECTED TO
DECREASE FROM WEST TO EAST THIS EVENING AS DRIER AIR FILLS IN,
WITH THE MOST WIDESPREAD SHOWERS LINGERING ALONG TERRAIN DUE TO
UPSLOPE ENHANCEMENT. GUSTY SOUTHWESTERLY WINDS WILL CONTINUE TO
SHIFT TO WEST- NORTHWESTERLY AND WEAKEN ACROSS SOUTHWEST ALASKA
THROUGH THIS AFTERNOON AND EVENING.
A PERIOD OF RELATIVELY QUIET WEATHER IS IN STORE FOR MUCH OF
SATURDAY ACROSS SOUTHWEST ALASKA AND THE BERING SEA AS A NORTH
PACIFIC RIDGE BUILDS OVER THE ALEUTIAN CHAIN AND INTO THE BERING.
DRY CONDITIONS ARE EXPECTED ACROSS SOUTHWEST ALASKA AND THE ALASKA
PENINSULA THROUGH SATURDAY. AMPLIFICATION OF THE UPPER LEVELS AS
THE RIDGE BUILDS OVER THE BERING WILL LEAD TO GUSTY NORTHWESTERLY
GAP WINDS THROUGH FAVORED BAYS AND PASSES ALONG THE NORTHERN
AKPEN. SMALL-CRAFT SUSTAINED WINDS WITH GALE-FORCE GUSTS ARE
EXPECTED TO PICK UP SATURDAY MORNING AND PERSIST THROUGH SATURDAY
EVENING WITHIN THE COASTAL WATERS ON THE PACIFIC-SIDE OF THE AKPEN
FROM CHIGNIK NORTHWARDS.
MORE ACTIVE WEATHER CONTINUES ACROSS THE BERING WITH A SERIES OF
FRONTS AND LOWS RIDING AROUND THE WESTERN AND NORTHERN PERIPHERY
OF THE NORTH PACIFIC HIGH. THE FIRST ARRIVES TO THE WESTERN
ALEUTIANS SATURDAY MORNING WITH A ROUND OF LIGHT TO MODERATE
RAINFALL AND SMALL CRAFT WINDS. AS THE RIDGE TRIES TO RETREAT
SOUTHWARD THROUGH SUNDAY INTO MONDAY, THIS WILL ALLOW FOR
WIDESPREAD SMALL CRAFT WINDS WITH GUSTS TO GALE FORCE TO ENCOMPASS
MUCH OF THE SOUTHERN AND CENTRAL BERING AS WELL AS MOISTURE
TRANSPORT FROM THE PACIFIC INTO THE BERING. THIS PATTERN WILL
RESULT IN MULTIPLE ROUNDS OF RAINFALL AND GUSTY WINDS ACROSS THE
ALEUTIANS AS THE LOWS ROUND THE RIDGE, WITH THE NEXT ROUND OF
RAINFALL EXPECTED TO REACH THE SOUTHWEST MAINLAND SUNDAY MORNING.
LONG TERM FORECAST (DAYS 4 THROUGH 7: TUESDAY THROUGH FRIDAY)
THE OVERALL UPPER-LEVEL PATTERN THROUGH WEDNESDAY WILL BE
DOMINATED BY A RIDGE OF HIGH PRESSURE EXTENDING FROM THE
NORTH PACIFIC ACROSS THE ALEUTIAN ISLANDS AND SOUTHERN BERING SEA
WITH A NEGATIVELY TILTED TROUGH WITH AXIS EXTENDING FROM THE
CHUKCHI SEA SOUTHEAST TO THE EASTERN GULF OF ALASKA.
MULTIPLE SHORTWAVES AND VORTICITY MAXIMA WILL MOVE FROM NORTHWEST
ALASKA INTO THE GULF, EMBEDDED IN THE NORTHWESTERLY FLOW ALOFT.
FOR TUESDAY, THE FIRST OF THESE FEATURES WILL HELP MAINTAIN GUSTY
GAP WINDS FROM ALASKA PENINSULA EAST ACROSS THE IMMEDIATE
SOUTHCENTRAL COAST TO PRINCE WILLIAM SOUND. A TRANSIENT RIDGE IN
THE WAKE OF THIS WAVE WILL PROVIDE SOME WARM AIR ADVECTION,
ALLOWING SNOW LEVEL TO RISE FROM AN EXPECTED MINIMUM AROUND 3,000
FT ON MONDAY. A SECOND, WEAKER WAVE MOVES THROUGH ON WEDNESDAY,
ALLOWING FOR A RETURN OF SCATTERED SHOWERS ACROSS THE ALASKA RANGE
AND THE HIGHER TERRAIN SURROUNDING THE COPPER RIVER BASIN.
BY LATE WEDNESDAY, THE UPPER-LEVEL PATTERN LOOKS TO BECOME MORE
AMPLIFIED, WITH THE NORTH PACIFIC RIDGE MOVING EAST AND LIFTING
ACROSS THE SOUTHERN MAINLAND THURSDAY MORNING. THE EASTWARD
PROGRESSION OF THIS RIDGE WILL ALLOW A TROUGH OVER THE WESTERN
BERING TO DEEPEN, RESULTING IN A STOUT SOUTHERLY WIND FLOW BETWEEN
THE TWO FEATURES. A STRONG SHORTWAVE WILL MOVE NORTH ALONG A
STALLED FRONTAL BOUNDARY, LEADING TO THE DEVELOPMENT OF A SURFACE
LOW SOMEWHERE BETWEEN THE PRIBILOFS AND KUSKOKWIM DELTA COAST.
THIS FEATURE, ALONG WITH ITS SURFACE FRONT, WILL DRIVE INTO
SOUTHWEST ALASKA WITH ANOTHER ROUND OF HEAVY RAIN AND GUSTY
SOUTHWESTERLY WINDS ALONG THE COAST FOR THURSDAY.
BY LATE THURSDAY, MODEL AGREEMENT BEGINS TO BREAK DOWN MORE
SIGNIFICANTLY, PARTICULARLY WITH REGARD TO THE EASTWARD
PROGRESSION OF THE UPPER-LEVEL RIDGE. THE GFS AND CANADIAN MODELS
ARE FAVORED FOR THE LONG TERM FORECAST, BOTH OF WHICH SLIDE THE
RIDGE AXIS OVER THE ALASKA PANHANDLE BY FRIDAY. THE RESULTANT FLOW
ALOFT BECOMES MORE SOUTHWESTERLY ACROSS THE ALASKA PENINSULA AND
SOUTHERN MAINLAND AS THE TROUGH ALSO SLIDES EAST. MULTIPLE
SHORTWAVE THEN LOOKS TO LIFT FROM THE NORTH PACIFIC TO THE ALASKA
PENINSULA BY THE END OF THE WEEK, WITH MORE RAIN AND GUSTY WINDS
FOR MUCH OF SOUTHWEST AND WESTERN HALF OF SOUTHCENTRAL ALASKA AS
YET ANOTHER STORM SYSTEM DRIVES NORTH ACROSS WESTERN ALASKA.
- TM
AVIATION
PANC...CEILINGS AND VISIBILITY WILL FLUCTUATE BETWEEN VRF AND MVFR
THROUGH TONIGHT, ALTHOUGH VFR IS EXPECTED TO PREVAIL WITH CEILINGS
AROUND 4,000 FT. ANY DROP TO MVFR WILL LIKELY BE IN RAIN SHOWERS
THAT MAY PASS OVER THE TERMINAL LATE THIS AFTERNOON THROUGH
EVENING. STRONG SOUTHEASTERLY WINDS AND GUSTS WILL CONTINUE
THROUGH AROUND MIDNIGHT BEFORE QUICKLY DIMINISHING OVERNIGHT. THE
STRONGEST OF THESE WINDS, WITH GUSTS AROUND 50 MPH, ARE EXPECTED
TO PERSIST THROUGH AROUND 7 PM THIS EVENING.
THE BIGGEST CHALLENGE WILL BE THE EXTENT OF CLEARING OVERNIGHT
AND INTO EARLY SATURDAY MORNING IN THE WAKE OF THIS SYSTEM. THE
FLOW ALOFT AND NEAR THE SURFACE WILL QUICKLY WEAKEN, BECOMING
LIGHT AND VARIABLE EARLY SATURDAY MORNING, BEFORE A DRIER AND
MORE NORTHERLY FLOW DEVELOPS AFTER SUNRISE. GIVEN THE WEAKER FLOW
DEVELOPING OVERNIGHT, THE FORECAST LEANS TOWARD CEILINGS LOWERING
BACK TO MVFR (AS LOW AS 1,500 FT) BY 12Z AND LINGERING THROUGH
18Z BEFORE LIFTING AND ERODING LATE SATURDAY MORNING AS A LIGHT
NORTHERLY WIND DEVELOPS.
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