424
FXAK68 PAFC 291401
AFDAFC
SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
601 AM AKDT SAT AUG 29 2026
SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 THROUGH 3)
KEY MESSAGES:
- DESPITE DRIER CONDITIONS TODAY, 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 (INCLUDING PASSAGE
CANAL), KACHEMAK BAY, KAMISHAK BAY, AND BAYS AND PASSES ALONG
SHELIKOF STRAIT.
- COLDER CONDITIONS SATURDAY NIGHT THROUGH EARLY NEXT WEEK,
INCLUDING THE POTENTIAL FOR SNOW IN MOUNTAIN PASSES EARLY MONDAY
MORNING AND NEAR FREEZING TEMPERATURES FOR LOWER VALLEYS TUESDAY
MORNING.
DISCUSSION:
LAST NIGHT'S SYSTEM IS QUICKLY PUSHING EAST THIS MORNING WITH SKIES
TRYING TO CLEAR BEHIND THE TROUGH AS DRIER NORTHWESTERLY FLOW TAKES
OVER. AS THE TROUGH CONTINUES TO MOVE THROUGH THE COPPER BASIN THIS
MORNING A COMPACT SURFACE LOW HAS DEVELOPED NEAR THE COPPER RIVER
DELTA WITH A MODERATE RAIN BAND WRAPPING AROUND THE LOW. THE LOW IS
CURRENTLY MOVING INLAND AND WILL WEAKEN SOME AS IT MOVES INTO THE
SOUTHEAST CORNER OF THE COPPER BASIN AND LOWER COPPER RIVER VALLEY.
WHILE CHANCES ARE LOW GIVEN LACK OF INSTABILITY, THERE IS STILL A
CHANCE THAT THIS LOW IS DYNAMIC ENOUGH TO SQUEEZE OUT A LIGHTNING
STRIKE OF TWO AS IT MOVES INLAND. THIS SYSTEM IS MOVING OUT FASTER
THAN MODELS ARE FORECASTING SO HAVE CUT DOWN ON RAIN CHANCES MUCH
QUICKER TODAY OVER THE COPPER BASIN.
FOR THE REST OF SOUTHCENTRAL, TODAY WILL SOME DRIER WEATHER AND
CLEARING SKIES AS DRIER WESTERLY TO NORTHWESTERLY FLOW TAKES HOLD
LEADING TO GUSTY OFFSHORE WINDS, MOSTLY ALONG THE COAST AND
EXTENDING INTO THE GULF. INLAND AREAS WILL SEE LIGHT WINDS AND WITH
MINIMAL CLOUD COVER LATER TONIGHT, GOOD RADIATIONAL COOLING WILL
ALLOW TEMPERATURES TO DROP INTO THE 40S FOR MOST INLAND LOCATIONS
WITH THE EXCEPTION OF THE COPPER RIVER VALLEY WHERE LOWS ARE
EXPECTED TO DROP INTO THE 30S. SUNDAY WILL SEE ANOTHER DAY STARTING
OUT DRY BUT INCREASING CLOUD COVER AS THE NEXT SYSTEM DROPS SOUTH
FROM THE SEWARD PENINSULA. THIS SYSTEM WILL BRING ANOTHER ROUND OF
MORE WIDESPREAD RAINFALL FOR SOUTHCENTRAL AND A COOLER AIRMASS. 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. THIS SYSTEM WILL MOVE THROUGH
RATHER QUICKLY AND DEPENDING ON HOW QUICKLY WE CAN CLEAR OUT CLOUD
COVER WE COULD SEE TEMPERATURES DROP INTO THE 30S AND FROST
DEVELOPING TUESDAY MORNING FOR MANY LOWER ELEVATIONS ACROSS
INLAND SOUTHCENTRAL.
- PP
.SHORT TERM FORECAST SOUTHWEST ALASKA/BERING SEA/ALEUTIANS (DAYS
1 THROUGH 3: TONIGHT THROUGH MONDAY)...
WEATHER ACROSS SOUTHWEST ALASKA IS LESS ACTIVE AS RIDGING BUILDS
OVER THE BERING. MOSTLY CLEAR SKIES AND COOLER TEMPERATURES ARE
EXPECTED AS NORTHWESTERLY FLOW PREVAILS. LOW STRATUS AND FOG ARE
SETTING UP OVER THE COASTAL AREAS OF SOUTHWEST ALASKA. THERE ARE
ALSO SOME AREAS OF LOW STRATUS IN THE BERING. DUE TO THIS COLD AIR
ADVECTION, ELEVATED GAP WINDS ARE EXPECTED IN THE ALASKA
PENINSULA TODAY.
SHORTWAVES WILL RIDE OVER THE STRONG RIDGE AND WILL BRING
RAINFALL AND GUSTY WINDS TO THE PRIBILOF ISLANDS BY SUNDAY
MORNING. BY EARLY SUNDAY AFTERNOON, THE SHORTWAVE WILL MOVE
INLAND, BRINGING WIDESPREAD RAIN TO THE SOUTHWEST MAINLAND. FOR
THE AREA UNDER THE RIDGE (FROM THE ADAK TO UNALASKA REGIONS),
WINDS CAN STILL BE GUSTY, BUT RAIN CHANCES WILL BE MINIMAL. GUSTY
WINDS WILL RETURN TO THE ALASKA PENINSULA SUNDAY AFTERNOON, BUT
WINDS WILL BE MORE SOUTHWESTERLY, SO GUSTY GAP WINDS ARE LESS
LIKELY. THIS PATTERN OF SHORTWAVES RIDING OVER THE RIDGE WILL
CONTINUE THROUGH MONDAY AND LIKELY TROUGH MID-WEEK, LEADING TO
REPEATED BURSTS OF RAIN AND GUSTY WINDS FROM THE ADAK AND ATKA
REGION, THROUGH THE PRIBILOF ISLANDS, AND INTO THE ALASKA
PENINSULA. FOG AND LOW STRATUS WILL BE POSSIBLE OVER THE AREA OF
RIDGING AND IN-BETWEEN SHORTWAVES ELSEWHERE. A STRONG UPPER LOW
WILL DROP OVER THE SOUTHWEST MAINLAND ON MONDAY, DRYING THINGS OUT
AND POTENTIALLY LEADING TO LOW TEMPERATURES DROPPING INTO THE 30S
FOR FAR INLAND AREAS DUE TO COLD AIR ADVECTION.
-JAR
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 WITH 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...VFR CONDITIONS AND LIGHT WINDS ANTICIPATED THROUGH THE
PERIOD.
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