631
FXAK68 PAFC 210040
AFDAFC
SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
440 PM AKDT SUN SEP 20 2026
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 THROUGH 3:
TODAY THROUGH WEDNESDAY NIGHT)...
A LARGE, OCCLUDED LOW PRESSURE SYSTEM CONTINUES TO SPIN ACROSS
THE NORTHERN GULF THIS AFTERNOON. RADAR RETURNS SHOW THE LOW'S
OUTER RAIN BANDS PIVOTING ACROSS THE IMMEDIATE GULF COAST, WITH A
FEW WAVES OF SHOWERS MAKING IT AS FAR AS WEST AS THE ANCHORAGE
BOWL. GENERALLY SPEAKING, LONGWAVE TROUGHING ALOFT DOMINATES ALL
OF ALASKA AND THE NORTH PACIFIC. A STRENGTHENING, DIGGING
SHORTWAVE TROUGH EMBEDDED IN THE LONGWAVE IS MOVING SOUTHEASTWARD
OVER THE ALASKA PENINSULA THIS AFTERNOON AND IS BACKING THE
OCCLUDED LOW NORTHWESTWARD TOWARDS CHENEGA BEFORE IT DRIVES INLAND
AND WEAKENS LATER TONIGHT. UNTIL THEN, EXPECT PERIODS OF MODERATE
RAIN SHOWERS WITH GUSTY WINDS ALONG THE IMMEDIATE GULF COAST.
EXPECT INCREASED RAIN SHOWERS FOR INLAND AREAS OF SOUTHCENTRAL AS
THE LOW MOVES INLAND, FAVORING THE COPPER RIVER BASIN THROUGH
MONDAY MORNING, THOUGH MORE INTERMITTENT SHOWERS ARE STILL ON
TRACK FOR THE ANCHORAGE BOWL. GUSTY SOUTHERLY GAP WINDS ARE
POSSIBLE BY MONDAY AFTERNOON FOR THE COPPER RIVER VALLEY AND
PALMER AREAS AS THIS REMNANT LOW MOVES NORTHWARD. LOW IMPACT GAP
WINDS FROM KAMISHAK GAP MOVING ACROSS THE BARREN ISLANDS IN THE
WAKE OF THIS SYSTEM WILL LEAD TO SOME AREAS OF SMALL CRAFT WINDS
WITH HIGHER GUSTS FOR THIS AREA THROUGH TUESDAY MORNING.
THE ROBUST SHORTWAVE TROUGH MOVING OVER THE ALASKA PENINSULA WILL
HELP SPAWN AN AREA OF LOW PRESSURE SOUTHEAST OF KODIAK ISLAND
LATE MONDAY MORNING TO EARLY MONDAY AFTERNOON. AT THE SAME TIME,
MODELS SHOW A MORE COMPACT LOW MOVING NORTHWARD FROM THE NORTH
PACIFIC AND ACROSS THE SOUTHERN GULF EARLY MONDAY AFTERNOON AND
BEGINS TO DEEPEN AS IT ALIGNS WITH UPPER LEVEL DIVERGENCE AND
POSITIVE VORTICITY ADVECTION FROM THE LONGWAVE TROUGH. MODELS ARE
IN GOOD AGREEMENT THAT THIS LOW TRACKS INTO THE EASTERN GULF WITH
SMALL CRAFT TO GALE FORCE WINDS AND BECOMES QUASI-STATIONARY AND
IN THE PROCESS OF OCCLUDING BY TUESDAY AFTERNOON. SOUTHCENTRAL
THEN REMAINS RELATIVELY QUIET BEFORE A MUCH MORE POTENT SYSTEM
MOVES CLOSER TO THE WESTERN GULF LATE WEDNESDAY AFTERNOON, THOUGH
MODEL AGREEMENT IS BELOW AVERAGE FOR THIS PERIOD. DUE TO THIS
BEING A POTENTIALLY IMPACTFUL SYSTEM FOR SOME, PLEASE STAY TUNED
TO THE FORECAST AS WE DRAW CLOSER TO THIS TIME FRAME.
-AM/TM
.SHORT TERM FORECAST SOUTHWEST ALASKA AND BERING SEA/ALEUTIANS
(DAYS 1 THROUGH 3: THIS AFTERNOON THROUGH WEDNESDAY AFTERNOON)...
KEY MESSAGES:
- GUSTY NORTHWESTERLY WINDS AND PERSISTENT SHOWERS FOR THE
ALEUTIANS AND ALASKA PENINSULA THROUGH EARLY THIS WEEK.
- TRENDING COLDER FOR SOUTHWEST ALASKA, THOUGH OVERNIGHT LOWS WILL
ULTIMATELY DEPEND ON CLOUD COVER. STILL, MANY LOCATIONS COULD
SEE OVERNIGHT AND MORNING TEMPERATURES NEAR OR BELOW FREEZING
TONIGHT THROUGH MIDWEEK, WITH GREATEST CHANCES (70% OR GREATER)
FOR INTERIOR SOUTHWEST.
- LOOKING AHEAD: WINDS TO GALE FORCE AND LIGHT TO MODERATE RAIN
FOR THE ALEUTIANS FROM LATE MONDAY INTO WEDNESDAY AS A
STRENGTHENING LOW PRESSURE SYSTEM ENTERS FROM THE WEST AND
INTERACTS WITH THE REMNANTS OF TYPHOON DUJUAN. CONFIDENCE
REMAINS FAIRLY LOW.
DISCUSSION:
FEW CHANGES TO THE FORECAST FOR THE NEXT 24 HOURS. THE UPPER LEVEL
PATTERN CONTINUES TO FEATURE A BROAD, LONGWAVE TROUGH EXTENDING
FROM THE BERING, ACROSS MUCH OF MAINLAND ALASKA, AND INTO THE
GULF. WEAK SHORTWAVES MOVING SOUTH ALONG THE BACKSIDE OF THE RIDGE
WILL BRING PERIODS OF GUSTIER WINDS AND MORE FREQUENT/HEAVIER
SHOWERS AS THEY TRANSIT ACROSS THE BERING SEA, ALASKA PENINSULA,
AND SOUTHWEST ALASKA THROUGH MONDAY.
FOR SOUTHWEST ALASKA, THE BIGGEST STORY CONTINUES TO BE INCREASED
CHANCES FOR TEMPERATURES NEAR OR BELOW FREEZING. AS THE AIRMASS
THAT WILL BRING THIS COLDER AIR WILL ALSO BE QUITE DRY, ANY SNOW
WILL ALMOST CERTAINLY BE LIMITED TO HIGHER ELEVATION MOUNTAINS,
WHERE OROGRAPHIC LIFT WILL HAVE A BETTER CHANCE OF SQUEEZING OUT
SOME PRECIPITATION. STILL, WITH OVERNIGHT LOWS FORECAST TO DIP
CLOSE TO OR EVEN BELOW FREEZING AT LOWER ELEVATIONS TONIGHT
THROUGH MIDWEEK, NOW IS A GOOD TIME TO START BRINGING THINGS
INDOORS IN PREPARATION FOR WINTER.
FINALLY, FROM LATE MONDAY INTO MIDWEEK, ATTENTION SHIFTS TO
SEVERAL FEATURES MOVING INTO THE BERING SEA FROM THE WEST. FIRST
WILL BE A LOW CURVING UP FROM JUST SOUTH OF THE KAMCHATKA
PENINSULA. SINCE YESTERDAY, THIS LOW HAS TRENDED FURTHER SOUTH IN
ITS TRACK. AS SUCH, GALE FORCE WINDS LOOK TO REMAIN MOSTLY OUT OF
THE COASTAL WATERS OF THE ALEUTIANS. THE SECOND FEATURE WILL BE
THE REMNANTS OF TYPHOON DUJUAN, WHICH WILL LIKELY INTERACT IN SOME
FORM WITH THE BERING LOW AROUND TUESDAY NIGHT. WHAT THIS
INTERACTION LOOKS LIKE, AND THE RESULTING STORM EVOLUTION(S), WILL
BE THE HINGE UPON WHICH THE MIDWEEK FORECAST RESTS.
UNFORTUNATELY, THERE'S STILL QUITE A BIT OF UNCERTAINTY WITH THE
EXTENT TO WHICH THESE FEATURES WILL INTERACT, AND HOW MUCH OF
DUJUAN'S ENERGY WILL ENTER THE ALEUTIANS VERSUS REMAINING FURTHER
AFIELD IN THE NORTH PACIFIC. AS SUCH, MANY SCENARIOS REMAIN AT
PLAY. WHAT WE CAN SAY IS THAT THE STORM RESULTING FROM THIS
INTERACTION HAS TRENDED WEAKER AND FURTHER SOUTH. WHILE A FURTHER
NORTH TRACK AND STRONGER STORM REMAINS POSSIBLE AND COULD LEAD TO
SIGNIFICANT IMPACTS, THE EMERGENCE OF MODEL SOLUTIONS FEATURING A
FURTHER SOUTH TRACK SUGGESTS THAT IMPACTS COULD ALSO BE LESS
CONCERNING THAN INITIALLY FORECAST YESTERDAY. EITHER WAY, OVERALL
CONFIDENCE REMAINS FAIRLY LOW, SO STAY TUNED TO THE FORECAST FOR
UPDATES.
-KC/JH
LONG TERM FORECAST (DAYS 4 THROUGH 7: THURSDAY THROUGH SUNDAY)
KEY MESSAGES:
- A VERY STRONG LOW PRESSURE SYSTEM WILL DEVELOP OVER THE BERING
SEA BETWEEN WEDNESDAY AND FRIDAY.
- STRONG WINDS, LARGE WAVES AND HEAVY RAINFALL ARE LIKELY NEAR
THIS STORM SYSTEM ACROSS MUCH OF THE BERING SEA, PRIBILOF
ISLANDS, AND PORTIONS OF SOUTHWEST TOWARDS THE LATTER HALF OF
THIS WEEK.
- A THREAT FOR COASTAL FLOODING WILL EXIST ALONG THE SOUTHWEST
COAST SOMETIME BETWEEN WEDNESDAY EVENING AND SATURDAY. THE
CONCERN FOR SIGNIFICANT COASTAL FLOODING HAS LESSENED (25% TO
35% CHANCE) DUE TO THE STORM LIKELY REMAINING FARTHER SOUTH.
DISCUSSION:
THE INTERACTION OF A LOW IN THE BERING SEA AND THE REMNANTS OF
TYPHOON DUJUAN IS THE FORECAST CHALLENGE FOR THE SECOND HALF OF
THIS WEEK THROUGH NEXT WEEKEND. WHAT MAKES THIS SYSTEM SO COMPLEX
IS THAT THE EX-DUJUAN SYSTEM WILL BASICALLY SPLIT ITS ENERGY ON
WEDNESDAY WITH A GOOD POTION OF ITS MOISTURE AND HEAT BEING
ENTRAINED INTO THE BERING SEA LOW WHICH WILL RAPIDLY STRENGTHEN
IT. THE OTHER PART OF ITS ENERGY WILL NOT GET ENTRAINED AND WILL
TRACK EASTWARD, SOUTH OF THE ALEUTIAN ISLANDS. THE AMOUNT OF
MOISTURE THAT IS ABSORBED INTO THE BERING SEA LOW WILL DETERMINE
HOW STRONG EACH LOW BECOMES. ATTEMPTING TO RESOLVE THIS IS GIVING
FITS TO ALL OF THE MODELS WHETHER THEY BE DETERMINISTIC, ENSEMBLE,
OR AI MODELS. ALL ARE STRUGGLING WITH THE TRACK, TIMING, AND
STRENGTH OF THIS INTENSIFYING BERING SEA LOW WHICH IS TO BE
EXPECTED.
HOWEVER, EVEN IN ALL THIS CHAOS, THERE ARE SOME THINGS THAT LOOK
MORE LIKELY THAN OTHERS. FIRST, MODELS ARE ALL BACKING OFF A THE
EXPECTED STRENGTH OF THIS LOW. YESTERDAY THEY RANGED FROM A
MINIMUM CENTRAL PRESSURE OF 935 MB TO 945 MB. TODAY THAT RANGE IS
CLOSER TO 960 TO 970 MB. THAT IS A SIGNIFICANT DIFFERENCE IN
STRENGTH AND A STRONG, BUT NOT EXTREME SYSTEM. SECOND, THE TRACK
IS TRENDING FARTHER TO THE SOUTH ON JUST ABOUT ALL MODEL TYPES.
THIS IS VERY IMPORTANT FOR THE THREAT OF COASTAL FLOODING IN THE
KUSKOKWIM DELTA AS THE FARTHER SOUTH THE LOW TRACKS, THE LESS
LIKELY COASTAL FLOODING WILL BE. THERE REMAINS A CHANCE THE LOW
CENTER TRACK AS FAR NORTH AS NUNIVAK ISLAND ON THURSDAY OR FRIDAY,
WHICH WOULD BE THE WORST SCENARIO FOR KUSKOKWIM DELTA STORM
SURGE. HOWEVER, THE MORE LIKELY SCENARIO IS THAT THE LOW CENTER
REMAINS FARTHER TO THE SOUTH AND WEST WHICH WILL KEEP WINDS FROM A
SOUTHEASTERLY TO NORTHEASTERLY DIRECTION WHICH WOULD ONLY PUT A
FEW AREAS (SUCH AS KWIGILLINGOK) AT RISK AND ONLY DURING
SOUTHEASTERLY WINDS ALONG THE FRONT.
THE ALEUTIAN ISLANDS FROM ATTU THROUGH DUTCH HARBOR WILL LIKELY
SEE THE STRONGEST WINDS IN THIS STORM. IT IS STILL TOO EARLY TO
REALLY NAIL DOWN WHERE AND WHEN THE STRONGEST WINDS WILL OCCUR.
HOWEVER, WITH THE ANTICIPATED WEAKER CENTRAL PRESSURE OF THE LOW,
MAXIMUM GUSTS ARE EXPECTED TO BE IN THE 70 TO 80 MPH RANGE WHICH
IS LOWER THAN IT LOOKED LIKE YESTERDAY WHEN THE LOW LOOKED LIKE IT
WOULD BE STRONGER.
EVEN WITH THESE TRENDS, THERE IS STILL A CHANCE THE ENTIRE FORMER
TYPHOON GETS ABSORBED INTO THE BERING SEA LOW AND INTENSIFIES
STRONGER THAN IT LOOKS TODAY. THIS WILL STILL BE A LARGE AND
STRONG LOW WITH ROUGH WEATHER EVEN AT A WEAKER STRENGTH, SO THIS
SYSTEM BEARS WATCHING CLOSELY FOR ANYONE WITH INTERESTS IN
SOUTHWEST ALASKA OR THE BERING SEA REGION.
AS FOR SOUTHCENTRAL AND THE GULF OF ALASKA REGION: THE LOW THAT
TRACK SOUTH OF THE ALEUTIANS WILL MAKE ITS WAY TO THE GULF OF
ALASKA REGION THURSDAY INTO FRIDAY. AS WITH THE THE BERING SEA
LOW, THIS ONE HAS A HIGH DEGREE OF UNCERTAINTY DUE TO IT STILL
BEING UNCERTAIN HOW MUCH OF THIS STORM'S ENERGY GET ENTRAINED
INTO THE BERING SEA LOW. AT THIS TIME, IT DOES APPEAR LIKELY THAT
A FAIRLY STRONG FRONT WILL MOVE INTO THE GULF OF ALASKA BY
THURSDAY AND BRING RAIN AND WIND TO THE GULF REGION. WHAT HAPPENS
NEXT WITH THIS LOW, AND WHETHER IT INTENSIFIES IN THE GULF OR
WEAKENS THERE, WILL BE DEPENDENT ON WHAT HAPPENS WITH THE BERING
SEA LOW.
AVIATION
PANC...THE NEXT ROUND OF RAIN AND MVFR CEILINGS ARRIVES THIS
EVENING AND OVERNIGHT AS A LOW IN THE GULF MOVES INTO THE PRINCE
WILLIAM SOUND. SHOWERS WITH THIS ROUND WILL PERSIST THROUGH
MONDAY MORNING. CEILINGS ARE ON TRACK TO LOWER TO IFR THROUGHOUT
THE MORNING HOURS AS VISIBILITY TICKS DOWN TO MVFR WITH ANY
HEAVIER SHOWERS. EXPECT MOSTLY LIGHT AND VARIABLE WINDS THROUGH
MONDAY MORNING. RAIN SHOWERS WILL CONTINUE THROUGH MONDAY
AFTERNOON WITH MVFR VISIBILITY AND IFR CEILINGS.
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