695
FXAK68 PAFC 211321
AFDAFC
SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
521 AM AKDT MON SEP 21 2026
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 THROUGH 3:
TODAY THROUGH WEDNESDAY NIGHT)...
THE BROAD, OCCLUDED SURFACE LOW THAT BROUGHT WIDESPREAD RAIN AND
GUSTY WINDS TO THE COAST YESTERDAY HAS WEAKENED CONSIDERABLY
OVERNIGHT AND IS MOVING ONSHORE NORTHEAST OF WHITTIER AS OF 4 AM.
THERE IS A HINT OF CYCLONIC CIRCULATION ON RADAR; HOWEVER, THIS
FEATURE WILL CONTINUE TO WEAKEN AND BECOME A SURFACE TROUGH AS IT
MOVES OVER INTERIOR SOUTHCENTRAL. THERE IS A STARK WESTWARD
DELINEATION IN THE PRECIPITATION WITH THIS FEATURE, AS A WEAK
NORTH-NORTHWESTERLY FLOW HAS KEPT THE WESTERN EXTENT OF THE SHOWER
ACTIVITY CONFINED TO EAST ANCHORAGE AND FAR EASTERN MATANUSKA
VALLEY EARLY THIS MORNING. SHOWERS WILL ALSO CONTINUE ACROSS
PRINCE WILLIAM SOUND AND THE COPPER RIVER BASIN THIS MORNING AS
THIS FEATURE LIFTS NORTH. GUSTY SOUTHERLY GAP WINDS WILL ALSO
CONTINUE THROUGH THE COPPER RIVER VALLEY TODAY AS THE WAVE LIFTS
NORTH AND A WEAK COASTAL RIDGE BUILDS IN ITS WAKE.
THE MAIN WEATHER FEATURE OF NOTE TODAY, HOWEVER, IS A DIGGING
SHORTWAVE TROUGH MOVING SOUTH OF KODIAK ISLAND THIS MORNING A
STRENGTHENING SOUTH OF KODIAK ISLAND. A DUE TO SOME WEAK UPPER-
LEVEL JET SUPPORT. SATELLITE IMAGERY THIS MORNING IS SHOWING THE
DEVELOPMENT OF A SURFACE OUT AHEAD OF THE UPPER-LEVEL TROUGH AXIS,
STRENGTHENING QUICKLY DUE TO VORTICITY ADVECTION AND WEAK UPPER-
LEVEL JET SUPPORT. THE UPPER-LEVEL TROUGH AXIS THEN BECOMES MORE
NEGATIVELY TILTED THROUGH THE DAY, ALLOWING THE SOUTH-
SOUTHWESTERLY FLOW ALOFT TO SHIFT SOUTHEASTERLY. THIS WILL DRIVE
MORE MOISTURE AND A SURFACE FRONT TOWARD THE KENAI PENINSULA WITH
MORE SHOWERS ALONG THE COAST AND A PERIOD OF RAIN ACROSS COOK
INLET NORTH TO MAT-SU VALLEYS LATE THIS MORNING THROUGH LATE THIS
AFTERNOON AS A SHORTWAVE ATTACHED TO THE SURFACE FRONT BOTH MOVE
NORTHWEST FROM THE GULF TO THE SUSITNA VALLEY.
THE SURFACE LOW AND UPPER-LEVEL THEN GET PULLED SOUTHWARD AND A
SHORTWAVE OVER THE NORTH PACIFIC TRACKS TOWARD SOUTHEAST ALASKA.
SHOWERS WILL TAPER OFF BY LATE MONDAY EVENING ACROSS INTERIOR
SOUTHCENTRAL AND BY TUESDAY AFTERNOON ALONG THE NORTHERN GULF AND
KODIAK ISLAND AS THE LOW DEPARTS AND A RIDGE BUILDS IN FROM
SOUTHWEST ALASKA. THE ADVECTION OF A DRIER AIRMASS WILL LEAD TO A
GENERAL DECREASE IN CLOUDS AND WINDS. THIS WILL RESULT IN COLDER
OVERNIGHT LOW TEMPERATURES FOR TUESDAY AND WEDNESDAY MORNING.
RIGHT NOW, WEDNESDAY MORNING LOOKS TO BE THE COLDEST WITH
WIDESPREAD TEENS AND 20S POSSIBLE FOR THE COPPER RIVER BASIN ALONG
WITH WIDESPREAD LOW TO MID 30S ELSEWHERE. EARLY WEDNESDAY MORNING
LOWS MAY EVEN FALL INTO THE UPPER 20S FOR TYPICALLY COLDER
LOCATIONS SUCH AS EAST ANCHORAGE, SOLDOTNA, BUTTE. AND WILLOW.
SOUTHCENTRAL THEN REMAINS RELATIVELY QUIET THROUGH MIDWEEK BEFORE
A MUCH MORE POTENT SYSTEM MOVES CLOSER TO THE WESTERN GULF LATE
WEDNESDAY AFTERNOON, THOUGH MODEL AGREEMENT IS BELOW AVERAGE FOR
THIS TIME FRAME. DUE TO THIS BEING A POTENTIALLY IMPACTFUL SYSTEM
FOR SOME, PLEASE STAY TUNED TO THE FORECAST AS WE DRAW CLOSER TO
THIS TIME FRAME.
-TM/AM
.SHORT TERM FORECAST SOUTHWEST ALASKA AND BERING SEA/ALEUTIANS
(DAYS 1 THROUGH 3: TODAY THROUGH WEDNESDAY)...
KEY MESSAGES:
- GUSTY NORTHWESTERLY WINDS AND PERSISTENT SHOWERS FOR THE
ALEUTIANS AND ALASKA PENINSULA CONTINUE THROUGH TONIGHT.
- 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 THROUGH WEDNESDAY AS A
STRENGTHENING LOW PRESSURE SYSTEM ENTERS FROM THE WEST AND
INTERACTS WITH THE REMNANTS OF TYPHOON DUJUAN. CONFIDENCE
REMAINS FAIRLY LOW.
DISCUSSION:
NORTHWESTERLY FLOW CONTINUES ACROSS THE BERING SEA AND SOUTHWEST
ALASKA AS THE BROAD, LONGWAVE TROUGH AXIS SLIDES EAST INTO THE
GULF TODAY. GUSTY WINDS AND SHOWERS ACROSS THE EASTERN BERING AND
THE ALASKA PENINSULA PERSIST THROUGH TONIGHT INTO TUESDAY MORNING,
WITH WINDS SLOWLY WEAKENING FROM NORTH TO SOUTH. GUSTS TO GALE-
FORCE ARE LIKELY TO CONTINUE THROUGH FAVORED BAYS AND PASSES ALONG
AND SOUTH OF THE NORTHERN AKPEN THROUGH LATE THIS EVENING AS WEAK
SHORTWAVES AND COLD AIR ADVECTION CONTINUE TO TRACK SOUTH ACROSS
THE AKPEN AND INTO THE NORTH PACIFIC. DRY, NORTHERLY FLOW ACROSS
THE SOUTHWEST MAINLAND CONTINUES THROUGH EARLY THIS WEEK, WITH
THE BIGGEST FOCUS BEING THE STRONG LIKELIHOOD OF LOW TEMPERATURES
DROPPING TO NEAR OR BELOW FREEZING. EXPECT NIGHTTIME AND MORNING
TEMPERATURES TO DROP INTO AT LEAST THE LOW TO MID 30S ACROSS MUCH
OF SOUTHWEST THROUGH THE FIRST HALF OF THE WEEK, WITH SOME
INTERIOR LOCATIONS THAT SEE LOWER CLOUD COVER POTENTIALLY DROPPING
INTO THE UPPER 20S.
FROM LATE TONIGHT THROUGH MIDWEEK, THE BIGGEST FORECAST CHALLENGE
CONTINUES TO BE THE EVOLUTION OF A POTENTIALLY STRONG BERING SEA
LOW PRESSURE SYSTEM. BY LATE TONIGHT, A LOW CURVING UP FROM JUST
SOUTH OF THE KAMCHATKA PENINSULA REACHES THE WESTERN ALEUTIANS,
BRINGING LIGHT TO MODERATE RAIN AND SMALL-CRAFT WINDS AND GALE-
FORCE GUSTS MAINLY CONFINED TO THE COASTAL WATERS SOUTH OF THE
ALEUTIAN CHAIN. THE SECOND FEATURE WILL BE THE REMNANTS OF TYPHOON
DUJUAN, WHICH WILL LIKELY INTERACT IN SOME FORM WITH THE BERING
LOW AROUND TUESDAY NIGHT AS IT TRACKS TO THE SOUTH OF THE ALEUTIAN
CHAIN. WHAT THIS INTERACTION WILL EXACTLY LOOK LIKE, AND THE
RESULTING STORM EVOLUTION(S), REMAINS UNCERTAIN AS RUN-TO-RUN
MODEL VARIABILITY CONTINUES TO SHOW A WIDE RANGE OF POTENTIAL
OUTCOMES REGARDING HOW MUCH OF DUJUAN'S ENERGY IS INGESTED INTO
THE BERING LOW. LATEST MODEL GUIDANCE HAS ONCE AGAIN TRENDED THE
STORM SLIGHTLY STRONGER AS COMPARED TO THE PREVIOUS FORECAST
PACKAGE, WITH VARIOUS MODEL GUIDANCE BEGINNING TO POTENTIALLY
SETTLE ON A MIDDLE-GROUND SOLUTION OF A STRENGTHENING LOW
TRACKING EAST ACROSS THE CENTRAL BERING WEDNESDAY INTO THURSDAY.
IF A STRONGER SOLUTION WERE TO PLAY OUT WITH THIS STORM, THERE IS
A HIGH LIKELIHOOD OF WIDESPREAD MODERATE TO HEAVY RAIN, GALE-FORCE
WINDS, AND POTENTIALLY STORM-FORCE GUSTS ACROSS THE ALEUTIANS,
PRIBILOF ISLANDS, AND MUCH OF THE BERING. OVERALL, CONFIDENCE
REMAINS FAIRLY LOW, AS SHIFTS IN THE FORECASTED STORM TRACK WILL
GREATLY IMPACT THE RANGE OF POTENTIAL IMPACTS, ESPECIALLY FOR
COASTAL SOUTHWEST ALASKA. STAY TUNED FOR FORECAST UPDATES AS
CONFIDENCE INCREASES AHEAD OF THIS STORM.
-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...RAIN SHOWERS WILL CONTINUE FOR MOST OF THE DAY. EXPECT
MVFR CEILINGS AND VISIBILITIES THROUGH MUCH OF THE DAY. SOUTHEAST
FLOW DEVELOPS BY THIS EVENING WHICH SHOULD PREVENT CEILINGS AND
VISIBILITY FROM DROPPING LOWER THAN MVFR. IN FACT, DESPITE SHOWERS
CONTINUING THIS EVENING AS AN UPPER-LEVEL SHORTWAVE MOVES OVER
THE AREA, THE SOUTHEAST FLOW WILL PROMOTE VFR CONDITIONS. HOWEVER,
CEILINGS MAY BE BELOW 5000 FEET, DESPITE VFR CONDITIONS. ANY
SHOWERS WILL TAPER OFF OVERNIGHT TONIGHT INTO EARLY TUESDAY
MORNING. LIGHT AND VARIABLE WINDS THIS MORNING WILL TURN
SOUTHEASTERLY OUT OF TURNAGAIN ARM AND INCREASE BY THIS AFTERNOON.
GUSTS SHOULD BE BELOW 25 KTS. GUSTS DIMINISH BY EARLY TUESDAY
MORNING AS WINDS BECOME LIGHT AND VARIABLE BY THEN.
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