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FXAK68 PAFC 201245
AFDAFC
SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
445 AM AKDT SUN SEP 20 2026
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 THROUGH 3:
TODAY THROUGH TUESDAY NIGHT)...
SATELLITE IMAGERY THIS MORNING SHOWS A TEXTBOOK OCCLUDED SURFACE
LOW CENTERED OVER THE CENTRAL GULF OF ALASKA. THE OCCLUDED FRONT
HAS WRAPPED AROUND THE CENTER OF CIRCULATION SEVERAL TIMES, WITH
THE MAIN FRONTAL FEATURE LIFTING TOWARD THE COAST OF SOUTHCENTRAL
ALASKA AS OF 4 AM THIS MORNING.
RADAR IMAGERY ALSO SHOWS SEVERAL BANDS OF SHOWERS ROTATING AROUND
THE LOW IN CONJUNCTION WITH THE OCCLUDED FRONT. THE MAIN BAND OF
PRECIPITATION IS BEGINNING TO PUSH OVER THE COASTAL MOUNTAINS WITH
A RAIN DEVELOPING FROM THE MAT-SU VALLEYS SOUTH ACROSS COOK INLET
TO KODIAK ISLAND. BEHIND THIS BAND ARE SEVERAL ADDITIONAL BANDS
OF HEAVY SHOWERS. VORTICITY ADVECTION, COUPLED WITH THE CYCLONIC
FLOW, SHEAR, AND STEEP LAPSE RATES DUE TO A COLD UPPER-LEVEL LOW
OVER THE GULF, HAS RESULTED IN SEVERAL EMBEDDED MESO-VORTICITES
WITH THESE STORMS (AS OBSERVED OVERNIGHT VIA THE DOPPLER RADAR ON
MIDDLETON ISLAND), INDICATIVE OF THE POTENTIAL FOR WATERSPOUTS
WITH SOME OF THESE STRONGER STORMS. AS SUCH, A MARINE WEATHER
STATEMENT REMAINS IN EFFECT FROM CAPE SUCKLING TO MONTAGUE ISLAND
SOUTH TO MIDDLETON ISLAND THROUGH 6 AM THIS MORNING.
THESE BANDS OF SHOWERS, WITH EMBEDDED THUNDERSTORMS, WILL
CONTINUE TO MOVE NORTH TOWARD CORDOVA AND PRINCE WILLIAM SOUND
(PWS) THIS MORNING AS THE SURFACE LOW MOVES EAST OF MIDDLETON
ISLAND. AS THE LOW REACHES HITCHINBROOK ENTRANCE THIS AFTERNOON,
SHOWERS WILL OVERSPREAD THE COPPER RIVER BASIN WITH ANOTHER ROUND
OF SHOWERS LIKELY MOVING WEST OVER THE MATANUSKA VALLEY SOUTH
ALONG COOK INLET BY EVENING AS AN UPPER-LEVEL LOW OPENS UP TO A
WAVE AND THE SURFACE LOW MOVES INTO PWS.
SHOWERS CONTINUE THROUGH MONDAY AS THE UPPER-LEVEL MOVES SLOWLY
NORTHWARD AND THE SURFACE LOW DISSIPATES INTO AN OPEN TROUGH.
GUSTY SOUTHERLY GAP WINDS ARE POSSIBLE BY MONDAY AFTERNOON FOR THE
COPPER RIVER VALLEY AND PALMER AREAS AS THIS WAVE MOVES NORTH.
SHOWERS TAPER OFF FOR INTERIOR LOCATIONS BY MONDAY NIGHT BUT MAY
LINGER ALONG THE NORTHERN GULF COAST AND KODIAK ISLAND THROUGH
TUESDAY MORNING. ANOTHER UPPER LOW DIVES SOUTH OVER THE AKPEN
ALONG THE LONGWAVE TROUGH SUNDAY EVENING. THIS LOW MOVES TO THE
NORTH PACIFIC BY MONDAY NIGHT THEN LIFTS NORTH TO THE GULF ON
TUESDAY. A SURFACE LOW DEVELOPS IN THE NORTH PACIFIC ON MONDAY AND
LIFTS NORTHWARD INTO THE GULF ON TUESDAY. THIS SECOND LOW LOOKS
TO BE WEAKER DUE TO COLD AIR PUSHED IN FROM THIS INITIAL LOW.
NONETHELESS, MORE SMALL-CRAFT WINDS AND SHOWERS WILL BE
PERSISTENT IN THE GULF ON TUESDAY, WITH SOME SHOWERS REACHING THE
NORTHERN GULF COAST AND KODIAK ISLAND. FOR THE REST OF
SOUTHCENTRAL, SEASONABLY COOL TEMPERATURES AND DRY CONDITIONS ARE
EXPECTED TUESDAY.
-TM/PA
.SHORT TERM FORECAST SOUTHWEST ALASKA AND BERING SEA/ALEUTIANS
(DAYS 1 THROUGH 3: TODAY THROUGH TUESDAY)...
KEY MESSAGES:
- GUSTY NORTHWESTERLY WINDS AND PERSISTENT SHOWERS FOR THE
ALEUTIANS AND ALASKA PENINSULA THROUGH EARLY THIS WEEK.
- SLIGHT (10-20%) CHANCE OF THUNDERSTORMS FOR SOUTHERN ALASKA
PENINSULA AND SURROUNDING WATERS FROM LATE MORNING INTO THIS
EVENING.
- 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 (60% OR GREATER)
FOR INTERIOR SOUTHWEST.
- LOOKING AHEAD: WINDS TO GALE FORCE AND LIGHT TO MODERATE RAIN FOR
THE ALEUTIANS FROM LATE MONDAY INTO TUESDAY AS A STRENGTHENING
LOW PRESSURE SYSTEM ENTERS FROM THE WEST.
DISCUSSION:
THE UPPER LEVEL PATTERN REMAINS STEADY OVER THE NEXT COUPLE OF
DAYS AS THE BROAD LONGWAVE TROUGHING EXTENDING FROM THE BERING,
ACROSS MUCH OF MAINLAND ALASKA, AND INTO THE GULF REMAINS IN
PLACE. THE WEAKER OF TWO UPPER SHORTWAVES ROUNDING THE BASE OF
THE TROUGH PROGRESSES SOUTHWARDS ACROSS THE SOUTHEASTERN BERING
THROUGHOUT THE DAY TODAY, WHILE THE STRONGER OF THE TWO AND ITS
ASSOCIATED SURFACE LOW LIFTS NORTH ACROSS THE GULF. THIS PATTERN
REMAINS FAVORABLE FOR THE GUSTY NORTHWESTERLY WINDS AND SHOWERY
CONDITIONS ACROSS THE EASTERN BERING, ALEUTIANS, AND ALASKA
PENINSULA TO CONTINUE THROUGH EARLY THIS WEEK. WIND SPEEDS SIMILAR
TO WHAT HAVE BEEN OBSERVED OVERNIGHT AND EARLY THIS MORNING ARE
LIKELY TO CONTINUE INTO EARLY THIS AFTERNOON, THANKS TO THE TIGHT
SURFACE PRESSURE GRADIENT IN COMBINATION WITH POSITIVE VORTICITY
AND COLD AIR ADVECTION ASSOCIATED WITH THE PASSING UPPER LEVEL
SHORTWAVE. BY LATE THIS AFTERNOON INTO THIS EVENING, WINDS BEGIN
TO SLOWLY TREND WEAKER AS THE SHORTWAVE CONTINUES INTO THE GULF,
THOUGH GUSTY SMALL-CRAFT WINDS AND GALE- FORCE GUSTS ALONG THE
AKPEN PERSIST THROUGH MONDAY.
FOR SOUTHWEST ALASKA, THE BIGGEST STORY WILL LIKELY BE
TEMPERATURES TRENDING COLDER. 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 TUESDAY, WHAT COULD BE THE FIRST OF
TWO STORMS WILL MOVE INTO THE WESTERN BERING SEA, BRINGING
STRONGER WINDS AND GREATER RAIN CHANCES TO AREAS WEST OF NIKOLSKI.
THERE REMAINS A FAIR AMOUNT OF UNCERTAINTY WITH HOW THIS STORM
WILL INTERACT WITH THE SECOND STORM, BUT WHAT IS NOT IN QUESTION
IS THAT THIS STORM WILL ALMOST CERTAINLY BE WEAKER THAN THE
SUCCEEDING STORM. STILL, THIS MONDAY/TUESDAY STORM COULD PACK A
BIT OF A PUNCH, WITH WINDS TO GALE FORCE AND LIGHT TO MODERATE
RAIN. WHILE THE DETAILS WILL CONTINUE TO BE IRONED OUT OVER THE
COMING DAYS, THE CURRENT EXPECTATION IS FOR THE INTERACTION OF THE
TWO STORMS TO RESULT IN A POTENTIALLY MUCH STRONGER STORM
DEVELOPING IN THE BERING FOR WEDNESDAY INTO THURSDAY. STAY TUNED
TO THE FORECAST FOR UPDATES.
-KC/JH
LONG TERM FORECAST (DAYS 4 THROUGH 7: WEDNESDAY THROUGH SATURDAY)
KEY MESSAGES:
- A VERY STRONG LOW PRESSURE SYSTEM IS LIKELY TO DEVELOP OVER THE
BERING SEA BETWEEN WEDNESDAY AND FRIDAY.
- THE POST-TROPICAL REMNANTS OF TYPHOON DUJUAN WILL LIKELY BE
ABSORBED INTO AN INITIAL WEAKER SYSTEM MOVING INTO THE WESTERN
BERING SEA, CAUSING THE LOW TO RAPIDLY INTENSIFY FROM WEDNESDAY
TO THURSDAY.
- VERY 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
THE WEEK AHEAD.
- A THREAT FOR COASTAL FLOODING WILL EXIST ALONG THE SOUTHWEST
COAST SOMETIME BETWEEN WEDNESDAY EVENING AND SATURDAY, BUT
THIS POTENTIAL IS HIGHLY DEPENDENT ON THE STILL UNCERTAIN TRACK
OF THE LOW AS IT HEADS ACROSS THE BERING SEA.
DISCUSSION:
MUCH ACTIVITY WILL BE BREWING AT THE START OF THE LONG TERM PERIOD
ON WEDNESDAY MORNING, MAINLY ACROSS PARTS OF THE BERING SEA AND
ALEUTIAN CHAIN. A COMPLEX TROUGH WITH MULTIPLE EMBEDDED SHORTWAVES
WILL BE SHIFTING AWAY FROM KAMCHATKA AND INTO THE WESTERN BERING
SEA, SENDING AN INITIALLY WEAK ATTENDANT SURFACE LOW INTO THE
WESTERN/CENTRAL BERING. MEANWHILE, THE REMNANTS OF TYPHOON DUJUAN
ARE ANTICIPATED TO BE CURVING NORTHEAST AWAY FROM JAPAN BY THIS
POINT AND DRIFTING SOUTH OF THE WESTERN PARTS OF THE ALEUTIAN
CHAIN. MUCH CALMER CONDITIONS SHOULD BE ONGOING ACROSS MOST OF
THE SOUTHERN MAINLAND BY THE MIDDLE OF NEXT WEEK AS A LONGWAVE
RIDGE OVER THE EASTERN BERING BEGINS TO SHIFT EAST INTO SOUTHWEST
AND SOUTHCENTRAL.
A COMPLEX INTERACTION BETWEEN THE INCOMING TROUGH/LOW HEADING INTO
THE WESTERN BERING AND THE REMNANTS OF DUJUAN MOVING OVER THE
NORTH PACIFIC IS PROJECTED TO UNFOLD STARTING AROUND THE MIDDLE OF
NEXT WEEK. THE CONSENSUS FROM DETERMINISTIC AND ENSEMBLE MODEL
SOLUTIONS IN TERMS OF HOW THIS PLAYS OUT HAS SHIFTED QUITE A BIT
COMPARED TO INDICATIONS FROM YESTERDAY. IT NOW LOOKS LIKELY
(ABOUT A 60-70% CHANCE) THAT DUJUAN'S REMNANT CENTER WILL CURVE
NORTH ACROSS THE ALEUTIANS AND PHASE WITH ONE OR MORE SHORTWAVES
DRIFTING ACROSS THE WESTERN BERING. AS THESE FEATURES MERGE, THIS
WILL RESULT IN A PERIOD OF RAPID DEEPENING OF THE RESULTING SINGLE
SURFACE LOW, PERHAPS BOTTOMING OUT IN THE 940-960 MB RANGE OR
LOWER AS IT REACHES MAXIMUM INTENSITY SOMEWHERE OVER THE CENTRAL
TO WESTERN BERING SEA ON THURSDAY.
A LARGE FIELD OF GALE TO STORM FORCE WINDS IS ANTICIPATED TO
DEVELOP AROUND THE LOW AS IT DEEPENS, WITH A SWATH OF HURRICANE
FORCE GUSTS POSSIBLE ON THE SOUTH SIDE OF THE LOW. MUCH OF THE
ALEUTIAN CHAIN, INCLUDING ADAK, ATKA AND UNALASKA, WILL HAVE THE
POTENTIAL TO SEE STRONG TO DAMAGING WIND GUSTS SOUTH OF THE LOW
CENTER AS EARLY AS WEDNESDAY EVENING. LARGE WAVES OF UP TO 20 TO
30 FT OR MORE ARE POSSIBLE AS WELL, PARTICULARLY ACROSS THE
SOUTHERN BERING SEA BETWEEN THURSDAY AND FRIDAY. STRONG WINDS WILL
ALSO AFFECT THE PRIBILOFS FROM LATE WEDNESDAY THROUGH AT LEAST
FRIDAY, WHERE LARGE BREAKING WAVES REACHING THE SHORELINE WILL
ALSO BE A POSSIBLE HAZARD. HEAVY RAINFALL RATES WILL ALSO BE A
CONCERN ACROSS MUCH OF THE ALEUTIANS AS A DEEP BAND OF TROPICAL
MOISTURE SURGES NORTH INTO THE LOW, ESPECIALLY BETWEEN WEDNESDAY
AND THURSDAY.
TURNING ATTENTION TO SOUTHWEST, THE FIRST IMPACTS FROM THIS SYSTEM
WILL ARRIVE ALONG THE LOW'S OCCLUDING FRONTAL BOUNDARY AS IT MOVES
UP THE AKPEN AND REACHES THE SOUTHWEST COAST FROM WEDNESDAY NIGHT
INTO THURSDAY. INTENSE SOUTHERLY GAP WINDS WILL RAMP UP AHEAD OF
THE FRONTAL PASSAGE ALONG THE AKPEN, INCLUDING SPOTS LIKE COLD
BAY, PORT HEIDEN, AND PILOT POINT. STRONG SOUTHEAST WINDS WILL
SHIFT UP TO THE COAST OF BRISTOL BAY AND THE KUSKOKWIM DELTA LATER
ON THURSDAY, WITH EARLY INDICATIONS SUGGESTING THE FRONT WILL
WEAKEN AS IT HEADS INLAND, LIMITING IMPACTS FROM STRONG WINDS TO
ALONG/NEAR THE COASTLINE. SOME SECTIONS OF COASTLINE THAT FACE
SOUTHEAST, NAMELY IN AND AROUND KWIGILLINGOK, COULD SEE MINOR
COASTAL FLOODING WITH THIS FIRST ROUND OF STRONG SOUTHEAST WINDS
ON THURSDAY.
POTENTIAL FOR MORE WIDESPREAD COASTAL IMPACTS IN TERMS OF EROSION
AND COASTAL FLOODING BEYOND THURSDAY IS MORE UNCERTAIN. MODELS
ARE IN RELATIVELY GOOD AGREEMENT THAT THE LOW WILL NEARLY STALL AS
IT REACHES MAXIMUM INTENSITY OVER THE WESTERN BERING AS IT
DETACHES FROM STRONGER STEERING FLOW ALONG THE PACIFIC JET.
HOWEVER, THE WEAKER STEERING FOR THE LOW THEREAFTER IS
CONTRIBUTING TO MUCH LOWER CONFIDENCE FOR THE TRACK OF THE LOW AS
IT DRIFTS EAST AND CLOSER TO SOUTHWEST THROUGH SATURDAY. ANOTHER
PERIOD OF STRONG ONSHORE WINDS WILL BE POSSIBLE IF THE LOW MOVES
IN A MORE NORTHEAST DIRECTION TOWARDS THE Y-K DELTA AFTER IT
BEGINS TO WEAKEN, BUT THIS HIGHLY UNCLEAR AT THIS TIME. LAND AND
MARINE INTERESTED ALIKE ARE ADVISED TO CLOSELY MONITOR THE
FORECAST FOR UPDATES AS WE FOLLOW THIS STRONG BERING STORM SYSTEM
OVER THE NEXT SEVERAL DAYS.
LOOKING BRIEFLY TO SOUTHCENTRAL, MUCH CALMER CONDITIONS ARE
EXPECTED UP UNTIL FRIDAY MORNING AS THE UPPER RIDGE MOVES DIRECTLY
OVERHEAD. THE FRONT ASSOCIATED WITH THE MASSIVE BERING LOW WILL
ARRIVE FROM THE WEST ON FRIDAY, SENDING GUSTY SOUTHERLY GAP WINDS
INTO PARTS OF THE REGION. RAIN MOVING IN WITH THE MOISTURE TAP
ALONG THE FRONT WILL BE MOSTLY CONCENTRATED ON THE SOUTHERN FACES
OF THE MOUNTAINS AS STRONG SOUTHERLY FLOP UPSLOPES INTO PARTS OF
THE CHUGACH RANGE, KENAI MOUNTAINS AND ALASKA RANGE. DRIER
CONDITIONS WILL MOSTLY PERSIST IN THE LEE OF THE MOUNTAINS OVER
MUCH OF THE INTERIOR VALLEYS THROUGH SATURDAY, WHILE THE HEAVY
RAINFALL POTENTIAL WILL REMAIN CONFINED MAINLY TO THE COASTAL
MOUNTAINS ACROSS THE WESTERN PRINCE WILLIAM SOUND AND EASTERN
KENAI PENINSULA.
-AS
AVIATION
PANC...VFR CEILINGS WITH OCCASIONAL MVFR CEILINGS ARE LIKELY
THROUGHOUT THE TAF PERIOD. THE MOST LIKELY PERIOD FOR MVFR
CEILINGS WILL BE THIS MORNING AND THIS EVENING AS MULTIPLE ROUNDS
OF RAIN MOVE OVER THE AREA. RAIN TAPERS OFF BY LATE THIS MORNING
INTO THE EARLY AFTERNOON. THE NEXT ROUND OF RAIN AND POTENTIAL
MVFR CEILINGS ARRIVES THIS EVENING AND OVERNIGHT AS A LOW IN THE
GULF MOVES INTO PRINCE WILLIAM SOUND. SHOWERS WITH THIS ROUND WILL
PERSIST THROUGH THE REST OF THE TAF PERIOD INTO MONDAY MORNING.
EXPECT LIGHT AND VARIABLE WINDS WITH MAJORITY OF WIND BEING OUT OF
THE NORTH AND AT OR LESS THAN 10 KTS.
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