932
FXAK68 PAFC 192355
AFDAFC
SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
355 PM AKDT SAT SEP 19 2026
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 THROUGH 3:
TODAY THROUGH TUESDAY)...
A DEEP, UPPER-LEVEL LONGWAVE TROUGH IS DIGGING SOUTH FROM THE
WESTERN COAST OF ALASKA TO THE NORTH PACIFIC. A POTENT UPPER-LEVEL
LOW AND 978MB STORM-FORCE LOW SITS AT THE BASE OF THIS TROUGH IN
THE SOUTHERN GULF. ITS FRONT HAS PUSHED INTO THE CENTRAL GULF AND
CONTINUES TO MOVE NORTHWARD. DOWNSTREAM, A RAPIDLY WEAKENING
UPPER- LEVEL SHORTWAVE MOVED INLAND OVER THE COPPER RIVER BASIN
THIS MORNING, WITH LINGERING SHOWERS AROUND THE NORTHERN GULF
COAST TO KODIAK ISLAND. A SURFACE TROUGH TO THE WEST OF THE THESE
FEATURES IS DRAPED OVER THE ANCHORAGE BOWL, WITH A FEW SCATTERED,
SLOW MOVING, AND LOCALLY HEAVY RAIN SHOWERS ACROSS ANCHORAGE AND
THE NORTHERN COOK INLET NORTH AND EAST TO THE MAT- SU.
THE FRONT ASSOCIATED WITH THE NORTH PACIFIC LOW WILL CONTINUE TO
LIFT NORTH TO THE NORTHERN GULF BY LATE TONIGHT. THE UPPER-LEVEL
AND SURFACE LOWS WILL TRAIL THE FRONT AS IT OCCLUDES. BY TOMORROW
MORNING (SUNDAY), THE UPSTREAM TROUGH IS REINFORCED BY AN ARCTIC
SHORTWAVE DIGGING SOUTH OVER THE EASTERN BERING AND AKPEN,
RESULTING IN FURTHER AMPLIFICATION OF THE LONG WAVE PATTERN. THIS
AMPLIFICATION WILL ALLOW THE OCCLUDED FRONT TO STALL ALONG THE
IMMEDIATE SOUTHCENTRAL COAST WHILE THE PARENT LOW CONTINUES TO
OCCLUDE AND LIFTS NORTH TOWARD MIDDLETON ISLAND, EVENTUALLY
MAKING LANDFALL NEAR PRINCE WILLIAM SOUND SUNDAY EVENING. THERE IS
PLENTY OF MOISTURE ALONG AND OUT AHEAD OF THE FRONT, ALLOWING FOR
PERSISTENT RAIN ALONG THE COAST (1 TO 3" AROUND PRINCE WILLIAM
SOUND) AND PERIODS OF RAIN SHOWERS FARTHER INLAND THROUGH MONDAY,
MAINLY ALONG THE WESTERN ALASKA RANGE.
MODELS ALSO CONTINUE TO SUGGEST THAT THE ATMOSPHERE LOOKS
CONDUCIVE FOR MARINE LIGHTNING (70-80% CHANCE) DURING THIS LOW'S
JOURNEY ACROSS THE GULF (NOW THROUGH SUNDAY EVENING). THIS IS
MAINLY DUE TO THE UPPER LOW COMPONENT OF THE SURFACE LOW
STEEPENING LAPSE RATES, AND THAT THE GULF WILL BE UNDER THE
INFLUENCE OF BEING BELOW THE LEFT EXIT REGION OF A 300 MB JET
STREAK, WHICH WILL FURTHER ENHANCE INSTABILITY. ASIDE FROM THAT,
WIDESPREAD WESTERLY TO SOUTHWESTERLY SMALL CRAFTS AND GALES ARE
ALSO TO BE EXPECTED IN THE WAKE OF THIS SYSTEM ACROSS THE GULF AS
THE COLD AIR ADVECTION ASSOCIATED WITH THE ARCTIC TROUGH SPILLS
SOUTHWARD STARTING SUNDAY AFTERNOON.
THE INITIAL LOW DISSIPATES BY MONDAY NIGHT. 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.
-PA/TM/AM
.SHORT TERM FORECAST SOUTHWEST ALASKA AND BERING SEA/ALEUTIANS
(DAYS 1 THROUGH 3: THIS AFTERNOON THROUGH TUESDAY AFTERNOON)...
KEY MESSAGES:
- GUSTY NORTHWESTERLY WINDS AND PERSISTENT SHOWERS FOR THE
ALEUTIANS AND ALASKA PENINSULA THROUGH EARLY NEXT WEEK. FOR THE
SOUTHERN ALASKA PENINSULA, GUSTS COULD REACH AS HIGH AS 50-60
MPH THIS EVENING, WITH A 20-30% CHANCE OF ISOLATED GUSTS TO 70
MPH.
- SLIGHT (10-20%) CHANCE OF THUNDERSTORMS FOR SOUTHERN ALASKA
PENINSULA AND SURROUNDING WATERS TOMORROW, FROM LATE MORNING
INTO THE EVENING.
- TRENDING COLDER FOR SOUTHWEST ALASKA, THOUGH OVERNIGHT LOWS WILL
ULTIMATELY DEPEND ON CLOUD COVER. STILL, MANY LOCATIONS COULD
SEE TEMPERATURES NEAR OR BELOW FREEZING BY MONDAY NIGHT/TUESDAY
MORNING, 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 FEATURES LONGWAVE TROUGHING THAT EXTENDS
ACROSS MUCH OF MAINLAND ALASKA AND INTO THE GULF. A LOW IS
CURRENTLY LOCATED AT THE BASE OF THE TROUGH NEAR KODIAK ISLAND,
WHILE A STRENGTHENING SHORTWAVE DEVELOPS INTO AN UPPER LOW AS IT
MOVES SOUTH ALONG THE WESTERN ALASKA COASTLINE. THESE TWO
FEATURES, ALONG WITH AN ARRAY OF WEAKER SHORTWAVES MOVING
SOUTHWARDS ACROSS THE BERING SEA, WILL BE THE DRIVING FORCE FOR
THE GUSTY AND SHOWERY CONDITIONS ACROSS THE EASTERN BERING, ALASKA
PENINSULA, AND PARTS OF THE ALEUTIANS THROUGH EARLY NEXT WEEK.
WHILE THERE WILL BE A DECENTLY LONG DURATION OF GUSTY WINDS, THE
STRONGEST WINDS WILL LIKELY OCCUR FROM THIS AFTERNOON THROUGH
TONIGHT. THE IMPETUS FOR THIS WILL BE A BACKGROUND OF RELATIVELY
TIGHT SURFACE PRESSURE GRADIENT, AS WELL AS POSITIVE VORTICITY
AND COLD AIR ADVECTION WITH THE ADVANCING, DEVELOPING UPPER LEVEL
SHORTWAVE. WHILE GUSTS UP TO 70 MPH REMAIN POSSIBLE THIS EVENING
(ESPECIALLY FOR COLD BAY, FALSE PASS, AND KING COVE), THE LACK OF
STRONG SURFACE FORCING ASSOCIATED WITH A NEARBY FRONT OR SURFACE
LOW MEANS THAT THE LIKELIHOOD OF THESE STRONGER GUSTS WILL REMAIN
FAIRLY LOW. LIKELY THE BIGGER STORY WILL BE THE DURATION OF THESE
GUSTY WINDS, WHICH LOOK TO PERSIST INTO 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, 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 CERTAINTY 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. STAY TUNED TO THE FORECAST.
-KC
.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 ARE EXPECTED TO PREVAIL THROUGH THE TAF
PERIOD, ALTHOUGH PERIODS OF MVFR CEILINGS REMAIN POSSIBLE WITH
RAIN SHOWERS MOVING ACROSS THE AREA THROUGH THIS EVENING. WINDS
ARE EXPECTED TO REMAIN VARIABLE UNDER 10 KTS.
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