935
FXAK68 PAFC 191220
AFDAFC
SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
420 AM AKDT SAT SEP 19 2026
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 THROUGH 3:
TODAY THROUGH MONDAY EVENING)...
A DEEP, UPPER-LEVEL TROUGH IS DIGGING SOUTH FROM THE WESTERN COAST
OF ALASKA TO THE NORTH PACIFIC. A POTENT UPPER-LEVEL LOW AND
978MB STORM-FORCE LOW SIT AT THE BASE OF THIS TROUGH, ITS FRONT
BEGINNING TO OCCLUDE AND PUSH INTO THE SOUTHWEST GULF OF ALASKA
SOUTH OF KODIAK ISLAND. DOWNSTREAM, A RAPIDLY WEAKENING UPPER-
LEVEL SHORTWAVE AND SURFACE LOW HAVE MOVED INLAND OVER THE COPPER
RIVER BASIN THIS MORNING, WITH RAIN OVER PARTS OF THE BASIN AND
LINGERING SHOWERS FROM MIDDLETON ISLAND INTO PRINCE WILLIAM SOUND
(PWS). 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 EAST ANCHORAGE NORTH AND
EAST TO THE MATANUSKA VALLEY. THESE SHOWERS ARE EXPECTED TO TAPER
OFF BY MID MORNING.
THE FRONT ASSOCIATED WITH THE NORTH PACIFIC LOW WILL CONTINUE TO
LIFT NORTH OVER THE WESTERN GULF TODAY AND OVER THE NORTHERN GULF
BY LATE TONIGHT. THE UPPER-LEVEL AND SURFACE LOWS WILL TRAIL THE
FRONT AS ITS OCCLUDES, PUSHING INTO THE SOUTHERN GULF BY SATURDAY
NIGHT. BY SUNDAY MORNING, 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 AND KODIAK ISLAND WHILE THE PARENT
LOW LIFTS NORTH TOWARD MIDDLETON ISLAND, EVENTUALLY MAKING
LANDFALL AROUND THE COPPER RIVER DELTA SUNDAY AFTERNOON. THERE IS
PLENTY OF MOISTURE ALONG AND OUT AHEAD OF THE FRONT, ALLOWING FOR
PERSISTENT RAIN ALONG THE COAST (1 TO 3" AROUND PWS) AND PERIODS
OF RAIN SHOWERS FATHER ISLANDS THROUGH THE WEEKEND.
MODELS ALSO CONTINUE TO SUGGEST THAT THE ATMOSPHERE LOOKS
CONDUCIVE FOR MARINE LIGHTNING (70-80% CHANCE) DURING THIS LOW'S
JOURNEY ACROSS THE GULF (SATURDAY AFTERNOON THROUGH SUNDAY
AFTERNOON), 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.
-TM/AM
.SHORT TERM FORECAST SOUTHWEST ALASKA AND BERING SEA/ALEUTIANS
(DAYS 1 THROUGH 3/ TODAY THROUGH MONDAY EVENING)...
KEY MESSAGES:
- STRONG NORTHERLY TO NORTHWESTERLY WINDS DEVELOP ACROSS THE
EASTERN ALEUTIANS AND AKPEN SATURDAY AFTERNOON AND EVENING, WITH
THE STRONGEST WINDS THROUGH FAVORED GAPS, INCLUDING COLD BAY,
KING COVE, FALSE PASS AND SAND POINT.
- COLDER AIR CONTINUES TO SPREAD SOUTH ACROSS SOUTHWEST ALASKA AND
THE BERING THROUGH THE WEEKEND, WITH FALLING SNOW LEVELS AND
SNOW POSSIBLE ACROSS HIGHER ELEVATIONS.
- WINDS GRADUALLY DIMINISH SUNDAY INTO MONDAY AS HIGH PRESSURE
BUILDS ACROSS THE BERING, THOUGH COOL AND SHOWERY CONDITIONS
PERSIST.
- A COLDER AND INCREASINGLY WINDY PATTERN REMAINS ON TRACK ACROSS
SOUTHWEST ALASKA, THE BERING AND ALEUTIANS THIS WEEKEND. ON
SATURDAY, A STRENGTHENING LOW MOVES SOUTHEAST OF THE ALASKA
PENINSULA AND INTO THE GULF WHILE HIGH PRESSURE BUILDS ACROSS
THE WESTERN AND CENTRAL BERING. THE TIGHTENING PRESSURE GRADIENT
BETWEEN THESE FEATURES WILL STRENGTHEN NORTHERLY TO
NORTHWESTERLY FLOW ACROSS MUCH OF THE BERING, EASTERN ALEUTIANS
AND AKPEN. THE LATEST GUIDANCE REMAINS IN GOOD AGREEMENT WITH
THE OVERALL EVOLUTION OF THIS SYSTEM, THOUGH SOME DIFFERENCES
REMAIN WITH THE EXACT STRENGTH AND POSITION OF THE LOW.
THE STRONGEST WINDS SATURDAY AFTERNOON INTO SATURDAY EVENING WILL
FOCUS ACROSS THE EASTERN ALEUTIANS AND AKPEN WHERE TERRAIN
ENHANCEMENT WILL RESULT IN LOCALLY STRONGER WINDS THROUGH FAVORED
GAPS. COLD BAY, KING COVE, FALSE PASS AND SAND POINT WILL BE AMONG
THE LOCATIONS MOST SUSCEPTIBLE TO STRONGER GUSTS. MEANWHILE,
COLDER AIR MOVING SOUTH ACROSS THE BERING WILL MAINTAIN SCATTERED
SHOWERS ACROSS THE ALEUTIANS AND PORTIONS OF SOUTHWEST ALASKA.
THERE ARE GALE-FORCE WINDS DEVELOPING ALONG PORTIONS OF THE AKPEN
SATURDAY NIGHT AS THE PRESSURE GRADIENT TIGHTENS.
BY SUNDAY, THE LOW CONTINUES EASTWARD INTO THE GULF WHILE HIGH
PRESSURE REMAINS OVER THE BERING. PERSISTENT NORTHWESTERLY FLOW
WILL CONTINUE ACROSS THE EASTERN BERING, EASTERN ALEUTIANS AND
AKPEN, THOUGH WINDS WILL GRADUALLY DIMINISH THROUGH THE DAY AS THE
PRESSURE GRADIENT RELAXES. COLD AIR ADVECTION WILL KEEP
TEMPERATURES BELOW RECENT VALUES, WITH SNOW LEVELS FALLING TO
AROUND 2000 FT OR LOWER. THIS MAY ALLOW SHOWERS TO FALL AS SNOW
ACROSS HIGHER ELEVATIONS OF SOUTHWEST ALASKA AND THE AKPEN, WITH A
RAIN/SNOW MIX STILL POSSIBLE AT TIMES NEAR PORTIONS OF THE
KUSKOKWIM DELTA COAST.
HEADING INTO MONDAY, THE INITIAL LOW CONTINUES TO PULL FARTHER
AWAY WHILE BROAD UPPER-LEVEL TROUGHING REMAINS ACROSS SOUTHERN
ALASKA. WINDS CONTINUE TO WEAKEN ACROSS THE EASTERN BERING AND
AKPEN, WITH GRADUALLY QUIETER CONDITIONS COMPARED WITH THIS
WEEKEND. HOWEVER, THE LINGERING COLD AIR MASS AND CYCLONIC FLOW
WILL MAINTAIN SCATTERED SHOWERS ACROSS PORTIONS OF SOUTHWEST
ALASKA AND THE ALEUTIANS THROUGH MONDAY EVENING. ATTENTION THEN
TURNS FARTHER WEST AS THE NEXT DISTURBANCE BEGINS APPROACHING THE
WESTER BERING/ ALEUTIANS BEYOND THE SHORT-TERM PERIOD.
LM
.LONG TERM FORECAST (DAYS 4 THROUGH 7: TUESDAY THROUGH
FRIDAY)...
THE LONGTERM PERIOD BEGINNING TUESDAY MORNING WILL START OUT WITH
A LONGWAVE TROUGH EXTENDING ACROSS MUCH OF MAINLAND ALASKA DOWN
INTO THE ALASKA GULF. A GALE FORCE LOW WILL LIKELY BE MATURING AND
REACHING MAXIMUM INTENSITY SOMEWHERE OVER THE CENTRAL TO EASTERN
GULF. CURRENT MODEL CONSENSUS SUGGESTS THIS SYSTEM WILL STALL OUT
OVER OPEN WATERS AS IT SLOWLY WEAKENS THROUGH THE MIDDLE OF NEXT
WEEK, RESULTING IN LIMITED IMPACTS TO SOUTHCENTRAL. OUT TO THE
WEST, A LONGWAVE RIDGE IS ANTICIPATED TO BE MOVING ACROSS MUCH OF
THE BERING SEA IN BETWEEN THE GULF LOW AND A SHORTWAVE TROUGH AND
ATTENDANT LOW EVOLVING NEAR THE KAMCHATKA PENINSULA ON TUESDAY.
MUCH OF THE REMAINDER OF THE LONG TERM BEYOND TUESDAY WILL HINGE
HEAVILY ON THE DEGREE OF INTERACTION BETWEEN THE TROUGH/LOW
MOVING OFF OF KAMCHATKA INTO THE WESTERN BERING AND THE REMNANTS
OF WHAT IS CURRENTLY TYPHOON DUJUAN OUT IN THE WEST PACIFIC.
DUJUAN WILL RECURVE NORTH AND EAST AFTER MAKING A CLOSE PASS WITH
JAPAN THIS WEEKEND, EVENTUALLY APPROACHING THE WESTERN PARTS OF
THE ALEUTIAN CHAIN AFTER TRANSITIONING TO AN EXTRATROPICAL LOW
AROUND TUESDAY TO WEDNESDAY NEXT WEEK. MODELS ARE STILL STRUGGLING
QUITE A BIT TO DETERMINE HOW THE REMNANTS OF DUJUAN WILL BEHAVE
AS THE CENTER GETS CLOSER TO THE SEPARATE LOW PRESSURE SYSTEM
PROGRESSING ACROSS THE BERING. SOME EARLIER DETERMINISTIC
SOLUTIONS AND CURRENT EPS/GEFS ENSEMBLE MEMBERS SUGGEST THAT A
STRONG PHASING INTERACTION COULD OCCUR BETWEEN THE TWO LOWS,
PERHAPS RESULTING IN A MUCH STRONGER LOW THAT DEEPENS RAPIDLY
SOMEWHERE ACROSS THE SOUTHERN BERING SEA AND ALEUTIANS/AKPEN AS
THE TWO SYSTEMS ESSENTIALLY MERGE. IF THIS COMES TO FRUITION
(ABOUT A 20-30% CHANCE), HIGH WINDS AND WAVES COULD BECOME A
SUBSTANTIAL HAZARD ACROSS A LARGE PORTION OF THE BERING SEA,
ALEUTIANS AND POSSIBLY SOUTHWEST TOWARDS THE MIDDLE TO LATTER PART
OF NEXT WEEK.
IN CONTRAST TO THE SCENARIO ABOVE, MUCH OF THE 12Z DETERMINISTIC
GUIDANCE COMING IN TODAY IS DEPICTING DUJUAN'S REMNANTS TAKING A
LITTLE MORE TIME TO MOVE NORTHEAST ACROSS THE NORTH PACIFIC,
EFFECTIVELY CAUSING IT TO MISS THE STRONGER INTERACTION WITH THE
OTHER LOW PROGRESSING ACROSS THE BERING SEA. THIS VERSION OF
EVENTS (MORE LIKELY SCENARIO, AROUND 70% CHANCE) WOULD KEEP
DUJUAN TRACKING OFF TO THE SOUTH OF THE ENTIRE ALEUTIAN CHAIN,
WITH AN OVERALL LOWER THREAT FOR STRONG WINDS AND LARGE WAVES
ACROSS THE BERING SEA NEAR THE SECONDARY LOW TO THE NORTH. EVEN
SO, THE LOW MOVING OFF OF KAMCHATKA COULD STILL PULL A SIGNIFICANT
AMOUNT OF MOISTURE NORTH FROM DUJUAN'S REMNANTS AS THEY PASS TO
THE SOUTH, ENOUGH TO SUPPORT A HEAVY RAIN THREAT ACROSS PARTS OF
THE PRIBILOFS, ALEUTIANS AND SOUTHWEST SOMETIME BETWEEN WEDNESDAY
AND FRIDAY AS THE SYSTEM TRACKS NORTHEAST TOWARDS THE WESTERN
COASTLINE. THE INFLUX OF WARM, MOIST AIR COULD ALSO HELP DEEPEN
THE KAMCHATKA SYSTEM TO A GALE FORCE LOW AS IT TRACKS ACROSS THE
BERING, SO THE WIND AND WAVE POTENTIAL ACROSS THE ALEUTIANS AND
SOUTHWEST WOULD CERTAINLY NOT BE ZERO IN THIS CASE. BOTTOM LINE,
ANTICIPATE A STRONG LOW TO AFFECT PARTS OF THE ALEUTIANS, BERING
AND SOUTHWEST NEXT WEEK, REGARDLESS OF EXACTLY HOW THE REMNANTS OF
DUJUAN PLAY A ROLE.
MEANWHILE, MUCH QUIETER CONDITIONS ARE EXPECTED FOR THE MOST PART
ACROSS SOUTHCENTRAL BY THE MIDDLE OF NEXT WEEK. A SEASONABLY COOL
AIR MASS WILL BE IN PLACE ACROSS THE REGION INITIALLY, BUT SOME
WARMING IS LIKELY TOWARDS WEDNESDAY AND THURSDAY AS THE BERING
RIDGE MOVES OVERHEAD. THERE COULD BE A THREAT FOR STRONG SOUTHERLY
GAP WINDS TO DEVELOP LATE IN THE WEEK ALONG WITH INCREASING RAIN
CHANCES, BUT THIS WILL BE HIGHLY DEPENDENT ON THE COMPLEX AND
UNCERTAIN INTERACTION BETWEEN MULTIPLE SYSTEMS OUT WEST AS
DESCRIBED ABOVE.
-AS
AVIATION
PANC...LIGHT AND VARIABLE WINDS COMBINED WITH LINGERING LOW-LEVEL
MOISTURE COULD RESULT IN PATCHY FOG NEAR OR OVER THE TERMINAL
SATURDAY MORNING, OTHERWISE MAINLY MVFR TO LOW VFR CEILINGS ARE
EXPECTED THROUGH THE MORNING HOURS. VFR CEILINGS ARE LIKELY TO
PREVAIL BY THIS AFTERNOON, ALTHOUGH PERIODS OF MVFR CEILINGS
REMAIN POSSIBLE WITH ANY SHOWER ACTIVITY THAT IS ABLE TO DEVELOP
THIS AFTERNOON THROUGH THIS EVENING.
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