009
FXAK68 PAFC 151238
AFDAFC
SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
438 AM AKDT TUE SEP 15 2026
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 THROUGH 3:
TUESDAY THROUGH THURSDAY EVENING)...
KEY MESSAGES (UNCHANGED FROM PREVIOUS DISCUSSION):
- A STRONG FALL STORM SYSTEM MOVING INTO WESTERN ALASKA WILL BRING
STRONG SOUTHERLY WINDS AND PERIODS OF HEAVY RAIN TO
SOUTHCENTRAL DURING THE FIRST HALF OF THE WEEK.
- A WIND ADVISORY IS IN EFFECT FOR ANCHORAGE STARTING TUESDAY
MORNING RUNNING ALL THE WAY THROUGH MIDDAY WEDNESDAY.
- A WIND ADVISORY IS ALSO IN EFFECT FOR COASTAL PORTIONS OF THE
WESTERN KENAI PENINSULA FROM TUESDAY AFTERNOON THROUGH MIDDAY
WEDNESDAY.
- A HYDROLOGIC OUTLOOK IS IN EFFECT FOR SUSITNA VALLEY, AS STEADY
RAIN COULD CAUSE LOCALIZED PONDING AND RESULT IN RIVERS REACHING
BANKFULL CONDITIONS.
DISCUSSION:
AS OF 4 AM, SOUTHCENTRAL IS BLANKETED IN CLOUD COVER WITH BANDS OF
RAIN LIFTING NORTHEAST FROM COOK INLET ACROSS THE MAT-SU VALLEYS
AND COPPER RIVER BASIN AS A WARM FRONT MOVES THROUGH THE REGION.
THIS SURFACE FRONT AS ATTACHED TO A MATURE SURFACE LOW POSITIONED
NORTHWEST OF NUNIVAK ISLAND AND MOVING SLOWLY TO THE NORTH AND
EAST, TOWARD NORTON SOUND. THE RAIN THAT HAS FALLEN OVERNIGHT HAS
NOT AMOUNTED TO MUCH, WITH A TRACE TO A FEW HUNDREDTHS OF AN INCH
FALLING FROM THE KENAI PENINSULA TO THE MATANUSKA VALLEY. SLIGHTLY
MORE HAS FALLEN, BETWEEN 0.10" TO 0.20", ACROSS THE SUSITNA
VALLEY.
THE FORECAST REMAINS VERY MUCH ON TRACK, WITH THE SURFACE LOW OUT
WEST REACHING MAXIMUM INTENSITY THIS MORNING AS IT MOVES ALONG
THE YUKON DELTA TODAY AND INTO NORTON SOUND BY EARLY WEDNESDAY
MORNING. A STRONG SOUTHEAST TO NORTHWEST PRESSURE GRADIENT BETWEEN
THE LOW AND HIGHER PRESSURE LINGERING OVER THE GULF WILL SUPPORT
A DEVELOPING ROBUST SOUTHERLY WIND FLOW ACROSS SOUTHCENTRAL ALASKA.
GAP WINDS WILL QUICKLY DEVELOP BY MID TO LATE MORNING THROUGH THE
TURNAGAIN ARM, KNIK VALLEY AND COPPER VALLEY AND PICK UP IN
INTENSITY AS THE DAY PROGRESSES, REACHING MAXIMUM STRENGTH DURING
THE AFTERNOON HOURS ON TUESDAY. PEAK GUSTS OF UP TO 50 MPH ARE
STILL FORECAST FOR THE WESTERN AND SOUTHERN PARTS OF ANCHORAGE AND
NEAR GLENNALLEN, WITH GUSTY WINDS, ALBEIT WEAKER, FOR PALMER AND
WASILLA. THERE WILL BE A BREAK IN THE RAIN LASTING SEVERAL HOURS
DURING THE MORNING HOURS FOR MOST PLACES AWAY FROM THE MOUNTAINS,
BUT THE BREAK WILL NOT LAST LONG.
FOR THIS AFTERNOON, THE LOW WILL BEGIN TO WEAKEN AS IT HEADS INTO
THE WESTERN INTERIOR. A TRAILING COLD FRONT WILL BEGIN TO SWEEP
ACROSS SOUTHCENTRAL FROM WEST TO EAST, SENDING ANOTHER BATCH OF
MODERATE TO HEAVY RAINFALL THROUGH THE REGION AS IT PASSES
THROUGH. GAP WINDS ACROSS THE MAT VALLEY AND TURNAGAIN ARM WILL
SHUT OFF QUICKLY BEHIND THE FRONTAL PASSAGE BY TUESDAY NIGHT.
HOWEVER, A SECOND CORRIDOR OF STRONG WINDS, AIDED BY COLD AIR
ADVECTION AND A TRAILING SHORTWAVE, WILL EXTEND FROM KAMISHAK BAY
UP THE COOK INLET, SENDING ANOTHER ROUND OF STRONG SOUTH WINDS
INTO ANCHORAGE AND MUCH OF THE COASTLINE OF THE KENAI PENINSULA,
WITH GUSTS AGAIN TOPPING OUT AROUND THE 40 TO 50 MPH RANGE
OVERNIGHT ON TUESDAY NIGHT INTO EARLY WEDNESDAY MORNING. GUSTS OF
30 TO 40 MPH ARE ALSO POSSIBLE ACROSS THE SUSITNA VALLEY TO
TALKEETNA. IT'S WORTH NOTING THAT WE STILL HAVE YET TO SEE MOST
OF OUR TREES TRULY START TO TURN YELLOW, SO THEY WILL BE MORE
SUSCEPTIBLE TO DAMAGE FROM THE GUSTY WINDS THAN WHAT WE WOULD
EXPECT LATER IN THE FALL.
BY EARLY WEDNESDAY, RAIN WILL BEGIN TO TAPER OFF AS A DRIER AND
COOLER AIR MASS WORKS IN BEHIND THE FRONT AS IT EXITS TO THE EAST.
A FEW LINGERING SHOWERS COULD CONTINUE ON AND OFF THROUGHOUT THE
DAY, BUT OVERALL IT SHOULD BE MUCH DRIER COMPARED TO TUESDAY.
GUSTY SOUTH TO SOUTHWEST WINDS WILL SLOWLY RELAX THROUGH WEDNESDAY
AFTERNOON AS COLD AIR ADVECTION WANES AND AS A TRANSIENT UPPER
LEVEL RIDGE BEGINS TO BUILD BACK OVERHEAD. SHOWERS WILL LINGER
MOSTLY AT HIGHER ELEVATION, BUT AN INCOMING SHORTWAVE COULD
PRODUCE A BROADER REGION OF RAIN AROUND PRINCE WILLIAM SOUND
WEDNESDAY NIGHT INTO THURSDAY. BY THURSDAY AFTERNOON, ANOTHER LOW
MOVES FROM THE BERING SEA INTO SOUTHWEST ALASKA, BRINGING A RETURN
OF SHOWERS TO KODIAK ISLAND.
-KC/TM
.SHORT TERM FORECAST SOUTHWEST ALASKA/BERING SEA/ALEUTIANS
(DAYS 1 THROUGH 3: TODAY THROUGH FRIDAY MORNING)...
KEY MESSAGES:
* A COASTAL FLOOD ADVISORY IN EFFECT UNTIL 10AM WEDNESDAY FOR THE
KUSKOKWIM DELTA COAST. WATER LEVELS ARE EXPECTED TO RISE
ANYWHERE FROM 1.5 TO 4.0 FEET ABOVE THE NORMAL HIGH TIDE LINE.
* A WIND ADVISORY IS IN EFFECT UNTIL 1AM WEDNESDAY FOR THE
KUSKOKWIM DELTA COAST AND INTERIOR KUSKOKWIM DELTA FOR SOUTH
WINDS OF 35 TO 45 MPH WITH GUSTS TO 60 MPH EXPECTED.
DISCUSSION:
A STRONG LOW PRESSURE SYSTEM NORTH OF NUNIVAK ISLAND CONTINUES TO
DEEPEN THIS MORNING AS IT HEADS TO NORTON SOUND BY THIS EVENING.
STRONG GUSTY WINDS WILL CONTINUE TO TURN SOUTHWESTERLY THROUGH
TODAY AND THIS EVENING. STRONGEST WIND GUSTS OF 45 TO 55 MPH WITH
A FEW GUSTS UP TO 60 MPH WILL PEAK THIS MORNING THROUGH THIS
EVENING BEFORE SLOWLY DIMINISHING OVERNIGHT. A WIND ADVISORY
REMAINS IN EFFECT UNTIL 1AM WEDNESDAY MORNING FOR THE KUSKOKWIM
DELTA COAST AND THE INTERIOR KUSKOKWIM DELTA.
ANOTHER ISSUE WITH THIS STORM SYSTEM WILL BE THE STRONG
SOUTHWESTERLY FETCH COMING IN OFF OF KUSKOKWIM BAY AND THE EASTERN
BERING SEA. A COASTAL FLOOD ADVISORY REMAINS IN EFFECT UNTIL 10AM
WEDNESDAY MORNING WITH WATER LEVELS APPROACHING 4 FEET ABOVE THE
NORMAL HIGHEST TIDE LINE ALONG THE KUSKOKWIM DELTA COAST. THE
STRONG FALL STORM MOVES INLAND OF NORTON SOUND AND NORTHCENTRAL
ALASKA THROUGH WEDNESDAY. HOWEVER, SHOWERY CONDITIONS WILL PERSIST
ACROSS SOUTHWEST ALASKA AS ADDITIONAL SHORTWAVES MOVE ACROSS THE
AREA FROM THE EASTERN BERING SEA.
BACK TO THE WEST, AN UPPER-LEVEL LOW AND ASSOCIATED SURFACE LOW
MOVE OFF OF KAMCHATKA AND INTO THE WESTERN BERING BY THIS
AFTERNOON. ITS FRONT MAKES IT TO SHEMYA THIS MORNING AND AFTERNOON
AND SWEEPS EASTWARD TO ADAK/ATKA AND THE PRIBILOF ISLANDS BY
EARLY WEDNESDAY MORNING AND THEN TO NIKOLSKI/UNALASKA/AKUTAN BY
WEDNESDAY EVENING. THE ALASKA PENINSULA (AKPEN) WILL SEE SHOWERS
BEGIN THURSDAY MORNING AS THIS LOW MOVES TO THE CENTRAL BERING
NORTH OF THE PRIBILOF ISLANDS BY THEN. THIS LOW WILL ALSO
REINFORCE SOUTHWESTERLY FLOW ALOFT ACROSS MAINLAND SOUTHWEST
THROUGH THURSDAY INTO FRIDAY WHICH WILL ALLOW FOR SHOWERS TO
PERSIST ACROSS THE AREA THROUGH THE SAME TIMEFRAME. MORE
IMPORTANTLY, THIS LOW PRESSURE SYSTEM IS EXPECTED TO BE WAY WEAKER
THAN THE ONE CURRENTLY IMPACTING THE SOUTHWEST COAST TODAY AND
INTO WEDNESDAY.
LONG TERM FORECAST (DAYS 4 TO 7)
RIDGING ACROSS THE EASTERN ALEUTIANS AND SOUTHWEST ALASKA BREAKS
DOWN LATER THIS WEEK AS A LOW AND ITS ASSOCIATED TROUGH MOVES
THROUGH THE BERING SEA. THIS BERING LOW AND ITS ASSOCIATED FRONT
BRINGS RAIN SHOWERS AND A RETURN TO CLOUDY SKIES. AS THE
FRONT MOVES TOWARD THE MAINLAND, PERSISTENT NORTHWEST FLOW WILL
OVERTAKE THE ALEUTIANS BRINGING CONTINUED RAIN SHOWERS, FOG AND
CLOUDY SKY. MODELS ARE IN BETTER AGREEMENT ON THE GENERAL TRACK
OF A SECOND LOW CROSSING THE BERING SEA AND REACHING THE CENTRAL
ALEUTIANS THIS WEEKEND. IN ITS WAKE, IT WILL BRING A CHANGE TO
NORTHERLY WINDS FOR THE AK PEN, EASTERN ALEUTIANS AND SOUTHWEST
ALASKA EARLY NEXT WEEK.
A RECEDING RIDGE OF HIGH PRESSURE IN THE SOUTHERN GULF OF ALASKA
BRINGS THE RETURN OF SOUTHWEST TO NORTHEAST FLOW INTO SOUTHCENTRAL
FOR THE WEEK'S END. THIS FLOW RESULTS IN RAINY AND CLOUDY
CONDITIONS FOR THE PRINCE WILLIAM SOUND AND EASTERN KENAI
PENINSULA FORM LATE THIS WEEK INTO THE END OF NEXT WEEKEND. TIMING
AND EXACT LOCATION DIFFERENCES ARE PRESENT THOUGH A WEAK LOW MOVES
THROUGH THE NORTHERN GULF OF ALASKA IN THE LATTER PART OF THIS
WEEKEND BRINGING RAIN TO ALREADY SATURATED PRINCE WILLIAM SOUND
COASTLINE.
AVIATION
PANC...SOUTHEASTERLY WINDS WILL INCREASE RAPIDLY TUESDAY MORNING,
WITH GUSTS AROUND 35 KT LIKELY (70 TO 80%) BY MID TO LATE
MORNING. VFR CONDITIONS WITH OCCASIONAL LIGHT RAIN WILL PREVAIL
THROUGH THIS MORNING. HOWEVER, CEILINGS MAY REMAIN BETWEEN 3,000
FT AND 5,000 FT AT TIMES. CEILINGS WILL LOWER TO MVFR THIS
AFTERNOON AS STEADIER RAIN DEVELOPS, WITH MVFR CONDITIONS
PERSISTING THROUGH LATE TUESDAY EVENING. THE SOUTHEASTERLY WINDS
DURING THIS TIME MAY DIMINISH SLIGHTLY. HOWEVER, GUSTY WINDS FROM
THE SOUTH WILL REDEVELOP BY LATE TUESDAY NIGHT WITH GUSTS UP TO 40
KT LIKELY (60 TO 70%) BETWEEN 10 PM TUESDAY AND NOON WEDNESDAY.
LM/TM
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