356
FXAK68 PAFC 161332
AFDAFC
SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
532 AM AKDT TUE SEP 16 2025
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 THROUGH 3: TODAY
THROUGH THURSDAY NIGHT)...
SATELLITE IMAGERY REVEALS A LARGE AREA OF LOW PRESSURE CURRENTLY
POSITIONED ACROSS THE NORTHERN GULF OF ALASKA, WITH A LOW CENTER
JUST OFF TO THE EAST OF KODIAK ISLAND. PRECIPITATION CONTINUES TO
DRIVE NORTHWESTWARD INTO THE PRINCE WILLIAM SOUND, KENAI, AND
CHUGACH MOUNTAINS AMID STRONG SOUTHEAST/EAST FLOW ON THE NORTH
FLANK OF THE LOW. LOW-LEVEL CROSS-BARRIER FLOW WILL LIMIT
SPILLOVER PRECIPITATION, BUT A FEW AREAS OF LIGHT PRECIP CAN'T BE
RULED OUT FOR PORTIONS OF THE WESTERN KENAI, ANCHORAGE, AND MAT-
SU TODAY... PARTICULARLY IN THE MORNING HOURS. THE LOW OPENS INTO
A TROUGH OVER THE WESTERN GULF THIS EVENING AND SHOWER ACTIVITY
QUICKLY WANES.
THE NEXT SYSTEM IS STILL ON TRACK TO LIFT INTO THE EASTERN GULF THIS
EVENING, MAKING IT INTO THE NORTHERN GULF COAST BY SOMETIME ON
WEDNESDAY. RECENT TRENDS IN MODEL GUIDANCE HAVE THIS LOW SLIGHTLY
SLOWER AND FARTHER EAST THAN PREVIOUS RUNS. CROSS-BARRIER FLOW WILL
BE FAIRLY LIGHT WITH THIS SYSTEM, MEANING THAT PORTIONS OF THE
COPPER BASIN CAN EXPECT RAINFALL TO SPREAD NORTH LATE ON TUESDAY AND
CONTINUE INTO WEDNESDAY. THERE IS SOME UNCERTAINTY IN HOW FAR THE
PRECIPITATION MAKES IT, WITH EASTERN PRINCE WILLIAM SOUND LIKELY TO
SEE RAINFALL AT SOME POINT ON WEDNESDAY MORNING, BUT HOW MUCH AND
HOW LONG IT STICKS AROUND IS NOT CLEAR AT THIS TIME. WESTERN PRINCE
WILLIAM SOUND IS MORE LIKELY TO REMAIN COMPLETELY DRY. THE LOW
QUICKLY WEAKENS WEDNESDAY EVENING AS IT IS SHREDDED ON THE COASTAL
MOUNTAINS AND ONLY LIGHT SHOWERS LINGER IN THE COPPER BASIN AND
EASTERN PRINCE WILLIAM SOUND.
BY THURSDAY, A TRIPLE POINT LOW DEVELOPS ALONG A FRONT EXTENDING OFF
A BERING SEA LOW. THE TRIPLE POINT LOW TRACKS INTO THE WESTERN GULF
AND BRINGS ANOTHER ROUND OF RAIN AND GUSTY EASTERLY WINDS TO THE
NORTH GULF COAST. DOWNSLOPING APPEARS STRONGER WITH THIS SYSTEM, SO
INLAND PRECIPITATION IS EXPECTED TO BE QUITE LIMITED.
-BROWN/QUESADA
.SHORT TERM FORECAST SOUTHWEST ALASKA/BERING SEA/ALEUTIANS (DAYS
1 THROUGH 3)...
THE NEAR AND SHORT TERM FORECAST REMAINS ON TRACK. AS OF THIS
MORNING, SATELLITE IMAGERY REVEALS A DECAYING, OCCLUDED SURFACE
LOW SITUATED AROUND 150 MILES EAST OF KODIAK. A MID LEVEL CLOUD
DECK ON THE NORTHWESTERN SIDE OF THE LOW HAS MIGRATED WESTWARD
ACROSS SOUTHWEST ALASKA, WHICH HAS BEEN ENOUGH TO KEEP OVERNIGHT
LOWS A TOUCH WARMER THIS MORNING. THE PRESSURE GRADIENT FOR
SOUTHWEST ALASKA SOUTHWARD TO THE AK PEN HAS DECREASED OVERNIGHT,
WHICH HAS CAUSED NORTHERLY WINDS TO BECOME LIGHT THIS MORNING.
FARTHER WEST, TRANSIENT RIDGING CAN BE SEEN DRAPED NORTHWARD
ACROSS THE AK PEN WHILE A GALE FORCE FRONT MOVES ACROSS THE
CENTRAL ALEUTIANS. OCCASIONAL STORM FORCE GUSTS ARE STILL POSSIBLE
IN SOME OF THE OFFSHORE BERING ZONES, CLOSER TO THE ~977 MB
PARENT LOW LOCATED JUST NORTH OF THE WESTERN ALEUTIANS. CIMSS
PRECIPITABLE WATER GUIDANCE SHOWS THAT THIS FRONTAL SYSTEM HAS
TAPPED INTO DEEP TROPICAL MOISTURE, WHICH HAS SUPPORTED A SWATH OF
MODERATE RAINFALL AS THE FRONT TRAVERSES THE ALEUTIAN CHAIN.
ALOFT, A LIFTING AND WANING SHORTWAVE HAS MOVED EAST-
NORTHEASTWARD TOWARDS THE AK PEN, WHICH IN TURN HAS CAUSED A
COLLAPSE IN UPPER LEVEL SUPPORT FOR THE SURFACE BOUNDARY. THIS
TREND LOOKS TO CONTINUE AS THE FRONT PIVOTS AND SURFACE TROUGHING
BECOMES FLATTER AND MORE ELONGATED. GUIDANCE SHOWS THAT RAINFALL
RATES AND INTENSITY DECREASES HEADING INTO THIS AFTERNOON, WITH
THE REMNANTS OF THE FRONT APPROACHING THE PRIBILOF ISLANDS AND THE
EASTERN ALEUTIANS. COINCIDENTALLY, THE SURFACE LOW NORTH OF THE
WESTERN ALEUTIANS BEGINS A CYCLONIC LOOP AND RETROGRADES. WHILE
DOING SO, THE LOW BREAKS DOWN AND BEGINS TO EVOLVE INTO A COMPLEX
LOW PRESSURE SYSTEM. OPERATIONAL MODELS ARE IN GOOD AGREEMENT THAT
THE SYSTEM THEN MOVES MOSTLY EASTWARD AND NORTH OF THE ALEUTIAN
CHAIN THURSDAY MORNING, WITH SOME GUIDANCE OPENING THE LOW INTO A
TROUGH BY FRIDAY MORNING. IN THE UPPER LEVELS, A LONGWAVE TROUGH
OVER THE EASTERN BERING AND BRISTOL BAY REGION KEEPS MUCH OF THE
WESTERN DOMAIN IN A NEGATIVE OR ANTI-CYCLONIC VORTICITY ADVECTION
REGIME WITH A FAIRLY ZONAL UPSTREAM FLOW, WHICH SHOULD SUPPORT LOW
IMPACT WEATHER HEADING INTO THE WEEKEND.
-AM
LONG TERM FORECAST (DAYS 4 THROUGH 7: FRIDAY THROUGH MONDAY)
THE ACTIVE WEATHER PATTERN CONTINUES IN THE EXTENDED FORECAST AS
A BROAD UPPER LEVEL LOW SLOWLY MOVES OVER THE ALASKA PENINSULA
INTO THE GULF OF ALASKA. WEST-TO-EAST ZONAL FLOW OVER THE MAJORITY
OF THE REGION WILL MAINTAIN THE ACTIVE PATTERN, HOWEVER DIMINISH
THE LIKELIHOOD FOR HIGHLY IMPACTFUL WEATHER PATTERNS. CONFIDENCE
IS STRONG THAT BY SATURDAY MORNING, A LOW PRESSURE SYSTEM WILL
ESTABLISH OVER THE NORTHERN GULF OF ALASKA, BRINGING THE POTENTIAL
FOR HEAVY RAIN AND STRONG WINDS TO THE SOUTHCENTRAL COAST.
DEPENDING ON THE LOW'S ORIENTATION, THERE IS THE CHANCE FOR A
BARRIER JET TO FORM ALONG THE MARINE AREAS OF THE NORTHERN GULF
COAST EARLY FRIDAY. THROUGH THE WEEKEND, RAIN IS EXPECTED TO
CONTINUE ALONG THE GULF COAST AND INTO SOUTHWEST ALASKA. AREAS OF
GUSTY WINDS THROUGH THE SOUTHERN GAPS AND PASSES OF THE ALASKA
PENINSULA AND EASTERN ALEUTIANS THAT WEEKEND AS WELL, GIVEN THE
PERSISTENT NORTHWESTERLY FLOW IN THE AREA. IN ADDITION,
SOUTHWESTERLY UPPER LEVEL FLOW WILL BRING THE POTENTIAL FOR RAIN
TO MOVE UP COOK INLET AND INTO THE MAT-SU VALLEYS.
-CL
AVIATION
PANC...VFR CONDITIONS WILL PERSIST THROUGH THE TAF PERIOD. A FEW
SHOWERS COULD MOVE OVER THE TERMINAL THIS MORNING, BUT CEILING
REDUCTIONS TO MVFR OR LOWER ARE NOT EXPECTED. LLWS WILL BE A SMALL
POSSIBILITY DUE TO STRONG SOUTHEASTERLIES ALOFT PERSISTING UNTIL
THIS AFTERNOON, HOWEVER, THE STRONGEST WINDS WILL LIKELY REMAIN
WELL ABOVE 2000 FT AND LIMIT POTENTIAL FOR SIGNIFICANT SHEAR IN
THE LOW LEVELS. NORTH WINDS AROUND 5 TO 10 KTS WILL PERSIST AT
THE SURFACE.
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