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FXAK68 PAFC 201352
AFDAFC
SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
452 AM AKST WED NOV 20 2024
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 THROUGH 3/TODAY
THROUGH FRIDAY NIGHT)...
A STRONG HIGH AMPLITUDE BLOCKING RIDGE IS CENTERED NEAR THE EASTERN
ALEUTIANS THIS MORNING, WITH A RIDGE AXIS EXTENDING NORTHEASTWARD
ACROSS MAINLAND ALASKA. THIS RIDGE WILL REMAIN IN PLACE THROUGH
THE END OF THE WORK WEEK, MAINTAINING DRY CONDITIONS FOR SOUTHCENTRAL,
KODIAK ISLAND, AND THE GULF OF ALASKA. THE FOCUS OF THE FORECAST
UPDATES THIS MORNING WAS ON GAP WINDS AND TEMPERATURES. NORTHERLY
OFFSHORE FLOW ALONG THE EASTERN SIDE OF THE RIDGE IS COMBINING
WITH TIGHT THERMAL AND PRESSURE GRADIENTS TO MAINTAIN STRONG AND
GUSTY GAP WINDS ALONG THE COAST - INCLUDING SEWARD AND RESURRECTION
BAY; WHITTIER AND PASSAGE CANAL; AND THOMPSON PASS, VALDEZ AND
DOWN THROUGH THE NARROWS AND ARM. THERE WILL BE SOME MINOR
FLUCTUATIONS IN THE STRENGTH OF THESE WINDS THROUGH THE END OF
THE WEEK, BUT THEY ARE NOT GOING AWAY ANYTIME SOON.
THERE WILL HOWEVER, BE A SIGNIFICANT WARMING OF TEMPERATURES.
THE RIDGE AXIS OVER THE MAINLAND WILL ROTATE SOUTHWARD ACROSS
SOUTHCENTRAL TODAY THROUGH THURSDAY, BRINGING MUCH WARMER LOW
LEVEL AIR FROM SOUTHWEST ALASKA. FOR INLAND VALLEYS OF
SOUTHCENTRAL WHERE WINDS ARE LIGHT, WARMING WILL BE GRADUAL AND
TEMPERATURES WILL LARGELY REMAIN BELOW FREEZING. HOWEVER,
TEMPERATURES IN THE MOUNTAINS - BETWEEN AROUND 2500 FEET AND
8000 FEET - WILL RISE ABOVE FREEZING, WITH TEMPERATURES AS HIGH
AS THE 40S. WARMING WILL BE MOST SIGNIFICANT FOR THE KENAI
MOUNTAINS AND WESTERN CHUGACH MOUNTAINS. AS NORTHERLY FLOW SINKS
DOWN THE MOUNTAINS TO THE COAST THE AIR MASS WILL WARM FURTHER.
THUS COASTAL LOCATIONS AT SEA LEVEL ALONG WITH KODIAK AND MUCH
OF THE GULF WATERS WILL ALSO SEE TEMPERATURES REACH THE 40S.
THE COPPER RIVER BASIN AND SURROUNDING MOUNTAINS WILL REMAIN
NOTABLY COOLER. THE WARMEST DAY LOOKS TO BE THURSDAY. AS THE
RIDGE AXIS SHIFTS DOWN OVER THE GULF, COLDER AIR WILL THEN
WORK BACK INTO SOUTHCENTRAL LATE THURSDAY THROUGH FRIDAY.
-SEB
.SHORT TERM FORECAST SOUTHWEST ALASKA AND THE BERING SEA/ALEUTIANS
(DAYS 1 THROUGH 3: TODAY THROUGH SATURDAY MORNING)...
A LARGE OF RIDGE OF HIGH PRESSURE, WITH ITS AXIS CENTERED OVER
THE EASTERN ALEUTIANS AND EASTERN BERING SEA, CONTINUES TO NUDGE
EASTWARD OF MAINLAND SOUTHWEST ALASKA TODAY. THIS WILL BE THE CASE
OVER THE NEXT FEW DAYS INTO SATURDAY WITH THE MAIN RESULTS FROM
THE RIDGE BEING WARMER DAYTIME TEMPERATURES AND COLD NIGHTS WITH
RADIATIONAL COOLING TAKING AFFECT WITH CLEARER CONDITIONS. THE
WILD-CARD WILL BE WHERE LOW-LEVEL MOISTURE GETS LOCKED IN AT THE
SURFACE AND WHETHER PATCHY FOG FORMS OR POCKETS OF LOW STRATUS
CLOUDS.
FARTHER OUT WEST AND BEHIND THE SPRAWLING RIDGE, A SERIES OF
SHORTWAVES WILL CONTINUE TO AFFECT THE WESTERN ALEUTIANS THROUGH
THURSDAY BRINGING LIGHT RAIN AND GUSTY SOUTHEASTERLY WINDS. SOME
SHOWERS MAY CLIP ADAK, ESPECIALLY ON THURSDAY. ENERGY MOVING
EASTWARD OFF OF KAMCHATKA WILL INTERACT WITH THE SHORTWAVES IN THE
WESTERN BERING/NORTH PACIFIC THURSDAY AFTERNOON AND SPIN UP A
SURFACE LOW PRESSURE IN THE WESTERN BERING THURSDAY EVENING. THIS
WILL HELP TO ENHANCE SHOWERS IN THE WESTERN ALEUTIANS WHILE
ENHANCING SOUTHEAST WINDS ACROSS THE CENTRAL ALEUTIANS FRIDAY. THE
FRONT THEN PUSHES EAST TO THE CENTRAL ALEUTIANS FRIDAY PROVIDING
ANOTHER ROUND OF SHOWERS TO THE AREA FRIDAY AND INTO SATURDAY
MORNING AS THE FRONT WEAKENS. THERE IS GOOD CONFIDENCE THAT THE
SYSTEM WILL TRACK NORTHWARD IN THE WESTERN BERING TO NEAR THE GULF
OF ANADYR DURING THE LATTER HALF OF THE WEEKEND.
LONG TERM FORECAST (DAYS 4 THROUGH 7: SATURDAY THROUGH TUESDAY)
A BROAD UPPER LEVEL RIDGE SPREADS ACROSS MOST OF SOUTHERN ALASKA
THROUGH THE FORECAST PERIOD. SURFACE HIGH PRESSURE EXTENDING FROM
A CANADIAN HIGH CENTER IS EXPECTED TO HOLD THROUGH THE WEEKEND.
WEATHER ACROSS THE MAINLAND WITH IS EXPECTED TO HAVE LIGHT WINDS,
OVERALL DRY CONDITIONS AND MODERATE TEMPERATURES IN THE ZONAL FLOW
OVER THE STATE, ALTHOUGH COOLEST OVERALL TEMPERATURES SHOULD
LINGER OVER THE EASTERN INTERIOR THROUGH TUESDAY. PRECIPITATION,
IF ANY, WILL BE LIGHT AND INTERMITTENT THROUGH THE WEEKEND WITH A
VERY SMALL AND BRIEF RISK OF FREEZING PRECIPITATION OVER INTERIOR
LOCATIONS. A FRONT IS EXPECTED TO BRING RAIN OR MIXED RAIN AND
SNOW TO WESTERN ALASKA LATE SUNDAY NIGHT, WITH LESSER AMOUNTS
WORKING INTO THE CENTRAL PARTS OF THE STATE THROUGH TUESDAY.
THE MOST ACTIVE WEATHER WILL OCCUR ACROSS THE WESTERN ALEUTIANS
AND BERING, AS A NUMBER OF SURFACE LOWS, FRONTS AND TROUGHS RIDE
UP OVER THE WESTERN FLANK OF THE RIDGE. THESE WEAK SYSTEMS BRING
AREAS OF OCCASIONALLY MODERATE RAINFALL AND SOME GUSTY WINDS.
FORECAST MODELS INDICATE STEPPING UP BY THE NEW WEEK WITH MORE
DEVELOPED LOWS WORKING OVER THE BERING INTO THE MAINLAND FROM THE
NORTH PACIFIC. THESE STRONGER LOWS BRING LOCALLY HEAVY RAINS AND
GUSTIER WINDS UP TO GALE FORCE OVER THE WESTERN ALEUTIANS AND
BERING, DRIFTING INTO THE CENTRAL ALEUTIANS AND BERING FOR MONDAY
AND TUESDAY.
.AVIATION...
PANC...VFR CONDITIONS AND LIGHT WINDS WILL PERSIST.
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