221
FXAK68 PAFC 200258
AFDAFC
SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
558 PM AKST TUE NOV 19 2024
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 THROUGH 3/TONIGHT
THROUGH FRIDAY AFTERNOON)...
KEY MESSAGES:
* WINDS HAVE PEAKED ACROSS MOST OF SOUTHCENTRAL AND WILL STEADILY
DIMINISH THROUGH TONIGHT, BECOMING LIGHT INLAND. GAP WINDS WILL
LINGER ALONG THE COAST THROUGH MUCH OF THE WEEK.
* THE COLDEST TEMPERATURES WILL BE TODAY THROUGH WEDNESDAY
MORNING, WITH WARMING TEMPERATURES FOR THE LATTER HALF OF THE
WEEK. DRY CONDITIONS WILL PERSIST THROUGH THE END OF THE WEEK
AND PERHAPS BEYOND.
OVERALL, THE CURRENT FORECAST REMAINS LARGELY UNCHANGED FROM THE
PREVIOUS FORECAST PACKAGE. THE BIGGEST UNCERTAINTIES IN THE
SHORT TERM WILL BE (1) THE TIMING AND MAGNITUDE OF PEAK GAP WINDS
ALONG THE COAST, AND (2) HONING IN ON MAX AND MIN TEMPERATURES
DUE TO NIGHTTIME RADIATIONAL COOLING AND THE INCOMING INVERSION.
DIVING INTO THE DETAILS... A STRONG HIGH AMPLITUDE RIDGE OVER THE
BERING SEA CONTINUES TO BUILD EASTWARD TOWARD MAINLAND ALASKA.
WINDS WILL STEADILY DIMINISH, BECOMING CALM FOR MOST INLAND
LOCATIONS LATER THIS EVENING. WITH A COLD AND DRY AIRMASS IN PLACE
AND LIMITED DAYLIGHT HOURS, TEMPERATURES WILL LIKELY HOLD STEADY
OR FALL AS THE WINDS DIMINISH. WHERE TEMPERATURES DO RISE WITH
AFTERNOON SUNSHINE, IT WILL BE BRIEF. TONIGHT WILL LIKELY BE THE
COLDEST NIGHT OF THE WEEK FOR A LOT OF LOCATIONS DESPITE SOME
PASSING CIRRUS CLOUDS AND WARMING UPPER LEVEL TEMPERATURES AS THE
RIDGE BUILDS IN. THE VERY STRONG SINKING AIR ON THE LEADING EDGE
OF THE RIDGE AND RESULTANT DRY AIRMASS WILL LEAD TO EFFECTIVE
RADIATIONAL COOLING AT THE SURFACE.
TEMPERATURES WILL THEN BEGIN TO STEADILY WARM EACH DAY FOR THE
REMAINDER OF THE WEEK UNDER THE INFLUENCE OF THE STRONG BLOCKING
RIDGE, WHICH WILL REMAIN CENTERED JUST UPSTREAM OVER BRISTOL BAY
AND THE ALASKA PENINSULA. FOR WESTERN PORTIONS OF SOUTHCENTRAL,
INCLUDING THE KENAI PENINSULA AND ANCHORAGE AREAS, TEMPERATURES
WILL WARM THE MOST AT ELEVATION, RISING ABOVE FREEZING BETWEEN
AROUND 1500 FEET AND 8000 FEET ELEVATIONS THURSDAY THROUGH FRIDAY.
DESPITE STRONG TEMPERATURE INVERSIONS, FOG IS UNLIKELY IN SUCH A
DRY AIRMASS. MEANWHILE, PERSISTENT NORTHERLY (OFFSHORE) FLOW EAST
OF THE UPPER RIDGE CENTER COMBINED WITH THERMAL AND PRESSURE
GRADIENTS BETWEEN INLAND AREAS AND THE COAST WILL MAINTAIN GAP
WINDS ALONG THE COAST ALONG WITH SOMEWHAT WARMER TEMPERATURES.
-SEB/CHEN
.SHORT TERM FORECAST SOUTHWEST ALASKA AND THE BERING
SEA/ALEUTIANS (DAYS 1 THROUGH 3)...
A LARGE RIDGE OF HIGH PRESSURE HAS BUILT OVER THE BERING SEA
NEUTRALIZING MUCH OF THE WEATHER PATTERN IN THE REGION. PORTIONS
OF THE BERING SEA UNDER THE RIDGE ARE SEEING CLEAR SKIES, WHILE
OTHERS ARE SEEING A RELATIVELY THIN LAYER OF MARINE STRATUS
BLANKETING THE SKIES. IN THE WESTERN ALEUTIANS, THE EASTERN EXTENT
OF A TROUGH IS RIDING UP THE EDGE OF THE RIDGE, GETTING STRETCHED
OVER THE WESTERN BERING INTO THE CHUKOTSK PENINSULA. THIS WESTERN
AREA OF THE BERING WILL SEE THE ONLY ACTIVE WEATHER, WITH
PERSISTENT RAINY WEATHER OVER SHEYMA AND NEARBY ISLANDS. AREAS OF
PATCHY FOG ARE POSSIBLE UNDER THE INFLUENCE OF THE RIDGE, AND AS
THE AXIS OF THE RIDGE BEGINS TO SLOWLY DRIFT EASTWARD TONIGHT,
THESE EFFECTS ARE EXPECTED TO SPREAD INTO COASTAL SOUTHWEST
ALASKA.
AS THE RIDGE APPROACHES THE MAINLAND, IT WILL BEGIN TO SPILL IN
WARMER AIR FROM THE WEST. THIS WARMER AIR WILL HELP ELEVATE THE
DAYTIME TEMPERATURES THIS WEEK, THE RIDGE IS ALSO EXPECTED TO
BRING IN CLEARING SKIES WHICH WILL ALSO ASSIST IN WARMING
SOUTHWEST DURING THE DAY. AT NIGHT HOWEVER, THESE CLEARING SKIES
WILL WORK TO QUICKLY RADIATE OUT AND COOL OFF. EXPECT SIMILARLY
COLD TEMPERATURES OVERNIGHT TONIGHT THAT WILL FLUCTUATE GIVEN THE
AMOUNT OF CLOUD COVER. AREAS INLAND SUCH AS THE LOWER KUSKOKWIM
VALLEY WILL LIKELY SEE MORE CLOUD COVER, BUT A DIMINISHED SIGNAL
FROM THE WARMER TEMPERATURES INCOMING FROM THE BERING. IN SUMMARY,
A GENERAL WARMING TREND IS EXPECTED THE NEXT FEW DAYS DURING
DAYTIME HOURS, AND COLD TEMPERATURES TO CONTINUE OVERNIGHT GIVEN
CONSISTENT CLEAR SKIES. PORTIONS OF THE SOUTHWEST COASTLINE TO SEE
AREAS OF FOG TO BECOME INCREASINGLY LIKELY BY WEDNESDAY NIGHT,
WITH A FOCUS OVER THE BRISTOL BAY COAST.
-CL
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 WILL PERSIST. GUSTY NORTHERLY WINDS ARE
EXPECTED TO DIMINISH THROUGHOUT THE EVENING AND BECOME NORTHERLY
AT 10 KNOTS OR LESS AFTER MIDNIGHT THROUGH WEDNESDAY.
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page