084
FXAK68 PAFC 190202
AFDAFC
SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
502 PM AKST MON NOV 18 2024
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 THROUGH 3/TODAY
THROUGH WEDNESDAY NIGHT)...
KEY MESSAGES:
* WIDESPREAD WINDY CONDITIONS WILL DEVELOP ACROSS SOUTHCENTRAL
THIS EVENING AND PERSIST INTO TUESDAY. THE STRONGEST WINDS ARE
EXPECTED IN THE MATANUSKA VALLEY, AND THOMPSON PASS/VALDEZ
AREAS. AREAS OF BLOWING AND DRIFTING SNOW ARE ALSO LIKELY ALONG
AREA ROADWAYS.
* AIR TEMPERATURES AND WIND CHILLS WILL CONTINUE TO TREND LOWER,
BRINGING THE COLDEST AIR OF THE WINTER TO SOUTHCENTRAL.
* THE COLD AIR OUTBREAK WILL NOT BE LONG-LIVED, WITH WARMING
TEMPERATURES DURING THE LATTER HALF OF THE WEEK. DRY CONDITIONS
WILL PERSIST THROUGH THE END OF THE WEEK AND PERHAPS BEYOND.
THE HIGHLY AMPLIFIED UPPER LEVEL FLOW OVER ALASKA WILL CONTINUE
WITH A STRONG RIDGE OVER THE BERING AND A TROUGH EXTENDING FROM
EASTERN MAINLAND ALASKA SOUTHWARD TO THE NORTHEAST PACIFIC. THE
APPROACHING UPPER RIDGE FROM THE WEST WILL BRING DEEP NORTHERLY
FLOW OVER MAINLAND ALASKA WITH COLD AIR ADVECTING SOUTHWARD ACROSS
SOUTHCENTRAL AND INTO THE GULF. THIS IS LEADING TO GUSTY GAP
WINDS THROUGH MOUNTAIN PASSES AS WELL AS BAYS ALONG THE COAST. AS
THE SURFACE LOW IN THE GULF CONTINUES TO EXIT SOUTHWARD, THE
STRONG PRESSURE GRADIENTS ACROSS SOUTHCENTRAL CONTINUE TO
STRENGTHEN AS HIGH PRESSURE BUILDS OVER INTERIOR ALASKA. FURTHER
MAINTAINING THE GRADIENT IS A SHORT-WAVE TROUGH DIGGING SOUTHWARD
ACROSS THE EASTERN INTERIOR TOWARD THE COPPER RIVER BASIN TONIGHT
INTO TOMORROW EVENING, ALLOWING FOR WIDESPREAD WINDY CONDITIONS
AND SUB-ZERO WIND CHILL TEMPERATURES THROUGH TOMORROW AFTERNOON.
MODELS ARE IN GOOD AGREEMENT ON THE TRACK OF THE MENTIONED UPPER
LEVEL SHORT-WAVE DIGGING SOUTHWARD ACROSS THE STATE AND CONTINUING
INTO THE GULF LATE TONIGHT/EARLY TUESDAY. THE PASSAGE OF THE
TROUGH WILL ENHANCE WINDS ACROSS THE REGION, WITH STRONG NORTHERLY
FLOW, COLD AIR ADVECTION, AND SUBSIDENCE BEHIND THE TROUGH. GIVEN
THE TRACK EAST OF THE VALDEZ/CORDOVA AREAS, AS WELL AS THE TIMING
OF FORCING MECHANISMS FOR WINDS NOT BEING IN SYNC, WINDS WILL BE
GUSTY BUT SHOULD NOT STRENGTHEN ENOUGH TO BECOME DAMAGING FOR
THESE AREAS. A HIGH WIND WARNING CONTINUES THROUGH EARLY TUESDAY
MORNING FOR THOMPSON PASS (75 MPH GUSTS). THE FORECAST FOR STRONG
WINDS ACROSS THE MATANUSKA VALLEY AND DOWN KNIK ARM TOWARD NORTH
ANCHORAGE IS ON TRACK, THOUGH THE ONSET HAS BEEN SLIGHTLY SLOWER
THAN EXPECTED. REGARDLESS, WINDS ARE EXPECTED TO PICK UP THIS
EVENING AND PERSIST THROUGH TOMORROW MORNING. THE SPECIAL WEATHER
STATEMENT HIGHLIGHTING THE LIKELIHOOD OF BLOWING SNOW CONTINUES
INTO TOMORROW MORNING AS BLOWING AND DRIFTING SNOW ACROSS ROADWAYS
AND REDUCTION IN VISIBILITY REMAINS A THREAT.
WINDS AND SUB-ZERO WIND CHILLS WILL BEGIN TO SUBSIDE TUESDAY
MORNING THROUGH TUESDAY AFTERNOON AS THE UPPER LEVEL RIDGE BUILDS
IN FROM THE WEST. CLOSER TO THE COAST, PRESSURE AND THERMAL
GRADIENTS WILL PERSIST ALLOWING FOR COASTAL GAP WINDS TO LINGER
THROUGH MID WEEK. BY WEDNESDAY, WARM AIR ALOFT WILL MOVE IN WITH
THE UPPER LEVEL RIDGE. THIS WILL GRADUALLY WARM TEMPERATURES
EVERYWHERE, WITH THE MOST AGGRESSIVE WARMING TAKING PLACE IN THE
MOUNTAINS. BELOW-ZERO LOW TEMPERATURES ARE EXPECTED TO PERSIST
THROUGH MIDWEEK FOR PORTIONS OF THE COPPER RIVER BASIN AS THE
EXISTING COLD AIRMASS IN PLACE IS SLOW TO WARM UP.
.SHORT TERM FORECAST SOUTHWEST ALASKA AND THE BERING
SEA/ALEUTIANS (MONDAY NIGHT THROUGH THURSDAY)...
KEY POINTS THROUGH MID-WEEK:
* STRONG WINDS THROUGH THE GAPS AND PASSES FROM COLD BAY TO PORT
HEIDEN INTO TONIGHT, DECREASING BY TUESDAY MORNING.
* THE FIRST ARCTIC AIR MASS MOVES OVER SOUTHWEST ALASKA THIS
EVENING.
* STRONG HIGH PRESSURE BRINGS WARM AIR TO THE ALEUTIANS, BERING
SEA AND MOST OF SOUTHWEST ALASKA LATE TOMORROW THROUGH MID-
WEEK.
AN INCREDIBLY LARGE RIDGE STRETCHING FROM THE WESTERN ALEUTIANS,
NORTHWEST TROUGH THE BERING, WILL CONTINUE TO DOMINATE THE
WEATHER PATTERN FOR THE WEEK. OVERNIGHT A WEAK UPPER LEVEL WAVE
WILL SLIDE ACROSS THE NORTHERN PERIPHERIES OF THE RIDGE, BRINGING
AN INCREASED CHANCE FOR LIGHT SNOW SHOWERS TO THE PRIBILOF
ISLANDS. THIS NORTHERLY WIND REGIME, WITH MOSTLY CLEAR SKIES,
WILL BRING IN AN INCREDIBLY COLD TEMPERATURES ACROSS THE INTERIOR
TONIGHT. ONE CAVEAT IS WHERE CLOUDS LINGER AND DO NOT THIN OUT
THIS EVENING, THEY WILL STICK AROUND OVERNIGHT HELPING TO KEEP
TEMPERATURES UP.
STARTING TUESDAY AFTERNOON, THE PREVIOUSLY MENTIONED UPPER LEVEL
DISTURBANCE WILL LOWER CLOUDS ALONG THE Y-K DELTA AND PRODUCE
FLURRIES. NO SNOW ACCUMULATION IS EXPECTED AS THE ATMOSPHERE WON'T
BE ORGANIZED FOR EFFICIENT SNOW PRODUCTION. AS THE WEEK PUSHES
ON, THE UPPER LEVEL RIDGE WILL KEEP INCHING EAST. A SURGE OF
WARMTH IS EXPECTED AS THIS HAPPENS. DAYTIME HIGHS FROM TUESDAY
WILL GO FROM THE LOWER SINGLE DIGITS TO MIDDLE AND UPPER 20'S BY
THURSDAY. THE LOWER LEVEL WARMTH WILL BE MAXIMIZED BETWEEN H92 AND
H85, ANOMALOUSLY REACHING THE 95TH TO 100TH PERCENTILE (OR
RECORD) FOR TEMPERATURE AROUND THE NOVEMBER 22-23RD DATE.
FOR THE WESTERN BERING, THE RIDGE OF HIGH PRESSURE WILL HAVE
TRANSITIONED EAST COME WEDNESDAY TO THURSDAY. A WEAK AREA OF LOW
PRESSURE WILL SHOOT NORTH OUT OF THE PACIFIC, CROSSING SHEMYA BY
THURSDAY AFTERNOON. WINDS WILL INCREASE TO THE EAST OF THIS LOW AS
A WARM FRONT LIFTS ACROSS THE ALEUTIANS, BRINGING MORE WARMTH AND
RAIN.
LONG TERM FORECAST (DAYS 4 THROUGH 7: FRIDAY THROUGH MONDAY)
ON THE ALASKA WEATHER MAP, HIGH PRESSURE MUSCLES ITS WAY ACROSS
THE SOUTHERN HALF OF THE STATE THROUGH THE FORECAST PERIOD. THIS
RIDGE BRINGS LIGHT WINDS, DRY CONDITIONS AND MORE MODERATE
TEMPERATURES IN THE ZONAL FLOW ACROSS MOST OF THE STATE THROUGH
THE WEEKEND, ALTHOUGH COOLEST OVERALL TEMPERATURES SHOULD LINGER
OVER THE EASTERN INTERIOR THROUGH MONDAY. PRECIPITATION, IF ANY,
WILL BE LIGHT AND INTERMITTENT THROUGH THE WEEKEND.
THE MOST ACTIVE WEATHER IS EXPECTED ACROSS THE WESTERN ALEUTIANS
AND BERING, AS A NUMBER OF LOW 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 WEAK WAVES THROUGH THE WEEKEND, BUT STEPPING UP BY
THE NEW WEEK WITH MORE DEVELOPED LOWS WORKING INTO THE PATTERN
FROM THE NORTH PACIFIC SUNDAY INTO MONDAY. 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.
AVIATION
PANC...VFR CONDITIONS WILL PERSIST. THE DEVELOPMENT OF THE GUSTY
NORTHERLY WINDS WAS DELAYED THIS AFTERNOON, BUT ONCE THEY DO
FINALLY DEVELOP, EXPECT WINDS TO STEADILY STRENGTHEN AND DURING
THE OVERNIGHT HOURS. THE STRONGEST CORE OF WINDS WILL COME OUT OF
THE MATANUSKA VALLEY AND DOWN KNIK ARM. HOWEVER, THERE IS NOTHING
TO DRIVE THESE WINDS ALL THE WAY SOUTH TO PANC. THUS, EXPECT WIND
GUSTS WILL PEAK RIGHT AROUND 30 KTS. WINDS WILL THEN QUICKLY
DIMINISH DURING THE DAY TUESDAY AS A RIDGE BUILDS IN FROM THE
WEST.
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