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FXAK68 PAFC 161419
AFDAFC
SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
519 AM AKST SAT NOV 16 2024
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 THROUGH 3/TODAY
THROUGH MONDAY NIGHT)...
A LONG-WAVE TROUGH IS CENTERED OVER NEARLY ALL OF ALASKA AND THE
BERING SEA AND EXTENDS SOUTHWARD INTO THE NORTH PACIFIC. THE
TROUGH IS ANCHORED BY A CLOSED UPPER LOW OVER NORTHWEST ALASKA.
OTHERWISE, A SERIES OF MOSTLY WEAK SHORT-WAVES ARE TRANSITING THE
LONG-WAVE WITH A GENERAL WEST TO EAST MOTION. MOST SIGNIFICANT
FOR SOUTHCENTRAL AND THE GULF THIS MORNING, A VERTICALLY STACKED
LOW OVER THE NORTHERN GULF IS SLOWLY EXITING EASTWARD. AREAS OF
LIGHT PRECIPITATION CONTINUE IN THE PRINCE WILLIAM SOUND AREA AND
UP INTO THE SOUTHERN COPPER RIVER BASIN. A POCKET OF WARMER AIR
RIGHT NEAR THE LOW CENTER IS LEADING TO RAIN IN CORDOVA, WHILE
PRECIPITATION ACROSS THE REMAINDER OF SOUTHCENTRAL IS ALL IN THE
FORM OF SNOW.
MEANWHILE, A WEAK SHORT-WAVE OVER COOK INLET IS TRACKING
NORTHEASTWARD TOWARD ANCHORAGE AND THE MAT-SU. KENAI RADAR AND
AREA SURFACE OBS SHOW A LARGE AREA OF LIGHT SNOW ACROSS MUCH OF
THE WESTERN KENAI PENINSULA, ANCHORAGE, AND THE MAT-SU. JUST
UPSTREAM, A SHORT-WAVE IS DIGGING OUT AHEAD OF THE AFOREMENTIONED
UPPER LOW CENTER - ACROSS SOUTHWEST AK AND TOWARD COOK INLET.
A COLD FRONT WHICH ORIGINATED WITH THE NORTHERN GULF LOW HAS NOW
CROSSED ALL THE WAY TO THE EASTERN GULF. THIS LED TO AN UPTICK IN
WINDS ACROSS THE GULF WATERS. HOWEVER, AN ARCTIC FRONT, WITH MUCH
COLDER AIR IS FOLLOWING BEHIND , CROSSING THE ALASKA PENINSULA
INTO THE WESTERN GULF EARLY THIS MORNING. THIS IS LEADING TO
RAPIDLY STRENGTHENING WINDS IN FOR THE KODIAK ISLAND WATERS,
ALONG WITH STRONG AND GUSTY GAP WINDS.
THE DIGGING SHORT-WAVE OVER SOUTHWEST AK WILL HELP KEEP LIGHT SNOW
GOING AS IT MOVES INTO COOK INLET TODAY. IT WILL THEN CONTINUE
DIGGING SOUTHEASTWARD INTO THE GULF TONIGHT, BRINGING AN END TO
THE UPPER LEVEL FORCING. HOWEVER, ARCTIC AIR WILL BE USHERED
ACROSS ALL OF SOUTHCENTRAL AND COMBINE WITH UPSLOPE FLOW TO
MAINTAIN LIGHT SNOWFALL ALONG THE NORTH TO WEST SIDE OF MOUNTAIN
RANGES. SNOW ACCUMULATION THROUGH TONIGHT WILL GENERALLY BE QUITE
LIGHT. THE HIGHEST SNOW ACCUMULATION, ON THE ORDER OF 3 TO 6
INCHES, WILL BE FOCUSED RIGHT ALONG THE FRONT RANGE CHUGACH IN
ANCHORAGE AND UP NORTH TO EAGLE RIVER AND PALMER. SNOW WILL
FINALLY TAPER OFF DURING THE DAY SUNDAY.
THE SHORT-WAVE WHICH DIGS INTO THE GULF WILL BE FOLLOWED BY THE
UPPER LOW CENTER, WHICH WILL OPEN INTO A TROUGH AS IT REACHES THE
WESTERN GULF SUNDAY EVENING. AN AMPLIFYING RIDGE OVER THE WESTERN
BERING SEA SUNDAY WILL CONTINUE TO AMPLIFY AS IT SHIFTS EASTWARD
TOWARD MAINLAND AK MONDAY. MEANWHILE, A SURFACE LOW WILL LINGER IN
THE EASTERN GULF, WHILE PRESSURE RISES OVER MAINLAND AK AND THE
BERING SEA. THE END RESULT WILL BE A PROLONGED PERIOD OF STRONG
GEOSTROPHIC WIND, PRESSURE GRADIENT GAP WINDS, AND COLD AIR
ADVECTION FOR SOUTHCENTRAL, KODIAK ISLAND, AND THE GULF WATERS.
SOME OF THE STRONGEST WINDS WILL BE TODAY THROUGH SUNDAY MORNING
OVER THE WESTERN GULF AND KODIAK ISLAND COINCIDENT WITH THE
STRONGEST COLD AIR ADVECTION AND TIGHTEST PRESSURE GRADIENTS.
WHILE THE UPPER LEVEL JET DOESN'T DEVELOP UNTIL MONDAY AHEAD OF
THE BUILDING RIDGE, LOW LEVEL FORCING IS IMPRESSIVE AND THE WIND
FORECASTS HAVE BEEN UPPED SIGNIFICANTLY WITH THIS MORNING'S
FORECAST PACKAGE. HURRICANE FORCE WIND GUSTS ARE LIKELY ALONG THE
SOUTH SIDE OF THE ALASKA PENINSULA INTO SHELIKOF STRAIT AS WELL AS
THE KAMISHAK BAY TO BARREN ISLANDS CORRIDOR. FORCING WON'T BE
QUITE AS STRONG OVER SOUTHCENTRAL, THOUGH STILL EXPECT WIDESPREAD
GAP WINDS THOUGH THE ALASKA RANGE AND THE COASTAL MOUNTAINS (KENAI
AND CHUGACH), WITH WINDS AFFECTING ALL OF THE PRINCE WILLIAM
SOUND/NORTH GULF COAST AREAS.
THIS WILL BE THE COLDEST AIRMASS OF THE WINTER FOR SOUTHCENTRAL.
TEMPERATURES WILL INITIALLY BE SLOW TO FALL FOR THE FIRST HALF OF
THE WEEKEND DUE TO EXTENSIVE CLOUD COVER AND GUSTY WINDS. CLEARING
SKIES SUNDAY THROUGH MONDAY WILL LEAD TO MORE PRECIPITOUS DROPS IN
TEMPERATURES, WITH WIDESPREAD SINGLE DIGITS BELOW ZERO TO SINGLE
DIGITS ABOVE ZERO EXPECTED BY MONDAY MORNING.
-SEB
.SHORT TERM FORECAST SOUTHWEST ALASKA AND THE BERING
SEA/ALEUTIANS (DAYS 1 THROUGH 3)...
SYNOPTICALLY, A LOW IN THE CHUKCHI SEA WILL SLOWLY ROTATE AND
MOVE SOUTHWARD ALONG THE SW ALASKA COASTLINE THE NEXT 48 HOURS
BRINGING CONTINUED WAVES OF MOISTURE THROUGH THE BERING SEA. ITS
SPEED AND SOUTHWARD PROGRESSION WILL BE INFLUENCED BY AN ARCTIC
LOW THAT WILL BRING MUCH COOLER AIR INTO SW ALASKA THIS WEEKEND.
ALSO, A DEEP TROUGH IN THE WESTERN BERING SEA WILL KEEP PERSISTENT
NORTH TO NORTHWEST WIND FLOW INTO NORTHERN ALEUTIANS AND ALASKA
PENINSULA THE NEXT 48 HOURS FURTHER KEEPING BOTH THE MOISTURE FLOW
AND COOLER AIR INTO THE NORTHERN ALEUTIANS AND ALASKA PENINSULA.
MORE SPECIFICALLY, THIS PERSISTENT NORTHWEST FLOW IN THE NORTHERN
ALEUTIANS THIS WEEKEND WILL BRING MOSTLY CONVECTIVE SNOW SHOWERS
TO THE AREA. WAVES OF MOISTURE FROM THE AFOREMENTIONED CHUKCHI LOW
WILL BRING SCATTERED SNOW SHOWERS RESULTING IN PERIODS OF REDUCED
VISIBILITY OVER THIS WEEKEND. HOWEVER, TWO CONCENTRATED WAVES OF
MOISTURE ARE EXPECTED TO BRING BRIEF PERIODS OF INTENSE SNOWFALL
DURING A 3 TO 6 HOUR DURATION. THE FIRST CONCENTRATED WAVE OF
MOISTURE WILL BRING PERIODS OF INTENSE SNOW SHOWERS FROM DUTCH
HARBOR TO NELSON LAGOON THIS EVENING INTO THE EARLY TOMORROW
MORNING. A SECOND WAVE OF MOISTURE WILL MOVE THROUGH THE THE AREA
FROM PILOT POINT WEST TO NELSON LAGOON FROM TOMORROW MORNING
THROUGH THE AFTERNOON HOURS. ELSEWHERE THIS WEEKEND, A FAST MOVING
LOW WILL BRING RAIN SHOWERS TO THE ALEUTIANS ISLANDS WEST OF ADAK
THIS EVENING THROUGH TOMORROW AFTERNOON.
THE EFFECTS OF THE ARCTIC LOW IMPACTING SOUTHWEST ALASKA WILL BE
SHORT LIVED BUT IMPACTFUL THIS WEEKEND. DAYTIME HIGHS TODAY AND
TOMORROW WILL RANGE FROM THE SINGLE DIGITS TO 20 DEGREES ABOVE
ZERO WITH LOWS IN THE TEENS BELOW ZERO TO SINGLE DIGITS ABOVE
ZERO. A STRONGER PUSH OF DRY, ARCTIC AIR MAKES ITS WAY TOWARD THE
COAST SUNDAY NIGHT INTO TUESDAY MORNING. WIDESPREAD HIGHS ON
MONDAY RANGE FROM THE TEENS BELOW ZERO TO THE SINGLE DIGITS ABOVE
ZERO WITH TUESDAY MORNING LOWS, THE COLDEST TIME OF THIS ARCTIC
PUSH, CURRENTLY RANGING FROM THE TEENS BELOW ZERO TO THE SINGLE
DIGITS ABOVE ZERO. THE MAIN FACTORS IN TUESDAY'S LOW TEMPERATURES
ARE THE RECENT SNOWFALL AND THE CLEARING SKY. SHOULD THE SKY
CLEAR, QUICKLY, RADIATIONAL COOLING FROM THE SNOWPACK COVERED
GROUND WILL RESULT IN TEMPERATURES FALLING SHARPLY. THOUGH
GUIDANCE IS STRUGGLING WITH THESE FACTORS, AS USUALLY THE CASE
DURING THE FIRST ARCTIC OUTBREAK OF THE SEASON, THE LIKELIHOOD
OF LOW TEMPERATURES BELOW 10 DEGREES FROM BETHEL SOUTHWARD TO
DILLINGHAM IS 80%. THE CHANCE OF TEMPERATURES BELOW 0 DEGREES IN
IN A LINE FROM LIME VILLAGE NORTHWARD TO ANIAK AND EASTWARD IS 70%
WITH PLACES WEST OF THERE, SUCH AS BETHEL AND DILLINGHAM AT 20%
TO 40%; WARMEST ALONG THE SOUTHWEST ALASKA COAST.
-DJ
LONG TERM FORECAST (DAYS 4 THROUGH 7: TUESDAY THROUGH FRIDAY)
THE PERSISTENT LOW OVER THE GULF OF ALASKA STARTS TO MOVE OFF TO
THE SOUTHEAST, AS A BUILDING RIDGE HIGH PRESSURE MOVES INTO THE
REGION FROM THE BERING SEA. THIS HIGH BRINGS COLDER TEMPERATURES
AND CLEARING SKIES TO SOUTH CENTRAL AND THE COPPER RIVER VALLEY
THROUGH FRIDAY AS THE HIGH REMAINS QUASI-STATIONARY OVER THE
REGION.
IN THE WEST, A NORTH PACIFIC LOW WILL ENTER THE EASTERN BERING
SEA THURSDAY EVENING. THIS SYSTEM WILL BE FORCED NORTHEASTERLY
ACROSS THE REGION AS IT RIDES OVER THE ENTRENCHED HIGH PRESSURE
RIDGE OVER MUCH OF THE STATE. THIS WILL BRING MODERATELY STRONG
SOUTHERLY WINDS ACROSS THE WESTERN ALEUTIANS AND INTO THE CENTRAL
BERING SEA THROUGH THE END OF THE WORK WEEK.
AVIATION
PANC...THE AREA OF SNOW WILL GRADUALLY SHIFT EASTWARD TOWARD THE
MOUNTAINS TODAY AS AN UPPER LEVEL SHORT-WAVE MOVES INTO COOK INLET
FROM THE WEST. THIS SHORT-WAVE WILL THEN EXIT SOUTHWARD TONIGHT,
CAUSING SNOWFALL TO DIMINISH, BUT COLD AIR ADVECTION WILL LIKELY
KEEP IT GOING FOR MUCH OF THE NIGHT. THERE WILL BE MULTIPLE
FLUCTUATIONS IN SNOWFALL INTENSITY AND IT MAY EVEN END FOR SHORT
PERIODS OF TIME AT THE TERMINAL. THUS, CONFIDENCE IN THE TIMING
OF LOWER OR HIGHER CONDITIONS IS GENERALLY LOW. HOWEVER, EXPECT
CEILINGS TO HOLD IN A FAIRLY NARROW RANGE BETWEEN MVFR AND LOW
END VFR. VISIBILITY WILL HAVE A MUCH WIDER RANGE, ANYWHERE FROM
IFR TO VFR.
WHEN SNOW FINALLY ENDS FOR GOOD, WHICH IS EXPECTED LATE TONIGHT OR
EARLY SUNDAY MORNING, EXPECT CONDITIONS TO QUICKLY IMPROVE DURING
THE DAY SUNDAY DUE TO ADVECTION OF DRIER AND COLDER AIR. THERE
APPEARS TO BE ENOUGH WIND AT THE SURFACE TO PREVENT FORMATION OF
LOW CLOUDS OR FOG AT THE TERMINAL IN THE WAKE OF THE SNOW. HOWEVER,
SUSPECT SOME LOW CLOUDS WILL LINGER JUST TO THE NORTH AND EAST,
AIDED BY UPSLOPE FLOW ALONG THE MOUNTAINS AND LIGHT WINDS AT THE
SURFACE.
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