789
FXAK68 PAFC 220201
AFDAFC
SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
501 PM AKST THU NOV 21 2024
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 THROUGH 3/TONIGHT
THROUGH SUNDAY)...
THE DOMINANT BLOCKING RIDGE CENTERED ALONG THE ALASKA PENINSULA
CONTINUES TO BE THE DRIVING FACTOR IN OUR WEATHER PATTERN FOR THE
NEXT FEW DAYS. ANTICYCLONIC FLOW AND ASSOCIATED SINKING MOTION
EXTENDS ACROSS THE EASTERN BERING SEA AND ALL OF SOUTHERN ALASKA
AND THE GULF OF ALASKA, LEADING TO VERY DRY CONDITIONS. WARM AIR
ALOFT STILL REMAINS OVER MUCH OF SOUTHCENTRAL, HOWEVER THE WARMEST
CORE OF AIR WILL BEGIN TO SHIFT SOUTHWARD AS THE RIDGE AXIS MOVES
TOWARDS THE GULF. THE STEEP TEMPERATURE INVERSION IN PLACE, ALONG
WITH A TIGHTENED PRESSURE GRADIENT OVER THE KENAI AND CHUGACH
MOUNTAINS, IS STILL PRODUCING GUSTY GAP WINDS ALONG THE GULF
COAST, ESPECIALLY IN WHITTIER AND SEWARD WHERE WIND GUSTS COULD
STILL GET UP TO 50-60 MPH THROUGH TOMORROW AFTERNOON.
CONDITIONS OVERALL WILL REMAIN RELATIVELY STEADY OVER THE NEXT FEW
DAYS WITH THE RIDGE REMAINING JUST TO THE WEST OF SOUTHCENTRAL.
WHILE THE RIDGE AXIS WILL COOL TEMPERATURES ALOFT OVER THE
MOUNTAINS, EXPECT THOSE AREAS TO REMAIN NEAR OR JUST ABOVE
FREEZING THROUGH THE WEEKEND. ADDITIONALLY, INLAND VALLEYS COULD
SEE A SLIGHT WARM UP FROM BITTER COLD TEMPERATURES, THOUGH
CONDITIONS SHOULD STAY BELOW FREEZING. GAP WINDS ARE EXPECTED TO
CONTINUE THROUGH SATURDAY AFTERNOON BEFORE WEAKENING DURING THE
EVENING/OVERNIGHT HOURS AND BECOMING CALM THROUGHOUT THE DAY ON
SUNDAY.
-BS
.SHORT TERM FORECAST SOUTHWEST ALASKA AND THE BERING
SEA/ALEUTIANS (DAYS 1 THROUGH 3: TODAY THROUGH SUNDAY MORNING)...
A LARGE BLOCKING RIDGE SITUATED OVER THE EASTERN BERING SEA
CONTINUES TO WARD OFF ACTIVE WEATHER IN THE REGION. THE MOST
PREVALENT WEATHER PATTERN BEING PRODUCED BY THE RIDGE REMAINS THE
WIDESPREAD AREAS OF LOW STRATUS AND FOG OVER MUCH OF THE BERING
AND PORTIONS OF SOUTHWEST ALASKA. OFFSHORE FLOW INITIATING EARLY
THIS EVENING OVER KUSKOKWIM DELTA MAY BEGIN TO DEGRADE AND SHIFT
THE FOG OUT OF THE AREA. THE WESTERN ALEUTIANS REMAIN THE ONLY
AREA SEEING AN ACTIVE PATTERN, WITH A TROUGH DRAPED NORTH TO SOUTH
OVER SHOWERS TO SHEMYA'S VICINITY AND GUSTY SOUTHEASTERLY WINDS
AS FAR AS ADAK. THROUGH TONIGHT, THE TROUGH WILL BEGIN TO LIFT
FURTHER INTO THE WESTERN BERING SEA, ORGANIZING INTO A LOW
PRESSURE SYSTEM NORTH OF SHEMYA BY NOON FRIDAY. THIS ROTATION
WILL BEGIN TO SWING THE SOUTHERN TAIL AND THE TROUGH,
TRANSITIONING IT INTO A FRONTAL BOUNDARY ADVANCING EASTWARD,
REACHING ADAK AND ATKA BY NOON FRIDAY BRINGING RAIN AND SOUTHERLY
WINDS.
MANY OF THESE DEVELOPMENTS DEPEND ON THE MOTION AND PROGRESSION OF
THE RIDGE, AND MANY MODELS STRUGGLE WITH INTERACTIONS BETWEEN
TROUGHS AND BLOCKING RIDGES IN OUR REGION. PARTICULARLY, IN
PRACTICE WE TEND TO SEE RIDGES PERSIST LONGER THAN ADVERTISED BY
MODEL SOLUTIONS, BUT WILL NONETHELESS IMPACT OUR CONFIDENCE
REGARDING THE PROGRESSION OF THE SYSTEMS FROM FRIDAY AFTERNOON AND
BEYOND.
THAT BEING SAID IT IS CURRENTLY EXPECTED THAT THE FRONT OVER THE
CENTRAL ALEUTIANS WILL LOSE SOME INTENSITY AS IT PUSHES UP AGAINST
THE WESTERN EDGE OF THE RIDGE BY FRIDAY AFTERNOON AND LINGER
THERE, LEADING TO PROLONGED SHOWERS BETWEEN ADAK AND NIKOLSKI.
HOWEVER, BY SATURDAY MORNING A SURGE OF MOISTURE DUE TO PHASING
WITH A LOW PRESSURE SYSTEM IN THE NORTHERN PACIFIC, WILL
REVITALIZE THE FRONT IN THE BERING, DRIVING INCREASED MOISTURE AND
WARMER TEMPERATURES INTO THE CENTRAL BERING NEAR THE PRIBILOFS BY
SATURDAY EVENING. DEPENDING ON THE RATE OF EASTERN ADVANCEMENT BY
THE FRONT, MAY BRING SHOWERS INTO COASTAL SOUTHWEST, NEAR NUNIVAK
ISLAND AND THE KUSKOKWIM DELTA, BY LATE SUNDAY MORNING/SUNDAY
AFTERNOON. THESE DEVELOPMENTS WILL CONTINUE TO BE MONITORED,
ADJUSTMENTS TO TIMING MAY COME AS WE APPROACH THE WEEKEND.
CURRENTLY, IT DOES APPEAR TO BE A LIGHT RAIN EVENT LATE THIS
WEEKEND, BUT CHANGES IN TEMPERATURE AND MOISTURE CONTENT MAY
IMPACT EXPECTED ACCUMULATIONS.
-CL
LONG TERM FORECAST (DAYS 4 THROUGH 7: MONDAY THROUGH THURSDAY)
ON THE UPPER LEVEL ALASKAN WEATHER MAP, A MODERATELY STRONG
SHORTWAVE MUSCLES ITS WAY ACROSS THE NORTHERN TWO-THIRDS OF THE
STATE, FLATTENING AND SHIFTING THE RIDGE TO THE EAST MORE THAN IN
PREVIOUS FORECAST RUNS. THIS EFFECTIVELY ANCHORS COLDER AIR
FURTHER SOUTH OVER THE MAINLAND THROUGH THE FORECAST PERIOD, AND
MATCHES MODEL CHANGES IN THE ENSEMBLE MEANS. A WELL DEVELOPED
SURFACE FRONT PUSHES INTO THE WESTERN ALASKA COASTS, WITH
PRIMARILY SNOW OVER NORTHERN AND INTERIOR AREAS CHANGING TO A
RAIN-SNOW MIX, WITH CHANCES OF LOCAL FREEZING PRECIPITATION OVER
PARTS OF SOUTHWEST ALASKA AND THE ALASKA PENINSULA ON MONDAY, AND
SOUTHERN INTERIOR AND SOUTHCENTRAL PORTIONS THROUGH WEDNESDAY. THE
FRONT DECAYS OVER THE CENTRAL INTERIOR BY WEDNESDAY.
A DEVELOPING NORTH PACIFIC LOW BRINGS ITS ACTIVE WEATHER TO THE
CENTRAL ALEUTIANS LATE MONDAY, SPREADING INTO THE AKPEN AND
WESTERN ALEUTIANS BY THURSDAY. LOCALLY HEAVY RAIN AND WINDS
INCREASING TO GALE FORCE EXTEND INTO THE SOUTHERN BERING TUESDAY
AND WEDNESDAY, DIMINISHING THURSDAY. IN THE DISTANT WEST, A
SIBERIAN HIGH IS WORKING ITS WAY INTO ALASKAN WATERS JUST AFTER
THE END OF THE FORECAST PERIOD.
AVIATION
PANC...VFR CONDITIONS AND LIGHT WINDS WILL PERSIST.
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