572
FXAK68 PAFC 141252
AFDAFC
SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
452 AM AKDT WED APR 14 2021
ANALYSIS AND UPPER LEVELS
THE UPPER LEVELS FEATURE A RIDGE NEAR THE WESTERN ALEUTIANS WITH A
LONG WAVE TROUGH FROM THE BERING EXTENDING INTO THE GULF WITH A
RIDGE TO THE EAST IN THE YUKON. THREE DISTINCT FEATURES WILL
AFFECT THE WEATHER OVER THE NEXT FEW DAYS OVER THE AREA. FIRST IS
A STRONG LOW PRESSURE SYSTEM EAST OF KODIAK ISLAND MOVING TOWARDS
THE KENAI PENINSULA TODAY ITS ACCOMPANYING FRONT IS PRODUCING
RAIN AND SNOW FROM CORDOVA INTO PRINCE WILLIAM SOUND AND THE KENAI
PENINSULA EXTENDING SOUTHWEST OVER BRISTOL BAY. TEMPERATURES ARE
IN THE 30S ACROSS MUCH OF SOUTHCENTRAL WITH RAIN IN MOST VALLEYS
AND SNOW IN THE MOUNTAINS. THE SECOND DISTINCT FEATURE IS A LOW
SOUTHEAST OF THE AKPEN THIS FEATURE WILL NOT AFFECT SOUTHCENTRAL
UNTIL LATER IN THE WEEK. A THIRD LOW IS NORTH OF NUNIVAK ISLAND
THIS FEATURE IS PRODUCING LIGHT SNOW SHOWERS ACROSS THE BERING.
OTHERWISE NORTHERLY FLOW FROM THE PRIBILOFS AND EASTERN ALEUTIANS
WILL PRODUCE SNOW SHOWERS WITH CURRENT TEMPERATURES IN THE LOW TO
MID 30S ACROSS THE AREA. A RIDGE BUILDING INTO THE WESTERN
ALEUTIANS IS BRINGING WARMER AND QUIETER WEATHER TO THAT REGION
TODAY. FINALLY PATCHY FOG AND LOW CLOUDS DOMINATE THE KUSKOKWIM
DELTA REGION WITH TEMPERATURES IN THE 20S.
MODEL DISCUSSION
MODELS CONTINUE TO HAVE GOOD AGREEMENT WITH MAJOR FEATURES WITH
HIGH CONFIDENCE IN THE FORECAST THROUGH FRIDAY. THEY CONTINUE TO
HANDLE THE LOW OVER THE GULF WELL WITH GOOD AGREEMENT WITH
PRECIPITATION AND WINDS. A SECOND LOW WILL MOVE INTO THE SOUTHERN
GULF BY THURSDAY WITH GOOD AGREEMENT WITH WINDS AND PRECIPITATION
FOR KODIAK ISLAND AND COASTAL AREAS OF SOUTHCENTRAL. ALL MODELS
ARE FORECASTING A RIDGE TO DEVELOP ACROSS THE MAINLAND OF ALASKA
AS A BLOCKING PATTERN SETS UP THIS WEEK ACROSS CANADA. MEANWHILE
MODELS ARE IN GOOD AGREEMENT WITH A FRONT MOVING ACROSS THE
WESTERN ALEUTIANS AND BERING WEDNESDAY AND THURSDAY.
AVIATION
PANC...TURNAGAIN WINDS WILL DEVELOP THIS AFTERNOON AND CONTINUE
OVERNIGHT AND MAY BE A BIT GUSTY AT TIMES UP TO 35 KNOTS. SOME
LIGHT RAIN IS POSSIBLE THIS MORNING BUT BETTER CHANCES LATER TODAY
IN THE EVENING HOURS, HOWEVER VFR CONDITIONS ARE EXPECTED TO
CONTINUE THROUGH THE TAF PERIOD.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 THROUGH 3/TODAY
THROUGH FRIDAY NIGHT)...
A LARGE VERTICALLY STACKED LOW OVER THE WESTERN GULF IS TRACKING
QUICKLY NORTHWARD TOWARD THE SOUTHERN KENAI PENINSULA, LED BY A
STRONG SHORT-WAVE AND JET STREAK DRIVING RIGHT INTO THE HEART OF
SOUTHCENTRAL ALASKA. THE FORECAST FOR THIS STORM IS MOSTLY ON
TRACK, WITH JUST SOME MINOR UPDATES THIS MORNING. THE BIGGEST
IMPACTS WILL BE ALONG THE COAST, WITH WIDESPREAD HEAVY
PRECIPITATION AND STRONG WINDS. THIS WILL LARGELY BE A RAIN EVENT
FOR THE ROAD SYSTEM AND COMMUNITIES OF PRINCE WILLIAM SOUND, WITH
HEAVY WET SNOW IN THE MOUNTAINS. PRECIPITATION-TYPE FOR INLAND
AREAS THIS MORNING IS A LITTLE MORE COMPLEX, WITH MANY AREAS ON
THE THRESHOLD BETWEEN RAIN AND SNOW. IN ANY CASE, DRY LOW LEVEL
AIR IS DELAYING ONSET OF PRECIPITATION INLAND AND IT WON'T LAST
VERY LONG AS DOWNSLOPE FLOW OFF THE COASTAL MOUNTAINS WILL KICK
IN BY LATE THIS MORNING.
THE LOW DOES LOOK A LITTLE WEAKER THAN PREVIOUS FORECASTS
INDICATED AS IT REACHES THE KENAI PENINSULA MIDDAY. THEREFORE,
HAVE LOWERED FORECAST WINDS WITH THE LATEST PACKAGE. EVEN SO,
WINDS WILL STILL BE STRONG AND GUSTY IN MANY AREAS. SPECIFICALLY,
STRONG GAP WINDS WILL DEVELOP AS THE LOW HEADS INLAND. THIS
INCLUDES THE USUAL CULPRITS OF TURNAGAIN ARM, KNIK RIVER VALLEY,
AND THE COPPER RIVER. GUSTY SOUTHEAST WINDS WILL DEVELOP IN ALL
OF THESE LOCATIONS BY MIDDAY, THEN STRENGTHEN THIS AFTERNOON AND
EVENING AS PRESSURE RISES BEHIND THE LOW CENTER TRACKING INLAND.
THE TRACK OF THE LOW IS FAVORABLE FOR WIDESPREAD GUSTY WINDS
ACROSS ANCHORAGE, THE MATANUSKA VALLEY, AND THE COPPER RIVER
BASIN. WINDS WITH THIS STORM WILL FINALLY BEGIN TO DIE DOWN
OVERNIGHT TONIGHT.
PRECIPITATION WILL ACCOMPANY THE LOW ACROSS THE KENAI PENINSULA
THIS AFTERNOON AND UP TO THE SUSITNA VALLEY THIS EVENING.
DESPITE THE STRONG SOUTHEAST FLOW ACROSS THE KENAI AND CHUGACH
MOUNTAINS, WILL LIKELY SEE AREAS OF LIGHT RAIN (OR SPRINKLES)
IN THE ANCHORAGE AREA LATE THIS AFTERNOON AND EVENING DO TO THE
CLOSE PROXIMITY TO THE LOW CENTER. THE HEAVIEST PRECIPITATION
WILL REMAIN ALONG THE COAST, WITH A TRAILING SHORT-WAVE TROUGH
APPROACHING AND UPSLOPE FLOW REMAINING STRONG. THE BEST CHANCE
FOR SNOW WILL BE OVER THE NORTHERN SUSITNA VALLEY/BROAD PASS,
WHERE THERE COULD BE SEVERAL INCHES OF WET SNOW TONIGHT.
PRECIPITATION AND WINDS WILL ALL COME TO AN END ACROSS INTERIOR
SOUTHCENTRAL ON THURSDAY. HOWEVER, ANOTHER SHORT-WAVE TROUGH
LIFTING NORTHWARD ACROSS THE GULF WILL CONTINUE TO PRODUCE PERIODS
OF RAIN (AND MOUNTAIN SNOW) ALONG THE COAST. THE TROUGH WILL
ROTATE WESTWARD ACROSS SOUTHCENTRAL THURSDAY AFTERNOON AND EVENING
BEFORE WEAKENING. THUS, THERE COULD BE SOME LIGHT RAIN SPILLING
OVER THE COASTAL MOUNTAINS INTO THE MAT VALLEY, ANCHORAGE, AND
WESTERN KENAI.
AN UPPER LEVEL RIDGE WILL BUILD IN FROM THE SOUTHEAST THURSDAY
NIGHT THROUGH FRIDAY NIGHT, LEADING TO DRY CONDITIONS AND
DECREASING CLOUDS. THE COMBINATION OF SUBSIDENCE WARMING UNDER
THE RIDGE AND INCREASING SUNSHINE WILL LEAD TO WARMING
TEMPERATURES. EXPECT FRIDAY AND BEYOND WE'LL START TO SEE MORE
50 DEGREE TEMPERATURES, ESPECIALLY FOR THE TYPICALLY WARMER
INLAND LOCATIONS.
SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 THROUGH 3)
AS SEEN ON SATELLITE AND OBSERVATIONS, FOG WILL CONTINUE THROUGH
THE MORNING HOURS ACROSS THE KUSKOKWIM DELTA.
A SURFACE LOW APPROACHING KODIAK ISLAND IS EXPECTED TO BRING SOME
INCREASED WINDS TO BRISTOL BAY AND WATERS SOUTH OF THE ALASKA
PENINSULA, ALONG WITH THE LOWER KUSKOKWIM VALLEY ON WEDNESDAY. A
RAIN/SNOW MIX IS ANTICIPATED ACROSS THE MIDDLE KUSKOKWIM VALLEY
BEGINNING WEDNESDAY AFTERNOON AND CONTINUING THROUGH THURSDAY
MORNING.
EXPECT CONDITIONS TO CALM THURSDAY NIGHT THROUGH FRIDAY AS A
RIDGE OF HIGH PRESSURE APPROACHES THE REGION. TEMPERATURES WILL
WARM AS PRECIPITATION WANES THROUGH THIS TIMEFRAME.
SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAY 1 THROUGH 3)
EXPECT NORTHERLY WINDS ACROSS THE CENTRAL AND EASTERN ALEUTIANS AS
A RIDGE OF HIGH PRESSURE BUILDS OVER THE BERING SEA THROUGH
THURSDAY. GUSTY CONDITIONS WILL PERSIST THROUGH GAPS AND PASSES
WITH OCCASIONAL RAIN AND SNOW SHOWERS.
WEDNESDAY AFTERNOON, ENERGY RIDING ATOP THE RIDGE WILL BRING
CHANCES FOR RAIN TO THE CENTRAL ALEUTIANS. OTHER THAN THIS, EXPECT
WARM AND DRY CONDITIONS TO PERSIST FOR MUCH OF THE BERING AND THE
ALEUTIANS UNTIL LATE THURSDAY/EARLY FRIDAY.
BEGINNING LATE THURSDAY/EARLY FRIDAY, A GALE TO STORM FORCE FRONT
WILL ENTER THE WESTERN ALEUTIANS AND BERING. AS IT APPROACHES THE
CENTRAL ALEUTIANS LATE FRIDAY, AN INCREASE IN WINDS, WAVES AND
PRECIPITATION WILL ACCOMPANY THIS FEATURE. PRECIPITATION LOOKS TO
START OFF AS RAIN FOR THE WESTERN BERING BEFORE THE POTENTIAL FOR
A WINTRY MIX WORKS ITS WAY INTO THE CENTRAL BERING.
MARINE (DAYS 3 THROUGH 5: FRIDAY THROUGH SUNDAY)
BERING SEA/ALEUTIANS:
HIGH PRESSURE EXPANDING ACROSS THE EASTERN BERING BY FRIDAY WILL
PRIMARILY LEAD TO NO SIGNIFICANT WEATHER AND GENERALLY LIGHT WINDS
THROUGH EARLY SUNDAY. A WEAKENING LOW DRIFTING SOUTH OF THE
WESTERN ALEUTIANS WILL BRING DIMINISHING SOUTHEAST GALES TO THE
FAR WESTERN BERING/ALEUTIANS THROUGH EARLY SATURDAY. THE HIGH WILL
SHIFT TOWARDS THE WESTERN BERING SUNDAY AS A LOW MOVES SOUTH OF
THE GULF AND ALASKA PENINSULA, ALLOWING NORTHEAST WINDS TO
INCREASE TO AS HIGH AS GALE FORCE ACROSS THE SOUTHERN BERING BY
SUNDAY EVENING. FORECAST CONFIDENCE IS HIGH OVERALL.
GULF OF ALASKA:
HIGH PRESSURE OVER THE GULF OF ALASKA WILL LEAD TO BENIGN WEATHER
CONDITIONS WITH LIGHT WINDS AND SEAS 5-10 FEET OR LESS THROUGH
SATURDAY. A BROAD LOW WILL APPROACH THE FAR SOUTHERN GULF AS IT
DRIFTS TOWARDS THE ALASKA PENINSULA ON SUNDAY. THIS WILL LEAD TO
INCREASING NORTHEAST WINDS UP TO GALE FORCE ACROSS THE SOUTHEAST
GULF AND THROUGH SHELIKOF STRAIT THROUGH SUNDAY EVENING. SOME
DIFFERENCES PERSIST WITH THIS LOW, BUT OVERALL FORECAST CONFIDENCE
IS GOOD.
LONG TERM FORECAST (DAYS 3 THROUGH 7: SATURDAY THROUGH TUESDAY)
THE LONG TERM PATTERN CONTINUES TO FEATURE AN UNUSUAL DEGREE OF
BLOCKING AT THE SYNOPTIC LEVEL THROUGH EARLY NEXT WEEK.
ANOMALOUSLY HIGH 500 MB HEIGHTS WILL SPAN ACROSS NEARLY THE ENTIRE
STATE AND ACROSS THE BERING THROUGH AT LEAST SUNDAY NORTH OF A
DEEP, CLOSED LOW OVER THE NORTH PACIFIC. THESE FEATURES TOGETHER
WILL SUPPORT A PRONOUNCED REX BLOCKING FORMATION. THIS WILL FAVOR
MILD, DRY AND INACTIVE CONDITIONS FOR NEARLY THE ENTIRE REGION,
WITH THE POLAR JET RECESSED WELL INTO THE ARCTIC AND THE PACIFIC
JET SIMILARLY REMAINING WELL SOUTH OF ALASKA, OR NEAR SUBTROPICAL
LATITUDES. OPERATIONAL MODELS AND THE ENSEMBLE MEANS STRONGLY
SUGGEST THIS MILD AND DRY PATTERN WILL CONTINUE THROUGH MONDAY AND
TUESDAY NEXT WEEK. HOWEVER, THE STRONGEST BLOCKING MAY BEGIN TO
SHIFT UPSTREAM BY THIS POINT AS AN OMEGA RIDGE BUILDS INTO THE
WESTERN BERING/KAMCHATKA, AND AS THE LARGE NORTH PACIFIC LOW
RETROGRADES NORTHWEST CLOSER TO THE ALEUTIAN CHAIN. DEPENDING ON
THE TRACK OF THE LOW CENTER, THIS COULD LEAD TO INCREASING
PRECIPITATION POTENTIAL NEAR THE AKPEN AND KODIAK ISLAND AREAS BY
AS EARLY AS MONDAY. THE PRONOUNCED RIDGE AXIS EXTENDING ALL THE
WAY FROM THE US WEST COAST TO THE AK INTERIOR SHOULD CONTINUE TO
FAVOR DRIER CONDITIONS AND AVERAGE TO ABOVE AVERAGE TEMPERATURES
FOR THE REST OF THE MAINLAND THROUGH THE END OF THE PERIOD. THIS
SHOULD SOLIDIFY A CLEAR TRANSITION TO MORE TYPICAL SPRING WARMING
FOR THE FORESEEABLE FUTURE. THE DEEP SNOW COVER WILL BE A LIMITING
FACTOR FOR GETTING TEMPERATURES SIGNIFICANTLY ABOVE AVERAGE, BUT
INCREASED MELTING AND RUNOFF IS HIGHLY LIKELY TO CONTINUE THROUGH
EARLY NEXT WEEK.
AFC WATCHES/WARNINGS/ADVISORIES
PUBLIC...NONE.
MARINE...GALE: 120,125,128,129,130,131,138,139,140,351,352
STORM: 119
FIRE WEATHER...NONE.
SYNOPSIS AND MODEL DISCUSSION...RC
SOUTHCENTRAL ALASKA...SB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CRK
MARINE/LONG TERM...AS
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