452
FXAK68 PAFC 070058
AFDAFC
SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
458 PM AKDT MON APR 6 2020
ANALYSIS AND UPPER LEVELS
A STRONG, VERTICALLY-STACKED LOW OVER THE INTERIOR CONTINUES TO
DOMINATE WEATHER OVER MUCH OF THE MAINLAND. THIS LOW HAS BEEN
RESPONSIBLE FOR THE WINDS ACROSS MUCH OF SOUTHCENTRAL THE PAST 36
HOURS. A STRONG UPPER LEVEL JET (300 MB 30,000') HAS OFFERED
SUPPORT FLOWING QUICKLY FROM WEST TO EAST AT 150 KTS. A "PARTING"
SHORTWAVE PASSED ACROSS THE SUSITNA VALLEY DOWN THROUGH THE KENAI
PENINSULA THIS MORNING. THIS FEATURE BROUGHT THE LAST, BEST SURGE
OF WINDS. OVERALL, THE WINDS SHOULD CONTINUE TO DIMINISH ACROSS
THE AREA. THINGS ARE RELATIVELY QUIET ACROSS THE BERING WITH JUST
ONE SMALLER SHORTWAVE PASSING BY THE PRIBILOF ISLANDS. THIS SYSTEM
HAS SOME COLD AIR BEHIND IT (850 MB -18C), SO WITH STEEP LAPSE
RATES, IT WILL BRING SOME HEAVY SNOW SHOWERS TO THE PRIBILOF
ISLANDS AND THE EASTERN BERING. ANOTHER FINGER OF THE 300 MB JET
IS PUSHING DOWN THE BACKSIDE OF THIS SYSTEM AT ABOUT 85 KTS.
FINALLY, THE MAIN PLAYER ASSOCIATED WITH A DEVELOPING STORM SYSTEM
CAN BE SEEN ON SATELLITE. ALL OF THE MOISTURE OVER THE N PACIFIC
IS SLOWLY DRIFTING NE TOWARDS THE GULF OF AK. THE SHORTWAVE OVER
THE BERING (AND ITS TRAILING COLD AIR ADVECTION) WILL WORK IN
TANDEM WITH THIS MOISTURE TO PRODUCE A STRONG SYSTEM JUST EAST OF
KODIAK ISLAND ON TUESDAY.
MODEL DISCUSSION
MODELS HAVE STRUGGLED GREATLY WITH THE UPCOMING STORM IN THE GULF
OF AK. YESTERDAY, ALL MODELS TRENDED IT FURTHER TO THE EAST AND
LEFT IT TO REALLY ONLY IMPACT WINDS AND WAVES ACROSS THE GULF.
NOW, ALL MODELS HAVE TRENDED SIGNIFICANTLY FURTHER TO THE WEST
WITH THE LOW. THE NET EFFECT WILL BE THE POTENTIAL FOR HEAVY SNOW
AND STRONG WINDS FOR KODIAK ISLAND. THIS FORECAST PACKAGE HAS
TRENDED TOWARDS THAT SOLUTION AND VASTLY INCREASED QPF, WINDS, AND
WAVES. HOWEVER, WE DID NOT GO 100% TO ANY ONE SOLUTION AS THE
MODELS CONTINUE TO SHOW SIGNS OF VARIABILITY. ALL THAT SAID, THERE
IS POTENTIAL TO BRING IN MORE SIGNIFICANT WEATHER TO KODIAK AND
THE GULF COAST IF THE EVENING MODEL RUNS PROVIDE BETTER CLARITY.
AVIATION
PANC...VFR CONDITIONS WILL PERSIST. SW WINDS WILL PERSIST THROUGH
THE DAYLIGHT HOURS BEFORE THEY TAPER OFF LATER THIS EVENING.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 THROUGH 3/TONIGHT
THROUGH THURSDAY)...
A FEW SCATTERED SNOW SHOWERS ALONG WITH GUSTY WESTERLY WINDS WILL
PERSIST THROUGH THE EVENING HOURS BEFORE DIMINISHING OVERNIGHT AS
THE UPPER-LEVEL TROUGH SLIDES EAST. THE LIGHTER WINDS AND
DIMINISHED CLOUD COVER WILL ALLOW OVERNIGHT LOW TEMPERATURES TO
DROP INTO THE TEENS ACROSS MUCH OF SOUTHCENTRAL, WITH SOME AREAS
OF SINGLE DIGITS WITHIN SHELTERED VALLEYS AND THE COPPER RIVER
BASIN. COOL AND DRY CONDITIONS CONTINUE ACROSS THE SOUTHCENTRAL
MAINLAND TOMORROW AS A RIDGE BUILDS OUT AHEAD OF AN UPPER-LEVEL
SHORTWAVE SLIDING SOUTHEAST ACROSS THE AKPEN. THIS SYSTEM WILL
INDUCE THE DEVELOPMENT OF A POTENT NORTH PACIFIC LOW THAT WILL
STRENGTH AS IT MOVES EAST OF KODIAK TUESDAY, WITH GALES INCREASING
TO STORM-FORCE WINDS ALONG THE NORTH GULF COAST BY LATE TUESDAY
NIGHT INTO WEDNESDAY MORNING.
WHILE THERE IS STILL A BIT OF UNCERTAINTY WITH THE EXACT TRACK OF
THIS LOW, THERE HAS BEEN BETTER MODEL CONSENSUS KEEPING THE
CENTER OF CIRCULATION CLOSER TO THE EAST COAST OF KODIAK ISLAND.
THIS WOULD YIELD STRONGER WINDS AND HEAVIER PRECIPITATION FOR THE
ISLAND BEGINNING TUESDAY MORNING, CONTINUING THROUGH THE EARLY
MORNING HOURS ON WEDNESDAY. IT ALSO LOOKS LIKE TEMPERATURES WILL
REMAIN COLD ENOUGH ALOFT AND JUST COLD ENOUGH NEAR THE SURFACE FOR
THIS TO BE MAINLY A SNOW EVENT, ALBEIT A HEAVY, WET SNOW. RAIN
MAY MIX IN AT TIMES ALONG THE IMMEDIATE COAST, BUT ACCUMULATING
SNOW IS EXPECTED, WITH 5 TO 10 INCHES POSSIBLE. A WINTER STORM
WATCH IS CURRENTLY OUT FOR THIS EVENT.
BY LATE TUESDAY, SNOW AND GUSTY NORTHERLY WINDS WILL ALSO DEVELOP
OVER CORDOVA, AHEAD OF THE STORM-FORCE FRONT. THE SNOW AND BLOWING
SNOW IS THEN EXPECTED TO SPREAD OVER THOMPSON PASS AND PARTS OF
THE SOUTHERN COPPER RIVER BASIN OVERNIGHT TUESDAY AND LINGER INTO
WEDNESDAY AFTERNOON. WITH A STORM TRACK FROM EAST OF KODIAK TO
YAKUTAT, AREAS OF SOUTHCENTRAL NORTH AND EAST OF THE KENAI AND
CHUGACH MOUNTAINS SHOULD REMAIN COOL AND DRY, ONLY HAVING TO
CONTENT WITH AN INCREASE IN CLOUD COVER. AS THE STORM EXITS ON THE
REGION ON WEDNESDAY, OFFSHORE GAP WINDS WILL ONCE AGAIN
STRENGTHEN ALONG THE NORTH GULF COAST AND PRINCE WILLIAM SOUND.
.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 THROUGH 3: TONIGHT
THROUGH THURSDAY)...
THE EASTERN PERIPHERY OF A LOW CENTERED EAST OF THE PRIBILOFS WILL
BE MOVING INTO THE KUSKOKWIM DELTA AND THE WESTERN CAPES TONIGHT.
THIS WILL CAUSE SNOW SHOWERS TO DEVELOP, BUT ACCUMULATIONS SHOULD
BE LIMITED TO A FEW INCHES AT MOST. DURING THE DAY TUESDAY, THE
SHOWERS WILL SHIFT SOUTHWARD, WITH THE SNOW SHOWER ACTIVITY
SHIFTING TO AROUND THE COASTAL BRISTOL BAY AREA. CLOUDS WILL
PERSIST OVER THE AREA THROUGH THURSDAY. ANOTHER FRONT WILL SKIRT
THE KUSKOKWIM DELTA ON THURSDAY, BRINGING ANOTHER ROUND OF SNOW
SHOWERS TO THE AREA. TEMPERATURES THROUGH THURSDAY WILL REMAIN
WELL BELOW NORMAL, WITH HIGHS IN THE UPPER 20S AND 30S, WHILE LOWS
ARE IN THE SINGLE DIGITS AND TEENS.
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 THROUGH 3: TONIGHT
THROUGH THURSDAY)...
A SMALL LOW CENTERED JUST EAST OF THE PRIBILOFS IS PRODUCING A
SMALL AREA OF GALE FORCE WINDS IN THE WATERS AROUND AND EAST OF
THE ISLANDS THIS AFTERNOON. THE MODELS HAVE FINALLY COME INTO
BETTER AGREEMENT THAT THE LOW WILL SHIFT SOUTHWARD. THE CENTER OF
THE LOW WILL BE NEAR THE PORT HEIDEN AREA ON TUESDAY MORNING.
THUS, SMALL CRAFT TO MINIMAL GALE FORCE NORTHERLY WINDS WILL
CONTINUE ON THE BERING SIDE OF THE ALASKA PENINSULA THROUGH
TUESDAY. A SECOND LOW WILL MOVE ACROSS THE NORTHERN BERING ON
TUESDAY, BUT IT WILL BE WEAK, AND WILL DISSIPATE ON WEDNESDAY.
A FRONT AND ASSOCIATED LOW WILL MOVE INTO THE WESTERN ALEUTIANS
TUESDAY AFTERNOON AND EVENING. IT WILL GRADUALLY SHEAR APART AS IT
MOVES INTO THE CENTRAL BERING, BUT A PORTION OF THE FRONT WILL
PERSIST INTO THE NORTHERN BERING ON WEDNESDAY. THE ASSOCIATED LOW
WILL TRACK NEAR THE WESTERN AND CENTRAL ALEUTIANS WEDNESDAY NIGHT.
MARINE (DAYS 3 THROUGH 5)
(THURSDAY THROUGH SATURDAY)
BERING SEA/ALEUTIANS
A 998 MB LOW JUST SOUTH OF THE RAT ISLANDS THURSDAY AFTERNOON
WILL SEND AN ASSOCIATED NEAR GALE FORCE FRONT INTO THE WEST
CENTRAL ALEUTIANS. THIS FRONT WILL REACH THE ALASKA PENINSULA BY
FRIDAY AFTERNOON AND LOOKS TO REMAIN JUST UNDER GALE FORCE. THE
ASSOCIATED LOW MOVES INTO THE NORTHWEST BERING AS ANOTHER LOW AND
ASSOCIATED FRONT APPROACHES THE WESTERN ALEUTIANS FROM THE NORTH
PACIFIC.
GULF OF ALASKA
A STRONG AREA OF HIGH PRESSURE CENTERED OVER THE COPPER RIVER BASIN
WILL KEEP THE GULF DRY WITH LIGHT WINDS FOR THURSDAY AND FRIDAY,
BEFORE A NEAR GALE FORCE FRONT APPROACHES THE SOUTHERN GULF ON
SATURDAY.
LONG TERM FORECAST (DAYS 3 THROUGH 7)
MODEL GUIDANCE REMAINS IN GOOD AGREEMENT ON THE UPPER LEVEL
PATTERN FRIDAY INTO SATURDAY AS AN UPPER LEVEL RIDGE DOMINATES
MOST OF THE MAINLAND OF ALASKA. THIS WILL CONTINUE THE THEME OF A
WARMING TREND IN TEMPERATURES WITH EACH DAY BEING WARMER THAN THE
PREVIOUS. OVERALL, A WARMER AND DRY PATTERN FOR THE MAINLAND.
BEYOND SATURDAY, SOME DIFFERENCES ARE BEGINNING TO EMERGE THAT
WERENT QUITE EVIDENT IN THE MODELS YESTERDAY. MODEL GUIDANCE IS
NOW HINTING AT A STORM SYSTEM OVER THE NORTH PACIFIC SOUTH OF THE
CENTRAL ALEUTIANS BEING DRAWN NORTHWARD THAT MAY UNDERCUT THE
RIDGE AND BRING A POSSIBLE PERIOD OF UNSETTLED WEATHER OUT THERE
FOR THE SECOND HALF OF NEXT WEEKEND. MODEL GUIDANCE THEN REALLY
SPREADS OUT BEYOND SUNDAY NIGHT OF NEXT WEEKEND WITH THE GFS
SHOWING A MORE AMPLIFIED RIDGE WHILE THE OTHER MODEL SHOWS A
FLATTER WEAKER RIDGE MOVING IN BEHIND THE AFOREMENTIONED STORM
SYSTEM. AN UPPER LEVEL TROUGH IS EXPECTED TO BE PRESENT OVER
EASTERN RUSSIA AND INTO THE NORTH PACIFIC SUNDAY NIGHT THROUGH
MONDAY SHOWING A POTENTIAL STORM SYSTEM MOVING NORTHWARD. THIS MAY
BRING A PERIOD OF UNSETTLED WEATHER AND INCREASE IN WINDS TO THE
ALEUTIAN CHAIN AND THE BERING DURING THIS TIME. HOWEVER, THE EXACT
TRACK AND STRENGTH OF THIS FEATURE IS STILL YET TO BE DETERMINED
WITH DIMINISHING FORECAST CONFIDENCE BEYOND SUNDAY.
AFC WATCHES/WARNINGS/ADVISORIES
PUBLIC...WINTER STORM WATCH 171.
MARINE...GALE 131 132 138 179.
STORM 119 120.
HEAVY FREEZING SPRAY 180-185.
FIRE WEATHER...NONE.
SYNOPSIS AND MODEL DISCUSSION...MSO
SOUTHCENTRAL ALASKA...TM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JW
MARINE/LONG TERM...PD/MV
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