967
FXAK67 PAJK 062303
AFDAJK
SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
303 PM AKDT MON APR 6 2020
SHORT TERM
/SUNDAY EVENING THROUGH WEDNESDAY/ ACTIVE SHORT TERM
PERIOD WITH SHOWERS ACROSS THE PANHANDLE THROUGH TUESDAY THEN A
POWERFUL STORM SYSTEM MOVES INTO THE GULF TUESDAY NIGHT AND
WEDNESDAY BRINGING THE NEXT ROUND FOR HEAVY PRECIPITATION AND
GUSTY WINDS.
WESTERLY FLOW OVER THE GULF MADE ITS WAY EASTWARD INTO THE
PANHANDLE WEDNESDAY AFTERNOON WITH GUSTS OVER 40 MPH OBSERVED IN
YAKUTAT AND GUSTAVUS. GUSTY WESTERLY WINDS ARE EXPECTED TO
DIMINISH THROUGH THE EVENING HOURS ACROSS THE NORTHERN PANHANDLE.
THE WEST WINDS ALSO BROUGHT MUCH COOLER AIR WITH IT CHANGING RAIN
OVER TO SNOW THROUGH THE EVENING. TEMPERATURES AT 850MB DROPPED
FROM AROUND -6C IN THE MORNING TO AS LOW AS -12C. THE COLDER AIR
ADVECTING IN STEEPENED LOW LEVEL LAPSE RATE ENOUGH TO INCREASE
SHOWER ACTIVITY ALONG THE COAST AND IN THE CENTRAL PANHANDLE.
THESE CONVECTIVE SHOWERS MAY PRODUCE BRIEF PERIODS OF HEAVY
SNOWFALL, EVEN IN AREAS WHERE SURFACE TEMPERATURES ARE IN THE
LOWER 40S DUE TO MUCH COLDER AIR ALOFT. EXPECT SHOWERS TO PERSIST
THROUGH MONDAY WITH THE OUTER COAST AND WEST FACING SLOPES
EXPERIENCING THE MOST SHOWER ACTIVITY. LIGHT SNOWFALL
ACCUMULATIONS POSSIBLE MONDAY NIGHT IN AREAS THAT RECEIVE HEAVIER
SHOWERS AS THE BOUNDARY LAYER COOLS SOME; HOWEVER NO SIGNIFICANT
ACCUMULATIONS EXPECTED.
SLIGHT RIDGING BUILDS IN AT THE SURFACE TUESDAY AHEAD OF A STRONG
STORM SYSTEM FORMING IN THE SOUTHWESTERN GULF. TUESDAY WILL BE THE
CALM BEFORE THE STORM AS RIDGING WILL BRIEFLY SHUT OFF MOST OF THE
SHOWER ACTIVITY ACROSS THE PANHANDLE. IN FACT, WITH ENOUGH DRY AIR
IN PLACE ACROSS THE NORTH, A FEW AREAS MAY EVEN SEE SOME SUN
BEFORE CLOUDS BEGIN STREAMING IN FROM THE SOUTHWEST.
..WINTER STORM TUESDAY NIGHT THROUGH WEDNESDAY
A DEEPENING TROUGH MOVES INTO THE NORTHERN GULF TUESDAY NIGHT
WITH A 110+ KT JET STREAK SLAMMING INTO THE PANHANDLE ON
WEDNESDAY. AT THE SURFACE, A STRENGTHENING AREA OF LOW PRESSURE
JUST OFF THE COAST OF KODIAK ISLAND TUESDAY EVENING MOVES
NORTHEASTWARD TOWARDS THE YAKUTAT AREA BY WEDNESDAY AFTERNOON. AS
THE LOW APPROACHES THE NE GULF COAST, IT WILL SWING A STRONG FRONT
WITH HEAVY PRECIPITATION INTO THE PANHANDLE LATE TUESDAY NIGHT.
WITH 850MB TEMPS STARTING OFF AROUND -6 TO -8C AND THICKNESS
VALUES BELOW 1290M TUESDAY NIGHT, EXPECT THE PRECIPITATION TO
START OFF AS SNOW EVERYWHERE. AS THE FRONT PUSHES INTO THE
PANHANDLE WEDNESDAY MORNING, EXPECT SNOW TO CHANGE TO RAIN PRETTY
FAST AS THICKNESS VALUES AND TEMPERATURES QUICKLY RISE. THIS WILL
BE THE FIRST HEAVY RAIN PRODUCER IN A WHILE FOR THE ENTIRE
PANHANDLE. REMAINING SNOW PACK ON THE GROUND AT SEA LEVEL MAY
EXPERIENCE SIGNIFICANT MELTING DUE TO ALL OF THE RAIN EXPECTED.
GFS AND THE GFS ENSEMBLES SHOW IVT VALUES OF 300-500 KG/M/S MOVING
INTO THE REGION WITH STRONG FORCING AND PW VALUES UP TO TWO
STANDARD DEVIATIONS ABOVE NORMAL ALONG THE COAST. PRECIPITATION
TOTALS OF 1 TO 2 INCHES OF RAIN EXPECTED AT THE SURFACE WITH
HIGHER AMOUNTS LIKELY AT HIGHER ELEVATIONS.
DUE TO THE HEAVY SNOW POTENTIAL AS THE FRONT APPROACHES THE
REGION, MULTIPLE STATEMENTS HAVE BEEN ISSUED. A WINTER STORM
WATCH HAS BEEN ISSUED FOR YAKUTAT, THE HAINES HIGHWAY AND THE
KLONDIKE HIGHWAY FOR LATE TUESDAY NIGHT THROUGH LATE WEDNESDAY
MORNING. SIGNIFICANT ACCUMULATIONS ARE POSSIBLE BEFORE THE
CHANGEOVER TO RAIN OCCURS. AT HIGHER ELEVATIONS ALONG THE KLONDIKE
HIGHWAY, PRECIPITATION MAY REMAIN SNOW THROUGH THE DURATION OF
THE EVENT. CURRENTLY HAVE 5 TO 8 INCHES OF SNOW IN THE FORECAST
FOR YAKUTAT AND THE HAINES HIGHWAY AND UPWARDS OF A FOOT OF SNOW
FOR WHITE PASS. LOCATIONS AT SEA LEVEL WILL SEE LOWER SNOW TOTALS
AND THEREFORE HAVE NOT ISSUED ANY PRODUCTS FOR THESE AREAS YET.
WOULD NOT BE SURPRISED TO SEE ADVISORIES ISSUED FOR JUNEAU AND THE
ICY STRAIT CORRIDOR AS HEAVY SNOW MAY PUT DOWN OVER FOUR INCHES
OF SNOW IN A SHORT AMOUNT OF TIME LATE TUESDAY NIGHT. WAS NOT
CONFIDENT JUST YET ON SNOWFALL TOTALS TO ISSUE ADVISORIES. THIS
WILL BE SOMETHING LATER SHIFTS WILL HAVE TO CLOSELY MONITOR OVER
THE NEXT 24 HOURS.
OVERALL FORECAST CONFIDENCE IS MODERATE THROUGH THE PERIOD.
LONG TERM...WEDNESDAY THROUGH MONDAY...AS OF 9 PM SUN
THE
PERIOD BEGINS WITH AN ATMOSPHERIC RIVER IMPACTING THE REGION.
OPERATIONAL MODELS CONTINUE TO FLUCTUATE ON THE TRACK OF THE LOW
ASSOCIATED WITH THIS SYSTEM BUT GEFS AND ENS IN FAIRLY GOOD
AGREEMENT AS AR MAKES LANDFALL AROUND 08/12Z AROUND CROSS SOUND
AND PUSHES S THROUGH THE PANHANDLE THROUGH THE DAY. IVT VALUES
REMAIN AROUND 300-500 KG/M/S, WHICH IS 3-4 STANDARD DEVIATIONS
ABOVE NORMAL. THIS DEEP MOISTURE WILL COMBINE WITH FAVORABLE SE
LOW LEVEL FLOW RESULTING IN A 6-12 HR PERIOD OF HEAVY PRECIP.
PARTIAL THICKNESS VALUES AND LOW LEVEL TEMPERATURE PROFILES
SUPPORT ACCUMULATING SNOW MAINLY N OF FREDERICK SOUND WED MORNING.
MODELED SNOW AMOUNTS OF 1-3 FEET SEEM EXCESSIVE, BUT EXPECT MOST
OF THE N PANHANDLE TO WAKE UP TO 2-4 INCHES BEFORE PRECIP
TRANSITIONS TO RAIN BY AFTERNOON. WIDESPREAD QPF OF 1-2 INCHES
WITH LOCALIZED AMOUNTS TO 3 INCHES IN OROGRAPHICALLY FAVORED AREAS
EXPECTED ACROSS THE REGION WITH THIS SYSTEM. PRECIP CHANCES WILL
DIMINISH THU WITH MODELS IN FAIR AGREEMENT ON UPPER RIDGE BUILDING
OVER THE W GULF MAINTAINING DRY AND COOL WEATHER IN NWLY FLOW
PATTERN INTO NEXT WEEKEND. MODEL SOLUTIONS COMING INTO BETTER
AGREEMENT WITH ANOTHER SYSTEM APPROACHING THE SE GULF WITH
INCREASING PRECIP CHANCES HEADING INTO NEXT WEEK.
AJK WATCHES/WARNINGS/ADVISORIES
PUBLIC...STRONG WIND UNTIL 6 PM AKDT THIS EVENING FOR AKZ019-020.
WINTER STORM WATCH FROM TUESDAY EVENING THROUGH WEDNESDAY
MORNING FOR AKZ017-019.
STRONG WIND UNTIL 4 PM AKDT THIS AFTERNOON FOR AKZ018.
WINTER STORM WATCH FROM TUESDAY EVENING THROUGH WEDNESDAY
AFTERNOON FOR AKZ018.
MARINE...GALE WARNING FOR PKZ022-043-052.
SMALL CRAFT ADVISORY FOR PKZ012-013-021-031-033>035-041-042-051-
053.
CM/BC
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