Area Forecast Discussion
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000
FXAK67 PAJK 310123
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
423 PM AKST FRI JAN 30 2015

.SHORT TERM...HIGH PRESSURE WILL BUILD OVER ERN INTERIOR AK AND NW
CANADA TONIGHT AND SAT. AN OCCLUDED FRONT WILL MOVE N TO THE
EXTREME SRN GULF BY LATE SAT AFTERNOON. MODELS WERE IN FAIRLY
CLOSE AGREEMENT ON THESE FEATURES ALTHOUGH THERE WERE MINOR DIFFS
ON POTENTIAL LOW PRESSURE WAVE THAT MIGHT MOVE NWD TO THE FAR SE
GULF LATE SAT. BASICALLY KEPT PRESSURE FIELDS AS IS.

MAIN FORECAST CONCERNS WILL BE WINDS/SEAS...TEMPS...AND FOG/LOW
CLOUD POTENTIAL. NLY PRESSURE GRADIENTS HAVE BEEN SLOWLY BUILDING
OVER THE NRN AREA THIS AFTERNOON...AND THIS WILL CONTINUE INTO
SAT. STILL EXPECT WINDS TO INCREASE OVER MUCH OF THE NRN AREA
TONIGHT AND SAT. LOOKS LIKE STORM FORCE WINDS OVER NRN LYNN CANAL
BY LATE SAT MORNING...WITH GALES FOR MUCH OF THE REMAINING NRN
CHANNELS BY THAT TIME. WITH THE NLYS BECOMING WELL ESTABLISHED ON
SAT...SEAS WILL BE ABLE TO BUILD ABOVE THE USUAL 5 TO 1 WIND/SEA
RATIO OVER LYNN CANAL AND NRN ENDS OF STEPHENS PASSAGE AND NRN
CHATHAM STRAIT. STRONGER WINDS WILL ALSO DEVELOP FROM THE S LATER
TONIGHT AND SAT AS OCCLUDED FRONT MOVES CLOSER TO THE AREA. THIS
WILL INCREASE ELY FLOW OVER THE SRN GULF AND E-NE FLOW SRN INNER
CHANNELS LATE TONIGHT AND SAT. THINK THE SRN GULF MAY REACH GALE
FORCE WINDS AHEAD OF THIS FRONT...WITH SCA WINDS FOR MANY OF THE
SRN CHANNELS. IN THE JUNEAU AREA...CONDITIONS WILL BECOME MORE
FAVORABLE FOR MTN WAVE DEVELOPMENT. THERE IS SOME UNCERTAINTY ON
HOW STRONG THE CROSS BARRIER FLOW WILL BE WITH THE NAM SHOWING THE
STRONGEST. AFTER COORD WITH LONG TERMER...DECIDED TO ISSUE A HIGH
WIND WATCH FOR DOWNTOWN JUNEAU AND DOUGLAS STARTING AT 21Z SAT.
WILL HAVE STRONG WIND HEADLINES FOR PAHN/PAGY AREAS AS WELL...WITH
STRONGEST WINDS IN THE PAHN AREA MAINLY NEAR AND ALONG LYNN
CANAL.

AS FOR TEMPS...MODELS HAVE STRUGGLED WITH HANDLING LEADING EDGE OF
ARCTIC AIRMASS THAT IS OVER THE FAR NRN AREA ATTM. NEAR SFC PART
OF THE AIRMASS IS COLDER THAN THE MODELS WERE SHOWING. KEPT THIS
COLDER TREND GOING INTO SAT FOR THE FAR NRN ZONES...BUT WAS LESS
COLD COMPARED TO THE MODELS THAN CURRENT TEMPS WERE SUGGESTING AS
THERE MAY BE SOME DELAY IN THE EVEN COLDER AIR ARRIVING UNTIL
AFTER A SHORTWAVE TROF MOVES BY LATE TONIGHT. SOME COOLER AIR WILL
MOVE IN FROM THE N AND NE FOR THE CENTRAL AREA LATER TONIGHT AND
SAT...BUT BULK OF COLD AIR WILL STAY ON E SIDE OF COAST MTNS. THE
SRN AREA WILL ALSO SEE A BIT OF COOLING MAINLY FROM OUTFLOWS THRU
THE COAST MTN PASSES...BUT TEMPS THERE WILL STILL REACH THE 40S IN
MOST OF THE COASTAL AND WRN PARTS OF THE SRN CHANNELS SAT. WILL
HAVE SOME PLACES WITH LARGE DIFFS IN TEMPS BETWEEN NEARBY SPOTS
DUE TO WINDS. WHERE WIND BLOWS TONIGHT OVER THE CENTRAL AND SRN
AREAS...KEEPING TEMPS UP SOMEWHAT (CLOSE TO FREEZING). WIND
SHELTERED AREAS THAT REMAIN MOSTLY CLEAR OR CLEAR OUT EARLY
TONIGHT SHOULD FALL WELL INTO THE TEENS AND 20S...COLDEST OVER THE
N.

THERE ARE SOME PESKY LOW CLOUDS AND A BIT OF FOG OVER THE CENTRAL
AREA THIS AFTERNOON. THIS IS DUE TO INVERSION BEING FAIRLY LOW AND
NOT ENOUGH WIND TO MIX DRIER AIR IN. THINK THE PAJN/PAGN/PAPG
AREAS WILL SEE FOG REFORM THIS EVENING AS WINDS WILL REMAIN LIGHT
IN THOSE AREAS. THINK WINDS IN MOST OTHER AREAS WILL BE ENOUGH TO
PREVENT FOG FORMATION...ALTHOUGH PAGS AND PAOH COULD BE A CLOSE
CALL. DRIER AIR FILTERING IN FROM THE N WILL HELP DIMINISH THE
LOWER CLOUDS THIS EVENING...AND FOG SHOULD BE MOSTLY GONE BY EARLY
SAT MORNING.

.LONG TERM...AS A CUT OFF LOW REMAINS WELL TO OUR SOUTHEAST IN THE
NORTH PACIFIC, A NORTHWESTERLY JET WILL SEND TWO PIVOTAL SHORT-WAVES
ACROSS THE NORTHERN PANHANDLE: ONE SATURDAY EVENING, AND THE
SECOND STRONGER ONE SUNDAY. THE FIRST WILL ADVECT COLDER AIR
INTO NORTHWEST CANADA. THIS SHORT-WAVE WILL HELP INCITE ENOUGH
INSTABILITY ALOFT TO FORCE MOUNTAIN WAVES INTO DOWNTOWN JUNEAU AND
DOUGLAS STARTING SATURDAY AFTERNOON, AS DISCUSSED ABOVE AND
CONTINUING THROUGH SATURDAY NIGHT. A STRONGER SHORT-WAVE CURRENTLY
PASSING OVER THE BEAUFORT SEA...WELL NORTH OF THE BERING STRAIT
WILL ROUND INTERIOR HIGH PRESSURE SATURDAY AND MAKE A BEELINE
SOUTH INTO THE PANHANDLE FOR SUNDAY. THIS SHORT-WAVE WILL
REINFORCE THE COLD AIR OVER CANADA, MAKING THE LAYER THICKER WITH
ADDED DENSITY, THUS PERHAPS INCREASING ACCELERATION OF MOUNTAIN
WAVES. THE HIGH WIND WATCH COMMUNICATES THE FAIR LIKELIHOOD OF
GUSTS OF 60 MPH OR GREATER THROUGH SUNDAY NIGHT. WITH THESE
EVENTS, MOUNTAIN WAVES CAN BE SELF-SUSTAINING, AND THERE IS A
CONCERN THAT THE WINDS WILL EXTEND INTO MONDAY. EVEN AS A CRITICAL
LAYER ALOFT IN THE ATMOSPHERE BETWEEN 400 AND 600 MB WILL HAVE
PASSED SUNDAY NIGHT, CROSS BARRIER FLOW AND AN INVERSION ALOFT
WILL REMAIN STRONG THROUGH MONDAY MORNING, THUS ADDING TO THE
UNCERTAINTY OF WHEN THESE WINDS WILL ABATE...EVEN AS WE ARE NOT
COMPLETELY CERTAIN AS TO HOW STRONG THEY WILL BE. WHILE THE WATCH
SPANS A LONG DURATION OF TIME THROUGH LATE SUNDAY NIGHT, THERE MAY
BE LULLS HERE AND THERE, POSSIBLY LATE SATURDAY NIGHT/EARLY SUNDAY
MORNING, CONFIDENCE IS NOT GREAT ENOUGH TO COMMUNICATE THESE LULLS
AT THIS TIME.

IN ADDITION, STORM FORCE WINDS DEVELOPING ON SATURDAY AFTERNOON
WILL CONTINUE THROUGH SUNDAY NIGHT MAKING FOR A VERY IMPACTFUL
WEEKEND OF FERRY TRANSPORTATION BETWEEN JUNEAU AND SKAGWAY/HAINES.
CONTINUED TREND OF AMPLIFYING WAVES TO GREATER THAN CUSTOMARY 5:1
RATIO WITH WINDS. IN ADDITION, STRONG WINDS POSTED FOR SHORT-TERM
IN HAINES/SKAGWAY LOOK PROBABLY TO CONTINUE THROUGH THE WEEKEND.

MOST OF THE EXTENDED FORECAST REMAINS UNCHANGED FROM MORNING
ISSUANCE. WE DID DRY THINGS A BIT THROUGH SATURDAY. HOW THIS DRY
RIDGY PATTERN BREAKS DOWN IS ALWAYS TOUGH FOR MODELS. ECMWF IS
CURIOUSLY INDICATING A POSSIBLE WESTERLY WAVE SPINNING UP WHAT
APPEARS TO BE A SNOW-MAKER FEATURE FOR THE NORTHERN PANHANDLE LATE
WEDNESDAY, BUT NONE OF THE OTHER MODELS ARE SHOWING THIS, AND EVEN
ECMWF HAS NOT BEEN CONSISTENT WITH IT. THUS WILL KEEP CHANCE POPS
FOR WEDNESDAY BECOMING LIKELY WEDNESDAY NIGHT. COOLED TEMPS A
LITTLE MID-WEEK TO TAKE INTO CONSIDERATION OF COOLING IF THIS
OCCURS. BEYOND MID-WEEK, IT LOOKS AS THOUGH SOUTHERLY FLOW LOOKS
SET TO MAKE A RETURN. THIS MEANS WET, AND LIKELY RAIN FOR THE
SOUTHERN/CENTRAL PANHANDLE. WITH THE SNOW EDGE A BIT UNCERTAIN
BETWEEN HAINES AND ICY STRAIT/JUNEAU CORRIDOR. I WOULD BET ON
RAIN.

USED ECMWF AND WPC FOR SOME UPDATES MIDWEEK...MAINLY TO POPS.
MINOR TWEAKS WERE MADE FOR WIND TO EXTEND POSSIBILITY OF HIGH
WINDS INTO SUNDAY NIGHT.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...HIGH WIND WATCH FROM SATURDAY AFTERNOON THROUGH LATE SUNDAY
     NIGHT FOR AKZ025.
         STRONG WIND FROM MIDNIGHT AKST TONIGHT THROUGH SATURDAY
     AFTERNOON FOR AKZ019.
         STRONG WIND THROUGH SATURDAY AFTERNOON FOR AKZ018.
MARINE...STORM WARNING FOR PKZ012.
         GALE WARNING FOR PKZ011-013-021-022-031-032-034-035-043.
         SMALL CRAFT ADVISORY FOR PKZ033-041-042-051>053.

&&

$$

RWT/JWA

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