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172
FXAK67 PAJK 281333
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
533 AM AKDT THU APR 28 2016

.SHORT TERM...AN UPPER LOW WAS CENTERED OVER THE ERN ALEUTIANS THU
MORNING...WITH A 100+ KT 300 MB JET PRESENT TO ITS S. THIS JET
WILL SPREAD EWD ACROSS THE NERN PAC THU AFTERNOON/NIGHT...WHILE TO
ITS N...MIDLEVEL VORT LOBES WILL ADVANCE NEWD ACROSS THE ERN GULF
AND PANHANDLE. AT THE SURFACE...LOW PRESSURE WAS POSITIONED OVER
THE WRN GULF...WHILE AN OCCLUDED FRONTAL BOUNDARY ARCED EWD ACROSS
THE CNTRL GULF...AND THEN SEWD TOWARD THE SERN GULF. THE FRONT IS
FORECAST TO MOVE ENE ACROSS THE ERN GULF THROUGH THIS
AFTERNOON...AND THEN DISSIPATE AS IT ADVANCES ONSHORE OVER THE
PANHANDLE. STRATIFORM RAIN /POSSIBLY MODERATE IN INTENSITY/ WILL
OCCUR ALONG AND AHEAD OF THE FRONT...AND THEN TRANSITION TO
SHOWERS BEHIND THE FRONT AS COOLER MIDLEVEL TEMPERATURES/STEEPER
LAPSE RATES SPREAD ACROSS THE REGION.

GALE FORCE ELYS WILL OCCUR ALONG/AHEAD OF THE FRONT OVER THE NRN
GULF MARINE ZONES INTO THE EARLY EVENING...WHERE AUGMENTATION DUE
TO BARRIER JET EFFECTS IS OCCURRING. A PERIOD OF GALES IS ALSO
POSSIBLE FOR CLARENCE STRAIT DURING THE LATE MORNING. MARINE WINDS
ARE THEN FORECAST TO WEAKEN THIS EVENING/TONIGHT...WITH POST
FRONTAL WIND DIRECTIONS TAKING ON A WLY COMPONENT.

VERY FEW GRID CHANGES WERE NECESSARY. MULTI-MODEL ENSEMBLE
APPROACH WAS USED FOR THE FEW UPDATES MADE.

.LONG TERM...GLANCING AT THE SATELLITE IMAGE OR READING THE
FORECAST THAT WE SUBMITTED THIS MORNING, ONE MAY BE FORGIVEN FOR
WONDERING WHETHER THIS IS ACTUALLY OCTOBER INSTEAD OF APRIL. ONE-
HUNDRED FORTY KNOT JETS ALOFT, THE WORDS /STORM-FORCE/ APPEARING
IN THE MARINE HEADLINES ALONG THE OUTSIDE WATERS, AND PRECIPITABLE
WATER VALUES EXCEEDING THREE STANDARD DEVIATIONS ABOVE NORMAL ALL
PORTEND A STORMY PATTERN FOR SOUTHEAST ALASKA.

WITH AN UPPER LOW ANCHORED JUST SOUTH OF THE ALASKA PENINSULA AND
A RELATED TROUGH AXIS EXTENDING ACROSS THE NORTHERN GULF, SHOWERS
WILL CONTINUE ACROSS SOUTHEAST ON FRIDAY. BUT GIVEN RISING
HEIGHTS BEHIND THE TROUGH AXIS IN RESPONSE TO A FAST-DEVELOPING
POTENT LOW OVER THE NORTH PACIFIC, SHOWERS WILL BEGIN DIMINISHING
FRIDAY NIGHT. MEANWHILE A GALE FORCE LOW CROSSES INTO THE EASTERN
GULF AND ACCELERATES TO STORM- FORCE BY SATURDAY AS IT APPROACHES
THE STEEP TERRAIN OF THE SOUTHEAST ALASKA COASTLINE. CONFIDENCE IS
HIGH FOR THIS FRONT, BUT GIVEN AN IMPRESSIVE LOW- LEVEL JET AT 925
MB EXCEEDING 50 KT IN SOME PARTS OF THE SOUTHERN PANHANDLE, WE
WENT AHEAD AND RAISED FREDERICK AND SUMNER TO GALES FOR SATURDAY
AND STRENGTHENED OUR PREVIOUS GALE FOR CLARENCE STRAIT. IN
ADDITION, BARANOF ISLAND SOUTHEAST TO ANNETTE ISLAND SHOULD
EXPERIENCE STRONG WIND GUSTS OF 40 MPH AND GREATER. POTENTIALLY
THESE STRONG WIND GUSTS MAY LIFT NORTHWARD INTO HOONAH, GUSTAVUS,
OR JUNEAU, BUT CONFIDENCE WAS ONLY HIGH ENOUGH TO NUDGE UPWARD
SLIGHTLY. WHATEVER THE CASE, SATURDAY LOOKS TO BE A WINDY DAY FOR
MUCH OF THE PANHANDLE.

IN ADDITION TO WIND, THIS DEVELOPING LOW AND FRONT HAS TAPPED DEEP
SUBTROPICAL MOISTURE. IT WOULD SEEM THAT SOUTHEAST ALASKA WILL
EXPERIENCE TWO ROUNDS OF POTENTIALLY HEAVY RAIN. THE FIRST TO
ARRIVE WITH THE STORM FORCE FRONT ON SATURDAY INTO SATURDAY
EVENING AND A SECOND GATHERING WITH A WAVE THAT FORMS ALONG A
STALLED FRONT TRAILING BEHIND THE FIRST SYSTEM DEEP INTO THE NORTH
PACIFIC. THIS WAVE WILL APPROACH THE SOUTHERN PANHANDLE BY LATE
SUNDAY. CONFIDENCE LESSENS WITH THE TRACK AND STRENGTH OF THIS
SYSTEM, BUT 00Z MODELS OFFER THAT IT WILL STAY OFFSHORE WHILE
CURVING NORTHWEST TOWARD POINTS WEST OF YAKUTAT. THIS PATH WOULD
DIRECT MORE POTENTIALLY HEAVY RAIN FROM SOUTH TO NORTH ACROSS
SOUTHEAST. WE STILL EXPECT ANYWHERE BETWEEN 2 AND 4 INCHES OF
RAINFALL ACROSS THE AREA FROM SATURDAY MORNING INTO MONDAY
AFTERNOON. QPF WAS CHANGED LITTLE FROM THIS TIME FRAME AS NEW
GUIDANCE HAS NOT DEVIATED FROM OUR FORECAST SIGNIFICANTLY. THE
SPECIAL WEATHER STATEMENT HIGHLIGHTING THE INCREASING POTENTIAL
FOR WIND, HEAVY RAIN, AND RIVER RISES IS STILL IN EFFECT.

LOOKING BEYOND MONDAY, THE WAVE MOVES ASHORE AND COOLER ONSHORE
FLOW WILL SUSTAIN SHOWERS MONDAY NIGHT THROUGH MID-WEEK WITH SOME
HINTS OF RIDGING GIVING US A BRIEF BREAK BY NEXT THURSDAY.
CONFIDENCE GOOD FOR IMPACTFUL WEATHER THIS WEEKEND.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING FOR PKZ036-051-052.
     SMALL CRAFT ADVISORY FOR PKZ022-033-035-041>043.
     SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ053.
&&

$$

GARNER/ADKINS

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