Area Forecast Discussion
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FXAK67 PAJK 291404
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
604 AM AKDT SAT AUG 29 2015

.SHORT TERM...LOW PRESSURE OVER THE EASTERN GULF HAS BECOME
ELONGATED WITH MULTIPLE SMALLER VORTICIES LOOKING AT SATELLITE
IMAGERY. SOME OF THE SHOWERS OFFSHORE HAVE INTENSIFIED OVERNIGHT
WITH SOME LIGHTNING STRIKES DETECTED IN MARINE AREA 43. THESE
CELLS LOOK STRONG ON THE RADAR IN AREA 42 AND 43 SO HAVE GONE WITH
ISOLATED THUNDERSTORMS IN THE FORECAST FOR THOSE AREAS THIS
MORNING AND A SLIGHT CHANCE OF THUNDER TO THE SOUTH. A FRONTAL
BOUNDARY REMAINS OVER THE SOUTHERN INNER CHANNELS AND UP THE
COASTAL MOUNTAINS AND THIS IS WHERE THE HEAVIEST AND MOST
PERSISTENT SHOWERS WILL BE TODAY. EXPECT SHOWERS TO BECOME
SCATTERED THROUGH THE AFTERNOON WEST OF THIS BOUNDARY
(JUNEAU/ANGOON/KAKE LINE).

THE LOW PRESSURE OVER THE OUTSIDE WATERS IS CAUSING SMALL CRAFT
LEVEL WINDS THROUGH SEVERAL MARINE AREAS EARLY THIS MORNING.
NORTHERLY WINDS THROUGH LYNN CANAL...EAST WINDS OUT OF CROSS SOUND
AND SE WINDS THROUGH CLARENCE STRAIT. THESE WILL DIMINISH THROUGH
THE MORNING AS THE LOW WEAKENS. BY THIS AFTERNOON THERE WILL BE LITTLE
PRESSURE GRADIENT AND LIGHT WINDS ACROSS THE PANHANDLE. MANY
PLACES WILL SEE LIGHT AND VARIABLE WINDS CONTINUING INTO THE
EVENING...THEN THE LOW CENTER LOOKS TO REDEVELOP OFFSHORE OF
YAKUTAT. THIS WILL CAUSE INCREASING SELY WINDS OVERNIGHT UP TO
SMALL CRAFT LEVEL THROUGH CLARENCE STRAIT AND OUT OF CROSS SOUND.

EXPECT SHOWERS TO INCREASE AS THE LOW REDEVELOPS AS WELL. THE
YAKUTAT AREA WILL LIKELY HAVE SOME MODERATE SHOWERS. HAVE ALSO
ADDED A SLIGHT CHANCE OF THUNDER OFFSHORE NEAR THE LOW CENTER
TONIGHT (MARINE AREAS 43/51/51).

MODELS HAVE COME INTO BETTER AGREEMENT WITH HOW THEY EVLOLVE THIS LOW
PRESSURE SYSTEM. BUT IT IS STILL AN UNUSUAL PATTERN FOR OUR
REGION...MEANING THE MODELS LIKELY HAVE ERRORS (OVER DOING POPS
FOR EXAMPLE). HAVE MADE SOME ADJUSTMENTS TO THAT EFFECT BUT
FORECASTER CONFIDENCE IS LOWER THAN N

.LONG TERM...UPPER TROF WILL REMAIN OVER THE GULF INTO EARLY NEXT
WEEK...THEN SHIFT SLOWLY EWD FOR THE LATTER PART OF THE WEEK.
SHORTWAVE TROF WILL AMPLIFY AS IT MOVES INTO THE SE GULF SUN. THIS
WILL CAUSE A SFC LOW TO DEVELOP AND MOVE ACROSS THE SE GULF
SUN...THEN ACROSS SE AK SUN EVENING. ANOTHER SHORTWAVE WILL DIVE
INTO THE ERN GULF MON WITH WEAKER SFC LOW MOVING ALONG WITH THAT
FEATURE. HIGH PRESSURE WILL BUILD OVER SE INTERIOR AK AND THE
YUKON EARLY NEXT WEEK. USED BLEND OF THE 00Z NAM AND ECMWF THRU
MON TO CAPTURE STRONGER SFC LOW FOR SUN AND RESIDUAL FEATURES
LEFT OVER EARLY NEXT WEEK.

FOR SUN...AS LOW DEVELOPS OVER THE SE GULF...OCCLUDED FRONTAL
BAND WILL ORGANIZE WITH IT AND MOVE ONSHORE LATE SUN MORNING. FRONT
WILL PRODUCE 25-30 KT WINDS AHEAD OF IT OVER THE SE GULF...WITH
30-35 KT WINDS ON SW SIDE OF LOW AS COLD ADVECTION INCREASES. A
WELL ORGANIZED BAND OF RAIN SHOULD AFFECT MUCH OF THE AREA SUN
WITH THE FRONT. RAIN COULD BE LOCALLY HEAVY SE OF PAGN-PASI LINE.
SOME SHOWERS WILL REMAIN OVER THE NE GULF AND PAYA AREAS NEAR WEAK
LOW IN THAT AREA.

SUN NIGHT AND MON...PRECIP WILL BECOME SHOWERY AGAIN AREA WIDE AS
COLDER AIR ALOFT MOVES IN BEHIND LOW AND FRONT. LATER SHIFTS WILL
NEED TO MONITOR POTENTIAL FOR TSTM ACTIVITY OVER MAINLY THE SRN
GULF AS MORE SHORTWAVE ENERGY MOVES THRU THAT AREA. WINDS WILL
GRADUALLY DECREASE OVER MUCH OF THE GULF DURING THIS TIME.

BEYOND MON...A DRIER PERIOD LOOKS LIKELY FOR MIDWEEK AS UPPER
TROF SHIFTS INLAND AND LOWER LEVEL FLOW BECOMES MORE NLY. LATE IN
THE WEEK...THE MODELS DIVERGE SOMEWHAT ON A SYSTEM THAT MAY END UP
IN THE GULF BY FRI...SO FORECAST CONFIDENCE DROPS CONSIDERABLY AT
THAT POINT.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ012-013-022-031-036.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ041-042.

&&

$$

FERRIN/RWT

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