Area Forecast Discussion
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000
FXAK67 PAJK 012347
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
347 PM AKDT WED OCT 1 2014

.SHORT TERM...WV IMAGERY SHOWS A TROUGH MOVING E ACROSS NRN B.C.
THIS AFTERNOON. BROKEN LAYER OF MIDLEVEL CLOUDS PERSISTS OVER THE
COAST RANGE...WHILE A VERY DRY AIRMASS AND MOSTLY CLEAR SKIES IS
CENTERED ALONG THE COAST AND ERN GULF. ANOTHER COLD NIGHT IS
EXPECTED ACROSS THE REGION TONIGHT DUE TO THE COMBINATION OF CLEAR
SKIES AND A COOLER AIRMASS SPREADING SWD BEHIND THE PREVIOUSLY
MENTIONED TROUGH. PATCHY FOG MAY DEVELOP OVER WIND SHELTERED
LOCATIONS TONIGHT...BUT IS CURRENTLY NOT EXPECTED TO BE AS DENSE
AS WHAT WAS OBSERVED WED MORNING /I.E. JUNEAU AIRPORT/ DUE TO
CONTINUED DRYING IN THE BOUNDARY LAYER AND INCREASED MIXING IN
RESPONSE TO STRENGTHENING OFFSHORE WINDS.

MEANWHILE...A VIGOROUS UPPER TROUGH AND DEEPENING SURFACE CYCLONE
POSITIONED S OF THE ALEUTIANS IS FORECAST TO ADVANCE NEWD INTO THE
SWRN GULF THROUGH THU AFTERNOON. THE 12Z ECMWF HAS STARTED TO COME
IN TO LINE WITH LATEST NAM/GFS/GEM...SHOWING A MORE CONSOLIDATED
SURFACE LOW ANCHORED TO A BENT BACK OCCLUDED FRONT. THE FRONT WILL
ADVANCE NNEWD INTO THE SERN GULF AND SRN PANHANDLE BY 00Z FRI.
STRONG LOW-LEVEL WAA AND ISENTROPIC UPGLIDE WILL BE PRESENT ALONG
AND N OF THE FRONT...RESULTING IN RAPID DEVELOPMENT OF RAIN FROM
THE SRN INTO CNTRL PANHANDLE DURING THU AFTERNOON. BEST
COMBINATION OF MOISTURE AND ASCENT WILL BE PRESENT OVER THE SRN
PANHANDLE DURING THIS INITIAL EPISODE OF RAIN...AND WILL BE THE
MOST PROBABLE LOCATION FOR HEAVY QPF VALUES.

ELSEWHERE...POCKET OF -20 TO -22C AIR AT 500 MB WILL SPREAD NE
INTO THE CNTRL GULF BY THU AFTERNOON. THE COLD AIR ALOFT COMBINED
WITH INCREASING BOUNDARY LAYER THETA-E ALONG AND S OF THE FRONT
WILL YIELD SUFFICIENT DESTABILIZATION FOR THE DEVELOPMENT OF A
COUPLE HUNDRED J/KG OF CAPE. DESTABILIZATION WILL BE FURTHER
ENHANCED BY ASCENT ASSOCIATED WITH A MIDLEVEL VORTICITY LOBE
EJECTING NE INTO THE AREA. THUS...EXPECT ISOLATED THUNDERSTORMS
WILL BECOME PROBABLE DURING THE LATE AFTERNOON OVER THE OUTSIDE
GULF WATERS.

MARINE WINDS WILL BE THE MOST SIGNIFICANT HAZARD WITH THE CYCLONE
OVER THE GULF DURING THE SHORT TERM. A 50-70 KT LOW-LEVEL ESELY
JET WILL SPREAD NWD ALONG/AHEAD OF THE SURFACE FRONT ACROSS THE
SRN AND CNTRL GULF BY THU AFTERNOON. THIS WILL YIELD HIGH END GALE
STRENGTH WINDS ACROSS ALL OF THE OUTSIDE WATERS. LLJ WILL
EVENTUALLY REACH CLARENCE STRAIT AND SRN CHATHAM STRAIT BY LATE
THU AFTERNOON FAVORING THE DEVELOPMENT OF GALE FORCE WINDS FOR
THESE LOCATIONS AS WELL. OUTFLOW/GAP WINDS WILL INCREASE TO GALE
OVER CROSS SOUND...AND SMALL CRAFT OVER ICY STRAIT...STEPHENS
PASSAGE...FREDERICK SOUND...AND SUMNER STRAIT. FOR THE LAND
AREAS...ZONE 27 /KLAWOCK AND CRAIG/ AND POSSIBLY 23 /SITKA/ WILL
EXPERIENCE GUSTS UP TO 45 MPH AS THE FRONT/JET MOVES INTO THE
SERN PANHANDLE. IN ADDITION...WINDS ARE EXPECTED TO BECOME GUSTY
OVER DOWNTOWN JUNEAU AND S DOUGLAS DUE TO INCREASING CROSS BARRIER
FLOW COLLOCATED WITH A STABLE BOUNDARY LAYER AND WIND REVERSAL
ALOFT.

.LONG TERM...STRONG LOW WILL MOVE INTO THE SW GULF THU
EVENING...THEN DRIFT NNE TO THE N-CENTRAL GULF AND SLOWLY WEAKEN
FRI. THIS LOW WILL DRIFT TO THE NW GULF FRI NIGHT AND REMAIN THERE
INTO SUN. OCCLUDED FRONT WILL MOVE NE ACROSS THE AREA THU NIGHT.
SECOND WRAP OF FRONT LOOKS LIKE IT WILL MOVE ACROSS THE NW HALF OF
THE AREA FRI. LOOKS LIKE ANOTHER LOW AND FRONT WILL MOVE NNE INTO
THE ERN GULF SAT NIGHT OR SUN. THE LOW OVER THE NW GULF WILL
LIKELY DRIFT ESE INTO THE ERN GULF EARLY NEXT WEEK. USED MAINLY A
BLEND OF THE 12Z GEM/NAM FOR THU NIGHT...THEN WENT WITH 00Z
ECMWF/12Z GEM BLEND FOR FRI-SAT EVENING. USED LATEST WPC FOR THE
MOST PART FOR LATE SAT NIGHT ONWARD.

STRONG OCCLUDED FRONT WILL BRING LOCALLY HEAVY RAIN TO THE AREA
THU NIGHT...ESPECIALLY OVER THE SERN HALF OF THE PANHANDLE. FRONT
WILL GO ALOFT AS IT MOVES THRU THE AREA AND THIS WILL DIMINISH
THE RAIN LATER THU NIGHT AND FRI MORNING...ALTHOUGH IT MAY TAKE A
LITTLE LONGER FOR THE FRONT TO MOVE E OF THE SRN PANHANDLE. SECOND
WRAP OF FRONT WILL MAINLY ENHANCE RAIN AND WINDS OVER THE NW HALF
OF THE AREA FRI. PRECIP MAY BECOME MORE SHOWERY BY FRI NIGHT BUT
FOR THE TIME BEING WILL MAINTAIN STRATIFORM WORDING FOR SIMPLICITY
AS TIMING OF THIS TRANSITION DIFFERS ACROSS THE AREA.

FOR THE WEEKEND AND BEYOND...NEXT SIGNIFICANT RAIN AND WIND EVENT
LOOKS TO BE AROUND SUN AS ANOTHER LOW MOVES INTO THE ERN GULF.
THIS SYSTEM MAY HAVE A JUICIER AIRMASS TO WORK WITH ALTHOUGH MODELS
SUGGEST THE MAIN AXIS OF HIGHEST PRECIP WATER VALUES WILL REMAIN
S OF THE AREA. PRECIP THREAT SHOULD BEGIN TO DIMINISH DURING EARLY
TO MIDDLE OF NEXT WEEK AS LOW MOVES ESE OUT OF THE NW GULF AND
EVENTUALLY TURNS LOW LEVEL FLOW MORE OFFSHORE FROM N TO S. ALSO
SHOULD BRING IN SOME COLDER AIR WITH IT...ALTHOUGH MODELS DO NOT
AGREE ON HOW COLD IT WILL GET.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND FROM THURSDAY AFTERNOON THROUGH THURSDAY EVENING FOR
     AKZ027.
         STRONG WIND FROM THURSDAY AFTERNOON THROUGH THURSDAY EVENING FOR
     AKZ023.
MARINE...GALE WARNING FOR PKZ022-033-035-036-041>043-051-052.
         SMALL CRAFT ADVISORY FOR PKZ011-021-031-032-034.

&&

$$

GARNER/RWT

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