Area Forecast Discussion
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FXAK67 PAJK 262325
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
325 PM AKDT SUN APR 26 2015

.SHORT TERM...THE VERTICALLY STACKED LOW OVER THE WEST CENTRAL
GULF OF ALASKA WILL PERSIST INTO EARLY NEXT WEEK WHILE SLOWLY
WEAKENING. THE ASSOCIATED FRONTAL BAND WILL HAVE HAVE SPREAD
THROUGH THE PANHANDLE THEN ARCS BACK INTO THE EASTERN PACIFIC.
THROUGH LATE TONIGHT AND MONDAY A DEVELOPING WAVE WILL MOVE NORTH
ALONG THE OLD FRONT BUT THEN APPROACH THE SOUTHERN PANHANDLE LATE
MONDAY AFTERNOON.

THE RAIN ACROSS THE PANHANDLE IS TRANSITIONING OVER TO SHOWERS.
THERE IS QUITE A POOL OF COOLER AIR ALOFT AS 500 MB TEMPERATURES
RANGED AS COLD AS -36 C ARE MOVING INTO THE EASTERN GULF. THIS POOL
OF COLD AIR ALONG WITH THE LIFT FROM AN UPPER LEVEL VORTICITY LOBE
ROTATES INTO THE REGION ABOUT THE UPPER LEVEL LOW. THE ADDITIONAL
LIFT WILL BE ENOUGH FOR ISOLATED THUNDERSTORMS TO DEVELOP. THEY
SHOULD STAY PRIMARILY OFF SHORE BUT DO EXPECT THEM TO LIKELY GRAZE
CHICAGOF AND BARANOF ISLANDS LATE TONIGHT AND EARLY MONDAY
MORNING.

WINDS ARE 25 TO 30 OUT OVER THE GULF OF ALASKA AND OUTER
COASTAL REGIONS. A FEW OF THE INNER CHANNELS ARE UP TO SMALL CRAFT
LEVELS BUT ARE PRIMARILY 20 KT OR LESS.

.LONG TERM...SUN AFTERNOON WV IMAGERY SHOWS A SHORTWAVE TROUGH
OVER THE N PAC ROUNDING THE BASE OF AN UPPER LOW CENTERED OVER THE
SRN GULF. LATEST MODEL GUIDANCE INDICATES THE SHORTWAVE WILL EJECT
NE INTO THE NERN PAC BY 06Z TUE...AND THEN LIFT N ACROSS HAIDA
GWAII BY 15Z TUE. THIS FEATURE THEN MOVES N OVER THE SRN/CNTRL
PANHANDLE THROUGH 00Z WED. DETERMINISTIC MODEL SOLUTIONS ARE
SUBSEQUENTLY CONVERGING ON THE DEVELOPMENT OF A COMPACT SURFACE
LOW PRESSURE SYSTEM MOVING N INTO THE PANHANDLE WITH ITS PARENT
UPPER TROUGH. THE 12Z GFS AND NAM WERE FASTER SOLUTIONS WITH THE
NWD MOVEMENT OF THE LOW COMPARED TO THE 12Z GEM AND ECMWF...BUT
THE 18Z GFS AND NAM HAVE TRENDED TOWARD A SLOWER EVOLUTION AS WELL.

AS A RESULT...UPDATED PRESSURE GRIDS REFLECT A HEAVIER WEIGHTING
TOWARD THE GEM/ECMWF...WHICH YIELDS STRENGTHENING NNELY WINDS
DURING TUE MORNING THAT RAPIDLY FLIP TO SLY AFTER THE PASSAGE OF
THE LOW. GALE FORCE WINDS APPEAR PROBABLE OVER CLARENCE STRAIT AS
THIS HAPPENS...WHILE NLY SMALL CRAFT WINDS OVER LYNN CANAL DURING
TUE MORNING/AFTERNOON WILL BECOME SLY SMALL CRAFT WINDS TUE NIGHT.
A SIMILAR EVOLUTION IS EXPECTED FOR STEPHENS PASSAGE AS A 30+ KT
SLY LLJ SPREADS N BY TUE AFTERNOON/EVENING. IN ADDITION...GUSTS
WILL APPROACH STRONG WIND CRITERIA OVER AKZ027-028 AS THE SLY LLJ
DEVELOPS IN THE WAKE OF THE LOW TUE AFTERNOON.

PW VALUES NEAR 0.8 INCH ARE FORECAST TO BE DRAWN NWD WITH THE
PREVIOUSLY MENTIONED SURFACE LOW...WHICH COULD AID IN PERIODS OF
HEAVY RAIN OVER THE SRN/CNTRL PANHANDLE DURING TUE. IN
ADDITION...500 MB TEMPERATURES NEAR -30 C WILL SPREAD EWD ACROSS
THE SRN OUTSIDE WATERS AND PANHANDLE AS THE SHORTWAVE TROUGH LIFTS
N OF THE AREA TUE AFTERNOON. SUBSEQUENT DESTABILIZATION WILL
RESULT IN THE REDEVELOPMENT OF A CONVECTIVE ENVIRONMENT...AS WELL
AS A SLIGHT CHANCE OF THUNDERSTORMS AS MINOR UPPER IMPULSES MOVE
ACROSS THE AREA.

AFTER TUE...MODEL GUIDANCE REMAINS IN FAIR AGREEMENT WITH THE
LARGE-SCALE UPPER AIR EVOLUTION THROUGH 00Z SAT...WITH DIFFERENCES
IN THE DEVELOPMENT OF AN UPPER RIDGE BECOMING MORE NOTICEABLE BY
SUN AND MON. GFS AND ECMWF WERE USED FOR POP/QPF THROUGH MOST OF
THE WEEK. WPC WAS THEN USED FOR PRESSURE AND POP GUIDANCE 00Z FRI
AND BEYOND...WHICH WAS COMPOSED OF A HEAVY ENSEMBLE BLEND.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING FOR PKZ051-052.
         SMALL CRAFT ADVISORY FOR PKZ021-022-033>036-041>043.

&&

$$

BEZENEK/GARNER

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