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FXAK67 PAJK 291332

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
532 AM AKDT FRI JUL 29 2016

.SHORT TERM...A low over the northern gulf passed over Middleton
Island overnight and continues to track slowly to the east.
Steady shower activity in Yakutat tapered off later in the night
while increasing over more easterly locations as the low moved
east. No heavy showers have been reported so far, but there have
been a few reports of moderate rain rates. This downward trend in
rain rates was expected, well forecasted by the models, and
reflected in QPF grid this morning. Showers will continue to move
south and east across the panhandle through the short term, but
the overall trend in shower activity will be a diminishing one.
Convective parameters once again suggesting the threat of
thunderstorms over the gulf or panhandle is very low, hence they
are not included in the forecast issued this morning. A slightly
cooler low level airmass has accompanied the low and todays temps
will be a few degrees cooler than yesterday for all but the far
southern zones. Likewise for low temps tonight. A surface ridge
over the panhandle continues to produce a strong southerly
gradient over the far northern inner channels and gusty conditions
are once again forecast for Skagway and the Klondike Highway.
Northern Lynn Canal remained southerly through the night and am
expecting 20 kts through the day today. Elsewhere on the inside,
winds 15 kts or less expected. On the outside, small craft
conditions due to seas north of Cape Edgecumbe for this morning
and westerly winds 25 to 30 kts over offshore zone 310 on the
south side of the low.

Previous forecast remains on track, so no changes to pressure
field. Only a few minor revisions to winds with the largest
change being to reduce winds over northern Lynn Canal from 25 kts
to 20 kts. Used NAM DNG5 for updates to POP grids for this
afternoon and tonight. QPF from DNG5 and NAM12. Temps adjusted
using both GFS and NAM MOS. Overall forecast confidence is

.LONG TERM...Somewhat progressive pattern for the long range
period as a large upper low over the arctic, north of Alaska,
exerts its influence even this far South. The broad upper trough
over the gulf in the short range will have stretched apart by Sat
with the few lingering pieces left in the SW gulf or having
drifted over the panhandle into Canada. Some weak ridging builds
in for the late weekend and early next week but it does not last
as the arctic upper low continues to force features to the east. A
new upper low caught in the westerly flow will displace the
ridging and move into the gulf by mid week.

At the surface, forecast is generally dry through early next
week as weak surface ridging combines with the upper level
ridging. However, I could not completely rule out some shower
activity for the northern panhandle Sat night into early Sun as a
weak upper trough and vorticity will be drifting through at that
time. Kept pops at a slight chance for that period. Winds will
also be rather quiet with 10 to 15 kt W winds in the gulf and
some 20 kt southerlies in lynn canal. Warmest time period will be
Sat and Sun as enough breaks in the clouds might open up for some
sun to warm things up a little. I did not go any higher then mid
60s though as flow continues to be onshore and enough clouds
should still be around to keep temps from getting too warm.

Rain returns to the forecast mid week as the next upper low moves
into the gulf. Feature will be weakening as it comes having
expended most of its energy and rain farther W. Surface
reflection will be rather weak as well so little in the way of
wind is expected for the gulf and panhandle. Long range models
appear to be handling this feature rather well as spread is not
that great and timing seems rather close between them. Exact
positioning is still a little tricky though, with the Canadian
forming the surface reflection a little farther south then
everyone else.

Overall not many changes to the long range forecast. Main changes
were for the Sat into Mon period as models are now suggesting
weaker surface ridging over the gulf. This lead to some lighter
winds for the gulf this weekend. Used mainly GFS for guidance


.AVIATION...Conditions ranging from IMC for low cigs over
northern locations to VMC in the south. Little change over central
and southern locations, but an improving trend is expected over
the northern locations as the low tracks east and weakens.
Weakly convective environment forecast, so no significant
turbulence expected. Slight chance for reductions to vsby tonight
in patchy fog and light winds.


.HYDROLOGY...The Taiya River fell below minor flood stage around
midnight and continues to fall. The flood warning was allowed to
expire on time overnight. Mendenhall Lake continues to rise with a
24 to 48 hour lag between heavier precipitation and observed water
level rising. Based on the current rate of rising water, the lake
may reach minor flood stage later today. No other concerns across
southeast Alaska.


.AJK Watches/Warnings/Advisories...
MARINE...Small Craft Advisory due to Seas for PKZ043-051-052.



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