Area Forecast Discussion
Issued by NWS
FXAK67 PAJK 272357
Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
357 PM AKDT SAT AUG 27 2016
.SHORT TERM...The latest satellite imagery shows some clouds
moving over the northern half of the area from Yakutat to the
Haines/Skagway area. These clouds are associated with an upper
level trof sliding southeast. The rest of the forecast area is
mostly clear with some thin high clouds. The entire long wave
upper trof will drift southeast through tonight with the clouds
increasing from north to south across the northern half. The
southern half will see clouds move over the area from the east as
a surface low will develop southwest of Haida Gwaii and drift
drift northeast through the next 24 hours. This weak low will
trigger some scattered showers late tonight into Sunday over the
southern third. The rest of the area will remain on the dry side.
Wind wise...there is a weak northernly pressure gradient at this
time with winds generally less than 15 kt but Northern Lynn Canal
is seeing 20kt this afternoon. These conditions will persist
through tonight but as the low slides closer to the southern
panhandle the winds over the northern areas will relax to be less
than 15 kt.
Temperatures will remain above normal through Sunday with lows
tonight in the upper 40s to mid 50s. The high temperatures for
sunday was a bit tricky due the amount and thickness of the cloud
cover. With that said highs tomorrow will be above normal and will
range from the mid 60s over the south and upper 60s over the
north. Temps could go into the lower 70s over the northern half if
there is more sunshine.
Overall there is about average forecaster confidence but lower
confidence on cloud cover. Used a mix of the high-res models and
the 18z nam.
.LONG TERM...Model run to run consistency with regard to a low
that will be located near Haida Gwaii at the start of the extended
range forecast period is still not very good. all are generally
keeping it in the far southeastern gulf, but vary on precise
location and strength. With the proximity to the southern
panhandle, changes to the location and strength of this feature
will result in potentially significant changes to winds over the
gulf, the inner channels, and the public zones. Consequently, no
changes to the pressure or wind grids were made through the early
part of next week.
Models were in better agreement with regard to wrap around showers
associated with the surface low and the related upper low. Blended
in SREF to existing PoP grids to increase chances of showers a
little over the southern half of the panhandle. Farther north,
trimmed back PoP through Monday afternoon based on the idea that
offshore flow will keep showers on the Canadian side of the coast
mountains. Scattered, occasionally numerous showers remain in the
forecast until next Thursday, when a ridge will push in from the
west. Close behind will be a front that is expected to arrive
sometime next weekend.
850mb temps are indicating that some cooler air will be advected
into the area courtesy of the upper low vicinity Haida Gwaii and
MOS guidance is showing this as well. Left highs for Monday mostly
unchanged, but did adjust highs and lows down for the remainder of
the extended range forecast period.
Overall forecast confidence is average.
.HYDROLOGY...There has been another release from Suicide Basin
into Mendenhall Lake. This is the sixth release this year. At this
time the forecast is for the lake to crest late Sunday morning
around 8.6 feet, which is below minor flood stage of 9.0 feet. The
inherent uncertainty in initial glacier lake volume will result in
varying crest height and timing. There is an SPSAJK product out
for the event please refer to that product for more information.
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