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647
FXAK67 PAJK 272308
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
308 PM AKDT TUE SEP 27 2016

.SHORT TERM...Low pressure tracking across the far southern gulf
has kept showers going across the panhandle today. Some showers
over the gulf have produced lightning and likely graupel (small
hail). Expect numerous showers to continue tonight along with a
slight chance of thunder over the gulf. Then showers will gradually
decrease from north to south through Wednesday afternoon as the
low progresses toward the Canadian Maritimes and flow over the
panhandle turns more offshore.

As the low moves eastward winds through the northern inner
channels will shift from SE to NE by Wednesday morning, then N-NW
through all the inner channels Wednesday afternoon. This flow
pattern will help to clear out the showers and expect decreasing
clouds in the afternoon. Breaks in the clouds between showers
during the early morning hours may be enough for radiation fog to
develop. Wet ground and low tide just after 6am will help in this.
Have included patchy fog during the early morning hours where wind
gusts were less than 15kt and other conditions were favorable.

Temperatures look to drop below 40 degrees across the northern
panhandle overnight. Some areas like Yakutat and out the Haines
Highway could see frost in the early morning (this would limit
amount of fog somewhat) since lows are forecasted to be about
34F. White Pass will likely see some snow if any showers pass over
this evening, but amounts should be very limited. Then decreasing
clouds in the morning and a shift to north winds will cause them
to drop below 30 degrees. Decreasing clouds and some sunshine
through the afternoon will make it feel warmer tomorrow, but
highs look to remain in the mid 50s.

Models were in good agreement. Small adjustments to the inherited
forecast were made with an ensemble approach of models along with
local effects. Forecast confidence is above average.

.LONG TERM...Dry windy weather still in the works for the long
range period as a large blocking ridge builds over the western
gulf. The ridge will be at its strongest Thu into Fri. By the
weekend, the base of the upper ridge will be pinching off with a
cutoff upper high getting left in northern and eastern Alaska and
the jet stream reconnecting across the northern Pacific. A
lingering upper low over NW Canada will keep flow aloft out of the
N or NW through mid next week.

The surface pressure pattern will largely follow what the upper
levels are doing. Except over interior Alaska and the Yukon late
this week into the weekend. The northerly winds on the east side
of the upper ridge are dragging down some colder air from the
arctic for Fri and Sat. Surface MSLP in the Yukon will spike up to
1035 to 1040 mb due to the strong cold air mass. Strong outflow
winds out of the usual mountain passes is the result. Winds are
expected to start increasing across the northern inner channels as
early as Thu and last through Sat at least. Peak winds are expected
Fri night as a low forms across Dixon Entrance on Fri constricting
the pressure gradient further. Lynn Canal and Taku Inlet will
likely reach gale force with gusty winds expected at Skagway,
Haines, Cross Sound, and the passes east of Yakutat.

A Taku wind event is also possible for downtown Juneau and Douglas
Fri as Outflow reaches its peak. Cross barrier flow will be
reaching 30 to 50 kt across the ridge. An inversion will be
present with the cold air outflow continuing across the northern
inner channels although it will not be as strong as it could be if
it were the middle of winter instead. There will even be a weak
critical level developing around 600 to 700 mb. Given these
ingredients, conditions appear favorable for gusts of 40 to 60
mph depending on how well developed the ingredient actually
become.

Into the extended the outflow dies down into the late weekend as
the cold air fueling it moves farther east into Canada. However,
dry conditions continue as what is left of the upper ridge
continues to block or divert storms incoming from the west and
northerly offshore flow continues at most levels over the
panhandle into mid week at least. Next chance of rain does not
appear until mid next week.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Small Craft Advisory for PKZ022-036-042.
&&

$$

Ferrin/EAL

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