Scientific Forecaster Discussion
Southeast Alaska forecast discussion
National Weather Service Juneau Alaska
256 PM akdt Sat Sep 20 2014
Short term...difficult decision today on the strength and track
of the next wave off the coast as the gale force low this morning
dissipates this evening. Chose the 20/12z European model (ecmwf) as the guidance
which was the deepest of the Ops models but consistent with the
track and storm force winds of the previous shift. Wind wind wind
was the challenge. Indicated strong wind headlines for the outer
coast and Ketchikan and gales and storms in the marine forecasts.
Confidence only moderate and if in error the wind speeds were
forecasted on the high side respecting this storm. Wet wet wet but
with moderate temperatures.
Long term...biggest story of the period will be storm force low
in the eastern Gulf that is discussed in the short range section.
This low will continue to move to the north and west on Sunday
night and move inland in the vicinity of Icy Bay. As the system
moves inland a ridge of high pressure rapidly builds in from the
south over the Panhandle Sunday night leading to a strong wind
event for much of the area. Jet stream shifts south of the area
middle week with a broad upper level low over the northeast Pacific.
This will result in drier offshore flow especially over the
northern half of Southeast Alaska. Models indicate this upper
level will get pushed to the east later next week as a trough
tries to reestablish itself over the central Gulf leading to a
return of onshore flow and increased rain chances late in the
Wind event will be ongoing in the eastern Gulf and along the
coastal areas. As high pressure builds in rapidly Monday evening
combined with a 50-60 knots low level jet...southerly winds will
increase quickly over much of the area. Expect strong wind gusts
of at least 40-50 miles per hour over much of the land areas and 30-40 kts
of wind in the marine locations. Have not extended strong wind
headlines from short term period into Sunday night with this
forecast package but they will be included with the next package.
Winds will gradually subside overnight...lingering longest over
the northern Inner Channels including Lynn Canal and near Skagway.
For the rest of the week...wind does not look to be as much of a
concern as the strongest winds remain well south and east of
Southeast Alaska in association with the upper low.
Rain will be falling across most of the Panhandle before
transitioning to showers overnight Sunday and into Monday as a
cooler airmass moves in with 850 mb temperatures falling close to
0-2 c. This results in snow levels lowering to around 4000 feet.
Showers gradually diminish later Monday with drier conditions on
Tuesday and into the first half of Wednesday. Model solutions
begin to diverge after that with bands of precipitation rotating
up from the upper low to the south. Indications of another front
pushing into the eastern Gulf by next weekend.
Used the 12z European model (ecmwf) as it was a good compromise for the storm
force low over the eastern Gulf at the beginning of the long range
period. Transitioned to latest wpc guidance after day 4.
Forecaster confidence remains a bit lower than average with storm
force low as models continue to show differences in timing and
exact track.For the remainder of the extended period confidence
public...strong wind from Sunday afternoon through Sunday evening for
Strong wind from Sunday afternoon through Sunday evening for
Marine...Storm Warning for pkz041>043.
Gale Warning for pkz022-033-035-036-051.
Small Craft Advisory for pkz011>013-021-031-032-034-052-053.
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