Scientific Forecaster Discussion
Southeast Alaska forecast discussion
National Weather Service Juneau Alaska
605 am akst sun Nov 29 2015
Short term...weather across the Panhandle overnight ranged from
accumulating snow around Haines and Skagway...steady rains over
the central Panhandle...ridge top winds to 80 miles per hour near Juneau...
and clear skies over southern Prince of Wales Island to
Ketchikan. The weather is associated with a stationary front that
at 5 am stretched from west of Yakutat and southward over the
Precipitation was steady just to the east of the front north of a
line from near Sitka to Juneau. It was all rain except for near
Haines and Skagway where snow was observed much of the night.
Winter storm warnings remain in effect along the highways near the
Canadian border. The warning along the Haines Highway will expire
at 9 am when snow is expected to change over to rain. The warning
along The Klondike Highway will expire at 6 PM when the snow is
expected to diminish. Satellite imagery clearly shows frontal
clouds edging slowly west-northwest so precipitation in general will
diminish from the southeast today. Skies are already clear south from
approximately Sumner Strait at 5 am.
The strong low level winds are due to the pressure gradient
between the offshore front and surface high pressure in British
Columbia and the proximity of the 80-100 knots SW winds aloft in the
middle and upper levels. The North American ensemble model shows the
rather deep core of high winds remaining over the forecast area
tonight then diminishing. The high res NAM also maintains moderate
east-southeast surface winds east of the front into this evening.
Forecasts did not need much updating. Precipitation amounts were trimmed
in some places and the areal coverage was shifted slightly north
to match morning observations. Forecast confidence is the short
term evolution of precipitation and winds is average.
Long term...a weak upper wave is forecast to move east across the
Panhandle Monday morning. As this occurs...a wavering quasi-
stationary frontal boundary located north-S over the region the past
few days will advance inland and weaken. However...a deep upper
wave will spread across the western/central Gulf by Monday afternoon. As
this occurs...the remnant surface boundary will surge north-northwest from the
southern Panhandle to the central Panhandle. Low-level sselys will
rapidly intensify in its wake...yielding small craft to gale
strength winds from southern Lynn Canal S to Clarence Strait. In
addition...strong winds with gusts to 40-50 miles per hour are expected by
Monday afternoon/night for akz027-028 and possibly 025. Moderate to
locally heavy rain is also likely as slys/moisture flux
An upper disturbance over the central Gulf will progress to the eastern
Gulf by Monday night and interact with the strong southerly moisture flux
occurring over the Panhandle...aiding in continued moderate
rainfall going into Tuesday /with snow expected at White
Pass...possibly advisory level/. Thereafter...progressive flow
regime persists through the remainder of the long term. Model
guidance shows a series of upper waves impacting the region.
However...as noted in previous shifts...spread in shortwave
details becomes substantial Wednesday and beyond.
Given the increasing forecast uncertainty after Wednesday...changes to
inherited long term grids were generally confined to Monday and Tuesday.
Pressure was nudged toward ECMWF/GFS...and pop/quantitative precipitation forecast were updated
with a GFS/ECMWF/NAM blend. Temperature grids were virtually left
public...strong wind until noon akst today for akz025-027.
Strong wind late tonight for akz027.
Strong wind until 9 am akst this morning for akz023.
Strong wind this evening for akz023.
Winter Storm Warning until 9 am akst this morning for akz019.
Winter Storm Warning until 6 PM akst this evening for akz018.
Marine...Gale Warning for pkz013-022-031-041>043.
Small Craft Advisory for pkz011-012-021-032>036.
Small Craft Advisory due to seas for pkz051-052.
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