Scientific Forecaster Discussion
Southeast Alaska forecast discussion
National Weather Service Juneau Alaska
516 am akdt Friday Oct 21 2016
Short term...wet and windy night across the southern Panhandle as
a gale force low moves into the southeast Gulf from the S. Highest gusts
so far have been observed at Ketchikan Airport with a 40 mph gust
around midnight. Other parts of the southern Panhandle have seen
gusts around 30 to 40 mph throughout the night. Winds farther
north have generally been low, except for Cross Sound where 25 kt
east winds are blowing.
Winds across the southern Panhandle will continue through Fri
afternoon as the main low will not be moving very fast. It is
forecast to move slowly north today then start taking a westward
jog tonight, slowly weakening as it GOES. 850 mb low level jet
winds remain around 40 to 45 kt over the southern Panhandle
through Fri afternoon before weakening. With the atmosphere rather
unstable, gusts to 40 or 45 mph are still expected to mix to the
surface through this afternoon so strong wind headlines remain up
for land areas with gales warnings or small craft advisories for
most marine zones. Winds will diminish Friday evening as the low
weakens and moves farther out to sea. Most northern Panhandle
winds will remain 20 kt or less for the period.
This system is cold core in nature with 500 mb temps above the
system dropping to -28 c. This cold air above the warm waters of
the Gulf is creating a somewhat unstable atmosphere over the southeast
Gulf. Resulting precip has been very convective in nature based on
satellite and radar imagery. Embedded thunderstorms have also been
observed as lightning detection has seen several lightning strikes
around haida gwaii and marine zone 41 overnight, but no strikes
over the southern Panhandle yet. Showers will continue across the
Panhandle through tonight with the highest chances across the
southern Panhandle as more easterly and northerly flow farther
north inhibit precip chances. Embedded thunderstorms will remain
possible across the southeast Gulf through tonight. Some of these storms
could make it into the extreme southern Panhandle but convective
potential drops off rapidly as you get into the Inner Channels so
I only have a slight chance of thunder for zones 27 and the very
southern part of zone 28.
Short range models were in decent agreement and generally were
consistent with previous forecasts. Exceptions to this were the
Canadian models which were an outlier to the northwest as far as low
position for the period. Generally favored a NAM/GFS blend for
guidance but most changes were for local effects.
Long term...two pattern changes in store for the extended
forecast. Wet weather will taper off Saturday into Sunday as
current low pressure system moving into the central Gulf weakens
with precip bands pulling off to the west. Transitioning to a dry
period with increasing northerly outflow winds starting late
Sunday into Monday as high pressure ridge builds over the central
Alaska Gulf with the Gulf low dropping to the south and developing
into an inverted trough over the eastern Gulf and Panhandle. Still
some potential for precip over the far southern Panhandle during
this time. Late in the week a developing low near the Bering Sea
and the associated front will track across the Gulf then over the
Panhandle returning the region to wet weather. Large amount of
uncertainty on the timing of this late week front.
Latest model runs still showing some spread on on exact track of
the Gulf low for the weekend. Starting to see more progression of
the low center to the northwest, especially with the Gem, but
overall the European model (ecmwf)/GFS are close to previous forecast. Models more
in line for the building ridge and developing inverted trough.
With high pressure over the Yukon and Gulf and inverted trough to
the south, localized northerly outflow winds pick up for Sunday
into Monday. Gale force winds likely for the northern Inner
Channels with at least Max small craft winds for the central Inner
Channels. Gusty winds for the usual outflow areas, such as
Skagway, with some indication of higher gust potential near
850 mb temperatures falling between -4 to -8 c for the start of
the week for northern areas. Low temperatures will be highly
variable with the colder air aloft in wind sheltered areas but
warmer where higher downslope winds develop. As next front moves
in later in the week mid level temperatures rise above 0 c, but
will need to watch for more snow potential at higher elevations
with lingering cold air mass.
Few changes made to inherited forecast, as it covered most of the
localized impacts, keeping with a blend of 00z GFS/European model (ecmwf) then
wpc as still some timing issues later in the week. Forecast
confidence is average.
public...strong wind through this evening for akz027-028.
Marine...Gale Warning for pkz036.
Small Craft Advisory for pkz022-033>035-041>043.
Small Craft Advisory due to seas for pkz051-052.
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