Scientific Forecaster Discussion
fxak67 pajk 232247
Southeast Alaska forecast discussion
National Weather Service Juneau Alaska
247 PM akdt Mon Oct 23 2017
Synopsis...a gale force low over the eastern Pacific tracks NE
through the central Panhandle Monday evening while weakening.
Another strong low will move NE through Dixon Entrance by Tuesday
evening. Outlook. A high pressure ridge will build over the
eastern Alaska Gulf Wednesday.
Short term.../Monday night through Wednesday night/ strong winds
and heavy rains were main impacts for the southern Panhandle today
and early this evening as the gale force Gulf low developed over
the southeast Gulf. Gusts of 40 to almost 50 mph were reported in zone
27 and 28. Weak atmospheric river produced rainfall amounts of
0.50 to nearly 2.00 inches over the southern regions. Rivers and
streams so far have been slow to react but are expect to rise,
however no flooding expected. As this low moves inland and weakens
will see a sharp decrease in rainfall rates and winds over the
Gulf and southern Panhandle. Wind directions will also rotate
counter clockwise as the low moves in. A southerly push as the low
center moves over the central Panhandle and 30 kt llj will cause
a brief increase in winds there before diminishing. There may be
just enough clearing between Post frontal showers tonight for
radiational fog to develop, but with shifting wind pattern held
off mentioning it for now. For Tuesday two lows will border the
area. One will be to the west nearing Kodiak and increase winds
over the western Gulf border. The other is another strong low
developing along the moisture stream oriented under the 300 mb jet
in the Pacific. While this will produce another round of strong
winds and heavy rainfall the low center will mainly be to the
south of the Panhandle keeping impacts limited for our region. A
building ridge Tuesday night into Wednesday will bring about some
clearing and a short period of dry weather. This dry period will
end once the next system tracks into the NE Gulf through
Some timing differences between models on speed of the low center
moving inland. Did nudge to NAM/GFS blend which were faster than
00z European model (ecmwf) weakening and moving the low inland. Newest model runs
all started to fall in line with the faster track. For the rest of
the time models were still mostly in line with previous forecast,
some lowering of pops Tue night for the central and northern
regions. Forecast confidence is average.
Long term.../Wednesday through Monday as of 10pm Sunday/the
extended forecast begins with a low pressure system crossing from
the southern Panhandle into Canada. A drying trend is expected
early in the extended forecast between Wednesday and Thursday with
minimal shower activity as a weak ridge of high pressure builds.
Between Thursday and Friday a low pressure system west of the
Aleutians will send a front northward across the Gulf. While
confidence is lower with timing and location of this front,
moisture associated with it is of tropical origin, which could set
up another atmospheric river scenario for Southeast Alaska. This will
pave the way for a wet weekend across Southeast Alaska.
Little change was made beyond Friday in the extended forecast.
Ensemble forecast members and operational models still carry
large discrepancies moving into the weekend. Tuesday's forecast
was altered to shift the low's location over the southern
Panhandle which transitioned into the start of the extended
forecast using the European model (ecmwf). Winds were increased around this low;
however, winds underneath the ridge on Thursday were decreased
over the Inner Channels and Panhandle.
Aviation...a low pressure system will move across the central
Panhandle this afternoon and evening. Rain will reduce ceilings
and visibilities to MVFR and IFR conditions at times. Gusty winds
will produce wind shear across southern and central areas of the
Panhandle in the 35 to 55 kt range. The stronger winds, higher
wind shear and lowest ceilings and visibilities will be across
the southern portions of the Panhandle.
Marine...gale force winds over the southeast Gulf diminish quickly this
evening along with gales over the southern Inner Channels. Seas
will remain at small craft levels due to swell for the current low
and next two systems for Tue. Not until the ridge builds are seas
rally expect to subside below 8 ft. Tuesday small craft winds
over the central Gulf from the low moving into Kodiak. Central and
northern inner channel winds will have a sharp increase in speed
then flip direction and diminish as the current Gulf low moves
inland. Tuesday into Wednesday while speeds will be mostly below
20 kt still getting plenty of direction flips as pressure
public...strong wind until 7 PM akdt this evening for akz027-028.
Marine...Gale Warning for pkz035-036-041>043.
Small Craft Advisory for pkz012-022-031>034-052.
Small Craft Advisory due to seas for pkz051.