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FXAK67 PAJK 242353

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
253 PM AKST Sat Feb 24 2018

.SHORT TERM.../Through Sunday night/ A storm force low over the NE
gulf will move SE across southern Baranof Island to the southern
panhandle tonight, then exit SE of the area Sun morning. The low
will weaken gradually late tonight into Sun. Another low will
develop along an eastward moving occluded front over the NW gulf
Sun night. Primarily used 12z GFS/NAM blend with a bit more weight
to the GFS as its slightly faster movement of the Sun night system
was preferred.

Will be allowing the WWY for zones 20/21/24 to expire at 4 pm, and
keeping WWY/WSW for zones 25/26 through 6 pm. Precip will
transition to showers early this evening over the inner channels.
Some warmer air moving in will cause at least a mix of rain and snow
showers over the S half of the area tonight. Think the N will see
precip taper off this evening as low moves S of the area and
increasing N flow develops. The showers will diminish over the S
later tonight and Sun morning as low moves out of the area.

There will be some colder air moving into the N tonight behind the
departing low. Should see clearing conditions developing Sun with
some ridging moving in. Any breaks will not last too long though
as clouds will be increasing again ahead of the next system Sun
night, with some precip expected over the outer coast and N half
of the inner channels by late Sun night. Looks like precip will
start as snow.

Winds will be strongest over the gulf on S side of low moving SE
tonight. Expect gale to storm force W-NW winds tonight with some
gradual diminishing later tonight and Sun as low moves out. Winds
should drop to SCA levels by Sun afternoon over the S gulf. Gale
force winds will be nearing the central gulf late Sun night as
next system moves in. Inner channel winds will be SCA level ahead
of low moving in tonight. N winds will pick up to SCA to gale
force over the N channels tonight as low moves S of the area.
These winds should drop off slowly Sun as pressure gradient
weakens. Inner channel winds should shift to southerly Sun night
and rapidly increase to SCA levels by late Sun night, especially
over the N half of the area.

.LONG TERM.../Monday through Saturday/ Active weather pattern
through the long range with some significant model changes in the
mid range. At mid levels starting Monday 500 mb high pressure
moves over the panhandle into western Canada with a trough digging
down from the AK interior and Yukon into the NE Gulf. The main
circulation over the arctic will rotate in more waves to the
south keeping a source of cold air over the region through mid
week. Between meridional pattern of the first wave on Monday and a
second deeper wave on Tuesday night into Wednesday there will be
a short period of zonal flow. Sharp ridging rebuilds over the gulf
late week setting up for an outflow wind event.

At the surface a deep closed low develops over the NE gulf Monday
with associated frontal boundary moving over the panhandle
through the day. Due to the remaining cold air expect another
snow event with potential of 1 to 3 inches for some locations. As
the front is showing a fast track expect this would keep lower
QPF totals and thus be a limiting factor for snowfall. After the
main front tracks east post frontal showers with onshore flow
will continue. Still uncertainty on the next system developing
over the eastern gulf Thursday but at this time looks like it
will track to the south and main impact will be increasing
pressure gradient and outflow winds. For the Monday system, models
now in better agreement of a stronger frontal boundary over the
gulf and thus have increased westerly winds to gale force, with
potential for localized storm force. Stronger winds expected at
higher elevations but at least picking up 20 to 25 kt southerly
winds over the inner channels. winds diminish by Tuesday as the
front moves inland and by Thursday, gradient flips to northerly
with increasing winds speeds.

Fair agreement between NAM and GFS for Monday, which were changed
from previous runs and inherited forecast. Used a blend of GFS/NAM
Monday to Tuesday then use of NBM/WPC for the rest of the long
range. Improved confidence on the higher winds for Monday with
the newly analyzed low but still some question on snow totals.
Lower confidence by mid week in the final track of surface
features but upper pattern meridional flow is likely.


.AJK Watches/Warnings/Advisories...
PUBLIC...Winter Storm Warning until 6 PM AKST this evening for AKZ026.
     Winter Weather Advisory until 4 PM AKST this afternoon for
     Winter Weather Advisory until 6 PM AKST this evening for AKZ025.
MARINE...Storm Warning for PKZ042.
     Gale Warning for PKZ012-041-043-051.
     Small Craft Advisory for PKZ013-021-022-031>036-052.
     Small Craft Advisory due to Seas for PKZ053.




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