Area Forecast Discussion
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FXAK67 PAJK 182136

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
136 PM AKDT Thu Apr 18 2019

.SHORT TERM.../through Saturday/ Larger scale upper trof will
remain across western AK and the AKPEN area through Sat. Several
shortwave trofs will move NE across the forecast area through the
period. A low W of Yakutat Bay will drift W into the NW gulf by
Fri morning. Several low level trofs (coupled with the upper level
shortwave trofs) will move across the area through the period. A
high pressure ridge will build N across SE AK through Fri, then
shift E of the area Sat. A stronger low will move NNE to the SW
gulf by late Sat afternoon, with an occluded front reaching the
central gulf around the same time. Models were in generally good
agreement, with the biggest point of contention being the exact
track of the low on Sat.

Main forecast concerns will be winds and precip potential/amounts.
With low level pressure gradient remaining fairly strong across
the N through Fri morning, winds will remain at SCA levels over
the northern inner channels (with a short period of gales early
tonight in Lynn Canal and Cross Sound). Keeping a strong wind
headline for zone 18 through Fri morning as well. Winds over the
N gulf will start around gale force on S side of low W of Yakutat
Bay this evening, then decrease to SCA levels later tonight as
low moves back to the W and weakens some. Should see 20-25 KT
winds for much of the N Fri into Fri evening, with some occasional
bursts of stronger wind as trofs move through, then wind should
decrease later Fri evening into Sat morning. The approach of the
occluded front will increase winds to at least SCA levels
(possibly gale force) over the eastern gulf by Sat afternoon.

Some fairly cold air aloft (around -35C at 500 mb) moving in from
the SW through Fri with some of the shortwave trofs, and this
will keep a showery environment across the area. The showers will
tend to maximize around the trofs moving through, as well as
along SW slopes. Did bump POPs up for these areas through Fri
night by blending in 15z SREF, except lowered POPs some over the
far N inner channels where some downsloping will occur in the
deep layer SW flow. Would not be surprised if some snow and/or ice
pellets mix in close to sea level during heavier showers, but am
staying with just rain showers as any mixed precip should be short
lived and not have any significant impact. Could see an inch or so
of snow around White Pass tonight. Do not think there will be any
TSTMS in this pattern as the lower level airmass is a little too
cool. Rainfall in the showers could reach 1/2 inch per 12 hrs
through Fri along SW slopes, especially over the NW half of the
area where deepest instability will be.

.LONG TERM.../Saturday night through Thursday/ As of 10 pm
Wednesday. A strong upper trough parked over Western Alaska will
not move all that much through the long range period. At most
expect it to deepen and then expand eastward into mid next week.
For the panhandle, it is the short waves and masses of cooler air
rotating around it that will shape the forecast for the weekend
and into next week as those features approach from the SW and W.

Of those features, A strong trough moving into the Western gulf
on Sat night will be the trigger for another strong surface low
and front in the gulf. Current model guidance is favoring a track
that is just east of Kodiak Island, which is farther west then
what was suggested yesterday. Yet, most guidance has settled on
this track (even the ECMWF which was much further S and E yesterday
has switched its tune). Its associated front will be moving
through the eastern gulf and panhandle at around the same time.
Timing and strength has not changed all that much, but with the
farther west track of the parent low, where the higher winds
develop is more toward the northern gulf rather then the SE gulf
now. Still expect widespread gusty and wet conditions for Sun as
the front moves through.

Damp conditions expected to continue into mid next week as SW flow
continues to dominate in the gulf bringing showers to the area.
The still lingering low from Sun will be drifting E across the
gulf at this time in a much weaker state. Though where it drifts
to is up for debate. Suggestions range from toward Haida Gwaii to
toward Cape Fairweather. There are also indications of more cooler
air moving into the area from the W for mid next week. Suggestions
from various models of 850 mb temps are getting down to -7C again
across most of the area next Wed and Thu could mean snow levels
down to a few hundred feet again if guidance remains consistent
over the next several days.


.AJK Watches/Warnings/Advisories...
PUBLIC...Strong Wind through Friday afternoon for AKZ018.
MARINE...Gale Warning for PKZ012-013-022-042-043-051-052.
     Small Craft Advisory for PKZ021-031>036-041.
     Small Craft Advisory due to Seas for PKZ053.




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