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FXAK67 PAJK 261243

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
443 AM AKDT THU MAY 26 2016

.SHORT TERM...Weakening upper low continues dropping south over
the southern panhandle early this morning. This low will weaken
and shift E`ward into British Columbia this afternoon as a ridge
builds over the western gulf and the interior. NW flow on the
eastern side of the ridge will direct a weak shortwave trough over
the Yukon S`ward and across the northern panhandle late this
afternoon and evening. As this happens, steep mid level lapse
rates of 7-8 C/km will overspread the extreme northern sections of
the CWA late this afternoon. Showers and scattered thunderstorms
should form this afternoon as daytime heating on the higher
terrain over the Yukon helps destabilize the atmosphere. Model
forecast soundings for Skagway indicate inverted V profiles and
25-35 kt of unidirectional northerly shear which could provide a
good enough environment combined with favorable shortwave timing
for a few of these thunderstorms to make it across the border into
the Skagway area. Thus have added a slight chance of
thunderstorms this afternoon. Confidence was not high enough to
include thunder chances for Haines as they are further away from
the best instability and lift.

For the remainder of the panhandle, expect a partly to mostly
cloudy day with higher overcast spilling over the ridge in the
northwest flow aloft. Temperatures should warm into the 60s north
with upper 50s south. Winds should be generally light with typical
afternoon sea breeze influences dominating. A couple of the hi-res
models are indicating a period of stronger northerly outflow
winds tonight in marine zone 51 and for some of the northern inner
channels. Did not have enough confidence to go with the stronger
winds so elected to keep the 15 kt northerly winds in the northern
areas tonight.

In general models are in good agreement through Thursday night.
Few changes were made to the previous forecast. Used hi-res ARW
and NMM for some cosmetic changes to winds over the inner
channels. Forecast confidence is high with lower confidence in the
thunderstorm activity across the northern panhandle.

.LONG TERM...Start of the long range continues the weather trend
seen in the short range. Fair amount of variation with new model
runs compared to previous solutions for the later periods of the
extended forecast. Upper level ridge over the gulf becomes pinched
off by Friday allowing a low over western Canada to track west
while a second low over the w gulf retrogrades west through
Sunday. The upper level Canadian low keeps vort max and lift
mainly along the coast mountains and southern panhandle, as the
low drops to the south, keeping chance showers over those areas.
Due to offshore flow more potential of clearing over the northern
panhandle and northeast gulf coast but enough moisture moving over
the mountains for cloud cover the linger. Similar pattern seen
over the past few days with generally northerly winds overall less
than 15 kts.

This pattern transition through Sunday is the likely the
cause of model uncertainty which becomes more significant
starting Monday. Development of a low tracking into the w gulf
with associated front moving into the s gulf began to be depicted
in 00z model runs. This feature would result in stronger gulf
winds and higher probability of precip over the gulf and
potentially the panhandle. More consensus that the low center will
be further west so would lean more towards drier weather for the
panhandle. However 06z runs already began to show wider variation
on timing and location of this feature. For now held off on using
operational or the available ensembles in grids until there is
more consistency.

Made little change to the forecast as the first portion still
close to new model runs and low confidence with later periods and
model variation. Forecast confidence is below average.


.AJK Watches/Warnings/Advisories...



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