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000
FXAK67 PAJK 191415
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
615 AM AKDT Fri Apr 19 2019

.SHORT TERM.../Friday through Saturday night/...This short term
forecast period represents a break between major rain and wind
events. At present, low pressure over the Yukon is weakening and
will dissipate by Saturday morning. To the south, the EASTPAC high
is building a ridge north into the eastern Gulf. The ridge will
sharpen up and shift east over the Panhandle and then into British
Columbia by Saturday morning. This will act to keep small craft
southerlies going over Lynn Canal and gusty conditions in Haines
& Skagway through this evening. Low level onshore flow will keep
skies cloudy and showers will persist through Saturday night.
Evaluated atmospheric instability for thunderstorm potential based
on some isolated storms that happened over southern Baranof
island yesterday. Although the upper atmosphere is quite cold, did
not feel there was sufficient CAPE or an intersection of
sufficient vorticity and steep enough lapse rates to support them.
Have thus left thunderstorms out of this short range forecast.
Meanwhile, the next major system is developing near 45N/160W. This
low will track northeast into the western Gulf late Saturday
night. As is often the case, this low will be occluded by the time
the associated front reaches the outer coast. Expect
precipitation from this front to arrive on the coast on Saturday
evening, spreading inland through the night. By Sunday morning,
all Southeast Alaska locations should be in light to moderate
rain.

Prior to the arrival of the front, winds over the eastern Gulf
will back to the southeast and reach small craft intensity by
Saturday morning. A barrier jet gale will form west of Icy Bay
early on, and gales will spread down to Cape Ommaney Saturday
evening, then the central outer coast of Prince of Wales Island
late Saturday night. Small craft winds over the ocean entrances of
the inner channels and Clarence Strait will have developed by then
as well.

.LONG TERM.../Sunday through Friday/ As of 10 pm Thursday. Upper
level trough over Western Alaska and the Western gulf continues to
be the main upper level feature of note through the extended
range. Several short waves and cooler air masses will be rotating
around it bringing unsettled weather to much of the panhandle and
gulf. There is some change possible in this pattern toward late
next week as the upper trough breaks down and a more zonal pattern
takes its place. Confidence on this is not very high however as
several ensemble members and various operational models have
lingering troughs interrupting this zonal pattern. Where these
troughs set up (if they set up at all) is the main confidence
issue as they range from the international date line to the
panhandle creating a wide range of possibilities for late next
week.

At the surface, the main story continues to be the low/front for
Sun. Gale force winds still expected over a wide area of the gulf,
and gusty conditions (up to 40 mph gusts) are still quite likely
for the panhandle on Sun (particularly the outer coast and
southern panhandle). Another slug of rain is expected as well (QPF
amounts range around 1 to 2 inches Sat night through Sun night
with locally higher amounts possible). Current trends in guidance
have increased the speed of the front leading to winds in the
northern gulf diminishing sooner then previously forecast.

Behind this front are continued showers in overall SW flow with
several short waves embedded in the flow. At least two significant
troughs are starting to be highlighted in the long range
guidance. The first is early Mon that forms a 990 mb surface
low/trough aimed directly at the the panhandle. This is a rather
substantial change from previous forecasts, but it has support
from a majority of operational models and ensemble members so have
a higher confidence on this solution sticking around. This
feature has the potential to keep higher winds and more
substantial rain going for the panhandle into Monday. Trough
number two is aiming for a timing mid week and is noticeably
weaker than the weekend systems, but still could produce more
rain and some gusty winds as it moves through Tue night.
Confidence on this feature is low to moderate as timing and how
strong it will be are still topics of debate for the various
models.

Second thing of note is another shot of cooler air coming for the
panhandle from the W for latter half of next week. 850 mb temps
still expected to drop to -7C across the area so some cooler temps
and snow levels dropping to the few hundred foot mark are not out
of the question for late next week.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Strong Wind until 7 AM AKDT this morning for AKZ018.
MARINE...Small Craft Advisory for PKZ012-013-052.
     Small Craft Advisory due to Seas for PKZ041>043-051.

&&

$$

Fritsch/EAL

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