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FXAK67 PAJK 231247

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
442 AM AKDT MON MAY 23 2016

.SHORT TERM...An upper level short-wave is passing east across
the Panhandle this morning. Bands of very light precipitation that
we are terming as sprinkles move east behind this system and
should cross into Canada by the afternoon. An interstitial ridge
between this short-wave and a stronger one dropping into the Gulf
right now may offer a brief break between these morning sprinkles
and afternoon/evening showers associated with the second system.
As we write Yakutat received a hundredth last hour. By most
accounts Yakutat is already west of the upper level ridge axis and
coverage of showers should only increase across the Northeast Gulf
and spread east into the northern Panhandle through the day. By
this evening, the second short-wave should lie over Mt.
Fairweather. This in itself should be enough to support light
scattered shower activity over Gustavus, Juneau, and Sitka that
will persist and expand south along the immediate coast and the
spine of the Coast Mountains into tonight.

Subsidence behind this system may generate enough momentum to keep
small craft westerlies rushing through Cross Sound and Icy Strait
well into the evening. And pressure falls over the Canadian Yukon
this afternoon/evening will sustain a small craft through northern
Lynn Canal. Otherwise, mainly lighter west to northwesterlies will
blow through the majority of the Inside Passages.

Temperatures will continue to be normal to slightly below normal
for this time of year with cloudy weather. Changes to the forecast
were minimal, but pops were manually diminished to better
describe the very light precipitation this morning. Forecast
confidence in details is average for a pattern with such weak
signatures, but impacts will be minimal.

.LONG TERM...No change to previous forecast. Models remain in
generally good agreement with light precipitation chances through
mid week as multiple impulses embedded within the northwesterly
flow move across the panhandle. A brief break in the precipitation
chances is still expected on Thursday before light rainfall moves
back into the area on Friday. As we head into next weekend model
solutions diverge substantially. The GFS favors phasing of southern
and northern stream energy resulting in strong southwest flow and
heavy precipitation over the panhandle. The ECMWF does not phase
the southern and northern stream energy leading to a less amplified
and faster solution. While precipitation chances would still be
high, amounts would be much less. Therefore, little confidence in
the forecast for next weekend.


.AJK Watches/Warnings/Advisories...
MARINE...Small Craft Advisory FOR PKZ012-021-022-041>043.



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FXAK67 PAJK 230001

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
401 PM AKDT SUN MAY 22 2016

.SHORT TERM...An elongated upper trof will move slowly E across
SE Alaska tonight and Mon. A strong upper shortwave trof will
move E across the far N Gulf of Alaska late tonight and Mon. A
broad surface ridge will remain over the Gulf of Alaska through
Mon. Models were generally close on these features. Did not change
pressures and only made minor tweaks to winds through Mon.

Main forecast concerns will be precip potential and winds. Right
now...there is a narrow band of precip over Prince of Wales Island
associated with a deformation zone across them. This deformation
zone will weaken through tonight as upper trof shifts E. Expect
the rain to become spotty over the S coast by this evening.
Also...some drizzle or light rain showers were near PAEL this
afternoon. Some of this may get inland as upper trof moves through
the area...but not expecting more than isolated to scattered
showers out of this. Kept POPs generally 20-30 percent to handle
the trof moving across the area tonight and Mon morning. The
strong shortwave moving across the N gulf will increase onshore
flow Mon over the N half of the area...and this will increase
precip threat as boundary layer will be deepening as well. Think
shower coverage will increase to scattered especially in the
afternoon across the N. Yakutat will see the increase in shower
coverage sooner...as early as late tonight but more likely Mon

Strongest winds will be over the gulf and along headlands along
the outer coast. 20-30 KT W-NW winds will continue with a slight
diminishing trend Mon in the gulf coastal waters and along outer
coast. However...there will be an increase to 20-25 KT for N Lynn
Canal Mon afternoon as mid-level flow backs from NW to SW and
enhances southerly pressure gradient there. There may be a period
of SCA level NW winds in Clarence Strait this evening as well.
Rest of the area will generally be 10-20 KT.

.LONG TERM...Active upper level pattern this week with multiple
troughs/short waves and ridges progressing west to east through
the week. This will make for a lot of on/off showers and more
uncertainty on timing.

Monday night the upper level trough/short wave discussed above
will strengthen at the mid-levels to a cut off low as it passes
over the northern panhandle. A jet streak on the south side of
the low will increase W winds and precip rates over the central
panhandle. This should be brief as this feature is moving through
much quicker than todays.

Upper level flow turns back NW by Tues morning...however the next
trough will quickly move across the gulf from the west Tues
afternoon. This looks to be a bit stronger with scattered showers
continuing. The trough strengthens further Tue night with a cut
off low developing over the northern Gulf at all levels. This low
will move SE along the Panhandle coast thru Wed with flow turning
back offshore behind it. Have increased showers ahead of the low
followed by decreasing clouds from north to south behind the low
Wed afternoon/evening.

Northerly jet stream sets up over the region on Thurs so continued
with forecast of partly cloudy skies for that day. The jet backs
to a more west direction on Friday which would allow for more
clouds and chance of rain into the area. Over the weekend there
potential for a stronger system to affect the area with moisture
tapped from another deeper system over the Pacific and thus an
increased precip threat. Models differ on which portion of the
panhandle will be impacted by this and on which day...so lower
confidence on the weekend precip forecast.

Used mainly the 12Z GFS/Canadian models for this forecast package
as they were in good agreement through the mid range.


.AJK Watches/Warnings/Advisories...
MARINE...Small Craft Advisory FOR PKZ012-022-036-041>043-051-052.



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