209
FXAK67 PAJK 191314
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
514 AM AKDT Thu Sep 19 2024

.SHORT TERM...Post frontal showers will continue through mainly
Thursday morning before clearing north to south through the day.
Looking at satellite, the low responsible for generating much of
yesterday`s showers has largely disintegrated. While numerous to
widespread showers are still present, expect these to diminish
quite rapidly over the course of the day. The deepening trough
upstream from the incoming low on Friday, discussed in the long
term section, will promote upper level ridging near the NE gulf
coast. From this ridging, mid level drying and clearing will
spread from north to south down the panhandle as the ridge
strengthens.

Therefore, main changes to the forecast included decreasing PoP
across the CWA. Furthermore, due to lack of forcing, reduced winds
across the inner channels tonight to 10 knots or less. Finally,
introduced widespread fog across the panhandle.

.LONG TERM...

Key Points:
Multiple lows impact the Panhandle through next week bringing wind
and rain. Most rainfall expected in the far southern region.
Potential break in rain Sunday.

For rainfall details see Hydrology section.

Early Friday a long wave trough will be departing the Panhandle
moving into western Canada, shutting off support to the surface
low positioned in the Gulf. With the loss of reinforcing dynamics,
expect the pressure gradient to weaken, allowing winds and rain
to diminish into Friday afternoon. This break will be short lived
as an extensive jet drops south of our region allowing multiple
embedded shortwave troughs to rapidly move into the Panhandle.
Current forecasts reflect a surface low associated with each of
these features, bringing elevated wind Friday into Saturday and
potentially Sunday. Snow levels are dropping but no impacts
expected at this time.

While the Panhandle is impacted by these lows this weekend, a
broad open long wave trough will begin to move into the Gulf.
Associated with this feature will be a 980 to 985mb surface low.
While the low takes residence near Cook Inlet Sunday the pressure
gradient will tighten over the Panhandle with winds increasing out
of the south again.

&&

.AVIATION...Showers are the rule of the morning for just about the
entire panhandle this morning. So far VFR or MVFR conditions
prevail though some brief periods of IFR in heavier showers are
being observed. The lowest conditions are along the outer coast
and up against the coast mountain range. Winds have quieted down
overnight with the Skagway area still seeing some gusts to 30 kt.
Improving conditions expected today as showers diminish and exit
the area from NW to SE. Expect mostly VFR conditions by this
evening and into tonight though some areas could see fog develop
late with the accompanying IFR vis and ceilings. Conditions
expected to deteriorate again Friday as the next system begins to
move into the area.

&&

.HYDROLOGY...Multiple rounds of heavy rainfall through the next 7
days. SPS issued for Friday into Saturday in the south.

First round, Friday into Saturday: Long range guidance is still
flip-flopping on location, extent, and magnitude of an Atmospheric
River (AR) that will be carried by the jet stream for this
weekend. Current ensemble prognosis indicates a weak AR event with
some outliers reaching moderate. With that said, guidance the
ECMWF extreme forecast index continues to shift this first AR
north a touch from Hecate Strait/Haida Gwaii; simply put, heavier
rainfall is becoming more of a reality in the southern Panhandle,
potentially breaking some record 24 hour values with rivers
responding region wide. No flooding is anticipated at this time.


Second round Monday into Tuesday: As a broad longwave trough
positions itself in the western Gulf Monday and Tuesday, the jet
axis will become positive, which will steer a more potent
atmospheric river into the Panhandle. Guidance is showing some
agreement that this could be a moderate to strong AR with most
rainfall expected in the central and south. ECWMF EFIs are
highlighting a significant shift from climate normal over most of
the Panhandle with further trend analysis required over the next
few days. Simply put we could see a more significant rainfall event
Monday and Tuesday.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Small Craft Advisory for PKZ012-022-053-641>644-651-652-661>664-
     671-672.

&&

$$

SHORT TERM...NC
LONG TERM....AP
AVIATION...EAL
HYDROLOGY...AP

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