524
FXAK67 PAJK 161409
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
609 AM AKDT Tue Jul 16 2024

.SHORT TERM.../into Wednesday/...The short term forecast can be
divided into two parts. The first part is the exit of the most
recent round of heavy rain, the second part is the incoming next
round of heavy rain.

Tuesday is starting with general onshore flow. This has been
producing periods of light rain being reported around the
panhandle, with winds on the lighter side. Wind reports over land
areas are around 5 to 10 mph and marine wind reports are around 5
to 15 knots. This kind of weather will linger around today.

Beginning tonight is when the next weather maker will move in. Early
this morning, the low is sitting about 800 miles SW of the
panhandle. This low will track towards SE AK along the front edge
of the 500mb trough that will move west-to-east through the gulf.
As this low tracks north, it will bring a surge of moderate to
heavy rain as well as stronger winds. The heavy rain could have
some flooding impacts - you can read more about that in the
HYDROLOGY section and in the recent Flood Watch that was issued.

Another impact will be the surge of stronger winds, upwards of 25
knots in the inner channels, that will move south-to-north. Wind
speeds around 15 to 20 knots will start to show up in the southern
inner channels late this evening. By tomorrow morning, wind speeds
around 15 to 25 knots will be found in southern Stephen`s Passage
and farther south. As the low moves north, the 20 to 25 knot
speeds will track north, reaching Lynn Canal by midday.

As the low wraps up Wednesday afternoon into Wednesday night, the
wind will slowly calm down and the moderate to heavy rain will
move southeast.


.LONG TERM.../Wednesday through Monday/...
To put it simply: with the way the ensembles and operational models
have been shifting surface features from run to run have low
confidence in the mid range and long range forecast. That`s not to
say latest runs aren`t showing good agreement for both ensembles and
some operational models. The main change is the flow pattern now
keeping any of those larger features late in the week further to the
south and thus putting SE AK under just onshore flow with lighter
precip, lower wind speeds, and looking at more breaks in the rain.
However...this was a change in just 24 hours...so...keep that in
mind as we progress.

Anyway, the 500 mb low previously over the AK interior drops
southward over the AK Gulf with lobes extending and continuing to
rotate around it, just further south. To the west a blocking pattern
develops with a ridge over the western gulf and another low past the
Bering. At the surface on Wednesday the remainder of the elongated
low from Tuesday goes northward along the Eastern Gulf. Good
moisture feed from the south producing another round of moderate to
heavy rain fall. BUT, total rainfall not in the realm of what
occurred Sunday and Monday. 24 hours amounts likely only in the 1 to
2 inch range. Thursday into Friday high pressure expands over the
Gulf moving the Wednesday system eastward and possibly dropping rain
chances for portions of the panhandle. Plus the high pressure should
keep the main part of Friday low that was going to hit SE AK to the
south and outside of our area, but still allow some rain bands to
cross over us.

&&

.AVIATION...

Another morning of LIFR to low VFR flight conditions across the
panhandle, anticipating similar trend as previous days. For much
of the panhandle, should see intermittent showers to continue with
predominate MVFR to low VFR conditions by this afternoon, CIGS
AoB 5000ft, and VSBYs dropping to 3-5 statue miles at times.
Strongest winds should remain confined to the northern panhandle
this afternoon, with sustained winds up to 10kts and isolated
gusts up to 20kts through this afternoon.

&&

.HYDROLOGY...

Rivers are either steady or trending downward this morning across
the Mendenhall Valley with Montana and Jordan Creek dropping
below flood stage overnight as the heavier precipitation comes to
end. A Flood Advisory remains in effect for Auke Lake near Auke
Bay with levels holding stead within Minor Flood. Further north,
the Chilkat River continues to slowly rise due to warm
temperatures aloft and elevated snow levels causing excess melt. A
Flood Advisory remains in effect for the Chilkat River through at
least Tuesday night.

Looking towards tonight and into Wednesday, a Flood Watch has
been issued for part the Northern Inner Channels, including
Juneau, for Tuesday evening through Wednesday morning as an
approaching system will push yet another round of potentially
moderate to heavy rainfall over the northern Panhandle. For now,
anticipating additional rainfall totals around 2 to 4 inches
within the Watch area through Wednesday night. This amount of
rainfall is not a rare occurrence in SE Alaska, however, much of
the watch area has already seen 3 to 6 inches of rain over the
past 72hrs. Which with saturated soils, will exacerbate already
swollen rivers and streams, especially within the Mendenhall
Valley. In addition, temperatures aloft will remain warm through
Wednesday with freezing levels near 10000 feet, leading to
increased snow and ice melt into our glacier fed rivers.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Flood Watch from this evening through late Wednesday night for
     AKZ325.
MARINE...Small Craft Advisory for PKZ031-034>036-641-642-661-662.

&&

$$

SHORT TERM...GJS
LONG TERM....PRB
AVIATION...NM

Visit us at http://www.weather.gov/Juneau