Areal Flood Advisory 2, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
313 PM AKDT Thu Jun 24 2021

.SHORT TERM...An occluded front across the region has a long
fetch of moisture directed at the panhandle. Sitka was the big
winner with amounts in excess of 3" this morning and sharp river
rises nearing bankfull. But rainfall has lightened up
considerably as of mid-day, after frontal passage which included
some gusty winds. Expect a lull in rainfall and decreasing winds
for most areas late tonight into Friday morning.

A new surface low developing along the front can be seen in the
form of low clouds on satellite imagery. This "wave" will track
northward through Friday, increasing rainfall again for the
northern panhandle. The heaviest rain will be focused on Yakutat,
but Sitka to Juneau northward have 60% or greater POP at some
point during the day. Exceptions to this are areas shadowed by SW
flow, like Hoonah and the Chilkat Valley.

Yakutat had around 2" of rain since yesterday evening. With the
new wave tracking north and a couple more rounds of moderate to
heavy rain, another 3" is likely through Saturday afternoon.

The south will see an inverted trough pushing in Friday night
with a shift to northerly winds. Very warm temperatures aloft and
freezing levels in excess of 10kft (already the case today) will
bring the potential for record high temperatures and well above
normal low temperatures. Mid 70s to around 80 are expected for the
southern zones Saturday. The upper level flow remains disconnected
from the surface pattern however, causing some uncertainty on the
cloud cover forecast. The mid-upper level flow remains SW through
the short-term and think that could keep some clouds around,
especially for the north, and limit potential peak heating.

.LONG TERM.../Saturday through next Thursday/...As of Wednesday
evening. A mountain of high pressure over southern BC and the
Pacific Northwest dominates the extended forecast. As a second
wave of moderate to heavy precipitation pivots to the west along
the the NE gulf coast Saturday, a surface ridge builds through the
SE Gulf. With all of this change, northern Inner Channel winds
will eventually shift from southerly to northerly Sunday to match
the northerlies of the southern Inner Channels.

Farther south across the southern Panhandle, 850 mb temperatures
climb from 10 C up to near 20 C Saturday and Sunday. As a result
warm days lie ahead for much of the southern half of the
Panhandle, precariously just southeast of the rain-cooled air to
the north. For this forecast update, temperatures where raised
across the board by 2 to 3 degrees across the central and
southern panhandle. Upper 70s are a safe bet for Prince of Wales
and Revillagigedo Islands this weekend. Even a few spots hitting
80 is certainly possible with Sunday expected to see the warmest
temperatures. Analysis of sounding climatology reveal the 17 C
mark at 850 as near record territory for the date.

As the wave lifts northwest through the weekend, clearing skies
will expand northward allowing these very warm 850 mb temperatures
to mix down to the surface more efficiently. While the synoptic
map is debatable on any thermal trough setting up in the south and
any migration to the north, channel breezes could play a role in
tempering expectations. But depending on how much sunshine
filters through the mid to high level clouds over the north and
the strength of channel breezes we could see widespread 70s in the
north even sooner than next Monday through Wednesday.

Next week as the main low to our west shifts to the central
Aleutians from Bristol Bay, we should experience relatively warm
temperatures throughout the Panhandle. Too early to say how warm,
but the potential is there for widespread 70s for sure with some
inevitable 60s to the south as the thermal trough migrates
northward and allows that Hecate Strait air conditioning to roar
back through Clarence Strait. Along with warm temperatures, dry
conditions are also likely for the first half of next week as high
pressure keeps a stable atmosphere. A wave from northern BC could
carry some convective moisture across the Coast Mountains into
the Inner Channels by next Wednesday, but it is way too early to
speculate whether this will actually happen. -CC/JWA

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Small Craft Advisory for PKZ012-022-031-033-041>043-051>053.

&&

Ferrin/CC

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