Small Craft Advisory 275, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
258 PM AKDT Wed May 19 2021

SHORT TERM...A ridge of high pressure remains in place Wednesday
afternoon and weakens while being forced east and south by the
advancing weather front from the western gulf and parent low south
of the central Aleutians.

The main forecast challenge today has been the stubborn marine
layer, which has remained along the Outer Coast and through Cross
Sound, Glacier Bay, and Icy Strait this afternoon. Low level
westerly flow has kept the marine layer from retreating much
despite daytime heating; therefore have kept low clouds in the
forecast through tonight in the Coastal Waters and along the Outer
Coast. Expect the marine layer to slowly advance further inland
tonight through Chatham Strait and possible across POW Island
again. Currently think areas along the Coast Mountains will remain
mainly clear; however confidence is low regarding the inland
extent of the marine later. Low level flow becomes southeasterly
during the day Thursday as the ridge axis pushes east of the
region. Southeasterly flow should begin to push low clouds back
offshore during the day.

The ridge will give way to the advancing front Thursday and Friday.
Rain starts in the Yakutat area around midnight Thursday night,
the outer coastal areas Friday morning and inner channels by
Midday. Expect the rain to start around 10 am Friday morning. This
frontal system has a source region in the mid Pacific so there is
a larger collection of QPF to wring out as the front passes over
the land areas. Rainfall totals for Friday-Friday night range
between 0.5 and 1.5 inches. Enough to wet everything back down and
give another boost to streams and rivers, it however, should not
lead to any flooding issues.

Wind of 30 to 40 kt expected to develop along the front with the
strongest from Icy Bay westwards towards Middleton Island. Expect
brief gusty winds of 30 to 40 mph for coastal communities on
Friday as the front moves through.

Little changes were made to the forecast. Updates were made to
temps, sky cover, and winds for the first 24 hours of the
forecast.

LONG TERM.../Friday to Wednesday as of 10 pm Tuesday/ The long
term forecast opens with a front pushing into the panhandle. Rain
and wind will be the story of the day with breezy conditions along
the outer coast and in many marine areas. The northern and
central panhandle currently look to be the most favored areas
w/regards to total rainfall, though do not expect flooding to be a
major concern. Chances of rain linger through Saturday, though do
not expect QPF totals as significant as on Friday. By Sunday,
forecast uncertainty sharply increases. The increase in forecast
uncertainty lies in the movement of the Friday front's parent low.
The ensembles are split on whether the low will quickly jog to
the SE or if it will move at a slower clip through the area. A
faster speed would favor lower precipitation chances by Monday in
the N panhandle as the moisture associated with the system is
pushed off to the SE and the ridge over the Gulf rebuilds. A
slower moving system would keep lingering chances of precipitation
over much of the area for a longer period of time. Am leaning
towards the low departing sooner rather than later, given broad
run-to-run consistency, but the possibility that this could change
does exist. Tuesday meanwhile brings with it a separate concern-
the possibility of an easterly wave advancing into the panhandle.
Have included chances of precip centered around more southern
parts of the area as a result, though it must be noted that this
is a low confidence forecast. Forecast confidence is average
through Saturday before rapidly dropping.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Frost Advisory from midnight tonight to 8 AM AKDT Thursday for
     AKZ019-025.
MARINE...Small Craft Advisory for PKZ043-051-052.

&&

CM/GFS

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