Frost Advisory 8, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
235 PM AKDT Thu May 21 2020

.SHORT TERM...This evening, satellite imagery shows mostly sunny
skies across the northern two thirds of the panhandle. Some
exceptions include the southern panhandle who is still seeing
influences from the surface low that exited to the SE of the
panhandle Wednesday and around Cross Sound, where remnants of
this mornings marine layer persists. Clouds will be on the
decrease through the evening for the southern panhandle as an
upper ridge begins to shift over the panhandle. By Friday
afternoon, the upper ridge will begin to break down as an upper
low begins to propagate to the east out of the Bering Sea. At the
surface, a low will have developed over the Aleutian Islands and
will push a front towards the panhandle this weekend.

Tonight, there will be the possibility of fog forming across the
southern panhandle with a moist boundary layer in place and clouds
clearing. That being said, clouds may hang around longer than
forecasted in which fog will be less likely. For now,
included patchy fog for Yakutat, Gustavus, Juneau, and the
southern inner channels south of Petersburg. The marine layer
will also likely form once again tonight. One area of uncertainty
is that with the approaching front from the west, higher stratus
clouds may prevent the marine layer from being as robust as usual.

By Friday, a front approaches the eastern gulf from the
southwest. Initially mariners can expect southeast winds of 25 kt.
As the front approaches Prince of Wales Island Friday night, we
do anticipate winds increasing to 30 kt. This front carries with
it some subtropical moisture as it originated in the baroclinic
zone associated with the north Pacific jet. Prince of Wales Island
and the southern Inner Channels should expect bands of moderate to
heavy rainfall associated with this frontal passage Saturday.
Rainfall across the northern Panhandle will be less certain in
time than the south, and will likely arrive a bit later, as
offshore flow should initially keep the lower atmosphere drier.
But rainfall in Juneau will begin late Friday night, instead of
Friday evening for much of the south and coast. For Saturday,
Precip will be blanketing the panhandle while winds reach full
gale along the central and southern coastal waters. With this in
mind we have pushed wind speeds up for Prince of Wales Island to
sustained 25 kt or so, with gusts to 40 mph.

Little changes made to temperatures for Friday and Saturday. With
850 temps around 35 degrees F and mostly sunny skies, expecting
mid 60s across the panhandle Friday and then upper 50s for
Saturday as front moves through.

.LONG TERM.../ Saturday to Thursday as of 9 pm Wednesday / The
weather pattern for Alaska is being dominated by a large upper
level low in the eastern Bering Sea north of Cold Bay. The broad
pattern shifts but overall the low remains fairly persistent in
the next week. The general low position being that far west
occasionally allows for an upper level ridge over the panhandle
and western Canada when it hasn't been forced away by trough being
rotated northeast about the Bering low. One of those troughs is
Sat/Sun and the second seems to Mon.

Looking at surface features, the Saturday frontal band should see
winds ahead of it to 30 to 35 kt, mainly for the southern outer
waters. Expect that winds over the southern and central panhandle
will be locally breezy as well.

The initial frontal band Friday night into Saturday will spread
some light rain in, however, it is the follow up wave that joins
the front Saturday morning that will bring better moisture to the
event. This new low will usher in the better rainfall totals for
the panhandle for Saturday and Sunday. A brief lull may occur late
Sunday into early Memorial Day holiday, although expect the
remaining showers to persist while diminishing. Incoming for later
Monday is another trough that moved around the south side of
Bering upper low and moving across the gulf. The potential is
there for some well organized bands of showers to move onshore
Southeast Alaska late Monday into Tuesday.

The longer range forecast solutions hint there will be another
quick building ridge over the eastern gulf and panhandle Tuesday
to Wednesday. Followed by another weather front from the
western gulf by the end of the week. Confidence is roughly
average in the extended forecast period.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...None.

&&

CC/Bezenek

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