Area Forecast Discussion
Issued by NWS Juneau, AK

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FXAK67 PAJK 032318
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
218 PM AKST Wed Mar 3 2021

.SHORT TERM...Satellite imagery this afternoon showing a low in
the SW AK Gulf which is expected to remain nearly stationary
while filling through early Thursday. Associated front is moving
north with small craft winds over the gulf and enhanced precip
bands along the coast mountains, especially over the southern
panhandle, but otherwise a fair number of breaks between showers.
850mb temps over the panhandle low enough for temps tonight in
the mid 20s to mid 30s allowing a mix of precip for central and
southern locations and mainly snow to the north. Snow
accumulations of an inch or two expected with higher amounts along
orographically enhanced locations.

As this low fills another low moves up from the N Pacific and
tracks into the SE Gulf. What is currently expected is this gale
force low to reach the Haida Gwaii coast by Thursday afternoon
then continue a northerly track while weakening, with low center
near Cross Sound by Friday afternoon. With this track will have
offshore flow and a dry slot for the northern panhandle Thursday
into early Friday before the frontal bands push in. Southern
locations get the brunt of precip initially, and with the track
and warmer air moving in, precip will fall as rain. Increasing
northerly winds resulting as the low moves in as gradient tightens
between it and high pressure over the Yukon. The persistent
question is where will this low go and how deep will it get. At
this time the GFS was the outlier depicting a deeper low which
stayed intact well into Saturday while had better agreement
between NAM/Canadian/ECMWF with a slightly faster northerly track
but more importantly fills the low into an open wave trough near
Cross sound by Friday afternoon. Ensembles were showing similar
trend and tracks. Due to the agreement went with a blend of
NAM/Canadian which results in winds weakening and precip
diminishing sooner than GFS. Lower confidence with the short range
forecast due to this model spread.


.LONG TERM.../Friday through Wednesday night/...The message today
remains mostly the same as yesterday, as the active pattern
continues through the beginning of long term with a possibility of
a precip break Sunday into Monday. Temperatures do not appear to
warm or cool substantially during the period and will hang close
enough to freezing to make snow a consideration in at least some
portion of the forecast area with each passing disturbance.

The long term begins with a weakening low moving north along the
outer coast. This low is expected weaken through the day giving
way to onshore southerly flow in between a high over BC and a low
in the western gulf. This next low will get pulled southeast
through the gulf and into the Oregon Coast by a strong southern
branch of the polar jet. With the low tracking SE of the area,
expect a northerly gradient to set up during the latter half of
the weekend and into Monday. Guidance has this pattern continuing
into next week as upper level ridging builds over the Aleutians
and the jet stream pulls any systems in the gulf well to the south
and east of the region.

In terms of sensible weather...the period begins with
precipitation moving south to north across the Panhandle as the
weakening low moves up the coast. A strong southerly push ahead of
the low will bring warmer air northward keeping P-type mainly rain
on Friday. The low dissipates Friday night leading to onshore
flow and showers into Saturday. The next system in the gulf that
gets pulled S and E of the region will remain far enough offshore
to keep the heaviest precipitation over the gulf. However, still
expect shower activity to persist across the southern half of the
Panhandle.

The welcomed drying trend begins Saturday evening as a northerly
gradient sets up across the region with relatively high pressure
to the north and the low to the south. Drying will take place
from north to south Saturday night with the far southern Panhandle
keeping at least a slight chance for showers into Sunday. At the
same time, northerly outflow will increase, especially across the
Northern Inner Channels and out of interior passes in the NE gulf
coast. Bumped up winds to small craft levels in Lynn Canal and
increased winds in typical outflow areas. Kept high temperatures
in the upper 30s to low 40s through this time frame, despite
northerly flow. It is that time of year again where days are
rapidly increasing, the sun angle is higher, and the interior of
Canada is beginning to moderate some. Downsloping events in March
have the potential to bring more moderate temperatures to SE AK;
compared to frigid arctic outbreaks in the middle of the winter.
With model 925mb temps in BC and the Yukon around -5C to -10C,
downsloping would warm surface temps up into at least the low 40s
across portions of SE AK.

Sunday and Monday still look to be the best for a break from the
active weather but confidence is lower for the extended period.
Models show another front approaching the coast by Tuesday
morning; however there is low confidence regarding the exact track
of this system. A track further offshore, as the latest GFS and
ECMWF show, would mean continued dry weather for the Panhandle.
Lowered POP for mid next week to slight chance to chance wording,
but did not take it out completely just yet. A blend of GFS and
ECMWF were used for the early part of the long term, with NBM and
WPC for the latter part. Overall confidence is above average
through the period.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Small Craft Advisory for PKZ022-041>043-051-052.

&&

$$

PRB/CM

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