Gale Warning 79, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
214 PM AKST Wed Feb 19 2020

.SHORT TERM...A strong front originating along the eastern
Aleutians at this time looks to dump heavy snow on the South
Klondike Highway, pour rain across Southeast Alaska, and spread
strong winds across the region. In fact, high wind gusts of 60 mph
now look possible for both Yakutat and Juneau, and cannot be ruled
out for a few other locations in the northern Panhandle and
eastern Gulf Coast. High wind watches will be posted shortly for
the Juneau and Yakutat. Looking at model soundings, impressive
wind speeds lie at the inversion level and just below. MOS numbers
push Juneau in excess of 30 kt sustained. Yakutat will be a
tougher case, but coordination with OPC highlighted the front's
instability and added group confidence for expanding storm force
winds from Cape Suckling southeast to Cape Edgecumbe. Inner
Channel winds were largely raised to gale force with the uncertain
exception of Lynn Canal where parallel flow may serve to limit
wind speeds but confidence is low. Likewise even in areas outside
the high wind watches in Juneau and Yakutat, we do expect gusts
from 40 to 50 mph likely. Due to consistent ridging, Skagway looks
to blow strong throughout most of the short-term period.

Now we turn our attention to Skagway. The previous winter storm
warning for the Klondike and White Pass verified in a big way,
with estimates of one foot of snow over the pass this morning. We
foresee another big event beginning Thursday morning as snow
quickly becomes heavy over the pass. Snow showers will keep
moderate snow in the forecast through Thursday night as well. All
in all, we expect another 8 to 12 inches of snow for White Pass
Thursday and Thursday night.

Finally, we expect good mixing with all these winds to keep
temperatures warm enough to produce rain and lots of it, rather
than snow for the rest of Southeast. In fact, we expect many parts
of the Panhandle to receive an inch of rain or more on just
Thursday alone.

Weather begins to calm down Friday. A ridge builds in with some
progressively cooler air pushing through into Friday night. But we
are expecting little if any snow accumulation. Instead just an
unimpactful mix of precip in showers. Winds also calm down
significantly as well, although some breezy conditions could
persist for the northern Panhandle through Friday morning.

Friday night as a new system prepares to undercut Southeast
Alaska, some light snow could increase into Saturday morning. But
this is early to nail things down.

Forecast confidence is moderately high. NAM, GFS, NAMNest and
other high res models were used to fine-tune the forecast.

.LONG TERM...The challenges of winter-time split flow persist in
the mid- range into early next week, as moist Pacific systems
rail across 50 N and occasionally from latitudes southward and
interact with persistent and colder Bering Sea systems that
periodically replant themselves in the Gulf of Alaska. This
introduces many complications that frankly models (and
forecasters) often struggle with. With temperatures marginally
hovering in the meteorologically scary neighborhood of the
mythically well-marked rain/snow line, small error potential can
span the impact scale from little to great.

After a vigorous front clears the Panhandle a maritime, a
relatively cool air mass spreads across Southeast Alaska,
supporting showers. These showers will fall as mainly rain for
the south and a mix for the north. Poorly resolved short- waves
could enhance some accumulations during this time, especially as
thicknesses and temperatures drop into Friday night.

Saturday, it increasingly looks as though the southern stream
energy becomes even more active as a storm looks to barrel into
the BC coast. This helps speed cooling across Southeast and
probably increases frontogenesis somewhere across either the
eastern gulf of Alaska or the Coastal Panhandle. Much of this
precipitation could fall as snow, given low thicknesses and
cooling 850 mb temperatures. While it is still an evolving story,
we lowered QPF during the weekend, as uncertainty is uncomfortably
high. Yet it is certainly plausible that a few communities could
get significant snow from this scenario. Eventually, either
Sunday or Sunday night the steering flow turns westerly and
potentially sets up another overrunning event late in the weekend
or early next week. But should the southern track rob the north of
moisture, this setup may be much ado about nothing.

Ensembles and operational runs then hint at a more deeply
subtropical system perhaps beginning as snow and ending as rain
for much of the Panhandle mid next week. When exactly this
happens, we are still merely wagering. But as we hinted earlier,
there is confidence that Southeast Alaska region-wide will
experience a cool-down this weekend into at least Monday before
warming into mid next week. This probably means more snow for
some.

Westerly winds Friday will be relatively high in the gulf with
widespread 30 kt and even some gale force winds. But as the system
to the south nears the BC Coast, winds largely diminish across the
Panhandle even as the Inner Channels flip north Saturday. Winds
look to have little impact this weekend until an anticipated
front arrives mid next week with strong southeasterlies.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Strong Wind Thursday afternoon for AKZ026.
     Strong Wind from Thursday afternoon through Thursday evening for
     AKZ027.
     High Wind Watch from Thursday afternoon through Thursday evening
     for AKZ025.
     Strong Wind from Thursday morning through Thursday afternoon for
     AKZ022.
     Strong Wind from Thursday morning through Thursday evening for
     AKZ023.
     Strong Wind Thursday afternoon for AKZ020.
     Strong Wind from Thursday morning through Thursday afternoon for
     AKZ021.
     Winter Storm Warning from 6 AM Thursday to 3 AM AKST Friday for
     AKZ018.
     Strong Wind through late tonight for AKZ018.
     High Wind Watch from Thursday morning through Thursday afternoon
     for AKZ017.
MARINE...Storm Warning for PKZ043-051-052.
     Gale Warning for PKZ022-031>034-036-041-042-053.
     Small Craft Advisory for PKZ012-013-021-035.

&&

JWA

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

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE JUNEAU AK
949 AM AKST WED FEB 19 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0830 AM     SNOW             SKAGWAY                 59.46N 135.31W
02/19/2020  E12.0 INCH                          AK   DEPT OF HIGHWAYS

            DOT ESTIMATED STORM TOTAL ACCUMULATION OF 12 INCHES IN 24
            HRS NEAR WHITE PASS

&&

CC