Gale Warning 27, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
252 PM AKST Wed Jan 23 2019

.SYNOPSIS...A weak front will track across the northern Panhandle
Wednesday evening. A stronger front will follow through the gulf
Thursday. A storm force front, strongest of the three, will then
push into the gulf Thursday night.

&&

.SHORT TERM...A weak front across the northern gulf has supported
some mixed precipitation over Yakutat and some light snow over
Haines/Skagway. The big conundrum today was how quickly southerly
winds would overtake the cold air entrenched in Haines/Skagway all
day. The entire forecast hinges on this one event. Southerly winds
did find their way into Lynn Canal mid-day, but Haines due to a
persistent northwest wind is remaining very cold at 22 F. We have
adjusted temperatures downward to keep the northerly winds going
a little longer and added snow and an inch of accumulation to
cover this. We now keep the rain at bay until around midnight or
so. Realistically, there will be no mix, but a complete changeover
to rain. However, we need to hedge.

Farther south we battled fog all morning, but higher clouds
spreading over the area helped raise very low stratus decks
sufficiently to allow visibility to rise. Between one frontal
passage and the next later Thursday, there may be enough breaks to
allow more patchy fog to develop across the south late tonight
into Thursday morning.

Judging by new solutions and guidance, our wind forecast needed
very little changes. We nudged a little to the GFS Thursday and
then to the GFS/NAM/Canadian Thursday night to better define
Thursday's gale force front and added a lot of strength to the
Thursday night system, now a little more scary with storm force
winds late Thursday night/Friday morning. We nudged to the NAMnest
on the inside Thursday night, but our experience with high res
model winds is that they transfer too much momentum to the surface
and overly mix winds in the midst of warm air advection, so we
did not go the full strength of the high res. In reality, we may
be under noting winds in Lynn Canal, but stronger periods will
become better defined in the future. We will basically have
persistent southerly breezes.

We decided to post a winter storm watch for the South Klondike
and Haines Highways above the towns of Skagway and Haines
respectively. A lot of whether we elevate to a warning, advisory,
or downgrade to no statement will depend on how much warm air
gets into the Chilkat Valley with each succeeding system. Somewhat
worrisome is the lack of great confidence in the southerly flow.
Pressure gradients hint at just enough backing of winds to keep
doubts roaming freer than we would like. Luckily the first couple
of systems will be quicker movers and rain and snow amounts will
be limited. But late Thursday night into Friday, we now suggest 5
to 9 inches possible with snow ratios on the lower side of
climatology.

POP/QPF changes were very conservative and minimal. We elevated
categorical pop to Haines and Klondike Highways while we raised
QPF late Thursday night and Friday morning. The NAM also raised
rainfall amounts for the rest of the Panhandle in the early Friday
morning time frame to mid- day Friday. But our assessment of 1 to
2 inches for the north and 2 to 4 for the south Friday and
Saturday still hold. Therefore we found no need to change the
Special Weather Statement.

We used elements of the GFS, NAM, Canadian, and ECMWF for changes
Thursday through Friday morning. Because of disagreements over a
wave late Friday, we left the forecast unchanged beyond Friday
mid-day.

.LONG TERM.../Friday through Tuesday/ As of 10 PM Monday, the
weekend forecast remains wet with an atmospheric river impacting
the Panhandle between Friday and Saturday. While it will be wet
across the Panhandle, ensembles continue to point the bulk of the
precipitation at the southern half of the Panhandle. Storm total
precipitation ranges between Friday and Saturday afternoon fall
between 2 and 4 inches for the southern Panhandle. Strong warm air
advection will accompany this event brining lows well above
freezing for the Panhandle this weekend, as high temperatures
push into 40s even over the northern Panhandle Friday. Saturday
the system will shift southeast with a north to south drying trend
expected through the day (precipitation will still be heavy
Saturday morning over the southern Panhandle).

Seasonable strong high pressure will build behind this system
through Sunday allowing the Panhandle to dry. This will also
introduce a chance for foggy conditions over the northern
Panhandle Saturday night into Sunday. Then early next week the
next system will push into the gulf, but timing remains
uncertain.

Overall the biggest changes to the forecast were an upward trend
in PoP values with 100% values now introduced for portions of
Friday and Saturday. Additionally, temperatures have been trended
upward once again to account for the strong warm air advection on
Friday. Forecast confidence is above average through Sunday and
below average Monday and beyond.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Winter Storm Watch from late Thursday night through Friday
     afternoon for AKZ018-019.
MARINE...Gale Warning for PKZ041>043-051-052.
     Small Craft Advisory for PKZ012-013-022-031-033-036-053.

&&

JWA/JB

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Special Weather Statement
National Weather Service Juneau AK
939 PM AKST Wed Jan 23 2019

AKZ023-024-026>029-250800-
Cape Decision to Salisbury Sound Coastal Area-
Eastern Baranof Island and Southern Admiralty Island-
Inner Channels from Kupreanof Island to Etolin Island-
Dixon Entrance to Cape Decision Coastal Area-
Southern Inner Channels-Misty Fjords-
Including the cities of Sitka, Port Alexander, Angoon,
Petersburg, Wrangell, Kake, Craig, Klawock, Ketchikan,
Metlakatla, and Hyder
939 PM AKST Wed Jan 23 2019

...HEAVY RAIN TO MOVE OVER THE AREA FRIDAY AND SATURDAY...

A weather system will lift out of the North Pacific and move over
the area starting Friday morning and will last through Saturday
afternoon. Rain will become heavy at times along with freezing
levels rising above 5000 feet. Possible rain amounts for this
time frame may range from 2 to 4 inches. There will be rises on
small streams due to the rain rates and added snow melt from the
mountains.

Stay tuned for updates on this evolving weather event.

AKZ025-250800-
Juneau Borough and Northern Admiralty Island-
Including the city of Juneau
939 PM AKST Wed Jan 23 2019

...HEAVY RAIN TO MOVE OVER THE AREA FRIDAY THROUGH SATURDAY
MORNING...

A weather system will lift out of the North Pacific and move over
the area starting Friday morning and will last through Saturday
morning. Rain will become heavy at times along with freezing
levels rising above 3000 feet. Possible rain amounts for this time
frame may range from 1 to 2 inches. There will be rises on small
streams due to the rain rates and added snow melt.

There is a significant snow pack across the area and people are
encouraged to make sure storm drains are cleared before the heavy
rains move over the area.

Stay tuned for updates on this evolving weather event.