High Wind in Alaska, January 15 to 18, 2020

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
246 PM AKST Tue Jan 14 2020

.SHORT TERM...A frigid air mass remains entrenched across the
Alaska Panhandle. While surface records are hard to come by,
sounding climatology notes that the 12Z Annette Sounding is one of
the coldest ever recorded for the date at -21.9 C at 850 mb. Cold
air advection probably got the better of us, with a downward
momentum in offshore winds at ridgetop level near Downtown Juneau
and Douglas. Winds began gusting strongly this morning, and then
began peaking around 60 mph or greater by mid-morning. This
correlated well to daytime mixing, thus our zero lead time high
wind warning was issued through 6 PM this evening as mixing levels
should back off with solar "heating."

The forecast remains dry and cold through the next three days. And
thus our only forecast challenge has been relating temperature
with the expected slight increase in winds each day. A Taku event
was studied today such that we issued a watch for another event
over Downtown Juneau and Douglas. Models are indicating a rise in
925 mb winds and while the times of strongest cross-barrier flow
in the low levels (Thursday morning) and critical level (zero
component cross barrier between 400 and 600 mb (Thursday
afternoon) do not coincide, we felt given today's events, that
there is an even greater chance that winds will match. Also of
note, is that we expect another period of strong cold air
advection across the mountains at this time which would aid in
downward momentum of wind gusts. Therefore, we issued a high wind
watch Thursday to go along with the warning today.

Finally, we edited temperatures. We raised air temperatures
across much of the Inner Channels Thursday night into Friday to
reflect current trends in order to better forecast the always
impactful heavy frenzing spray. We also tried to increase a
warming trend for the south/central Panhandle on Friday as we do
expect clouds to increase during this time period, which in
addition to warm air advection should support a good rise in
temperatures.

Forecast confidence is good through Friday.

.LONG TERM.../Friday onward/ Signs of change are still in the
cards for the long range period as precipitation and less outflow
returns for the weekend. Overall expected upper level pattern has
not changed much since yesterday with a ridge over Western Alaska
transitioning to a broad trough by early next week. About the only
change from yesterday is that the merging of the upper lows over
the AK Peninsula late week has been pushed back by about half a
day.

For the panhandle, Strong outflow and cold temperatures expected
to continue into Fri. Freezing spray remains an issue for many
marine areas and low wind chills are still expected in windy
areas. Little change in the forecast here.

Long range guidance has gotten better for the low trying to move
north into the eastern gulf Fri. However compared to yesterday the
low is stronger, and the track is farther out to sea. Also due to
this, the arrival of significant precip into the southern
panhandle is slower by about 6 to 12 hours. Now instead of the
precip arriving Fri evening, it will more likely be late Fri night
before the precip moves in to the south, and will not impact the
north until Sat at least. The deep cold air will still be present
so significant snowfall is still possible for the southern
panhandle, just at a later time then previously forecast. There is
the possibility that later model runs will push this timing even
further back as we get closer to the event so limited the
possibility of precip to likely as a result. Favored ECMWF and
WPC for updates here.

Southerly flow continue behind the first low that will bring
another system into the southern panhandle for early next week.
However model agreement is poor with the only certainty being that
there will still be precipitation in the area with more southerly
flow gradually warming temperatures into early next week.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...High Wind Warning until 6 PM AKST this evening for AKZ025.
     High Wind Watch from late Wednesday night through Thursday
     evening for AKZ025.
     Strong Wind from 6 PM AKST this evening through Wednesday
     afternoon for AKZ025.
     Strong Wind through Wednesday afternoon for AKZ019.
     Wind Chill Advisory from 11 PM this evening to 10 AM AKST
     Wednesday for AKZ019.
     Wind Chill Advisory from 9 PM Wednesday to 9 AM AKST Thursday
     for AKZ019.
     Wind Chill Warning until 10 AM AKST Thursday for AKZ018.
     Strong Wind through Wednesday afternoon for AKZ018.
MARINE...Heavy Freezing Spray Warning for PKZ031.
     Heavy Freezing Spray Warning for PKZ012.
     Heavy Freezing Spray Warning for PKZ013-032.
     Gale Warning for PKZ012-013.
     Small Craft Advisory for PKZ021-022-031>035-041>043-051-052.

&&

JWA/EAL

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