Area Forecast Discussion
Issued by NWS
FXAK67 PAJK 031448
Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
548 AM AKST Sat Dec 3 2016
.SHORT TERM...The storm force low from yesterday has finally
tracked into the Yukon and the long expected southerly push up the
far northern inner channels happened overnight. Winds at Eldred
Rock went from light north at 11 pm to south at 28 kts by 1130 pm.
The southerly push took a lot longer to reach Skagway, but finally
arrived at 4 am - also going from light to strong southwesterly in
less than 1 hour. Strong wind headlines in Skagway for southerlies
this morning, and northerlies late tonight. A surface low remains
over the far northern gulf, with a col connecting to the Yukon
low. A ridge extends southeast from the interior and another
extends northwest along the long axis of the panhandle.
Eventually, the col will be pinched off and the northern ridge
will come to dominate the region, shifting the gradient to the
north. As this happens, the low over the northern gulf will begin
to track off to the southeast and a very cold low level airmass
will start to descend south into the forecast area towards the end
of the short range forecast period. Look for overnight lows
Saturday night to be markedly colder than Friday night.
Low level warm air advection associated with yesterday`s storm has
finally run out. High temperatures today will occur early in the
day and then begin a steady fall through the afternoon and over
night. Precipitation will begin as rain showers in many places,
but the transition to snow showers will progress through the day,
generally from north to south. QPF values in the morning forecast
do not support accumulations more than an inch or two, but as is
the case with showers, precipitation can be heavy at times, so a
quick inch or two over a short period of time cannot be ruled out.
Snow has been steady along the Klondike Highway all night. Snow
has been on and off along the Haines Highway. No word yet on how
much has fallen there. Look for more snow along the highways today
Very cold temperatures aloft and instability at the surface has
prompted the inclusion of a slight chance of thunderstorms over
the gulf as well as portions of the inner channels and public
zones. Thundersnow a definite possibility today and tonight.
Marine winds lower now, but westerly to southwesterly gales still
exist over a large portion of the eastern gulf. Seas got ups to 33
feet over the gulf, but are now down to 20-22 feet with a long
period southwesterly swell.
Used NAM12 for updated to Pressure and wind. PoP and QPF a blend
of NAMDNG5 and Canadian NH. Temps adjusted up early on based on
present conditions. Overnight lows from GFS MOS.
.LONG TERM...Long range forecast mainly dominated by strong cold
high pressure in the Yukon. This High is forecast to be as strong
as 1045 mb by Monday morning producing a very strong northerly
pressure gradient across the northern panhandle with cold air
spilling over the mountain passes. The result is strong northerly
winds in the usual outflow areas across the panhandle particularly
Lynn Canal (40 to 45 kt gales expected there), and some of the
coldest temperatures of the season so far (teens and 20s common
with single digit or lower temps in the extreme northern
panhandle). The combination of high winds and cold air will also
lead to freezing spray in the northern inner channels starting Sun
evening. Right now water and air temps are forecast to be just a
little too warm for heavy freezing spray to occur but if air temps
become colder then currently expected that could easily change.
This influx of cold air will also dry the panhandle out late
weekend into early next week but as early as Tue precip will be
returning at least for the central gulf and northern gulf coast.
Current model trends are moving toward a weak low passing near
Kodiak with a front heading into the central and northern gulf. SE
flow ahead of the front will bump up against the arctic boundary
from the cold air over the panhandle causing overrunning precip
that has the potential to spread east through Wed. Disagreement
between models on how far east this precip will get with some
bringing it as far as Juneau, while others only get as far as
Cross Sound before eastward movement stalls. Given model
disagreement still present decided to stay with the current chance
pops for the gulf and northern gulf coast at that time.
Farther out, model agreement remains poor as the strong low that
was suggested it was going to approach the southern gulf mid to
late next week now has some models suggesting that it will not
even make it that far north. Low track forecasts also have a wide
range of suggestions with little consistency run to run. Main
trend right now from all of this is actually a drier and colder
mid to late week period for the panhandle as the front from this
low barely makes it into the southern panhandle and generally is
rapidly falling apart as it tries to move northward. Decided to
mainly keep the previous extended forecast as is to see if this
drier trend continues to be suggested.
PUBLIC...Strong Wind until 9 AM AKST this morning for AKZ018.
Strong Wind from late tonight through Sunday afternoon for
MARINE...Gale Warning for PKZ012-022-041>043-051.
Small Craft Advisory for PKZ011-013-021-031>036-052.
Small Craft Advisory due to Seas for PKZ053.
Visit us at http://www.weather.gov/Juneau