Area Forecast Discussion
Issued by NWS
FXAK67 PAJK 210047
Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
347 PM AKST Fri Jan 20 2017
.SHORT TERM...Dry cold air continues to push into SEAK with help
of strong N winds. Clear skies will be the rule across the
Panhandle through Saturday. Pressure gradients favor strongest
winds in N-S inner channels. Observations Fri afternoon in Lynn
Canal show consistent gusts in the range of 50 to 80 kts
supporting Storm Warning in effect...along with freezing spray...
into Sat. The colder temps are leaking out of the Yukon interior
where temps were around -35F earlier today. Wind chill readings
through White Pass where -20F to -30F.
Main short term forecast issues today were winds and temperatures.
I lowered minimum temps for Sat morning most areas by about 3-6
degrees. In wind sheltered areas from about Juneau northward low
temps near zero likely. All but far southern Panhandle could stay
below freezing all day Sat.
Taku wind event in Juneau area still looks marginal at best. Most
likely time period would be from late Fri evening to late morning
Sat. Winds aloft over mountains are not exceptional. So stayed
with Strong Wind headline rather than issue any warnings at this
time. As mentioned above the strongest winds are related to low
level pressure gradient from N to S. Storm Force winds already
occurring in Lynn Canal. Small Craft Advisory speeds gradually
spreading to Frederick Sound and possibly northern Clarence over
night tonight. This cold dry weather period will be short lived as
conditions change later in weekend. See Long Term forecast
.LONG TERM...At mid levels high pressure ridge over the panhandle
will continue to shift eastward was trough extending down from
the AK interior tracks from the western gulf then over the
panhandle through Monday. At the surface a wave moving up from the
N pacific will form a closed low in the NE gulf late Sunday into
early Monday. At first most precipitation from the wave will
remain over the gulf but it will start the transition from
previous clear skies, dry weather and cold temperatures. By early
Monday frontal boundary tracks over the panhandle bringing first
round of precip. Should still be enough cold air in place at the
surface for an over running snow event before the big warm up. For
now only getting a few inches of snow due to lower QPF amounts.
The strong northerly winds over the panhandle and inner channels
will diminish and flip to the south with the first wave.
By Tuesday the real change in weather pattern happens. 500 mb
level flow shifts to the southwest with ridge axis over western
British Columbia and series of waves/troughs pushing into the
gulf. This pattern will continue through the week and bring in
warm moist air as one by one surface waves track up from the south
and associated fronts cross over the panhandle. Except for high
elevations sites expect everywhere below at least 1500 to 2000
feet to get rain as temperatures rise into the upper 30s to mid
40s. Ensembles in the very long range have some indication of a
shift back to a cooler pattern, but this is still a ways off. As
the series of surface waves/fronts track into the gulf Tuesday
onward gulf winds will pick up to southerly max small craft to
gales under low level/ barrier jet.
Refreshed the forecast starting with a NAM/GFS blend then
transitioned to more ECMWF by day 3 into 4. For the rest of the
time frame updated with the WPC ensemble which used a blend of
ECMWF/GFS. Tricky part of the forecast is the early Monday wave
and how far east it will progress and when it does how much snow
will be pumped out of it. As it is fairly fast moving and the warm
up begins before precip really starts think only a few inches of
accumulation. Forecast confidence is average.
PUBLIC...Strong Wind from 9 PM AKST this evening through Saturday
afternoon for AKZ025.
Strong Wind through Saturday afternoon for AKZ018.
Strong Wind through late tonight for AKZ029.
MARINE...Heavy Freezing Spray Warning for PKZ011.
Heavy Freezing Spray Warning for PKZ012.
Storm Warning for PKZ012.
Gale Warning for PKZ013-031.
Small Craft Advisory for PKZ011-021-022-032>035-041-043.
Small Craft Advisory due to Seas for PKZ042-051.
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