Area Forecast Discussion
Issued by NWS
FXAK67 PAJK 261431
Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
531 AM AKST Sun Feb 26 2017
.SHORT TERM...Rather quiet but somewhat cold morning across the
panhandle today. Skies have been mostly clear overnight for most
areas but thickening high level clouds have started moving in from
the NW. Winds are also on the gradual decline from the breezy
condition seen yesterday with most areas seeing 15 kt or less of
wind. The result is that temperatures across the area have been
allowed to drop into the 20s with some teens observed in isolated
areas of the northern panhandle.
For the next 24 hours the only weather feature of note is a weak
trough that will be moving through the panhandle from the NW to
SE. The main effect that this feature will have is increased mid
to high level cloud cover today that will suppress high
temperatures this afternoon. Expected high temperatures will only
be in the 30s rather then the 40s that were observed yesterday.
The secondary effect is that this trough will have enough dynamics
that some showers could be stirred up in the gulf this afternoon
and evening with some of them affecting the outer coast. I do not
think they will travel any farther inland but I can not rule out
some flurries or sprinkles in the inner channels this afternoon
and evening. As such I have included scattered to isolated
showers along the outer coast and mention of flurries or sprinkles
for the southern 2/3rds of the inner channels. Any snow
accumulations from showers will be very light.
The trough moves out of the area tonight with some showers or
flurries/sprinkles lingering in the southern panhandle this
evening. Otherwise I expect skies to clear out again tonight as
offshore flow strengthens late. The clearing skies and light
winds will allow temperatures to again drop into the 20s and teens
across the panhandle.
Short range models were generally in good agreement but differed
on how far inland to take the showers that develop over the gulf
this afternoon. The GFS was the least aggressive by hardly
bringing any precip into the inner channels while the Canadian
was the most aggressive. Decided to mainly used the Nam for
guidance today as a good middle ground for the showers.
.LONG TERM...Upper level trough digs southward from the AK
interior over the AK gulf Monday night into Tuesday. This trough
will be main weather feature through the long range as blocking
pattern forms upstream. Still large model spread due to issues
phasing southerly flow with this northerly stream. At the surface
a closed low develops over the N Gulf Monday night then deepens
though Tuesday and either a) remains nearly stationary through the
week keeping steady stream of moist air moving over the panhandle
or b) tracks over the south central panhandle with a more
organized front by Tuesday. This dries out the northern half of
the panhandle due to off shore flow before next wave moves in.
With either solution the cold air that is becoming established
over the panhandle will set up for over running snow event. Amount
of snow fall depends on eventual track of the surface waves under
the upper level trough. Amounts range from a few inches to
upwards of a foot or more through the week.
Besides the winds remaining mostly northerly and increasing as the
next surface waves moves in. It is the same story with wind as
the snow fall: highly dependent on where the waves move and how
deep they get. Mostly likely gulf winds and northern inner channel
winds reaching gale force but could see higher outflow gusts.
Model solutions overnight fell into two camps. ECMWF/Canadian
which keep the low over the N Gulf, keep weaker but more
consistent precip over the panhandle, and were more in line with
inherited grids. The GFS/NAM solution tracks the Tuesday wave over
the S Panhandle, has more intense but spatially variable precip,
but has much larger run to run variability. Decided to use the
ECMWF/Canadian blend to refresh grids due to the better run to
run consistency. While weather will occur in the long range
confidence on the exact details of the weather is low.
MARINE...Small Craft Advisory for PKZ041.
Small Craft Advisory due to Seas for PKZ042-043.
Visit us at http://www.weather.gov/Juneau