Gale Warning 323, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
332 PM AKST Sat Dec 30 2017

.SHORT TERM...Currently, an upper level ridge building over the
eastern gulf is our dominant feature for the SE Alaskan
panhandle. On IR satellite imagery, we can see our next weather
front moving east through the gulf that is associated with a
deepening trough over the western gulf. In addition, WV satellite
shows a jet streak aloft helping to strengthen the upper level
low. Courtesy of the ridge of high pressure and the continued
offshore flow, today has remained a relatively quiet weather day,
with clear skies and calm conditions. These conditions will
persist through tonight, save for developing gales along the front
over the eastern gulf waters.

Now, moving on to the main story, the weather front mentioned
previously will continue to push east tonight and begin to impact
the panhandle Sunday. This front will combine with an additional
developing low west of Haida Gwaii, and this setup should be
conducive for an overrunning event, triggering precipitation as
warmer air lifts over the sufficient cold air already in place
nearer to the surface. Models then continue to show another
weather front, this one oriented more east to west, lifting across
the northeastern gulf coast Monday night, providing an additional
shot of precipitation for mainly portions of the northern
panhandle. Stronger warm air advection with this next front will
likely cause a transition to rain, so the uncertainty with this
forecast revolves around when this transition will occur. Model
analysis of 925 mb temps currently have the freezing line
beginning to push north Monday morning. As of right now, we have
forecasted 4 to 8 inches of snow accumulation throughout the
panhandle, and we have issued a Winter Storm Watch. Additional
snow accumulation may be possible for higher terrain, and upslope
flow may provide additional snow accumulation for some areas.
Snow lovers, mother nature saw your snow dances and thought you
deserved a little something for New Year's. May the odds be ever
in your favor.

Our models of choice for updates to the forecast were the NAM and
ECMWF, as these models have been verifying more with current
conditions. All of the operational models still have some spread
regarding the developing low near Haida Gwaii tomorrow night,
which is why we have slightly lower confidence regarding this
forecast. As additional details become available, we will update
our forecast accordingly.

.LONG TERM.../Monday night through Friday night/...A significant
change in the synoptic weather pattern will already be in progress
by the beginning of this long range forecast period on New Year's
Day. A deep upper level trough will have just displaced the upper
ridge that has dominated our weather these past couple weeks.
Near the surface, a slightly warmer and moist airmass will have
already pushed in and produced an overrunning snow event that will
encompass most if not all of the panhandle. In the wake of this
front, weak low level warm air advection will press in from the
west by Monday afternoon. At this time, the biggest change in
temperatures will be an increase in daytime highs on Monday with
most locations rising into the upper 30s or lower 40s and the
potential is definitely there to transition precipitation from
snow to rain. Overnight lows will likely fall back near or below
freezing Monday night in most locations, so a change back to snow
is possible for Monday night and especially so for the northern
half where PoP values are relatively high. Similar daytime highs
and overnight lows are expected for the remainder of the work
week. A second front on Tuesday and then a third on Wednesday
night will keep precipitation - both snow and rain - likely for
most of the coming week.

Pressures and winds for Monday and Monday night updated with a
GFS/ECMWF blend to capture a weak low that tracks north over the
eastern gulf on Monday. Used latest WPC from Tuesday onward.
Temperatures nudged per AKGFS22 and GFS MOS. PoP and QPF early on
from ECMWF and GFS with some help from SREF early on, then WPC.
Overall forecast confidence is average.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Winter Storm Watch from Sunday afternoon through Monday morning
     for AKZ021-023>029.
     Winter Storm Watch from Sunday afternoon through Monday morning
     for AKZ020-022.
     Strong Wind through late tonight for AKZ018.
     Winter Storm Watch from Sunday afternoon through late Monday
     night for AKZ018-019.
     Winter Storm Watch from Sunday morning through Monday morning
     for AKZ017.
MARINE...Gale Warning for PKZ022-043-051-052.
     Small Craft Advisory for PKZ012-031-041-042.
     Small Craft Advisory due to Seas for PKZ053.

&&

Voveris/SS

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