Small Craft Advisory 657, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
249 PM AKST Mon Dec 25 2017

.SHORT TERM...It was a white Christmas for most of the
panhandle today, with lingering snow cover and Yakutat
and Gustavus seeing snow showers throughout the day. Chance of
snow is expected later tonight, with little to no accumulation
expected.

As an upper-level ridge remains in place over British
Columbia, the pattern will continue to be cold and dry through
the remainder of the short-term period and 500 mb temperatures
in the -20 to -30C degree range. Minor adjustments were made to
minimum temperatures, while maximum temperatures had to be brought
down 2-3 degrees in some places. Looking into the extended, there
will be a decreasing trend in temperatures from Wednesday onward,
with the possibility of Saturday to be the coldest day and
greatest model spread. The diurnal range in temperatures will be
greater at this time due to the clear, dry conditions.

The pressure pattern was nudged along to the GFS, as this had the
most consistency between past model runs and the progression of
the pressure pattern. With the gradient tightening overnight
coupled with cold air advection, this could lead to increased
northerly outflow, especially near Haines and Northern Lynn Canal.
These areas are where most of the wind edits were focused with
some minor adjustments made to the outer waters. This pressure
pattern is seen to waver back and forth as the ridge slowly
deteriorates on Wednesday and two new lows move northward through
the Gulf by late Wednesday.

Models weren't quite sure how to handle the POP pattern being so
dry, and therefore had to decrease POP's towards late Wednesday/
early Thursday. And although snow levels have been brought down to
0 across the panhandle, the pattern remains too dry for
significant snow accumulations currently. If we had enough moist,
southerly flow (similar to the system that we saw just a few
weeks earlier), there would no doubt be some higher accumulations
across the panhandle.

Good continuity remains among models for the duration of the
period.

.LONG TERM.../ Wednesday to Monday / High pressure over Canada
persists Wednesday and Thursday, while a low in the western
gulf/North Pacific moves towards Haida Gwaii by Friday. This low
will only give a glancing blow to the the southern Panhandle
Friday night. The low of interest is in the Bering Sea with a
front that will start to sweep across the gulf Sunday.

The front on Sunday will bring in more moisture and with cold
temperatures, snow returns to most of the Panhandle from the south
spreading north and along the outer coastal areas into the
weekend. Temperatures will begin to warm into the mid to upper 30s
by the end of the weekend, by Monday the southern area and coastal
area up through Sitka will likely have turned to all rain.

Keeping the risk of freezing spray in the forecast for Lynn Canal
and possibly northern areas of Glacier Bay as cold temperatures
continue into the early part of the weekend.

Models are struggling to come to a common solution, resulting in
the changes to the forecast to be small using mainly the WPC for
pressure and wind, nudging POP/QPF with GFS and WPC, ECMWF and NBM
added value to the temperatures.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Gale Warning for PKZ012.
     Small Craft Advisory for PKZ013-031.
     Small Craft Advisory due to Seas for PKZ041>043-051>053.

&&

SS/RWT/KAV

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