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Southeast Alaska forecast discussion 
National Weather Service Juneau Alaska
516 am akst Thursday Dec 25 2014

Short term...weakening occluded front along the outer coast will
move inland today. Another weak occluded front will move to the
eastern Gulf this afternoon...then drift onshore Southeast Alaska tonight. Used
blend of the 06z NAM and 00z European model (ecmwf) as they had best handle on the
main features.

Main forecast concerns will be precipitation potential/type...temps...and
winds. Right now a somewhat broken band of precipitation is moving through
Southeast Alaska with weakening occluded front...with the least precipitation over the
far north. Think most areas will see precipitation diminish through the day as
front moves past the area...although a few showers behind the
front cannot be ruled out. Will hang onto the steadier precipitation the
longest in the pajn/papg/Hyder zones. Snow is now mostly limited
to the north of the pajn Airport...and expect a changeover from S to north
near sea level by early afternoon as winds become southerly. Not
expecting more than an inch at this point this morning. With
second front...will see some enhancement to the showers coming in
tonight. Think ptype will remain liquid near sea level tonight as
well...as southerly winds continue.

Most temperatures were left above MOS guidance tonight given the airmass
and likelihood of significant clouds. Even most places over the north
are above MOS today as it does not warm things up enough
concurrently with the wind shift to S.

As for winds...most wind will be in northern Lynn Canal tonight as
30-40 knots west-SW flow in middle-levels maintains enhanced trough north of ero.
Went with Small Craft Advisory there tonight. Kept southern Lynn Canal at 20 knots but they
could see a little stronger this evening. Winds ahead of the first
occluded front should remain below Small Craft Advisory...but increase to Small Craft Advisory over
the northern Gulf by late afternoon or early evening. Will have rough
seas though due to fairly long fetch west-southwest flow...so will maintain Small Craft Advisory
for seas for the southeastern Gulf coastal waters through tonight.

Long term...ec has finally come around to agreement with the
other models on friday's weak wave and low over the Gulf...it
impacts primarily the central and southern Panhandle and weakens
as it moves east and south. Precipitation will be more showery with this
system and mostly light with some light snow on the north end in
the Haines and Juneau vicinity. Updated the grids with the new ec/NAM
tweaks early in period on mostly moisture fields. This will be the
last system in the series as a Continental air mass takes over
rapidly Friday night over the entire Panhandle. Upper ridging
builds in rapidly after this last front. The drying along with low-
level cooling trend appears likely to persist until at least
Tuesday with the exception of Yakutat and the western reaches
where a front comes in on late Monday and into the northern
Panhandle late on Tuesday. Nocturnal radiational cooling will be
strong for most areas during the Sat-Monday period as skies should be
partly cloudy at worst with the possible exception of foggy or
low-overcast areas. For Sat-sun period updated grids with new
NAM/ec/GFS data for mostly wind and thermal tweaks including
bringing up Lynn Canal winds to Small Craft Advisory level as gradient will favor
northerly flow and 1050+ high builds in. On Monday the large and
high-amplitude upper rige extends from the central Panhandle
southward to off the US Mainland West Coast. As it begins to
retreat late Monday...grid winds needed updating to delay the
trough moving in from the west over the outside
waters...gradients still mostly very weak over the Inner Channels
at that time with the exception of those areas prone to
north/northeast flow in the northern and eastern portions of the
Panhandle. The frontal system to the west on Monday/Tuesday is trending
slower on the models and appears likely to have trouble pushing
eastward as its dynamic roots remain over the western Gulf on the
models. All 3 models are remarkably similar in their current
handling of the upper ridge early next week but cannot rule out
precipitation entering western reaches by Monday PM. Proceeded with
relatively high confidence of this scenario playing out.

So...looks like a series of potential fronts beginning about
Tuesday for the Panhandle with the general outlook for a potential return
to upper ridging late next week on current guidance...fantasy-land
day 7-8 for the models. Migrated from mostly ec grid updates for
Sunday/Monday to primarily wpc guidance for the remainder of the
extended. Ec was the model of choice overall, also for wpc Alaska
earlier today, although GFS and Gem forecasts were generally
supportive through tues,

&&

Ajk watches/warnings/advisories...
public...none.
Marine...Small Craft Advisory for pkz012-051-052.
Small Craft Advisory due to seas for pkz041>043.

&&

$$

Rwt/Wesley

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