Scientific Forecaster Discussion
fxus66 ksew 080444
Area forecast discussion
National Weather Service Seattle Washington
844 PM PST Sat Dec 7 2019
Synopsis...an upper trough will shift inland tonight with
decreasing showers and drizzle. An upper ridge will build
offshore on Sunday for dry weather through early Tuesday. The
next system should slide through later Tuesday with unsettled
conditions persisting thereafter.
Short term /tonight through Tuesday/...a weak upper trough will
shift inland tonight. A few showers will linger as well as some
drizzle with lots of low level moisture.
An upper ridge will build in from the west Sunday and Monday for
dry weather. Sunday looks cloudy but low clouds will at least
lift a bit later in the day for less gloom. There might even be
some filtered sunshine or sunbreaks on Monday as the low levels
dry a bit more.
A weakening front will move into the area on Tuesday with areas
of light rain developing at the coast in the morning and then over
the interior in the afternoon. Temperatures will be slightly
above normal each of the next few days.
Long term /Wednesday through Saturday/...previous
discussion...model differences enter the picture midweek with
respect to some weak shortwave ridging that follows the late
Tuesday front. We may catch a short dry break at some point on
Wednesday, but deterministic models and ensembles remain in good
agreement that a broad upper trough will take up residence over
the northeast Pacific during the later half of next week with a
series of systems reaching the area. There are fairly typical
timing differences in the extended period, but an active pattern
with lower snow levels than those of late looks like a good bet.
Aviation...a weak upper trough over the area will shift inland
tonight with an upper ridge building in from the west on Sunday.
Westerly flow aloft will become northerly on Sunday. At the
surface, weak low pressure will be over the area with light winds.
The air mass is stable with low level moisture.
Widespread low clouds and areas of reduced visibilities through
Sunday morning. Ceilings should lift in the afternoon but low
clouds will continue.
Ksea...low clouds tonight and Sunday morning. Ceilings will lift
Sunday afternoon but low clouds will continue. Light winds.
Marine...weak low pressure tonight will give way to high pressure
by Monday with light winds. A front will approach the area on
Tuesday and weaken over the area Tuesday night. Another stronger
front should reach the area Wednesday night and push inland on
Hydrology...river flooding is unlikely for the next 7 days.