Scientific Forecaster Discussion
fxus66 ksew 091649
Area forecast discussion
National Weather Service Seattle Washington
845 am PST Mon Dec 9 2019
Synopsis...low clouds cover much of The Lowlands this morning
but should break up in the afternoon. A weak front will move
through western Washington Tuesday afternoon and evening. Stronger
weather systems will give western Washington wet and breezy
weather Wednesday night through Friday.
Short term /today through Wednesday/...low clouds and some fog
patches cover The Lowlands this morning--and then a little
sunshine is likely for the afternoon. A transitory upper ridge axis
just offshore will shift through the region tonight and Tuesday as
it is dented by a weakening front. The front will spread some rain
to the coast by the middle of the day and into the I-5 corridor by
late afternoon. Ridging pokes back up over western Washington behind
the system Tuesday night and Wednesday morning ahead of the next
stronger frontal system that will arrive late in the day Wed.
Long term /Thursday through Sunday/...a more active pattern is
likely for the second half of the week with wet breezy weather
Wednesday night through Friday. An upper trough in the northeast
Pacific Wed-Fri will weaken, progress east, and a shortwave on
Saturday will mainly affect northern California--leaving western
Washington on the cool showery side of the westerlies for a day. As
another trough develops in the North Pacific early next week,
downstream ridging occurs over the Pacific northwest starting on
Aviation...an upper level ridge centered offshore will move
inland tonight. Light flow in the lower levels will persist
through Tuesday morning. The airmass is moist and stable, with a
drying trend expected this afternoon.
Mixed bag of conditions this morning, with ceilings below 1000
feet and visibility 1-3sm in fog. Isolated visibilities 1/2sm or
less. Cloud tops 1000-1500 feet. Mid level deck dissipating with
ridge moving overhead this morning which will allow the sun to
work on the shallow fog layer. Low clouds should scatter out near
midday. High level clouds will increase tonight ahead of the next
system on Tuesday, but not in time to prevent some areas of fog
from reforming around midnight tonight.
Ksea...current ceilings below 500 feet with visibility 1-3sm in
fog and low clouds. Improving trend from 17z-21z with clouds
scattering out by the early afternoon hours. Fog could reform
after midnight, dropping visibilities down again. Light northeasterly
winds through tonight 2-6 knots. Felton/Borth
Marine...weak high pressure will remain over the area today. A
weakening front will then move through the area on Tuesday,
bringing Small Craft Advisory strength easterlies to the western
Strait of Juan de Fuca and small craft strength southeasterlies to
the coastal waters.
A stronger frontal system will then move through the area Wednesday
and Thursday. Gales are possible for the coastal waters with this
system Wednesday night. In addition, west swell will build to
around 15 feet Wednesday night and Thursday.
Hydrology...river flooding is unlikely for the next 7 days.
Pz...Small Craft Advisory from 6 PM this evening to 2 PM PST Tuesday
for coastal waters from Cape Flattery to James Island 10 to
60 nm-coastal waters from James Island to Point Grenville
10 to 60 nm-coastal waters from Point Grenville to Cape
Shoalwater 10 to 60 nm.
Small Craft Advisory from midnight tonight to 2 PM PST Tuesday
for coastal waters from Cape Flattery to James Island out
10 nm-coastal waters from James Island to Point Grenville
out 10 nm-coastal waters from Point Grenville to Cape
Shoalwater out 10 nm.
Small Craft Advisory from 2 am to 2 PM PST Tuesday for West
Entrance U.S. Waters Strait of Juan de Fuca.