Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Seattle Washington
246 am PDT Tuesday Oct 13 2015
Synopsis...a dissipating front will keep areas of drizzle in the
Puget Sound sound area and south interior this morning...with some
sunshine to the north and west parts of western Washington. An
upper ridge will bring sunny days Wednesday through Friday...with
night and morning fog especially Wednesday. The next front should
arrive Saturday and keep rain in the forecast through Monday.
Short term...the remains of a cold front are dissipating over
western Washington early this morning as a large upper ridge
starts building over the region. The front brought a half inch to
locally more than an inch to the north coast...Olympics...and a
few spots in the Cascades. Precipitation has been decreasing
overnight though...and by 2 am it was limited to mainly the Puget Sound
sound region...south interior...and west slopes of the Cascades.
Patchy fog started forming overnight as well.
The upper ridge will build slowly over the region today. Some
light precipitation...which we will call areas of drizzle...will
linger over the areas mentioned above but it will gradually end
as the air mass dries. Areas further north and west of the frontal
remains should have some sunshine today.
The upper ridge will build more strongly over the offshore waters
of the Pacific northwest tonight and Wednesday...with 500 mb
heights over western Washington rising to 5800 meters or so.
Skies will be mainly clear...so areas of fog should form tonight
and continue Wednesday morning.
The ridge will shift inland on Wednesday night and Thursday. Low
level offshore flow will increase. That should limit fog and
bring warmer weather...with highs Thursday mainly in the middle 60s
to lower 70s. Mcdonnal
Long term...the upper ridge should bring another day of dry
weather Friday as it shifts further east. A relatively weak cold
front will move through the forecast area Saturday...followed by
its upper trough Saturday night. Another relatively weak system
should move through Sunday night and Monday. Mcdonnal
Aviation...flow aloft is moderate westerly and the surface pressure
gradients are light northerly. The air mass is moist and stable with
widespread IFR ceilings and some visibility restrictions in fog and
drizzle this morning. Low level moisture will be slow to clear. Low
conditions can be expected through 19z with gradual clearing over
the north interior from midday...later over Puget Sound sound.
Ksea...the terminal will probably spend most of the morning with
ceilings under 1000 feet. Slow clearing after 20z. Northerly wind 3-
6 knots. Chb
Marine...light northerly gradients will continue through Wednesday.
Winds will be generally light. A Small Craft Advisory for hazardous
seas is in effect on the coast but the swell will fall below 10 feet
Around Wednesday night northerly flow will increase. Small Craft
Advisory strength wind is possible then over the inland waters
but for now have left the winds at 10-20 knots. Easterly wind at the
West Entrance is likely Thursday. Chb
Pz...Small Craft Advisory for hazardous seas coast and West Entrance.
Small Craft Advisory for rough Grays Harbor bar.
You can see an illustrated version of this discussion at