Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Seattle Washington
330 PM PDT Sat Oct 25 2014
Synopsis...a deep low will reach the coast late this afternoon and
then fill as it moves northeast. Rain and very windy conditions will
occur this evening over western Washington. Sunday and Monday will
be showery. Another weather system will arrive Tuesday. Wet and
breezy weather is likely at times through the end of the week.
Short term...buoy and metar observations from the Oregon coast show
strong winds are headed toward Washington. A deep low will reach the
central Washington coast around 00z and slowly fill as it moves
northeast. By around 04z it will cross Admiralty Inlet resulting in
a very strong surface pressure gradient from south to north across
the Seattle metropolitan area. A High Wind Warning is in effect for all
zones from Everett south including the southwest interior and the
coast. Sustained wind speeds of 20-40 miles per hour with gusts up to 60 miles per hour
High wind in the Seattle area is rare...especially this early in the
year. Most trees still have their leaves...which means they are more
likely to topple in high wind. Power outages are possible tonight.
The low is expected to continue northeast into southern British
Columbia. Wind will spread to the northwest interior but at this
point the conditions are expected to be sub high wind. A Wind
Advisory is in effect there.
Showers and breezy conditions will follow on Sunday. The snow level
in the mountains will fall below 5000 feet or so and some snow on
the higher passes is likely. Showers taper Sunday night and at least
the first part of Monday will probably be dry. The next front
arrives on the coast Monday afternoon and spreads rain inland Monday
night...with Tuesday a cool showery day. Burke
Long term...Wednesday appears to be a mostly cloudy day with
scattered showers. Another organized system arrives Thursday. At
this point the GFS and Euro diverge with the Euro staying wet and
the GFS turning showery. Not confident on any details but the
forecast will stay moist into the weekend. Burke
Hydrology...the Skokomish River appears to be bottoming out near 15
feet. It will rise again in response to heavy rain today and
tonight. It is possible the river will get close to flood stage late
today or tonight. For now the forecast takes the stage at Potlatch
to between 15.5 and 16 feet. Flood stage is 16.5 feet.
A break in the rain will allow the skokomish to recede river Monday.
Another front Monday night and Tuesday will bring 2-3 inches of rain
to the skokomish basin. Will need to keep a watch on this but the
current forecast keeps the river below flood stage.
Otherwise...flooding on other rivers is unlikely over the next 7
Aviation...southwest flow aloft over western Washington this
afternoon will veer to westerly tonight as a vigorous frontal system
and its upper trough move through the area. The air mass will be
moist and somewhat unstable. Northwest flow aloft will develop
Sunday ahead of a weak upper ridge.
Areas of rain are moving through western Washington this afternoon
as a vigorous frontal system approaches the region from the
southwest. Offshore northerly flow is keeping the lower levels of
the air mass generally dry for mainly VFR conditions. Conditions
will deteriorate late this afternoon and early this evening as the
frontal system reaches the area...and as moist onshore flow follows
the front. There could also be isolated thunderstorms along the
coast through this evening. Winds will rise dramatically as the
surface low associated with the frontal system tracks northeast
across western Washington this evening...with areas of sustained 20
to 35 knots winds and gusts 40 to 55 knots. There should be gradual
Ksea...northeast winds 15 knots or less will continue this afternoon...
then shift to south or southwest around 6 PM and rise quickly to
20-30 knots gusting 40 knots. The wind should peak around 11 PM...and wind
as high as 35 knots gusting 50 knots is possible. Winds will ease to
southwest 10-16 knots Sunday. Mcdonnal
Marine...a 987 mb low will move northeast across the coastal waters
this afternoon and make landfall near tahola around 5 PM today. The
low will track across the north part of western Washington this
evening. Winds will rise rapidly with the arrival of the low...with
gales over the coastal waters becoming west to northwest as the low
moves inland and locally reaching 45 knots. Gales will develop over all
inland waters zones too...with westerlies in the central and eastern
Strait of Juan Delaware fuca probably reaching 45 knots.
High pressure will move across the area Sunday and winds will ease.
Another vigorous frontal system will move through the forecast area
late Monday through Tuesday. That feature has a good chance of
producing gales over the coastal waters and some of the inland
waters like the East Entrance Strait and northern inland waters.
Washington...High Wind Warning coast...southwest interior...Seattle/Tacoma
Wind Advisory northwest interior and east Puget Sound sound lowlands.
Pz...Gale Warning all waters.
Small Craft Advisory for rough bar conditions Grays Harbor.
You can see an illustrated version of this forecast discussion at