Scientific Forecaster Discussion
fxus66 ksew 191735
Area forecast discussion
National Weather Service Seattle Washington
935 am PST Thu Jan 19 2017
Synopsis...a broad upper level trough will remain over the
offshore waters through the weekend. A series of systems rotating
around it will bring showers and breezy conditions at times to
western Washington along with seasonable temperatures. By early
next week, a ridge of high pressure will build into the Pacific
northwest for the possibility of several dry days.
Short term...showers on the radar will continue through the rest
of the day and decrease slightly overnight. A dying surface low
pressure system along with its stacked upper closed low will
approach the Washington coast Friday morning keeping a good chance
of showers in store through at least Saturday. In addition to the
showers, the low will also create a tight pressure gradient across
the Cascades resulting in windy conditions for the passes and
likely the foothills as well on Friday morning. Jsmith
Long term...a slightly more organized frontal system rotating
around a separate stacked surface low will arrive Sunday.
However, the jet stream remains well to our south over northern
California and the system will likely be losing steam as it
arrives. The models bring the trough onshore over Oregon on Monday
as upper level ridging begins to build offshore. This looks to set
the stage for some drier weather by late Monday into Tuesday and
persisting through much of the remainder of next week. 27/jsmith
Aviation...an upper level trough will move across the area today,
spawning showers. Westerly flow aloft today will become more
southwesterly tonight. The air mass is moist and slightly unstable.
At the surface, moderate southeasterly gradients will become more
easterly tonight as a low pressure center approaches the coast.
Ceilings are 4-6k ft around Puget Sound but are MVFR in the north
and on the coast. Current VFR ceilings are likely to fall to MVFR in
showers today and tonight.
Ksea...the ceiling should be predominantly VFR broken-ovc040-060, but
will drop to bkn020-030 as showers move across the terminal. The
afternoon and evening are the likeliest time for showers. Surface
winds will remain southerly 8-14 knots. Chb
Marine...a surface trough over the coastal waters this morning will
move inland today. This will maintain Small Craft Advisory strength
winds over most waters today.
A front will approach the area tonight, then move northeast across
the coast on Friday. Easterly flow will strengthen with a gale
probable over the outer coastal waters on Friday. At this point the
models are keeping winds over the near shore waters below gale
levels although a gale is not out of the question. A gale watch is
in effect for the outer waters, and for now, advisory level winds
have been advertised for the near shore waters. Easterly winds will
develop over the inland waters with east winds 15-25 knots possible in
the central Strait.
More fronts will arrive Saturday and again Sunday with Small Craft
Advisory strength winds likely with each one. By Monday, light
offshore flow will develop as high pressure builds over the region.
A large west swell approaching 20 feet may still reach the coast on
Hydrology...a Flood Warning remains out for the Skokomish River in
Mason County. With precip rates continuing to diminish...the
threat of additional flooding is similarly decreasing. The threat of
river flooding across the area will become low for the remainder of
the forecast period. An extended period of dry weather appears
likely to develop early next week.
Pz...gale watch from Friday morning through Friday afternoon 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 until 6 am PST Friday for coastal waters
from Cape Flattery to James Island 10 to 60 nm-coastal
waters from Cape Flattery to James Island out 10 nm-coastal
waters from James Island to Point Grenville 10 to 60 nm-
coastal waters from James Island to Point Grenville out 10
nm-coastal waters from Point Grenville to Cape Shoalwater
10 to 60 nm-coastal waters from Point Grenville to Cape
Shoalwater out 10 nm.
Small Craft Advisory for rough bar until 4 PM PST Friday for
Grays Harbor bar.
Small Craft Advisory until 4 PM PST this afternoon for Admiralty
Inlet-East Entrance U.S. Waters Strait of Juan de Fuca-
northern inland waters including the San Juan Islands.
Small Craft Advisory for hazardous seas until 4 am PST Friday
for West Entrance U.S. Waters Strait of Juan de Fuca.