Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
FXUS66 KSEW 112253
Area Forecast Discussion
National Weather Service Seattle WA
300 PM PST Wed Jan 11 2017
.SYNOPSIS...A dry, cold, and stable air mass will dominate the
weather through Friday. Westerly flow aloft will develop later
Friday allowing temperatures to moderate. A weak front will arrive
Saturday night, increasing clouds and bringing a chance of rain to
the coast and north. A series of warmer and wetter systems will
arrive early next week.
.SHORT TERM...The cloud shield over the southern half of Western
Washington has hung tough today, however in the last few visible
satellite images it shows signs of dissipating. The Seattle area is
forecast to clear this evening, with the Olympia area clearing after
midnight. A cold and dry air mass will remain over the region
Thursday. Highs will be in the 30s Thursday, with overnight lows in
the teens and 20s tonight and Thursday night.
On Friday, a temporary flattening of the upper ridge could allow
some mid and high clouds to spread across western sections. Highs
will rise a bit, into the 35-40 range. What had been a decent
looking system on Saturday in earlier models, then became weaker in
subsequent runs, is now completely dry. There will likely be clouds
Friday night, but some sun now seems likely on Saturday over the
interior. Highs will be 40-45.
.LONG TERM...A weak front is present in the models Saturday night,
and there is a chance of rain on the coast, in the mountains, and
over the north Sunday. Another weak system arrives Monday. Highs
both Sunday and Monday will probably be 40-45. A much stronger
system will probably bring rain Tuesday to all areas. The GFS and
Canadian models have rain, heavy at times, for about a 36-hour
period Tuesday through Wednesday night. The Euro also has rain, but
focuses the heaviest precipitation south of the area. Temperatures
will rise into the low 50s both Tuesday and Wednesday. Burke
.HYDROLOGY...River flooding is not expected through Monday. A period
of heavy rain around next Tuesday will cause rises on area rivers.
Minor flooding on a few rivers is possible. Note: Snow is not a
significant contributor to flood flows on western Washington rivers.
Even when there is snow on the ground, river flooding is almost
exclusively caused by runoff from heavy rain.
.AVIATION...The remnants of a weak low pressure system over the
northwestern Oregon coastal waters will dissipate overnight. A
1023 mb high over south-central British Columbia will sag
southward into eastern Washington on Thursday. At the upper
levels, an upper low over northwestern Oregon will move
southeastward into California while a ridge of high pressure aloft
over the Gulf of Alaska moves southeast toward the area. The air
mass will become increasingly dry and stable with northeast flow
Left-over low and mid level moisture over the coastal waters and
from about a KHQM-KPAE line southward will dissipate from the
night this evening leaving good VFR conditions through Thursday.
KSEA...Mid and high level clouds will gradually dissipate by 04Z
leaving good VFR conditions tonight and Thursday. North wind 5-7
knots will veer to the northeast and east this evening through
.MARINE...A 1023 mb high over south-central British Columbia will
slowly sag into eastern Washington tonight through Thursday. The
remnants of a weak low over the northwestern Oregon coastal waters
will dissipate this evening. Light offshore pressure gradients are
expected tonight through Saturday.
A weak front will move through the coastal waters late Saturday
night or Sunday. Southeasterly pressure gradients will increase on
Monday as a stronger front approaches the coastal waters. Albrecht
You can see an illustrated version of this discussion at