Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
FXUS66 KSEW 232337
Area Forecast Discussion
National Weather Service Seattle WA
330 PM PST Mon Jan 23 2017
.SYNOPSIS...An upper ridge will result in generally dry weather
this week. A dissiating trough could bring spotty light rain late
Wednesday or Thursday. By Sunday, a front may bring some rain to
.SHORT TERM...An upper level ridge along 140w will shift eastward
over the Pacific Northwest on Tuesday. This will maintain mostly
clear skies and near average temperatures. Light surface flow and
residual near surface-based moisture may result in some patchy fog
across the interior the next couple of mornings. Lows will be in the
30s except some upper 20s to around 30 in typical cold pocket
locations. Highs will be near average in the mid or upper 40s.
The GFS shows some light spotty QPF over the area Wednesday into
Thursday as a splitting trough tries to break through the ridge.
Other models including the nam-12 do not bring as much low level
moisture and lift, indicating little in the way of clouds and no
precipitation. Will stick with the dry solutions at this point since
any split front would more than likely take precipitation to our
south through Oregon/CA.
.LONG TERM...A large scale upper ridge remains in place over the
region through about Saturday. This would maintain dry weather and
slightly above average temperatures. Offshore flow would dry the air
mass with only patchy fog in the most prone sheltered spots.
Some models flatten the ridge by Sunday and bring a progressive
front through Western Washington with some rain. The 18z GFS run is
not as strong with the trough but still shows some light measurable
rain. Light rain is also shown by the 12z ECMWF, so the chance pops
remain in the forecast. Models differ on the details early next
week, but generally point toward split westerly flow and some weak
systems reaching the area. Expect a little more unsettled weather,
onshore flow, and only light precipitation. Mercer
.AVIATION...An upper level low will weaken over northern
California tonight while a high amplitude ridge forms offshore.
The flow aloft over Western Washington is northerly. The air mass is
dry and stable with VFR conditions expected this evening.
Patchy low clouds and fog may form overnight with clear skies and
light winds. MVFR to IFR cigs are possible through the morning,
especially in the interior. Low clouds should dissipate by 18-20z. 33
KSEA...VFR conditions continue this evening. Light N winds at the
surface, becoming E/NE by 04z. Patchy low clouds may form overnight
with MVFR cigs possible through Tuesday morning. 33
.MARINE...Northerly flow will prevail across Western Washington
tonight as a 996 mb low shifts south and weakens off the OR/CA coast.
Meanwhile, seas are still at 10-12 feet and a Small Craft Advisory
for Hazardous Seas remains in effect. Seas will subside under 10
feet late tonight. High pressure will bring generally light winds to
the area Tuesday and Wednesday. A weak trough will dissipate over
the Coastal Waters Wednesday night into Thursday.
A warm front will clip the Coastal Waters on Friday. 33
.HYDROLOGY...River flooding is not expected for the next 7 days.
PZ...Small Craft Advisory for hazardous seas until 4 AM PST Tuesday
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 AM PST Tuesday for
Grays Harbor Bar.
You can see an illustrated version of this discussion at