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Area Forecast Discussion (AFD)

Issued by Seattle/Tacoma, WA (SEW)

FXUS66 KSEW 171055

Area Forecast Discussion
National Weather Service Seattle WA
300 AM PST Sat Nov 17 2018

.SYNOPSIS...A dry weather pattern with areas of night and morning
fog will persist into early next week. Overnight temperatures 
will be on the cooler side, dropping into the 30s and even upper 
20s by Sunday morning at some locations. A weather system will 
bring wet weather back by mid to late next week.


.SHORT TERM...The last clouds evaporated over the last few hours and 
Western Washington is mostly clear this morning. There is patchy 
fog. Temperatures are mostly in the 40s with some 30s--freezing 
temperatures are not yet here. Today will be sunny after the areas 
of fog clear. Highs will be in the low to mid 50s. With a northerly 
breeze through the Puget trough it may seem chillier.

A sharp upper ridge off the coast this morning will slowly move 
inland through Monday. This will keep skies clear. Areas of fog will 
form each night and linger in the mornings. High temperatures will be 
in the low to mid 50s each day. The next two nights are going to be 
cool, with lows in the 30s and upper 20s. Some of the fog will be 
freezing fog. Meanwhile the mountains will remain sunny, with 
the freezing level 10,000 feet or higher. Burke

.LONG TERM...Tuesday looks like the last dry day for awhile. A 
weather system will approach the coast during the day, and clouds 
will increase across the area. Highs on Tuesday will again be in 
the low to mid 50s. The GFS and Euro differ slightly about when the 
rain will begin, with the Euro a bit slower. It does seem rain will 
start some time on Wednesday, so have kept the forecast of rain 
likely for Wednesday.

Model timing varies quite a bit after that, and so do the forecast 
tracks of the various fronts, with the Euro sending most of the 
energy into Oregon and the GFS moving the fronts right through 
Washington. For now a the forecast is for rain at times, with high 
pops but relatively low QPF, and there will be some dry periods 
between fronts. Highs will be somewhat lower than what we have been 
experiencing, mostly in the 45 to 50 range. The snow level will fall 
to 4000 to 5000 feet, which means most ski areas and passes will get 
snow at times. Burke


.AVIATION...Northerly flow aloft will continue through this 
afternoon as an upper level ridge moves onshore. Low level flow will 
also be northerly. Mainly VFR cigs under clear skies at this hour, 
other than localized areas of lingering low clouds. Some lowering to 
MVFR cigs is possible into the morning hours where low clouds 
develop, though widespread low clouds are not expected. Some patchy 
fog is possible as well leading isolated LIFR VSBYs, but expect it 
to be mainly limited to fog-prone areas as northerly wind speeds 
range from 5-15 knots. Clear skies tomorrow night into Sunday will 
lend to more widespread fog development.

KSEA...Few lingering low clouds exist, but the majority of cloud 
shield has broken apart. VFR cigs should continue through the 
morning hours. There is a slight possibility for MVFR cigs due to 
low clouds (mainly 12z-17z), though confidence is not high of their 
formation. Otherwise, clear skies will prevail into the afternoon 
and overnight. Northerly winds near 10 kts will continue thru the 
TAF period.

There may be a period of LLWS during the morning hours, possibly 
continuing into the early afternoon. Sfc winds will be northerly 
with winds just above sfc out of the east around 15 knots. JD


.MARINE...High pressure over British Columbia with lower pressure 
over southwest Oregon will result in northerly flow today. The flow 
will become easterly tonight as higher pressure builds east of the 
Cascades while lower pressure prevails over the coastal waters. 
Easterly (offshore) flow will then persist through Monday.

Anticipate an active pattern to develop about the middle of next 
week, leading to the possibility of gale force southerlies over the 
coastal waters next Wednesday.


.HYDROLOGY...River flooding is unlikely over the next seven days.


PZ...Small Craft Advisory until 4 PM PST this afternoon for Coastal 
     Waters From Cape Flattery To James Island Out 10 Nm-
     Northern Inland Waters Including The San Juan Islands.

     Small Craft Advisory until 5 PM PST this afternoon for Puget 
     Sound and Hood Canal.