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Area Forecast Discussion (AFD)

Issued by Seattle/Tacoma, WA (SEW)

                            
000
FXUS66 KSEW 161731
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
930 AM PST Wed Jan 16 2019

.SYNOPSIS...Wet and active weather will return to part of the area 
today, with more widespread precipitation affecting the area 
interior this evening into Friday. Precipitation will initially be 
light to moderate, with a wetter, windier system expected to impact 
the region Friday night into Saturday. Unsettled weather will 
continue through the middle of next week, before a drier pattern 
ensues.

&&

.SHORT TERM...A weak system brushing the area today, bringing 
light showers to the coast and southern interior. QFP values will 
remain light, with little or no impact with this first wave. 

A closed low approaching the Pacific Northwest will bring more 
widespread rain into the area from the southwest late tonight. 
Easterly low level pressure gradients may tighten up as the surface 
low approaches the coast, resulting in some gusty easterlies 
Thursday morning. Wind speeds will likely remain below advisory 
criteria at least initially. Rain will linger through Thursday night 
as a frontal boundary move inland. Winds will become southwesterly 
behind the front late Thursday night into early Friday morning. This 
will likely be the breeziest period with some potential for advisory 
level winds.  

.LONG TERM...from previous discussion...Rain looks to taper to 
showers briefly Friday afternoon as a weak short wave ridge passes 
overhead ahead of the next rain maker. Still seeing evidence of a 
notable atmospheric river associated with this system which looks to 
pull another round of moderate to locally heavier rainfall across 
much of the CWA even as the parent low lifts northeast to the 
central BC coast. Luckily given the large displacement of the parent 
low and the atmospheric river by Saturday afternoon, much of the 
rain will scour out of the area. Could see another quick break in 
the widespread rain thru early Sunday but given a look upstream, 
another shortwave will approaching the coast. Another round of rain 
appears likely at this point. 

After Sunday's system, a broader ridge tries to build in. At this
point in time, the ridge appears dirty, with moisture riding over
top of it and perhaps allowing for intermittent periods of rain
thru mid week. Thereafter, a major pattern change is still
forecast to occur, one in which a high amplitude trough will 
build across the eastern US, and a high amplitude ridge will set
up along the West Coast. If you're a cold weather lover, you 
might want to head east, otherwise, western Washington will 
provide for a period of rain-free weather thru the end of the 
week.

Kovacik

&&

.AVIATION...Southerly flow aloft will continue today and tonight 
with an upper trough offshore. A frontal system will spread rain 
into the area from the southwest tonight as the upper trough 
approaches. At the surface, easterly offshore flow will continue 
with high pressure inland and lower pressure offshore. The air mass 
is mostly dry and stable.

There are mainly mid and high clouds today. Moisture will increase 
from the southwest tonight as a frontal system arrives. Offshore 
flow should keep the low levels relatively dry. Rain will spread 
into the area but ceilings are expected to remain VFR, even towards 
the coast. 

KSEA...Mid and high clouds at times today. Ceilings will gradually 
lower tonight as rain develops but they are expected to remain VFR. 
Easterly wind 5-10 knots increasing to 10-15 knots tonight and 
becoming a bit gusty. Schneider/CHB

&&

.MARINE...Southerly flow will increase across the region today and 
tonight as a low center moves northeast offshore. Gale force winds 
are forecast on the coast and at the west entrance, with small craft 
advisory winds elsewhere. Another strong system will reach the area 
on Friday with seas building to 15 to 18 feet. This system will move 
inland Friday night and Saturday, maintaining strong southerly flow 
over the waters. A weaker trough may clip the area on Sunday. CHB

&&

.HYDROLOGY...A return to a period of wet weather will begin today
and continue through early next week. The accumulation of rainfall 
with each passing system over time is expected to spark a response 
in river levels. Given some of the higher rainfall totals expected 
across the Olympics, the Skokomish may reach flood stage by this 
weekend. Elsewhere, not expecting river flooding over the next 7 
days at this time.

Kovacik

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 7 PM PST this evening 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-West Entrance U.S. Waters 
     Strait Of Juan De Fuca.

     Gale Warning from 7 PM this evening to 4 PM PST Thursday 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.

     Gale Warning from 7 PM this evening to 6 AM PST Thursday for 
     Coastal Waters From Cape Flattery To James Island Out 10 Nm-
     Coastal Waters From James Island To Point Grenville Out 10 
     Nm-Coastal Waters From Point Grenville To Cape Shoalwater 
     Out 10 Nm-West Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 4 PM PST Thursday for Central U.S. 
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters 
     Strait Of Juan De Fuca.

     Small Craft Advisory from 6 PM this evening to 4 PM PST Thursday 
     for Northern Inland Waters Including The San Juan Islands.

     Small Craft Advisory from 7 PM this evening to 10 AM PST 
     Thursday for Admiralty Inlet-Puget Sound and Hood Canal.

&&

$$

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