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Area Forecast Discussion (AFD)

Issued by Seattle/Tacoma, WA (SEW)

FXUS66 KSEW 140349

Area Forecast Discussion
National Weather Service Seattle WA
850 PM PDT Sat Jul 13 2019

.SYNOPSIS...Generally dry weather tonight will stretch into Sunday. 
The weather will shift back to a more unsettled pattern Monday 
afternoon through much of next week. will linger into Sunday with 
more unsettled weather returning for much of next week. 


clouds this evening with some mid and high clouds streaming into 
the area from the southwest this evening will keep skies partly to 
mostly cloudy through the evening. This will be aided by a weak 
upper level shortwave approaching the area. This may result in a few 
showers...mainly over the mountains into early Sunday morning. At 
low levels onshore flow will help support a healthy stratus deck and 
morning clouds Sunday. Skies will scatter out Sunday with partly 
sunny skies and normal high temperatures into the mid 70s. 

Another upper level shortwave will approach the area overnight 
Sunday into Monday bringing a bit more moisture and a better shot of 
showers by Monday afternoon and evening. Despite this, showers will 
be pretty limited with plenty of dry conditions through Monday night 
into Tuesday morning. Showers will linger into Tuesday - but mostly 
over the mountains as the upper level shortwave moves overhead. 
Temperatures Monday and Tuesday will likely run a bit cooler than 
Sunday, but still pretty close to normal - in the low to mid 70s for 
much of the interior and upper 60s along the coast and strait. 

discussion...Overnight Tuesday into Wednesday, a rather strong 
strong cyclone will slide down the Gulf of Alaska, characterized by 
a 120+kt upper level jet streak. A frontal system will likely 
accompany this system, and the left exit region of the expansive and 
rather strong jet streak will move across western Washington. This 
could bring a more organized area of rainfall to western Washington. 
Obviously some discrepancy exists between deterministic GFS and 
ECMWF with regards to timing and intensity, though comparing their 
sfc patterns to ensemble guidance yields a solution more towards the 
GFS at this time. Should this verify, though details are sure to 
change this far out, showers would spread in from the north during 
the morning hours Wednesday and progressively push southeast thru 
the day with the sfc front. Thereafter, an unsettled pattern looks 
to continue through the remainder of the week as much of the 
northern US looks to remain in the heart of the polar jet. Prefer 
the evolution of the pattern in the ECMWF (based on ensemble 
guidance) from Thursday onward for now. This may yield additional 
periods for somewhat decent rainfall.



.AVIATION...Southwest flow aloft will gradually veer to 
westerly overnight with moderate onshore flow at low levels. A mixed 
bag of clouds and ceilings over night with lingering cumulus clouds, 
increasing mid and high level clouds streaming into the area from 
the southwest and marine stratus developing late tonight. Expect 
ceilings to remain VFR - well above 3000 feet this evening - 
lowering to MVFR levels with ceilings 2500 to 3500 feet by daybreak 
Sunday morning. Isolated showers will be limited to portions of the 

KSEA...VFR ceilings this evening lowering to just MVFR levels around 
12/13Z. . Winds S-SW 4-8 knots becoming W briefly late evening.


.MARINE...Moderate onshore flow will continue with weak high 
pressure along the coastal waters. Small craft criteria westerlies 
in the central and eastern Strait will continue throughout the 
evening hours. Winds will ease somewhat during the morning hours, 
but are expected again each afternoon and evening into early next 
week with advisory level winds spilling into the adjacent waters of 
Admiralty Inlet and the Northern Inland waters at times.


.HYDROLOGY...The daily hydrology discussion has ended until the
start of the next rainy season; it will only be updated as needed
until then.


PZ...Small Craft Advisory until 5 AM PDT Sunday 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 3 AM PDT Sunday 
     for Admiralty Inlet-Northern Inland Waters Including The 
     San Juan Islands.