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Area Forecast Discussion (AFD)

Issued by Seattle/Tacoma, WA (SEW)

FXUS66 KSEW 200341

Area Forecast Discussion
National Weather Service Seattle WA
841 PM PDT Fri Jul 19 2019

.SYNOPSIS...Warm and dry weather for the weekend into early next
week. A weak weather system will bring cooler temperatures later
Tuesday into Wednesday before high pressure returns for the end of
next week. 


.SHORT TERM /TONIGHT THROUGH MONDAY/...An upper trough over the
area will shift east tonight. It looks like any associated 
lingering isolated shower threat has ended. Some low clouds are 
likely at the coast later tonight with weak onshore flow but the 
interior should stay mostly cloud free. Clear skies and light 
winds should allow lows to fall into the 40s many areas tonight
which is a bit chilly for mid July.

A short wave upper ridge will move over Western Washington on 
Saturday for a dry and sunny day after patchy coastal clouds burn 
off. Highs will warm several degrees to near or slightly above 

The upper ridge will shift inland on Sunday but upper heights 
will remain about the same and the air mass (as depicted by 850 MB
temperatures) will actually warm a few more degrees. This should 
translate into a few more degrees of warming with highs in the 
lower to mid 80s for much of the area. 

Increasing low level onshore flow should cool highs a few degrees
on Monday but it looks dry with highs still slightly above 
normal. There should also be clouds at the coast and partially 
into the Southwest Interior Monday morning with the added onshore 
flow. Otherwise, it will be another sunny day. Schneider

.LONG TERM /TUESDAY THROUGH FRIDAY/...Previous discussion...Trough
continues to shift east toward the coast on Tuesday and then 
moves onshore Wednesday. Models and their ensembles continue to 
advertise less than impressive moisture associated with the 
system. It's possible we may see a few showers but chances look 
low enough to leave the forecast dry for now with just some 
increased cloud coverage. Regardless, will see additional cooling 
as onshore flow increases. Flow becomes more zonal for the end of 
next week as high pressure attempts to rebuild across the area. 
Still some disagreement between model solutions on the degree to 
which this occurs but likely will see a slight warm up again. CEO


.AVIATION...An upper trough will shift inland tonight with an
upper ridge moving overhead on Saturday. Westerly flow aloft. At
the surface, onshore flow will weaken and turn more northerly
tonight and Saturday. The air mass is dry and stable.

It should be mostly clear tonight and Saturday. The exception
will be the immediate coast where some low clouds are possible
later tonight and Saturday morning. 

KSEA...Mostly clear. Northerly wind 5-10 knots. Schneider


.MARINE...Varying amounts of onshore flow will prevail for the
next several days with small craft advisory strength west winds in
the Central and Eastern Strait of Juan de Fuca most evenings.
Onshore flow will weaken a bit this weekend then increase again
early next week. Schneider


.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 Saturday for Central U.S. 
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters 
     Strait Of Juan De Fuca.