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Area Forecast Discussion (AFD)

Issued by Seattle/Tacoma, WA (SEW)

                            
000
FXUS66 KSEW 240347
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
847 PM PDT Sun Jun 23 2019

.SYNOPSIS...Onshore flow will continue. An upper trough will move 
over the Pacific Northwest by the middle of the week with showers 
increasing. The trough will move out of the area late in the week.

&&

.SHORT TERM /TONIGHT THROUGH WEDNESDAY/...KATX shows weak echoes
and light showers or drizzle in Snohomish and northern King 
counties this evening, where there's convergence. These showers 
may linger into the overnight hours with a few hundredths
possible. No planned updates from the previous forecast. 33 

Previous discussion...Deep moisture and onshore flow will 
continue through tonight. The NWAC sensor at Paradise Mount 
Rainier shows a half inch of rain so far--in what looks like heavy
drizzle averaging 0.03" an hour since late last evening. 
Meanwhile up high on the mountain the webcams at Schurman and Muir
were sunny. Hurricane Ridge also had sunshine today and most of 
the central Olympics had sun--as did the San Juans and Bellingham 
area, and also an area just south of the Olympics. Elsewhere most 
of Western WA remains cloudy this afternoon. A few areas of late 
afternoon clearing or sunbreaks will be about all we can expect on
Monday too. We might see a PSCZ drizzle area develop again 
overnight, but most of the drizzle or 'showers' will be on the 
west slopes of the Cascades tonight and Monday morning. Tuesday 
will probably be a little warmer and brighter--with less low level
moisture in lighter onshore flow. An approaching upper trough 
will increase the chance of showers Tuesday afternoon or evening 
as the flow aloft becomes southerly and the air destabilizes. 
Showers are a good bet Wednesday as the low nears and unstable 
southerly flow aloft picks up while temps cool aloft.

.LONG TERM /THURSDAY THROUGH SUNDAY/...Previous discussion...The 
upper low center will move ashore Thursday and then on Friday it 
should be east of the Cascades. Another vort center might wrap 
around the low and start a new low center near Vancouver Island--
the GFS shows that happening and then a weak low peters out over 
northwest WA through the weekend. The ECMWF is similar in that it 
takes the main low up into Alberta but peels a weaker vort max off
the B.C. coast-- but that drifts westward and there doesn't look 
like much shower activity over Western WA--but there isn't a ridge
either. 

&&

.AVIATION...Onshore flow continues across western Washington 
tonight with low clouds over much of the lowlands. Expect MVFR 
cigs overnight with light showers in the central interior, near 
KPAE, due to convergence. The flow aloft is westerly. Cigs will 
gradually improve Monday afternoon for VFR conditions. 33

KSEA...Light showers or drizzle in the vicinity tonight with MVFR
cigs expected. N wind to 10 kt will become S by 09-12z. Gradual
improvement to the cigs Monday afternoon for VFR conditions. 33

&&

.MARINE...A Gale Warning continues for the central/east Strait of
Juan de Fuca this evening. High pressure over the NE Pacific will
maintain onshore flow this week. Highest wind and waves will be 
found through the Strait of Juan de Fuca during the afternoon and 
evening hours, with Gales or Small Craft Advisory winds possible. 
33

&&

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

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 8 AM PDT Monday for Central U.S. 
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters 
     Strait Of Juan De Fuca.

     Gale Warning until 11 PM PDT this evening for Central U.S. 
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters 
     Strait Of Juan De Fuca.

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

&&

$$

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