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Area Forecast Discussion (AFD)

Issued by Seattle/Tacoma, WA (SEW)

                            
000
FXUS66 KSEW 211550
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
850 AM PDT Sun Jul 21 2019

.SYNOPSIS...Warm and dry weather returns today. A weak weather 
system will bring cooler temperatures later Tuesday into Wednesday
before high pressure rebuilds over the region for warmer and 
drier conditions Thursday and Friday.

&&

.SHORT TERM /TODAY THROUGH TUESDAY/...Dry and stable weather
will continue across western WA today. Skies are mostly sunny 
with a few patches of stratus along the coast. It will be warmer 
today and the interior will reach the 80s with a few low 90s 
possible, especially away from the sound. The coast will be cooler
with NW onshore flow - highs on the beaches will be in the 60s. 33

Previous discussion...Increasing onshore flow will bring some 
stratus part way inland tonight. With some marine air in place, 
high temperatures on Monday will be few degrees cooler.

An upper trough offshore will reach the coast by late Tuesday. The 
cooling trend will continue with highs back to near normal. Low 
clouds should cover most of the lowland Tuesday morning then burn 
back to near the coast in the afternoon. Models continue to generate 
some instability over the Cascades ahead of the trough on Tuesday 
afternoon and evening so a slight chance of thunderstorms was added 
there.

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...Previous discussion...The
upper trough quickly kicks out of the area by Wednesday afternoon
or evening with heights rising as a low amplitude ridge builds 
into the region. Onshore flow looks to remain persistent through 
the extended period thereby keeping temperatures near or little 
above average with generally dry conditions. 27

&&

.AVIATION...Another morning of clear skies across the western 
Washington TAF sites. Some areas of stratus are seen in satellite 
imagery along the coast but that is the extent of any cloud cover. 
Some fog was reported at Bellingham but appears to have diminished 
per recent observations. Going forward thru the afternoon, cloud 
cover should remain confined to ocean as low pressure remains intact 
offshore of the BC coast. Clear skies should be the rule into the 
evening. A few mid and high level clouds may pass by overnight into 
Monday morning, but VFR will largely be the rule. The exception will 
be the coast, mainly affecting HQM where another round of fog and 
stratus (MVFR to IFR cigs) will be possible through late Monday 
morning. Winds generally W/NW with a few sites more NE at under 
10kts becoming light and variable overnight. 

KSEA...Clear skies. Light NE wind this morning becoming NW by the 
afternoon at 5-10kts.

Kovacik

&&

.MARINE...Morning sfc analysis shows an expansive area of high 
pressure from the northern Rockies into the southern Canadian 
Prairies with low pressure located well offshore the Washington 
coast. This argues for weak offshore flow this morning and tranquil 
waters. As the day progresses, low pressure offshore will inch 
closer to the state of Washington and a thermal trough will expand 
north from northern Nevada into Washington. This will help the lower 
level flow become onshore where it will gradually strengthen. A 
westerly push of wind is expected down the Strait of Juan de Fuca 
this evening and overnight tonight, where the small craft advisory 
will continue to remain in place. These winds will briefly ease 
Monday morning into the afternoon before rising back to small craft 
advisory strength given another westerly push. All other waters are 
expected to remain somewhat tranquil and below advisory limits 
through early next week as onshore flow continues.

Kovacik

&&

.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 from 5 PM this afternoon to 5 AM PDT Monday 
     for Central U.S. Waters Strait Of Juan De Fuca-East 
     Entrance U.S. Waters Strait Of Juan De Fuca.

&&

$$

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