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Area forecast discussion 
National Weather Service Seattle Washington 
312 PM PDT Fri Jun 23 2017 


Synopsis...an upper ridge, combined with low level offshore flow, 
will give hot and dry conditions to much of the area Saturday 
through Sunday. Onshore flow will usher cooler marine air into the 
area Sunday night as the upper ridge moves off to the east. 
Temperatures will cool to near average for late June early next 
week, and the marine air will give late night and morning 
cloudiness to the area. No rain is expected over the next week. 


&& 


Short term...skies remain clear across the region this afternoon. 
The air mass has gradually warmed today with temperatures about 5 
to 10 degrees higher than they were 24 hours ago. 500 mb heights 
are expected to rise to close to 5900 meters this weekend. Warming 
and ridging aloft combined with increasing offshore flow and low 
level compressional heating will add to the warmth of the 
boundary layer this weekend. Afternoon high temperatures will be 
close to record levels on Saturday and will likely break records 
on Sunday. 


The hottest day at the coast is expected Saturday, including 
places like Forks and Hoquiam as offshore winds increase. Areas 
around the southwest interior and greater Puget Sound area to the 
south of Everett will also reach the upper 80s to mid 90s (highest 
in the southwest interior). Forecasts generally follow the warmer 
third of the mean of raw 2 meter temperatures from the mesoscale 
models and GFS MOS and are little changed from previous forecasts. 


Models continue to show the thermally induced low shifting inland 
over Puget Sound on Sunday with easterly cross Cascade gradients 
peaking during the morning to midday. This will bring the hottest 
temperatures of the year so far to the I-5 Metro areas including 
Seattle and Bellevue. Lows Sunday morning will only fall into the 
60s in portions of the greater Puget Sound Metro areas. Highs 
will likely rise to around 90 in Everett and into the lower to mid 
90s Seattle and Bremerton southward. A heat advisory remains in 
effect for the Seattle-Tacoma- Bellevue Metro areas southward to 
the southwest interior and east toward the Cascades for midday 
Saturday through Sunday evening. 


With the heat in the interior on Sunday and the upper ridge moving 
off to the east, marine air will spread into the gaps and onto the 
coast Sunday night and early Monday and will continue to deepen 
into the interior on Monday. Temperatures on Monday are uncertain 
with some solutions showing highs only in the lower 70s inland and 
others showing mid 80s in the Seattle area and east Puget Sound 
lowlands as clouds rapidly burn back to the west during the 
morning hours. At this time, the partial marine push scenario is 
indicated in the forecasts, and forecasts will be revised once 
solutions become more consistent. Albrecht 


Long term...the upper level pattern is forecast to be progressive 
over the next week or so with troughing moving into the area early 
to mid week and ridging returning later next weekend. 


For the Tuesday through Friday period, the forecast will indicate 
night and morning clouds with clearing inland during the afternoon 
hours. Temperatures are expected to fall to near or slightly below 
normal Tuesday or Wednesday then moderate slowly late in the week 
as the marine layer deepens and moderates. At this time it appears 
that conditions will remain dry for the next week or so. Albrecht 


&& 


Aviation...an upper level ridge will remain over the region for 
contd northwest flow aloft. Northerly low level flow will become offshore or 
easterly tonight, continuing thru Saturday. VFR conditions will 
prevail. 


Ksea...VFR. Winds will be northerly 7-14 knots, strongest thru 
early this evening. 


&& 


Marine...the flow will become offshore or northeasterly tonight 
due to a thermally induced trough of low pressure becoming 
established just off the coast. Expect offshore flow to persist 
during much of this weekend. 


The thermally induced trough of low pressure will shift east of 
the Cascades Sunday afternoon. This will cause the flow to become 
onshore and then strengthen Sunday night, resulting in gale force 
winds over parts of the Strait of Juan de Fuca. Strong onshore 
flow will prevail Monday before weakening some on Tuesday. 


&& 


Fire weather...hot and dry conditions this weekend will be somewhat 
favorable for grass and brush fires over The Lowlands. On both 
Saturday and Sunday, minimum relative humidity values will be below 20% in the 
afternoons. Some recovery will occur each night. Moderate northeast 
wind at times will mean the weather parameters approach red flag 
thresholds each afternoon. However, fuel moisture is generally too 
high to give much of a threat of explosive fire development. In 
addition, snow still covers much of the terrain above 4000 feet in 
the mountains. The exception is so-called "fine fuels," grass and 
brush, in The Lowlands, which has dried considerably in recent days. 
Favored areas for brush fires, such as along highways, will have 
some risk of fire this weekend. Burke 


&& 


Sew watches/warnings/advisories... 
Washington...heat advisory from noon Saturday to 9 PM PDT Sunday for Bellevue 
and vicinity-Bremerton and vicinity-east Puget Sound 
lowlands-Hood Canal area-Seattle and vicinity-southwest 
interior-Tacoma area. 


Pz...Small Craft Advisory until 10 PM PDT this evening for coastal 
waters from James Island to Point Grenville out 10 nm. 


&& 


$$ 



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