Cape Flattery to Cape Shoalwater WA between 150 and 250 NM Offshore Forecast
|Tonight...E To Se Winds Less Than 10 Kt. Seas 4 To 6 Ft.|
|Fri...Variable Winds 5 To 15 Kt, Diminishing To Less Than 10 Kt. Seas 4 To 5 Ft.|
|Fri Night...W To Nw Winds Less Than 10 Kt. Seas 3 To 5 Ft.|
|Sat...W Winds 5 To 15 Kt, Becoming 5 To 10 Kt. Seas 3 To 4 Ft.|
|Sat Night...W Winds Less Than 10 Kt. Seas 3 To 5 Ft.|
|Sun...W To Sw Winds Less Than 10 Kt. Seas 4 To 5 Ft.|
|Sun Night...N Winds 5 To 15 Kt, Increasing To 10 To 20 Kt. Seas 4 To 5 Ft.|
|Mon...N Winds 10 To 20 Kt. Seas 4 To 6 Ft.|
|Mon Night...N To Nw Winds 5 To 15 Kt, Becoming S To Sw. Seas 5 To 7 Ft.|
|Tue...S Winds 10 To 20 Kt, Increasing To 20 To 30 Kt. Seas 5 To 8 Ft.|
|Tue Night...S Winds 25 To 35 Kt. Seas 9 To 16 Ft.|
| 809 PM PDT Thu Sep 17 2020 |
Northern and Central Washington Coastal and Inland Waters - PZZ100
Weak onshore flow will continue for the rest of the week with high pressure over the coast and lower pressure inland. Smoke will continue to reduce visibilities over the interior waters. Gradual improvement is expected as a weather system makes its way through the area tonight into Friday.
| Area Forecast Discussion|
National Weather Service Seattle WA
821pm PDT Thu September 17 2020
An approaching Pacific storm system will bring increasing potential for showers and even thunderstorms to portions of Western Washington tonight and more widespread precipitation on Friday. Smoke will continue to linger across the area tonight with improvement Friday into Saturday. Beyond this, the large scale pattern will shift to a more progressive and active paradigm through much of next week, with potential for a stronger, more organized storm system midweek.
Short Term - Tonight Through Sunday
Main focus tonight is on area of convection over western OR with thunderstorms drifting north into S/SW WA. So far most of the cells have been fading near the OR/WA border with just a few lighting strikes over Grays Harbor county. In any case, will continue to monitor with more cells downstream. Otherwise, no major changes from the previous forecast. 33
Previous discussion...Smoke continues to linger over much of Western Washington this afternoon and evening. Some improvement has occurred, mainly along the coast will be aided by developing low level northwesterly flow this afternoon and evening. The approaching upper level low over the eastern Pacific will bring increasing potential for showers from the south this evening, including a chance of thunderstorms. This is likely to remain limited to Central Washington Coast Southward and the interior south of Puget Sound tonight. The threat for thunder will extend into the Central Washington Cascades late this evening and diminish after midnight - while the potential for more widespread showers spreads northward through Friday morning. Precipitation amounts through Friday afternoon look fairly solid, ranging from around 0.50 in over the Central Washington coast and Western Lewis County to 0.10 in from the metro area northward. Smoke will linger over the area Friday, particularly over the interior, supported by southerly flow aloft, however conditions associated with the smoke should begin to improve through the day.
The upper level trough will begin move onshore Friday afternoon and evening, slowly opening up and adopting a negative tilt as it extends into the Great Basin through the day Saturday. This will keep showers over the area, particularly over the Cascades through the day Saturday. This will also help flow aloft will become more westerly Friday evening, which coupled with more mature onshore flow will go a long way towards further mixing and improvements to air quality over the interior.
The upper level pattern will become more zonal Sunday with shower potential lingering, mainly over the north Cascades and possibly the Olympics. Skies will remain generally cloudy with some potential for clearing and a few sun breaks during the afternoon, and near normal temperatures in the upper 60s.
Long Term - Monday Through Thursday
Previous discussion...The large scale pattern becomes zonal across much of the northern Pacific, setting the stage for what looks to be a more active paradigm in the extended. This looks to range from perhaps a weakly forced system early in the week to a stronger, more organized Pacific system mid to late next week. The ensemble systems have been consistently highlighting the development of this system, with some variability in the timing and strength - none the less strongly hinting a fairly organized system with widespread precipitation. Of note, the shift to a more active pattern is conducive for maintaining an improved air quality profile over the area through the extended.
A combination of persistent dry fuels in the Cascades and Cascade Foothills and the prospect for thunderstorms/ associated lightning from late this afternoon into tonight may give rise to critical fire weather conditions in the very short term. However...there are some limiting factors that must be taken into account. First...lingering smoke over W WA...including over the areas mentioned above...may limit the amount of convection and thus limit the number of storms that develop. Secondly...there is a very limited window of opportunity when it comes to fire starts. Current forecasts suggest that fuels will react pretty quickly to incoming system with ERC values taking a major dive Friday. In addition...the chance for wetting rains will linger over W WA Friday and Saturday. Thus...any strikes from this evening/tonight that do cause an ignition will run into a generally unfavorable burn environment for the following 36-48 hours. As such...will not issue any headlines with the afternoon forecast package but will brief following shift to monitor conditions. A short-fused Red Flag might yet still be warranted if there is a high amount of lightning coverage in Fire Weather Zones 656...657...658 and 659.
Weak high pressure will remain near the coast with lower pressure inland through Monday. Smoke will reduce visibilities over the interior waters tonight with improving conditions expected Friday and Saturday as the next weather system moves through the region. Offshore wave heigheights 2 to 4 feet becoming 5 to 7 feet over the weekend. Winds will generally stay below Small Craft Advisory levels through Friday but may briefly reach criteria at times over the weekend in both the Strait of Juan de Fuca as well as the offshore waters.
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...None.