Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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542 FXUS66 KSEW 150905 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 205 AM PDT Mon Jul 15 2024 .SYNOPSIS...
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An upper level ridge will remain in control over Western Washington through the week for continued dry conditions and above normal temperatures. Minor day to day variations in onshore flow will bring the marine layer locally inland each night and morning. A subtle shortwave entering the area on Wednesday may bring an increased risk of convection over the Cascades.
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&& .SHORT TERM /TODAY THROUGH WEDNESDAY/...
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A stronger marine push underway will bring stratus inland across much of the interior lowlands near and west of Puget Sound this morning. As of 08Z, the marine layer had already reached Bremerton. The low clouds will be relatively quick to burn back to near the coast later this morning, but the increased marine influence will knock several degrees off of high temperatures today. Opted to discard the inferior NBM numbers and go closer to old fashioned MOS...which puts Seattle in the upper 70s today. The cooling trend will be short-lived as thermally induced low pressure expands northward from the Willamette Valley on Tuesday. This will result in less of a marine layer across the interior on Tuesday morning and high temperatures will respond accordingly with 5 to 10 degrees of warming for most of the interior. Even coastal areas will see some sunshine Tuesday afternoon with high temperatures warmer than recent days. Models remain relatively consistent with the idea of a negatively tilted weak short shortwave lifting northward across the area on Wednesday. This will introduce the possibility of some elevated instability and possible thunderstorms for the Cascades. Given the elevated nature of the instability, I wouldn`t be too surprised if the thunderstorm threat also includes some of the lowlands, but we`ll have a better handle on this as the time period in question draws closer. This shortwave will also likely induce another marine push Wednesday evening...for another inland intrusion of stratus and a temporary cooling trend to begin the extended forecast period. .LONG TERM /THURSDAY THROUGH SUNDAY/...Strong upper ridging centered over the Four Corners region will continue to provide dry conditions and above normal temperatures heading into the end of the week. Models have the ridge retrograding westward slightly and gaining some amplitude toward the weekend with 500 millibar heights approaching 590 decameters over Western Washington. Some degree of low level onshore flow should keep temperatures from getting out of hand, but it wouldn`t be too surprising to see some interior locations from Seattle southward approaching the 90 degree mark once again. 27
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&& .AVIATION...
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Westerly zonal flow aloft becoming southwesterly ahead of an incoming shortwave trough. Marine stratus is making its way into the interior, bringing low-MVFR to IFR ceilings. Stratus will likely reach the Seattle area terminals between 10-12Z this morning, and persist into this morning, burning off quickly after sunrise. Stratus will evaporate and retreat quickly through the early morning hours, but will persist along the coast throughout the day, with only a very brief break to VFR conditions in the late afternoon/early evening possible at HQM. Tuesday`s marine push does not look as substantial, only bringing impacts to the coast (HQM) and Strait of Juan de Fuca (CLM). There is a lower chance (25-30%) the stratus makes it all the way into PWT. Light S/SW winds will continue through this morning, becoming more W/NW this afternoon and evening. KSEA...VFR conditions early this morning. Marine stratus pushing in between 10-12Z this morning, bringing MVFR to IFR ceilings through 16-17Z. Stratus will evaporate, leaving clear skies through the remainder of the TAF period. S/SW winds up to 10 kt will slowly veer tomorrow afternoon becoming NW by 00Z Tuesday. LH
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&& .MARINE...
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High pressure situated offshore will continue into the early week, allowing for diurnally driven pushes through the Strait of Juan de Fuca and marine stratus along the coast. Winds continue to blow 20-25 kt through the Strait of Juan de Fuca early this morning, but expect winds to taper off throughout the early morning hours. A Small Craft Advisory remains in effect for the Central and Eastern Strait of Juan de Fuca through this morning. Northwesterly winds continue through early Wednesday across the coastal waters, becoming southerly ahead as a weak low pressure system moves eastward towards the region late week. Several additional pushes of westerlies down the Strait of Juan de Fuca are expected on Wednesday and Thursday evening, which may require additional headlines. Seas remain around 3 to 6 ft through the week. LH
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&& .FIRE WEATHER...
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High pressure will persist over the Pacific Northwest for continued warm and dry conditions, with low level onshore flow providing good relative humidity recoveries each night. Flow aloft will start to turn southerly Tuesday night into Wednesday, with an increased potential for convection in the Cascades, with RH values remaining in the mid to upper 30s during this time. It is worth noting that especially with a pattern like this, with our fuels already being so receptive, all it takes is a rogue lightning strike from a thunderstorm to light these fuels. Will continue to monitor this threat as latest model guidance is not latching on to any specifics. For now, will monitor for the potential of thunderstorms and elevated instability. Mazurkiewicz/27
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&& .SEW WATCHES/WARNINGS/ADVISORIES...
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WA...None. PZ...Small Craft Advisory until 8 AM PDT this morning for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.
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&& $$