textproduct: Seattle/Tacoma

SYNOPSIS

High pressure overhead will maintain dry conditions, cloudy skies, and areas of patchy fog through Monday morning. A series of splitting systems will bring slight chances of rain to western Washington Monday and Tuesday ahead of a series of systems that will bring increasingly more lowland rain, mountain snow, and breezy winds through the end of next week.

SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/

Low stratus continues to remain firmly entrenched over the interior lowlands this afternoon, with some patches of sun breaking through the cloud deck. However, any sun breaks will be short lived with clouds filling back in this evening aided by high pressure aloft and light winds. Residual moisture from recent rains will also result in patchy fog early Monday morning, which may pose localized visibility limitations during the morning commute for fog-prone areas. However, light easterly winds in the early morning may help to reduce fog formation under the stratus. As the upper level ridge axis nudges eastward on Monday, light rain showers offshore will slide inland Monday evening, though rainfall amounts will be very light. As a cutoff low develops to the south Monday night into Tuesday and weak ridging develops offshore, moisture will be nudged out of the area, allowing warmer and drier conditions to briefly settle in for most areas by Tuesday afternoon. However, sunny skies may be few and far between through Tuesday, with temperatures near or a few degrees above normal.

LONG TERM /WEDNESDAY THROUGH SUNDAY/

Ensembles continue to show good agreement over a series of increasingly stronger systems passing over the region as the rest of the week goes on. A frontal system on Wednesday is expected to bring a round of widespread rain and high elevation snow to western Washington, with the bulk of the moisture focused over the Olympic Peninsula and North Cascades. Areas east of the Olympic Mountains will likely see a high degree of rain shadowing with this system, resulting in only a few hundredths of rain accumulation.

Another weather system will follow closely behind, and will be stronger than Wednesday's system. While shadowing will occur once again east of the Olympics, higher elevations will see roughly half of an inch to an inch of liquid while the lowlands see a tenth or two of rain accumulation into Friday morning. Snow levels will hover around 5000 feet as this system passes through, resulting in a few inches of additional snow accumulation over higher terrain.

Forecast confidence decreases into next weekend, depending on how far northward an upper level ridge will build over the western US. The ridge could either keep conditions warm or dry, or remain too weak to ward off an incoming atmospheric river system. While the bulk of the moisture of this system looks like it might make landfall over British Columbia, western Washington may see some of the heaviest rain so far this fall with up to 2 to 3 inches of liquid over the mountains and generally a half inch to an inch over the lowlands. The vigorous system could also bring widespread breezy winds alongside the precipitation if the storm takes aim at the Pacific Northwest, and waves could inch towards High Surf criteria along the immediate coastline.

Beyond next weekend, longer range models continue to show potential for high winds, heavy rain, and heavy snow across the Pacific Northwest during the second week of November. While conditions remain highly uncertain at this time, potential impacts will continue to be monitored as we settle into the month of November.

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AVIATION

A mix of VFR and MVFR this afternoon, as the stratus continues to slowly erode this afternoon over Puget Sound terminals. Still expecting improvement around 23Z-00Z. Another round of IFR/LIFR stratus and fog is possible Monday morning. Residual moisture from recent rains will result in patchy fog, which may pose localized visibility limitations in fog-prone areas. However, light easterly winds and mid to high clouds moving inland Monday morning may help reduce fog formation, instead resulting in low stratus. Improvement to VFR after 18Z-20Z. Light northerly surface flow, becoming more light and variable tonight.

KSEA...The stratus continues to slowly burn off this afternoon, with improvement to VFR likely after 23-00Z. Low clouds below 1000 ft are possible (50-55% chance) Monday morning. Additionally, light easterly winds and mid to high cloud cover should limit the potential of fog at the terminal. Clouds expected to lift after 19Z for VFR conditions in the afternoon. Light NW winds this afternoon at 5 kt or less, becoming NE in the evening.

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MARINE

High pressure will continue building over the waters through Monday. A weather system will brush the coastal waters Monday morning, leading to an increase in southerly surface winds. Winds gusts may briefly approach 21 kt at times over zones PZZ170 and PZZ173 through the afternoon hours. High pressure will move inland on Tuesday ahead of the next system that arrives on Wednesday. Southerly winds will increase over the coastal waters on Wednesday with a 55-80% chance of small craft winds. A stronger system will arrive on Friday, bringing stronger winds across the coastal waters and the interior waters. Latest guidance suggests a 70% chance or higher for small craft winds and a 25-40% chance of gales. Another system expected on Saturday with the potential (50-75% chance) for small craft winds over the coastal waters and interior waters.

Seas around 3-5 feet today will continue building to 8-11 feet by Monday morning, for which a Small Craft Advisory has been issued through early Tuesday morning. It is likely that Small Craft Advisory may have to be extended for the outer coastal waters, as seas around 10 feet look to linger through late Monday morning. Seas will decrease below 10 ft late Tuesday, before increasing above 10 feet on Thursday. Seas continue to trend higher with the system Friday, with latest guidance now suggesting seas around 15-20 feet.

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SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory from 1 AM Monday to 1 AM PST Tuesday for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From Cape Flattery To James Island Out 10 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From James Island To Point Grenville Out 10 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm-West Entrance U.S. Waters Strait Of Juan De Fuca.