textproduct: Seattle/Tacoma

SYNOPSIS

High pressure overhead and a thermal trough shifting inland today will provide one more day of mild temperatures. A system to the north will flatten the ridge Monday, with near-zonal flow aloft and onshore flow at the surface maintaining seasonable conditions, morning clouds and afternoon sun breaks throughout the week. Chances for rain increase by next Friday, though confidence remains low.

SHORT TERM /TODAY THROUGH TUESDAY/

Current satellite imagery not too dissimilar from 24 hours ago with stratus and fog largely dominating the interior lowlands while higher elevations are party to clear skies. There are exceptions to this, such as while the river valleys in the SW interior are socked in, not so much for the remainder of the area. Also worth noting is that while the coast is also partaking of the foggy conditions, the northern and southern portions /from UIL north and from HQM south/ are seeing generally clear conditions. As such, inherited Dense Fog Advisories will remain in place as locations within those headlines still seeing visibilities of less than 1/2 mile. The gap between the two advisories along the I-5 corridor, including the Seattle and Tacoma metro areas, will remain outside of headline consideration at this time. While some spots in those areas are meeting criteria, it is not widespread enough nor consistent enough to warrant inclusion as visibilities in that area fluctuate. For example, at times here at the NWS office one could not see the other side of Lake Washington, yet 15 minutes later it re-emerged from the fog. Will continue to monitor in case a short-fused headline is needed. However, with the moisture layer proving to be a little bit thinner than yesterday at this time, there is some optimism for fog/stratus to burn off by late this morning. That said, the past few days have had trouble shrugging off low clouds until the early afternoon hours...so cautiously taking an around noon-ish approach to when one can expect to see clouds begin to break up. This might have a degree or two cooler impact to inherited forecast high temperatures for today, but not enough change to warrant a morning forecast update.

Remainder of forecast is on track. Please refer to Previous Discussion section for details.

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From Previous Discussion...Despite high pressure overhead forcing light offshore flow, lower levels have not quite dried out enough to prevent another round of low stratus expanding across the lowlands this morning. Although slightly drier, low clouds may potentially linger into the early afternoon once again today. While temperatures today will once again depend on the timing of the eroding stratus, a thermal trough shifting inland will aid in warmer temperatures. Highs across the lowlands are favored to reach the low to mid 70s, with some areas along the Cascade foothills and valleys reaching the upper 70s to even lower 80s.

This brief warm-up will be short-lived, however, as the upper level ridge flattens tonight as a weather system moves inland over British Columbia. This will bring a return to onshore flow as near-zonal flow develops aloft, bringing more seasonable temperatures alongside morning low clouds and afternoon sun breaks. There will be little change day to day between Monday and Tuesday, with dry conditions, highs generally in the mid 60s to lower 70s, and lows in the upper 40s to lower 50s.

LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/

Much of next week will bring more of the same as zonal flow aloft and onshore flow at the surface maintain near- normal temperatures and morning clouds. There will be little change day to day through Thursday, with highs once again in the mid 60s to lower 70s and lows in the upper 40s to lower 50s.

Forecast models have come into slightly better agreement over cooler and wetter conditions on Friday as a trough passes over the Pacific Northwest. However, models continue to hint that the incoming frontal system and associated precipitation may break apart as the system moves into western Washington, which would by no means bring a wash out. Chances for rain increase Friday afternoon into Saturday, though the intensity and coverage of the potential incoming rainfall remain uncertain at this time.

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AVIATION

An upper-ridge and light offshore flow remains across the region today. West to west-southwest flow aloft with easterly flow in the lower levels. Patchy fog and low clouds are currently developing across the area so far this morning. This activity will become widespread cross the interior and portions of the coast with IFR/LIFR cigs and vis. VFR conditions are slated to return by 19- 21z. An additional round of low clouds/fog is in store overnight Sunday into Monday morning as low-level flow turns onshore.

KSEA...VFR as of 0930z but fog/low clouds will spread across the terminal by 12-14z with IFR/LIFR conditions and remain in place throughout the morning. VFR skies are to return by 19-21z and last for the remainder of the day. An additional round of low clouds/fog is in store overnight Sunday night into Monday morning as low-level flow turns onshore. Northerly winds 4-8 kt turning more southerly Monday morning.

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MARINE

One final round of offshore flow today as a thermal trough forms along the coast. Winds will turn onshore again Sunday night into Monday as low pressure shifts inland and surface high pressure builds offshore. Onshore winds will be strongest through the Strait of Juan de Fuca as a SCA remains in effect for the central/eastern zones. The NBM has a 50-80% chance of SCA gusts being met while the REFS is a bit more bullish with 70-90% chance, increasing forecaster confidence. Westerly pushes are favored throughout the upcoming week of varying strength. A more organized system appears favorable towards the week's end.

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SEW WATCHES/WARNINGS/ADVISORIES

WA...Dense Fog Advisory until 10 AM PDT this morning for Downtown Everett / Marysville Area-Foothills and Valleys of the North Cascades-Island County-Lowlands of Lewis and Southern Thurston Counties-Lowlands of Western Skagit and Northwestern Snohomish Counties-Lowlands of Western Whatcom County-Shoreline / Lynnwood / South Everett Area.

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.