textproduct: Seattle/Tacoma

UPDATE

No changes made to the inherited forecast. The previous discussion remains below along with an updated marine/aviation section:

SYNOPSIS

A weak front will bring increasing clouds and cooler temperatures to Western Washington into Saturday along with chances for some rain. Upper ridging will build back into the Pacific Northwest for warmer, dry conditions Sunday through Tuesday. Onshore flow increases again during the middle of next week.

SHORT TERM /TODAY THROUGH SUNDAY/

Clouds are increasing across the area early this morning ahead of a frontal system that will slide onshore across Western Washington late this afternoon. Initial precip chances are fairly meager outside of a few showers near the coast and in the North Cascades. Onshore flow is slated to increase further on Saturday ahead of an upper trough and meso models are starting to latch onto the idea of some convergence developing Saturday morning. So, areas north of the King County line might wake up to some damp ground on Saturday morning. Apart from that, Saturday will feature mostly cloudy skies with temperatures struggling to get north of 70 degrees across much of the interior. Heights begin to rise on Sunday as upper troughing lifts northward back in British Columbia. This will allow some sunshine to return to most areas by Sunday afternoon with temperatures nudging upwards closer to normal for the time of year.

LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/

A warming trend continues into Monday and Tuesday as a very strong ridge centered over the Northern Great Plains exerts a little more influence over the area. Light onshore flow continues during the period, but 500 millibar heights at or above 580 decameters will be sufficient to boost temperatures from Seattle metro southward back into the lower to mid 80s with low end chances for moderate HeatRisk.

The forecast picture turns a little more uncertain toward the middle and end of next week...at least, from a temperature perspective. Confidence is high in continued dry conditions. Generally speaking, ensembles are now trending toward a declining influence in anomalous upper troughing to our west and/or northwest as strong ridging becomes firmly established over the Intermountain West. As we approach mid-July, this is typically the case in most years. So, what does this mean for Western Washington? It means that we're quite likely looking at the return of an extended period of above average temperatures at the end of (and just beyond) the current 7 day forecast.

27

AVIATION

Areas of stratus has lead to a degradation of ceilings across the area, mainly along the coast and the peninsula. This layer looks to stick around through the morning hours before improving to VFR around 20z-22z, though expect mid to high level clouds to continue into Saturday. Stratus may stick around longer along the coast and may not fully dissipate at KHQM, though cigs could fluctuate between MVFR and low-end VFR after 21z Fri. Expect mainly west to southwest winds 4 to 8 kts.

KSEA...VFR conditions observed and are expected today, though mid to high level BKN/OVC layer may continue at times into Saturday. Southerly winds around 5 kt or less this morning, increasing out of the NW 5-10 kt after 00z.

MARINE

High pressure over the waters will weaken today as a weak surface low shifts southward toward to just west of north Vancouver Island on Saturday morning. An associated weak frontal system will cross the waters Friday afternoon into Friday night with little to no impact.

High pressure will rebuild Sunday into Monday and remain in place into midweek. Diurnally driven increases in westerlies can be expected in the Strait of Juan de Fuca each the next several days. 27

FIRE WEATHER

The current onshore pattern will continue through the weekend which will lead to continued excellent nightly RH recoveries. Light drizzle or rain chances exist Friday into Saturday, mainly for the Olympics and Cascades. Rainfall amounts during this period would generally total less than 0.10". A ridge of high pressure rebuilds into the region Monday and Tuesday. While the onshore pattern will largely remain in place, warmer daytime temperatures and clear skies will likely lead to RH values dipping into the 20-40% percent range, with the lowest values in the south interior and Cascades Valleys. This will allow fine fuels to continue to dry with elevated fire weather conditions. Some modest cooling is slated to arrive by the middle of next week, but may well be short-lived.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory from 5 PM this afternoon to 3 AM PDT Saturday for Central U.S. Waters Strait Of Juan De Fuca- East Entrance U.S. Waters Strait Of Juan De Fuca.