textproduct: Seattle/Tacoma

UPDATE

Showers formed over the Olympics before sunset. These showers are now moving off the Olympics to the southeast into Mason and Thurston county. Have done a quick update to add showers to the forecast to these areas this evening. The showers will dissipate by midnight. Remainder of the forecast unchanged. Upper level low moving out of the area tonight with low level onshore flow increasing bringing the marine layer into the interior Monday morning. Updated aviation and marine sections below. Felton

SYNOPSIS

Some showers linger through tonight as an upper low remains south of the region. This system moves away into Monday, with the start of a warmer and drier trend that continues into midweek. Onshore flow increases through Monday, with a push of morning low clouds. Light offshore flow helps temperatures to peak around midweek, followed by the next disturbance bringing a return of cooler temperatures and rain chances later in the week.

SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/

The upper low departs the region into Monday, with stronger onshore low-level flow bringing a blanket of marine stratus to start the day. Weak lingering lift could bring some light rain, but on the whole it'll be a dry day and expect to see areas of sun develop into the afternoon hours. This begins a drying and warming trend that will continue into midweek, with temperatures a bit warmer Tuesday in between weather systems. Cullen

LONG TERM /WEDNESDAY THROUGH SUNDAY/

Ensemble guidance remains in good agreement that a strong high will continue building across the southwestern U.S. toward midweek, with the Pacific Northwest remaining in a weak northwesterly flow pattern in between the stronger weather systems. This will bring high temperatures into the lower 80s in many spots Wednesday and Thursday. The low-level flow may turn weakly offshore around midweek, to bring lower humidities across the region. Even with this warm up, there's not much sign of HeatRisk moving above the minor (yellow) category; probabilistic guidance suggests less than a 10% chance for nearly all of the area.

There's a bit larger spread in ensemble guidance later in the week, but the return of a weak trough still appears the most likely scenario around Friday, ushering cooler temperatures and rain chances back into the region. That said, the ensembles are not particularly well clustered and significant ranges in the strength and timing of this shift remain. As such, the forecast carries some low rain chances through the late week and into next weekend, and expect the temperatures and rain chances to fluctuate a bit as this evolution ideally comes into clearer focus in the days ahead. Cullen

AVIATION

Northwesterly flow aloft with low level flow turning onshore this evening. VFR conditions at all area terminals this afternoon and will continue throughout the evening, with the exception of KHQM where MVFR cigs have already arrived. Marine stratus will continue spreading over the area through 04z-07z, lowering conditions down to MVFR/IFR. Stratus will start to impact interior terminals by early Monday morning, around 09z-12z. Expecting a mix of MVFR/IFR conditions at most terminals throughout Monday morning, before marine stratus dissipates, with a return to VFR by the afternoon (19z-21z).

KSEA...VFR conditions with increasingly westerly winds 5 to 7 knots. VFR continuing through the evening before marine stratus moves over the area overnight. Latest guidance shows a 30-35% chance of MVFR conditions starting around 10z-12z, lasting through 17z-19z. Stratus will erode by the afternoon, with VFR conditions returning by 20z. Winds will turn southerly overnight and into Monday, staying around 4 to 8 knots.

Mazurkiewicz/21

MARINE

A low pressure system will move inland tonight. Behind that, broad high pressure will slowly build in Monday and through the week. Northwesterly winds will begin to pick up over the coastal waters on Tuesday, and may increase to near 20 kt through the outer coastal waters Wednesday night into Thursday. A weak frontal system looks to move through the region late in the week.

An onshore push tonight, following the departing low pressure system, will increase winds through the Strait of Juan de Fuca. Guidance remains in good agreement for Small Craft Advisory gusts through portions of the central and eastern Strait of Juan de Fuca, and will maintain the advisory. Some models ease the winds more gradually and gusts could hold on a bit later into Monday morning.

Seas remain around 3-6 ft through Wednesday, increasing to around 7- 10 ft late in the week and may become steep as waves are driven by the increasing northwest winds.

62

FIRE WEATHER

No significant fire weather concerns develop through the start of this week. With warmer and drier conditions, expect to see conditions to trend back to seasonal levels of concern after the previously cool and wet pattern. There's some indication that light offshore flow develops midweek and may bring minimum humidity values close to critical thresholds and around Wednesday, but the offshore winds do not appear significantly strong or long-lived to bring higher levels of concern at this time.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory until 5 AM PDT Monday for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.