textproduct: Seattle/Tacoma

SYNOPSIS

An upper level ridge will build across the Pacific Northwest early this week, resulting in warming temperatures through Tuesday. Temperatures will peak on Tuesday, resulting in Minor to Moderate HeatRisk as well as much lower daytime relative humidity values. Onshore flow increases Wednesday as the upper ridge weakens. The next disturbance approaches Western Washington later in the week.

SHORT TERM /TODAY THROUGH WEDNESDAY/

Mostly clear skies and light winds prevail across western Washington this morning, through temperatures much warmer compared to yesterday- -in the mid 40s to low 50s. High clouds will begin to move in from the east this afternoon. Temperatures remain on track to warm into the 70s across much of the area, with some locations reaching close to 80 such as the inland coast, Southwest Interior, and Cascade Valleys.

Offshore flow developing this afternoon and tonight will keep lows much warmer, staying in the low to mid 50s. The warming trend peaks on Tuesday, with highs ranging from the upper 70s near the water to the mid to upper 80s through the interior. More inland locations may get close to 90. Remember the waters are cold, with many river and lake water temperatures in the 50s and 60s. Ocean water temperatures remain the low 50s.

The pattern changes on Wednesday as an upper level shortwave trough, as well as weak surface frontal system traverse the area. This system will bring in increased cloud cover, locally breezy conditions with stronger onshore flow, and much cooler temperatures with highs returning into the low to mid 70s, and 60s along the coast. Precipitation chances across much of the area will be minimal, however, with some upper-level instability present, there is a 15% chance of showers and thunderstorms across the Cascades on Wednesday afternoon/evening.

LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/

Onshore flow continues across Western Washington late Wednesday into Thursday with temperatures returning closer to seasonal normals. Latest ensemble guidance continues to consistently bring the next deeper upper level trough into the region later in the week and into the weekend. This will maintain continued cooler and cloudier conditions, along with rain chances at times. As the core of the cooler temperatures aloft pass overhead on Saturday, we will see around a 15% chance of an isolated thunderstorm or two across much of the area.

AVIATION

Northerly flow aloft continues with an upper level ridge just offshore. VFR conditions prevail through the TAF period. Mostly clear skies continue this morning, with high clouds moving in this afternoon. Light NE to calm winds will become more N/NW during the day, up to around 5 to 10 kt. Winds transition to more NE/E tonight, after 06Z Tue.

KSEA...VFR conditions prevail through the period with increasing high clouds this afternoon. NE winds 6 to 10 kt becoming more NW after 18Z, up to 8 to 12 kt with occasional gusts 18-20 kt this afternoon. Winds ease but become more NE to E tonight.

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MARINE

High pressure will begin to weaken over the coastal waters as a weak thermal trough develops and works up along the coastline. Winds will remain north/northwest today, but will briefly switch to easterly overnight along the coast and through the Strait. The thermal trough then gets forced inland Tuesday by an incoming system, allowing winds to return to northwesterly during the day Tuesday.

A weak front will traverse the area waters on Wednesday, allowing for stronger onshore flow. High pressure will return in its wake, allowing for enhanced wind through the Strait of Juan de Fuca beginning Wednesday. An extended period, through late week, of Small Craft Advisory winds is likely. There also remains a 40-70% chance for gale force gusts on Thursday evening. Winds will slowly ease over the weekend as a broad low pressure system moves through the area waters.

Seas generally remain in the 4 to 7 ft range through the week.

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FIRE WEATHER

An upper level ridge will setup a dry and warm pattern through Tuesday across the region with light offshore flow developing as a weak thermal trough builds north over the Puget Sound region. Tuesday remains on track to be the warmest day, with daytime high temperatures reaching into the 80s and a few spots touching 90. Winds still appear to be relatively light, but a few gusts to 15-20 mph near the Cascades and over the exposed ridgetops remain possible. Poor overnight recoveries are expected tonight into Tuesday morning, with daytime RHs Tuesday likely to approach 20%. However, this stretch appears short-lived, with a resumption of onshore flow bringing higher humidities for the second half of the week. Cullen

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...None.