textproduct: Seattle/Tacoma

SYNOPSIS

A weak system clipping the region has brought in an expansive cumulus field with partly sunny skies. A warming trend is expected through Tuesday. Thereafter, conditions become more unsettled with a chance for isolated thunderstorms on Wednesday. Cloudy and cooler conditions will persist through the end of the week.

SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/

The upper level clouds have largely moved out of area this afternoon, with an expansive cumulus field over much of western Washington. Temperatures thus far are in the 60s, with the opportunity for a few more degrees of warming potential. High pressure bumps back in early this week, with warming temperatures through Tuesday. Tuesday looks to be on track for the warmest temperatures this week, with widespread upper 70s to mid 80s across the region. The warmest temperatures are forecast to be in areas from south King County in through Mason and Grays Harbor County. The Cascade valleys will also be well into the 80s. These locations are giving a 50 to 70% chance of reaching Moderate HeatRisk, which can impact the most sensitive demographics-especially with limited access to cooling. Given the pattern, minimum relative humidity values on Tuesday are forecast to be between 25 to 30% in the Cascades and 35 to 40% throughout much of Puget Sound. The winds, although light, seem to be slightly northeasterly which could drive these RH forecasts even lower. Overnight temperatures will be cool enough to offset some of it being in the low to mid 50s. Relief will be in short order as the pattern turns unsettled into the second half of the week.

LONG TERM /WEDNESDAY THROUGH SUNDAY/

The pattern becomes more unsettled Wednesday through the second half of the week. A cutoff low offshore of the OR/CA border amplifies and nudges the ridge off to the east. While the exact track of that cutoff low is still carrying some uncertainty, it does provide potentially favorable conditions for a few thunderstorms Wednesday morning into early afternoon. Southerly flow and an increase in CAPE could favor some orographically enhanced storms in the southern WA Cascades and foothills. Right now, it seems as though some of the ingredients are misaligned with the generally necessary solar insolation of the day, but this will be monitored as Wednesday approaches.

Broader troughing in the NE Pacific keeps onshore flow into Washington for the rest of the week, allowing some weaker systems to move in. Scattered showers could occur during this timeframe but are unlikely to produce significant rains.

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AVIATION

Flow aloft between west to southwest throughout the TAF period. MVFR cigs over Puget Sound terminals are gradually lifting to VFR this afternoon. For tonight, mostly VFR again - can't rule out areas of MVFR stratus throughout the interior as the flow remains onshore. Stratus along the coast will keep KHQM under MVFR/IFR into Monday morning as well. Can't rule out low stratus creeping into South Sound (KOLM) as well. A slow burn off to widespread VFR by Monday afternoon. Low-level onshore winds expected to become lighter overnight before increasing out of the north on Monday afternoon.

KSEA...VFR so far this afternoon. However, areas of stratus are set to redevelop this evening in moist onshore flow. The NBM has a 25- 30% chance of ceilings under 3,000 ft after 07z through 18z Monday. If manifest, VFR is set to return by Monday afternoon. Surface winds becoming variable this afternoon before turning more out of the north around 00-02z.

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MARINE

Post-frontal onshore flow in the wake of a weak front. A westerly push is currently brining SCAs through the Strait of Juan de Fuca through tonight. Winds remain relatively light elsewhere and primarily out of the north through the week. A potential system midweek may bring another push through the strait. Additionally, while low stratus is expected off the coast next couple mornings, there is potential for some pockets of fog over the coastal waters (especially in areas where the wind is calmer). Combined seas around 4-6 ft through the week (with a brief jump to 6-8 ft midweek).

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HYDROLOGY

The daily hydrology discussion has ended until the start of the next rainy season; it will only be updated during this time as needed.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory until 3 AM PDT Monday for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.