textproduct: Seattle/Tacoma

SYNOPSIS

Broad low pressure over the Pacific Northwest will keep chances for showers and isolated thunderstorms in the forecast through Sunday. Drier and warmer conditions expected for the beginning of next week. A weak system will brush the area Thursday.

SHORT TERM /TONIGHT THROUGH SUNDAY NIGHT/

Low pressure will remain the dominant feature over the Pacific Northwest through this weekend. Satellite imagery shows the low center just off the coast of central Oregon and will likely remain there as it slowly weakens through the weekend. Low is stacked vertically, and the upper level low supporting it will also slowly fill in through the weekend. As such, chances for scattered showers and isolated afternoon thunderstorms will be greatest today and Saturday. Much of western Washington will have some chances to see showers, but the best chances for thunderstorms will remain across the Cascade and Olympic Mountains, as well as portions of the Cascade foothills. Storm motions will generally be slow (15 kt or less) so storms will not have time to drift fully into the lowlands or onto the coast. Going into Sunday, chances for showers become more confined to the higher terrain and marginal (15% or less) chances for isolated thunderstorms.

Skies generally remain partly to mostly cloudy, with high temperatures in the mid 60s to low 70s. Lows in the upper 40s to mid 50s.

LONG TERM /MONDAY THROUGH FRIDAY/

Models remain consistent on finally ejecting the upper level trough out to the east Sunday night into Monday. Following, that will leave western Washington generally in dry, split to northwesterly flow as ridging tries to develop while an upper level low develops off the coast of California. This will allow for more sunny and drier conditions across the area for the start of next week, with temperatures expected to rise into the mid to upper 70s, perhaps near 80 in some spots by Wednesday. The pattern gets more uncertain as the evolution depends on the interaction between a develop upper level trough coming down along the British Columbia coast and the remnants of Hurricane Marie getting pulled up and east towards the west coast. Temperatures look to trend cooler, back towards the low 70s, and chance for rain will start to return to the forecast late Thursday and into Friday.

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AVIATION

Variable flow aloft continues as an upper level low moves slowly over western Washington. Widespread VFR conditions this afternoon with patches of mid-level clouds across the area. VFR conditions likely continuing throughout the rest of the evening. There is a chance of some isolated thunderstorm and shower activity across the area, but will mainly remain in the higher terrain of the Cascades, so will not be expecting any impacts to terminals. N/NE winds generally around 4 to 8 knots into Saturday morning. Low clouds may develop around lower prone terminals briefly early Saturday morning, but chances remain low (20%) of any impact to conditions (MVFR/IFR).

KSEA...VFR conditions this afternoon with some mid to high level clouds around. Winds likely variable this afternoon, turning to N/NE at times and remaining generally light (3 to 6 kts). Winds will maintain more of a north direction by Saturday morning, with conditions remaining VFR.

MARINE

No significant marine conditions expected on the whole, with winds and seas largely remaining short of any advisory criteria. The one concern is for any thunderstorms that develop this afternoon, and to a lesser extent Saturday and Sunday afternoon. Any of these would produce lightning and potentially gusty outflow winds. Otherwise, northerly winds develop over the waters this weekend into next week. A marginal westerly push through the Strait of Juan de Fuca around Monday looks to be the next potential period of advisory strength conditions. Seas will generally hold around 4 to 5 ft over the coastal waters, with a mostly short period component this weekend and into the start of next week.

SEW WATCHES/WARNINGS/ADVISORIES

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