textproduct: Seattle/Tacoma

SYNOPSIS

A trough will be departing south and well offshore tomorrow into Tuesday, with zonal flow through the middle of the week. The next few mornings will be on the colder side for potential frosts, namely in the south Puget Sound and Chehalis Valley. A weak system is possible late in the week for light rain.

SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/

The latest forecast remains on track this evening with no updates. High clouds are moving onshore courtesy of the upper level trough transiting south, but far offshore. Low temperatures tomorrow morning will be in the mid 30s for areas including Olympia and south through the I-5 corridor. Mid 40s are expected elsewhere. Lows decrease a few degrees further into Tuesday morning for frost potential in the aforementioned areas but also the Cascades and valleys. Patchy morning fog will remain possible through early in the week and will be more likely in the valleys and typically fog prone locations.

LONG TERM /WEDNESDAY THROUGH SUNDAY/

Extended models and the ensembles are favoring Gulf of Alaska troughing to build on the deeper low moving into southern California Wednesday and beyond. Positioning of the low becomes less clear by Friday into next weekend but the indication as of now isn't for much in the way of impactful weather. Some light rain may be possible Thursday into Friday. Snow levels during that time come down to around 4,000-4,500 feet, so some light snow flurries may be possible at these elevations and higher if precipitation does materialize.

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AVIATION

Southwesterly flow aloft is expected tonight into Monday as an upper trough digs southward offshore. Increasing high level moisture later tonight is expected to limit areal coverage of low clouds on Monday morning with the exception of more fog prone locations in the Southwest Interior and extreme southern Puget Sound for the potential of IFR/LIFR conditions. Impacted terminals expected to improve by the afternoon, for widespread VFR conditions. Light northerly to calm winds tonight. Winds will shift more southerly Monday morning then transition back northerly in the evening.

KSEA...VFR conditions will continue tonight. High and mid level moisture spreading in the region ahead of upper trough digging southward offshore. The expectation remains that this will limit fog development tonight and will keep low ceilings/vis out of upcoming TAF for now. Surface winds light and variable late tonight into Monday A.M. Winds will shift more southerly late Monday morning, before transitioning northwesterly after 19Z-21Z at 5-7 kt.

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MARINE

A low pressure system passing southward well offshore will keep winds northerly or weakly offshore into Monday. Weak high pressure will remain across the waters into the middle of the coming week for rather quiet conditions. A larger swell train near 10-12 feet generated by active weather well offshore is expected to reach the coastal waters around Thursday along with an increase in onshore flow. A front may reach the waters toward the end of the week.

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SEW WATCHES/WARNINGS/ADVISORIES

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