textproduct: Seattle/Tacoma

SYNOPSIS

A trough will move across the region late Monday into Tuesday. A warmer and drier trend will commence mid to late week as a ridge starts to build into the region, however shower and thunderstorm chances increase again heading into next weekend as the next system approaches the region.

SHORT TERM /TODAY THROUGH WEDNESDAY/

500mb pattern remains largely unchanged as broad troughing continues over the NE PAC and ridging noses into the PNW. Low- level onshore flow readily apparent on satellite as marine stratus once again stretches from the coastal waters to the western WA interior under mid-high level cloud coverage. It'll be another day of morning clouds afternoon sun across the area with high temperatures around seasonal average. Monday's weather is expected to be carbon copies of both Tuesday and Wednesday's. Global deterministic model guidance are in lock- step over a Rex Block continuing over the NE PAC, maintaining a rather stagnant pattern. Morning clouds and afternoon sun with highs in the mid 70s to lower 80s in the forecast. Overnight lows will be generally in the 50s.

LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/

Ensemble guidance suggest near normal temperatures and onshore flow at the low levels maintaining morning clouds with afternoon clearing for the midweek time period. Dry conditions likely continue through the end of the week. Around Friday, expect that the ridge over the Rockies/Great Basin amplifies with the next upper trough approaching the west coast. This will likely bring a shift in the pattern with the potential for precipitation and cooler temperatures, along with thunderstorm chances increasing into Saturday.

AVIATION

A retrograding upper trough will maintain diffluent flow over western Washington this morning. Marine stratus with LIFR cigs continues to inch its way eastward across the area this morning, and is expected to reach the metro area by around sunrise. Some locations are beginning to see impacts to visibility as the stratus lowers to ground level. Models are indicating a fairly rapid clear out this morning, with most terminals clearing out by around 17-19Z, with areas along the coast and Strait of Juan de Fuca being the last to clear. VFR conditions then prevail with high clouds passing overhead. Stratus is then expected to redevelop late tonight and spread inland overnight into Tuesday morning. Light west to northwest winds will increase to around 4 to 8 kt by late this morning and persist through the rest of the day.

KSEA...VFR cigs early this morning will deteriorate to LIFR once marine stratus arrives at the terminal, around 12-13Z this morning. Models are indicating a fairly rapid clear out time, around 17-19Z. VFR conditions then prevail through the remainder of the day, with stratus expected to return again early Tuesday morning. Light and variable winds will return to NW/N this morning and increase to around 5-8 kt by late morning and remain like so through tonight. 62

MARINE

High pressure will remain over the far offshore waters and slowly build through the week, which will maintain northwesterly winds over the coastal waters. Winds look to increase late tonight into Tuesday over the outermost waters, which may develop steep seas around 6-7 ft with a dominant period of 7 seconds. The threat for steep seas may continue through mid-week. Westerly pushes down the Strait of Juan de Fuca look to continue into next week, but will weaken each day. Gusts may occasionally reach 20-25 kt at times, in particular this evening and Tuesday evening (up to 50% chance), but no additional headlines are planned at this time. 62

FIRE WEATHER

Onshore flow and excellent overnight humidity recoveries will help mitigate fire weather conditions across western Washington through the first half of the week before a warming and drying trend commences mid to late week.

While some uncertainty remains in the long term pattern, guidance continues to suggest that the next storm system will arrive by the weekend, increasing the chances for shower and thunderstorm activity across the area and potentially resulting in the return to elevated to critical fire weather conditions.

SEW WATCHES/WARNINGS/ADVISORIES

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