textproduct: Seattle/Tacoma

SYNOPSIS

A lingering ridge of high pressure will bring one more day of warm temperatures to western Washington today with the potential for an isolated thunderstorm or two. A transition to onshore flow and cooler conditions will take place on Wednesday along with a chance of some precipitation. Cooler and unsettled conditions will continue into the weekend as a trough of low pressure over the Northeast Pacific sends a series of weak frontal systems across the area.

SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/

Short-lived isolated thunderstorms have been firing up this evening along the Olympic Peninsula and Puget Sound. Latest radar observations show a batch of thunderstorms moving north from Oregon towards Western Washington. If they manage to hold themselves together, expect the storms to move across Puget Sound in the next 30 minutes to hour. Isolated thunderstorms remain possible through tonight across the region. 29

Lingering upper level ridge has continued to bring warm conditions across the area this afternoon, with high temperatures in the mid to upper 70s, along with some locations in the Cascade foothills in the lower 80s. The ridge will shift eastward tonight with an incoming trough offshore. With southerly flow aloft and associated moisture with this incoming trough, we could see an isolated thunderstorm or two, particularly over the Southern portion of the Cascades this evening as orographics give the instability a boost (20-30% chance) The main hazard associated with any thunderstorm is frequent lightning, brief erratic winds, and heavy downpours. Again, could see an isolated thunderstorm or two move towards the interior, but confidence is low at the moment. Otherwise, we will see some scattered showers develop and move northward later tonight and through Wednesday morning and fill in through the interior.

We'll see the upper level low track over the area on Wednesday, keeping showers and unsettled weather in the forecast with significantly cooler temperatures. High temperatures on Wednesday will be in the upper 50s and lower 60s - almost a 15 degree temperature difference from the day before.

A shortwave will cross over the area on Thursday with a slight warm up with temps in the lower 60s, with shower chances being mainly confined to the Cascades. Will likely be a dry day for the interior locations.

LONG TERM /FRIDAY THROUGH TUESDAY/

A series of troughs look to cross over western Washington over the weekend and into early next week. A trough on Friday will help favor some instability over the area once again, resulting in a slight chance of thunderstorms mainly over the North Cascades. Cooler temperatures in the upper 50s to lower 60s look to stay around for much of the weekend, with chances of precipitation in the forecast through at least Monday. Conditions look to dry out by Tuesday with temps warming into the mid/upper 60s.

Mazurkiewicz

AVIATION

Southwesterly flow aloft will persist through the TAF period as an upper level trough approaches the region. Showers and some isolated thunderstorms have started to pop up along the Olympic Peninsula over the past few hours and latest radar shows a new batch of showers and thunderstorms moving up into the region from the south. While current conditions remain VFR across the area this evening, conditions could quickly drop down to MVFR or even IFR in any heavier shower or isolated thunderstorm activity as showers continue to move up into the area. At this time, confidence remains too low for inclusion of thunder in any single TAF site, however conditions will continue to be monitored and updated through the evening hours.

Winds are southwesterly this evening, generally persisting between 7-12 kt, though could get gusty to 20-25 kt in the vicinity of shower activity. Expect ceilings to lower to more widespread MVFR overnight as showers fill in across the region. Showers will taper through the afternoon hours on Wednesday, except for a convergence zone that looks likely to develop across the central Sound Wednesday afternoon into evening. Winds will remain out of the southwest into Wednesday, with a couple spots becoming breezy later in the day.

KSEA...VFR conditions, with southwesterly winds persisting between 7-12 kt. Gusts to 20-25 kt will be possible through evening, especially in any stronger shower activity. Isolated thunderstorms may approach the terminal tonight into the overnight period, though confidence is too low for inclusion in the TAF at this time. Isolated thunderstorms may move into the vicinity of the terminal as early as 04-05Z. Ceilings will lower to MVFR overnight as general shower activity increases. Showers will decrease through the afternoon on Wednesday. A PSCZ looks to develop Wednesday afternoon and persist into Wednesday evening, but looks to largely stay to the north of the terminal at this time.

MARINE

Showers and isolated thunderstorms moving into the area may briefly reduce visibilities across portions of the interior waters tonight. Winds have also increased a bit over the waters, especially through the Strait of Juan de Fuca. Small craft advisory winds will persist in the central Strait zone this evening and tonight. A more widespread round of onshore winds increases tomorrow through the day, bringing higher end advisory winds to 30 kt through the Strait. There remains lower (20-30%) chance of isolated gale gusts in the central Strait tomorrow, but confidence isn't high in this. Otherwise, seas building over the coastal waters with a mix of a longer period and shorter period wave groups will bring confused seas that may be more hazardous than the wave heights (5-7 ft) would otherwise suggest. Otherwise, onshore flow continues through the Strait of Juan de Fuca later this week with northerly winds over the coastal waters. Another round of building seas to 8-9 ft over the coastal waters around Saturday from a distant disturbance.

Cullen/14

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 5 AM PDT Wednesday for Central U.S. Waters Strait Of Juan De Fuca.