textproduct: Seattle/Tacoma

SYNOPSIS

Upper level ridging over western Washington will flatten out as a system passes to the north with near zonal flow aloft expected by Monday. This will keep temperatures near seasonable normals as well as return onshore flow to the area. The pattern of morning clouds giving way to afternoon sun will persist at least through mid-week. An approaching frontal system for the end of the week could bring the next chances for precipitation, however some uncertainty exists.

SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/

Mostly clear skies over W WA this afternoon although stratus still lingers along the coast. With clouds breaking up a little earlier than yesterday, area temperatures largely on track with the forecast with current obs ranging in the mid 60s to around 70. This puts expected highs for most locations in the lower 70s still well within reach.

Forecast remains consistent in that the upper ridge will continue to shift eastward today with the ridge axis making it to the Rockies by this evening. Coupled with a trough passing to the north, zonal flow aloft will set up overnight, helping to bring a return to onshore flow at the surface. Forecast dilemma for the immediate short term is will the return of onshore flow exacerbate the morning fog issues the area has been having. Currently agreeing with NBM that potential for widespread fog likely to be mitigated by the clouds that will move in overnight. Sure, they will be stratus-y, but with the ridge gone, they should not make it all the way to the ground. Otherwise, dry conditions remain in place for the short term.

The import of cooler marine air will shave a handful of degrees off of daytime highs, making them a bit more seasonable. Highs both Monday and Tuesday are expected to range from the low to upper 60s, with a few isolated spots in the SW interior shaking hands with 70.

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LONG TERM /WEDNESDAY THROUGH SUNDAY/

A building upper level ridge off the coast of California mid-week will nudge zonal flow to a little more northwesterly by Wednesday evening. This will give daytime highs a bump of about a degree or two, ranging in the mid 60s to lower 70s. More widespread 70-plus temps can be found on Thursday as this minor ridging gets a little more time to work. Coastal sites may not see much change in temperatures, however interior lowland spots will range from the upper 60s to mid 70s, with the SW interior being on the higher end of that scale.

Models remain in agreement about a frontal system moving its way through W WA Friday...but all the details remain up in the air. Deterministic GFS has pushed FROPA back to Friday evening or Friday night while deterministic ECMWF remains consistent, bringing the system through Friday afternoon and evening. Most ensemble members favoring the ECMWF timing...providing enough sway to cause the NBM to reflect this thinking in its forecast. This seems reasonable enough for now, but no matter the timing, models seem to be in hearty agreement that this front looks to fall apart as it moves through. While higher elevations should still see something with PoPs coming in at 60-70 pct for the event, PoPs in the lowlands are considerably lower, still largely ranging 20-40 pct. It is still some time out though, and plenty of opportunity for additional variances to emerge. This system will cool temperatures regardless if it rains, with daytime highs for Friday and the weekend in the mid 50s to lower 60s...with some mid 60s possible, mainly on Friday.

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AVIATION

High pressure continues over the West with dry and stable conditions across western Washington. The flow aloft is westerly. Low clouds and fog will likely reform overnight with LIFR to VLIFR ceilings and visibility across the interior lowlands. Low clouds and fog will scatter out 18-21z with VFR conditions expected thereafter. 33

KSEA...VFR this afternoon and evening with low clouds returning overnight and Monday morning. Light N winds becoming S to 5 kt by 09- 12z. 33

MARINE

A thermal trough will shift inland tonight with the flow turning onshore. Highest wind and waves will be through the Strait of Juan de Fuca - a Small Craft Advisory is in effect. Another push down the strait is forecast Monday evening. Onshore flow will continue through the week with another strong push on Friday as a front moves inland. 33

SEW WATCHES/WARNINGS/ADVISORIES

WA...None.

PZ...Small Craft Advisory until 5 AM PDT Monday for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.