textproduct: Seattle/Tacoma

SYNOPSIS

Weak upper level trough remaining over the area through Saturday. Upper level ridge building Sunday with Western Washington on the backside of the ridge Monday and Tuesday. Weak system moving through Wednesday with an upper level trough over the area Thursday.

SHORT TERM /TODAY THROUGH SUNDAY/

Satellite imagery shows front that brought Bellingham 85 percent of their normal monthly July rainfall ( 0.75 inches, normal 0.88 inches ) dissipating over the Northwest Interior early this morning. Doppler radar still has a few showers over the North Cascades and foothills. Cloudy skies over the area with temperatures at 3 am/10z in the lower 50s to near 60.

Not much left of the front but still a chance of showers for the Northwest Interior this morning. Elsewhere low level flow fairly light keeping skies cloudy through the morning hours. No upper level ridging to provide some subsidence to get rid of the low level moisture. Will have to rely on the near solstice sunshine. This should at least bring about partly sunny skies this afternoon. Highs still below normal, in the mid 60s to mid 70s.

Little change in the pattern tonight and Saturday with a weak upper level trough still over the area. Low level onshore flow will reestablish the marine layer over the interior overnight with skies once again cloudy by sunrise. Like today the early July sun will work on the marine layer with the layer thinning out enough for some sunshine in the afternoon. Lows in the upper 40s to mid 50s. Highs in the mid 60s to mid 70s.

Large upper level ridge centered over the four corners region will begin to build northwest Saturday night into Sunday. 500 mb heights rising into the lower 580 dms by 00z Monday. Low level flow remaining onshore but turns northwesterly Saturday night. This will weaken the marine layer over the area resulting in more sunshine Sunday. The onshore flow will put a cap on the daytime highs. Most places in the interior getting into the 70s. Highs on the coast in the mid to upper 60s. Lows Sunday morning mid 40s to mid 50s.

LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/

Main story in the extended period is the lack of a good upper level ridge over Western Washington through next week. Some ridging Sunday night into Monday but the ridge axis is well to the east. Low level flow remaining onshore. Flow aloft turning southwesterly as an upper level trough digs offshore between 130W and 140W. Monday looks to be the warmest day of the forecast period with highs in the mid 70s to mid 80s over the interior and mid to upper 60s on the coast.

Upper level ridge moving east Tuesday with 500 mb heights beginning to fall over Western Washington. Low level onshore flow picking up a touch resulting in a slightly cooler day with highs back into the 70s for the interior and mid 60s on the coast.

Weak front moving into the area Wednesday for a chance of rain along the coast, and over the Olympics and North Cascades. Cooler with more cloud cover. Highs in the mid 60s to lower 70s for the interior and lower 60s for the coast.

Weak upper level troughiness hanging around behind the system Thursday with post frontal onshore flow. Models might be giving climatology a little too much credit with highs in the 70s over the interior and mid 60s on the coast. Will not be surprised if we end up a little cooler than the current forecast.

AVIATION

A mix of MVFR/IFR cigs this morning with lowered visibility in light showers/drizzle. Shower activity expected to diminish by the afternoon. Improvement for the interior terminals expected this afternoon after 20-22z. Another round of MVFR cigs possible tonight, with latest probabilities around 40-70%. It is unlikely any improvement will be seen along the coast and Strait of Juan de Fuca. Calm to light SW winds early this morning will increase to 5-8 kt this afternoon. WNW winds this evening at PAE will drift south to BFI/SEA this evening by 01/02z. Winds return back to SW to BFI/SEA after 08z/09z.

KSEA...MVFR at the terminal this morning with lower clouds filling in. There is a slight chance (20-30%) of IFR between 10z-16z. Ceilings rebound in the afternoon to VFR after 21. MVFR cigs return after 10z, with latest probabilities around 40-50%. SW winds through the afternoon around 5-7 kt will shift WNW after by 02z. Winds then transition back to SW after 09z.

29

MARINE

Broad high pressure over the northeast Pacific with lower pressure inland will maintain onshore flow for the majority of the forecast period. This will result in diurnally driven westerlies through the Strait of Juan de Fuca that may reach advisory level. Today's westerlies are expected to reach advisory thresholds. Stronger westerlies expected on Saturday, with a 70-90% chance of winds exceeding 21 kt. Another weak front will move over the waters late Friday/early Saturday. High pressure is expected to rebuild over the waters behind the front this weekend into early next week. High pressure will weaken on Tuesday as another frontal system moves over the waters.

Seas remain 5 feet or lower through mid Saturday and will build to 8- 10 feet by Sunday. Seas will subside below 10 feet on Monday.

29

FIRE WEATHER

Even with the slight warming trend into next Monday the low level onshore pattern will remain intact. This will keep good overnight relative humidity recoveries in the forecast and help subdue fire weather concerns despite the warmer temperatures. Another front in the middle of next week will bring a chance of showers to portions of the mountains and the coast keeping fire weather concerns at a minimum. Felton

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory from 5 PM this afternoon to 5 AM PDT Saturday for Central U.S. Waters Strait Of Juan De Fuca- East Entrance U.S. Waters Strait Of Juan De Fuca.