textproduct: Seattle/Tacoma

SYNOPSIS

An upper level trough will move through Western Washington today. An upper level ridge will build offshore tonight and Monday then move inland Tuesday and Wednesday. The ridge will shift eastward Thursday and Friday with increasing low level onshore flow at the end of the week.

SHORT TERM /TODAY THROUGH TUESDAY/

Surface gradients have turned flat through Puget Sound this morning as the transition to northerly flow begins to take shape. Remnant convergence zone activity continues this morning, but this should dissipate toward midday. Attention then turns toward a significant weather pattern shift for the week ahead as a warming trend couples with the flow aloft importing regional wildfire smoke into the area. More on this to come in the afternoon discussion. Previous discussion follows with update to aviation portion. 27

Satellite imagery shows mostly cloudy skies over most of the area this morning. Mostly clear skies only over the Central and Southern Puget Sound. Convergence zone over Snohomish and Southern Skagit county not producing much shower activity at 3 am/10Z. Temperatures were in the upper 40s to near 60.

Convergence zone this morning will continue to not produce many showers. The zone will dissipate this afternoon. Upper level trough swinging down from the north with the trough axis right over Western Washington at 00Z Monday. Not much moisture associated with the trough. Best chances for showers will be in the North Cascades. Slight chance ( 10-15 percent ) of an afternoon thunderstorm in the North Cascades as well. Highs will remain below normal, in the 60s and lower 70s.

Trough axis moving east of the area tonight with an upper level ridge building offshore. The combination of light northerly flow in the lower levels and dry north northwesterly flow aloft behind the trough will help clear skies out across the area. While the clouds will decrease the chances for smoke, especially aloft, will increase with the northerly flow. It will be a chilly morning for the first week of August. Lows in the mid 40s to mid 50s.

Upper level ridge continuing to build offshore with the ridge axis approaching 130W late in the afternoon. No cloud cover but the north northwesterly flow aloft and light northerly flow at the surface will bring smoke at all levels into the area especially over the interior. Highs warming into the 70s.

Upper level ridge axis continuing to drift eastward towards Western Washington Monday night and Tuesday. 500 mb heights rising into the mid 580 dms by Tuesday afternoon. Upper level flow becoming west northwesterly which will help reduce the amount of smoke aloft. Low level flow remaining light northerly keeping the threat of low level smoke in the area. Warming trend continuing with highs in the 80s and lower 90s inland and near 80 on the coast. Lows in the 50s. HeatRisk increasing into the moderate category for most of the area Tuesday afternoon. Felton

LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/

Upper level ridge axis moving over Western Washington Tuesday night will remain over the area through Wednesday night. Low level flow north northeasterly. Highs Wednesday in the 80s to mid 90s inland and near 80 on the coast. If the low level smoke is thick enough these temperatures will be too warm. Lows in the mid 50s to mid 60s. Moderate HeatRisk for most of the area with a 20-40 percent chance of major HeatRisk over the Southern Puget Sound.

Thursday a transition day with the upper level ridge axis shifting east and the low level flow turning onshore later in the day. Highs along the coast cooling into the lower to mid 70s. The transition to onshore flow looks to not happen in time for any cooling over the interior. Highs again in the 80s to mid 90s. Like Wednesday moderate HeatRisk for most of the area with a 20-40 percent chance of major HeatRisk over the Southern Puget Sound.

Upper level ridge axis well to the east Thursday night and Friday with increasing low level onshore flow. This will push any low level smoke out of the area. Highs cooling into the mid 70s to mid 80s inland with highs near 70 on the coast. Lows in the 50s and lower 60s.

Westerly flow aloft with low level onshore flow Friday night and Saturday producing a "normal" first half of August day with some morning clouds and afternoon sunshine. Highs in the 70s and lower 80s inland and mid to upper 60s on the coast. HeatRisk returning to the minor category. Felton

AVIATION

Westerly flow aloft will become north to northwesterly tonight as an upper trough axis shifts east of the Cascades. Light low level onshore flow will turn more northerly tonight into Monday. Areas of MVFR ceilings this morning will lift and scatter by this afternoon with remaining convergence zone activity dissipating. VFR conditions will prevail from mid-afternoon through the evening. A shallow IFR/LIFR stratus layer is expected to form along the immediate coast early Monday morning, but is not expected to impact interior terminals.

KSEA...MVFR ceilings are expected to persist through around 18Z before lifting as remnant convergence zone activity erodes. VFR ceilings at or above 4000 feet are expected for much of the afternoon before scattering out toward sunset. Surface winds light southerly veering W/NW toward 21Z then solidly N/NW and increasing to 10-13 knots with a few higher gusts toward 00Z. Winds will ease to NE 4 to 7 knots overnight.

27

MARINE

A shortwave trough will traverse across area waters today as a thermal surface trough snakes northward along the US West Coast. It doesn't appear strong but as a result we've issued SCAs for the central/eastern Strait and coastal waters. REFS probabilities of SCA gusts being met (21 kt) range between 80-100% for these aforementioned areas this afternoon-evening. High pressure will rebuild over the coastal waters today and remain in place into early next week as thermally induced low pressure continues to expand northward across the interior for relatively quieter conditions across area waters.

41

FIRE WEATHER

Continued onshore flow today will keep fire weather concerns at a minimum. Warming trend beginning Monday, with elevated fire weather concerns Tuesday through at least Friday. Minimum relative humidity values dropping into the 20s Tuesday and as low as the upper teens Wednesday and Thursday for the Cascade Valleys and South Puget Sound with high temperatures in the 90s. Fire weather concerns easing next weekend with the return of low level onshore flow and cooler daytime high temperatures. Felton

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory from 4 PM this afternoon to 2 AM PDT Monday for Central U.S. Waters Strait Of Juan De Fuca- East Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory from 4 PM this afternoon to 3 AM PDT Monday for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From Cape Flattery To James Island Out 10 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From James Island To Point Grenville Out 10 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm.