textproduct: Seattle/Tacoma

SYNOPSIS

Drier conditions with seasonable temperatures through the weekend. High pressure builds over Western Washington next week bringing continued dry weather and well- above average temperatures through at least midweek.

SHORT TERM /TONIGHT THROUGH SUNDAY NIGHT/

No planned updates tonight and the current forecast remains on track. 33

Previous discussion...Clouds continue to clear for most areas this afternoon with temperatures in the 60s and 70s. The upper low remains positioned offshore of Cape Flattery and will slowly progress northeastward into British Columbia through Saturday. This will result in another round of morning stratus across Western Washington Saturday AM. Temperatures will remain seasonable again on Saturday with highs in the 60s along the coast, and 70s for the interior. High pressure slowly begins to build over the Pacific Northwest Sunday, resulting in less morning cloud cover, and temperatures warming into the 80s for some locations by the afternoon.

LONG TERM /MONDAY THROUGH FRIDAY/

Upper level ridging further builds into Western Washington Monday through midweek. This will result in a more significant warming trend, with temperatures rising into the 80s and low 90s during this period. Widespread Moderate HeatRisk is expected for interior locations, with a 20 to 50% probability of Major HeatRisk for Cascade Valleys and portions of central Puget Sound Tuesday and Wednesday. Uncertainty begins to increase in ensembles in regards to potential weak troughing offshore of the west coast by late Wednesday/Thursday. At this time, a slight cooling trend may begin on Thursday and continue into Friday. Another aspect of the forecast that will be further monitored is the existence of any monsoonal moisture around the Thursday period which could result in POP chances, at least for the Cascades and Olympics. NBM POPs at this time remain low (around 10 to 20%), but will be dependent on the vicinity to troughing offshore. JD

AVIATION

VFR conditions across all western Washington terminals this evening, with another onshore marine push expected to bring increased low end VFR to MVFR ceilings inland tonight. Isolated areas of IFR/LIFR in low stratus are favored overnight along the Pacific Coast and through the Strait of Juan de Fuca. Deteriorated conditions in low clouds will likely persist through much of the morning Saturday before the clouds begin to break up. A return to VFR is expected for most areas Saturday afternoon, with potential for MVFR ceilings to continue along the coast and through the Strait. West to southwest winds this evening generally 8 kt or less will shift west/northwest this evening and turn back to southerly Saturday morning with light winds 10 kt or less.

KSEA...VFR this evening with light southerly winds shifting northerly briefly overnight. Winds will flip back to the southwest Saturday morning. Ceilings are favored to remain VFR tonight, with a low chance (15% to 20%) of MVFR stratus developing over the terminal. Ceilings may once again bounce between VFR and MVFR overnight, with a return to VFR by 16z Saturday.

15

MARINE

A low/trough offshore will continue to move inland today with high pressure rebuilding offshore. There will also be a thermal trough building under a ridge going into next week. While flow does not appear to go offshore completely, there will be varying degrees of onshore pushes through the Strait of Juan de Fuca, as well as some north/northwest winds in the coastal waters early next week. The next potential for winds over 20 kt is a 40-60% chance of gusts over this threshold in the Strait of Juan de Fuca Saturday evening. Potential for these winds next week remains low at this time.

Seas of 3-6 ft will increase to 6-9 ft early next week, with seas potentially becoming choppy as periods decrease to around 8 seconds Sunday into Monday. Seas decrease back down to 4-6 ft the remainder of next week.

HPR

FIRE WEATHER

Fire weather concerns will linger throughout the forecast period as a hotter and drier pattern returns quickly over Western Washington, especially Monday through much of next week. This has the potential for increasing fire activity from any new lightning starts from Thursday's convection.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...None.