textproduct: Seattle/Tacoma

UPDATE

Satellite imagery shows some high clouds over the North Coast otherwise clear skies across Western Washington this evening. Northerly low level flow going light overnight but the marine layer has been dissipated by a couple of days of sunshine so not expecting much in the way of stratus in the morning even on the coast. 500 mb heights rising a little tomorrow peaking in the mid 580 dms. With southwesterly flow aloft could see some high clouds at times the next couple of days. Warmer Tuesday and Wednesday with highs in the mid 70s to mid 80s over the interior and lower to mid 70s coast. First look at 00z models still indicating the possibility of convection Thursday. Current forecast on track. No update this evening. Previous discussion follows with updated aviation section. Felton

SYNOPSIS

High pressure aloft will rebuild across the region into Wednesday for warm and drier conditions. An area of low pressure may bring a threat of showers and thunderstorms around Thursday before high pressure regains control over the weekend for a return of dry conditions and well above normal temperatures.

SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/

Mostly clear conditions this afternoon across Western Washington with localized stratus along the coast. High pressure will continue to build over the region as an area of low pressure dives southwards well offshore. Dry, warm conditions continue for the majority of the area through Wednesday. Temperatures will warm into the 80s for much of the interior Tuesday into Wednesday, resulting in continued Minor HeatRisk and areas of Moderate HeatRisk. Although POPs remain very low on Wednesday afternoon, will need to monitor the threat for convection over the Cascades with increasing instability. Otherwise, haze aloft will be around into midweek with continued southerly flow.

LONG TERM /THURSDAY THROUGH MONDAY/

Uncertainty increases in ensembles for Thursday into Friday as the upper low located offshore meanders closer to the Pacific Northwest. However, there has been an uptick in POPs for the Thursday period on the NBM. Looking at Cluster Analysis, ECMWF/CMC ensembles generally bring the upper low track closer to W WA by Thursday, with the GEFS maintaining more of an offshore solution (more ridging over W WA). Dependent on the track, there is a threat for showers and thunderstorms during this period with more S/SE flow aloft. Given the potential in elevated instability, convection could occur during the overnight and morning periods as well, from late Wednesday night into early Friday. This will need to be monitored closely as this would pose a fire weather concern, as well as impact any outdoor events.

Upper level ridging is then expected to build next weekend into early next week, resulting in the return of dry conditions and warming temperatures. The threat for Moderate HeatRisk increases early next week, with widespread probabilities of 50% or greater for Moderate HeatRisk.

AVIATION

Southwesterly flow aloft continues into Tuesday as high pressure remains over the region with a area of low pressure offshore. VFR conditions at all area terminals will continue into the overnight hours as conditions remain stable. Winds generally from the NW to NE this evening around 8 to 12 knots and will decrease overnight, turning more variable into Tuesday morning.

KSEA...VFR conditions throughout the forecast period. N/NE winds this evening to around 5 to 10 knots. Winds will decrease into the overnight hours, and will remain N/NE with speeds around 3 to 6 knots.

Mazurkiewicz/15

MARINE

Surface high pressure will remain over the coastal waters throughout the next couple of days. Diurnally driven westerly pushes down the Strait of Juan De Fuca will continue, with a Small Craft Advisory out for this evenings push. The coastal waters may see a few wind gusts up to 20 kts on Thursday and Friday as a low pressure system tracks through the waters, but confidence is low at this time.

Coastal seas remain at 4 to 6 feet through midweek, with seas slightly increasing to 7 to 8 feet with periods of 6 to 8 seconds.

Mazurkiewicz

FIRE WEATHER

Warming temperatures are on track through the middle of the week, with minimum relative humidity values dipping into the upper 20 to low 30 percent range throughout western Washington. A bit of a change is possible by midweek as thunderstorms get reintroduced into the forecast for Thursday. While this forecast is still highly variable, the potential for new ignitions on dry fuels due to lightning strikes is of notable concern. Less is known about exact rain amounts and whether these storms will contain wetting rains, but these details will become more available over the next few forecast cycles. It's important to note that even if thunderstorms do not occur, elevated fire weather conditions are likely to persist due to the warmer and drier weather that is forecast to continue well into the weekend.

21

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory until 1 AM PDT Tuesday for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.