textproduct: Seattle/Tacoma

SYNOPSIS

High pressure has shifted offshore with a weak disturbance increasing cloud cover across the region today. High pressure returns on Friday and Saturday, with a return of foggy and cold mornings. Another weak system approaches, but the ridge remains strong enough to keep the region blocked through the first half of next week.

SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/

A cooler and cloudier day across the region with a weak the ridge weakening and shifting offshore, allowing an impulse to slide down. This weak system may bring a few light showers to the coastal areas. While there isn't much moisture with it, temperatures will again drop below freezing so any moisture could freeze and create slick spots on untreated surfaces. Upper level high pressure rebounds Friday and Saturday with a slightly cooler air mass, leaving high temperatures will stay in the low to mid 50s both days. Temperatures will also cool slightly overnight, with low temperatures in the mid to upper 20s. Renewed fog development each night and early morning could bring the potential for slick conditions and reduced visibility in the freezing fog.

LONG TERM /SUNDAY THROUGH THURSDAY/

A highly amplified synoptic pattern will remain in place across much of North America moving into the early portion of next week. This will initially keep a mean upper ridge position along the West Coast. There are, however, signs of this pattern changing toward the middle of next week that will favor the return of more typically active, wetter weather. Model ensembles depict broad positive height anomalies extending northward into Alaska being replaced by a mean upper trough over the Gulf of Alaska toward the Wednesday and Thursday time frame. While this isn't expected to introduce any particularly impactful weather as of yet, it will put Western Washington in closer proximity to a few frontal systems that will bring the first meaningful chances of precipitation in nearly two weeks. 27

AVIATION

Upper level ridging centered offshore and a broad upper trough east of the Rockies are producing northwest flow aloft over Western Washington today. A dissipating frontal system is spreading abundant high and mid level moisture across the region this afternoon with a few showers near the coast. VFR prevails across most of the interior except for a few pockets of IFR near Hood Canal. MVFR ceilings are expected to persist overnight along the coast. The weak system will exit late tonight with a recurrence of areas of IFR/LIFR ceilings in low clouds and fog expected once again on Friday morning...especially across south Puget Sound and outlying valleys. Primarily VFR is expected areawide Friday afternoon as increasing low level northerly flow acts to scour out much of the low level moisture.

KSEA...Primarily VFR conditions are expected into this evening under varying degrees of high/mid clouds. Confidence in the evolution of low cloud development tonight remains low. A period of IFR ceilings is expected Friday morning, but increasing low level northerly flow should help erode it by mid to late morning. Surface winds light and variable today becoming north/northeasterly 5 to 8 knot late tonight into Friday morning. 27

MARINE

High pressure will then build back into the waters Friday while a thermal trough builds northward along the coast. Offshore flow returns and may be breezy at times, especially along the central and western Strait of Juan de Fuca and along the gaps in the coastal terrain. Fraser Outflow will increase early Friday morning and will also bring breezy northeasterly winds to portions of the Northern Inland Waters on Friday. While gusts to around 20 kt are the most likely scenario, there's around a 30-40% chance of gusts to 25-30 kt and if this increases, a small craft advisory may be needed. Offshore flow will persist through the weekend, but will be weaker.

A weak frontal system looks to reach the waters by early next week, allowing for winds to gradually shift back to the south across the area waters by Monday. Southerly winds look to increase Tuesday into Wednesday as another, stronger frontal system approaches the region. Seas will hold steady between 3-6 ft through the weekend, but look to build closer to 10 ft near the middle of next week as the stronger systems move back into the area.

HYDROLOGY

No river flooding is expected during the next seven days.

SEW WATCHES/WARNINGS/ADVISORIES

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