textproduct: Seattle/Tacoma

SYNOPSIS

A warm front will bring widespread lowland rain and mountain snow for the highest elevations today with showers lingering into Saturday. A cooler system remains on track into early next week with heavy mountain snow and the potential for an early morning rain/snow mix for parts of the interior lowlands.

SHORT TERM /TODAY THROUGH SUNDAY/

The current forecast remains on track with no planned updates. 33

Previous discussion...In the upper- levels, high pressure resides over the NE PAC with upper-troughing downstream over the Intermountain West. At the surface, a surface low to the south of the Aleutian Islands is dragging a warm front across western WA this morning. With it, light rainfall is being observed throughout the lowlands and is forecast to remain well into the day. Pass level snow will be a none-factor as snow levels rocket over 5,000 ft by the afternoon before topping out around 8,000-8,500 ft overnight into early Saturday. Rainfall amounts 0.25 to 0.50" for the interior lowlands and coastal areas through early Saturday AM. Cascade foothills and mountains are trending higher with totals expected to range between 0.50 to 1.00".

Stout ridging remains in place over the NE PAC on Saturday but models are hinting at it retrograding slightly on Sunday. Saturday appears drier as most of the precipitation takes focus over the BC Coast Mountains. That said, showers are forecast to remain at times, mainly for the mountains given orographic lifting. But as mentioned, riding will shift ever so eastward on Sunday - opening up the pattern to more precipitation and cooler air aloft. Snow levels are forecast to plummet around 6,000 ft Saturday morning to Sunday evening as mountain pass level snow returns. This set up will kick- start a period of active weather throughout the upcoming week with lowland rain, breezy winds and much needed heavy mountain snow. Highs in the short term around average with temps in the lower 50s with overnight lows in the 40s.

McMillian

LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/

Ensemble guidance continues to maintain a rather cold and wet pattern in place across the start of next week. With strong westerly flow aloft remaining in place, expect consistent snow across the mountains. With temperatures near freezing through the lowlands each morning, there will be the potential for some snow falling depending on the timing of heaviest precipitation. While this may be enough to bring a light dusting to some lowland spots at some point, the chances for notable accumulations greater than around a half inch remain somewhat low for any particular location. Onshore flow during this time period likely provides another limiting factor for the air mass getting significant cooler. Confidence begins to decrease a bit late in the week with ensemble guidance becoming increasingly out of sync with the phasing of the ridge/trough pattern. If heights rise toward midweek, this would bring just rain to the lowlands but continued snow to the mountains - this is the most likely scenario at this point, but only slightly so.

AVIATION

North to northwesterly flow aloft as upper level ridging builds over the eastern Pacific. MVFR cigs becoming more widespread this morning ahead of an incoming warm front and widespread rainfall. Reduced visibilities are likely with heavier showers. MVFR cigs will continue today through Saturday morning with increasing probabilities of IFR ceilings in the morning. Surface winds mainly out of the S-SW with gusts near 20 kt for interior terminals.

KSEA...MVFR conditions in place as of 1130z. Rain showers will become more of a steady rain this afternoon, with visibility reductions at times. S-SW surface winds for much of the upcoming TAF period with gusts upwards of 20 kt this afternoon. Rainfall should end overnight Friday but lower ceilings (down to IFR) are favored to continue into early Saturday.

McMillian/HPR

MARINE

Little change to the pattern over the waters for the next few days with onshore flow and a few weak disturbances near the waters. Winds increase Sunday and Monday with a front pushing through, bringing around a 60-70% chance of advisory strength winds to much of the waters. Seas remain around 6 to 8 ft dominated by a west swell at around 10 seconds. Seas over the coastal water will build behind Sunday's weather system, likely bringing seas back above 10 ft. A stronger system is possible next week.

HYDROLOGY

Heavy precipitation over the Olympics will force rises on the Skokomish River with the potential for flooding mid to late next week. No other river flooding is expected during the next seven days.

SEW WATCHES/WARNINGS/ADVISORIES

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