textproduct: Seattle/Tacoma

SYNOPSIS

A ridge of high pressure will produce a warming trend through Tuesday. A transition to onshore flow and cooler temperatures will take place on Wednesday along with a chance of some precipitation. Cooler and unsettled conditions are expected into the upcoming weekend as a trough of low pressure over the Northeast Pacific sends a series of weak frontal systems across the area.

SHORT TERM /TODAY THROUGH WEDNESDAY/

A ridge of high pressure aloft will rebuild into the area today with low level flow turning northerly. After areas of morning clouds, mostly sunny skies are expected today along with modestly warmer temperatures. The low level turns offshore tonight as thermally induced low pressure expands northward along the coast. Temperatures will warm further on Tuesday with most of the region getting into the 70s and lower/mid 80s. A few spots across the interior will briefly reach moderate heatrisk criteria. The low level flow turns onshore late in the day on Tuesday...with a cooling sea breeze for the coast. The forecast Tuesday night and Wednesday remains something of a a conundrum. A closed off and negatively tilted upper low will approach the coast somewhere between far northern California and Oregon. Model solutions remains split in their handling of this. Of note, the 00Z ECMWF deterministic run and many of it's ensembles bring the low further north putting Western Washington squarely in the crosshairs of some elevated instability and diffluence aloft. Should this occur, we could be talking about some nocturnal convection popping up Tuesday night into early Wednesday morning. The GFS suite of ensembles are less enthused about this scenario, but about half of them do generate some precip on Wednesday. Needless to say, uncertainty in the Wednesday forecast remains high, but cooler temperatures and a chance of showers or isolated thunderstorms looks like a safe forecast. Stay tuned.

LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/

A mean upper trough position takes up residence over the Northeast Pacific for the second half of the week. This will lead to cooler conditions and some light precip at times Thursday into Saturday. There's general agreement that weak upper ridging will attempt to make some inroads late in the weekend for perhaps drier conditions and temperatures recovering to around seasonal normals.

27

AVIATION

Northwest flow aloft behind a trough will become more neutral during the day, returning to southwest as a ridge passes over the region. Satellite is tracking a few areas of lower stratus this morning. The densest areas are along the coast and in the mountains, with a few patches in the interior beginning to fill in. Majority of the ceilings will be in the VFR/MVFR category this morning, with a chance of IFR/LIFR along the coast/southwest interior briefly this morning. The ridge overhead will result in low clouds clearing by roughly 15-19Z late this morning with clear skies. NE winds 3-6 kt this morning will turn to the north 6-12 kt today, becoming NE again under 5 kt tonight. Chance of low cigs/vis Tuesday morning remains confined to the coast.

KSEA...Pockets of stratus in and around the terminal this morning will keep at least a chance of MVFR going through late morning, with clearing taking place shortly after (VFR). NE winds around or less than 5 kt will turn to the north 6-12 kt during the day, decreasing to under 5 kt from the northeast tonight.

HPR

MARINE

A post-front push through the Strait of Juan de Fuca will weaken early this morning as high pressure builds again in the eastern pacific via a ridge. Coastal waters may have a couple pockets of fog underneath the stratus early this morning. There is also a thermal trough expected for Tuesday that may bring a brief period of offshore flow. Models have a trough/front passing through midweek, with a 40% chance of showers over the interior waters. While winds for most waters will remain light through the week, there will continue to be pushes of winds (likely greater than 20 kt) through the Strait of Juan de Fuca at times - particularly Wednesday and Friday. Seas will hold around 4-6 ft through the week, with a brief jump up to 6-8 ft midweek.

HPR

HYDROLOGY

The daily hydrology discussion has ended until the start of the next rainy season; it will only be updated during this time as needed.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory until 3 AM PDT early this morning for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.