textproduct: Seattle/Tacoma

SYNOPSIS

Overall, a cooler and drier pattern is expected to persist across western Washington through the first half of the week with ridging offshore, though a weak disturbance moving across the region Monday night into Tuesday will bring some showers to the area. A change to a wetter pattern is likely late in the week as the ridge weakens and opens the door for stronger and wetter systems to approach western Washington.

SHORT TERM /TODAY THROUGH TUESDAY/

Dry conditions are expected across western Washington today as a ridge of high pressure continues to build into the area from the northeastern Pacific. Clearing overnight has allowed for some fog development across portions of the South Sound and East Puget Sound lowlands, which has brought some visibilities down to 1 mile or less in spots. The areas of fog remain rather shallow however, so expect fog to dissipate by the mid to late morning hours today to make way for some sun. In addition to fog, it will also be a chilly start to the morning as clearing has allowed for temperatures to cool to near freezing in spots, especially across portions of the southern Sound away from the water and along the Chehalis Valley. Afternoon highs today will be in the mid to upper 40s across the area.

Another chilly and foggy start is likely for portions of western Washington on Monday morning, especially across the southern Sound and Chehalis Valley. A weak disturbance will then drop down into the area under the northwesterly flow aloft Monday night into Tuesday, bringing chances of light rain to the lowlands and snow to the mountains. At this time, this system does not look to be very impactful to the area, with most spots across the lowlands only expected to receive a couple hundredths to around a tenth of an inch of rain. Light snow accumulations are expected for the mountains, mainly between 1-3 inches, with only some light snow (roughly around an inch or less) expected at the passes.

LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/

Conditions will dry out again Tuesday night into Wednesday as the ridge of high pressure over the northeastern Pacific builds back into the region. The pattern then becomes a bit more uncertain heading into the second half of the week as ensemble clusters remain split on the degree of ridging over the northeastern Pacific. The majority of the GEFS members hint at the ridge weakening, allowing for wetter systems to move into western Washington, while the majority of the ENS members suggest somewhat drier solutions with more of an amplified ridge persisting over the Pacific. Will need to see how guidance resolves the scenarios over the coming days, but the current forecast from Thursday onward generally trends towards the wetter solutions at this time.

Temperatures look to warm the second half of the week, from lows in the 30s and highs in the 40s on Wednesday and Thursday to lows in the 40s and highs in the 50s by Friday and Saturday.

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AVIATION

An upper level ridge just offshore will begin to move inland today into Monday. The northerly flow aloft will weaken and become westerly Monday. Clear skies are being reported at most terminals this morning, with light east/northeast winds under 5 kt or calm winds. Thin radiational fog has formed in the Chehalis Valley/South Puget Sound areas (from KCLS to KOLM to KPLU). Another small area is also present this morning around KAWO. These areas continue to see lower visibilities through as late as 18Z this morning (given the cooler temperatures, some freezing fog may mix in at times). Additional water/river areas will likely see patchy radiational fog this morning. Ceilings will remain clear through the day, with ceilings filling in Monday morning (most will see VFR decks between 3,000 - 10,000 ft but again probabilities remain medium for additional radiational fog or low ceilings in the morning in the same spots as this morning and potentially up through metro Seattle). Very light 3-6 kt or calm winds out of the east/northeast are expected across most terminals.

KSEA... Thin radiational fog will be in the vicinity to the south and east this morning. Probability for the terminal itself is too low to include in the 12Z TAF (but will continue to monitor for a possible TEMPO, if necessary - between 15Z and 18Z if the fog continues to advance towards the terminal). There are some discrepancies between the NBM and HREF/REFS as to fog forming Monday morning (ranges from 5% all the way to 40%). High clouds may help hinder development, but as of early this morning it's a low confidence forecast. Winds will remain light north/east 3-5 kt.

HPR

MARINE

High pressure will move inland next few days under a ridge coming ashore. Conditions are expected to remain calm through Tuesday with seas at 4 to 6 ft and calm or light offshore winds. A weak front will skirt the outer coastal waters Tuesday and Wednesday. At this time, the best chance of winds exceeding 20 kt remains in the outer coastal waters Tuesday. Seas will build back up to 9 to 12 ft Tuesday through Wednesday, then decrease back down to 4 to 6 ft with light winds Thursday with another system potentially passing through next weekend. This system may bring winds exceeding 20 kt to the Strait of Juan de Fuca, as well as 9-12 ft seas going into next weekend.

HPR

HYDROLOGY

River flooding is not expected over the next 7 days.

SEW WATCHES/WARNINGS/ADVISORIES

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