Area Forecast Discussion

SYNOPSIS

After today, a pattern change will bring more fall- like weather to the area with periods of rain, high elevation mountain snow and gusty winds. Active weather will continue as we move into next week.

SHORT TERM /TODAY THROUGH FRIDAY/

Western WA will see one last dry day today before the overall weather pattern turns more fall-like and active. We will see patchy fog this morning, especially across the south sound, with cool temperatures in the 30s and 40s. Expect highs in the 50s this afternoon with increasing clouds through the day. A cold front and trough will move inland tonight for wetting rains along the coast and in the mountains. The interior will see light measurable rain with overall amounts generally less than a tenth of an inch.

The next weather system moves in late Thursday and Friday as a deep low shifts east into B.C. This system will bring windy conditions to the coast and north interior (Everett northward) Thursday night through Friday morning. The probability of strong winds remains low, however, minor wind impacts are still possible. This system will be wetter with 1-2" of rain over the coast and Olympics, up to an inch in the Cascades, and 0.50-1.00" in the interior through Friday night. In addition, this system will bring building seas with high surf conditions possible along the coast. See marine discussion below. 33

LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/

A parade of systems will barrel through the Pac NW over the long term period keeping the weather active. There's little break in the pattern and expect more fall-like weather through next week. These systems will bring more rain, high elevation snow, and windy conditions. 33

AVIATION

Southwest flow aloft will develop today and increase as a frontal system approaches the region. The front will shift onshore across Western Washington late this evening. Areas of LIFR fog and low clouds across the Southwest Interior, south Puget Sound, and outlying river valleys will dissipate toward 18Z. High and mid level clouds will increase through the day with ceilings lowering to MVFR in rain along the coast near or after 00Z. These conditions will spread to interior terminals 03Z-06Z tonight.

KSEA...Confidence in amount of fog development in the vicinity of terminal remains fairly low this morning. Light surface winds and mostly clear skies remain favorable for at least some fog development before increasing surface winds and higher clouds arrive. VFR will prevail mid-morning into this afternoon before ceilings deteriorate to MVFR in rain toward 06Z. Surface winds light southeasterly early becoming southerly and increasing to 8 to 11 knots this afternoon/evening.

27

MARINE

South/southwesterly winds will start to increase over the coastal waters this morning as the front approaches the area. Small Craft Advisories begin across outer coastal waters first, then including the inner coastal waters by afternoon and in/near strait entrances tonight as winds increase. Southerly winds will also increase this afternoon through the interior Salish Sea from the central Puget Sound up through the southern Strait of Georgia, but winds are expected to remain below advisory thresholds. The front moves through late this evening and winds slowly ease into early Thursday. Seas build back to 10-12 ft tonight and continue into Thursday.

Conditions become more active Thursday night into Friday as another stronger frontal system traverses the area waters. Winds increase area-wide overnight, with 60-80% chances for gale force wind gusts across portions of the coastal waters and the East Strait of Juan de Fuca through Friday morning. Winds look to slowly weaken during the day Friday. Seas will also begin to increase Thursday night, in conjunction with the winds but also as a large, long-period swell group arrives to the coastal waters. Seas will most likely rise to around 15-18 ft, through ensemble guidance shows a 25-40% chance of seas exceeding 20 ft. Seas look to maximize by mid-day Friday before easing Friday night.

The next frontal system, however, will be on its heels with winds increasing once again on Saturday, with higher (50-70%) chances for gale force winds across the coastal waters through early Sunday morning. Winds remain elevated overnight before easing on Sunday. Seas rise once again late Saturday up to 16-20 ft during the day Sunday. Seas ease slightly Sunday night.

Conditions look to remain hazardous going into next week. Additional frontal systems move near or through the area waters almost every day, bringing additional periods of strong to gale- force winds. Deep low centers over the Gulf of Alaska will continue to generate and send several series of large, longer- period waves to the coast, keeping seas at least above 12 ft.

62/27

HYDROLOGY

River flooding is not expected through the next seven days. However, a series of increasingly wet weather systems will bring rain (and high mountain snow) to the region, especially from Friday onward. While current forecasts are not expected to cause flooding, this will begin to saturate soils and raise base flows that could bring a concern with subsequent storms systems.

SEW WATCHES / WARNINGS / ADVISORIES

WA...None. PZ...Small Craft Advisory from 2 PM this afternoon to 1 AM PST Thursday for West Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory from 4 PM this afternoon to 2 AM PST Thursday for Admiralty Inlet-East Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory from 1 PM this afternoon to 10 PM PST this evening for Coastal Waters From Cape Flattery To James Island Out 10 Nm-Coastal Waters From James Island To Point Grenville Out 10 Nm-Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm.

Small Craft Advisory from 8 AM this morning to 10 PM PST this evening for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm.