textproduct: Seattle/Tacoma

SYNOPSIS

Weak upper ridging over the Pacific Northwest keep conditions dry through late Tuesday. A stronger early season system Wednesday into Thursday results in more widespread rainfall and gusty winds. The deep upper low lingers over the Pacific Northwest into next weekend for continued unsettled weather and cooler conditions.

SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/

The latest forecast remains on track this evening with no updates. High clouds continue to stream overhead of western Washington this evening, but otherwise a dry and very mild day with high temperatures right around normal-- in the low to mid 70s. Marine stratus will develop overnight and move inland from the coast but remain mostly confined to west of the Salish Sea; high clouds remain overhead. Low temperatures in the upper 40s to mid 50s.

An anomalously strong (for this time of year) low pressure system will begin to move towards western Washington from the north on Tuesday with a weak warm front moving through in the afternoon. Clouds will increase and most locations will stay dry but there will be a slight chance for a few showers across portions of the area. High temperatures will be a few degrees cooler for most, in the upper 60s to mid 70s.

The associated cold front with this low pressure system will begin to approach the Olympic Peninsula overnight Tuesday into Wednesday morning, before then slowly traversing the area late Wednesday into early Thursday. This system will bring in some significant early-season rainfall across the entire region. In particular, the Pacific coast and the Olympic Mountains will have the highest chances of seeing greater than 1" of rainfall. The highest peaks of the Olympics could see up to 1-2" (50-60% chc in the 24 hours ending 5AM Thursday). Areas around the Seattle metro and southward, as well as the Cascades, will likely see around 0.5"-0.75" of rain, with areas north of Seattle seeing between around 0.25-0.5" due to the rain shadowing of the Olympics. Nevertheless, everyone is forecasted to see measurable rainfall. In addition to rainfall, winds will also increase across the area on Wednesday. The Pacific coast and the northwest interior and Salish Sea islands have the best (50-80% chc) chances to see wind gusts of over 35 mph, while gusts between 20-30 mph are expected elsewhere. Full foliage on trees may produce more significant or widespread impacts than otherwise expected during the winter when trees are bare, especially in areas experience gusts greater than 35 mph. Temperatures will be cool on Wednesday with the rain, with highs in the 60s and lows in the upper 40s to mid 50s.

LONG TERM /THURSDAY THROUGH MONDAY/

Unsettled conditions are expected to continue on Thursday as the low pressure system continues to moves southward along the coast on Thursday. Chances for showers and isolated thunderstorms will be possible throughout the day, with the highest chances across southwestern Washington (up to 25-30% chc). 10-20% chances exist elsewhere across western Washington. Winds will also begin to taper throughout the day and become light by Thursday evening. Broad upper level troughing is expected to persist over the Pacific Northwest Friday into the weekend, through model solutions begin to diverge on exactly how to handle the weakening and departure of this system. Ensemble cluster analysis shows highly divergent solutions for next week, or in other words, high uncertainty.

62

AVIATION

Southwesterly flow aloft continues with upper level troughing offshore. VFR conditions prevail this evening into tonight with high clouds streaming overhead. Marine stratus will redevelop along the coast tonight and slowly creep inland Tuesday morning. The areas with the best chances of seeing low ceilings will be OLM, HQM, and CLM with a 40-50% chance. However, there will be a 20-25% chance of seeing them farther inland across the Seattle metro. VFR conditions continue afterwards through the day Tuesday through mid- level clouds increase throughout the day with chances for showers beginning in the evening.

N winds this evening will become light overnight, switching to S/SW tomorrow and increasing to around 8-15 kt by Tuesday afternoon. Gusts 20-25 kt will be possible along the coast and around the Puget Sound area.

KSEA...VFR conditions through the TAF period. There remains a 25-30% chance of MVFR or lower cigs between 14-17z. NE winds this evening around 5-6 kt will become light tonight. Winds switch S early Tuesday morning and increase to 8-12 kt with gusts up to 20 kt Tuesday evening.

62/29

MARINE

High pressure will ease tonight into Tuesday before a stronger low pressure system begins to approach the coastal waters late Tuesday night. South to southeasterly winds will begin to increase Tuesday evening, with winds peaking during the day on Wednesday. Likelihood remains high through the coastal waters (60-90% chc) and through portions of the East Strait of Juan de Fuca, Strait of Georgia, and Admiralty Inlet (50-70% chc) for seeing gale force wind gusts through Wednesday evening. Elsewhere, winds will remain in Small Craft Advisory thresholds. The cold front will traverse the area waters Wednesday evening, following which winds will begin to decrease. Additional advisories may be needed into Thursday as southerly winds remain elevated through the interior waters from Puget Sound to the Northern Inland Waters, through winds greatly decrease area-wide by Thursday afternoon as the low pressure system weakens and moves southward into Oregon. Broad low pressure will remain over region through the end of the week.

In addition to winds, chances for thunderstorms will pose a threat to the area waters Wednesday and Thursday, through probabilities are marginal (10-20% chc). Lightning and an isolated waterspouts are the primary threats.

Seas 4-6 ft will increase Wednesday as the system moves through. Seas rise to around 8-12 ft, with the largest waves in conjunction with the strongest winds. Seas return to around 6-8 ft Friday into the weekend.

62

FIRE WEATHER

Fire weather concerns remain low through the next week. A stronger fall weather system will bring significant rainfall starting early Wednesday, with wetting rains expected area- wide. 1-2" will be possible along the Pacific Coast and the Olympic Mountains. Rainfall may pose a minor threat to highly sensitive and brand-new burn scars. Windy conditions are also expected across the area with gusts ranging from 20 to 35 mph. The bulk of the rain will fall on Wednesday. Chances for showers and isolated thunderstorms continue through the end of the week, but the risk of new starts is lower due to the isolated coverage and the increased fuel moisture from the wetting rains.

62

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Gale Watch from Tuesday evening through Wednesday evening for Admiralty Inlet-Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From Cape Flattery To James Island Out 10 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From James Island To Point Grenville Out 10 Nm- Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm-East Entrance U.S. Waters Strait Of Juan De Fuca-Northern Inland Waters Including The San Juan Islands.