textproduct: Seattle/Tacoma

SYNOPSIS

Mostly zonal flow will persist over western Washington as high pressure amplifies over the Great Basin region to the south. Warm conditions are expected throughout the week, with morning clouds and patchy fog, giving way to sunny afternoons. Rain chances increase into Friday as a front moves through. Cooler conditions arrive this weekend through early next week.

SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/

High pressure at the surface remains offshore with lower pressure inland. A zonal flow pattern with a weak ridge overhead and a jet streak in southern Canada will continue to funnel the onshore pattern through midweek. Most of the fog and low stratus has cleared out on satellite, though a pocket remains and will likely remain in the east portion of the Strait of Juan de Fuca area through the evening. Another round of fog and stratus is likely to form again Wednesday morning. The north/south interior and Olympics are the favored areas to see the lowest cloud decks/visibilities in the morning. and will clear by early afternoon. Probabilities for fog on Thursday morning are considerably less, but can't rule out a few valley areas seeing development. Temperatures in this period will continue to remain mild, and slowly increase up to Thursday with a few spots even seeing highs into the low 70s. Overnight lows will range from the upper 40s to low 50s. Winds will remain out of the northwest at around 5-10 mph for most areas.

HPR

LONG TERM /FRIDAY THROUGH TUESDAY/

The next frontal system will sweep across the region later Friday through Saturday. While still some spread within the ensemble guidance, around 60-70% of members suggest a fairly deep upper trough moving through the region. This will bring some increased winds across the area ahead of the system on Friday, with rain continuing into Saturday. That said, rainfall amounts aren't looking too impressive with totals around a tenth to a quarter of an inch through late Saturday. Colder air then settles into the region this weekend. Two things to consider with this for the weekend into the start of next week: 1) Any additional showers could bring some light snow accumulations above around 4,500 ft or so. 2) For the foothills and outlying locations, overnight lows could begin to dip down into the 30s. While confidence isn't high, those with agricultural concerns should keep an close eye on the forecast for potential frost headlines for the start of next week. Cullen

AVIATION

The current onshore pattern will continue through the TAF period with higher pressure offshore. There remains a pocket of IFR/LIFR stratus this afternoon (from KPAE northward into the north interior/Strait of Juan de Fuca). A large pocket of this stratus will likely retain in a portion of the strait through the evening (while the remaining north interior areas see the stratus lift slowly late this afternoon/evening. Another pocket of MVFR remains west of KOLM, but this will scatter out this afternoon. Remaining areas currently have VFR conditions, which will increase in coverage through this evening. Overnight, additional fog/low stratus is likely to reform (particularly in valleys in the north/south interior and the Olympics), and clear early Wednesday afternoon. Winds will remain out of the north at 5-10 kt, with lighter winds overnight.

KSEA...VFR conditions through the evening. LIFR conditions are likely to move in and in the vicinity of the terminal again Wednesday morning, mainly from 10Z through 18Z before clearing. Winds out of the north 5-10 kt, decreasing to 5 kt or less overnight.

HPR

MARINE

High pressure over the waters will remain for the next few days. In the short term, the primary marine impact will be continued fog over portions of the waters. Improvement over the eastern Strait of Juan de Fuca and adjacent waters has been quite slow, which will likely result in widespread visibility less than 3 NM again late tonight through early tomorrow morning. Confidence remains a little lower in how widespread the dense fog will be, so will continue to evaluate the need for an advisory as it expands tonight.

Otherwise, a building thermal trough along the Oregon coast will make its way north to the Washington coast, bringing northerly winds to the coastal waters. The strongest winds look to remain south of the local area, but there's around a 20-30% chance of some gusts to 25 kt across the inner coastal waters off of Grays Harbor on Wednesday and especially Thursday afternoon. Similarly, some marginal advisory gusts through the central Strait may develop Thursday as winds return onshore. Chances remain too low for any advisories at this time, but it remains worth watching. More significant marine weather is expected Friday as the next frontal system reaches the coastal waters, pushing inland through early Saturday. This will likely (>80% chance) bring widespread advisory winds to the coastal waters and the Strait of Juan de Fuca, with seas building to at least 8-9 ft over the coastal waters. Current probabilities of reaching 10 ft remain around 60% for the end of the week. Cullen

SEW WATCHES/WARNINGS/ADVISORIES

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