Area Forecast Discussion

SYNOPSIS

Cooler and wetter conditions will settle over the region through the middle of the week, with chances for thunderstorms this afternoon over the Cascades. Drier and more seasonable conditions will return by the end of the week and into the weekend as a high pressure ridge builds offshore.

SHORT TERM /TODAY THROUGH THURSDAY/

An upper level low pressure system will slowly progress inland over Oregon throughout much of the week, bringing in cooler temperatures alongside periods of rain. Wrap around moisture has already made its way northward into southwestern Washington this morning with light accumulations. Showers will continue to move northward into the region throughout the day today. Temperatures will cool considerably today as this system works its way into the region, with highs reaching the mid 50s to low 60s. Instability from the aforementioned low may also produce some lightning strikes over the western Cascades this afternoon, but any thunderstorms are unlikely over the lowlands.

The upper level low will continue to meander eastward towards the Intermountain West on Wednesday, maintaining chances for shower activity and cooler temperatures. Wednesday will be the coolest day of the week, with temperatures mostly peaking below the 60 degree mark across western Washington. Snow levels will remain above 5000 to 6000 feet through mid week, limiting any snow accumulation to the higher mountain peaks.

Conditions will dry out for much of the region on Thursday as moist northwest flow develops aloft, with light showers tapering off over the Cascades. Temperatures across the region will begin to rebound, with highs reaching the upper 50s to lower 60s. Cloudy skies Thursday morning will give way to mostly sunny skies by the late afternoon.

LONG TERM /THURSDAY NIGHT THROUGH MONDAY/

Forecast models continue to show an upper level ridge building offshore through the extended, though models are showing variability over how far eastward the high pressure will expand. Northerly flow aloft will maintain seasonable temperatures through the weekend, though both ensembles and deterministic models are hinting at the potential for showers to develop on Sunday and Monday as a positively tilted trough brushes the eastern edge of the high pressure ridge.

15

AVIATION

South to southeasterly flow aloft remain in place over W WA as a cutoff upper level low off the northern California coast gradually shifts eastward. Surface winds have largely shifted south to southwesterly over most terminals, although some have gone light and variable. Little variation in direction for much of the TAF period for most terminals, although CLM and PAE, being more susceptible to influence from the Strait, could see a more northwesterly direction emerge late this afternoon/early this evening. Speeds expected to increase areawide by late this morning, generally ranging 8-12 kts.

VFR conditions in place this early morning and will continue throughout the remainder of the morning, possibly into the early afternoon. Cigs will continue to lower throughout the day as the combination of the aforementioned upper low cycling moisture into the area with onshore flow returning, also adding moisture, allows for an increase in low-level cloudiness. Widespread MVFR conditions expected to emerge this afternoon, however some sites could see them sneak in as early as late morning, such as terminals more prone to lower cigs /HQM, OLM and PWT/. Showers expected over the area late this afternoon or early this evening and that risk will extend into tonight. Activity is expected to taper off during the overnight hours, although lower cigs will remain in place.

KSEA...VFR conditions will continue for much of the early morning period and likely into mid-morning before MVFR conditions likely hold off until late morning/early afternoon...as latest obs and model solutions have backed off on inherited aggressive timing. Afternoon shower development still on track, with precip at the terminal still expected in the late afternoon and into the evening before activity tapers off overnight. Even though rain ends, plenty of low-level moisture will keep cigs MVFR for the remainder of the TAF period. Surface winds S/SW 4 to 8 knots this morning before rising to 8 to 12 knots this afternoon and into the overnight . period.

18

MARINE

Weak low pressure will remain over the inner coastal and interior waters into midweek with broad high pressure remaining well offshore. A modest increase in onshore flow today may be enough to boost winds in the Central and Eastern Strait to low-end SCA criteria. As such, left inherited headline in place. Gusty north to northwesterly winds and steepening seas are expected over the outer coastal waters on Wednesday. Models have been very consistent over the past 72 hours /at least/ that seas are likely to exceed 10 ft over the majority of the Coastal zones. Given that level of confidence and in collaboration with PQR, went ahead and issued an SCA to cover this event. Although winds increase, SCA thresholds for wind are only met out in the outer coastal waters. Rough bar conditions may emerge for Grays Harbor bar Wednesday evening, but with that being 4 periods out /today, tonight, tomorrow, tomorrow night/, felt it best to leave that potential headline to future shifts. Winds ease, seas subside and the flow turns more northerly late this week in response to a strengthening surface ridge over British Columbia.

18/27

HYDROLOGY

No river flooding is expected over the next 7 days.

SEW WATCHES / WARNINGS / ADVISORIES

WA...None. PZ...Small Craft Advisory from 3 PM this afternoon to 11 PM PDT this evening for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory from 11 AM Wednesday to 11 AM PDT Thursday for 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.