Index, WA 98224 Weather

Synopsis

Upper level low off Vancouver Island will slowly move south ending up west of Hoquiam by late Friday afternoon. The low will weaken Friday night and Saturday before moving inland as an upper level trough Saturday night. Upper level ridge building over Western Washington Sunday. The ridge will remain over the area into the middle part of the week. A weak system will try an move through the ridge Wednesday.

Short term

Satellite imagery shows upper level low off Vancouver Island early this morning. Doppler radar has showers rotating around the low over most of Western Washington at 3 AM/10Z. Temperatures were in the 40s.

Upper level low slowly moving south in the next 36 hours. Showers rotating around the low moving through Western Washington at times. With the cool and unstable air mass over the area some daytime "heating" could also produce showers late in the afternoon/early evening hours. Snow levels remaining around 3000 to 3500 feet but precipitation amounts will be light leading to small new snow accumulations in the mountains. Highs Thursday and Friday in the lower to mid 50s. Lows tonight in the mid 30s to lower 40s.

With a stronger jet streak on the back side of the low, the low will begin to elongate and weaken Friday night. This will turn the flow aloft southerly which will keep the shower activity closer to the center of the low confining pops to the coast later Friday night. Lows in the mid 30s to lower 40s.

Low continuing to elongate and weaken Saturday with the jet moving inland well south of the area. Shower activity remaining confined to the coast. Highs in the mid 50s. Felton

Long term

Models in good agreement with elongated weakening upper level trough moving through Western Washington Saturday night. Not much moisture associated with the trough as it moves through the area. Upper level ridge west of the trough building over Western Washington Sunday into Sunday night. The ridge will remain in place into the middle of the week. A weak warm front will try and brush the coast the first part of the week but odds are high the front will only produce some cloud cover. By Wednesday another weak system will try and ride over the top of the ridge. Like the warm front the odds are high it will only produce some cloud cover for the area. Highs in the 50s. Lows in the 30s.

With 0.15 inches at Seattle-Tacoma airport, Wednesday was the 4th day in a row with measurable rain at the airport. Last time there was a streak this long was a 5 day streak May 12th through the 16th. Felton

Aviation

An upper level trough will remain offshore of Western Washington today into Friday, resulting in southwesterly flow aloft today turning more southerly tonight. Surface winds largely light and variable with speeds 5 kts or less, although some terminals are reporting southerlies with slight variations to the southeast or southwest with speeds slightly increased, ranging 4 to 8 kts. This latter direction and speed will become more widespread by this afternoon, although a return to some variability in direction is possible by this evening.

The air mass is somewhat unstable which will maintain the chance for showers throughout the TAF period. As such, a variety of cigs over W WA at the time of this writing. IFR conditions have emerged at OLM and PWT where low-level moisture often results in these conditions. While some improvement into MVFR will be possible this morning, lower cigs will linger here until the early afternoon. Some isolated MVFR obs are also present, but the majority of terminals are currently reporting VFR conditions. As the aforementioned showers remain possible, occasional dips down into MVFR cannot be ruled out, but overall the expectation is for widespread VFR conditions to persist throughout the TAF period.

KSEA: VFR conditions with showers being reported on the 09Z ob. While this may result in occasional dips down into high-end MVFR during the early morning hours, the overall expectation is for VCSH to persist but cigs remaining within VFR category. Overall southeasterly winds expected for the TAF period, however models remain consistent in a brief period around 00Z where north to northwesterly winds may be possible. Speeds will remain consistent throughout the period, ranging 4-8 kts.

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Marine

Low pressure out over the coastal waters will allow for offshore flow to persist into this weekend. A weak disturbance passing around this low may allow for increased winds for the coastal waters at times Friday and Saturday. Models have been shaky on speeds however, with some speeds approaching SCA criteria depending on the model run. At this time, will pass on any headline issuance but will advise future shifts to continue to monitor this time frame.

Seas will continue to ease, currently running 5 to 7 ft, subsiding slightly further to 4 to 6 ft by this evening before bottoming out at 3 to 5 ft this weekend. Looking ahead, seas will likely build early next week back to around 10 ft with the arrival of a long period swell into the coastal waters.

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Watches, warnings and advisories

WA: None. PZ: None.