Seattle, WA 98109 Weather

Synopsis

Upper level low remaining well south through Wednesday with zonal flow aloft over the area. Weak upper level trough moving through Thursday into Thursday night. Western Washington in between systems Friday. Lots of uncertainty remains in the weekend forecast with the best chances for a front moving through later Saturday into Sunday morning. Upper level ridge building Monday.

Short Term

Satellite imagery shows high clouds over the southern portion of the area with low clouds and fog near the water in Whatcom, Skagit and Snohomish counties. Clear skies elsewhere. Temperatures at 3 AM/10Z were in the mid 30s to upper 40s.

Not much going on today weatherwise. Large upper level low well south and light flow aloft over the area. Light northerly flow in the lower levels not strong enough to prevent fog and low clouds from forming especially near the Puget Sound. This scenario is also favorable for the development of Lake Washington stratus just after sunrise. All of the low clouds and fog will be gone by late morning. Highs in the upper 50s to mid 60s.

Little change in the upper pattern tonight. In the lower levels flow going light offshore but not strong enough to prevent patchy fog forming again in the early morning hours. Lows in the lower 30s to lower 40s.

Shallow low clouds and fog dissipating in the morning hours Wednesday. The light offshore flow will add a couple of degrees to the highs, mostly in the 60s. While not expecting any records we are getting to the time of year where record highs can be in the mid to upper 60s.

Weak upper level trough developing offshore Wednesday night with the trough axis near the coast by 00Z Friday. Nothing in the way of precipitation with the approach of the trough, just an increase in cloud cover. Lows in the mid 30s to mid 40s. Highs much cooler, in the mid to upper 50s.

Long Term

Extended models in good agreement early on with the upper level trough moving through Thursday night for a chance of showers especially in the mountains. Zonal flow aloft Friday with nothing embedded in the flow.

Once again confidence is low in the weekend forecast with a wide variety of solutions in the model ensembles. The solution with the most members is a front moving through the area Saturday night/Sunday morning. There is another group of solutions that has the front brushing the area during the same time frame. There is even a few solutions with an upper level ridge building over Western Washington. There is good agreement that said upper level ridge will build/be over the area Monday. At this point will go with the chance of rain Saturday, rain likely/chance of rain Saturday night into Sunday morning scenario with a drying trend Monday. Highs in the mid and upper 50s. Lows in the mid 30s to lower 40s. If we get the ridging Sunday night there is a good chance Monday will be the coolest morning of the season. Felton

Aviation

Southerly flow aloft turning more southwesterly by late this afternoon/early this evening and into Wednesday. At the surface, many terminals reporting light and variable winds while SEA, PWT and PAE favoring north to northeasterly winds with speeds 4-8 kts. As winds pick up in speed slightly late this morning to 5-10 kts, the north to northeasterly direction will continue to be favored in general.

Widespread VFR conditions in place for much of W WA this early morning, however lower cigs already present at BLI and PAE bringing isolated IFR/LIFR conditions there. As of this writing, starting to see some fog development at OLM as well and would expect at least IFR conditions to emerge there by 14Z this morning. Universal VFR conditions expected to resume by late morning and remain that way for the rest of the TAF period. Model guidance is hinting at isolated low cigs/fog by early Wednesday morning, but confidence is low regarding which terminal or terminals may see it.

KSEA...VFR conditions expected through the period, although latest guidance suggests prospects of low cigs/fog near 12Z Wednesday. As stated above, confidence is low at this time and will wait to see if this solution persists in future hi-res runs. NE winds 4-8 kts this morning shifting more NW by afternoon. Speeds will remain within that 4-8 kt range for the period, although may lean toward the higher end of that range in the afternoon and early evening.

18