Mount Vernon, WA 98273 Weather

Synopsis

A dissipating frontal system will spread some clouds across Western Washington today along with cooler temperatures. High pressure briefly rebuilds into the region on Friday before an area of low pressure brings a chance of rain to the area over the weekend into early next week. Dry conditions return areawide by the middle of next week.

Short Term

The last time it was this dry in Seattle three weeks into October, Michael Jackson, Whitesnake, and Pink Floyd had the top three albums in the U.S. (1987). And that statistic is likely to hold at least for a few more days. A weak front will fall apart as it comes ashore today. We'll see a few clouds and cooler temperatures today, but that'll be about the extent of it. High pressure briefly rebuilds into the area on Friday for a little more in the way of sunshine, but cooler temperatures (really, just more seasonal) will remain in place.

Forecast uncertainty starts to ramp later Saturday and beyond. Anomalously strong upper ridging building into southeastern Alaska over the weekend will aid in cutting off an upper low sliding southward down the British Columbia coast. And the models continue to really struggle with the path of the low. In a general sense, the ECMWF suite of ensembles are more aggressive with bringing some precip to the area and the GFS less so. The NBM is something of a compromise and spreads at least a chance of rain to the northwest half of the CWA by Saturday evening.

Long Term

Most of the forecast area retains at least chance PoPs Sunday into Monday as the models keep an upper trough over the region before eventually kicking it eastward. Beyond that, eerily quiet conditions are slated to return. Ensemble 500 millibar height plots from the Euro, GFS, and Canadian at days 6 through 8 keep anomalously strong upper ridging over the Gulf of Alaska and broad troughing just offshore of California. That's a recipe for a pretty quiet period of weather here in Western Washington.

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Aviation

Southwesterly flow aloft as a deteriorating front moves through W WA today. In the wake of this system, this flow will shift northwesterly by tonight and remain that way into Friday. Surface winds akin to previous mornings with terminals either reporting light and variable winds or favoring a north to northeasterly direction with speeds generally less than 5 kts. This afternoon, direction is expected to shift more west to southwesterly in the wake of the front with speeds increasing to range 5-10 kts.

As with the prior two mornings, much of W WA remains VFR although patchy fog has already started to develop, giving rise to isolated patches of MVFR, IFR and LIFR conditions. This has already started to impact BLI and OLM with rapidly varying conditions, oscillating between VFR and IFR/LIFR conditions and, as with prior to mornings, cannot rule out that this may impact other terminals on the east side of the Sound. That said, forecasts for these terminals have TEMPO groups to cover this possibility with timing akin to yesterday morning...with the main time of concern between 15-18Z. Although as in any fog situation, additional forecast amendments will likely be needed to cover this better. Any low clouds will scatter out 18-20z, but gradually lowering high and mid clouds through the balance of the day. Low stratus likely returns to the area Thursday night with stronger onshore low-level flow.

KSEA...VFR at the time of this writing with high clouds present. Cannot rule out prospect of a brief arrival of fog and low ceilings toward 15z thanks to high cirrus remaining thin. Any low clouds/fog that develops is expected to scatter out by 18z with VFR ceilings and increasing west surface winds to 10 kt in the afternoon and evening hours.