Almost every September there is a transition to fall-like weather, and there is no going back. We are in that transition right now.
For Washington state, regular rains will return, temperatures in the 80s and 90s will be a memory, and wildfire season will be over.
Before I tell you the weather forecast, let’s take a look at this month’s climate.
As for temperature, the average September maximum temperature in Seattle (thin red line) ranges from the mid-70s like summer to the mid-60s (the vertical red line shows today). It’s not 90 degrees at the end of the month anymore. Ever.
As for measurable rainfall, there is only a small upward trend after the typical “wet” period in late August.
But there is one interesting oddity I noticed: we usually get a pretty big shower in the middle of the month. Take a close-up look at the rainfall climatology below: you can see the spike in rainfall in the middle of the month. Buy why?
Enough about the climate…..let’s look at the weather forecast for the next week or so.
Temperature forecasts for Seattle and Pasco call for fall-like weather.
Temperatures in Seattle will remain at 60 degrees for the next ten days.
Pasco, in the Tri-Cities, temperatures dropped to the 70s and stayed there.
And yes, there will be some localized rain to end any talk of wildfires from the top of the Cascades to the west.
Rainfall totals are expected, although Tuesday (below) is forecast to see light to moderate rainfall from the Cascades to the Pacific Ocean, with significantly higher values in the Rocky Mountains. Importantly, wildfire-prone eastern Oregon is also seeing some moisture.
The next 96 hours (as of Thursday morning) were the same but a little wetter.
The reason for this transition to wet-cool conditions is because a series of upper levels will form over or move into the West Coast, which is illustrated by the upper level (500 hPa, about 18,000 ft) weather map on Sunday afternoon.
Enjoy the fall weather. Our trees will be lush and the smog will soon be a thing of the past.
