Perfect early fall weather ahead; plus fire season update and hot summer stats

September is here and the weather looks amazing most of the time over the next week or so. I was out of town most of Labor Day weekend so I missed the great lightning show across the south and southwest metro area. This was just one amazing shot from Annie Snyder in West Salem. Setting sun was behind her, rain to the east with the (double) rainbow, then lightning thrown in as well. What a catch!

Thunderstorm in Salem 9/2/2023(Annie Snyder - West Salem)

These were very wet storms that brought up to 1″ of rain in some of southern/west metro spots. Nothing fell in the city of Portland

But the big rain was along the Marion/Clackamas county line from Scotts Mills up Butte Creek. Some spots picked up 1.50″ or more. Large hail (up to 1″ size) accompanied those storms

WHAT DO WE SEE THROUGH MID-MONTH?

Comfortable, warm days and cool nights are likely through the 15th. Expect lots of days in the 75-80 degree range
Most days will feature mainly sunny or partly cloudy skies; no sign of long gray periods ahead
Little or no rain falls through the 15th
No sign of a hot spell OR dry/dangerous easterly wind for at least the next 8 days.

Basically we have a dependably warm/dry period for at least the next 10 days. Enjoy!

BRIEF SUMMER RECAP

I’ll publish another post later this week or early next when all the summer data comes in. But I think we all know it was another hot one. Meteorological summer ended August 31st. August 2023 was the warmest month on record in Portland, just barely edging out LAST August. Notice the theme...most of them have occurred in the last decade (in yellow)

Some other stats:

PDX: 3rd hottest summer. All 5 hottest summers have been since 2018

SALEM: 4th hottest summer, 2021 and 2022 were #1 and #2

REDMOND: 4th hottest summer

ASTORIA: 6th warmest summer, 2015 and 2016 were #1 and #2

We’ve picked up 24 days at/above 90 in Portland, the third consecutive summer to do so

WHAT’S AHEAD

Upper level troughing the past few days has given us cooler temperatures, cloud cover, and light showers. That changes heading into the 2nd half of the week. Here’s the 500 millibar (18,000′) pattern right now...

Notice the troughing goes away by Saturday and is replaced by a stronger system sitting in the Gulf of Alaska; we’ve got a nice 2nd weekend of September on the way!

A weak disturbance swings by later Sunday and Monday. It’ll only give us more clouds, cooler temps, and a shower chance

But it’s right back to upper-level ridging along the West Coast much of the rest of next week. Here’s the view from the ECMWF model NEXT Thursday

The result is that we’ll see very little rain through mid-month. Only a few scattered ECMWF ensemble forecast members produce .10″ rain in the next 2 weeks.

This is the time of year when the rain chance starts to pick up. Here’s one way of showing the increase

Or...how about the first time we pick up at least 1/2″ rain in September or October? Often it’s by the 2nd/3rd week of September. Except last year we waited until the 3rd week of October; that’s very rare

FIRE WEATHER

The first round of thunderstorms that last week of August started numerous forest fires over/west of the Cascades. We are VERY fortunate that temperatures cooled right after that time. Some showers have fallen in the mountains, and there’s no sign of a dangerous hot/dry easterly wind for at least another week. Take a look at the nearly smoke-free skies across Oregon this afternoon

16 large fires are burning in Oregon, during most of August there were only 4. Yet less than 100 acres burned in the past 24 hours; most of them are just smoldering or burning slowly. With dry weather ahead, it’s fair to assume fire activity will pick up a big more in the next week. I don’t see any additional lightning outbreaks = good news!

MOST Septembers/Octobers we don’t see much fire smoke in the metro area; but we all remember when it DOES happen! Each horizontal line here shows maximum PM 2.5 concentration for the past 24 years in September/October. Notice we’ve had 3 “events” during that time: Eagle Creek Fire (Gorge) in 2017, Cascade Mega-Fires in 2020, and last year’s October fires in the Cascades. Notice the general decrease in air quality each October; that’s the beginning of fall inversions = more pollutants trapped in the lowest atmosphere.