Happy Fall everyone! The past two weeks have been a classic mix of autumn weather in the Pacific Northwest: periods of rain and wind, some sunny days, and seasonable temperatures mostly in the 60s and low 70s. This is quite a far cry from last year, when summer-like conditions continued into the 3rd week of October. Leaves are actually beginning to turn on time this week as a result, and peak foliage in the lowlands looks to be only 1-2 weeks away.

We actually have a brief taste of summer-esque warmth on the way for Thursday-Sunday this week, when Portland could hit the low 80s for one final round this year. But first…

I’m not going to do a long summer summary this year. Mark Nelsen from KPTV Fox 12 News wrote an excellent blog back in mid-September, with tons of stats. To briefly cover the key points though: it was another historically hot summer in much of the PNW, and the 3rd hottest on record at PDX. Arguably you could say that summer began around May 11-12 this year, which is extremely early. Even though May is categorized as a spring month. But from mid-May through mid-September, we had only two significant rainfall events at PDX, and less than 2″ rain during the entire 4+ month period. The very long summer dry season left native vegetation looking parched, though vegetable gardeners enjoyed another bumper crop year.

THE STATS

June: 66.4° (+2.2)

July: 73.4° (+3.2)

August: 75.4° (+4.8) WARMEST MONTH EVER RECORDED

We just barely beat last August for mean temps, though that was due to warmer nights this year. That makes Summer 2023 another extremely warm one. As the graph for Northwest Oregon shows, there was a “sea change” in our summer climate around 2013-14. We haven’t had a classic cool summer since the early 2010s!

The graph is a bit squished due to the screenshot format, but it’s the best I could do on phone. What stands out for the Willamette Valley region is that our summers started to trend upward in the early/mid 2000s, but then cooled again for several years after (with the notable exception of 2009). But the trend since 2013 has taken us into truly uncharted territory. In fact, at least in the Portland urban heat island, it’s possible that we have shifted from the “cool Mediterranean” zone to the “hot Mediterranean” like what was traditionally found in southern Oregon and northern California. Basically Portland has become almost like the “old time” summers in Roseburg or Grants Pass (or for that matter, The Dalles).

100+ days: 4 (4-way tie for 5th place)

90+ days: 26 (4th)

85+ days: 58 (new record)

80+ days: 91 so far (new record)

60+ nights: 60 (2nd)

Here’s the big theme: we didn’t set records for 90+ or 100+ days this year, but we did have a record number of 85+ and 80+ days. In fact there was a 10-week period between the mid-June rain event and the late August rain, in which there were only 8 days below 80°. That part was very unusual. Typically we get at least one solid stretch of cloudy skies & temps in the 70s at some point between late June and August. This year we could only manage a few random upper 70s in the middle of all those 80s and 90s.

Also, 2nd place for number of 60°+ nights? Uggh…that’s a major contributor to sleep difficulties if you don’t have A/C.

Then September had a warm 1st half and cool 2nd half, ending up less than 1 degree above normal. Fairly generous rain in the final week of the month helped put a smoldering end to our fire season.

LOOKING AHEAD

We have four very nice days coming up! More like late summer than fall, in fact: A ridge of high pressure will form in the upper levels, and remain near the West Coast until Sunday. Here’s the GFS map for 5am Friday morning:

Today will feature full sunshine and temps likely approaching 80, which we haven’t seen in a while. Tomorrow and Saturday should be even warmer, in the 82-85 range. East wind should pick up for today and tomorrow and then subside a bit by Saturday. Keep in mind that the same airmass in summertime could probably get us to 92-95° instead. The October sun is weak though…and that means we don’t get the same surface heating we see in summer.  Instead we get what some call “Indian summer,” but I have a special term for when it happens earlier in the fall:  Mixolydian summer. That means it’s almost exactly like summer during the daytime, but nights are longer and cooler. (The name comes from music theory; Mixolydian is a scale mode similar to the major key, but with one lowered note to make things sound cooler and edgier!)

Sunday night the ridge moves out and a trough flirts with us early next week. Tuesday morning:

This will likely bring back cool temps and rain, at least for a little while. As of right now it’s still unclear how the end of next week unfolds.

There is an annular eclipse in SW and south central Oregon on Saturday the 14th, peaking shortly after 9am in our region. I’m going to be in central Oregon, most likely either Sunriver or La Pine, to view it. In mid-October sky conditions can be fickle, especially if a trough sets up nearby. That could potentially complicate things even east of the Cascades, and be a total loss for the west side. On the other hand, even in a dry pattern morning fog could be a big issue for the western valleys. Going to the east side at least improves your chances at this time of year, though.

Even if you aren’t in the zone of full annularity, you still have the ability to observe a partial eclipse, weather permitting. Safe eclipse glasses are a must for this event, no matter where you are. Even 5% of the sun uncovered is enough to cause serious vision loss!

Get out and enjoy the next few days…we probably won’t be this warm again until late next spring!

Karl