We are entering the final stretch of Summer 2020. Just a little over two weeks left in August. So far this summer has been near normal temperature-wise. Notice no real anomaly (much warmer or cooler than average) since mid-May
Of course the first half of June was very wet, but since that time it’s been VERY dry. PDX has only seen 0.26″ rain in the past 8 weeks! But that’s not unusual and I sure don’t see any sort of real rain in the next 10 days.
We do have at least a four day heat wave on tap.
- Expect hot weather Saturday through Tuesday. The first two days will feature high temperatures somewhere between 98-102 degrees in the western valleys of Oregon and extreme SW Washington
- Next week looks warm/hot even after we get a “cool down” Monday.
- Very warm temps make it to the ocean beaches Saturday and at least part of Sunday.
- There’s no sign of thunderstorms west of the Cascades through this stretch
- By early next week we will have reached our yearly “allotment” of 90 degree days. That’s 13 days, but about to become 14-15 when new climate normals come out next year. For the 2011-2020 period, we’ve averaged 17 per year! This year we’ve seen one in May, June, six in July, and one in August (so far)
Weather Geek Talk
A strong ridge of high pressure has begun developing over the Western USA. By Sunday/Monday it looks about like this around 18,000′
Models have been trending with a stronger ridge and hotter atmosphere overhead this weekend and beyond. Today there is excellent agreement that over Salem we’ll see 850mb (C) temps jump to +19 tomorrow, +25-26 Saturday PM, +22-24 Sunday PM, then down to +18-20 Monday/Tuesday. I just checked my “August Chart” for 850mb temps. In the 10 year period from 1999-2009, the highest afternoon temp in August was 24.5 degrees. Folks, this is a “top tier” heat event coming up!
Alright, so what about surface wind direction? That becomes very critical from mid-August into fall. No offshore flow and we’re not going to hit 100 degrees. Tomorrow the pressure gradient goes flat across the Cascades/Gorge. No windsurfing at Hood River and calm conditions for that fire out in Mosier. But a “thermal trough” develops along the coastline tomorrow night and Saturday. Here’s a classic sea level pressure map for a heat wave; click for a closer view. Saturday at 5pm
I see 3-4 millibars easterly flow through the Gorge Saturday. Add in the crazy hot atmosphere overhead + all sunshine = we’re headed to/above 100 degrees. In theory we could be as high as 104, but I decided to go with a 102 Saturday, assuming easterly flow won’t be TOO strong. That’s after checking the 2008 and 2016 heat waves that produced 100+ temps in mid-August. You can check out blog posts from each of those events (lower right side of this page). Maybe most interesting is that there’s no reason to panic if it’s only 80-82 at noon Saturday; we can easily jump 20 degrees after noon in this pattern.
Saturday night should be a VERY warm night; possibly only dropping to around 70 well after midnight in the city. Easterly flow goes away Sunday, but with such a warm start + hot atmosphere we should still hit 100 in the afternoon. Of course if we have any significant high cloud cover (some models show that), we won’t hit 100. Here’s 2pm Sunday as the thermal trough is about to push east of the Cascades
Finally, a strong push of marine air should drop us 5-10 degrees Monday; “only” a high around 90 or so. But notice this chart shows 850mb temps (from ECMWF model) remaining above average through most of the next two weeks. Green is the average temp (notice it goes downhill in late August), blue is average of all 51 ensemble members. Each thin line is one ensemble member
Enjoy the cool temps tonight, and try to stay cool this weekend. Here’s our ocean beaches forecast; the left side forecast temp for each day is the central Oregon coast. Right side is up on the north coastline, including Long Beach peninsula. In general it’ll be quite a bit warmer the next few days up around Cannon Beach and Seaside
I’ll be on vacation tomorrow through most of next week so probably no posts until Saturday the 22nd.
Chief Meteorologist Mark Nelsen