A Hot Monday; Cooler Temps Ahead Rest of This Week

July 20, 2020

10pm Monday…

It finally happened, after a very cool start to July we’ve seen two consecutive hot days. We hit 90 in Portland yesterday and 93 today

This tied for the warmest/hottest temp so far this summer. At this point we’ve seen 4 days at/above 90 in Portland this summer. Keep in mind all the other numbers below refer to the entire summer. A typical summer will see around 13 days at/above 90 in Portland. Some crazy hot summers in there! (2014, 2015, 2017, 2018). Last year and this have been so much more reasonable.

June was wet (although not cool), and the first 10 days of July were very cool. That prompted the annual worry-fest about whether “this could be the year without a summer”. But the past 10 days have brought our temperature for the month close to normal. This definitely isn’t and will not be the year without a summer

Something really sticks out on this map…do you see it?

It’s Newport. Check out the HIGH of 52 today; similar to a January day out there! And it’s much cooler than other coastal stations in the 60s to lower 70s. What’s going on? It’s the very chilly Pacific Ocean sea surface close to the coastline. The latest sea surface temps here, along with some buoy water temps

Notice most of the Pacific offshore is in the 60s, or at least upper 50s and 60s. But a narrow ribbon of 48-55 degree water is right along the beaches. This is called “upwelling”. Gusty northerly and northwest wind blowing down the coastline causes a slight “rightward” movement in surface water (farther offshore). That allows cold subsurface water to replace it; I remember learning about it during a 5th grade school visit to the beach. I sure remember that field trip from Monitor Grade School. We all got into BIG trouble for wading into the ocean and had to write an essay about how bad we were…but I digress a bit. Scary to think about as a parent now!

Diagram credit: NOAA

You can read more about upwelling here and how critical it is for our fisheries along the PACNW coastline.

The downside is of strong upwelling? Colder than normal water temperature right long the coastline = chilly onshore wind. When we turn hot and the marine layer is thin, temperatures will vary dramatically depending on location. For example that Newport high of 52 is at the airport right at South Beach.

Looking at those other high temps, I would say the high at Newport was really more like 60 degrees. You get the idea…right on beaches = cold, slightly inland = just a little cool.

So what’s ahead? More of the same. We haven’t seen significant rain in a month and no model shows showers in the next 10 days either! Check out the ECMWF ensemble forecast for the next two weeks; this is 24 hour precipitation. Only 5 of the 51 ensemble members produce more than .10″ rain in Portland through Monday August 3rd

A weak push of marine air tonight should keep us below 90 tomorrow, then a major push tomorrow evening means highs around 80 for Wednesday-Friday. Models then develop upper-level ridging (warming) overhead Saturday through next Monday/Tuesday. Expect warming again. This is the typical seesaw west of the Cascades in midsummer. Very warm, cooling, then warm again

Looking at this you can pick out the days that are best for certain activities. Mow the lawn on cooler Thursday, hit the lake or your pool tomorrow and this weekend. Regardless, enjoy our fantastic Pacific Northwest summer weather free of high humidity and extreme heat!

Chief Meteorologist Mark Nelsen