Cold Nights & A Sunny April Week Ahead

April 11, 2021

9:30pm Sunday…

I’ve been on vacation the past 9 days, a bit of bike riding down in the Moab (Utah) area with my son. Sorry, not many pictures because I was having fun. Actually I was home part of that time as well; but I’m back at work this evening. Calling it “work” is a bit of a stretch meteorologically since we are in a VERY stable weather pattern for at least the next 7 days.


First, the record cold this morning. We’ve seen LOTS of late season frost the past month, because we’ve seen much drier than normal weather. Keep in mind we’ve seen less than 2″ of rain in six weeks in Portland! Drier air = less cloud cover = colder nights. Basically west of the Cascades we’ve been in more of a “continental climate” than usual. Right now dewpoints are down in the 20s in the metro area. Sometimes we don’t see them get that low all April long. Our spring in Portland (so far) is similar to a typical spring you would experience east of the Cascades. Wide temperature range; nights running cooler than average, but daytime slightly warmer. Last night we saw widespread cold readings. Look at the Portland metro lows:

Lots of upper 20s, even a few mid 20s…pretty cold for mid April! Portland airport dropped to 32 degrees, the first time we’ve seen frost beyond April 10th since 1982. Quite an impressive reading considering the metro area is much larger than 40 years ago, more of an urban “heat island” now. Plus our climate has warmed a bit in general. We don’t see many record lows in Portland the last couple of decades. Record lows were also set in several other locations west of the Cascades

My peach tree is blooming and still LOOKS okay. Maybe it needed to be under 27 degrees to do significant damage, we will see within the next couple of weeks.

Tonight won’t be quite as chilly as the airmass has warmed a bit. Sure, some frost for outlying areas, but everyone should be at least 2-3 degrees warmer than last night.


When I came in and looked at the maps/models today, it became obvious we are in for almost continuous sunshine for the next week for much of Oregon and SW Washington. That includes the coastline.

In the upper atmosphere, a ridge of high pressure (zigzag blue line) and its sinking airmass is developing just to our west and north, keeping weather systems away. But a cold pool of air (upper-level trough) is coming down the back side of that out of Canada. By Tuesday it is centered over the Idaho/Nevada/Utah area.

It’s far enough south and east of us to keep cloud cover away. But we get a relatively strong northeast flow overhead. That’s offshore flow. Even though the air starts cool, this pattern under strong April sunshine will push our temperatures above normal. By Thursday the setup is strong high pressure to the north with a low south. This can be (and will be) a very stable weather pattern. It’s called a “Rex Block”.

Then between Thursday and Saturday the warm ridge expands south and east over us as the low moves away. A warming atmosphere means high temperatures climb from just above average to MUCH above normal. We’re headed from the lower 60s tomorrow to mid-upper 70s Saturday west of the Cascades. After tonight the widespread frosts west of the Cascades should disappear as well.

Meanwhile a deep layer of offshore wind flow continues all week, although it may weaken briefly Wednesday/Thursday. Check out the WRF-GFS cross-section over Portland; Wednesday afternoon (right side) through Sunday afternoon (left side). Yellow line is around mountain pass elevation.

Offshore flow almost the entire time, plus a warming atmosphere. No cloud cover (maybe a few thin high clouds). It doesn’t get better than this anytime April through June!

At this point we don’t appear to be setting up for record high temperatures…all in the 80s mid-April and beyond. But we’ll go from a perfectly average 60, to around 70 by Wednesday/Thursday, to upper 70s Saturday and possibly Sunday. For the weather geeks, 850mb temps need to make it to at least +10 over Salem this time of year to hit 80 in Portland with perfect conditions. That COULD happen Saturday, we will see. Regardless, this 7 Day forecast is something else for mid April!

When will it end? ECMWF ensemble precipitation forecasts imply the ridge breaks down somewhat next week, so it’s safe to assume showers will appear at some point after NEXT Monday

That’s it for now, enjoy the sunshine!

Chief Meteorologist Mark Nelsen