The last 12 days (not including today) have been a classic example of “Mediterranean summer” weather in the Pacific Northwest and the Portland Metro.  There have been almost no clouds in the morning, and temps have been 82 degrees or warmer every day since July 25.  Basically we had about 6 hot days followed by several reasonably warm days.  Of course in late July and early August, even “warm” days (i.e. mid 80s) feel quite hot in the afternoon.  

 

Most Portland summers experience at least several weeks of this kind of warm to hot weather; if not all in one stretch then in two or three bouts between June and early September.  There are a few exceptions of course, the most recent example being 2011.  There was no appreciable warm pattern until the 2nd half of August, and our longest stretch of heat that year came in September.  So basically only 2-3 weeks of Mediterranean temps, and it all came at the very end of the season when kids were heading back to school. 

 

Today’s rain showers mark the end of about 6 1/2 weeks with no significant rainfall in the city, other than a few light sprinkles.  The total was 0.19″ this morning…not enough to water your lawn or garden, but still a pretty significant rain event considering that we are in the middle of the ‘dog days.’  As you may recall we had a strong ‘Juneuary’ pattern a couple months ago, but then the rain suddenly died out during the 3rd week of June.  Dry is not the same as warm though; there was a long stretch of marine clouds and cool temps for a two-week period centered on the 4th of July.  Beginning around the 12th-13th of July, we finally started to see high temps trending above 80 degrees most days.

 

Looking ahead…it appears today’s cool and rainy pattern is just going to be a temporary blip.  We have more sunshine and at least near-average temps coming up for the weekend and early next week.  Weak upper-level ridging tries to make a comeback on Sunday and Monday; here is the 500mb anomaly map for Sunday afternoon:

 

That will give us at least a couple more days similar to the beginning of August:  ample sunshine and highs in the vicinity of 85.  Probably some low 80s in there as well.  But by next Wednesday, a weak upper-level trough is hanging out in our region instead:

 

 

Things get a little more serious as we go into next weekend.  The anomaly maps for the afternoon of Sunday the 16th:

 

Uh-oh…that looks like a serious punch of cool air, likely with some more rain somewhere between Eugene and Vancouver.  It’s still 10 days away so there’s plenty of time for maps to revise the forecast.  But it appears that we have another bout of below-normal temperatures (at least during the daytime) on tap for some time in mid-August.  The 12z GFS ensembles for this morning hint at this cool/wet pattern coming up:

 

Depending on the depth of the trough and how cool the airmass is, our weather late next week and the following weekend could feel quite like early fall; or at least, “fake fall.”  It’s a bit more common to see this pattern pop up in late August; we haven’t seen this kind of early cool spell for quite a few years.  But remember…a fake fall is usually just that.  We can still get lengthy stretches of sunny 80s well into the month of September, and even early October on rare occasion.  Of course the deeper into the autumn months that we go, the cooler the nights will be; even if the days still feel like summertime.

 

I don’t think we’re going to get any kind of chilly low temps next week, though.  The change in daylight by the 13th-14th of August isn’t really enough yet, to give us the kind of nighttime cooling that we sometimes see at month’s end.  Most likely it will take the form of cool and overcast days, with high temps only in the low/mid 70s for a while.  Nights in and near Portland would probably cool off into the 50s, just not the widespread 40s we tend to associate with a “real” autumn chill.

 

Depending on how much rain (if any) that we get in the long term, we just might sneak through this summer without a serious flare-up of wildfires.  The cool, wet June and marine clouds in early July, helped to put a delay on the onset of fires; only in the past week or two have we seen large ones beginning to pop up in a few spots, such as near Hood River.  

 

For now though, enjoy the return to summer sunshine for a few days!  -Karl