Last Monday morning, Portland Airport reported 0.01″ of rainfall in the gauge.  For practical purposes that amount is meaningless. But for the weather geeks, it means that our long stretch of no measurable precip at PDX since July 6 has come to an end.  At 67 days, it is the second longest period on record with no more than a trace of rain:

Be careful not to get caught up in “longest dry streak” climatology!  Suppose we had exactly 0.02″ of rain once every week for 6 months straight.   Then it would be (by far) the driest 6-month period on record, even if we never go more than 7-10 days at a time without a sprinkle.

More to the point, Portland hasn’t seen a soaking rain for 3 months now, by that I mean 0.25″ or more in a single day or 0.5″ over 3 days. And that is somewhat unusual. While it’s normal for the rain ‘faucet’ to shut off for 2-3 months every summer, we usually see at least a couple days with significant rain in the middle of the dry season. In the old days of the 20th century, in fact, it was common for July and August to each see nearly an inch of precip.  Summers were still (usually) dry back then, but it was more of an “oceanic dry” as opposed to “Mediterranean dry.”

A few days ago, weather models looked quite promising that we would see significant rainfall this weekend as a cool trough slid in from the North Pacific. But now it appears that the energy is going to dive south into California and extreme southern Oregon instead. Here is the ever-reliable 18z GFS for Saturday:

That’s great news for the fires in Northern California, but not good for us.  In fact NW Oregon and Western Washington stay mostly dry all the way through next weekend!

This means that vegetation in our immediate area will remain extremely dry for the time being. It also would leave us vulnerable to another round of fire risk, should another east wind event develop before our first real fall rain. Some recent models have hinted at that possibility in the long range, some time in the last week of September. But it’s definitely too early to know.

In the meantime, expect clouds and cool autumnal temperatures Friday and Saturday, only in the 60s in the western valleys. It will be the coolest weather pattern we’ve seen since early June. Then we go back to sunshine beginning on Sunday. Not hot, and the nights should stay cool enough to feel like early Fall!

-Karl