Summer has arrived early in the PACNW; no end in sight to the unusually warm and dry weather

Remember when it seemed like the cool and wet weather just wouldn’t end back in April? What a change! May ended up the warmest on record in Portland and rain pretty much disappeared after the first week of the month. So now it’s been about a month of much warmer than normal temperatures and mainly dry.

Take a look at 80 degree days so far compared to previous years AT THIS POINT. Last year we had ONE 80 degree day by June 5th. This year’s = 16. That’s the 2nd highest number of 80 degree days. I think Salem was something like 3rd highest; so it’s not just about an extra warm urban heat island in Portland.

Portland hasn’t seen measurable rain in 22 days; pretty rare for late May to early June. It’s unlikely we get anything other than a few drops (at most) during the next week. IF we don’t get more than a tenth or so before the 15th, it’ll be the driest mid-May to mid-June we’ve seen

I’ve noticed just during this last week that grasses along the freeways are drying quickly, turning from green to brown. Often that doesn’t happen for another 3 weeks or more. That means the top layer of the soil is drying out quickly! I’ve begun watering everything at home as if it’s July and you should be doing so as well. Take a look at the “rain frequency” chart for Portland during the summer months

This graphic shows the chance of rain on ANY ONE DAY as we go from June through mid September. Locals know that late July to early August is the driest time of the year around here, that shows up nicely on the graphic. But also notice the drop off once we hit mid-June; seems about right doesn’t it? Soon after Rose Festival ends we often turning reliably warmer and drier. Each year is different, but it seems many years we get a first heat wave (3 days at/above 90) in that 2nd half of June as well. I’m hoping we get some sort of cool trough at some point in the 2nd half of this month to give us at least an inch of rain before the summer dry spell really kicks in.

Unfortunately my gut feeling is that the summer dry spell has already begun and the chance for significant rain (an inch or more) is slipping away quickly. Why? Take a look at what we’re seeing in the weather forecast models. First, the big picture shows higher than normal upper-level heights (stronger ridging that normal). The main (and weak) jet stream is well north of us. An upper-level low has been lingering over California for quite awhile; cooler than normal down there. This setup is keeping Pacific weather systems farther north than usual for late spring and early summer = little or no rain. This setup is allowing thunderstorms to pop up each afternoon over the southern half of Oregon, but these should remain south and east of NW Oregon and SW Washington

By Saturday that low over California has moved east, only to be replaced by another!

That leaves us dry, although thunderstorms are still possible east of the Cascades in that easterly flow north of the California low. Noticed the ANOMALY chart for the same time shows we are still seeing higher than normal heights overhead

Jumping ahead 5 days, the anomaly through the 16th shows those higher than normal heights continuing most of NEXT week. This is the ECMWF ensemble average, but other models are similar.

This tells me the dry or nearly dry weather continues for another 5-10 days. There are SLIGHT hints that the ridge might be slightly farther offshore in the 10-15 day period and allow a cooler trough/troughs to drop in...maybe. This is the 16th-21st 5 day average

Looking at ensemble 24 hour rain total through 15 days, there are hints the 3rd week of June (”2″ and “3″ in my writing means 2nd and 3rd weeks of June) could be showery. This is the Canadian model.

That said, a week or two ago there were hints this coming weekend could be wet too. That didn’t/won’t happen.

SUMMARY

This unusually dry/warm pattern continues until further notice
But there’s no sign of hot weather for at least a week after tomorrow
Thunderstorms should remain over the Cascades and eastward the next few days, but one could slip west of the mountains Thursday or Friday. That’s most likely south of Portland.
There’s a chance (but just a chance) we get some sort of showery pattern sometime after the 15th, but not before that time.
Keep watering everything!