Are springs getting wetter? Not really, but lots more rain ahead THIS May
It was dry today! Morning clouds gradually broke up to afternoon sunshine west of the Cascades. Tomorrow (Wednesday) should be a spectacular spring day. Dry and about 10 degrees warmer. All of us in the I-5 corridor west of the Cascades should make it into the 70s. I expect little or no morning cloud cover and just thin high clouds drifting across at times.
Today on Twitter I had someone ask if the heavy rain was a sign of climate change (global warming). I promptly said NO, it’s just a return to wet spring conditions we haven’t seen for awhile. But I figured it’s time to take a closer look. Here’s what I found:
1. Total rainfall has not changed dramatically in the mid-late spring the past 100 years, there is very little change in the past century west of the Cascades. That’s at Salem, Portland, or even Redmond (Central Oregon)
2. There appears to be a very slight increase in rainfall during that time.
3. We have consecutive years with wet springs, then a few dry will follow. Or quite a few years wet with a really dry one sandwiched in. You get the idea, it appears to be somewhat random.
Get ready for a few graphs. Here’s the entire April+May rainfall record from Salem. This goes back to the late 1800s. Each bar is one April/May total rainfall. Click for a better view:
First, notice the wide variation from year to year. Some years very wet (1991, 1993, 1996), some quite dry (last year). The black line is the 10 year average. Not much change right? Maybe a minor peak in the late 1990s? The red line is the long term regression line. There has been a minor increase in rainfall during these 125+ years. What about Portland?
Similar wide yearly variation. Same up/down motion over the decades with that 10 year average. A bit of an increase in spring rain overall like Salem. We just went through 4 dry springs, so it was time for a wet one and here we are.
In case you’re wondering about east of the Cascades, in a severe drought right now, this is Redmond
Quite a change from year to year. We’re in a desert environment here, so a “wet” year is 2″ or more. 10 year average peaked around 2000 as well. Still, not a huge change over the past 80 years, but maybe a few more wet springs the past 20 years? It didn’t make it onto this image, but the regression line shows a minor increase across the entire period of record. It’s getting slightly wetter in spring in Redmond compared to many decades ago.
We’ve had some VERY dry May weather the last few years. In fact we haven’t had a wet May since 2013! I think it’s payback time...
We have a LOT of wet weather scheduled for Thursday through Sunday, and possibly next Monday. After the break tomorrow, a strong westerly jet punches right in the PACNW Thursday & Friday. The view Thursday night up around 18,000′
Then Saturday the one upper-level trough is swinging through with a deeper trough developing way out to the west
By Sunday a cold upper-level trough dips farther south with rain/snow way down into Central California. We are in a cool/unstable/showery airmass that day
The ECMWF model is likely too wet, but I think somewhere between 1-2″ rain is likely in the western lowlands by Sunday night. Notice the 3″ of rain in the Cascades. Much of this WILL fall as rain Thursday/Friday since freezing levels will be high
With the cool/unstable airmass, we’ll probably get a round of thunder & hail showers once again over the weekend. And with the large upper-level low overhead, the possibility exists that significant rain COULD fall in parts of Central Oregon. Fingers crossed!
There are hints that we dry out a bit next week. But looking at the GFS ensembles, it’s clear that plenty of members bring more showers overhead later next week.
At this point I’m not sold that we’re entering a warm/dry period starting next week. Models have been putting off a warming/drying trend recently. I’m thinking in this La Nina spring that we’ll see more troughs dropping in from the northwest. We will see.
The main message here is that we have a very wet 4 days ahead...I have plans to clean the garage, maybe catch up on some streaming? I know I won’t be doing any gardening after tomorrow for quite a few days!
Chief Meteorologist Mark Nelsen
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