9pm Sunday…

Well, it rained a bit yesterday, but officially nothing in Portland today. Showers were widely scattered and mainly concentrated over the Coast Range and Cascades. Saturday’s showers showed up and were about what I expected, but not today.

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Officially nothing measurable fell in Portland, which means it’s still the driest April on record with just five days left this month. I think there’s a very good chance it’ll remain the driest April we’ve seen…more on that below

WHAT’S AHEAD

A cool upper-level low (pool of cold air overhead) is sitting along the West Coast this evening. It’s going to stick around for one more day

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But that trough leaves late tomorrow as strong and very warm high pressure builds in the upper atmosphere. By Thursday its hot anywhere south of southern Oregon and quite warm here. We could be close to 80 again Thursday

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The ridge flattens for the first weekend of May, which may (or may not) lead to some decent showers

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But there doesn’t appear to be another cold trough headed our way for at least 10 days! By Wednesday the 5th of May, weak ridging is overhead again

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I’m only showing you one operational model, the ECMWF, but others are similar with upper level heights running higher than average the next 10 days…which takes us into the first week of May. It’s pretty clear that the much anticipated turn towards a wet spell is looking a bit weak. The GFS, ECMWF, & GEM models barely produce 1″ of rain in the lowlands of western Oregon & southwest Washington the next 10 days. And these numbers seem “irrationally exuberant” when compared with the upper-level maps.

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To summarize:

  1. This record dry spring will continue into the first week of May.
  2. You will need to continue watering this week, since I don’t see any significant rain (0.25″ or more) until at least Friday evening
  3. It’s possible we still don’t get a soaking next weekend either, but we don’t know yet.
  4. We have three guaranteed dry days Tuesday through Thursday as the ridge builds overhead

RECORD DRY SPRING

I figured we could get at least 1/2″ of rain this weekend through tomorrow plus a bit more later next week. Not typically a tough feat in April. That’s why I was poo-pooing the idea of seeing our driest April on record. But as of tonight it’s looking quite likely once the clock strikes midnight this Friday. The last 7 years…

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Notice last year was also in the top 5 driest Aprils… If we get more than .27″ rain before midnight Friday, it WON’T be the driest April on record at PDX. That may happen

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Of course something we have been talking about for the past few weeks has been the record dry spring. It’s amazing to think we’ve seen less than 2″ rain in all of March and April! This year just 1.81″ at PDX so far. These records go back to 1940. I also checked the downtown location (records back to around 1880); there appear to be only two other springs so dry, 1885 & 1926. Its the driest spring in Salem since 1926 as well…so far

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This is the 2nd spring with very dry March-April conditions. 2017 was a soaker eh?

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WHAT DOES THIS MEAN FOR MAY/JUNE, OR SUMMER?

First, there’s no reason to freak out (yet) over the lack of spring rain.

IF we get deep into May with these conditions, I’ll start getting concerned. If the dry pattern continues into early-mid June then we have a serious problem. That’s only six weeks away.

We already know that we need at least normal rain from this point forward to fill reservoirs like Detroit and Green Peter. And we also know drought conditions continue to creep north through Oregon.

Lack of mountain snow and warm temperatures have caused a faster-than-normal melt in the Cascades. The snow melt season had been delayed due to a chilly March, but now snowpack is below average in most of Oregon

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Does a dry March+April mean we’re headed for a serious drought? Possibly, I did a little bit of research this evening. I looked at the ten driest springs (up to this point) and then looked forward into May and June to see what happened. Here you go:

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Yep, it was a divided verdict. In 2-3 years we saw a soaking in May, or June, or a combo of both in 4 of those years. But in 6 of those years, drier than normal conditions continued as we headed into early summer (June). It is interesting that only one May saw less than 1″ of rain. That shows you how unusual it is to have a sub 1″ rain month in spring in Portland. That’s what we’re seeing right now.

The following summers? I didn’t check rain since we don’t get much in July/August anyway, but I did check temperatures. Only 1 of the 10 summers could be considered a “cool” one. All the rest were average or hot. Does that mean we will see a 9th consecutive warm/hot summer? We don’t know, but this would imply a dry spring can lead to at least a normal/warm summer.

So…there’s a decent chance we continue with a dry-ish spring, but there’s no reason it can’t still turn around.

For now, keep watering! Chief Meteorologist Mark Nelsen

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