Finally! The “Rain Faucet” is about to take a break….

Finally! The “Rain Faucet” is about to take a break….

What a wet spring it’s been!  After getting more than double the normal rainfall for March, we’ve pulled it off again for April.  As of the 28th, 1.65″ have fallen at DLS, with little chance of more between now and Sunday night.  That will make this the 3rd wettest April in airport history.

More to the point:  this spring has been consistently dreary and drippy, with many more rainy days than normal, very few sunny days, and NO warm spells.  March had 19 days with measurable rainfall (traces don’t count), way more than the historical average of 10 days.  But how many has April had?  There we encounter an annoying data discrepancy:  Wunderground says we had 15 days with measurable rain, while NWS Pendleton insists only 13 days.  D’oh!  At least both sites agree on the 1.65″ monthly rain total…

By the way…the month of April has trended considerably wetter over the past 50-60 years.  Based on the NWS Pendleton data, between 1951 and 1980 the airport averaged 0.50″ in April.  Compare this to 1981-2010, when the average was 0.79″ !

Here is the graph for historical April precipitation, for the North Central Oregon region as a whole:

The little black dots on the green zigzag line, represent each April’s rainfall total for the region.  The gray line represents the average rainfall for the ENTIRE historical period, 1940-2016.  As you can see, we tend to yo-yo back and forth between wet and dry Aprils.  In particular, here in the Cascade rainshadow the variability from one spring to another can be dramatic; notice how the really dry Aprils have nearly zero rainfall while the wettest ones are more than double the long-term average.

The blue line is what we call a “trend line,” used to look at the long-term climate picture.  As you can clearly see, it slopes upward, a sign that our April climate is getting wetter.  However, there are often cycles of wet and dry years (or warm/cold for that matter), in the short term.  The red curve is an effort to track these short-term cycles, by comparing each year’s rainfall to the few years before and after.  Notice how before about 1975, the red curve is below the grey line most of the time; from the late 1970s onward it spends far more time in the upper half of the graph.  This is testament to the string of wet Aprils in the late 1980s/90s (and again in the early 2010s), as well as the higher climatological averages we’ve seen since 1980.  Drier Aprils were far more common in the middle 20th century; in fact, 8 of the 9 driest Aprils occurred before 1978!

Another weird feature of this spring has been the total lack of warm spells.  Would you believe we STILL haven’t hit 70 in The Dalles?!?  Today was actually the date of the 2nd-latest spring 70 on record (April 28, 1963).  The all-time record comes on Monday.  There’s a slight chance that we could sneak up to 70 degrees tomorrow Saturday, in which case we’d set a new 2nd place position.  However…at this point the odds are that we don’t hit 70 until next Tuesday or Wednesday.  So 2017 will probably, in fact, set a new record for late 70 in The Dalles!

Looking at next week, the first week of May….as of right now it sure doesn’t look like a springtime “heat wave” pattern where we see temps well into the 80s.  But we will likely see at least one day in the 70s, possibly as many as three days (Tuesday-Thursday).  More to the point….early May is looking much, much drier than March or April have been.

We may not be warm the entire time, presumably due to weak disturbances occasionally brushing by.  But the basic idea with respect to rainfall, is that the spring faucet is now switching to the “OFF” position for a week or two.  That means mostly dry conditions, and seasonably mild temps at the least. If you live on the west side and your garden is waterlogged, this might give you a fighting chance to plant something in a couple weeks’ time.  Here in the Gorge, I think it’s going to be a while yet before gardens and the native vegetation start to develop an “early summer look.”  Unless May ends up historically warm and dry, I bet a certain amount of late-spring lushness remains, well into June this year.

One thought on “Finally! The “Rain Faucet” is about to take a break….

  1. Wow, that trend line is really interesting. Some of the atmospheric science professors/post docs at the UW who’ve studied atmospheric rivers (Cliff Mass, Mike Warner, just to name a few) have found that they will increase in severity due to global warming, but the type of precipitation we’ve seen this year has been more of a persistently dreary precipitation, with few major flooding events, and therefore isn’t a good indicator of climate change.

    Still, the fact that (at least here on the west side) the fact that the past two winter have been some of the wettest ever certainly raises some eyebrows… could global warming result in a more persistent pattern of onshore flow with fewer periods of ridging? I don’t know and it’s too early to make conclusions after two years of data, but it’s an interesting question to ponder.

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