A “Normal” Spring So Far; But Much Drier & Warmer Ahead

April 17, 2018

5pm Tuesday

I’ve heard some whining the past few days, people wondering when we’ll get out of this “cold & wet spring”.  Would it surprise you to know that isn’t really true this year?

It’s been pretty close to normal! Take a look at the numbers.  First, much of the USA has been colder than average this month:

conus_mtd_t2avg_anom_2018

Notice the Pacific Northwest is a bit cooler than average, but that’s nothing compared to the cold month so far east of the Rockies!

Here in Portland, as of the 15th of the month, temperatures were right at average.  March was one degree below average.

Mark Spring So Far 1

So yes, it has been slightly cooler than average.  But these numbers are exactly like 2017 so far…interesting eh?  It’s no colder than last year, but the previous 3 (2014-2016) springs were warmer than normal up to this point.  Apparently this spring (so far) the pendulum has gone back to cool.

How about rain?  That’s an easy one…it’s been a wet April so far.  We had exceeded our typical monthly rainfall by the 15th.  Yet March was DRIER than normal.

Mark Spring So Far 2

So if we take the 45 day period (spring so far), rainfall this season has only been slightly above normal.  I think the perception of a “cold and wet spring” only comes from the past two weeks; quite a bit of gray and consistently wet weather.

What about a changing climate?  I just gave a talk last week and included these two graphics.  They show 100 years of spring temperatures and rainfall in Oregon climate zone 2.  That’s the lowlands of NW Oregon where many of us live.

They show springs over the past 100 years have been trending WETTER although you see some decadal trends in there too:

SpringRain

Are springs getting colder?  Definitely not.

SpringTemps

The trend is WARMER, although you see some interesting trends…cooling springs late 1930s through late 1950s.  After warming, cooling again early 1990s to around 2011.

Looking ahead, I see a somewhat dramatic change ahead.  The jet stream will be lifting north and the few upper-level troughs that move by will be weaker/milder than recent events.  We’re going from cool March-like showers to a much slower May-like weather pattern.   Our lawns/gardens/fields will finally get a chance to dry out.  Check out the ECMWF ensemble precipitation forecast for the next two weeks:

ecmwf_ens_rain

The lower part of the graph shows accumulated precip from the operational model (blue) and the 51 member ensemble average (green).  Note the operational model gives us less than .10″ in the next two weeks!  That would be extremely unusual in April, but possible.  More likely is the ensemble average showing dry days late this week, a shower or two early Saturday, then a few more dry days.

How about temps?  MUCH BETTER.  Not excessively warm, but well above average this 2nd half of the month.  I’m quite confident we’ll see widespread low-mid 70s next Monday/Tuesday, but maybe no higher.

SUMMARY

A major weather pattern change is underway

  1. It’s going to feel like May much of the next 10+ days
  2. Many days will be dry in the next two weeks.

Chief Meteorologist Mark Nelsen