Spring Equinox Today & Showers Return

March 20, 2017

8am Monday…

What a beautiful Sunday it was with bright sunshine and comfortable afternoon temps.  That was only our 5th dry day in Portland this month, a month in which our rainfall is running almost double the normal total through the first 20 days of the month.

What really sticks out to me is how slowly plants/grasses/trees are coming alive this year, especially in contrast to the last two very warm late winter/early spring periods.  It’s obvious why:

Wow, that January cold departure of nearly 8 degrees is one of the largest, or THE largest, of my career here.  It was a cold month!  But combine the entire 3 month winter period and it was the coldest winter in Portland since I was 10 years old.  THAT explains why vegetation is so slow to get going this year.  March has been close to normal…just slightly below.

A few hours ago the Vernal, or Spring, Equinox occurred.  That means the sun is now halfway between its winter low and summer high position.  Yep, if you consider only incoming energy from the sun, we’re halfway to “summer heat”.  But of course it takes time for the land/oceans/atmosphere to warm so the seasons lag a bit behind.  Here in Portland, on average we tend to see warmest temps about 6 weeks after the summer solstice but only about 2 weeks after the winter solstice.

Note that I use the phrase “astronomical spring”.  That’s one thing that drives me nuts…I don’t know how the “start of spring” ever became associated with this date.  It’s pretty obvious in most temperate climates that the “season” begins well before the solstices/equinoxes.  In meteorology we stick to weather only so we consider all of March a spring month.  Yes, it can snow in a spring month, just as it can be hot in a fall month.  But we consider spring those 3 months between winter and summer.

It’s also quite obvious that the wet pattern is going to continue for a while longer, into the beginning of Oregon’s Spring Break this coming weekend.  Sorry kids!

By the way, while putting together a winter recap for our local AMS chapter meeting tonight I stumbled across this picture.   I snapped it at the end of the last Gorge ice storm of the season (February 9th) when I happened to be at home.  Click on the picture and take a very close look.  At that point I had just under 1/2″ ice on trees/objects and the temperature had climbed to around 33 degrees.

Do you see the green trees in the distance at the top of the clearcut maybe 1/2 mile away at most?  There is no ice just 200-400′ higher in elevation!  The cold layer of air in the Gorge was getting thinner and thinner and 50 degree air was over the top of that for many hours before this time.    You’re looking through a freezing layer of air stuck in a small valley into the very mild air overhead!  That pic should go in a meteorology textbook (minus last summer’s pool).  Within an hour after I took that picture the southerly wind punched through and all the ice was off the trees in a half hour or less.  Lots of noise!  Within a few days beyond that time (around Valentine’s Day) all the ice/snow was finally off my driveway for the first time in 5 weeks.

Today will be showery, although I don’t think it’ll be real wet.  A gusty east wind is blowing through the Gorge too, but at least it’s way to warm to produce freezing rain this time.

Chief Meteorologist Mark Nelsen