April 18, 2014

Crater Lake Contrail Fest

The high resolution image around noon Tuesday from the NASA MODIS Terra satellite was quite interesting (see below).  There was a general veil of high cirrus clouds over the region and some large cloud bands extended downstream from major volcanic peak (see my previous blog for an explanation about those lines).  You could also lo- level clouds west of the Cascade crest over western Washington and NW Oregon.

If you look closely you see some fine lines over the southern part of the domain...those are aircraft contrails. In fact, there were HUGE numbers of contrails.  Here is a close up view of the contrails around Crater Lake in the southern Oregon Cascades.  There were not only a lot of flights, but the contrails were not dissipating very fast.  Why?  Because the air was already at 100% relative humidity...that is why there was so much thin cloudiness around.  The moisture from the planes...the contrails...just enhanced the thin clouds already there and since the atmosphere was saturated already, there was little evaporation of the contrails.

With the contrails thickening the clouds over a large area, there can be major large-scale radiative impacts.  The thickened clouds can reflect more of the solar radiation to space and can also have big effects on infrared radiation heading to space and back to earth.    So if you want to understand climate change, contrails are a small, but significant issue that needs to be considered.

Do contrails cool or warm?  The best estimates now are that they warm the planet due to their impacts on infrared energy (they radiate infrared energy back to earth) outweighing the cooling impacts of reflecting some solar radiation back to space.  That contrasts with the other lines produced by humans seen on satellite imagery:  ship tracks (see image below).  Such lines, produced by the enhancement of the number of cloud droplets in low-level stratocumulus and stratus clouds by combustion products in commercial ships, clearly cool the planet.  In such clouds, the infrared effects are far weaker, so that the reflectance of solar radiation dominates.

Finally, last night a very strong Puget Sound Convergence Zone formed as a Pacific front moved through the region (see radar image below at 10 PM, yellow is heavy rain)

 The 24h precipitation ending 7 AM from Seattle RainWatch (which combines radar imformation with rain gauages) shows the impact of the convergence zone, with some areas getting more than 4 inches!
And some rain gauges (over the same 24 h period) observed three inches and more (see below).   There was a strong rain shadow to the NE of the Olympics yesterday, with some locations getting only a few hundredths of an inch).   Just amazing isn't it?  A hundred times more rainfall roughly 50 miles away.  And far wetter in Seattle's eastern suburbs than along its Puget Sound shoreline.


  1. I'm always fascinated by the science behind contrails and the "wake" of aircraft moving through the skies. Thanks for this. 'Also interesting to realize that ships do the same thing to a degree.

    I do wonder though; do contrails heat or cool the minds of those folks who believe they are actually chemtrails? ;)

  2. Yeah. Thanks, Cliff. But, I will tell you, I am a bit bummed out by another (so far) lousy Seattle spring. The Seattle Mariners look great by comparison. And, no, Cliff, that is not a good thing...

  3. Love this blog Mr. Mass - keep up the good work! I'd be fascinated to hear your take on the crazy (and brief) windstorm that Tacoma experienced around 7pm this past Thursday. It had been blustery all evening but for about a two minute period the winds ramped up to around 70 mph before subsided back to where they had been (in the process bringing down 6 very large trees at Point Defiance). The News Tribune had an article about it today (Arpil 19th) but didn't give much of a description of what caused such a massive localized wind.


Please make sure your comments are civil. Name calling and personal attacks are not appropriate.

A Forecast Failure and the Next Snow Event

 The weather prediction business is a humbling one.      Yes, forecasting systems have gotten far better, but occasionally they disappoint, ...