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!