The sky is beautiful this morning (see below). An impressionist’s dream.
What you’re seeing is mesoporous convection: shallow cumulus clouds forming due to instability in the middle stratosphere (I’ll explain this later).
The French Impressionists loved such beautiful skies, as illustrated by this lovely painting by Monet (Port in Argenteuil)
Here is another painting by Monet that is even more like the one I saw this morning. Monet was supposed to be a meteorologist…..
The Seine River at Vetheuil
By 2024, we may be able to do what Monet never dreamed of….observe such clouds from space. And for your viewing pleasure, here’s what NOAA’s GOES-West satellite observed at roughly the same time as my photo above.
Do you see small cloud formations in western Washington and northwestern Oregon? These are notable features.
We can get an idea of the height of these cloud formations using another high-tech sensor system that Monet couldn’t have dreamed of: laser altimeters operated by the Puget Sound Clean Air Agency. These surface-based units use vertically oriented laser beams to scatter clouds and smoke (see below). The time it takes for a scattering beam to reach and return from the cloud provides the cloud’s height.
The aforementioned clouds formed at an altitude of 5 to 6 km above the surface (about 16,000 to 20,000 ft above sea level) at about 1:30 this morning.
But our bag of high-tech tricks doesn’t stop there! We have balloon-launched weather stations called radio probe around the area, including Quillaytue on the Washington coast and Salem, Oregon.
Here are the temperature (red line), dew point (blue dashed line), and winds from the Layer Radiosonde launched this morning at Salem, positioned in the middle of the cloud field. Temperature (°C) is on the x-axis and pressure altitude (hPa) is on the y-axis. 500 hPa is about 18,000 ft.
There is a layer (indicated by the red arrow) where the dew point and temperature are the same. Such a layer is saturated (100% relative humidity) and associated with clouds. It matches the ceiling height quite well. The red temperature line also shows a rapid decrease in temperature with height in that region, consistent with an unstable, well-mixed layer.
So why do we have those beautiful cumulus clouds at that shallow level?
It involves an approaching low pressure center aloft (see above, 500 hPa, about 18,000 ft) – as shown on the forecast map at 8am this morning. The low pressure front (northeast) has both an upward motion and a southerly wind. The upward motion causes the air to cool (air cools by expanding as it moves to a lower pressure), which causes the relative humidity to increase (because cold air can hold less water vapor than warm air). The southerly wind (from the south) also helps move some of the moist air up from the Arizona “Monsoon” region.
Another high-tech possibility is viewing water vapor from space! Such an image shows the moisture plume this morning
The movement of low pressure into the area today will kick off a significant push of cool marine air onshore tonight. Tomorrow you will see MUCH COOLER temperatures and low clouds.
Have a nice weekend!
