UFO Sky

Last night, I was walking my dog in Magnuson Park and was impressed by the sky--there was a number of beautiful, sometimes multi-level, lens-shaped lenticular clouds.   In fact, after I got home I received a picture of one of them from Andrew Weller (see below).

Some of the local web cams showed the beautiful lenticular clouds as well, such one available on the KING-5 site:

As described in my NW weatherbook, the appearance of lenticular clouds is often a sign of an approaching weather system.   Such clouds are the result of air being pushed upwards by mountains and then oscillating up and down in the lee (see figure).   These are also known as mountain waves. When the air rises, it cools, and can become saturated--producing lens-shaped clouds.  And with all our terrain and multiple mountain peaks,  our sky can become a chaotic collection of such clouds.

To get lenticular clouds, you need a decent wind approaching the mountains and a sufficiently moist atmosphere that some modest upward motion will give you a cloud..... exactly what typically occurs as a weather system approaches from off the Pacific.

Take yesterday.    The satellite image Friday afternoon showed an approaching trough and weak front (see infrared image at 2 PM Friday).

But as the system approached, the winds and moisture aloft were changing--and the lenticular clouds provided a sign of that change. 

Below are the vertical soundings produced by a balloon-borne radiosonde at Quillayute, on the Washington coast.  Temperature is on the X-axis and the Y-axis is height in pressure (700 hPa corresponds to roughly 10,000 ft).   Winds are on the right, the left-most black line is dew point temperature, the right line is temperature.  The closer the lines are together, the closer the atmosphere is to saturation.  The plots are for 5 PM Thursday and 5 PM Friday.

On Thursday, the winds were light in the lower atmosphere and from the west to north.  The atmosphere was not even close to saturation.  No clouds. 

But the situation was quite different on Friday afternoon.  The winds had greatly strengthened and were uniformly from the southwest, and the atmosphere had moistened considerably, with the dew point very close to the temperature.  A little lift from the mountain waves could produce lenticular clouds.

Lenticular clouds over Mount Rainier started the UFO craze in 1948.   But they are clearly more of a sign of approaching weather systems than some alien visitation. Native Americans in our region had a saying that when Mount Rainier wore its hat, then rain would come soon.    They had real insights into our local weather.