Know the Wind

 

#2221 "Singleton Squally Snow" 6"X 8" oils

Know the wind and you know the weather!

Understanding the winds in the free atmosphere was where we started a couple of years ago with "Cloud Shapes and Lines in the Atmosphere". The patterns in the sky are created by winds within the atmospheric frame of reference. The relative winds do the sculpting and the shapes are the same around the globe. Those patterns reveal the wind and those winds lead to a better understanding of the weather through conceptual models like the "Conveyor Belt" and "Isentropic Surfaces". You will find several entries on each top if you search my Art and Science Blogs. Each Blog tried to add another piece to the atmospheric puzzle. 

It is also important to appreciate the wind in the not so free atmosphere! The planetary boundary layer (PBL) is the lowest part of the atmosphere directly influenced by contact with the earth. Heat, moisture and momentum are interchanged constantly within the PBL. Friction turns the free atmosphere winds (20 to 50 degrees) while dragging the speeds down (sometimes by 50%). The surface winds you experience veer (turn clockwise in direction) and increase in speed in order to transform to the winds of the free atmosphere at the top of the PBL. 

Cumulus clouds within the PBL reveal that the air is positively buoyant. Such a happy PBL is referred to as the Convective Planetary Boundary Level (CBL). The turbulent mixing and interaction between the earth and the atmosphere can be very deep and even extend up to the top which is called that tropopause. A larger percentage of the free atmospheric winds can get to the surface in a CBL. 

Stratus clouds indicate that there is negative bouyancy within the PBL. A stably stratified planetary boundary layer (SBL) means that any exchanges of characterisitics between the earth and atmosphere occur within a shallow layer. The stable profile of a SBL limits how much free atmosphere energy can get to the surface. 

A quick look at the lowest clouds in the atmosphere will tell you what is happening in the PBL - this is the take home message. The painting from 6:00 pm on Friday February 9th, 2019 was in the wake of a very strong cold front. Multi-lake snowsqualls originating from Lake Michigan were making it as far as Singleton Lake. It was a cumulus PBL!

It was a day after a major winter storm crossed Ontario. The winds were gusting to 45 knots and perhaps stronger. I do not own an anemometer but things tend to break with wind gusts of 50 knots. The Arctic air over the Great Lakes was cold enough to create classic lake effect snowsqualls. What was very unusual was that the squalls reaching Singleton were actually originating from Lake Michigan with a bit of a boost from Lake Huron too. The weather is never dull.

The next few Blogs will develop some more observations from the planetary boundary layer (PBL)

Warmest regards and keep your paddle in the water,

Phil the Forecaster Chadwick