Calm Before the Storm

"The calm before the storm." It's a period of quiet weather that sometimes precedes major storms. The air is nearly calm, the sky has an innocent look, betraying what is about to happen. But there is a reason for it. Quite often large scale vertical air motions are downward ahead of major storm systems. What goes up must come down. Large storm systems feature vast regions of rising motion. Rising motion, with sufficient moisture, causes the air to cool to its condensation temperature and develops clouds and eventually precipitation. Around the storm there must be compensating areas of downward motion - areas where clouds dissipate or do not appear threatening. It is the calm before the storm.

Here are three photos taken early this afternoon in Cedar Falls, Iowa. The first looks south, the second southwest, and the third west. The south and southwestern views feature altocumulus and cirrus clouds. Altocumulus are middle level clouds and the cirrus are higher. No precipitation falls from altocumulus. Cirrus often has fall streaks, downward streamers of ice crystals that do not reach the ground. It is why cirrus often look wispy. The west view shows cirrus obscured by falling ice crystals. The photo is looking almost straight up into the cloud layer.  The fall streaks are falling directly toward the camera causing an indistinct cloud base. 

A plume of moisture in a relatively milder west to east flow aloft is responsible. Areas of weak upward motion creates the altocumulus and cirrus. This is the leading edge of a band of weak upward motion well in advance of a major storm centered off the West Coast. That storm should reach Iowa by late Monday with a big dose of winter weather due to continue into Wednesday. So today is the, "calm before the storm." Sunday and Monday our weather gradually gets more complicated.

Altocumulus (top right), altostratus (bottom), and cirrus (middle) south 30Jan2016, 12:30 p.m. cst

altocumulus SW 30Jan2016 12:30 pm cst

altocumulus (left) and Cirrus fall streaks, west, 12:30 p.m. cst