Hello weather junkies. Although the winds were expected to be breezy to light, a sudden strong gust of wind changed direction and speed. In this blog, let’s explore why wind speed and direction may change.
On July 14, 2024, thunderstorms occurred in the Chesapeake region, causing increased wind speeds. Even on sunny days, clouds and storms can form, causing weather changes. Below is a surface analysis from 18z (2:00 p.m.). This chart shows us the front, wind direction, and temperature. East of the Appalachian Mountains, a shortwave trough stretches from north to south, from Maine to Virginia. A shortwave trough is a disturbance in the middle of the atmosphere that provides lift to an area and helps mix warm and cold air to create storms.
Why are there afternoon storms?
As soon as the sun rises in the morning it heats the earth's surface. The earth's surface and other materials such as buildings retain and accumulate this heat throughout the day. Now, there are molecules called thermals that want to rise to an area that is warmer than their surroundings. As the thermals rise, they cool and expand as they collide with each other, creating space and becoming less dense. Eventually, their relative humidity reaches a saturation point and they condense into clouds.
This image was captured by the Weather Pro Net station at Tory Point. On the right, you can see the recorded observations collected on the fly. As you can see in the circled area, winds picked up around 3:30 PM EDT, with gusts reaching into the 40s. Note the second circle at the bottom: the wind direction is initially southerly and then changes to westerly.
This is what we call the outflow boundary. The leading edge of a thunderstorm separates cold air from warm air, similar to a front, and rain can follow. Note in the summary section to the right that both pressure and temperature dropped at 3:45 PM ET.
This is a radar image from the NWS service showing a line of thunderstorms extending from New Jersey to the Chesapeake River in a SE-ESE direction. Afternoon storms like this are called popcorn storms. They are often brief but can still pose a threat. These types of popcorn cells usually start due to heat during the day. Despite the presence of a shortwave disturbance west of the Chesapeake region, the storm system formed due to a natural uplift process. When the air is buoyant, strong updrafts are produced, also known as “free convection”. As we discussed earlier, warm air rises, expands, and cools.
Key concepts and considerations:
- The sun's solar radiation heats the earth.
- Warm air rises, cools, and expands.
- Look for darker clouds.
- The temperature decreases.
- Wind speed and direction change.
- Even flying insects can get in.
- Finally, you feel a cool breeze hit you, and then it starts to rain.
