Filed under: Boundary Layer Features, Convection, Mesoscale Features, Thermodynamics
A large majority of human populations live on the coast of some sort of large bodies of water, be it either lakes or oceans. Day after day, people living in these areas experience the effects of land and sea breezes. While not a “severe” weather event in any stretch of the imagination, the breezes can become strong in the right conditions, and can provide the trigger required to initiate thunderstorms.
Formation
The land/sea breeze is caused by the land and the water heating up at different rates. It requires less energy to raise the temperature of the land. Since both the land and the water receive the same amount of energy, it makes sense then that the land will end up hotter than the water. As the land heats up, the air over the land heats up and expands, creating lower pressure over the land than over the water. As a result, air from over the lake will move inland in an attempt to fill in that low pressure area.
A Sea Breeze is when the air is moving from the water onto the land, and a Land Breeze is when the air is moving from the land onto the water.
Structure
At night, the land cools faster than the water. What goes up must come down. Overnight, the water is then warmer than the land, and the process reverses. Air moves from the land to over the water, then rises, then moves back over the land, then sinks.
Common Weather
The most common element to the land/sea breeze is, naturally, the breeze. It’s strength is proportional to how different the temperature of the land and the water is (the higher the difference, the stronger the wind), but averages in between 15-30km/h. It is possible, however, with the right conditions for sea breeze winds to reach as high as 60km/h (this sometimes occurs near cliffs on the west coast of the United States where the breeze can be redirected and channeled. A sea breeze creates a weak front inland that can cause the air to rise as fast as about 1m/s, which if there is instability in the low levels, can be enough to create thunderstorms. A land breeze promotes inversions over the land, giving clear skies and light winds at night.
Filed under: Cold Front, Convection, Precipitation Events, Synoptic Features, Thermodynamics
The weather effects each of us, every day. A lot of people have expressed to me interest in learning about the weather, but it’s definitely not easy. I’ve decided that each week, I’ll post a short-ish post explaining the basics of various weather phenomenon; this week: The Cold Front.
For many people, cold fronts are one of the most noticable weather events out there. They are fast moving features that often produce severe weather and result in drastically different weather after they have passed through.
Formation
All over the globe, air has a tendency to form into large areas with similar characteristics. We call these air masses. One example is could be a large area where it is hot and humid. In the wintertime, often there are extremely large areas of cold, dry air. These air masses move through the atmosphere, and fronts are developed. A cold front is the boundary on the leading edge of colder air moving into warmer air. It does not matter how cold the cold air mass is or how hot the hot air mass is, as long as they have a temperature difference, the cold front will form.
Structure
Cold fronts have a very defined structure that is based on a simple physical principle: density.
From high school physics, we know that the density of a gas is defined by it’s temperature and it’s pressure. Similar to how oil and vinegar have different densities, so do warm and cold air. Cold air is more dense than warm air. Because it is heavier, as the cold air (blue) pushes into the warm air (red), it begins to undercut the warm air and push it upwards at a very sharp angle. This causes a very narrow, relatively intense band of precipitation to form along cold fronts. Cold fronts move fairly quickly as the cold air digs underneat the warm air, and the weather associated with the front will be fairly short lived at any one location, usually lasting no longer than a few hours.
Common Weather
In the summer time, the passage of a cold front can often produce thunderstorms, or other significant weather features such as squall lines, supercells, and mesoscale convective complexes. These are all different forms of organized thunderstorms that last for a very long time. Due to the sharp upward push of the warm air, cold fronts can often produce short-lived, severe weather such as heavy rain with potential flooding, thunderstorms with large hail, and even tornadoes. In the summer, cold fronts can offer a reprieve from hot, humid weather. In the winter, the passage of a cold front can result in long stretches of cold weather and clear skies.
Next week, warm fronts. If there are any questions regarding this week, just leave them in the comments!
