Author: Jason Cooley

#WeatherWednesday – RFD

Hello and happy #WeatherWednesday everyone! I hope you found the last write-up about atmospheric instability and stability useful and interesting. To change things up we will switch to a mesoscale meteorology lesson today. We are going to discuss what the term “RFD” means! As many of you know, a supercell is what we call a storm with a sustained, rotating, and tilted updraft. The most frequent severe weather is caused by supercell thunderstorms. One of the biggest defining features of a supercell is the presence of RFD, or rear-flank downdraft. On radar, this is visualized by a “hook echo”,...

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#WeatherWednesday – CAP versus CAPE

Happy #WeatherWednesday guys and gals! Have you always wondered what the meteorologists on TV or weather websites really mean when they say the atmosphere is stable or unstable? We will discuss what that means and how “the cap” or “CAPE” relate to these descriptors. A stable atmosphere is characterized by ¬†air that is warmer aloft than the theoretical temperature of an air parcel that is vertically displaced from the surface. This warmer air can be a variety of thicknesses and magnitudes. In this context, the stability is stronger as this temperature differential between the atmosphere and the surface parcel increases and/or the as thickness that differential exists grows. This layer is called the cap. Colder air is denser than warm air and will SINK in the fluid atmosphere. Warm air RISES. Since you need air displacing upward to trigger thunderstorms, a cap will prohibit vertical motion and storms unless a “lifting mechanism” is strong enough to force air to erode the cap due to momentum and cooling effects of evaporation. So what’s the opposite of stability and a cap? It is instability, or CAPE (Convective Available Potential Energy). This is the potential energy for a surface air parcel to accelerate **opposing gravity** upward until it reaches stability again. Here is where the environment is colder than the theoretical surface parcel temperature allowing the relatively warmer air to continue rising...

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#WeatherWednesday – Fog

Happy #WeatherWednesday everyone! I hope you liked the astronomy infused refresher lesson on solstices in our last discussion. This time we’ll go back to qualitative meteorology today and talk about fog. Fog development and sustenance follow simple thermodynamic principles. This means if conditions are ideal for fog, there will be fog. Fog forms the same way clouds higher in the sky do. It happens when air is cooled to its dew point. The dew point is defined as the temperature in which a sample of air will reach condensation (become visible suspended water droplets). The dew point is governed...

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#WeatherWednesday – Explanation of the Solstice

Happy #WeatherWednesday, weather peeps! It’s the first full day of summer in the Northern Hemisphere! Today’s topic of discussion is an explanation of the solstice. The summer solstice was at 11:24pm CDT (0424 UTC) last night. For our friends in the Southern Hemisphere, winter has started (brrr, maybe). The shortest nights and longest days of the year occur this week. If you were to live north of the Arctic Circle, the midnight sun would be the highest in the sky. This is because of the position of the Earth in its orbit around the sun. Some people out there...

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#WeatherWednesday – Doppler Radar

Happy #WeatherWednesday everyone! Last time we talked about 5/27/1997 as a 20th-year-anniversary special post. Today we get back to a more technical lesson! Radio Detection And Ranging, or “radar” for short, is our primary method of detecting precipitation type, location, intensity, and even more. The type of radar we will discuss today is the most typical radar used by NWS and media stations: the Doppler radar. Doppler radar is composed of many different parts including a radar dish/antenna, transmitter components to produce electromagnetic waves, and wave guide/ feed horn to direct the EM waves into the dish for reflection...

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