Summer along the Rio Grande in Texas. There's always going to be interesting weather when you're low enough in latitude and close enough to access Gulf of Mexico moisture...and this evening doesn't let us down....with the introduction of the TUTT...a Tropical Upper-Tropospheric Trough, Yes, it is a real weather term...I didn't make it up.
So, what is it and what does it do?
Looking at the satellite image below (specifically over the Big Bend region of Texas), we can see very distinct counter-clockwise rotation of moisture in the atmosphere...this is because of a Low Pressure circulation. Further north...along the Texas Panhandle through Kansas, we can see storms forming and moving along a line from southwest to northeast....this shows the periphery of the Subtropical Ridge...which tends to form over the Central United States during the summertime.
When a Low Pressure undercuts this Subtropical High-Pressure Ridge, it takes on tropical features, sort of like a Tropical Storm or Hurricane (although not nearly as intense, thank goodness). In fact...these Tropical Upper-Tropospheric Troughs, or TUTTs, can even induce tropical storms in some cases.
Being that this TUTT is not over the open water, however...it's just bringing tropical-like weather with it...in the form of clouds and thunderstorms due to it's nature of having cold air...and therefore deep instability...aloft. This little guy should stick around for the next day or so...so we'll be seeing more of him.
Well, to start from the basics...temperatures are the reason weather even exists. If there was no sun to heat the earth (and unevenly, at that), there would be no weather. This is because temperature differences create pressure and air density differences, and those are what cause weather to occur (think Low Pressure, High Pressure, etc).
Well...it so happens that Temperature and Pressure are directly proportional (known as the Ideal Gas Law in Physics). If the temperature goes up, so does the pressure. Think of a water kettle on the stovetop with boiling water inside. Why does it whistle when the water is boiling? Because the heated water in the container caused high pressure...which had to escape out the little whistle on top.
So, as widespread surface temperatures rises, widespread upper-level HIgh Pressure gets stronger. In this case, temperatures topping out at 125*F Monday Afternoon in Needles, California (just south of Las Vegas) have largely contributed to very strong High Pressure over the Southern United States (known as the Subtropical High Pressure). Wind flow has been directed around this Subtropical High Pressure to force Tropical Storm Danielle well south of the Texas Gulf Coast.
So, blistering hot temperatures in the desert do have a purpose.
- Dan, the Weatherman