It’s been a while since I wrote a blog. I figured I’d write one for the sake of trying to explain why it has been so windy in the Rio Grande Valley over the past couple of months. I will also brief on the severe weather in Texas and how it affects the RGV.
Why Is It So Windy In The RGV?
The National Weather Service in Brownsville wrote a great article in 2008 about the windy conditions for the months of February through April, and can be found here. I was originally going to write my own article on why it’s so windy in the Valley, but I stumbled upon this link on their website and didn’t want to steal their information. They have a lot, more in depth facts than I would have talked about, anyway. I will basically summarize their article here and add a few things of my own.
Starting around February, high pressure at the surface becomes dominate in the central and eastern Gulf of Mexico. This high pressure may or may not be enhanced by La Niña, a subject I will avoid because of further confusion. This high pressure gives the Valley its southerly and southeasterly flow at the surface. In addition to this surface high pressure in the Gulf of Mexico, lee troughing (low pressure) occurs at the foothills of the mountains in Mexico towards the west. Circulation around a low pressure is counter-clockwise. The combination of the high pressure over the Gulf, and the lee troughing in Mexico increases the pressure gradient, and thus making the wind stronger out of the south and southeast. Figure 1, below, is showing the general locations of the two pressure systems. Generally, however, the location of the high is further east.
The upper atmosphere also plays a roll on the surface winds as well. At 500mb (~5500 meters, or ~18,000 feet), a digging trough around the 4-corners region usually indicates a decrease of surface winds in the mid and upper Valley, but tends to increase winds near the coast. This is because a 500mb trough at that location tends to decrease pressure at the surface, but also makes the high pressure stronger over the Gulf of Mexico, thus strong winds near the coast. Figure 2 shows an example of a digging trough that will lift towards the Southern Plains and Midwest over the next few days. This pattern is fairly common during this time of year. The image was from a 00Z 4/11/2011, upper air map.
Another reason why it is so windy in the Valley is because of the interaction of the surface Gulf high pressure and the Plains surface low pressure. The pressure gradient, just like the Sierra Madre Oriental low, is very tight. As summer approaches, the jet stream begins to shift northward, and so do the strong surface low pressures. Therefore, winds should die down around the Valley the closer it gets to summer, as the pressure gradient won’t be as strong.
What Does This All Mean?
Basically, this pattern will stick with us for at least the remainder of the month, and possibly into May. However, winds will begin to die down a bit towards the end of April or early May, I predict. So, hold on to those hats and skirts for a little while longer.
COLD FRONT ON THE WAY
In other weather news, severe weather is hitting central and north Texas hard at this hour. The Storm Prediction Center has issued numerous Severe Thunderstorm Watches and Tornado Watches yesterday and earlier tonight, including a few for north and central Texas. Current RADAR shows most of the severe weather in northern Texas, with storms in central Texas dying down a bit from previous hours. Figure 3, below, show current RADAR (~2:00am CDT).
For The Valley….
A cold front will be passing through early Monday morning (between 8 and 10am CDT). There won’t be drastically colder air behind the front, in fact temperatures will remain in upper 80s and the lower 90s for tomorrow and the rest of the week before another front approaches. Drier air will be filtering through for a couple of days. I don’t see any rain ahead of the front, mostly because there is a strong capping inversion over the Rio Grande Valley. I hope I’m wrong, but at this point, if any precipitation falls, it will be very brief. Thus, the drought will continue on. This will enhance fire danger around the RGV. Strong, northerly winds combined with low humidity and dew point temperatures will just add fuel to the fire. Below is an image from a temperature profile sounding from Brownsville at 00Z this evening.