Why Texas Is So Dry

It has been very dry in Texas, while other parts of the nation are very wet and stormy, like the massive tornado outbreak in the Carolinas which claimed at least 45 lives. Wondering why it is so dry in Texas? Well, there is La Nina, but it is dying and maybe heading into a neutral phase, which is neither cool or warm. Typically, La Nina causes the jet stream to be further north than usual. During El Nino, the jet stream is typically further south than normal, which gives Texas a wet winter and spring, which means cooler. Also, there is a persistent area of high pressure over Texas and Southwest, which pushes the jet stream further north.

Here is a 500 millibar (18,000 feet) Geopotential Height Anomaly Map from March 1 to April 15, 2011. Source is from NOAA Daily Climate Composite

The area of high pressure at the upper level is pretty much over Texas.

Compare this from March 1 to April 15, 1997. Spring of 1997 was one of the wettest ever for Southeast Texas as the strong El Nino of 1997-1998 was developing. Source is from NOAA Divisional Data

The area of high pressure is further west and north. The jet stream is also further south, which allows low pressure to travel further south.

The other culprit is a persistent warm air aloft blowing from the southwest in the upper atmosphere at the 850 millibar or 5,000 feet level. The dry and warm air is blowing from the deserts of Mexico and goes unabated if there are no low pressure systems to keep them in check. The ground level is very humid, especially in the Houston area. Don’t let that fool you because at the upper level it is drier, which serves as an inversion and cap. Here is a map of temperature anomaly from March 1 to April 15, 2011.

It is warmer than normal at 5,000 feet. It is the same one that deprives us rain and keeps us dry.

Since, the jet stream is further north, which pushes low pressures further away from Texas. This means the energy for storms to form is further away and less chance for rain and storms to form. Why? Lower pressure allows lift in the atmosphere. That is why stormy weather often occurs from a low pressure system. Also, the persistent area of high pressure produces winds in the upper level that blows in dry and warm air from the deserts of Mexico. For the warm air aloft to crack, the low pressure system and jet stream has to be further south or the upper wind patterns has to come from the east, which occurs in the summer. These easterlies give us rain and sometimes allow tropical cyclones to make landfall on Texas.

About these ads

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s