|The Roles of Geography and Climate|
in Forecasting Weather in South Texas
Texas is the second largest state in the United States, and is home to a wide array of Climates and
Geography, that all make for diverse weather, and extremely challenging weather forecasts. The City
of San Antonio, can be exceptionally hard to forecast for, as it lies in a transition zone between two
climates, and also happens to be in a location where the topography of Texas begins to change as
well. Hence, Geography plays a critical role in Weather Forecasts here in South Texas.
San Antonio lies in South Texas, about 140 miles from the Gulf of Mexico. Throughout the year, it is
dominated by an Easterly, Southeasterly flow off the Gulf of Mexico, which keeps the area rather
humid. This flow brings in steady moisture and humidity, which gives this area, a
Humid Sub-Tropical Climate.
In West Texas, the area is dominated by a Dry Westerly Flow from the Desert Southwest, the Deserts of
Mexico, and is mostly dominated by a Continental Tropical Air mass. Low humidity, and low dew points
are very common in this area of Texas, which extends from El Paso, eastward, to just West of the
San Antonio area. In the Fall, Winter and early Spring, this is the typical atmospheric setup
that is in place. You get Cold Fronts coming in from the West, or from the North, and they meet
up with the warmer, moisture laden air from the Gulf, right here in South Texas, many times here
in San Antonio. The clashing of air masses usually happens directly over this area.
The San Antonio area lies in a very unique location here in South Texas. Once you begin heading West
from San Antonio, the climate begins to dry out, and quickly switches over to a Semi-Arid Climate, the
desert climate of West Texas. It's a dramatic change. You drive west from San Antonio, and within 100
miles, you are in Desert areas. San Antonio also happens to lie along the Balcones Escarpment. The
Balcones Escarpment is where the flat coastal plains of South Texas, begin to change in elevation, from
gradual rolling hills to the higher altitude of West Texas. The sea level throughout the Escarpment
changes anywhere between one, to five hundred feet, but that change in elevation is sometimes enough
to impact the weather.
Geography can throw a complicating variable into the forecast at almost any time of the year. During the late
Spring, Summer, and early Fall, warm, moist air from the Gulf of Mexico, moves North and West across the
Coastal Plains of South Texas. As this moist air mass travels West, it is forced to rise when it hits
the Balcones Escarpment, which has a slightly higher altitude. When that happens, flooding rainfall
often will occur because of the height change and Orographic lifting. You never know if the slight
change in elevation, in some cases, only a couple of hundred feet, will be enough to get the air
to rise even further, contributing to the development of convective storms. If there is enough
lift, you get heavy rainfall since you have such a juicy air mass, that is already rising because
of the orographic processes over the Balcones Escarpment. Because you never know how the atmosphere
is going to react, it is very hard to forecast where and when storms will develop. Flash
Flooding in a lot of cases results over communities that lie in the Balcones Escarpment, and
the amount of precipitation, and duration, is always difficult to forecast. A classic example
of this was the South Texas Flood Event of 2002.
The Balcones Escarpment adds complicating factors to a forecast during the Fall, Winter, and early Spring, which
is typically when we see the clashing of air masses, in the form of fronts, or storm systems that move through
our area. The Escarpment not only marks a change in the topography, but it also marks a transition zone of
climates, between the Humid Subtropical Climate to the East, and the Semi-Arid Climate to the West. Storm
systems that are usually associated with Cold fronts, and many times Arctic Cold fronts, move through
our area quite often between the Winter and early Spring. A lot of time, prior to the passage of
the Cold Fronts, San Antonio is the Warm Sector, dominated by Warm Air Advection, and in a humid
moist Southerly flow off the Gulf of Mexico. That humid moist air, usually does not make it too
far West from San Antonio. And it is in this area, where the Cold Unstable Air, clashes with
the Warm Moist air from the Gulf. The result is usually severe weather, and severe
thunderstorms. Again here, the reaction that will take place when the air masses collide, is
hard to forecast and determine, until it happens. That reaction, many times, happens very
close to San Antonio, if not directly over the forecast area, which is where the Escarpment
is located, and where two climate zones converge. There is very little lead-time, in terms
of identifying what's already occurring, and what will be happening. Areas to the East
like Houston, don't have this problem. The storms will fire up over San Antonio, or just
to the East of San Antonio, giving Houston the lead-time it needs to see what's coming
to their city. They already know what's taken place with the clashing of air masses, and
have a better handle on what will be coming their way since the squall lines have already
developed. Quite often, a weather forecast may miss the possibility of Severe Weather,
Heavy Rains, and Flash Flooding, resulting from the explosive collision of air masses.
Some of the expert opinions on this topic have come from the Chief Meteorologist at my station, Steve Browne, at
KSAT-TV. Steve Browne has been forecasting weather in the San Antonio market, and here in South Texas for
over a decade, and has recognized this problem when putting his forecasts together. Recognizing the roles
that Geography and Climate play in putting forecasts together for our area, have made him the leading
Weather Authority here in South Texas.
There are also many case studies that have looked at the role that the Balcones Escarpment plays in Flash
Flooding situations, which involve moist humid air advecting towards the West.
One of the things that I think can be done to get a better grasp of the local conditions would involve
Weather Balloon Soundings, here in San Antonio. Right now, the sounding information we get for our area
comes from two separate locations. They are Del Rio, and Corpus Christi, Texas. Del Rio is about
140 miles Southeast of San Antonio, and sits in the Drier Semi-Arid Climate of South Texas. Corpus
Christi is about 140 miles Southeast of San Antonio, and sits in a more Humid Tropical Climate. These
locations are relatively close by, but the climate differences are big enough that we don't get a
good grasp of the atmospheric profile over South Texas, from those two readings. Having weather
balloon soundings here in San Antonio, would give us a better grasp of the "true" atmospheric
conditions over our area, and would allow us to see more accurately the conditions that are
in place, which would only help improve our forecasts, especially when it involves the clashing
of air masses with Winter Storm Systems, or with Moisture Advection from the Gulf. In both
situations, it would help us get a better grasp of the Flash Flooding Potential, Severe Weather
Threats, and would give us some concrete information that could be used as Climatological
tools in the future.
1) "FLOODING ALONG THE BALCONES ESCARPMENT, CENTRAL TEXAS"
S. Christopher Caran and Victor R. Baker (pages 1-14): Walter Geology Library - University of Texas, Austin