This summer was an extreme one for rainfall here in Texas. It was so wet that lakes formed out in the deserts of West Texas. San Antonio Springs flowed again. And the typically parched and yellowed land around us just stayed green.
To find out why, TPR freelancer Daniel Ramirez spoke with Keith White who is a meteorologist with the National Weather Service. Earlier this month, he explained why the summer temperatures have been so mild. TPR followed up with him, via phone and email, to specifically find out what made it so rainy.
This interview has been edited for length and clarity.
TPR: Can you explain how the wet soil conditions of spring set up the conditions for our summer weather?
Keith White: The increased moisture impacts temperature in several ways. High soil moisture means more of the sun's energy goes towards evaporation than heating. High atmospheric moisture typically also limits heating somewhat during the day, and limits cooling at night. It also leads to the additional cloud cover, which has those same impacts (less cooling at night, less warming during the day).
TPR: What exactly was behind all the rainfall this summer?
WHITE: One of the primary drivers of summertime weather in our area is what's known as the subtropical ridge. It's a large area of high pressure that typically keeps us mostly dry, sunny, and warm through summer, especially the second half of it. This year, largely due to the widespread drought in the western U.S., it spent a lot more time located to the north and west of it's climatological average location. This kept the west coast and northern U.S. much warmer than usual, while locally we saw more periods of lower pressure and wetter weather that led to the cooler daytime highs.
TPR: Not only did we see heavy rainfall, but we also saw a high variability of rainfall across the area. For example, you told me about one rainfall event in July that dropped 6-8 inches in western Bexar County but saw less than an inch at the San Antonio airport. Is that pretty characteristic of how storms work around here?
WHITE: Yeah, absolutely, especially in the summertime when there's not a whole lot of steering flow in the upper atmosphere. A lot of our storms that do develop end up being very slow moving. And so as a result of that, some areas can see really impressive rainfall amounts, while locations only a few miles away can see a whole lot less. And that's true all the time. It's like that most summers here when it does rain, usually very spotty, usually very slow moving. And so, when you look at just one day's rainfall amounts, you'll see very spotty maps where one area has larger amounts and most of the area has very little. But if you take all of the rain throughout the summer and add it up, and average it out, you know, then those areas of variability start to average out usually.
TPR: So is there any rhyme or reason as to why it might fall heavier in one area as opposed to another?
WHITE: Typically, just random chance, the geographic impacts on rainfall are typically going to be on a larger scale than what we see here in south central Texas. For instance, if you look at average annual rainfall, most people will now notice that the further east you are in our region, the more rainfall you get.
TPR: So we know that climate change is making weather both more extreme and more unpredictable. Is there any link between this year's extreme precipitation and climate change?
WHITE: There is not a specific direct link that we can show. Indirectly, there may have been some impact on this summer's pattern from climate change. And while we know that over time, climate change will lead to a gradual increase in the frequency and severity of both drought and heavy rainfall events, it is very difficult to attribute specific events directly to climate change. That said, I would expect that some research will probably be done at some point, you know, on whether or not there are some links to climate change with our pattern this summer, and I would expect that there would be at least some component, especially given how stark the drought that we've seen in the last year, then over the course of the last, you know, 12 to 16 months.
