Question:
What causes no rain corridors? I live in Cameron TX (76520). For the past few rain storms, the rain has been moving North and East.
Examples – Texas had 5 days of rain in a row last month. 4.5 of the 5 days, the rain moved North and East about 10 miles to the East and 5 miles to the West, forming a corridor of no rain. It is happening again today and is projected for tomorrow. In this case, the corridor is wider, but it is having the same effect. I noticed the same thing last fall. It seems to be a pattern. Any ideas as to why?
Answer:
Patterns of rain and no rain can occur for a variety of reasons:
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- In the short term, things tend not to change. In meteorology, we call this “persistence“, meaning that an existing pattern tends to persist for a period of time.
- A related reason this happens is random variability. Random variations tend to lead to “hot spots” and “cool spots” (in this case rain activity, I’m not referring to temperature here), but when you look at the variability over years and even decades the short-term patterns tend to smooth out and go away as different areas randomly get rain in different patterns over time.
- A non-random reason this could happen is because there’s a physical reason for a pattern to persist like this in the long (not short) term. For example, mountains cause what are called “rain shadows“, where the upwind portion of a mountain gets a lot of rain and the downwind portion not so much and is in the “shadow”. Or in the case of the Great Lakes, it’s common for very narrow bands of lake-effect snow to occur down-wind of the lake, burying localized spots under feet of snow while areas just a few miles away get nothing at all.
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Since you’re in Texas, where the terrain tends to be relatively flat without large, inland bodies of water, I expect what you’re seeing are patterns due to random variation. Rain in Texas commonly moves to the north and east in the cooler months, and it’s normal to get “streaks” of heavier and lighter rainfall as storm systems move through (we get the same thing here in Oklahoma). Wait long enough through enough rain events, and eventually the corridor of no rain will get rainfall while the other areas may or may not.
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