Weather forecasters have a rule of thumb, which goes "do not predict rain in the middle of a drought".

This is a reasonable rule because prolonged droughts and rainy spells tend to be the result of persistent weather patterns. Much of our annual rainfall comes from fairly marginal situations (where the probability of rain may be in the 20-40% range). In a drought, almost by definition, these marginal rain situations fail to materialize. The overall pattern is simply too strong of an influence to be overcome.

This year we have seen just such a pattern over southeast Texas. A strong upper-level high has remained parked over Texas, northern Mexico and the Gulf of Mexico. Meanwhile, an upper-level low pressure trough has persisted over the East Coast, bringing cooler and wetter than normal conditions there while Texas has baked under an unrelenting sun.

So, it is with some trepidation that I mention the possibility of some rain later this week into the coming weekend. Right now it doesn't look like a drought-breaker by any means, but I suspect that any rain looks good to us right now.

The primary reason for an increased chance of rain will be an expected shift of the upper-level high to the west, which would bring the low pressure trough further west as well and also set up an upper-level wind flow from the north. This would allow disturbances in the upper-atmosphere to travel south into our region, hopefully bringing a few thunderstorms with them. Another reason, though somewhat uncertain at this point, is a fairly decent surge of moisture associated with a weak tropical wave in the Atlantic east of the Windward Islands. This may move through the Caribbean and may ultimately work its way into the Gulf of Mexico, increasing overall moisture levels there.

Of course, given the paucity of rainfall over the past 3 months, this may all turn out to be just another mirage in an arid scenario. I certainly hope not!!

Following is an upper-level weather map showing the projected location of the upper-level high and low pressure trough in a few days (coutesy of NOAA). Also, following are a 4-5 rainfall forecast map and a view of the moisture surge east of the Windward Islands: