In the last 13 days Columbus has had only .10" of rain at the airport in this, our second wettest month of the year based on long-term averages. (I have had even less at my house.) It has also been mighty hot: Columbus has had 12 days in a row with highs above 95º. I know this is the South and it does get hot in the summer, but this year, like in 2010 and 2011, we're pushing it to the extreme.
Today we could get relief on both counts, and if we don't, then Friday looks almost as promising. Our First Alert staff of meteorologists have been calling for this boost in rain chances for several days, and we would seem to be primed as we look ahead to this afternoon. The map shown to the left is a contour of precipitable water from this morning, measuring the water vapor in a column of air and estimating how much rain would fall if it all fell on one spot. Those values today are quite high for any time of the year, so we can infer that there's plenty of moisture waiting to be wrung out as rain.
This map to the right is an index measuring instability, called the K index. It's used mainly for predicting warm season airmass thunderstorms. Anything 30 or above is unstable enough for storms to pop up with little provocation, so look at the 40 contour just north of us. With a value that high it won't take much to trigger storms this afternoon, especially since the wind flow is coming from the northwest today.
There are other tools we use before we tweak the forecast in one direction or another, but in a summertime situation I check these two first, and they are telling me that the activity this afternoon and evening will be much more expansive than it's been recently. That still doesn't guarantee your garden will get a good soaker this afternoon, but the odds are quite a bit higher.
Keep in mind, too, that within a hot airmass like the one we're in now, an ordinary, isolated thunderstorm can produce some pretty strong downburst winds, even reaching severe limits. That's why the Storm Prediction Center has put our area under a "marginal" risk for severe winds in a few of the stronger storms. They're not usually too destructive, but you don't want to be caught outside in one, so stay in touch with WRBL First Alert Weather as we pass along any warnings that may be issued.