In my recent blog entry Texas Drought: A Fingerprint, I illustrated how unusual this year’s precipitation has been compared to previous years. Now, with just a few days left in August, I’d like to show you just how unusual the combination of summer temperatures and summer rainfall has been.

Here is a plot of Texas average summer (June-August) temperature versus Texas summer precipitation. Records go back to 1895. I’ve left off 2011.

I’ve labeled a few of the years. Some of the summers of the 1950s show up toward the left, but the warmest summers were 1934, 1980, and 1998. All of them had below-normal rainfall; indeed, there’s a strong inverse relationship between summer rainfall and summer temperature.

Where do you suppose 2011 will fall on this diagram? I’ll give you a hint: it looks like Texas will come in just a bit over 2.5 inches for the summer. This will easily make it the leftmost point on the diagram. (If that’s not amazing enough, remember that the eight months prior to this summer were the driest eight consecutive months on record.)

But how warm? If you’re being conservative, you might follow the best-fit line and guess an average temperature around 84 F, close to a record for the summer. If you’re more gung-ho, you might notice that the past five years have all been well above the historical best-fit line, including wet years (2007), dry years (2009), and years in between (2010), and speculate that this summer’s average temperature will be a record-breaker, up around 85F or maybe even a few tenths of a degree warmer.

With three days remaining, here’s how it’s actually shaping up:

Can you spot the outlier? The year 2011 continues the recent trend of being much warmer than the historical precipitation-temperature relationship would indicate, although with no previous points so dry it’s hard to say exactly what history would say about a summer such as this one. Except that this summer is way beyond the previous envelope of summer temperature and precipitation.

August is also shaping up to be, shall we say, rather warm. Here’s the historical distribution of August temperatures:

These are average temperatures (the average of the daily maximum and minimum temperatures). There was one rather nippy August, when the temperature averaged 77.2 F (it was also the fifth-wettest August on record), but the rest of the Augusts follow a neat little distribution with the most common values being around 82-83F.

So do you think this August will set a record? Yeah? By how much? Do you think we’ll shatter the previous record by a full degree and come in somewhere around 86.5F?

If so, think again:

We’re on track for an August average temperature of 88.1 F. There’s still time for it to change by a few tenths, but not only will we shatter the previous August record (by over 2 F), but we’ll also break the all-time record for warmest month by about 1 F. The all-time record, by the way, was set just last month.

The good news is that the weather pattern seems to be breaking down and tropical thunderstorms seem likely to move in by the end of the week. This will bring temperatures back down to closer to normal for this time of year, and hopefully start making a little dent in the drought.

The bad news is that a few inches of rain isn’t going to make a huge difference. It’s been so dry that we need above-average rainfall in September just to avoid setting another record: driest 12 consecutive months on record.