Rainfall and rankings in Deep South Texas for the period October 2010 to April 18 2011 (click to enlarge)
It Really Has Been That Dry!
Heat Adds Trouble; Little Relief in Sight

The 2010/11 Dry Season and History
As the 2011 Drought hurtles along, many are asking: "Just how dry has it been, anyway? Is this some kind of record"? The answers, for many, are "extremely dry", and "yes". Between October 1st, 2010, and April 18th, 2011, total rainfall has averaged within the top 10 driest since records have been kept, in some cases back to the late 19th century. Most locations with sufficient records are in the top three driest all time. Most areas west of highway 281 were at all time record, with swaths of the brush country and Rio Grande Plains having less than an inch of rain in nearly seven months, on par with desert climates from west Texas to California. Particularly notable are Brownsville, whose 2.69 aggregate ranks second only to the 1.99 inches which fell for the same period in 1903/04 (records date to 1878); and Rio Grande City, whose 1.37 beats all available records dating to 1897/98. Hebbronville, (2.21) ranks driest all time, but was missing 20 days (10 percent) of the period (records dating to 1904). The map below shows water year (beginning October 1st 2010) percent of normal precipitation through April 18th. Note pockets of southwestern Hidalgo and southeastern Starr County, with less than 5 percent of average.

Photo taken along FM 1017 in central Jim Hogg County showing dried scrub brush and grassland on a ranch, March 25th, 2011 (click to enlarge)
Dried brush and grasses along Farm to Market 1017, about 20 miles southeast of Hebbronville, Jim Hogg County.

The Heat is On, Too
Typically in Deep South Texas, spring drought combines with warm to hot temperatures, since increasing energy from the sun is used almost exclusively for heating rather than for heating and evaporation (from dew or wet ground) or evapotranspiration (from growing/green plants). Since the latter half of February, temperatures have been running some 4 to 6°F above the 30 year average (1971 to 2000), with embedded periods when temperatures averaged 7 to 12°F above average (February 15th to 28th, March 17th to 29th, April 7th to 11th). The chart below shows the monthly trend from mid March through mid April. The forecast until the last week of April strongly suggests summer like heat and increasing humidity for Deep South Texas, with temperatures 5 to 9°F above seasonal averages. Little, if any, relief is in sight to close out April.

With temperatures, humidity, and sunshine increasing, heat index, or "feels like" temperature, will rise to 100 to 105°F or higher at times. Remember to hydrate frequently if outside for long periods of time, and never leave children unattended: Beat the Heat, Check the Back Seat!.

Chart of temperature trends from mid March to mid April 2011, McAllen, Texas (click to enlarge)
McAllen temperatures trends, March 17 through April 17, 2011. Note virtually no bars extend into the blue coloring (below average), and nearly all rise into the red (above average).
Water year percentage of normal, October 1st 2010 through April 18, 2011, for Deep South Texas/Rio Grande Valley (click to enlarge)

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