July was a long, hot month in Del Rio. With sixteen days at or above 100°F and an average temperature 1.9°F warmer than normal, High Pressure, as predicted, played a very large role in setting 2017's high temperature record at a current 107°F while keeping rainfall at just over a half-inch in Del Rio locally through the month.
In fact, much of Texas is either in - or approaching - drought conditions to start off the month of August due to high temperatures combined with lower-than-normal rainfall in July.
Overall, confidence in this forecast remains mediocre. Just two weeks ago, the Climate Prediction Center (CPC) issued a forecast for August indicated above-normal temperatures, not below-normal as their current forecast shows. Both indicated wetter-than normal conditions, but so did July's forecast - which turned out to be somewhat of a flop.
However, after some personal investigation comparing the Del Rio 2016-2017 temperature trends to those of 1999-2000 - largely because of the similarities of experiencing warmer than normal winters, early spring seasons, and hot July's - I found that in August of 2000, temperatures were cooler than experienced in July (even though August is typically warmer than July) - which, when compared to the trends of 2017, could stand to back-up the cooler-than-normal forecast, statistically speaking.
If, as advertised, August is wetter-than-normal, it would be no surprise to see cooler-than-normal weather simply due to the excess of cloud cover overhead. Not only do clouds block incoming solar radiation, moisture itself takes longer to heat than dry air, basically not allowing afternoon temperatures to peak quite as high as possible under drier conditions.
With that being said, I'll leave you with a cool infrared satellite loop from the University of Wisconsin for the past 7 days. I could watch this over and over again!
The NWS Climate Prediction Center continues to label Texas has "warmer than normal", however, this is hardly substantiated and ls largely carried over from the previous Presidential agenda. In fact, in June - Del Rio's average temperature was just below normal (although very marginally).
The trend continues with CPC's forecast - so, as skeptical as I am, forecast guidance does indicate strong, upper-level High Pressure over the Central United States over the next month - which is scientifically related to widespread warm weather.
Locally, however, especially along the Rio Grande Plains, our temperatures are largely dependent on cloud cover - especially during the afternoon. So, if the High Pressure settles in a tad too far north this month, the local atmosphere may continue to route significant moisture (cloud cover) up the Rio and into the region, keeping our overnight temperatures warm, but afternoon temperatures cooler than normal (although it will still feel quite hot, no doubt). Heat Advisories will likely the the story for much of the month, generally issued for Heat Index values (computed based on temperature and relative humidity) generally above about 105°F - or in other words, temperatures that "feel" like 105°F, usually because of the high humidity.
The positioning of the High Pressure also will dictate moisture sources and atmospheric dynamics/energy potential for rainfall, although CPC projects the Del Rio area as "normal". Should we find ourselves too far south of the High Pressure, we could see substantially more rainfall - and even possibly tropical weather. During the summer locally, rainfall is often accumulated in pockets due to afternoon thunderstorms. It is uncommon for severe weather in July in Del Rio. However, strong thunderstorm wind gusts are the main threat. It is always a good idea to keep your eyes on the Gulf of Mexico as well...as one Tropical Storm has made landfall this year.
Summer along the Rio Grande in Texas. There's always going to be interesting weather when you're low enough in latitude and close enough to access Gulf of Mexico moisture...and this evening doesn't let us down....with the introduction of the TUTT...a Tropical Upper-Tropospheric Trough, Yes, it is a real weather term...I didn't make it up.
So, what is it and what does it do?
Looking at the satellite image below (specifically over the Big Bend region of Texas), we can see very distinct counter-clockwise rotation of moisture in the atmosphere...this is because of a Low Pressure circulation. Further north...along the Texas Panhandle through Kansas, we can see storms forming and moving along a line from southwest to northeast....this shows the periphery of the Subtropical Ridge...which tends to form over the Central United States during the summertime.
When a Low Pressure undercuts this Subtropical High-Pressure Ridge, it takes on tropical features, sort of like a Tropical Storm or Hurricane (although not nearly as intense, thank goodness). In fact...these Tropical Upper-Tropospheric Troughs, or TUTTs, can even induce tropical storms in some cases.
Being that this TUTT is not over the open water, however...it's just bringing tropical-like weather with it...in the form of clouds and thunderstorms due to it's nature of having cold air...and therefore deep instability...aloft. This little guy should stick around for the next day or so...so we'll be seeing more of him.
Dan Schreiber is a freelance meteorologist with experience