May Pattern Change Ends Drought/Dryness for Most


Los Angeles Street with Palm Trees Through Rain Drop Splattered Windshield

After a very wet May, which saw several locations rank in the top ten wettest on record (see attached files 1 and 2), the Severe to Exceptional Drought was largely eliminated, with the last vestiges across the Brush Country/Rio Grande Plains of Starr, Jim Hogg, and Zapata. In the next week or so, these areas are likely to improve - and nearly all of the Deep S. Texas region should be out of drought and probably abnormal dryness as well. The first two days of June saw continued impressive rainfall, especially in Hidalgo County, where 2 to 3+ inches in many areas was equivalent to the totalmonthlyaverage. This has turned moisture deficits into moisture surpluses; never a bad thing during the peak of many crops growing seasons and a big help to livestock and municipal water needs. 

After many successful long-range predictions of "dry" fronts and generally above-average temperatures through April, which steadily worsened drought and further lowered the lake level at Falcon International Reservoir - causing at least one municipal water supply to institute conservation requirements in April - May's weather turned to the tables on what was expected to be a continuation of dry and warm/hot conditions. Instead, May ended up being the wettest since the mid-2010s, and among the top ten wettest at several locations, including Port Mansfield (1), McAllen (2/3), and Falcon Dam (7). The prior pattern, which had favored more rainfall in north Texas while keeping the Valley dry (due to drying low to mid level westerly winds), shifted (below). The persistent upper level trough in the southwest U.S.finallyallowed stronger energy "waves" to spin closer to the Valley - which increased deeper tropical moisture into the region and "lifted" that moisture into lines/clusters of thunderstorms. The first bout was at the start of the month, with others following on May 11/12, May 15/16, May 17-19, and May 29. June followed where May left off; another linear system swept through the region on the 1st, and additional rains from multiple sources are expected into the weekend (June 3-5) (attachment 3).  

The Summer Outlook

So, what's next? More uncertainty in the rain forecast. The wet and relatively cool (due to clouds and rain) start to June is likely to sway the month into the wetter/"cooler" than average territory for much of the eastern half of Texas, including the Valley. But there are hints of a transition back to hotter and drier than average conditions by late June/early July, which could continue well into August. August then becomes a wild card of its own due to the expected active Atlantic Basin season. A westward shift of the "La Canicula" ridge into the New Mexico/Arizona region could open the door to more Gulf of Mexico/western Caribbean tropical activity, but if/when this would begin is highly uncertain, leading to a low confidence on the seasonal rainfall forecast. Here are key takeaways (these are also included in the attached PDF, which is also posted as headline news athttps://weather.gov/rgv

  • Drought is, or will be, over for all areas for most of June...
  • ...But hot/very hot temperatures in July combined with little to no rainfall could return abnormal dryness to some areas. Should these conditions continue deep into August, moderate drought could resurface.
  • Dangerous heat index values ("feels like temperatures") of 110 or higher may occur in July and August, depending on the position of the "Canicula" ridge and any rainfall that would suppress temperatures
  • While Falcon Reservoir is getting a touch of relief from the May/early June rains, the total and Texas share of water remainsbelow  values in June 2020. A hot-very hot and dry July/August could trigger water supply issues and conservation needs in portions of the Valley
  • While wildfire spread/growth potential has been quelled by the rains, those same rains are generating a growth "spurt" of fine and moderate fuels (grasses and brush). Mid to late summer drying could turn that into high fuel loads, which would become something to watch beginning in late summer but perhaps peaking in autumn if typical rainfall does not return in September.  

In addition to the everpresent focus on hurricane and flood preparedness, please add preparedness actions forexcessive heat,water conservation, and wildfire safety as summer nears its peak. More on summer safetyhere

The latest Drought Monitor for the Rio Grande Valley/Deep S. Texas region was posted this morning. The map, which did not include any rainfall after 7 AM on the 1st, can be found at

https://weather.gov/rgv/drought

Note that drought monitors are updated weekly and posted each Thursday morning. The image at the link updates automatically.

Thanks everyone, and stay safe this summer!


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