Signs of a strong La Niña pattern have been very evident across Central Texas since around the end of September. We’ve seen a parade of dry fronts through most of the fall months which is typically our second wettest time of the year. This stretch of dry weather lead to drought conditions expanding and worsening incredibly fast.
By the beginning of December, Extreme Drought conditions had developed across Central Texas, which is the fourth-worst category. Only Exceptional Drought conditions are worse. At Austin Camp Mabry on Dec. 29, the monthly rainfall total was only 0.84″ making the rainfall deficit -1.41″ for the month, and -2.32″ for the year.
As 2020 was coming to a close, all signs were pointing to a major rainfall deficit for the year. But in a meteorological Hail Mary, forecasts earlier in the week began signaling a cutoff low in Northern Mexico would bring some beneficial rains to Central Texas around New Years Eve. And they did not disappoint!
An upper low cutoff from the main jet stream moved into Northern Mexico on December 30th, which sparked numerous showers and thunderstorms heading into New Year’s Eve. Cutoff lows in Northern Mexico are notorious rainmakers for Central Texas due to their relative slow movement and near endless supply of warm waters from the Gulf of Mexico. Models were indicating rainfall totals through New Year’s Eve night in the 1″ to 3″ range.
As heavy rain and thunderstorms spread across Central Texas New Year’s Eve morning, rainfall amounts tallied up quickly. The upper low finally began to exit out of Northern Mexico and directly overhead by the afternoon. Rainfall came to an end, but parts of the Hill Country actually received a couple of inches of snow as the low exited in the early evening!
In the final hours of 2020, we managed to pick up some incredibly beneficial rains. So much so, that Austin Mabry ended December 2020 with a surplus of rain. The monthly rainfall total for December at Mabry was 4.07″ which is a surplus of 1.67″! The year ended in a surplus as well with 35.08″ of rain, which is a surplus of 0.76″.
All in all, most of Central Texas picked up some very healthy rains as indicated by the totals above from the LCRA. Hydromet. However, even though we ended the year in a surplus of rain, whether or not the drought will be eliminated is uncertain at this time.
Drought conditions are calculated by several indices that monitor rain, soil moisture, and groundwater levels. How long these scales are impacted by the lack of rainfall determine how long it will take to recover.
Short-term droughts last for a few weeks to a couple of months, and thus need only one or two heavy rainfall events to recover from. But a long-term drought can last several months to several years and will need multiple heavy rain events, spread throughout many months, to recover from.
Our current drought is right on the cusp between a short and a early long-term drought. Therefore, we will be waiting for the latest drought update to be released on January 7th which will include the rains from New Year’s Eve into it’s calculations. Regardless, the rains were more than welcome!
Looking ahead, the Climate Prediction Center is forecasting near normal precipitation for the middle of January. Something that, if plays out, will continue to aid in eliminating the drought for Central Texas.