El Niño-like pattern could bring heavy rain
Texas is still in the middle of an El Niño winter, which typically means above-average rainfall for the Lone Star State. However, total rainfall has not quite lived up to the El Niño hype so far.
Most locations have seen near- or slightly below-average rainfall since Dec. 1, the start of meteorological winter.
San Antonio, for example, has accumulated only 2.27 inches of rain since Dec. 1. That is 25% below average. Houston, though, has seen more rain, accumulating 5.44 inches during that time frame, but that is still 11% below average for the city.
One of the only areas to have seen above-average rain is parts of North Texas. The Dallas-fort Worth area has received rainfall amounts 14% above average since the start of meteorological winter.
Pattern shift coming
Texas likely will see heavy rainfall next week because an area of low atmospheric pressure will move from the Pacific Ocean eastward toward Texas. Instead of an arctic cold front, which typically brings dry air, this system will have ample Pacific moisture in the mid-levels of the atmosphere interacting with moisture from the Gulf of Mexico in the low levels of the atmosphere.
This is a familiar pattern during an El Niño winter, and it could bring the threat of heavy rainfall for many areas in Texas. Because we’re still several days away from the start of any rain event, possible rainfall amounts are still being worked out, but many weather models are starting to agree that they will be heavier than normal.
When will the rain start?
Most long-range weather models agree that a few showers will be possible in Texas starting Sunday evening. However, it’s likely the rainfall will become heavier and more widespread across Texas on Monday and Tuesday. It won’t rain the entire time, but many areas could have multiple rounds of heavy rainfall during the Jan. 22-24 timeframe.
As multiple disturbances of low atmospheric pressure continue to move eastward from the Pacific, more rounds of rain could arrive in the second half of next week as well. Because of this, the National Weather Service’s outlook for the next six to 10 days includes a 70-80% chance of above-average rainfall throughout Texas.
The forecast confidence decreases as we move further into the future, but long-range models continue to indicate high rain chances even as we push into the following weekend, Jan. 2728.
How much rain will fall?
It’s still too early to have high confidence in exact rainfall amounts, but we can start looking at the trends. The National Blend of Models takes into account dozens of different weather models and blends them to create a “best guess” of how much rain could fall in a particular period. The NBM output through Jan. 24 shows up to several inches of rain throughout much of Texas.
The exact numbers shown on the current NBM map are not important because the forecast will change a bit between now and next week. However, the NBM does show us what areas are most likely to see the heaviest rainfall. In this case, parts of Southeast Texas, including Houston, have the best chance of heavy rainfall, potentially totaling upward of 5 inches by the end of next week.
Many other parts of Texas also have the potential to see multiple inches of rain, including San Antonio, Dallas-fort Worth and everywhere in between. Rainfall likely will be much lower as we move into the western side of the state.