An active day of weather is expected as a dynamic upper-level storm system brings the potential of severe thunderstorms and heavy rainfall. I know that having yet another severe weather threat on the three year anniversary of December 26, 2015 is going to set off nerves, but we’re going to sit down and go through today’s setup in a simple and non-hyped manner.
Those of you who joined us for yesterday’s blog update know that the severe weather outlooks are based on the probability of severe weather occurring within 25 miles of your location. Severe weather hazards won’t differ much regardless of whether you’re in a level one or level three risk, but their chance of occurring will increase as you move up in risk levels.
Today’s primary risk will be from damaging straight-line winds and the possibility of tornadoes. Large hail and localized flooding are also threats. This event will begin in earnest near and after sunset – with a significant severe weather risk continuing into the night. We’re emphasizing that night-time threat for those who may be traveling through our region and those who might be in bed.
A level one risk of severe weather includes the eastern half of the Texas Panhandle for the afternoon hours. Isolated to scattered thunderstorms this afternoon may produce large hail and isolated tornadoes. Unlike areas farther south and east, this threat will mainly end by the early evening.
A level two risk includes West-Central Texas, the Big Country, Concho Valley, Edwards Plateau, North Texas, East Texas, portions of Southeast Texas, and South Texas for the afternoon through overnight hours. Generally speaking, most of the risk will be after 4 PM. However, there is a chance for isolated activity before that time. We’ll discuss that in earnest in a bit.
Finally, we now have an upgraded level three risk for portions of the Hill Country, Central Texas, and the Brazos Valley. This is where confidence is highest in the threat of isolated severe thunderstorms this afternoon and early evening, followed by a line of severe thunderstorms moving from west to east tonight.
What does each risk level mean?
Pay attention if you’re in or close to any of the risk areas. Don’t get caught up on where each risk area ‘line’ is located. Mother nature doesn’t care about lines drawn on a map.
Level 1 risk has a 5 percent chance of severe weather within 25 miles of your location
Level 2 risk has a 15 percent chance of severe weather within 25 miles of your location
Level 3 risk has a 30 percent chance of severe weather within 25 miles of your location
Severe weather can include quarter size hail or larger, wind gusts of 58 MPH or higher, and/or a tornado.
Thunderstorms are already ongoing this morning across the Big Country and western North Texas. These are elevated above a strong inversion (or cap). Some of those are capable of producing hail and enough lightning to wake the Kraken, but have a minimal wind/tornado risk.
By the mid-afternoon hours (2-3 PM) we may see an uptick in thunderstorm coverage and intensity across southwestern North Texas, the Big Country, and into the Hill Country. Conditions by this point will be trending toward favoring surface-based thunderstorms and some of the storms may become supercelluar. This would result in the possibility of an isolated tornado risk, mainly west and south of the D/FW Metroplex. Obviously, mother nature can play by her own rules, so just keep this general timeframe in mind for some isolated mischief.
Thunderstorms may also be ongoing across the Texas Panhandle and West Texas during the early to mid-afternoon hours. An isolated tornado risk may also occur here along with the risk of localized damaging wind gusts and large hail. The threat for storms will end in both regions by the early evening.
Around dinner-time (6 PM) we could have showers and thunderstorms underway across North Texas, Central Texas, the Brazos Valley, and Southeast Texas. Much of this activity may actually be ‘elevated’ above a stout cap and well below severe limits. Some small hail along with heavy rain would be probable.
A line of strong to severe thunderstorms will be developing by early evening across Northwest Texas, the Big Country, south into the Concho Valley and Edwards Plateau. Storms may initially be semi-discrete but would tend to form into line segments fairly quickly. This is the beginning of a squall line that will move from west to east tonight – impacting the eastern half of Texas. There is uncertainty on how far west the ‘solid’ squall line will develop, meaning some may ‘luck out’ if the line develops farther to the east.
The squall line will move from west to east tonight, and eventually, stretch from Northeast Oklahoma south/southwest into South Texas. Wind shear is going to be quite strong, but the atmosphere will tend to become more stable in a layer just above the surface across Texoma toward the Arklatex. Essentially, the northern edge of the level 2 severe weather risk is ‘drawn’ where that more stable ‘layer’ of air is anticipated to be located. That layer will tend to lower the risk of tornadoes and damaging wind gusts at the surface, but some hail and strong winds are still possible.
The highest threat of damaging straight-line winds and embedded, brief tornadoes in the squall line will be across the Hill Country, southern North Texas (just south of the D/FW Metroplex), Central Texas, extending east into the Brazos Valley. Generally speaking, the highest threat should be south of Interstate 20, but if we see higher instability advect a bit northward, that could extend up to the Interstate 20 corridor. It’s going to be a close call.
Any storms that fire up just ahead of the squall line tonight across the aforementioned regions will be in a very favorable environment for low-level rotation and possible tornadoes. I don’t think we’ll see too many of these ‘pre-frontal’ storms this evening, but we’re going to have to watch closely if one gets going. They’ll occur well after sunset and be moving northeast at 50+ MPH.
By 2 AM the squall line should extend from near Paris to Tyler to Bryan/College Station to Seguin. Damaging straight-line winds and brief tornadoes will still be possible at this point as the squall line continues moving east. In fact, the threat of severe weather will continue into the morning hours on Thursday across East Texas. The threat will not end until storms move into Lousiana after sunrise on Thursday. The upper-level lift will be lower south of Interstate 10, so the squall line should generally be weaker across South Texas tonight. In fact, it may only consist of a line of showers.
A severe weather event will unfold from this afternoon through Thursday morning across the eastern half of Texas. Damaging straight-line winds, large hail, localized flooding, and tornadoes are threats. Much of the severe weather threat will occur tonight, during the night-time hours and when folks are asleep. Have a way to receive weather warnings (tornado warnings come out as wireless emergency alerts over cell phones). Those traveling need to remain weather aware. If you have friends/family traveling make sure they know that bad weather is possible. Know where you’ll go if a warning is issued for your area.