We’re tracking what is expected to be the first significant severe weather event of 2018 this Saturday into Saturday night from northeastern Texas through the western Tennessee River Valley. Not only will the severe storms be a risk, but also the flooding rains that continue to slam the region. The main threats with these storms will be damaging winds with gusts up to 70-80 mph in addition to several tornadoes. Based on the atmospheric setup, we don’t think the tornadoes will be extremely strong and damaging, but there will likely still be tornadoes that will be on the minor side.
We’re going to be watching a very potent upper-level low moving eastward from the Southwest US while a strengthening surface low develops on the leeward side of the Colorado Rockies and tracks toward the Upper Midwest. This upper-low will produce very strong winds at the lower levels with winds up to 80 mph. These storms that develop will be able to carry some of these strong winds to the ground and produce the damaging wind gusts. Now we’re not going to be looking at much directional sheer, which is when winds change direction as they go up in height, but there will be speed sheer. Speed sheer is when winds increase in speed as they go up in height. This will create a rolling effect or spin in the atmosphere, therefore making for the threat of tornadoes. There are other favors we look at when forecasting severe storms. That includes instability. The Convective Available Potential Energy (CAPE) values illustrate how unstable the environment will be in order for thunderstorms to grow. CAPE values will be on the lower-end, mainly between 500 and 1500 J/kg, but will likely be high enough to produce powerful storms. Lastly, you need moisture and there will be a good deal of it present. Typically, you need dew points of at least 60 degrees for thunderstorms to develop and grow. Dew points in this situation will be in the 60s and 70s as moisture flows in from the Gulf of Mexico.
Based on this, we’re thinking widespread severe weather with strong winds and tornadoes can be expected from the ArkLaTex through the western Tennessee River Valley, as shown on our map below.
Now let’s talk timing. A line of thunderstorms, likely sub-severe, will develop Saturday morning from south-central Oklahoma southward through central Texas. They will slowly move east ahead of a powerful cold front, strengthening as they move. By the midday hours, they’ll likely move into eastern Oklahoma and will extend southward through the Dallas area and back down into the Austin area. In the early-afternoon, that line of storms will begin to take on severe characteristics, extending from southern Missouri through western Arkansas and into the ArkLaTex region. There will also be weaker storms approaching the Houston area between Houston and Austin. By the mid-afternoon and early-evening, that line will move into the western Ohio River Valley, central Arkansas, and eastern Texas. This seems like the peak timing for the worst storms, and the most powerful storms will likely occur in Arkansas and into western Tennessee based on the best atmospheric dynamics. Then during the first half of Saturday night, the line will reach the Ohio Valley while stalling out over southeast Texas, making for a flooding threat. These storms in southeast Texas should remain on the weak side. Then as we get into early-Sunday morning, the severe weather risk will lessen as the storms move into the Gulf Coast states. Isolated severe storms are still possible, however.
Please stay safe and keep ahead of the storms by making sure you have severe weather alerts set for you phone.