There are still uncertainties regarding the overall scope of Friday’s severe weather threat. One is how far west thunderstorm initiation will occur tomorrow. The second is regarding cloud cover and how much ‘juice’ thunderstorms will have to work with. Strong wind shear and a deepening surface low will off-set the second uncertainty to an extent, but having more juice (instability) would tend to increase the severe weather threat.
This morning’s update from the Storm Prediction Center has introduced a level 3 risk of severe weather across Northeast Texas, Southeast Oklahoma, a good chunk of Arkansas, and northwest Lousiana. The standard level 2 risk includes the eastern half of North Texas and portions of East Texas. Specifically, the risk runs east of a Whitesboro to Grand Prairie to Fairfield to Lufkin line. A level 1 risk runs about 50 to 60 miles west and south of the level 2 risk.
These severe weather risk levels are based on the probability of severe weather occurring within 25 miles of a given point (such as your house). Higher the risk level the higher the chance of severe weather impacting your area.
For the sake of being conservative, I’m going to share a narrative of what the European weather model is showing for Friday afternoon and Friday evening. This model is probably the most aggressive in terms of thunderstorm potential and happens to also be the farthest west. It is entirely possible that tomorrow plays out farther east, but given the tendency for drylines to lolly-gag in some of our storm setups, we’ll go with this solution for now.
By late afternoon Friday, a deepening surface low should be located in the Texas Panhandle or in northwest Oklahoma. This surface low will actually be fairly deep (the pressure will be low), so it’ll be a windy day across the Southern United States. This low will continue to deepen (pressure lower) as it moves east Friday night across Oklahoma and begins to eject northeastward – eventually creating a winter storm across parts of the Midwest. As the pressure lowers the wind increases from surrounding areas of higher pressure to help fill that void (trying to make everything equal). That process occurs over a very large area. A surface dryline will extend southeast from the surface low into North Texas, bending back toward the south/southwest toward the Edwards Plateau.
The Euro model has a more unstable airmass east of the dryline across North Texas by the late afternoon hours Friday. It breaks the cap with isolated to widely scattered storms forming near Highway 281 eastward to Interstate 35/35W. While I wouldn’t be surprised at I-35 having some storm issues tomorrow, I don’t know about them forming as far west as 281. A few other models don’t even have anything on/west of I-35, but again, we’re taking a more conservative approach and sharing a more aggressive solution.
Those storms would move east/northeast at a decent clip given the strong winds aloft. With strong wind-shear (both speed and directional) along with more than adequate instability for late November, I’d expect those storms that did form would become severe with large hail and localized damaging winds. If low-level winds remained out of the south/southeast we would also have some tornado threat. If storms formed west of I-35, they could bring that severe weather threat into more populated areas of North Texas before moving east late tomorrow afternoon and early tomorrow evening.
Additional thunderstorms would develop as the dryline quickly surges east of Interstate 35 early tomorrow evening. Thunderstorm coverage would increase and we would probably see a transition from semi-discrete thunderstorms toward more of a broken squall line. Damaging wind gusts and large hail would be likely with the strongest storms. Brief tornadoes are also a threat with embedded supercelluar structures within the squall line. If we had any thunderstorms out by themselves ahead of the squall line, or a ‘broken squall line’ with messy supercelluar storm structures, there would be a tornado threat.
The threat of storms will be highest from near sunset toward midnight tomorrow evening across Northeast Texas and East Texas. While a few severe storms are possible farther south of Interstate 20 tomorrow evening, the strongest upper-level forcing is expected to be across Northeast Texas into adjacent states. The highest threat of severe storms should exit Northeast Texas and move into Arkansas early Saturday morning. A few storms may continue as a cold front overtakes the dryline and that cold front moves south/east early Friday into Central Texas, the Brazos Valley, and into the Piney Woods of East Texas. The threat of severe storms would be lower by that point.
The above scenario is one of the more aggressive possibilities for tomorrow. If the atmosphere remained more stable and/or thunderstorms didn’t develop until they were on or east of I-35, the severe weather threat would still exist in Northeast Texas but would be lower for North Texas and areas farther south tomorrow afternoon/evening. Future severe weather outlooks and forecast updates will be able to determine which solution is more probable – and we’ll be able to become more specific in both timing, impacts, and highest threat areas in later updates.