Tornado Threat: June 17
As the remnants of Tropical Storm Bill move northward through the southern Plains, a modest threat for tornadoes may develop on Wednesday. Typically with landfalling tropical systems, the northeast quadrant is where there is an enhanced threat for tornadoes. These tornadoes are often brief and weak, as the environments tend to be very moist with limited instability, although wind shear can be locally quite strong.
There was a marginal risk for tornadoes today in eastern Texas as Tropical Storm Bill made landfall, but as of 8 p.m. CDT, there had been no reports of any severe weather in the area, let alone tornadoes. The setup for today, Tuesday, included rather low-end parameters for tornadoes. Speed shear was fairly limited, just in the 10 to 15 knot range for most of the area. While instability was modest, thunderstorm development stayed sub-severe. A band of thunderstorms was noted during the afternoon, but a lack of discrete cells and unimpressive storm relative helicity did not support a more substantial threat.
Moving into Wednesday, the setup should become somewhat more favorable or isolated tornadoes. As it appears based off of the latest guidance, the environment should support at least one or two brief tornadoes from northeastern Texas into portions of eastern Oklahoma. With the remnants of Bill weakening, there should be some more breaks in the cloud shield and perhaps better coverage of discrete thunderstorms. Although wind shear and low level helicity are progged to be more favorable than today, the best instability should remain displaced off to the east. Nonetheless, if any discrete storms can develop Wednesday afternoon or early evening, particularly from far northeastern Texas into eastern Oklahoma, there should be a risk for a tornado or two.
The mesoscale evolution of the setup should result in better confidence come Wednesday morning. The 18z 4km NAM was spinning up a few semi-discrete cells by mid to late afternoon across southeastern Oklahoma. It would appear that the best thermodynamic environment for tornadoes would be out ahead of the main precipitation shield. However, with a relatively strong low-level jet and solid kinematic support during the early evening, it is conceivable that there could also be a threat for embedded brief tornadoes in an arcing band of convection into the night. This would be just to the immediate northeast of the center of low pressure.
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