11PM Day 1 Convective Outlook for Friday, August 29. THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE SOUTHERN AND CENTRAL HIGH PLAINS AND IN PARTS OF THE SABINE RIVER VALLEY
SUMMARY
Thunderstorms with potential for hail and isolated severe gusts will be possible today across parts of the southern and central High Plains. A few marginally severe gusts could also occur over parts of the Sabine River Valley.
Southern and Central High Plains
At mid-levels, flow will be northwesterly over much of the central U.S. today, as a ridge remains in place over the central High Plains. At the surface, a low is forecast to move eastward through southwestern South Dakota as a lee trough deepens across western Nebraska and eastern Colorado. As surface temperatures warm and low-level convergence increases, scattered thunderstorms are expected to develop near the surface trough. Along and to the east of the trough, surface dewpoints in the lower to mid 60s F will contribute to an axis of moderate instability by afternoon. In addition, RAP forecast soundings along this corridor show moderate deep-layer shear, owing mostly to speed shear in the mid-levels. This instability/shear environment could be enough for a marginal severe threat late this afternoon and early this evening, with the primary threats being for hail and isolated severe gusts.
Sabine River Valley
A mid-level trough will move across the eastern U.S. today, as cyclonically curved northwesterly flow remains over much of the Southeast. At the surface, a slow-moving front will be positioned from east Texas eastward into the central Gulf Coast states. Thunderstorms are expected to be ongoing near the front in the morning. This convection should move southeastward across the lower Mississippi Valley during the day. To the southwest of this convection, the airmass will remain undisturbed from southeast Texas into southwest Louisiana. This will allow for stronger surface heating, which should result in a pocket of moderate instability by afternoon. Isolated thunderstorms that develop within this pocket of instability could produce marginally severe wind gusts, mainly when low-level lapse rates become steep in the mid to late afternoon.