ST. LOUIS (KTVI) – The latest weather data continues to point to the potential for some significant severe weather late Saturday afternoon into Saturday night. Warm and humid air is streaming north into the region this evening and that flow will persist through Saturday, creating an extremely unstable atmosphere by Saturday afternoon for areas along and south of I-70.
Much of Saturday will be dry, through at least 3 p.m., so plan outdoor activities accordingly. However, after 3 p.m., storms will blossom rapidly over western Missouri and quickly grow into an expansive complex of fast moving, violent wind producing storms, what we call a “DERECHO.” Winds within this complex could exceed 70 mph and will be capable of extensive wind damage similar to that of a tornado. In addition, some very large hail–golf ball to baseball-sized–will be possible in the strongest cells. And finally, there will also be a risk of a couple of short-lived tornadoes near the leading edge of the fast moving storm complex.
Current thinking is that storms will sweep across the viewing area sometime between 5 p.m. and 10 p.m. Saturday. They will last about 30 to 60 minutes in any one location, with most severe portion of the storms lasting for 10-15 minutes. That window could shift a little earlier or a little later once we get a better idea of exactly where and when the storms will develop.
At this point, the greatest threat for all modes of severe weather will be near and south of I-70 sometime after 5 p.m. Saturday. However, people north of I-70 will still have a chance for showers and storms with a somewhat lower risk of severe hail and wind. The entire region should remain very aware of the fast changing weather conditions Saturday and stay tuned for further forecast refinements regarding timing, location and possible intensity.