We have a text book setup for the potential for microbursts, some of which could be damaging. The temperatures are going to warm up into the mid to upper 90s by Thursday afternoon (with 100+ in the River Valley) before the cold front moves in from the NW. The high heat and dew points remaining in the low to mid 60s will lead to low relative humidity during the afternoon/early evening. The model forecast soundings for Thursday late afternoon display the classic inverted-V indicating strong downburst potential. The mid and upper-level flow will also be very weak, indicating ideal conditions for collapsing thunderstorms... leading to microbursts.
Technical jargon: The bases of the storms (LCLs) Thursday are expected to be around 7,500 feet above the ground with an level of free convection (LFC) around 7,700 feet agl (only 200 to 300 feet above the LCL). The convective temp for Thursday afternoon is 96... meaning at that temp air will start rising and form into storms above the cap with no convective inhibition (CINH).
Threats: The main threats from the storms Thursday will be downburst winds (microbursts) up to 80 mph and large hail up to ping pong (1.5" in diameter). The tornado threat will be near zero due to the very elevated storms and the weak low, mid, and upper level flow.
Timing: This is always the tricky one to predict, but I say storms begin to develop around 4 to 6 PM in the late afternoon. Initial severe development will be in NE OK & SW MO... with very isolated storms in NWA. After 6 PM... the scattered severe storms slowly make their way into NWA. The peak of the storm activity for our viewing area will be 6 to 11 PM from NWA into the River Valley. Obviously timing can always change, but I think it's going to be an early evening event.
-- Dan Skoff, NWA Weather Authority Chief Meteorologist