ZCZC SPCSWOMCD ALL ACUS11 KWNS 181640 SPC MCD 181640 ARZ000-MOZ000-OKZ000-181845- Mesoscale Discussion 0857 NWS Storm Prediction Center Norman OK 1140 AM CDT Sun May 18 2025 Areas affected...Northeast Oklahoma into northwest Arkansas and far southwest Missouri Concerning...Severe potential...Watch possible Valid 181640Z - 181845Z Probability of Watch Issuance...40 percent SUMMARY...Elevated thunderstorms developing across northeast Oklahoma into northwest Arkansas and southwest Missouri may pose a hail threat through early afternoon. Confidence in the coverage and duration of this threat is uncertain, but convective trends will be monitored. DISCUSSION...Isentropic ascent over a residual convective outflow across northeast OK/northwest AR has promoted scattered thunderstorms within the past hour. Based on forecast soundings and surface observations, this convection is likely being driven by ascent within the 850-700 mb level on the eastern fringe of an EML. Steep lapse rates above this layer (around 8 C/km) is supporting MUCAPE values between 1500-2000 J/kg, and strong flow within the 850-250 mb layer is supportive effective shear values around 50 knots. Consequently, organized convection is possible and may pose a severe hail threat through the next few hours. Weak ascent along the outflow boundary may be insufficient for sustained deep convection despite the favorable convective environment, and stable conditions in place downstream across northern AR/southern MO should limit the spatial extent of the threat. As such, overall coverage, duration, and intensity is uncertain. However, if convection can persist through mid afternoon, additional heating may support a higher potential for sustained/intense storms. Watch issuance is currently not likely, but convective trends will continue to be monitored given the environment. ..Moore/Hart.. 05/18/2025 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...LZK...SGF...TSA... LAT...LON 35089407 35239499 35779567 35999572 36219568 36719447 36709389 36459356 36179327 35929306 35639287 35389299 35269311 35139351 35089407 MOST PROBABLE PEAK HAIL SIZE...1.00-1.75 IN NNNN