Overview The GFS has been hinting at a negatively tilted trough sweeping the plains on Friday for a few runs. Exact details are still evolving. But, both GFS and ECMWF put this trough across the OK/TX region. Latest 00z (20170418) GFS looks rather favorable. Timing seems to line up well with peak afternoon heating. Surface At the surface plentiful moisture should be available with the Wed system pushing only to the OK/TX border. By 21z there should be upper 60 Tds throughout the warm sector. While not definitive on placement yet, there will be cyclogenesis somewhere from SW Okla to perhaps SW KS. This is aid in backing surface winds to S and possibly SSE at 20kts. Upper 500 hPa trough ejects over OK right around 21z. 7-5 LR of 8.5° C/km combined with substantial surface moisture will lead to strong instability approaching 3,000 MLCAPE. There is beautiful diffluence at 250 hPa (nearly 90°) At 850 hPa the LLJ isn't particularly strong the previous night but begins to ramp up between 18z and 21z day of event. By 21z winds of 35-40 kt form the SSW at 850 hPa will be common across the warm sector. By 00z there will be widespread 0-3km helicities of 250+ m2/s2. Conclusion Still lots of uncertainty with this forecast as it keeps changes from run to run. It seems ECMWF has been more consistent with the 500 trough than the GFS. But every few run the GFS paints a rather ominous picture. Will be interesting to see the 12z NAM on 4/18 Special Treat A PDS Tornado sounding for KOUN right before the OKC Thunder game in OKC!!!