The northwesterly flow shown above (blue arrows) may guide batches of thunderstorms across northern or even central Oklahoma early/mid week. These would form as a result of weak mid-level troughs moving by, and upslope surface flow onto the higher terrain of western Kansas and Colorado. The ridge will probably be too strong for them to get this far south.
The pattern aloft will be similar to what we suffered under much of the summer: a large subtropical high parked overhead. This provides a sinking motion for the heat, while Gulf surface flow will keep the low-level moisture in place.
So it looks like hot and humid weather will prevail until the 16th or 17th, when a cold front brings some prospect of cooler and less humid weather.
Now though, it’s mid-September. We have very high soil moisture content and lots of green vegetation. These factors mean we’re talking low to possibly mid 90s, and not 100+.
I seriously doubt we’ll see 100 again this year in Texoma, but it will feel like it over the next few days given the high daily Heat Index values expected.
By the way, the Autumnal Equinox, the astronomical start of fall, is coming quickly: It will take place 10:09p.m. CDT (Texoma time) on Wednesday 22 September.