It appears likely that severe weather will occur as early as Sunday (April 7th) evening in southwest OK and northwest TX. The only thing that would hinder storm development is a temperature inversion in the PBL. If this cap breaks, isolated severe weather will be possible under 2000-2500 J/kg CAPE, 50-60 knot surface-500mb shear, 60-65 degree dewpoints and a lifted index of -9 or lower.
On Monday (April 8th), a dryline will setup in western OK that will extend into south-central KS and northwest TX. Capping inversion will still be strong on Monday afternoon through early evening, but with more diffluence aloft than Sunday, the cap will be more sustainable to break. Once again, 50-60 knot surface-500mb bulk shear will exist over west-central OK and extend as far north as south-central KS and as far south as northwest TX. A narrow swath of 2000-3000 J/kg CAPE will also exist in this same region, along with 60-65 degree dewpoints (though models differ, slightly). Latest and previous GFS runs have a strong cap over southwest OK and northwest TX, with some weakness in central OK, northern OK and southern/western KS. ECMWF also shows this weakness in the temperature inversion in northern OK and southern KS. This will be the most likely area where storms will develop, if they develop at all. In reality the best setup will be determined where the surface low develops. Models differ on the exact location. The best lift will be in the warm sector, near the low, east of the dryline and south/along the warm/stationary front. If this area could tap into some high CAPE, this would be a very dangerous time frame. Even 78 hours out (in the time of writing this), it is still a very tough forecast. The evolution of the upper and mid-level low will be a key factor in the time and location of severe weather.
Things are even more sketchy on Tuesday (April 9th). A dryline will most likely setup again in western OK. 04/05 12z GFS has the upper level low lifting northeast by Tuesday morning, and thus the threat of severe weather will exit the OK and KS area, making it a threat for central MO, eastern OK, and northwest AR by Tuesday evening. This is something that is possible, but I am ruling out for now. I will stick to its previous runs. This involves a very well defined surface low somewhere in central or southern KS. This low will have an associated dryline and cold front that will quickly push east and southeast, respectively. With plenteous moisture return from the Gulf of Mexico, severe weather will once again be likely in OK, KS, TX and MO and points eastward by late night. By early Tuesday afternoon, the dryline will be set in central OK. Any capping inversion east of this line will easily break with the surface low propagating east and northward. Dewpoints will be in the mid-60s in southeast OK and northeast TX. CAPE values probably won’t maximize until late afternoon/early evening. Once again, it highly depends on what the upper-level trough/low does. This will influence the surface low and depending on its track, severe weather will depend. The ECMWF is slower with the system and wants to bring the low farther south than any of the other numerical weather models. If this occurs, severe weather will be likely from south-central OK through north-central KS on Tuesday evening. If a faster, more northern track occurs, eastern OK, northeast TX, western MO, and western AR might get a period of isolated supercells before a squall line takes form. We should know more in the next 24-48 hours.
As stated above, Wednesday (April 10th) will depend on the location of the upper-level trough/low and the surface low. The slower ECMWF has a trailing cold front from western MO, extended through northern TX by early Wednesday evening. It has the surface low located in southeastern MO by then. Strong lift will be enhanced by this cold front. Anywhere from northeast TX through southern IL has a chance at seeing severe weather Wednesday afternoon through evening. This extending though the lower and middle Mississippi River Valley. However, it is still too soon to pinpoint exact locations of severe weather for Wednesday. I will get back to you with this one.