A related thread can be found at
http://www.stormtrack.org/forum/viewtopic.php?t=6357
Nobody can accurately forecast severe storm and tornado occurrence beyond a few days. The OVERALL synoptic pattern certainly doesn't look favorable for tornado outbreaks or strong tornado events in the plains for the foreseeable future, but that's based on model forecasts, which become more and more guess-casts in time. I can, with fair confidence, say that we shouldn't expect a strong tornado event in the plains for at least a week, with ANOTHER (if we haven't seen enough already) cut-off upper low forecast to drift from the Missouri river vally southward into eastern Texas through the week, leaving most of the plains in northerly flow. Given the time of year, I'd say that the southern plains window is starting to close, so my eyes turn, naturally, northwards towards KS/NE. Again, this year has been very unclimatological, so any forecast based on climatology probably won't verify too well.
On a lighter note, I would try to chase during the June 1-6 timeframe. This spring, there are/have been two periods during which I cannot/couldn't chase. The first was the May 12-15 period (missed the May 12th, 13th supercells). The second will be the June 1-6 period; book your calendars now!
So... it would do no good to try to forecast chase chances for the period from late May through MID-JUNE (that's a month out!). We may be able to identify synoptic patterns that may or may not be favorable for the development of severe storms a few day in advance, but anything into the mesoscale or lower is worthless beyond a day or two. Anything farther out would be like looking at a CPC temperature graphic and saying that above-average temps for the next month must signal ridging and no tornado chances -- ludicris.