As discussed in last night’s Facebook Live, it’s no secret that May is Oklahoma’s peak severe weather season. So far we haven’t seen that many severe weather days. However, all of that is about to change starting this weekend and continuing through the 1st of June.
Strong cold fronts and an off-kilter weather pattern has kept the instability confined to the Gulf of Mexico for most of this Spring. Now things are changing to more of a typical setup with deep moisture working back into Oklahoma along with higher daytime temperatures. This leads to very high instability measured as CAPE (Convective Available Potential Energy). The output is in joules/kg which is just a way to measure energy. The higher the CAPE values, the more unstable the atmosphere will become. CAPE values in excess of 5000 are rare and leads to explosive severe thunderstorm development, which could literally be 15 minutes from the time a cloud base forms.
Next week we’ll have several days above 5000 somewhere across Oklahoma and even surrounding states of KS and TX. This will be the area to watch for severe storms. In addition, with the higher heat, comes an increase in the CAP (aka lid, or temperature inversion layer). The stronger the CAP the harder it is for a storm to form. This can either prevent storms from occurring at all in an otherwise high CAPE environment, or keep them isolated allowing the storms to take advantage of such. And yes, sometimes the CAP breaks all over and you get multiple storms. It’s a very tricky forecast and one that isn’t able to be fine tuned until 24-36 hours out. That’s when we’ll have an idea of how much instability will be present, the location of the surface boundaries, and if the CAP will break to allow severe storms to develop.
The type of severe storms we’ll see will be supercells. These will have the typical threats with them: large hail, damaging wind, and tornadoes. Wind shear is adequate next week for any or all of these modes. We’ll take each event one day at a time. There could be a couple of days where nothing happens next week, just like it could be a situation where we see severe storms each day somewhere across Oklahoma. I’ll update you accordingly. -AT
Posted below is output from the GFS computer model for each day’s CAPE values (Monday-Friday). This gives you an idea that the instability is here to stay.