Ahead of the front, conditions were still rather stable and surface moisture was limited with dewpoints in the low 40s across eastern Oklahoma into western Arkansas and only in the low to mid 50s across east Texas and much of Louisiana. The flow today will continue to be southerly so some advection of moister air will flow northward through these regions increasing the low level moisture. Mix this will surface heating that will allow afternoon temperatures to rise into the mid 60s across southern Missouri, upper 60s/low 70s across Arkansas and eastern Oklahoma and mid 70s across much of eastern Texas; chilly temperatures aloft associated with the strong upper level system; the surface front; and upper level dynamics and you set the stage for thunderstorm development. Question is, will these become severe? The overall atmosphere will become marginally unstable enough for severe weather to develop and the Storm Prediction Center has deemed enough of a risk exists to issue a "Slight Risk" for severe storms for extreme southern Missouri through most of Arkansas eastward to the Mississippi River through 7 am Sunday with the highest risk being late this afternoon through the evening hours.
Initially, these storms will likely develop as isolated super cells that will provide for medium to large hail and a few isolated tornadoes; however the overall tornado risk is low. As the storms evolve they will merge and become linear providing for the potential of high winds as the lines begin to bow out. When they bow it is possible, still, that a short-lived weak tornado could form on either end of the bow. These are known as bookend vortices.
The entire storm system will progress eastward through Saturday night and early Sunday morning. The remaining showers and storms will progress through Mississippi, western Tennessee and into Alabama, early Sunday morning; however, they will likely no longer be severe as conditions will not be favorable. The front will lag, though and that means the possibility of new severe storms firing Sunday afternoon/evening. The question is how far west will they begin to fire and that will be highly dependent on the amount of clearing that can occur behind the morning showers/storms. The setup is looking similar to that which occurred on Thursday but a bit further eastward. As a result, anticipating that new storms will begin to develop early Sunday afternoon just west of I-65 and progress rather quickly eastward through eastern Alabama much of Georgia and south Carolina. Storm Prediction Center has issued a "Slight Risk" of severe weather to cover these areas. Similar to what is expected today, initial storms will likely be single cells that will hen form into lines producing the highest severe risk of large hail and damaging winds.
Note, you may experience hail that appears rather large and size and wonder why there is no warning in affect. The reason is that the National Weather Service recently changed the severe criteria of hail size. Previously, the severe criteria was "penny size" or officially ¾ of an inch diameter hail. Now the criteria is "quarter size" or 1" diameter hail. This will likely impact the number of warnings issued. I already noticed this during the recent storms that occurred Thursday here in the Tennessee Valley. We had several reports of penny size hail but only had a couple of warnings and they were mainly for the couple of tornadoes that occurred.
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