Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0255 AM CDT Fri Apr 21 2023 Valid 241200Z - 291200Z ...DISCUSSION... The ECMWF model has shown good run-to-run consistency with the overall weather pattern, depicting an upper wave diving southeastward across the Great Basin on Monday/D4, and reaching into the southern Plains during the Tuesday/D5 to Wednesday/D6 time frame. As this general solution develops, stronger winds aloft will overspread a moistening air mass from TX across the Gulf Coast states, and areas of severe storms will be possible. However, given the subtle nature of the upper wave emerging into the Plains with a positive tilt, and moisture return into an initially cool air mass, predictability issues exist regarding timing and location of potential severe storms. Scattered storms are expected on Tuesday/D5 over parts of northern into eastern TX with modest theta-e advection in the low levels. However, the main upper trough will still be well to the west, with height rises over the southern Plains. Cool temperatures aloft may favor hail in some of this activity. By Wednesday/D6, stronger southwest flow aloft with 40-50 kt 500 mb winds will continue eastward across TX and into the lower MS Valley, and low-level moisture will be well established. Areas of moderate to strong instability could develop over parts of southern and eastern TX, but again, predictability is currently low, both due to the slowing upper trough movement and the probability of antecedent areas of storms throughout the period. Weak low-level winds, in general, could mitigate the overall risk, although large hail does appear likely where heating occurs. Predictability lessens further the D7/D8 period, but an eastward shift in storm activity is expected across the Southeast, where moderate westerlies aloft overspread the better moisture over the coastal states. Potential for severe storms exists, but predictability will depend on proper timing of the upper wave.
