Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0352 AM CDT Sat Oct 17 2020 Valid 201200Z - 251200Z ...DISCUSSION... ...Tuesday/Day 4 and Wednesday/Day 5... The medium-range models are in good agreement on Tuesday, moving an upper-level trough across the central United States. A surface low is forecast to develop in the southern Plains as moisture return takes place across the south-central states. Thunderstorm development will be possible Tuesday afternoon and evening along the northern edge of the moist sector from the central Plains into the mid Mississippi Valley. Although an isolated severe threat may develop at that time, the models keep instability relatively weak that far north suggesting the potential could remain marginal. The moist airmass is forecast to continue advecting northward on Wednesday with an east-to-west gradient of moisture setting up from the lower Missouri Valley into the Ohio Valley. This will be the favored corridor for thunderstorm development Wednesday afternoon and evening. Although deep-layer shear will be strong along this corridor, instability is forecast to remain weak suggesting any severe threat would again be marginal. ...Thursday/Day 6 to Saturday/Day 8... Model solutions diverge on Thursday with some advecting the moist airmass into the Upper Midwest with others keeping the moist sector further south. As an upper-level trough moves into the central and northern Plains on Thursday, thunderstorm development will be possible along the northern edge of the moist sector once again. A large variance in the amount of forecast instability among the solutions makes uncertainty substantial on Thursday. If enough instability can develop along the northern edge of the moist sector, then an isolated severe threat would be possible. On Friday and Saturday, the models move a cold front southeastward from the mid Mississippi Valley into the Southeast. Thunderstorm development will be possible along the front each day. However, the models are currently forecasting weak instability ahead of the front. This combined with substantial uncertainty makes predictability quite low late in the Day 4 to 8 period.
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