431 ACUS48 KWNS 090835 SWOD48 SPC AC 090833 Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0333 AM CDT Sun Aug 09 2020 Valid 121200Z - 171200Z ...DISCUSSION... ...Wednesday/Day 4 and Thursday/Day 5... The medium-range models move a shortwave trough across the northern High Plains on Wednesday. A corridor of moderate instability is forecast across the central and northern Plains Wednesday afternoon. Some solutions suggest that thunderstorm development may occur along the western edge of the stronger instability in the western and central Dakotas late Wednesday afternoon. If this scenario plays out, then a severe threat would be possible across the Dakotas during the late afternoon and early evening. On Thursday, the models are in decent agreement with cyclonic west-southwest mid-level flow located in the northern Plains. An axis of moderate instability is forecast in the eastern Dakotas by afternoon. In spite of this, the models keep the airmass capped suggesting that convective coverage would remain sparse. If the cap is weaker than forecast and convection does develop, then an isolated severe threat can not be ruled out for parts of the northern Plains Thursday afternoon and evening. ...Friday/Day 6 to Sunday/Day 8... An upper-level trough is forecast to move across the northern Rockies on Friday as a mid-level jet moves into the northern High Plains. Although the ECMWF and GFS differ on the timing of the upper-level trough, both solutions suggest convection could develop by evening in parts of eastern North Dakota and northwestern Minnesota. Forecast instability and shear would be strong enough for an isolated severe threat under this scenario. On Saturday and Sunday, the models are in good agreement, moving a cold front southeastward across the upper Mississippi Valley and into the Great Lakes region. Isolated severe thunderstorms could develop along parts of the front each day. But uncertainty is substantial at this range concerning various factors including the magnitude of instability and the timing of the front. ..Broyles.. 08/09/2020
