Issued: 8pm on Sunday, September 27th 2020
Technical Forecast Discussion
Short Term (Sunday 9-27-2020 through Tuesday 9-29-2020)
Weak PVA resulting from a weak subtropical shortwave will work to lower heights over the forecast area on Sunday. Increasing differential PVA along with weak WAA will generate sufficient negative omega for clouds on Sunday afternoon. As this area of positive vorticity is advected north and eastward, the subtropical trough will become less amplified due to negative differential thickness advection. To our west, a tight height gradient is driving strong jet stream winds over the plains and Midwest states. This in turn is driving strong shear and curvature vorticity near this feature. This positive vorticity will be advected eastward throughout the day Sunday through Monday, propagating lower heights further east. Strongly increasing differential thickness advection will work to dig this trough south and eastward in the early morning hours on Monday. By mid morning Monday, positive differential thickness advection will close an upper low at 500 mb over Lake Michigan. With a tight height gradient becoming tighter, a jet streak looks to form over northeastern Iowa and southwestern Wisconsin. At the right entrance of another speed max over Michigan, Ontario, and Quebec, cyclogenesis will occur during the morning hours Monday over southern lower Michigan and northeastern Indiana. Because of a very strong vort axis due to the strong jet winds, low pressure perturbations along this axis will drive surface confluence, and therefore strong frontogenesis off the end of the surface low. Rapid intensification of this cyclone will occur over Lake Erie as very strong upper level divergence will be occurring throughout the day Monday. FROPA in southeastern Ohio will occur late in the day on Monday. With very weak thermodynamic profiles, convection associated with this strong cold front will not likely be severe (although with excellent shear profiles it is definitely possible). One or two convective sells along the cold front tomorrow may produce an isolated damaging wind gust. Behind this front, much cooler temperatures will be the story for Tuesday. Highs should be in the lower and middle 60s throughout the day Tuesday, with clouds and rain likely due to negative omega generated by PVA and WAA aloft.
Long Term (Wednesday 9-30-2020 through Saturday 10-3-2020)
Split flow on Wednesday between a polar and subtropical trough will occur. Our region will sit right in between the two troughs, keeping the area fairly average for Wednesday. Clearing out of clouds and precipitation should be expected for Wednesday. However, off to our north and west, strongly decreasing differential thickness advection and strong PVA will dig another trough down into the forecast area by evening Wednesday. This trough will be a polar trough, and bring much cooler temperatures into the forecast area. A strong jet streak brought about by a very tight height gradient will manifest itself over the northeast plains and northern Midwest by Wednesday night, bringing about cyclogenesis at the left exit of this feature throughout the day Wednesday. Frontogenesis will also occur with this feature, as the cold front slides to the south and east into our area by 2 AM Thursday morning. This will bring about widespread stratiform precipitation Wednesday night into Thursday. Thursday’s highs should reach the lower 60s across the entire state. Lows may bottom out to near freezing Thursday night. NVA Thursday should prevent widespread rain, although some lake effect showers may occur in the northeastern part of the state. A similar setup should occur on Friday, with highs only reaching the lower 50s up north, and upper 50s here in southern Ohio. Saturday, more clouds and scattered precipitation should be expected as PVA and slight WAA move back in. Highs will likely still be in the 50s across the state Saturday
