Issued: 1pm on Wednesday, October 7th 2020
Technical Forecast Discussion
Short Term (Wednesday 10-7-2020 through Saturday 10-10-2020)
Strong NVA occurring over the forecast area is continuing to build a ridge. This will work in tandem with negative differential thickness advection to further amplify this feature as the week goes on. Due to a very strong height gradient, a strong jet streak has taken shape over lower Michigan, Wisconsin, and eastern Minnesota. At the left exit of this, strong upper divergence is driving strong cyclogenesis over Lake Huron and eastern lower Michigan. This cyclone will follow its forcing eastward throughout the day Wednesday. Trailing this strong SFC cyclone, an axis of confluence driven by low pressure perturbations caused by a shear VORT axis will drive frontogenesis over central Lower Michigan. As the SFC cyclone moves eastward throughout the day Wednesday, the front will slide to the south and east, impacting the forecast area Wednesday night. However, with low theta-e values downstream of the front, along with positive omega being driven by NVA and WAA, precipitation is not expected with FROPA. A few scattered clouds may be stirred up by this. Upper convergence upstream of the trough will drive a strong SFC anticyclone that will move in behind the front. With sinking motion being driven by this, along with the aforementioned positive omega, skies should remain mainly clear under the presence of this SFC high (Wednesday night through about midday Friday). However, this SFC high will be a cold core high, which will bring fall like temps back into the area Thursday and Friday. Highs should be in the lower and middle 60s these days (with a few 70s possible Friday). This calm weather will not last into the weekend, however. A VORT max associated with Hurricane Delta will move its way up the Mississippi valley into the Ohio Valley Friday afternoon through Saturday. With axes of positive VORT (driven by shear effects) advecting into our area Friday afternoon into Saturday, along with strong aloft WAA, clouds should be expected to move in due to negative omega on Friday afternoon. By Friday night, stratiform precipitation should move in as well, lasting through the day Saturday. With the lack if diabatic heating Saturday, highs should only reach the upper 50s and lower 60s.
Long Term (Sunday 10-11-2020 through Tuesday 10-13-2020)
Delta’s remnants will continue to affect the area throughout the day Sunday. The heaviest precipitation should be Saturday night into Sunday. However, throughout the day Sunday, very strong decreasing differential thickness advection will work to erode the VORT max and trough of the system (along with shear presented by the land, and lack of warm water feeding into the system). The system should be eroded by Monday morning. Continued increasing differential PVA and aloft WAA will generate sufficient negative omega to allow clouds and precipitation to hang around through at least Monday morning. However, NVA will start working with the negative differential thickness advection to build a highly amplified ridge into the area Monday night into Tuesday morning. Strong differences exist between guidance as to how this ridge will behave, along with how a strong western trough will propagate throughout the day Tuesday. The GFS, being less aggressive with decreasing differential thickness advection with the trough, propagates the trough east into the forecast area Wednesday. This will provide a much cooler solution to the forecast over the long term. The EURO, however, being very aggressive on decreasing differential thickness advection associated with the trough, tilts the trough negatively over the central plains, occluding the trough and associated cold front at the surface. This solution will keep above average temperatures in the forecast area through next weekend. Much more will be known about the overall pattern for next week in later discussions–stay tuned.
