Issued: 4pm on Sunday, August 30th 2020
Technical Forecast Discussion
Short Term (Sunday 8-30-2020 through Tuesday 9-1-2020)
An oscillation between NVA and PVA over the next 12-24 hours will keep heights mainly neutral over the area. The weak PVA will drive some clouds throughout the day on Sunday. Other than a few passing clouds, however, Sunday looks absolutely beautiful for this time of year. Highs will be mild–in the upper 70s and lower 80s, with little humidity. The beautiful weather for this time of year will be short lived, however. A mid level VORT max will gain strength via conservation of angular momentum off the Cascades over the next 6 hours or so. Once this feature gains strength, heights will begin to fall downstream because of PVA. Positive differential thickness advection will work to slightly dig, and tilt this feature more negatively as it continues to propagate further eastward. This feature should be strongly negatively tilted by noon local time Monday, and located over Minnesota. because of the slight digging nature of this feature, height gradients will be tightened, and a jet streak will begin to develop as a result. Weak cyclogenesis will occur at the left exit of this jet streak, over SW Minnesota and NW Iowa. A vort max will drive a sfc trough, driving an axis of confluence to the south of this low. This will result in frontogenesis of a cold front early Monday morning. This front will follow its forcing low throughout the day Monday, and reach the Chicago area by late Monday evening. In our region, positive differential vorticity advection, along with WAA at 500 mb will create negative omega throughout the day. Relatively modest MLCAPE will present the chance of convection throughout the day Monday, although no severe weather is expected at this time. Stratiform rain and convection should exit the forecast area Monday afternoon/evening. Cyclolysis/frontolysis should begin to occur as the system makes its way further east due to differential thickness advection taking on a negative sign. This will allow the VORT max to retreat back to the north, allowing the low to fill, and fronts to dissipate. Highs on Monday should mainly remain in the middle and upper 70s, with a few possible 80s here or there. Due to a lack of PVA during the first half of Tuesday, clouds/rain will not arrive in time enough to prevent highs from reaching the lower and middle 80s. Slight chances of rain should reach the forecast area by 7/8 PM Tuesday evening. Precip should remain mainly stratiform, as CAPE values will be little to none.
Long Term (Wednesday 9-2-2020 through Saturday 9-5-2020)
Precip should evade areas north of US-50 Wednesday. While positive differential vorticity advection will exist, a slightly barotropic, to near CAA environment at 500 mb will prevent omega from going negative. Another VORT max coming off the Pacific will dig due to positive differential thickness advection. Like the previously mentioned VORT max in the short term, this will gain strength coming off the Cascades, and dig itself down to the upper Midwestern states by Thursday morning. Because of the newly formed tight height gradient, a jet streak will develop, with a strong SFC cyclone forming at the left exit of this. This strong cyclone, along with a positive VORT axis will drive the development of a cold front. This front should reach the Chicago area by late Thursday afternoon into Thursday night. Precipitation will be slightly possible here in southern Ohio throughout the day Thursday due to weakly negative omega. Unlike the previous cyclone, planetary vorticity will assist the maintenance of this cyclone as it retreats north to the Hudson Bay. This will allow the cold front to continue to race eastward into Ohio by late Thursday night/early Friday morning. Due to the nocturnal nature of this front, along with the weakness of the front due to a lack of supporting VORT aloft, rain should evade the area with this FROPA. After FROPA, temps should return to the upper 70s and lower 80s, after a brief trip to the middle and upper 80s. Some PVA will be present Saturday. However, with CAA aloft, precipitation will not be likely. A strong cold core high will develop at the right exit of a jet streak Saturday, making it a very pleasant day for this time of year. Mainly sunny skies, with temps in the upper 70s and lower 80s to begin the weekend looks likely as of this time.
