Issued: 2pm on Wednesday, September 16th 2020
Technical Forecast Discussion
Short Term (Wednesday 9-16-2020 through Saturday 9-19-2020)
PVA from the remnants of Hurricane Sally will slightly lower heights over the area over the next 24 hours or so. The associated VORT max with this feature will continue to propagate just north of east over the southeast states into Thursday. Over our area, weak positive differential PVA and WAA aloft will stir up a few clouds going into Thursday. However, with the center of the system very far off to the south, precipitation chances will be very low going into the day on Thursday. A possible isolated shower may present itself Thursday morning, or early Thursday afternoon in the southern portion of the forecast area, but elsewhere will stay dry. After this feature moves off to the east (off the coast of the Carolinas), an axis of positive vorticity associated with a prevalent closed upper low in Canada will dig itself down because of positive differential thickness advection. The associated advection of this feature, along with the positive differential thickness advection will dig this feature down into our area Friday morning. Confluence aloft over northern Minnesota will force anticyclogenesis at the surface. This surface anticyclone will be associated with much cooler air to the left of the flow in the jet. As this trough continues to dig down into our area throughout the day Friday, the cold core surface high will continue to follow. Meridional northerly flow will assist in surface CAA Friday and Saturday. With the high will come large scale sinking motion across the entire area–a perfect setup for mainly clear skies across the entire forecast area. With the jet overhead, watch for haze from the west coast wildfires to present itself Friday into Saturday. Highs for the early weekend will be much below average–middle and upper 60s. Lows could reach the upper 30s in spots on Saturday night, as clear skies will be present. If there are any plans for the weekend, it will be absolutely beautiful for this time of year. Off to our west, weak NVA will work to build a weak ridge over the plains throughout the day Saturday.
Long Term (Sunday 9-20-2020 through Tuesday 9-22-2020)
Going throughout the day on Sunday, the ridge to our west will become much more amplified, reaching all the way up into eastern Manitoba by 8 AM eastern time. This will be due to the previously aforementioned NVA, now working in tandem with negative differential thickness advection. This will work to warm highs slightly on Sunday, possibly reaching the 70s again on Sunday afternoon. Influence from the cold core high will still be in place, keeping mainly clear skies overhead for Sunday. Discrepancies exist between the models regarding the overall pattern going into the beginning of next week. The EURO places Hurricane Teddy about 500 miles off the coast of the SE on early morning Monday, meeting a VORT axis from the trough that will dig through the area on Friday. This solution will phase these two systems just off the east central coast, and cause more large-scale troughing over our forecast area. The GFS, however, paints a different picture. With a much weaker and faster moving trough than the EURO, the Teddy will not reach the right area in time to phase with the trough. This will present the area with a slightly warmer solution than the EURO’s. Discrepancies exist due to differences in the extent of aloft temperature advection, which forces trough digging and strengthening. Much more will be known in the coming days. However, with the track record of the EURO, I would favor its solution at this time. In any case, highs will be in the upper 60s and lower 70s to start next week, with mainly sunny skies.
