Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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888 FXUS63 KDTX 250400 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 1200 AM EDT Wed Sep 25 2024 .KEY MESSAGES... - Scattered thunderstorms are expected this evening. There is an isolated risk of severe storms along/south of an Ann Arbor to Detroit line. - There is a low chance for showers Wednesday, with dry weather forecast Thursday and Friday. - Daytime highs will mainly be in the 70s for the rest of the week. && .AVIATION... Low pressure will track from southwest Lower Michigan this evening to the central Lake Huron basin by Wednesday morning. Low to midlevel thetae content has lifted north of I 69 late tonight. A lack of an organized cold front and dry air advection will keep the low levels saturated overnight. The forecast remains fairly pessimistic for IFR and LIFR conditions in lower ceiling heights the latter half of tonight. Daytime heating will bolster MVFR ceilings Wednesday before a cold front and northwesterly flow clears things out Wednesday evening. For DTW/D21 Convection...Tsra no longer expected with this event. DTW THRESHOLD PROBABILITIES... * High for ceiling at or below 5000 feet tonight. * Low for ceiling below 200 feet overnight from 08 to 12z. && .PREV DISCUSSION... Issued at 259 PM EDT Tue Sep 24 2024 DISCUSSION... A mid level short wave and associated sfc low will lift northward across Lower Mi tonight. This short wave is ejecting away from the ongoing development of a closed mid level low over the Mid Mississippi Valley. Respectable moisture transport/isentropic ascent combined with the northward advection of instability will support numerous showers and scattered thunderstorms this evening. The associated sfc warm front is forecast to lift into Se Mi this evening. ML CAPE values of 500 to 1000 J/kg are forecast to lift into the I-94 corridor and points south this evening. This combined with modest deep layer shear and at least a short period of good low level cyclonic curvature on the hodograph suggests some mini supercells are possible this evening, mainly in the south. While the upper low meanders across the Mid MS and TN Valleys on Wednesday, northern stream trough amplification will evolve into another closed mid level low to the northeast of Lake Huron by Wednesday night. Lingering low level moisture and sfc troughing overhead Wednesday combined with weak larger scale ascent via the northern stream trough will support a low chance for light showers. Diurnal heating support afternoon highs into the upper 60s to low 70s. Mid level subsidence and sfc high pressure will then expand across Lower Mi from the west Wed afternoon and evening and will usher in a much drier airmass. Mid level ridging and sfc high pressure will then hold across the Great Lakes region through the end of the work week. Despite the north-northeast flow, the airmass will not be very cold. Diurnal heating should allow highs to be in the 70s while the dry air will promote nighttime lows down into the 40s and 50s. The upper low meandering over the TN valley and the remnants of Helene lifting inland from the Gulf Coast is forecast to interact/phase by the weekend. There is ample ensemble spread with respect to how quickly this system drifts northward toward the Great Lakes. Some members even struggle to bring the moisture into Se Mi in light of the strong ridging over the northern lakes. At this stage in the forecast, a chance of showers will be maintained through the weekend. MARINE... Low pressure over southern Lake Michigan this afternoon will continue to track northeast, moving through central Lake Huron tonight. Mainly light winds in and around the low, but both waterspouts and thunderstorms are possible with the cyclonic low level flow and instability through tonight. Behind the low on Wednesday, northwest winds still look to be mostly light, but locations over northern Lake Huron look to briefly top out in the 20- 25 knot range. Winds then dropping at or below 15 knots Wednesday night into Thursday as high pressure builds back into the region. Winds becoming northeast to end the work week as the high moves off into Eastern Canada and low pressure lifts north out of the Southeastern United States. The pressure gradient will be tightest over Lake Erie, and gusts of 25 to 30 knots appear likely Friday- Saturday morning. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ AVIATION.....CB DISCUSSION...SC MARINE.......SF You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.