562 FXUS63 KDTX 020343 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 1143 PM EDT Fri Oct 1 2021 .AVIATION... VFR conditions will hold into Saturday evening before low level moisture returns on south/southwest flow in advance of the next approaching low pressure system. A transition to low stratus with pockets of showers should be ongoing towards the end of this forecast period. .DTW THRESHOLD PROBABILITIES... * Low for ceilings at 5000 feet by late Saturday evening...medium overnight Saturday night. && .PREV DISCUSSION... Issued at 311 PM EDT Fri Oct 1 2021 DISCUSSION... Lower amplitude upper ridging will continue to mark conditions tonight and early Saturday, as the mean ridge axis only slowly exits eastward in response to pending height falls timed to arrive for the back half of the weekend. Deep column stability within a dry and seasonably warm resident air mass ensures continued mostly clear skies during this window. Generally moderating thermal profile boosted Saturday via persistent, yet modest warm air advection within deepening southwest flow and the early day window of full insolation. Highs will make a run toward 80 degrees in many locations -- a solid 10 degrees above average for early October. Lead wing of ascent fixated within some initial modest height falls and an accompanying uptick in mid level moisture transport then arrives during the late afternoon and evening hours. Dry low level environment likely slow to dislodge initially, but sufficient moisture depth expected to materialize within the background of improving large scale ascent to support a chaotic/scattered precip chance Saturday night. Deeper moisture plume then in residence throughout the Sunday and Sunday night periods. Eastern expanse of height falls associated with a closed low centered over northern Illinois will migrate into the area during the daylight period Sunday. Noted increase in mass convergence within a favorable corridor of upper diffluence, weak isentropic ascent and eventually some degree of frontal convergence maintains a higher likelihood for periodic shower production during this time. Late day diurnal boost likely as low level lapse rates modestly steepen beneath an already weakly unstable mid level profile. This supports at least an isolated thunder mention, but with limitations to potential cape magnitude and generally weak flow discouraging a more organized response. Broad mid level circulation slowly pivots across lower Michigan Sunday night and Monday. Tendency for deformation to strengthen within a narrow trowal axis fixated along the lingering elevated frontal zone maintains potential for unsettled conditions within the background of perturbed cyclonic flow this period. Some uncertainty yet in defining the southeastward pace and overall magnitude of the governing mid level dynamics, offering less clarity in the overall response by Monday. Main height fall center then relocates, at least briefly, south of the area for the middle of next week. This yields dry conditions with temperatures hovering at seasonable levels. MARINE... High pressure departs to the mid-Atlantic region this afternoon with an area of weak low pressure expanding into the western Great Lakes tonight. This tightens the southwest gradient tonight through Saturday with wind speeds increasing to generally around 15 kt. Some showers are possible across northern Lake Huron, but most locations south should remain dry through tomorrow before the better surge of moisture works in tomorrow night. Broad low pressure then spreads across the central Lakes on Sunday with periodic showers and a chance for some thunderstorms as well. Winds will remain below headline criteria as the low is expected to remain relatively weak and expansive. Cooler air settles in for the late weekend into early next week with northeast flow developing as the low exits to the south and east. HYDROLOGY... Unsettled conditions will develop Saturday night and persist through the remainder of the weekend period as a low pressure system slowly tracks across the area. This will lead to periods of showers, with some isolated thunderstorms. Rainfall totals between one quarter and three quarters of an inch will be possible before rain ends by Monday. This will lead to ponding on roadways, but no flooding concerns are expected. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. Lake Huron...NONE. Lake St Clair...NONE. Michigan waters of Lake Erie...NONE. && $$ AVIATION.....DG DISCUSSION...MR MARINE.......TF HYDROLOGY....MR You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.