236 FXUS63 KDTX 220342 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 1142 PM EDT Sun Jun 21 2020 .AVIATION... The western edge of short wave impulses lifting across Ohio may support some light showers around metro Detroit early this morning. Latest model soundings and regional observations suggest these will remain high based, cigs above 5000 feet. With dewpoints across much of the area in the 60s and a weak gradient, there is some concern for some MVFR type vsby restrictions in fog. The extent of high clouds will be a limiting factor and will support keeping morning fog out of the TAFs. For DTW...The lack of instability suggests no thunderstorms with the early morning showers. In fact, the better instability and forcing will remain west of metro through most of the day Monday, limiting convective potential possibly well into the evening. DTW THRESHOLD PROBABILITIES... * Low in thunderstorms Monday. && .PREV DISCUSSION... Issued at 822 PM EDT Sun Jun 21 2020 UPDATE... The late afternoon convection has exhausted much of the available instability. Several mid level short wave impulses are noted in satellite imagery from eastern Kentucky into northwest Ohio. The lead impulse in Ohio is already driving some showers toward Toledo. While some shearing of these lead impulse is expected to take hold, there does appear to be some weak mid level deformation forcing on the northwest flank of the wave poised to impact the far eastern section of Se Mi from Monroe up through metro Detroit to Port Huron tonight, supportive of a chance for some light rain. The current forecast has a reasonable hand on this. Current radar trends, however, suggest the forcing arriving several hours earlier than the current forecast. So an update will be issued to increase the timing of the rain chances across the east tonight. With the additional energy lifting into northern Ohio from Kentucky, the forcing may still persist into early Mon morning along the eastern edges of the forecast area. Poor mid level lapse rates and the lack of diurnal instability suggests overall thunder chances tonight are pretty low. PREV DISCUSSION... Issued at 300 PM EDT Sun Jun 21 2020 DISCUSSION... Tail end of shortwave trough pivoting through the western/northern Great Lakes still looks to initiate scattered convection across the area this afternoon. That said, a fairly impressive subtropical plume of moisture in advance of this feature has lead to poor lapse rates through the column and extensive cloudiness through the morning has limited daytime heating. Both of these will inhibit the development of notable instability for the remainder of the day. Still, a wedge of partial clearing from SW lower MI into parts of the forecast area should allow for some disorganized development of showers and some thunderstorms which will fade by early/mid evening due to the lack of any decent upper support or low level forcing. Tonight, an upper level wave within the moisture plume will slowly work into the SE corner of Michigan from its current positioned from the Tennessee to southern Ohio Valley regions and bring some shower chances (which may persist into Monday morning given the slow movement of the wave involved). Lapse rates will only get worse with the influx of this deep layer of moisture so this activity should be limited to scattered rain showers or perhaps just an area of light rain/sprinkles. Once this activity clears, heating during the afternoon will contribute to some destabilization and lead to a few additional showers and thunderstorms late in the day/evening that will be forced by weak pre-frontal troughing in advance of a more significant shortwave pivoting into the area around the base of upper low pressure to the north of the Great Lakes. The trough axis associated with this shortwave will progress through the region late Monday night into Tuesday and provide a good chance of rain showers and perhaps a rumble of thunder at times. As this feature pivots into the upper level circulation to the north, the net result in the upper level flow will be for the upper trough/low to settle south and expand further through the Great Lakes. This will maintain a cooler weather pattern with highs in the 70s to near 80 through the mid week period next week. Precipitation chances will generally be relegated to widely scattered or isolated afternoon/early evening showers that develop under the upper level cold pool associated with the upper trough/low. Some warming can be expected by the Friday/Saturday period as this upper trough finally wobbles off to the east and a wavy zonal upper flow pattern becomes established on the southern edge of strong westerlies over southern Canada. This should result in a return of middle 80s for temperatures with a slow return of humidity into next weekend. A couple of shortwaves within this flow will also bring a better chance of periodic showers and thunderstorms to the area after the relative quite of mid week. MARINE... After a lengthy stretch of benign marine conditions, a slightly more active pattern is in store beginning this afternoon. Isolated to scattered showers and a few thunderstorms will move over Lake Huron this afternoon and early evening before dissipating. An area of showers then looks to clip western Lake Erie, Lake St. Clair, and possibly southern Lake Huron tonight into early Monday as weak low pressure tracks in from the Ohio Valley. Thunderstorms are not likely within this activity. A more organized low moves over Lake Michigan Monday evening and tracks across Lake Huron on Tuesday, bringing a good chance for showers and possibly a few storms across the marine zones. The passage of this system introduces a cooler west/northwesterly flow into the region by late Tuesday. Periods isolated to scattered showers will then be possible through the midweek as a broad upper low wobbles over the Great Lakes. HYDROLOGY... Scattered showers and thunderstorms associated with a trough will bring scattered showers and thunderstorms to parts of the area into this evening. While localized totals may reach one quarter of an inch or more, basin averages will be much lower. Additional showers and thunderstorms may bring similar rainfall conditions by Monday evening with a more general period of showers persisting on into Tuesday as a strong shortwave pivots through the area. While totals may reach or exceed half an inch locally, no flooding is anticipated from this activity aside from localized ponding of water on roadways and poorly drained areas. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. Lake Huron...NONE. Lake St Clair...NONE. Michigan waters of Lake Erie...NONE. && $$ AVIATION.....SC UPDATE.......SC DISCUSSION...DG MARINE.......TF HYDROLOGY....DG You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.