FXUS63 KDTX 210752 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 352 AM EDT Sun Jun 21 2026 .KEY MESSAGES... - Dry weather with increasing clouds today. - Showers and thunderstorms increase coverage tonight, especially south of I-69 where rainfall totals range from 0.5 to 1 inch. The best chance of locally higher amounts is toward the Ohio border. - Showers linger Monday morning then dry weather follows in the afternoon and evening. - Cooler than normal temperatures continue through at least the middle of next week. && .DISCUSSION... Early morning satellite and surface analysis indicate patchy fog and stratus leading up to sunrise, especially toward the Tri Cities and Thumb where wet ground augments surface based moisture. The fog component continues to expand through sunrise and then quickly dissipates. Otherwise, the day starts with full sun as broad but weak high pressure builds from the Midwest into Lower Mi to govern conditions through today. Clouds are on the increase this afternoon in a combination of high based cumulus and thickening cirrus off the central Plains MCS debris shield. The slightly below normal temperature theme of recent days continues today as abbreviated afternoon peak heating leaves highs in the mid 70s. The inbound cirrus cloud shield this afternoon is a prelude to increasing coverage of showers and a few thunderstorms across southern Lower Mi this evening which continue through the night and Monday morning. This pattern is driven by the central Plains low pressure/MCS combo in progress as the short wave and mesoscale features migrate into the mid MS and OH valleys tonight. Pronounced mid/upper level circulation noted over SD/NE in WV satellite imagery early this morning adds confidence to the moisture transport scenario expected to be the primary driver of showers/elevated storms across southern Lower Mi tonight. Backed 850-700 mb flow ahead of this short wave carries moisture and elevated instability into Lower Mi to fuel the expanding area of showers/general storms. Consensus of deterministic model QPF holds totals below 1 inch which is now reflected in the latest NBM run. Attention is also given to HREF PMM QPF keeping higher end totals around 1.5 inches in play, which is plausible given the potential for strong mesoscale interactions between the north flank of the MCV, the short wave, and upper jet entrance region during the peak of the event around 06Z tonight. The stronger forcing gives showers a chance to reach farther north toward the Tri Cities and northern Thumb while the bulk of greater rainfall still occurs south of I-69. The scenario transitions to a shearing deformation pattern which keeps showers focused over southern Lower Mi through Monday morning. This additional rainfall is accounted for in the system total but produces generally less than an additional 0.25 inch until ending by early afternoon as the deformation axis moves eastward. The rest of Monday and Monday night end up with dry weather as a short wave ridging moves from the Midwest into the Great Lakes along with accompanying surface high pressure. The mid/upper level long wave flow remains low amplitude and progressive through mid week with the next low pressure system currently projected for Wednesday. && .MARINE... A diffuse area of high pressure will hold across the Great Lakes through today, supporting a continuation of lighter winds. A compact low pressure system will then move through the Ohio Valley and southern Great Lakes tonight into Monday morning. Rain showers are expected to be most concentrated across Lake Erie up to Lake St. Clair. Elevated northeasterly winds will increase and persist through the daylight hours Monday. The longer onshore fetch on Lake Erie will support higher waves by daybreak Monday. A Small Craft Advisory is in effect there for late tonight and Monday. && .HYDROLOGY... Showers and thunderstorms expand over southern Lower Mi tonight as an unseasonably strong low pressure system moves from the central Plains through the mid Mississippi River Valley late Sunday and into the Ohio River Valley Sunday night. Widespread shower and thunderstorm activity develops along the northern periphery of the low pressure system and may bring locally heavy rainfall to southern portions of SE Michigan. While uncertainty exists on the exact placement, the potential exists for a large area of rainfall amounts ranging from 0.5 to 1 inch generally south of the I-69 corridor. There is also a chance for localized totals around 1.5 inches from about the I-94 corridor to the Ohio border. Trends will be monitored for signs of any northward shift on the track of the low pressure system that would produce a chance for a corresponding northward shift to higher rainfall totals and the potential for urban flooding. Otherwise, the above mentioned totals limit flooding potential to ponding of water on roads and similar prone areas until the rain moves out by Monday afternoon. && .PREV DISCUSSION... Issued at 126 AM EDT Sun Jun 21 2026 AVIATION... General nocturnal stability overnight will maintain mostly clear skies. Potential exists for a period of fog prior to daybreak, mainly across FNT and MBS. Observational trends suggest fog could become more dense at MBS owing to the recent rainfall, leading LIFR/IFR visibility restrictions. Dry and stable conditions will maintain benign conditions for the daylight period Sunday. Standard higher based diurnal cu to emerge with daytime heating. Low pressure system tracking through the Ohio valley will bring thickening mid cloud and increasing rain chances around 00z, with a steady decline in cloud base likely thereafter heading into the overnight period Sunday. D21/DTW Convection... No thunderstorms expected through Sunday. DTW THRESHOLD PROBABILITIES... * Low for ceiling at or below 5000 ft Sunday. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...Small Craft Advisory from 4 AM to 5 PM EDT Monday for LEZ444. && $$ DISCUSSION...BT MARINE.......AM HYDROLOGY....BT AVIATION.....MR You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.