


Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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053 FXUS63 KDTX 121345 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 945 AM EDT Sat Jul 12 2025 .KEY MESSAGES... - Showers and thunderstorms return this afternoon, capable of isolated severe gusts to 60 mph and torrential rainfall which could produce localized flooding. - The combination of heat and humidity today will lead to max heat indices in the upper 90s for Metro Detroit, prior to the arrival of thunderstorms. - Mainly dry and more seasonable temperature-wise Sunday, then warming back into the 90s midweek. && .UPDATE... Low pressure and mid level jet max tracking through the Straights this morning with a weak surface troughing extending south into south central Lower Michigan. 12z DTX sounding showed good speed bump around 800 MB, along with the pronounced surface based inversion, which will need to be eroded. 700 MB temp also fairly warm at 9 C. None-the-less, surface dew pts in the lower 70s with temps warming toward 90 degrees around noon/by early afternoon will be sufficient for SBcapes aoa 2500 J/kg. The issue is the upper level trough over Minnesota and associated height falls/mid level cooling is not looking to be a factor for us, and we will have to utilize a more subtle height fall center/PV advection coming up from the western Ohio Valley to support shower and thunderstorm development with the weak low level trough/convergence sliding east through the day. Based on timing and slightly backed flow due to marine influences, areas over eastern areas of the CWA look to have greatest coverage of storms and potential of severe storms. Precip loaded downbursts producing wind gusts of 50-60 MPH being the main hazard, along with torrential rainfall potentially producing localized flooding with relatively slow movement of storms and possible training as outflow boundaries get going. Update was mainly to adjust highest pops (70+) over far eastern areas, and highlight noon-8 PM as the main window. && .PREV DISCUSSION... Issued at 703 AM EDT Sat Jul 12 2025 AVIATION... Warm and humid air entrenched across the area governS aviation conditions today and at least through this evening. Patchy MVFR fog to start is short-lived as mid July daytime heating quickly ramps up this morning. Full VFR then leads to another round of thunderstorms expected to blossom and feed off the heat and humidity this afternoon and evening. Weaker showers/storms could begin by late morning toward MBS and then expand in coverage and intensity through the afternoon eventually affecting all terminals by late afternoon. Expect numerous overall coverage with clusters of severe intensity bringing potential damaging wind in addition to IFR/MVFR restriction in heavy rainfall. This activity occurs ahead of the primary cold front which could bring a stray shower or storm late tonight followed by a short period of MVFR ceiling leading up to sunrise Sunday morning. For DTW/D21 Convection... An afternoon time window for thunderstorms remains on schedule. Earlier initiation is possible toward MBS and the northern reaches of D21 while timing of more direct impacts at DTW is still closer to 21Z. THRESHOLD PROBABILITIES... * Low for ceiling 5000 ft or less outside of thunderstorms today and this evening. Moderate with the cold front late tonight. * Moderate for thunderstorms this afternoon. PREV DISCUSSION... Issued at 356 AM EDT Sat Jul 12 2025 DISCUSSION... Periodic convection with renewed potential for some severe thunderstorms returns today as an active pattern holds firm over the Great Lakes. Upstream convection exits into northern Lower through the remaining morning hours while mid-level is underway over Southeast Michigan. Thermodynamic profiles are still supportive of an elevated mixed layer with over 500 J/kg of MUCAPE before deep- layer southwest flow slides into the region. A shortwave trough with a 50+ knot jet core at 500 mb ejects across western Lower today and starts to phase with a more amplified trough tilting from neutral to negative over the Upper Midwest. Main corridor of CVA should largely reside west of the forecast area as midday convection starts to initiate, likely between 16Z and 18Z. This activity predominantly develops along the CAPE gradient, in the vicinity of the western CWA border. Main plume of instability, marked by MLCAPE of 1000-1500 J/kg, will quickly blossom and overspread Southeast Michigan through the early afternoon hours. Surface reflection from the parent wave takes a more north- northeasterly track which slows the advance of its attendant cold front. Wind progs indicate the more pronounced south-to-west wind shift closer to 06Z (Sunday), thus the pre-frontal surface trough axis will serve as the more important dynamic mechanism to amplify convection. Perhaps more importantly, the majority of the latest NWP suite supports surface-based free-convection with ELs above 35 kft once surface dewpoints revisit the lower 70s and 2m temperatures jump to near 90F within the expanding warm sector. Shear parameters are not overwhelmingly impressive, but remain sufficient to help organize some linear structures. Severe threat still mainly focused on wind hazards (isolated gusts to 60 mph) and torrential rainfall. For what it`s worth, ML data has carried higher severe wind probabilities with run-to-run consistency. Also of note, prior to the onset of precipitation, the greater Metro Detroit area could see heat indices approach 100F, but it will be marginal since mid-70F dewpoints appear to be the exception rather than the norm. The front makes gradual inroads into Ontario late tonight which corresponds to a drying locally, from west to east. Subset of CAMs indicate a secondary storm response along the actually cold frontal slope, but intensity should be significantly lower if this materializes. Post-frontal airmass characterized as cooler and drier for Sunday, although temperatures should run near climatological averages (mid 80s). Can`t completely rule out a few showers for the extreme southeast portion of the CWA with the slowed boundary. Longer wavelength trough axis aloft then backs the temporarily zonal flow aloft with little sensible fanfare. A rebound in geopotential heights is in store for next week as synoptic-scale anticyclonic gyre organizes over The Southeast. This promotes moderating thermal profiles with negligible storm potential Monday and Tuesday. Zonal jet centered over the 50th parallel delivers a weak wave extending into southern Lower Michigan as soon as Wednesday that could spur convective activity. Model divergence has emerged in the medium- range solutions for the extent of thermal troughing over the state, but NBM output exudes confidence with a cold FROPA by Friday. MARINE... Renewed chances for showers and thunderstorms today ahead of and along a cold front, which brings chances for strong to severe thunderstorm development capable of producing wind gusts aoa 35 knots. Winds veer toward the southwest then continue toward the west after the passage of the front. Mainly dry conditions and light winds expected in the wake of the front, and through early next week. HYDROLOGY... Some heavy showers and storms are likely today as a hot and humid airmass builds back into the region. The environment will support pockets of heavy downpours with rainfall rates possibly exceeding 2 inches per hour. Localized flooding concerns exist for some areas that experience clustering of cells. Flooding threat will largely be for small streams, low-lying roadways, and otherwise poorly drained areas. Activity should wane from west to east early tonight as drier weather settles in for the rest of the weekend and early next week. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...Small Craft Advisory until 10 PM EDT this evening for LHZ421-422. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ UPDATE.......SF AVIATION.....BT DISCUSSION...KGK MARINE.......AM/KGK HYDROLOGY....KGK You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.