789 FXUS63 KDTX 230746 AFDDTXArea Forecast Discussion National Weather Service Detroit/Pontiac MI 346 AM EDT Tue Sep 23 2025
.KEY MESSAGES...
- A Dense Fog Advisory is in effect for portions of Southeast Michigan through 9am.
- Scattered showers and thunderstorms will be possible through the middle of the week. Localized heavy rainfall may be possible.
- Temperatures in the 70s throughout the week which will generally be at to slightly above normal.
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.DISCUSSION...
The main influence on weather over the next few days will be a thermodynamic environment that includes a moist troposphere below 8.0 kft agl and little to no stability in the column. In fact, model soundings support unstable conditions continuing during the Tuesday and Wednesday overnight periods with midlevel lapse rates steeper than moist adiabatic. PWAT values are projected to hold at around 1.30 inches during the coming days. As a result, the primary concern through Thursday will be the potential for heavy rainfall with shower and thunderstorm activity and the possibility of flash flooding.
For this morning, a lack of surface wind with moist near surface conditions has led to fog development for the lower elevation areas south of the Irish Hills. Some HRRR condensation pressure deficit data suggests this will continue through daybreak or 13Z. Unsure and uncertain how much fog will really develop or fill in over the urban heat island but the potential does exist for some fog in Detroit. Added areas of fog into the forecast and will monitor trends this morning. If it becomes widespread could issue a Dense Fog Advisory.
Very subtle forcing mechanisms at play today with weak quasi stationary baroclinic zone hanging out around Saginaw Bay and the warm sector to the south. Models show closed upper low circulation meandering very slowly/drifting southward from the U.P. and Lake Superior likely only accentuating the boundary. A weak upper level jetlet is shown to eject eastward along the southern periphery of the closed low directly into Lower Michigan. Plan view of thetae shows moisture ribbon/higher thetae content advecting into the area timed with the jet streak. This is forecasted to slide across the northern cwa invof the aforementioned baroclinic zone this afternoon. So while precipitation/shower thunderstorm chances will exist across all of the cwa, the most likely location for activity is north of the M59 and I 69 corridors. Slow storm movement of west to east brings the potential for heavy rainfall at any one location. Difficult to really message rainfall amounts given the convective setup, but the modeled interquartile ranges of QPF is not outright concerning.
For tonight, a persistence in elevated instability brings the potential for additional shower and thunderstorm activity tonight. Stalled out activity and/or training along boundaries may result in heavy rainfall.
One big model trend in the latest guidance is for an increase or convergence in model solutions for vertical velocities late Wednesday afternoon particularly across the south half of the cwa. This is in response to upper level low pressure and prior MCV remnants phasing into and ejecting northward across the Ohio River Valley. The trend has been to move timing of this low pressure up prior to Wednesday night. Latest guidance including the NAM and EPS membership suggest bulk of the frontogenesis and strong isentropic lift associated with the near surface circulation will just miss the area to the south and east. Control run of ECMWF still brings a direct hit. Obviously, this is something that will need to be monitored, possibly even a Flood Watch, as any northward jog could bring heavy rainfall axis into the forecast area under a SHARS type scenario.
Mainly dry conditions are possible for the end of the week and and next weekend as models are suggesting midlevel and surface ridging in place. Despite northwest flow, not seeing any signal for cold air so above normal temperatures of upper 70s and near 80 degrees is a real possibility. Humidity values are more uncertain and could be running a little high in the latest forecast.
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.MARINE...
An upper level trough is draped over the Great Lakes and will linger through mid week while slowly dropping southeast. Low pressure system currently spinning over the northern lakes will help force a stalled front southward today while additional weak wave may ripple along the front. This will lead to an extended period of unsettled weather with multiple rounds of showers with occasional embedded thunderstorms. Pressure gradient is weak and winds aloft are also weak so chances of any stronger winds or gusts with storms are lower. Winds will become northeasterly today behind the front and remain northeasterly through midweek.
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.PREV DISCUSSION... Issued at 1156 PM EDT Mon Sep 22 2025
AVIATION...
The combination of light winds, clearing skies, and higher surface moisture will bring favorable conditions for fog development during the early morning hours. MVFR/IFR VSBYs in play with a chance for periods of LIFR as well. Early night observations shows dense fog currently focused near the southern Michigan border that is expected to slide northward towards the metro terminals with time tonight. Additional areas of fog are starting to develop across the Thumb under clear skies. Morning fog will gradually lift during the first few hours after sunrise and will be followed by renewed chances for showers and isolated thunderstorms during the afternoon and early evening. Coverage of activity may be more isolated, so will be highlighted by PROB30 groups. Winds will remain light and out of the southwest with a mix of MVFR and low VFR ceilings.
For DTW/D21 Convection...Low potential for thunderstorms this afternoon. Most favorably time frame is between 17Z to 23Z. Confidence is too low to mention in TAFs at this time.
DTW THRESHOLD PROBABILITIES...
* Medium for ceilings at or below 5,000 feet early this morning.
* Low for cigs/vsby to fall to 200ft and/or 1/2sm early this morning.
* Low for thunderstorms to impact DTW this afternoon.
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.DTX WATCHES/WARNINGS/ADVISORIES... MI...Dense Fog Advisory until 9 AM EDT this morning for MIZ063-068>070- 075-076-082-083.
Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. &&
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DISCUSSION...CB MARINE.......DRK AVIATION.....AA
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NWS DTX Office Area Forecast Discussion