698 FXUS63 KDTX 190720 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 320 AM EDT Thu Jun 19 2025 .KEY MESSAGES... - Light to moderate rain continues this morning with better coverage across the Tri-Cities and northern Thumb. Additional chances for showers and thunderstorms this afternoon and evening. - Chance (20-40%) for showers and thunderstorms again Friday and Saturday. - Hot and dry Sunday and Monday. High temperatures in the 90s and heat index around 100 are likely, with minimal relief at night. && .DISCUSSION... An area of deformation aligning with wrap around moisture from the departing low pressure system will continue to support widespread light rainfall through the Tri-Cities and northern Thumb. Isolated to scattered coverage will be possible for locations south. The lack of instability will hamper thunderstorm chances, keeping rainfall rates in check, but the prolonged rainfall across the Tri-Cities will produce an additional half-inch to inch of new accumulation leading into the late morning hours. The continued departure of the low will back flow and release the residual moisture into Southeast Michigan ahead of a trough axis which will expand light rainfall across the greater portion of the cwa through the late morning and early afternoon hours. Advection of moisture out of the state will bring a window in the late afternoon to early evening for destabilization which will renew chances for some isolated to scattered coverage of showers or thunderstorms. The CAPE gradient along the the edge of the departing cloud shield can lead to a differential heating gradient and may serve as a mesoscale trigger for CI. Degree of organization will depend on magnitude of instability recovery from morning precipitation, but at this time HREF P(>500 J/kg CAPE) nears 100% through the Tri-Cities, as scouring of cloud cover takes place from west to east. While severe weather is not anticipated with afternoon and evening activity, EBWD values of 20-25 knots can support some degree of organized convection and steep low-level lapse rates with DCAPE value around 800 J/kg can aid in 45-55 mph gusts from a microburst. All storm chances end late tonight with the lack of diurnal heating, with some additional showers and thunderstorm chances again for tomorrow afternoon through Saturday morning along an elevated warm front front that accelerates in on the nose of a mid-level jet. Tomorrow through the weekend will see the enhancement of a significant upper-level ridge that will become the dominant feature of interest through early next week with strong multi-model ensemble support for anomalously high mid-tropospheric heights and temperatures. The EPS show 500mb heights reaching or exceeding the 99.5th percentile over SE MI Sunday into Monday and likewise with 850mb temperatures nearing or exceeding the 99.5th percentile as 850mb temperatures rise aoa 22C. It is worth noting that the ECMWF and corresponding ensemble solutions may be amplifying the forecasted ridge somewhat noting the warm biases observed from last year, but regardless, strong agreement among GEFS members in conjunction with the EPS suite lends to an extremely high confidence forecast for the expansion of well above normal temperatures through early next week. 850MB temperatures aoa 22C along with dry conditions will allow temperatures to reach the 90 degree mark Saturday, and exceed the 90 degree mark Sunday and Monday, with mid 90s possible for much of the cwa, especially through the urban corridor. Dew points in the upper 60s to low 70s will bring oppressive humidity and will allow heat indices to rise into the upper 90s to low 100s Sunday and Monday. EPS EFI values for max temperatures reach .9-.99 both days, with shift of tail values near or above 1 through the urban corridor and portions of the Tri-Cities and Thumb. This highlights a notable displacement (upper 10%) of ensemble solutions when compared to M- Climate data and reinforces that hot temperatures are inbound, potentially challenging prior records. Last, this heat wave will also bring very warm overnight low and will provide no relief as forecasted lows hold in low to mid 70s Sunday morning through Tuesday morning. Another round of 90 degree temperatures are possible Tuesday afternoon, but the introduction of rain chances lowers confidence in forecast trends. && .MARINE... Small Craft Advisories take effect today for outer Saginaw Bay to Harbor Beach, and for Lake St Clair and Lake Erie, associated with wind and waves trailing the governing low pressure system as it exits the region. An active shower and storm pattern continues through the end of the week while gradually shifting farther north across the Great Lakes while heat and humidity build across the region during the weekend. && .PREV DISCUSSION... Issued at 1159 PM EDT Wed Jun 18 2025 AVIATION... Variable ceiling conditions exist across Southeast Michigan as relatively warm/mild low to midlevel temperatures exist particularly south of KMBS. Persistent large scale deformation is expected to bring prevailing showers to much of Southeast Michigan during the overnight. Given the high likelihood for precipitation with a relatively moist environment prefer to carry MVFR to IFR ceilings. Colder and drier air is expected advect quickly into Southeast Michigan after 12Z which should lead to improving conditions. A period of wrap around light precipitation is anticipated between 15-18Z Thursday. Dry conditions Thursday afternoon and night. For DTW/D21 Convection...Thunderstorm activity is no longer anticipated. THRESHOLD PROBABILITIES... * High for ceiling aob 5000 ft tonight and early Thursday. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...Small Craft Advisory until 4 PM EDT this afternoon for LHZ421-441. Lake St Clair...Small Craft Advisory until 10 AM EDT this morning for LCZ460. Michigan waters of Lake Erie...Small Craft Advisory until 10 AM EDT this morning for LEZ444. && $$ DISCUSSION...AM MARINE.......BT AVIATION.....CB You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.