471 FXUS63 KDTX 272245 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 645 PM EDT Sat Apr 27 2024 .KEY MESSAGES... - Additional showers and storms are possible Sunday and Monday with above normal temperatures before a cold front arrives on Tuesday. && .AVIATION... Convective development is forecast across northwest Lower Mi this evening as instability expands along/in advance of a southward moving cold front. While upscale growth of this convection is anticipated during the evening hours, it is expected to decrease in coverage/intensity as it slowly sinks southward toward MBS in the 05 to 08Z time frame. Meanwhile, recent ACARS soundings out of DTW and FNT show a weakly capped environment which will likely keep deep convection isolated over most of the area through the evening. Decoupling of the boundary layer this evening will lower sfc wind speeds, however increasing winds just atop the nocturnal stable layer will be supportive of some low level wind shear during the night. A secondary influx of moisture and instability from the south overnight will support another round of showers with a few embedded thunderstorms late tonight through Sun morning. This added moisture influx and showers will contribute to widespread MVFR and IFR based clouds. For DTW/D21 Convection...There appears to be some weakening of the cap across the southern portions of the airspace. So some of these showers may gain enough depth to support an isolated thunder risk this evening. Otherwise, another round of moisture and elevated instability advection overnight will drive scattered to numerous showers across the area Sunday morning with some embedded thunderstorms. The risk for thunderstorms to the airspace will be greatest in the 09Z to 15Z time frame. DTW THRESHOLD PROBABILITIES... * Low in thunderstorms tonight. Moderate Sunday morning. * High in ceilings aob 5000 feet overnight and Sunday morning. && .PREV DISCUSSION... Issued at Issued by National Weather Service Grand Rapids MI DISCUSSION... The overarching theme has been a delayed onset of precipitation across much of southeast Lower MI. Water vapor imagery presentation is quite harsh-looking with pronounced implied subsidence. Moreover, upper flow upstream towards the southwest implies the presence of a shortwave ridge possibly being bolstered by now-weakening convection over the IL/KY border region. To support the idea of prolonged weak to moderate upper subsidence and indications that near-surface frontal convergence will be on the weak side, it makes sense to expect a later onset of precipitation. even farther northwest towards the Tri-Cities, it could be well after midnight until that area receives measurable precipitation and the Detroit Metro is now looking at 3am or later for the onset of measurable precipitation. This will of course be well after the diurnal instability peak so severe chances for southeast Lower MI look a bit less than before. As noted previously, we are looking at a prolonged unsettled period from Sunday into Monday night thanks to a latitudinally aligned quasistationary front across southern Lower MI with a slow southward drift. Sufficiently robust and prolonged low-level moisture convergence will replenish conditional instability and provide modest forced ascent that necessitate a continued mention of thunderstorms in the forecast. As noted before, highs south of the front could be very warm with maximum temperatures towards the OH state line reaching or exceeding 80F on Sunday. Tuesday and Tuesday night currently look dry, but after that, predictability really starts to suffer with the approach of a band of strong upper southwesterlies capable of yielding episodic PV forcing with details in position and timing remaining murky. MARINE... A healthy pressure gradient exists over Lake Huron through tonight as strong low pressure crosses Lake Superior, but very warm airmass over the cold lake is stabilizing the lower levels. As a result, south/southwesterly winds peak through this evening at 20-25 kt, diminishing thereafter as a cold front settles across the lake from the north. This front is likely to touch off rounds of showers and thunderstorms this evening into Sunday as it stalls, and continuing into Monday as it lifts back north as a warm front. Easterly winds increase on the cold side of the front over the northern half of the lake Sunday night into Monday as the flow becomes constricted between strong high pressure over Hudson Bay and low pressure approaching from the southwest. Winds of 25-30 kt are expected during this time, with internal guidance suggesting a 30% probability of gales. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ AVIATION.....SC DISCUSSION...TJT MARINE.......DBT You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.