Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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085 FXUS63 KDTX 220700 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 300 AM EDT Sat Jun 22 2024 .KEY MESSAGES... - Flood watch this afternoon-tonight for Midland/Bay/Saginaw counties. - Slight risk of severe thunderstorms this afternoon into tonight over much of southeast Michigan, with damaging winds being the main hazard, but isolated tornadoes also possible. - Hot and humid today with high temperatures in the 90-95 range south of I-69 with heat indices peaking out just under 100 degrees this afternoon. && .DISCUSSION... Jet forcing tracking through Central Lower Michigan yesterday afternoon allowed for convection to keep re-firing and track across the Tri-Cities region, resulting in localized rainfall amounts of 4+ inches. There remains potential training of storms today as the deep moisture plume hangs around Saginaw Bay (PW values aoa 2 inches) area and a surface wave then tracks through Central Lower Michigan this evening. Expecting MLcapes to build to around 1500 J/kg , which will lead to efficient rain producers, and easily could see 2-4 inches of rainfall, with isolated higher totals not out the question. Now, there is some uncertainty if the bulk of the storms will reside just north of the Tri-Cities, but this set up is worthy of a flood watch for this afternoon through tonight. Still looks like locations south of M-59 will be capped during the day as the mid level dry slot with 700 MB temps of 11 C tracks through, persisting into the early evening hours. This should allow the Detroit Metro area and points south to climb into the low to mid 90s with the favorable southwest flow, pushing heat indices to near 100 degrees. Deep moisture plume coming out the Plains will track through the rest of the CWA tonight. Significant differences amongst the models with the strength and placement of the low over northern Lower Michigan this evening/tonight, but there does appear to be a consensus with a strengthening low pressure system as it moves through northern Lake Huron/Georgian Bay. This is concerning, as low wind shear, both 0-6 km and 0-1 KM will be ramping up with low level jet in excess of 50 knots developing. Instability/capes may prove sufficient with 1000-850 MB cape progged to reside in the 500-1000 J/kg range, per NAM. If storms arrive earlier in the evening, organized severe storms with rotation are in play. SPC day 1 has upgraded much of southeast Michigan into slight chance. Hopefully, as the night wears on, the near surface layer will be just stable enough to keep stronger winds and any rotation above the surface, or instability could also end up being even more modest and we fail to generate thunderstorms all together as line approaches the Detroit Metro Area. Several solutions indicating the line dissipating, with just some leftover scattered activity along the cold frontal passage late tonight. However, preference will continue to skew the forecast toward a broken or solid line of showers/thunderstorms (see RRFS A) with the good large scale forcing/heights falls/PV advection for summer standards. Modest cold advection to follow for Sunday, with 850 MB temps progged to lowering into the lower teens by Monday morning per 00z Euro. None-the-less, the 500 MB trough axis swinging through the Central Great Lakes may still touch off a few showers, mainly over the Thumb region, as 500 MB cold pool (-15 C) tracks through Lake Huron. Warming back up early next week, as shortwave ridging arrives by Tuesday morning, ahead of a strong northern stream upper level wave/trough expected to sweep through on Wednesday, triggering storms and leading to modest cool down for end of the work week. && .MARINE... Stalled front that has been hovering around southern MI the last couple days will get pulled back north today generally across Mid MI which should result in more shower and thunderstorm activity lifting north today as well. This will also allow southwesterly winds to spread back across the southern Lakes ushering in another hot airmass keeping stable conditions across the waters. A stronger, more organized low pressure system will then track east across northern MI tonight which will pull a cold front through the region on Sunday. Increased winds ahead of the front have been topping out near 25 knots for a couple days now, and continue to do so but stable conditions and possibly short duration may limit the need for a small craft advisory but will continue to monitor. && .HYDROLOGY... Flood watch in effect for Midland/Bay/Saginaw this afternoon into tonight. The potential exists for repeated rounds of showers and thunderstorms. Total rainfall amounts of 2 to 4 inches possible with locally higher amounts not out of the question. With yesterday`s locally heavy rainfall, flooding would be likely if those totals verify. A line of showers and thunderstorms is then expected to spread east into the rest of southeast Michigan this evening and tonight, and if these storms hold together, rainfall amounts of half an inch to two inches can be expected, which may cause minor urban/low lying flooding. However, the activity may weaken significantly through the night, and lower rainfall totals under half an inch are not out of the question by the time the storms arrive over Detroit Metro Area. && .PREV DISCUSSION... Issued at 1057 PM EDT Fri Jun 21 2024 AVIATION... An isolated shower or thunderstorm remains possible overnight, but overall convective potential remains minimal as greater nocturnal stability gains traction with time. Attention overnight turns to prospects of fog development as winds lighten and saturation improves at the surface. MBS appears the most susceptible to a meaningful visibility restriction in fog, but any location may witness a brief dip in visibility during the pre-dawn hours. A northward advancing frontal zone will offer renewed focus for shower and thunderstorm development Saturday afternoon, particularly across central lower Mi including the MBS area. Forecast will offer a tsra mention at MBS/FNT, with diminishing potential with southward extent from this corridor. For DTW/D21 Convection...Greater potential for thunderstorms will focus north of the airspace Saturday afternoon and evening. An approaching cold front may bring renewed potential late Saturday night. DTW THRESHOLD PROBABILITIES... * Low for thunderstorms impacting the airspace Saturday night. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...Flood Watch from noon EDT today through late tonight for MIZ047-048- 053. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ DISCUSSION...SF MARINE.......SF HYDROLOGY....SF AVIATION.....MR You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.