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Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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894 FXUS63 KDTX 151837 AAA AFDDTX Area Forecast Discussion...UPDATED National Weather Service Detroit/Pontiac MI 237 PM EDT Mon Jul 15 2024 .KEY MESSAGES... * An active period of thunderstorms occurs tonight into Tuesday morning as another thunderstorm complex tracks into the Great Lakes from Wisconsin. * Isolated damaging wind gusts, large hail, and localized flooding are possible with any thunderstorms tonight. Storm motion is west to east at 40 mph. * A break in thunderstorm activity this afternoon allows temperatures to rise toward highs near 90 with maximum heat index in the mid 90s. * A slow moving cold front keeps showers and thunderstorms in the forecast for Tuesday, especially as potential for strong to severe thunderstorms and flooding rainfall linger Tuesday morning. * There is a chance of showers Wednesday in a much more benign pattern. * High pressure brings cooler and less humid weather into the region for the late week period. && .AVIATION... MVFR cloud cover continues eastward out of the CWA with diurnal cumulus developing behind. VFR conditions will persist through the rest of the afternoon today as no additional rainfall is expected until tonight. Northwesterly winds both at the surface and through the column are expected to back to become southwesterly tonight. The next system will move into the area in the early morning hours, impacting the area between roughly 1am and 6am. Ceilings are generally expected to remain borderline VFR/MVFR, but have introduced borderline MVFR/IFR conditions into the tempo group for the thunderstorms tonight as the potential for lower clouds and heavy rainfall rates could easily drop ceilings and/or obscure visibilities to IFR. For DTW/D21 Convection...Storms currently expected between 06-09Z tonight, but adjustments and a more refined time window are likely as the system approaches. Strong winds, lightning, and heavy rainfall are all possible hazards with this system. DTW THRESHOLD PROBABILITIES... * Medium for thunderstorms tonight. * Medium for ceilings aob 5,000 feet this afternoon, Medium early tomorrow morning. && .PREV DISCUSSION... Issued at 343 AM EDT Mon Jul 15 2024 DISCUSSION... Storms ongoing across Lower MI are on the lead flank of a mature MCV reinforced by the convective system that originated in southern WI last evening. That MCS is now tracking along the larger scale instability gradient into northern IN after grazing SW Lower MI. The parent MCV over Lower MI is enhancing backed flow out ahead of the center in support of a pseudo elevated warm front and the resulting eastward extension of storms. The enhanced wind profile is also shown to beef up effective bulk shear into the 30-40kt range in hourly mesoanalysis while MUCAPE holds in the 1000-2000 J/kg range. DCAPE of 1000-1500 J/kg combined with sub 1000 J/kg surface based CAPE are used in this case as a sign there is at least some wind gust access to the surface vs a stronger inversion for any storms with greater organization. Elevated instability is also adequate for hail approaching 1 inch while the leading banded structure makes flooding an increasing component of hazards (see Hydrology section) until the parent MCV exits into Ontario by noon. Subsidence trailing in the wake of the morning MCV bolsters predictability on a dry forecast for this afternoon. Early exit of the system allows a cloud decrease and temperature recovery post morning rain cooled boundary layer conditions. Afternoon high temperatures make a run toward 90 combined with Td around 70 for max heat index in the mid to upper 90s, below Heat Advisory threshold but still oppressive for a few hours late this afternoon. The hot and humid air in place sets the stage for the next convective system on schedule for tonight. Consensus of 00Z hi-res and regional model solutions point to another post midnight event for SE MI. Surface based storms are projected to initiate along a stronger cold front moving into the upper Midwest this afternoon which then grow upscale again into a mature MCS across Lower MI tonight. Damaging wind is the primary hazard for severe intensity storms in SE MI, however heavy rainfall and flooding show increasing potential. The cold front follows closely behind the convective system Monday night but stalls overhead Tuesday morning as larger scale mid level height falls occur over the northern Plains and upper Midwest. A combination of storm outflow and the larger scale cold front could become the focus for new storm development on the heels of the MCS as an extension of nocturnal/low level jet forcing through Tuesday morning. The cold front finally exits into Ontario and Ohio by Tuesday night followed by a chance of showers as the mid level trough swings through the Great Lakes Tuesday night and Wednesday. It is a much more benign setup compared to recent days as cooler and less humid air fuel standard intensity showers with low end rainfall amounts. A broad area of surface high pressure follows with a high predictability pattern of dry weather for the late week period. MARINE... An unsettled pattern is in-place to start the workweek with storms inbound from a MCS that originated over the Upper Mississippi Valley last evening. Locally higher winds/waves and some hail are possible this morning before the convective activity dissipates/departs into southern Ontario. The afternoon hours look to be rather quiet and quasi-stable before a secondary wave combines with an influx of low- level moisture which helps sustain another organized line of nocturnal storms. Once again, hazardous marine conditions will be driven by the evolution and intensity of storms as they cross the local waterways. A cold front slides into the region Tuesday with some low-end potential for surface convergence and convective redevelopment before the front clears through and brings about an airmass change. Dry and cool air driven by strong ridging over the Upper Midwest then offer more favorable boating conditions. A longwave trough over Canada descends on the region Wednesday with modest NNW flow and a few showers followed by thermal troughing Thursday. HYDROLOGY... An active pattern of thunderstorms this morning and again Monday night and Tuesday morning present a risk for flooding across SE Michigan. Numerous thunderstorms this morning are capable of brief 1 inch per hour rainfall rate. Totals in the 1 to 2 inch range are possible with locally higher amounts where multiple storms track over the same location. A break in activity is anticipated this afternoon and evening until another round of thunderstorms moves in late Monday night into Tuesday morning. This system will be capable of similar rainfall rates and totals added on to what occurs this morning. Roads, urban locations, and other flood prone areas will be most vulnerable to this heavy rainfall along with rivers that are already elevated from heavy rainfall last week. Stay updated on the latest forecasts as new information helps identify specific areas of flooding concern around southeast Michigan. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...Flood Watch from midnight EDT tonight through Tuesday morning for MIZ068>070-075-076. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ AVIATION.....BC DISCUSSION...BT MARINE.......KGK HYDROLOGY....BT You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.