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Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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402 FXUS63 KDTX 150004 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 804 PM EDT Sun Jul 14 2024 .KEY MESSAGES... * A thunderstorm complex tracks into the Great Lakes from Wisconsin early Monday morning. * Isolated damaging wind gusts, large hail, and localized flooding will be possible with any thunderstorms tonight as storms track west to east at 40 mph. * Warm and humid conditions expected Monday with heat indices in the mid 90s. * Additional chances for strong to severe thunderstorms and flooding rainfall exist Monday night and Tuesday. && .AVIATION... Cloud shield associated with earlier MCV has pushed east bringing VFR conditions through the remainder of this evening with light winds out of the southwest. Attention again turns to upstream convection developing across WI/IL and spreading eastward late tonight/early tomorrow morning across Lower Michigan. Expectations are for this system to be weakening as it moves into southeast Michigan. Moderate confidence in this system holding together for TEMPO groups to remain in the TAFs. Have adjusted timing slightly given latest model guidance with a start time more around 08Z across FNT and all terminals south. Left PROB30 for MBS as confidence isn`t as high for activity to reach into the Tri-Cities yet. After convection comes to an end in the morning, lower VFR to possible MVFR clouds should linger into the afternoon with a period of dry conditions. Mixing depths by early tomorrow afternoon bring potential for gusts up to 20 knots. For DTW/D21 Convection...Another system develops upstream across WI and IL this evening and moves across Lower Michigan during the overnight period. Showers and thunderstorms should be able to make it into southeast Michigan, but is expected to be weakening with time. Moderate confidence exists in storms arrival to D21 airspace by around 08Z. Strong wind gusts will be the main threat. DTW THRESHOLD PROBABILITIES... * Medium for thunderstorms early tomorrow morning. && .PREV DISCUSSION... Issued at 359 PM EDT Sun Jul 14 2024 DISCUSSION... Advertised active pattern is well underway this afternoon as a warm and unstable airmass settles over the Upper Midwest and Ohio Valley. The MCS has stayed comfortably to our south, accelerating toward the instability reservoir over central Indiana-Ohio. This is in contrast to the local environment where observed surface temperatures have lagged behind models by 2-3 degrees, maintaining a weak but effective capping inversion so far this afternoon in the absence of strong forcing. Otherwise, dewpoints near or above 70 degrees have resulted in muggy conditions despite near-normal temperatures in the mid 80s. While an isolated shower or thunderstorm is possible this evening as currently noted over Lenawee-Monroe Counties, the more robust convective response is expected overnight into early Monday morning as an MCS again traverses into the Great Lakes. MCS initiation will occur further east than last night, over Wisconsin, forming along a frontal zone/convergence axis and propagating southeast along the instability gradient. There will again be an attempt to lift this gradient into lower Michigan with help from both a convectively- enhanced shortwave and ~30 knot nocturnal low level jet. This provides a more favorable environment for the MCS and/or its remnant MCV to persist into SE Michigan compared to last night, supporting primarily a heavy rainfall risk as any convection will exhibit high precipitation efficiency and training potential. Localized rainfall amounts in excess of 2 inches will be possible, please see the Hydrology section for more details. Nocturnal timing will be resistant to surface-based convection, but if elevated instability materializes then cannot rule out a few stronger precipitation cores capable of producing hailstones of 0.75" to 1" diameter mainly after 10 PM this evening. Showers and thunderstorms linger for the first half of the day Monday, along with convective debris to result in a chaotic and low predictability cloud forecast. While the potential is there for portions of SE Michigan to exceed 90 degrees, morning cloud cover is expected to suppress daytime heating enough to keep majority of locations below heat advisory criteria. That said, temperatures in the upper 80s and dewpoints in the low 70s will produce heat indices in at least the mid 90s for Monday. Pending any outflow interactions, Monday afternoon-early evening generally remains dry. The warm and unstable airmass holds steady Monday night and Tuesday, with increasing large-scale support for organized convection as an expansive upper trough and surface low move into the upper Midwest. Eastward progression of the system will lift a warm front into the area late Monday night, preceding yet another nocturnal MCS that presents a more organized strong to severe threat late Monday-early Tuesday morning. Nocturnal timing of the MCS suggests the system will lose its surface-based inflow and weaken by the time it reaches SE Michigan, but this is not a guarantee should the warm sector be well-established by then. SPC has designated a Marginal Risk for most of the cwa for Monday night, although areas west of I-75 are in a Slight Risk for severe weather. Heavy rainfall will again be a concern with these storms. Final push of convective potential comes Tuesday as a cold front tracks across the Great Lakes, which will eventually usher in a cooler and drier Canadian high pressure system for the remainder of the week. MARINE... Initial round of afternoon thunderstorm activity associated with a forward propagating MCS has largely held just south of the Lower Peninsula keeping the central Great Lakes dry, thus far. Low-end convective potential still remains through the rest of the afternoon before the next surge of storms pushes in late tonight or early Monday morning. This activity likely takes on the form of a secondary MCS/MCV originating from a more pronounced shortwave trough aloft that will pivot over southern Lake Michigan and then turn northeast, toward southern Lake Huron. Monday afternoon looks to be rather quiet/stable before a more potent wave drives a better organized convective line across the Great Lakes Monday night. Both systems pose a heightened risk for locally higher winds/waves and some hail. A cold front lags the convection Tuesday before it eventually clears through, offering more seasonable temperatures and quieter conditions by midweek. HYDROLOGY... Isolated thunderstorms are possible this evening ahead of a thunderstorm complex that will track into the Great Lakes late tonight through early Monday morning. This thunderstorm complex will be capable of torrential downpours with a quick inch or more of rainfall possible as several storms may move repeatedly over the same area. There is still a signal for a moisture gradient to set up near the Ohio Border to urban Detroit corridor, which could result in even higher totals in excess of 2 inches south of I-94. Urban and low-lying areas along with elevated river basins will be most vulnerable to this heavy rainfall. Additional chances for thunderstorms exist Monday night and Tuesday with similar heavy rainfall concerns. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ AVIATION.....AA DISCUSSION...MV MARINE.......KGK HYDROLOGY....MV You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.