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Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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208 FXUS63 KDTX 040731 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 331 AM EDT Thu Jul 4 2024 .KEY MESSAGES... - Typical summer airmass in place today. Widely scattered light showers tied to convection over the northern Ohio Valley look to work into the area this afternoon and evening. - Low pressure arrives Friday bringing more numerous showers and scattered embedded thunderstorms for much of the day. - Additional scattered nuisance showers possible Saturday afternoon as an upper trough drifts over the central Great Lakes. - Drier, sunnier conditions return to close out the weekend Sunday. && .DISCUSSION... Despite the "cold" frontal passage last evening, overall environment remains largely the same over SE MI with dewpoints still holding in the 60s and 850mb temps in the mid-upper teens (C). While past model trends prior days suggested the frontal boundary would push far enough south over Ohio to keep associated activity likewise south, latest trends, particularly within the CAMs, suggest a much muddier picture. Shortwave wave feature is progged to ride along this boundary over northern Ohio supporting a complex of showers/storms to our south. The northern periphery of the stratiform component of this complex looks to partially shed north into southern lower MI early afternoon, after ~19Z, resulting in high-based widely scattered coverage of a light shower-drizzle-virga mix. Additionally, some signal exists for an isolated convective development chance along the edge this stratiform `shield`, focused over areas north of I-69, where lesser cloud cover supports the generation of a few hundred J/kg of MLCAPE combined with potential lake breeze interaction increasing low level convergence and upper jet divergence residing directly overhead. Overall, its a messy setup that carries inherit low predictability for any one area actually seeing rain, though aforementioned trends can`t be ignored so have introduced slight chance PoPs (15-20%) across the region for the latter half of the day. Low pressure rapidly develops over the Plains Thursday before reaching the western Great Lakes early Friday. Surface circulation draws the staled frontal boundary over the Ohio Valley back north into southern MI Friday afternoon while also beginning to undergo the occlusion process. Result is a complex frontal setup over SE MI as both the warm/occluded fronts work into the region. Areas under the warm sector- most likely along/south of I-69, will see the return of lower 70 dewpoints as a ribbon of enhanced theta-e is wrapped in from the mid-Mississippi. While this moisture axis would support a respectable instability axis (between 1000-1500 J/kg of MLCAPE), ample cloud cover likely prevents this from being fully realized. Regardless, moisture-rich environment beneath seasonably strong synoptic forcing, both from the mature low/mid-level trough as well as left exit region jet divergence, should support scattered to numerous showers with embedded scattered thunderstorms through the afternoon-evening hours before the arrival of the mid-level dry slot late evening/overnight. Upper trough tracks over the central Great Lakes Saturday allowing thermal troughing to settle into the region and drop 850mb temps to around 10C. Cooling aloft in concert with favorable synoptic difluent flow aloft looking to support the diurnal steepening of lapse rates as well as potentially generate at least of few hundred J/kg of mixed-layer instability. This offers chances for isolated to scattered showers across SE MI for the afternoon-early evening hours. Low amplitude mid-level ridging and accompanying weak surface high pressure then briefly work across southern lower MI for Sunday bringing drier, sunnier conditions. && .MARINE... Weak high pressure builds into the central Great Lakes through the day with light westerly winds early becoming light and variable. Overall benign weather prevails, but may see an isolated pop-up shower near the nearshore waters in the afternoon or evening. Wind then organizes out of the east by Friday morning as the next low pressure system moves into the western Great Lakes. This system sends a warm front through during the day Friday with scattered to numerous showers with embedded thunderstorms. The cold front will follow late on Friday with winds veering around to southwest by Saturday morning at around 10 to 20 knots. Unsettled weather with light showers remains possible on Saturday as troughing is slow to depart. && .HYDROLOGY... Low pressure arrives over the Great Lakes Friday generating numerous showers with scattered embedded thunderstorms for much of the daylight hours. Gulf moisture is looking to be wrapped into this system pushing precipitable water values near 2 inches. Basin wide average rainfall totals between 0.25-0.5 inches are most favored given the progressive nature of rain expected. However given the moisture rich environment, locally higher amounts around 1 inch would be possible under any thunderstorms. Minimal flooding potential expected outside the usual low lying areas. && .PREV DISCUSSION... Issued at 112 AM EDT Thu Jul 4 2024 AVIATION... Predominant VFR conditions this taf period as a drier low level environment holds firm. Some thickening of higher based cloud occurs within a broader region of mid level moisture transport north of a weakening region of convection transiting the Ohio valley today. Plausible this process offers an initiation point for widely scattered convective activity this afternoon and evening, particularly as peak daytime heating engages lake breeze activity. Confidence in occurrence at any one location carries too low of predictability at this stage to offer a more definitive mention. Otherwise, modest wind field from s southerly component into the afternoon, with some acknowledgement for a direction shift this evening with inland lake breeze penetration. For DTW/D21 Convection...widely scattered convection is possible in the airspace after 19z. DTW THRESHOLD PROBABILITIES... * Low for thunderstorms Thursday between 19z and 00z. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ DISCUSSION...KDK MARINE.......TF HYDROLOGY....KDK AVIATION.....MR You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.