Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000 FXUS63 KDTX 190731 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 331 AM EDT Thu Sep 19 2019 .DISCUSSION... Modest convective activity ongoing within the upstream corridor of instability draped from the northern Great Lakes into the eastern Great Plains early this morning. This action will struggle to survive into the daylight hours while any potentially organized convection remains tied to the instability gradient over the Midwest anyway. Thus, with southeasterly return flow continuing to dominate locally, expect little change from yesterday aside from the potential for a partial coverage of high cirrus debris originating invof the Upper MS River Valley early morning. Highs once again near 80 degrees. Low to mid 60s dewpoints over the Lower OH Valley will begin creeping into the area tonight into the weekend as the prevailing pattern remains generally unchanged and light moisture advection continues. This will place a rising a floor on overnight lows each night while modest afternoon mugginess typical of late September accompanies continued daytime highs in the 80s. Only item of interest in the near term is potential for a weak MCV to trigger isolated/scattered showers or t-storms on Friday as low-level instability builds. 4-km NAM and NMM are aggressive in their depictions of this scenario, but analysis of forecast soundings reveals stout capping centered around 850mb and what appears to be erroneous triggering of convective QPF. Nonetheless, there is a some consensus among the various NWP, including the ECMWF, that a convectively induced shortwave will propagate along the periphery of the resident mid-level ridge potentially grazing the forecast area Friday afternoon. A stronger outcome may therefore warrant an upward revision to pops into the SCHC category, but maintained a dry forecast for now. More likely scenario is simply a greater coverage of lower-based diurnal cu than previous days, especially over southern and eastern areas. As the western US longwave trough runs its course and energy releases into the central CONUS and northwest Ontario, subsequent deamplification of the downstream ridge will allow the instability gradient to be forced through Lower Michigan Sunday into Sunday night warranting inclusion of showers/tstorms. High temps thereafter settle closer to climatological average values. && .MARINE... Ridge of high pressure anchored over the Mid Atlantic will maintain benign marine weather through the end of the week. Southeast winds will veer to the south today, prevailing from this direction to finish the week. && .PREV DISCUSSION... Issued at 1153 PM EDT Wed Sep 18 2019 AVIATION... A cold front in the Midwest sends only high clouds over Lower Michigan tonight as it reaches western Upper Michigan and dissipates through Thursday. Dry/VFR conditions are also maintained by high pressure centered over Quebec that continues to extend westward into the central Great Lakes tonight. The high becomes centered over the New England states and maintains control of aviation weather in SE Michigan through Thursday evening. DTW THRESHOLD PROBABILITIES... * None && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. Lake Huron...NONE. Lake St Clair...NONE. Michigan waters of Lake Erie...NONE. && $$ DISCUSSION...JVC MARINE.......CB AVIATION.....BT You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.

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