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Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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123 FXUS63 KDTX 161749 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 149 PM EDT Fri Aug 16 2024 .KEY MESSAGES... * Another round of scattered thunderstorms may develops this afternoon-evening. This activity will be capable of heavy rainfall and an isolated storm could produce damaging wind. * Broad coverage of low pressure stalls across Lower Michigan this weekend. The system supports showery and unsettled weather with temperatures on the cool side of normal through Sunday. && .AVIATION... Morning band of showers held longer into the afternoon complicating the forecast for this evening. A cold front remains well to the west over southern Lake MI and should pass over the area this evening with a couple hours of destabilization ahead of it in a narrow warm sector. Computer models have all backed off a bit from generating broader coverage of showers and storms ahead of the front lowering confidence. But it remains warm and humid with the warm front and cold front still to pass through so will hedge away from convection and go with a tempo for showers this evening. If/when convection can develop, will amend the impacted airports as needed. Better support for showers comes tonight and the ongoing tempo from 06-10Z still looks good. Yet another round of showers and possible storms will come Saturday afternoon as the upper low drifts overhead. Ceilings will lower on Saturday with the low in place. For DTW/D21 Convection...Low probability exists for thunderstorms this afternoon/evening as early day showers held longer into the day reducing the amount of instability that could rebuild into the area. The cold front will pass through this evening with a couple hours to try to reorganize ahead of it so still a chance of activity between 20-00Z. Took out thunder and left showers as confidence in widespread thunderstorms is low. Additional rounds of showers will exist tonight after 06Z with a trough swinging through and again on Saturday afternoon with the upper low in place. DTW THRESHOLD PROBABILITIES... * Low for thunderstorms through the evening. * Medium for cigs at or below 5000 ft this afternoon and evening. && .PREV DISCUSSION... Issued at 339 AM EDT Fri Aug 16 2024 DISCUSSION... Scattered showers and drizzle tied to the lead edge of theta-e advection between 800-900mb starts to push east of the area by mid- morning. This is quickly followed by remnant convection along the surface warm front lifting out of IL/IN which tracks across SE MI late morning-early afternoon. With only few hundred J/kg of MLCAPE available during this window, thunder holds on the isolated/scattered side and non-severe. Latest trends amongst the vast majority of CAMs is for the warm front to clear the region by ~19-20Z resulting in steady theta-e advection into southern lower MI raising surface dewpoints into the lower 70s. This looks to be sufficient to allow instability to recover from morning activity with 1000-1500J/kg of MLCAPE developing by late afternoon-early evening. Overall shear is on the marginal side with 0-6km struggling to reach 30kts, owing to a weaker overall column wind profile likewise struggling to get much up 30kts. That said, an isolated strong to severe storm is still in play with damaging wind gusts being the primary hazard as DCAPE`s approach 1000 J/kg. Mid-level lapse rates aren`t anything special, generally 6-6.5C/km at most, precluding a large hail threat. Additionally, as is typical in these humid airmasses, locally heavy rainfall is likely under any thunderstorm. Occlusion of the low over the upper Midwest offers a brief break in rain chances early tonight behind evening convection as a mid-upper dry slot swings through southern MI. Additional showers/remnant upstream convection then arrive latter half of the night as the now fully closed, stacked low drops southeast over Lake Michigan. Daytime Saturday is marked by a transition to less organized but numerous convective showers and scattered thunder as the low/parent trough drift directly overhead. The loss of daytime heating will lead to a reduction in coverage Saturday night however with the slow speed of the low, likely only over the Ontario Peninsula by Sunday, results in a largely persistence forecast for daytime Sunday as diurnal heating reinvigorates scattered to numerous showers. Dry conditions return by Monday as the low reaches the Northeast though upper troughing remains firmly in place over the central Great Lakes. Northerly flow in the low`s wake draws cooler Canadian air south lowering 850mb temps to around 10-11C and results in highs generally in the lower 70s with upper 60s possible in the Thumb. Breezier day also looks likely Monday as increasing mixing depths within this CAA regime supports a partial mixing down of 25-30kt flow aloft. In general gusts between 20-25mph are favored though stronger winds around 30mph are not out of the question, particularly over the Thumb. MARINE... An upper low located over the western Great Lakes at issuance will gradually drift eastward through the weekend, governing local conditions until early next week. First wave of showers and thunderstorms departs this morning, but will likely see additional activity fill in this afternoon-evening. Thunderstorm activity later today will have potential to become strong/severe, capable of localized wind gusts over 35 knots, erratic waves, and lightning. Otherwise, winds/waves subside through the morning, settling around 5-10 knots by this afternoon. Thunderstorm potential will linger overnight and through most of the weekend under influence of the slow-moving upper low. Winds will eventually shift from southerly to northerly once the low passes through, which will prompt an uptick in winds and waves that may necessitate Small Craft Advisories early next week. The low fully departs by middle of next week, with drier weather expected. HYDROLOGY... Showers and remnant thunderstorms cross the region this morning with additional scattered thunderstorms likely developing this afternoon- evening. The humid airmass will support locally heavy rainfall with storms this afternoon capable of dropping a quick inch or so of rain. A broad low pressure system then stalls over Lower Michigan for this weekend supporting numerous showers and scattered thunderstorms focused particularly in the daylight hours. Total rainfall from this morning through Sunday evening is expected to be 1-1.5 inches on average, though localized totals between 2-3 inches possible dependent on strength and frequency of thunderstorms. Localized minor flooding of urban, low-lying, and otherwise flood prone areas remains possible in the strong thunderstorms, but the off and on nature of the rainfall is not expected to cause significant flooding. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ AVIATION.....DRK DISCUSSION...KDK MARINE.......MV HYDROLOGY....KDK You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.