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Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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864 FXUS63 KDTX 140817 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 417 AM EDT Sun Jul 14 2024 .KEY MESSAGES... - There is a diminishing threat for severe intensity thunderstorms this morning leaving an isolated storm possible this afternoon. - Another round of strong to severe thunderstorms is possible tonight from mid evening into the late night. - The main hazards tonight are large hail to one inch, damaging wind gusts to 60 mph, and heavy rainfall with localized flooding. - Increasing heat and humidity fuel the storms while lifting high temperatures into the upper 80s and lower 90s. Peak heat index reaches the lower to mid 90s today and upper 90s Monday. - Thunderstorms with potential for severe intensity and flooding continue Monday and Tuesday. The primary time window for greater storm activity is currently projected for later Monday night into early Tuesday. && .DISCUSSION... Convective trends remain the highlight of this forecast cycle as an active storm pattern is established from the northern tier of states into the Great Lakes today. Storms are fueled by an increasingly hot and humid air mass building high temperatures into the upper 80s with heat index reaching the mid 90s today. Highs around 90 are reachable Monday with heat index in upper 90s. These numbers approach heat advisory levels but are also vulnerable to interference from clouds and rain cooled air both today and Monday. The larger scale zonal mid and upper level flow configuration maintains the corridor for additional storm complexes Monday into Tuesday when a stronger low pressure system and cold front bring a pattern change for the late week period. The ongoing SW Lower MI/IN/IL storm cluster is the remains of yesterday`s surface based convection across the upper Midwest that grew upscale into a respectable MCS. It is now past peak organization having outrun a better shear profile while tracking along the MLCAPE gradient. Remnants of this system graze SE MI early this morning accompanied by a component of elevated showers and storms feeding off 850-700 mb moisture transport extending toward the Tri Cities and Thumb. This is followed closely by yet another low level jet forced storm cluster also in progress from MN into WI that at least remnants of which are expected to survive into western Lower MI by mid morning as the larger scale instability axis builds northward. Assuming a slightly farther north track does materialize, then this system is also expected to outrun the better upstream shear profile and follow a standard weakening trend in the transition from nocturnal to surface based instability. It is then prudent to assume some redevelopment is possible in SE MI on the leading edge of any residual weak MCV and as surface based instability recovers this afternoon. Negative factors to monitor are too much persistence of clouds and stable air from the morning shower/storm pattern and a lack of a defined surface based focusing mechanism. These variables combined with a wide range of CAM and regional model solutions this far east of larger scale weather features present lower than average predictability in this part of the forecast. Assuming afternoon storms are able to form, they would move into Ontario and Ohio and leave a short break for this evening. The weak cold front analyzed roughly from the MN arrowhead into the central Plains this morning then becomes the focus for yet another round of storms in WI late today. This activity tracks through WI into Lower MI tonight with improved potential for severe intensity given the farther east initiation and several hours of earlier timing in the convective cycle. The 00Z HREF mean MUCAPE gradient is in a similar west to east position with an incrementally improved downstream wind shear profile to support some longevity of upscale growth. A linear convective mode is most likely by the time the potential system reaches SE MI making damaging wind the primary hazard and which may be the best fit for the new Day 1 convective outlook. The trailing cold front stalls near the Ohio border region while still presenting heavy rainfall potential from additional nocturnal development late tonight and Monday morning (see hydrology section below). The stalled front moves quickly northward during Monday as a larger scale short wave and surface low pressure reflection arrive in the upper Midwest. This wave precedes larger scale mid level height falls across central Canada which offers improved predictability due to improved organization of low pressure and frontal forcing. This is reflected in a final round of thunderstorms Monday night and Tuesday with continued heavy rainfall potential as the associated cold front moves slowly through Lower MI. The front clears the area Tuesday night and is followed by broad high pressure promising a chance to dry out during the late week period. && .MARINE... The arrival of a warm front is expected to bring a shift to southwest flow today and expanded coverage of both morning and afternoon thunderstorm activity. Marginal afternoon Small Craft Advisory conditions are possible for Saginaw Bay, but decided to forego a headline due to the isolated/brief nature of peak gusts to around 25 knots. The warm and muggy airmass holds firm across the region Monday through at least the first half of Tuesday offering several additional opportunities for thunderstorms as packets of upper level energy arrive in staggered succession. Periods of stronger storms are possible Sunday through Tuesday which could pose a heightened risk for locally higher winds/waves and some hail. A cold front arrives late Tuesday bringing more seasonable temperatures and quieter conditions by midweek. Occasional waves could approach 4 ft over Saginaw Bay Tuesday. && .HYDROLOGY... The potential for heavy rainfall and flooding continues in an active thunderstorm pattern today through Tuesday. Storms today present a decreasing heavy rainfall risk while activity tonight increases, especially late tonight and Monday morning. Thunderstorms will be capable of torrential downpours with a quick inch or more of rainfall possible Sunday night and Monday morning as lines of storms moves repeatedly over the same areas. The best chance for this to occur is from the urban Detroit corridor to the Ohio border as a front stalls west to east over the area. In this case, rainfall amounts may exceed two inches although there is low confidence in exactly where this boundary may set up. Heavy rainfall will occur amongst already saturated soils and elevated rivers from the last week`s rain. Localized flooding is possible, especially in low-lying and urban areas. Heavy rainfall and flooding potential then continues later Monday, Monday night, and into Tuesday as a corridor of storms is maintained until a cold front sweeps through the region by late Tuesday. && .PREV DISCUSSION... Issued at 1208 AM EDT Sun Jul 14 2024 AVIATION... VFR conditions will prevail through most of the night under light south winds before the upstream complex of thunderstorms moves across TAF sites between 11Z and 15Z this morning. Expectation is for this complex to weaken as it arrives, but it still will be capable of some gusty winds with any of the stronger embedded thunderstorms. Some uncertainty exists with any redevelopment of showers and thunderstorms in the afternoon and latest guidance leans towards more isolated activity if any. Given the low confidence for the afternoon, will leave any mention of rain or thunderstorms out of the TAFs at this time. Conditions after the morning complex will be predominately VFR as winds turn out of the southwest with gusts to around 20 knots. For DTW/D21 Convection... Upstream thunderstorms move across Lake Michigan tonight and into SE MI/D21/DTX during the 11Z to 15Z time frame this morning. Thunderstorms should be weakening intensity as they arrive, but some gusty winds will be possible. There is a chance for shower and thunderstorm redevelopment in the afternoon, but too much uncertainty exists with instability return after the morning complex. DTW THRESHOLD PROBABILITIES... * Medium for ceilings aob 5,000 feet this morning. * Medium for thunderstorms this morning. Low this afternoon. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ DISCUSSION...BT MARINE.......KGK HYDROLOGY....BT AVIATION.....AA You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.