Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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801 FXUS63 KDTX 141437 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 1037 AM EDT Sun Jul 14 2024 .KEY MESSAGES... - Low chance for an isolated strong to severe thunderstorm this afternoon, followed by another round of potential strong to severe thunderstorms from mid evening through tonight. - 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. && .UPDATE... Remnant MCV from the first wave of nocturnal convection is just now exiting into Lake Huron, with cloud cover clearing in its wake. The 14.12z KDTX sounding observed just weak elevated instability with MUCAPE values around 300 J/kg atop a strong capping inversion (CIN around 100 J/kg) as two waves of nocturnal convection have delayed theta-e advection into southern lower Michigan. Latest observational trends however have shown some northeastward moisture transport ahead of the upstream MCS, which in combination with developing pockets of sunshine should bring MLCAPE values toward 1000-1500 J/kg by mid- day. Nearly all of the hi-res guidance is underestimating the longevity of the MCS and the influence of its remnant MCV that will move across SE Michigan during peak heating this afternoon. Locally enhanced convergence and shear invof the MCV could trigger thunderstorm redevelopment across SE Michigan this afternoon (about a 30% chance between 1pm-6pm), although will be complicated by reintensification of the MCS that will track just to our south. Should any thunderstorms develop this afternoon, a wet microburst with gusts of 40-60 mph or large hail up to an inch cannot be ruled out. Will dive into the details of evening-overnight convection with the afternoon forecast package. Considering the effects of this MCS on expected moisture transport for the afternoon, did lower dewpoints by several degrees to bring heat indices down into the low 90s. && .PREV DISCUSSION... Issued at 606 AM EDT Sun Jul 14 2024 AVIATION... Low confidence convective forecast today and tonight as a few different features work across the region. There is a decaying MCS currently diving southeast through SW lower MI, a second MCS behind it, a boundary of deeper moisture early in the day, and a cold front later tonight. So chances of showers and thunderstorms exist through much of the day but likelihood to impact any specific point is low. We`ll target the morning MCS forcing with a tempo for showers as it currently exists. Will handle any pop up afternoon activity with amendments as needed and put in a prob30 to introduce the cold frontal activity tonight as that has an actual feature to focus along. Winds will be out of the southwest through the period below 10 knots but with a few gusts possible into the teens. For DTW/D21 Convection... MCS activity is quickly waning so will go with a tempo for showers to account for any lingering effects from it or the MCS behind it. Isolated thunderstorms will be possible this afternoon but low confidence on placement or timing for any activity. A cold front will then drop into the region tonight with showers and thunderstorms along it. These storms could get strong to severe with wind and hail threats. A very moist atmosphere will also lead to heavy rain with any storm that develops. DTW THRESHOLD PROBABILITIES... * Medium for ceilings aob 5,000 feet this morning. * Low for thunderstorms this morning and afternoon. Medium tonight. PREV DISCUSSION... Issued at 417 AM EDT Sun Jul 14 2024 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. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ UPDATE.......MV AVIATION.....DRK DISCUSSION...BT MARINE.......KGK HYDROLOGY....BT You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.