Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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167 FXUS63 KDTX 211916 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 316 PM EDT Fri Jun 21 2024 .KEY MESSAGES... - Marginal risk of severe thunderstorms this afternoon and Saturday afternoon/evening, with damaging winds being the main hazard. - Hot and humid through Saturday. High temperatures 85-90 today and 90-95 on Saturday, as heat indices peak out just under 100 degrees for Saturday. && .DISCUSSION... Scattered convection has begun firing this afternoon across central/southern MI which will continue through this evening as diffuse shortwave energy transits the area atop the lingering stalled frontal boundary. Overall environment remains the same from prior days with MLCAPEs between 1000-1500 J/kg and mediocre shear aob 25kts resulting in a continuation of pulse-type convection with isolated damaging downbursts possible. With PW at 1.72" from the 12Z DTX RAOB sounding, locally heavy rainfall is likely beneath any thunderstorm especially given the slower storm speeds as background flow is 30kts or less through ~400mb. Any lingering convection still expected to taper off around 03Z early tonight as instability wanes and shortwave energy vacates. Stalled frontal boundary that has lingered over southern lower MI the past couple days is forced back north tonight in response to developing surface low pressure over the north-central Plains. While associated shower and thunderstorm activity initially holds north of the CWA Saturday morning, shortwave energy/mid-upper height falls reaches SE MI by Saturday afternoon likely resulting in a southern expansion of ongoing activity over northern lower MI into areas along/north of I-69. Favorable diurnal timing with SBCAPEs around 1000 J/kg and slightly better kinematic profiles (relative to previous days) as bulk shear tops out around 30-35kts supports the potential for scattered, more organized thunderstorms during the afternoon and evening hours. A few strong to severe storms will be possible within this activity particularly over the Tri-Cities/Thumb with isolated damaging wind gusts being the primary hazard. Given the boundary looking to hang out near the Saginaw Valley, can`t completely rule out the chance for an isolated brief tornado though forecast hodographs are fairly marginal. Moisture rich environment also supports heavy downpours likely leading to locally heavy rainfall, see hydrology for more information. Low pressure eventually tracks somewhere over central to northern lower MI late Saturday-Sunday driving a respectable cold front across SE MI through the overnight hours into Sunday morning. This timing falls solidly within the diurnal minimum for instability limiting severe potential with model guidance all generally favoring a gradually decaying line of showers and thunderstorms moving across the area. Shortwave clears the region by midday/early afternoon Sunday ending further rain chances. For the southern portions of SE MI which likely miss out on afternoon-evening rain, persistent deep layer southwest flow in advance of the approaching cold front pushes 850mb to into the upper teens to near 20C. Highs in the low to mid 90s look likely though with dewpoints generally holding in the upper 60s, heat indices remain sub-advisory between 95-98F. Upper trough slides over the Great Lakes Monday allowing 850mb temps to fall to 10-12C (down from 18-20C on Saturday) keeping highs in the lower to mid 80s. Cooldown is shortlived as troughing is replaced by induced ridging in advance of another upper trough beginning to dig south out of the Canadian Prairie. This allows southwest flow to redevelop in the lower levels pushing 850mb temps back into the upper teens with Tuesday highs returning to the upper 80s to lower 90s. Aforementioned trough arrives over the Great Lakes midweek bringing the next chances for widespread showers and storms. && .MARINE... Generally high pressure spread across the region keeping a hot and stable airmass in place through Saturday. A stalled weak front will remain across the southern Great Lakes helping to touch off scattered thunderstorms through this evening. Then the pattern gets a little more progressive offering some mid level support for more organized and frequent storms Saturday across much of Lake Huron. The hot air will help minimizing wave heights through Saturday outside of any thunderstorm wind gusts. A more organized low pressure system will pass through the northern Michigan Saturday night pulling a cold front through the region on Sunday likely resulting in more widespread convection and wind speeds then could reach or exceed 25 knots with waves building to around 4 feet. Small craft advisories may be needed. && .HYDROLOGY... A moist and moderately unstable airmass holds in place today with scattered thunderstorms continuing through this evening. These storms will be capable of producing highly localized rainfall amounts in excess of 2 inches in less than 3 hours due to their slow movement. This amount of rain would result in urban/low lying flooding. Additional showers and thunderstorms are possible over areas along/north of I-69 Saturday afternoon-evening. With an unchanged airmass, locally heavy rainfall is likely from these storms with rainfall rates near or in excess of 2 inches per hour. Additional showers and storms work across the area overnight Saturday as a cold front crosses the area. This activity likely weakens through the night resulting lower totals- rain amounts between 0.1-0.5 inches generally favored. && .PREV DISCUSSION... Issued at 134 PM EDT Fri Jun 21 2024 AVIATION... Early morning showers clear out, but isolated popup thunderstorms are still expected across the CWA this afternoon and evening as a stationary front remains overhead. Front migrates northward this afternoon which in combination with daytime instability, creates the environment for aforementioned storms to pop up. Have gone with a TEMPO over PROB30 due to the imminent timing of the storms, but confidence is low on the full extent of the event. Any storms that do move overhead will produce MVFR to IFR conditions, based on the strength of the downpour. All storms look to be clear of the area by 02Z tonight at the latest, shifting instead to the northern Lower Peninsula and Lake Huron. Some light fog is possible overnight, mainly at MBS where light winds off the lake produce favorable conditions for sustained fog. The next chances for showers and storms come on Saturday afternoon and evening. MBS and FNT see the greatest chances for development with the stationary front maintaining north/south position. Low pressure center moves into the area on Sunday, dragging a cold front across the region and bringing with it additional chances for showers and storms. After frontal passage, the pattern of daily isolated popup showers looks to be broken, with high pressure and clearer weather filling in behind to start next week. For DTW/D21 Convection... Conditions remain favorable for thunderstorms with mid afternoon to evening timing. The combination of Erie/St. Clair lake breeze and stationary front near the MI/OH border provide the best chances for storm development until the front moves north of DTW later tonight. DTW THRESHOLD PROBABILITIES... * Moderate for thunderstorms impacting the airspace this afternoon and evening. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ DISCUSSION...KDK MARINE.......DRK HYDROLOGY....KDK/SF AVIATION.....BC You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.