Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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641 FXUS63 KDTX 261953 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 353 PM EDT Sun May 26 2024 .KEY MESSAGES... - A line of showers and thunderstorms moves into the region between 5 PM and 10 PM this evening. - There is a Marginal Risk of severe weather this evening from I-69 south with a Slight Risk for Lenawee and Monroe counties. Isolated damaging wind gusts to 60 mph remain possible. - There is also a Marginal Risk of excessive rainfall. See the Hydrology section of this AFD. - The Memorial Day outlook calls for cooler, more seasonable temperatures with scattered showers and thunderstorms. && .DISCUSSION... Continuing to monitor a broken line of thunderstorms that extends from roughly South Bend to Wilmington at press time. Thus far, the line has remained sub-severe with recent gust observations ranging between 35-45 mph. The enhanced forward propagation of the southernmost portion of the line, which is well into southern Ohio at this point, has effectively slowed progress of the northern line to now reach southeast MI closer to 5 PM. As expected, MLCAPE has struggled to build above 500 J/kg amidst dry boundary layer conditions so not anticipating much intensification although entrainment/evaporative cooling potential still does pose a threat for strong to borderline severe gusts. The most widespread impacts of this line will be frequent lightning and heavy downpours, with 6- hour MRMS QPE values showing widespread rainfall totals of a half inch to localized inch along this line. The leading line of showers and thunderstorms exits into Lake Huron by 10 PM this evening, leaving a much broader pool of low level moisture in its wake while low level portions of the warm front lift northward. The result is continued scattered shower activity overnight, aided further by lingering elevated instability that will maintain low end thunder chances through Monday morning. Heaviest rainfall overnight looks to remain south and east of the state line, with just the northern fringe of the low level jet and moisture axis clipping SE MI. Widespread heavy rainfall potential will also be mitigated by a strong post-convective push of mid level dry air. Localized heavy downpours however remain possible in any stronger convective cells, which could bump QPF over an inch in some spots. Drier air arrives mid-day Memorial Day as the parent surface low migrates into central lower Michigan, drawing a cold front west to east across the state. This brings an end to shower activity around noon, followed by a brief period of low amplitude ridging and deep static stability above 3.0 kft agl through Monday evening. Trapped low level moisture keeps a blanket of cloud cover overhead with a few sprinkles possible in the afternoon, while post-frontal cold advection brings H8 temperatures into the single digits and corresponding daytime highs in the low 70s for the holiday. Even as the surface low departs Monday night, broad upper troughing maintains an unsettled pattern Tuesday and Wednesday with additional shortwaves pivoting through the flow. Transient moisture accompanies these systems to support glancing periods of precipitation before the trough axis finally swings through mid-week. Deep northwest flow throughout maintains cool thermal profiles with temperatures settling in the upper 60s to low 70s for the early half of the week. Conditions to then dry out latter half of the week with the arrival of an amplified ridge axis. && .MARINE... Low pressure brings the first round of storms into the area this evening. Strong low level easterly flow has already been able to mix down 30 knot gusts, so a Small Craft Advisory has been issued for the nearshore area of Lake Erie through 8pm tonight. Winds will briefly die down overnight to 10-15 knots, but return to strength on Monday evening with the passage of a cold front. Abundance of Small Craft Advisories with this system, beginning with western Lake Erie currently in effect through 8pm tonight. Conditions around the tip of the thumb are expected to pick up tonight, so Small Craft Advisory will go into effect beginning at 6pm tonight. All zones are up to criteria by noon tomorrow, with the zones of Lake Erie, Lake St. Clair, and nearshore areas of Lake Huron from Harbor Beach to Port Huron expected to drop below criteria overnight Monday into Tuesday. These advisories are set to drop off at 4am Tuesday. Gustier conditions are expected to hang around a little bit longer around the thumb, so the Saginaw Bay and Port Austin to Harbor Beach zones have the advisory active until 4pm. Gale potential out over the open waters looks marginal for now, and have decided not to go with a gale watch at this time. Cooler conditions with westerly flow are expected behind the front. && .PREV DISCUSSION... Issued at 1231 PM EDT Sun May 26 2024 AVIATION... An upper level trough will lift across Se Mi between 21Z and 03Z today. Despite the ample dry air currently over Se Mi, an axis of deep layer moisture and elevated instability along region of ascent will produce a line of thunderstorms as the trough moves across the region. An influx of low level moisture within the warm sector of a deepening sfc low combined with the development of a subsidence inversion will support low cloud development tonight in the wake of the evening convection. Model soundings are suggestive of low end MVFR and IFR ceilings prevailing and trends have been increasing in the latest probabilistic guidance. The cold front will move across Se Mi early to mid morning on Monday. This front will provide a chance for additional thunderstorms, limited by overall weak instability. For DTW/D21 Convection...A slow moving solid to broken line of thunderstorms is expected to traverse the airspace this evening. The line will move from southwest to northeast across the airspace between 21Z and 02Z. A cold front will then produce a low chance for additional thunderstorms, more likely to be scattered, between 08Z and 15Z Monday. DTW THRESHOLD PROBABILITIES... * High in thunderstorms this evening. Low overnight and Monday morning. * High in ceilings aob 5000 feet tonight and Monday. * Low in crosswind thresholds being exceeded Monday afternoon. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...Beach Hazards Statement until 8 PM EDT this evening for MIZ083. Lake Huron...Small Craft Advisory from noon Monday to 4 AM EDT Tuesday for LHZ442-443. Small Craft Advisory until 4 PM EDT Tuesday for LHZ421-441. Small Craft Advisory from noon Monday to 4 PM EDT Tuesday for LHZ422. Lake St Clair...Small Craft Advisory from noon Monday to 4 AM EDT Tuesday for LCZ460. Michigan waters of Lake Erie...Small Craft Advisory from noon Monday to 4 AM EDT Tuesday for LEZ444. Small Craft Advisory until 8 PM EDT this evening for LEZ444. && $$ DISCUSSION...MV MARINE.......BC AVIATION.....SC You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.