Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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872 FXUS63 KDTX 261631 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 1231 PM EDT Sun May 26 2024 .KEY MESSAGES... - A line of showers and thunderstorms moves into the region between 4 PM and 10 PM this evening. - There is a Marginal Risk of severe weather late today into tonight from I-69 south with a Slight Risk for Lenawee and Monroe counties. Isolated damaging wind gusts are the main threat. - 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. && .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. && .PREV DISCUSSION... Issued at 1105 AM EDT Sun May 26 2024 UPDATE... Advertised line of thunderstorms extends from roughly northern Illinois to western Kentucky and has taken on an increasingly northeastward trajectory as slow-moving upper level features on the northern flank of the system stall near the Iowa-Wisconsin border. Line motion is currently southwest to northeast around 40 mph which brings the line into Lenawee County between 3-5 PM and through the rest of the forecast area between 4 PM and 10 PM this evening. Despite neutral to weakly stable conditions over eastern Illinois currently, this line of storms has produced gusts of 40+ mph and is moving into an increasingly favorable environment over Indiana. The expectation is that as the line moves into Indiana, it will eventually overtake the warm front before reaching SE Michigan. This will dramatically increase dry air entrainment into storm inflow, as the 12z sounding depicts very dry and statically stable conditions below 500mb, which will likely contribute to some weakening of the line. For reference, forecast MLCAPE struggles to reach 500 J/kg before the line arrives, with highest instability located downstream of Lake Erie (generally from Detroit to Ann Arbor and points south). For any updrafts that can maintain their strength, steep mid and low level lapse rates combined with increasing mid-level flow would support the chance for storm organization and strong downdrafts, highlighting isolated wind gusts as the primary severe threat for today alongside frequent lightning and heavy downpours. Cannot rule out a rotating storm, but shallow equilibrium levels and dry low levels keep probabilities low for large hail or tornadoes. Stratiform rain fills in behind the leading line, but the primary strong to severe storm threat ends by 10 PM this evening. A Marginal Risk is in place south of I-69 with a Slight Risk for Lenawee and Monroe Counties. PREV DISCUSSION... Issued at 314 AM EDT Sun May 26 2024 DISCUSSION... A strong shortwave will eject from NE/KS into the western/northern Great Lakes late today into tonight. This mid level feature will become negatively tilted as it pivots around upper low pressure centered near Lake Winnipeg. This shortwave will induce cyclogenesis over WI late today with the surface low then tracking into northern lower MI and deepening to near 990mb by Monday morning. A band of convection is expected to arc into the area along this trough axis later today (arriving between 4pm-6pm). Initially, this band of showers and thunderstorms will tap some degree of surface instability along/south of a warm front lifting north through the Ohio Valley. This front, however, will struggle to lift into lower MI late in the day and band of convection will have to rely increasingly on the advection of elevated instability into its flank as a southwesterly LLJ pivots into the area by evening. While this will limit severe potential, given the fact that wind shear increases to near 40 knots as the wind field strengthens in response to the encroaching shortwave, any notable push of unstable air into the region (surface based or not) should support a small chance of severe weather into at least portions of the forecast area. As such, the areas north to the I-69 corridor are outlooked for a marginal risk of severe weather with the far southern part of the area outlooked for a slight risk in anticipation for spotty large hail and/or damaging wind gusts with a few of the storms. The most concentrated convective activity will focus on the evening period with just scattered showers and a few thunderstorms possible overnight into Monday as the surface low pressure reaches northern lower MI and begins to occlude. Mild weather will continue Monday, but a cold front will pivot east through the area during the day. This will set up a temperature gradient from the mid/upper 60s over the Saginaw Valley to the lower/mid 70s over east/southeastern parts of the area. Gusty southwest to west winds will accompany this front with wind gusts to 30 mph or so by afternoon. The aforementioned upper low pressure system near Lake Winnipeg will pivot southeast into the area into the midweek period in the wake of a fast moving Pacific shortwave that races into the deepening upper trough over the area. This will bring cooler temperatures in the 60s to near 70 from Tuesday into Thursday. There will also be a chance of showers and a few thunderstorms from Monday night into Tuesday night, but peaking late Tuesday as the remnants of this main upper low shift through the area. A substantial upper level ridge shifts east over the area by late in the week bringing a return of temperatures in the 70s to around 80 from Friday into next weekend. The next notable Pacific shortwave will more than likely impinge on the area by sometime next weekend. This will bring some chance of showers/thunderstorms back into the forecast towards the tail end of this 7 day forecast. MARINE... Easterly winds today as brief high pressure moves across the region. The next low pressure system is expected to impact the region beginning this evening. Warm frontal passage overnight is expected to strengthen winds over the lake and bring chances for showers and storms. Low level flow will be quite strong with this system, reaching up to 40 knots 1000 feet above the surface. Small temperature inversion will keep some of the wind at bay, but stronger gusts will still have little trouble mixing down. Monday the cold front will move through, bringing further chances for showers/storms as well as surface winds up to 20 knots over Saginaw Bay and northern Lake Huron. Winds will have a harder time mixing down on Monday, but errant gusts to 30 knots are still possible. Small Craft Advisories will likely be needed Monday, but there is still uncertainty in the timing and extent of the impacts. HYDROLOGY... Showers and thunderstorms are expected late today into tonight as a strong low pressure system lifts into the area. Locally heavy rain will be possible with some of the thunderstorms as moisture quality within the atmospheric column improves into this evening. Forecast basin average rainfall amounts range between one quarter of an inch to three quarters of an inch, but higher amounts in excess of 1 inch will be possible in a few stronger storms. Forecast adjustments are likely due to the convective nature of the rain. The main concern would be for localized flooding of prone urban areas across the Detroit Metro region. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ AVIATION.....SC UPDATE.......MV DISCUSSION...DG MARINE.......BC HYDROLOGY....DG You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.