Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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348 FXUS63 KDTX 031727 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 127 PM EDT Wed Jul 3 2024 .KEY MESSAGES... - Scattered showers exit eastward with a weak cold front this afternoon. An isolated thunderstorm, capable of gusty wind and locally heavy rainfall, also remains possible south of the I69 corridor. - Today`s front ushers in a typical summer air mass for the July 4th holiday. Partly sunny sky helps lift temperature to highs in the mid to upper 80s with moderate humidity. - Showers and thunderstorms spread back across Lower MI Friday as the next low pressure system sets up in the Midwest. && .AVIATION... Frontal zone is noted on satellite extending SW-NE from KMGC to KMBS at TAF issuance. Ceiling observations within the frontal band range from MVFR to low VFR alongside isolated showers. Larger degree of solar insolation compared to upstream observations favors the optimistic VFR forecast locally until the front clears to our east by 00z. Decreasing cloud cover to follow overnight. Modest instability will struggle to generate deep convection this afternoon with dry subsident air working in aloft, so convective initiation will be limited. Still, there is a low (~20%) chance for a pulse- type thunderstorm to impact one of the Detroit terminal sites between 20z-00z. Southwest winds subside below 7 knots tonight with a 30-60 degree shift to the west-northwest post-front. Just some mid- high cloud lingers for daytime Thursday along with light west- southwest winds. For DTW/D21 Convection...There is a low (~20%) chance of a pulse- type thunderstorm to impact the airspace between 20z and 00z. Storm motion will be to the east-northeast at around 30 knots. DTW THRESHOLD PROBABILITIES... * Moderate for intervals of 5000 foot or less ceilings before 00z. Low tonight and Thursday. * Low for a pulse thunderstorm between 20z and 00z. && .PREV DISCUSSION... Issued at 328 AM EDT Wed Jul 3 2024 DISCUSSION... SE MI is residing within the warm sector of a low pressure lifting into the northern Great Lakes this morning which has led to dewpoints creeping back into the 60s. This moisture advection continues through the afternoon as the theta-e plume draped along the Mississippi is partially drawn into the region pushing Td`s near or just above 70F, particularly south of M-59. Rain chances initially are confined to the Saginaw Valley-Thumb area as decaying convective remnants currently over northern IL/southern Lake Mi lift northeast early this morning. An additional window for a couple (thunder)showers comes late morning-early afternoon for these areas as the "cold" frontal boundary starts to sag into southern lower MI. System relative flow has a large parallel component to the SW-NE oriented front greatly reducing low level convergence along it with the end result expected to be a fairly sparse coverage of widely scattered showers. Earlier timing also puts an upper bound on potential CAPE available (likely around 500 J/kg at best) keeping any thunder more isolated in nature. These chances shift south and east through the rest of the afternoon, reaching the Detroit Metro area after ~19Z. Even with the later/slightly more favorable timing, CAMs continue to struggle to generate much in the way of convection in advance of the boundary likely owing to ample cloud cover that will be in place reducing insolation and subsequent greater instability. Should frequent/large enough breaks in this cloud occur however, it wouldn`t take long to fully realize the ~1000 J/kg MLCAPE potential that the area is residing beneath. There is just enough bulk shear (25-30kts) that could support an isolated stronger cell with damaging wind gusts being the potential hazard (again assuming we see enough breaks to get initiation). Overall chances of this are low however with better potential focused to our east as noted in the new Day 1 SPC outlook. Frontal boundary pushes east of the region late evening, after ~23Z ending any further rain chances. Only marginally cooler air follows this front (850mb temps only fall by 1-3C) with the main impact instead shunted the theta-e plume and associated upper 60-lower 70 dewpoints back into Ohio and Indiana. Short range model solutions still suggest this frontal boundary holds south enough of the state border to keep additional convective development likewise confined south of the CWA as a series of shortwaves ride along it daytime Thursday. This outcome offers lesser cloud cover and more sun pushing highs back into the mid to upper 80s, despite the very modest cooling aloft. Worth noting there is some signal for diffuse ripples of vorticity embedded within the upper jet that is progged to be directly over lower MI to spark a brief isolated showers late afternoon-evening. That said, low confidence in this scenario so have opted to keep dry forecast (sub 15% PoPs) running in this update. Active pattern doesn`t relent for the late week period as another surface low develops over the north-central Plains before lifting towards the Straits Friday into Saturday. Respectable moisture transport accompanies this system as it wraps in lingering Gulf moisture from the mid-Mississippi pushing PW values over 1.5" and surface dewpoints near 70f again. Occluding front looks to lift through SE MI centered around the afternoon hours, which in combination with aforementioned moisture-rich environment, should widespread coverage of showers and embedded thunderstorms. MARINE... A cold front will move over the Great Lakes this morning and afternoon which will veer wind direction to the west-southwest by the afternoon. There will be a window between 4AM-4PM today where gust potential will near 25 knots across the Saginaw Bay with the southwest flow, but will preclude the issuance of a Small Craft Advisory as model soundings exhibit a stable profile, lowering confidence of 25 knot gust potential for any 3+ hour window. There will be a low chance for a shower or storm along the front. High pressure will fill back in tomorrow, bringing light winds through the day. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ AVIATION.....MV DISCUSSION...KDK MARINE.......AM You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.