Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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871 FXUS63 KDTX 022335 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 735 PM EDT Tue Jul 2 2024 .KEY MESSAGES... - Chance of light showers tonight, mainly across the Saginaw Valley and Thumb region. An isolated non-severe thunderstorm is also possible early Wednesday morning. - Warm and humid on Wednesday with a continued chance of showers and thunderstorms. An isolated strong to severe storm will be possible during the afternoon, capable of producing strong wind gusts and heavy downpours. - Typical heat and humidity for the 4th of July holiday. Isolated showers and thunderstorms will be possible late in the day south of M-59. && .AVIATION... Batch of mid/high clouds continues to drift across Southeast Michigan early this evening. There has been plenty of virga/sprinkles across the north and this will be the case for the next several hours as high based showers bubble near MKG. Farther upstream, a complex of thunderstorms is expanding across Southwest Wisconsin, Eastern Iowa, and Northern Missouri. This activity will plod to the east overnight. The convection will move into a hostile environment by the time it reaches Lake Michigan. Expectations are for the coverage to decrease dramatically, only leaving a residual region of clouds and a few embedded showers. The clouds may be MVFR for a time at MBS and FNT, with a reduced chance reaching farther south. There remains the low likelihood that a deeper shower or storm may develop during the early afternoon hours across the Detroit airspace - especially if any prolonged breaks in the cloud cover arise. Overhead, winds will strengthen substantially just above the surface overnight. Thus, have introduced low-level wind shear in the current suite of terminals. Furthermore, the boundary layer depth will quickly emerge into the reservoir of higher momentum, supporting gusty southwest winds by mid-morning. For DTW/D21 Convection... There is a low chance for a thunderstorm as a front washes through Wednesday afternoon. DTW THRESHOLD PROBABILITIES... * Low for ceiling 5000 ft or less Wednesday morning, moderate Wednesday afternoon. * Low for thunderstorms Wednesday afternoon. && .PREV DISCUSSION... Issued at 331 PM EDT Tue Jul 2 2024 DISCUSSION... A mid-level trough and associated surface low moving from Manitoba into northwestern Ontario will have increasing influence over local conditions tonight into Wednesday. The system is currently directing a shortwave and plume of 700-500mb moisture advection over west and mid MI, producing pockets of light to moderate showers. The SW upper jet will steer most of this moist flow north of the forecast area, but trends in radar presentation and surface obs bring at least a chance for a few late afternoon sprinkles mainly north of I-69. Otherwise, we continue to be governed by dry SSE flow below 700mb which should hold overall dry conditions through tonight. Another shortwave follows a similar track into northern Lower MI overnight into early Wednesday morning, bringing a renewed chance for showers and an isolated elevated thunderstorm mainly for the Tri-Cities and Thumb. Instability will be minimal and severe weather is not anticipated. Low pressure developing today along the trailing cold front over the Midwest tracks northeast across northern Lower MI Wednesday morning, sending a surge of higher low-level theta-e across the state to start the day. Much warmer and muggier conditions will be in store with HREF mean dew points rising to around 70 degrees. This will be paired with highs in the mid to upper 80s. With mean flow parallel to the SW-NE oriented cold front and neutral PV advection and height fields providing little organized forcing, expectation is for just widely scattered showers through the day as the front eases eastward across the state. A window emerges late in the day southeast of a line from Jackson to Sandusky where daytime heating and resultant instability (MLCAPE near 1000 J/kg) may be enough to induce better convective development as the front moves through. Should this play out, a conditional marginal severe threat exists as bulk 0-6km shear of 30 kt may support an isolated stronger cell with damaging wind gusts and heavy downpours the most likely threats. There remains a sizable camp of hi-res guidance that pushes the front through before convection gains much traction, with 30 to 50% of 12z HREF membership showing <500 J/kg of SBCAPE by 6pm. This faction of solutions suggests little to no severe threat. The front then departs to our south and east Wednesday night with slightly lower dew points settling in and dry conditions likely thereafter. Weak cool advection behind the front keeps a seasonably warm and humid air mass around for the 4th of July holiday. Highs again will be in the mid to upper 80s with dew points in the upper 60s and weak winds keeping a muggy feel to the air. Model soundings show a respectable cap in place much of the day, but weak height falls associated with a low amplitude shortwave arriving during the evening may be sufficient to allow for isolated convection late in the day. Given the relatively warm mid-levels, any instability would be lean and do not expect an organized severe threat at this time. Friday presents a higher probability for showers and thunderstorms as a higher amplitude upper low tracks in from the Midwest, bringing a corridor of more focused height falls and associated ascent during the latter half of the day. Blended guidance advertises a 60-70% PoP peaking during the mid afternoon to early evening. Wind shear will be favorable for organized severe weather with a 50 kt jet streak passing overhead, but instability progs remain modest with only 15% of LREF members showing >1000 J/kg SBCAPE. The most likely outcome at this stage looks to be numerous showers with scattered thunderstorms. Slightly cooler weather for Saturday as the upper trough sinks across the Great Lakes. At least scattered light shower activity appears likely as moist cyclonic flow wraps around the low across the state. Medium range progs show a strong ridge developing over the SW CONUS this weekend and persisting into the early part of next week. This favors a troughy, active summertime pattern over the local area with periodic chances for showers and thunderstorms. MARINE... Return flow from the departing high pressure that is now centered over New England has reinforced southeast flow over the Great Lakes, which will hold through tomorrow morning. A weak surface low will move across Lake Michigan later this evening, strengthening the pressure gradient across the lakes which will support gusts on the order of 20 to 25 knots across Lake Huron today. Rain showers with possible embedded thunderstorms will continue mainly across Lake Huron through tonight as low pressure approaches. A cold front is then expected to move over the Great Lakes tomorrow morning and afternoon which will veer wind direction to the west- southwest. There will be a window between 4AM-4PM tomorrow 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 tomorrow. Otherwise, high pressure fills back in Thursday, relaxing wind speeds and gust potential. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ AVIATION.....Mann DISCUSSION...TF MARINE.......AM You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.