Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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166 FXUS63 KDTX 291038 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 638 AM EDT Sat Jun 29 2024 .KEY MESSAGES... - Widespread showers and some embedded thunderstorms continue through this morning. - There is a low chance for an isolated strong to severe thunderstorm late this afternoon into the late evening. - Damaging wind gusts and locally heavy rainfall are the main threats if something develops this afternoon. Hail would be possible near the Tri-Cities late this evening if stronger cells survive out of northern lower MI ahead of an approaching cold front. - High pressure builds in behind a cold frontal passage on Sunday and brings cooler and drier weather for early next week. && .AVIATION... Deeper moisture surging into Southeast Michigan will maintain a chance for showers, with isolated thunderstorms, throughout the morning period. Observational trends suggest a dip in cloud base to lower VFR/MVFR within this window. Trailing diurnal stratocumulus expected lingering into at least a portion of the afternoon period, but may tend to mix out with time. Prevailing winds from the southwest turning gusty, nearing 25 knots at times this afternoon. While conditions appear less favorable for shower and thunderstorm this afternoon and evening, an isolated cell or two cannot be ruled out. Standard reduction in wind gust potential with loss of daytime heating this evening. A cold front brings a wind shift to the northwest overnight, with some potential for a brief shower or storm along with renewed increase in cloud. For DTW/D21 Convection...Main window for possible tsra focused on this morning, although with coverage likely remaining isolated. Local heavy downpours will be the main impact of these embedded thunderstorms. DTW THRESHOLD PROBABILITIES... * High for ceiling aob 5000 ft this morning, medium into the afternoo. * Low for thunderstorms this morning. && .PREV DISCUSSION... Issued at 316 AM EDT Sat Jun 29 2024 DISCUSSION... A mid-level shortwave is in the process of crossing lower MI this morning coincident with the lead edge of a richer theta-e plume lifting up the Mississippi. This will support widespread moderate to heavy showers throughout the morning in addition to a few embedded thunderstorms as weak elevated instability expands into southern lower MI. While no severe weather is expected within this activity, locally heavy rainfall carries a fairly high potential as PW values exceed 2" (nearing daily climo max) in combination with a deep warm cloud layer pushing 11-12kft. Morning shortwave clears the region by late morning-early afternoon with SE MI residing firmly within the overall system`s warm sector. Southwest flow continues to advect an impressive Gulf-originating theta-e plume into the area through the afternoon resulting in dewpoints climbing into the lower 70s across the area with mid 70s possible over the southern portion of the area (Detroit to the Ohio border). Result is MLCAPEs ranging between 1000-2000J/kg, highest over the those southern locales. Kinematically, with the mid-upper trough sagging into the central Great Lakes, overall bulk shear is favorable for convective organization at 35-45kts. Main question remains however to what degree convection is above to fire this afternoon-evening as subsidence in the wake of morning activity will likely be lingering over the area providing a modest cap. There is signal amongst a few high res solutions, such as the ARW and to a lesser extent the HRRR, for a remnant MCV feature to lift out of the Midwest this afternoon towards northern IN/OH, potentially creeping into far southern MI, supporting the development of scattered convection along or south of the stateline this evening. Though worth noting, at this time, confidence in this scenario is low. In the absence of this feature, CAM guidance is generally unsupportive of convective development late this afternoon-evening due to the aforementioned subsidence. `Best` potential instead looks to occur along the cold front as is drops out of the northern Great Lakes. This frontal timing however has slowed compared to prior day`s model runs, and now appears to cross the area between 02-07Z falling mostly within the diurnal instability minima. Additionally, system- relative streamlines are fairly parallel to the frontal boundary limiting its low level convergence and subsequent coverage of convective development. Should a few cells manage to fire this afternoon-evening (which again carries low confidence in occurrence), there is good setup for these updrafts to become organized leading to strong to severe storms with damaging wind gusts and locally heavy rainfall as primary threats. Hail can`t be ruled out in the strongest updrafts given the available instability and shear though would be a secondary threat. While convective potential is a bit better along the cold front given at least some (albeit weak) forcing mechanism, late day timing greatly hampers any severe potential. Instability will have largely waned over areas south/east of the Tri-Cities by the time it arrives and with the Tri-Cities residing in the edge of the main moisture axis, MLCAPEs only top out around 1000 J/kg this evening which will likewise be in the progress of waning by the time of fropa. With current timing, several hundred J/kg look to still be available around the Saginaw Valley/western Thumb and combined with straight, elongated forecast hodographs, can`t completely rule out an isolated strong storm (hail being main threat)... though chances aren`t great. Northerly flow develops Sunday in the wake of the frontal passage as Canadian high pressure builds in from the upper Midwest. Impressive thermal troughing also settles over the Great Lakes as 850mb temps fall to 5-6C (which is below the 10th percentile for the day climatology). Highs likely struggle to break into the 70s, particularly in the Thumb, as a result even with the significantly drier airmass promoting sunnier skies. Surface ridge axis doesn`t cross the area until Monday night maintaining below average and dry weather to start the new work week. Temperatures moderate back to at or above normal by midweek as high pressure shifts east setting up southwesterly return flow. This however also likely advects Gulf moisture back into the region ahead of approaching northern Plains low pressure. MARINE... Incoming low pressure system will bring chances for showers and storms through the day today. Tightening pressure gradient will allow for strong southerly flow over Lake Huron. Winds veer southwesterly through the afternoon and evening, aligning flow direction with the maximum fetch of Saginaw Bay. Low-level flow will also have little trouble mixing down 30+ knot gusts, leading to a Small Craft Advisory being issued for Saginaw Bay from 12pm to 10pm today. Winds veer to the north-northwest on Sunday behind the cold front, maintaining speeds over 20 knots around the nearshore areas of the Thumb and over central Lake Huron. Gusts to 25 knots or greater are also possible. Due to fetch direction and length, the potential for waves to meet Small Craft Criteria exists on Sunday despite a lesser concern for gusts mixing down. Behind the low, drier conditions and gentle winds will take over on Monday. HYDROLOGY... Widespread rain, with a chance for embedded thunderstorms, continue to track across the area this morning before largely clearing by 10- 11AM. Periods of heavy downpours are likely given the warm and humid airmass in place. Basin averaged mean precipitation amounts are forecast to vary between a quarter to three-quarters of an inch, however, highly localized rainfall totals between 1-2 inches will be possible with heavy downpours, especially with any thunderstorm activity. Given current radar trends, areas between I-69 and I-94 have the greatest chance to see these higher rainfall totals due to potential for repeated heavier bursts. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...Small Craft Advisory from noon today to 10 PM EDT this evening for LHZ421-422. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ AVIATION.....MR DISCUSSION...KDK MARINE.......BC HYDROLOGY....KDK You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.