Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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207 FXUS63 KDTX 061956 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 356 PM EDT Mon May 6 2024 .KEY MESSAGES... - There is a risk for isolated strong to severe storms Tuesday evening southwest of a Midland to Port Huron line between 6 PM and 11 PM. - Some gusts to 60 mph are possible with potential for isolated large hail to 1 inch in diameter. - Cannot rule out an isolated weak tornado or two Tuesday evening. - Mainly dry, breezy, and warmer Wednesday, then cooler again Thursday with additional opportunities for showers and thunderstorms. && .DISCUSSION... Ridging with central surface pressure of 1018 mb continues to anchor the Great Lakes by flanking the northward progression of scattered showers and storms attributed to troughing over the Ohio Valley. Locally, expect near seasonable temperatures and dry conditions the rest of today and tonight with prevailing easterly flow and a persistent stream of high cirrus. Expansive closed low occupying the western two-thirds of CONUS (producing widespread severe convection) retrogrades from the western Dakotas into eastern Montana Tuesday while the wave broadens meridionally. This pushes the system`s elongated warm front northeastward into Lower Michigan with rapid moistening arriving after 15Z. Mean 850-700 mb layer dewpoints jump from around -30C early Tuesday morning to +5C after 18Z as the magnitude of water vapor transport increases sharply with the transition to cyclonic southwesterly flow. Current analysis depicts a line of convection extending from the Mid-Mississippi Valley up to the southern Canadian Prairies, closer to the actual surface low. CAMs highlight a tendency for decay as storms cross Lake Michigan and interface with a dry and stable ambient airmass. Most areas remain dry, at least through 18Z. Height field adjustments along the eastern periphery of the system lend some uncertainty to the upstream evolution of convection as a secondary shortwave emerges and shears into southern Lower. The warm sector will fully encompass the region by 22Z, as a secondary (and more robust response) convection response arrives with additional storms track west to east. Given the slightly later arrival time and flatter diurnal curve, confidence in SBCAPE has trended lower as the main instability axis remains better centered over southwest Lower. All hazards are in-play Tuesday evening for Southeast Michigan given the +60 knots of 0-6 km bulk shear, southeasterly winds, and pockets of higher instability as mid-level lapse rates cool. A secondary surface low emerges as the triple point, and given the current curvature reflected in forecast hodographs, isolated rotating structures will be capable of generating some weak mesocyclones, augmented by the frontal intersections. Cannot rule out a few isolated weak tornados and some overachieving thunderstorm gusts. SPC has upgraded the CWA to a Slight Risk near the MI/OH border with a Marginal risk elsewhere (excluding The Thumb). Storms largely depart/dissipate by 03Z with increasingly zonal flow aloft. Warmer and more stable as dewpoints drop into the upper 40s to lower 50s Wednesday with decreasing sky opacity. Well-mixed boundary-layer supports some decent afternoon gusts in the 25-30 mph range. The next system crosses through Indiana and Ohio Wednesday with some additional shower/storms possible for southern Lower. The primary upper trough then splits again Thursday, taking aim at the Great Lakes Thursday while the broader longwave jet pattern remains quasi- stationary. Additional showers and storms are likely with much cooler temperatures Thursday, related to cold frontal forcing. The synoptic pattern unlocks Friday as an amplified ridge drops through the Upper Midwest. Drier weather will be short lived as a trailing PV anomaly drops into the region Saturday. && .MARINE... High pressure currently centered over Lake Huron gradually drifts east into Ontario tonight through the first half of Tuesday maintaining light easterly flow. Midwestern low pressure lifts a warm front into the central Great Lakes Tuesday afternoon/evening bringing widespread showers and thunderstorms with some strong to severe storms possible over the southern Great Lakes. System`s cold front quickly follows overnight setting up cooler westerly flow Wednesday, turning northeasterly Wednesday night. Cooler airmass combined with a tighter gradient due to secondary low development over the Ohio Valley supports a moderate uptick in wind strength Wednesday and Thursday with gusts topping out between 15-25kts each day. Saginaw Bay could see gusts near 30kts Thursday due to NE winds channeling down the bay. && .PREV DISCUSSION... Issued at 203 PM EDT Mon May 6 2024 AVIATION... VFR conditions will prevail through today and tonight as a surface high pressure drifts east across Lake Huron into Ontario. This will bring a light east to northeast wind at 10 knots or less through the remainder of the afternoon and evening. High clouds will clear out further this evening leaving mostly clear skies overnight. A warm frontal zone lifts into lower Michigan tomorrow morning. Increasing low level moisture will boost lower cloud potential in the morning and afternoon with a more southeast wind direction. For DTW/D21 Convection...Chance for thunderstorms increases after 18Z tomorrow. DTW THRESHOLD PROBABILITIES... * Medium in cigs aob 5000 feet Tuesday morning, high Tuesday afternoon. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ DISCUSSION...KGK MARINE.......KDK AVIATION.....AA You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.