Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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576 FXUS63 KDTX 130925 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 525 AM EDT Mon May 13 2024 .KEY MESSAGES... - Clusters of showers and a few thunderstorms move west to east over the area while diminishing coverage this morning. - Showers and thunderstorms redevelop this afternoon and continue tonight mainly north of metro Detroit. Locally heavy rainfall is the primary hazard while storms otherwise remain below severe intensity. - Showers and thunderstorms continue Tuesday, increasing coverage toward Detroit while decreasing coverage north to south from the Tri Cities area. _ After a round of slightly below normal temperatures Tuesday, readings rebound warmer with dry weather Wednesday and Thursday. && .AVIATION... VFR conditions hold through the day as a frontal boundary stalls over central MI later this morning resulting in mainly mid/high cloud over SE MI. This front becomes the focal point for additional shower/storm redevelopment this afternoon-evening, mainly confined to MBS and FNT. Rain gradually expands southward over the course of this evening as the front sags south, eventually reaching the Detroit terminals overnight. Increasing low level moisture with column cooling behind the front affords the potential for ceilings to lower towards or into MVFR territory with this later day/night rain. Breezy conditions likely during the daylight hours with gusts peaking in the 20-25kt range out of the SW. Winds weaken with the loss of sun late this evening and eventually turn to NNE late tonight-early Tuesday post frontal passage. For DTW/D21 Convection... Main convective potential holds north of the airspace through this afternoon. This changes later this evening as the front gradually sags south shifting convection likewise south. While there is a low chance for showers or a storm tonight over DTW (currently advertised in Prob30 group), better rain chances come early Tuesday morning. This timing is expected to greatly limit any thunderstorm development as the front, and any instability, will be pushing south of the terminal around this point. DTW THRESHOLD PROBABILITIES... * None. && .PREV DISCUSSION... Issued at 357 AM EDT Mon May 13 2024 DISCUSSION... Showers and thunderstorms rode strong elevated moisture transport across Lower Mi during the late night. Earlier activity showed peak intensity on the leading theta-e gradient where 00Z model analysis fields indicated a 40-50 kt low level jet around the 850 mb level. Resulting nocturnal instability and shear were and continue to be on the weak end of the spectrum with 700-500 mb lapse rate hovering around 6.5 C/km within a wind profile of sub 20 kt effective bulk shear. Any lingering storms in this environment have a pulsey character with a few higher reflectivity flare-ups until exiting into Ontario by early morning. After the early morning convection, a stray shower is possible until peak heating ramps up this afternoon and as the low level moisture axis settles west to east across southern Lower Mi. The cold front still becomes the focus for a new round of surface based convection with some clarity on the frontal position in central Lower Mi by mid afternoon peak heating. HREF mean MUCAPE peaks around 1000 J/kg during the 18-21Z time period limited primarily by sub 6 C/km 700- 500 mb lapse rate within a similarly low shear wind profile. A pulsey storm mode is the favored with coverage north of metro Detroit both this afternoon and tonight, on target for the SPC general thunder outlook. Metro Detroit is expected to stay dry today after getting brushed by activity early this morning. Some breaks of sun across the warm sector allows a run into the lower 80s for afternoon high temperatures. The latest 00Z model cycle remains in good agreement on the larger scale scenario projecting the front to stall in southern Lower Mi tonight. This frames locally heavy rainfall as the primary concern as severe storm parameters remain muted while a broad plume of PW in the 1 to 1.5 inch range builds across the area. The front stalls while the southern stream low pressure system moves into the mid MS valley but is not yet close enough to reach this far north with its own rainfall. New convection in southern Lower Mi then remains frontally forced while transitioning to a nocturnal and elevated character focused mainly north of the surface frontal position, along and north of the I-69 corridor up through the Tri Cities and northern Thumb. Bulk weather features continue to have above average predictability while convective trends carry more uncertainty regarding coverage, intensity, and total rainfall. The current 00Z HREF mean QPF has a similar placement but is noticeably lower compared to 24 hours ago, less than 1 inch for the 12 hr period, and is likely a reflection of the weaker larger scale forcing. Mid level flow within the frontal zone decreases to 20 knots or less but still with some frontogenetic packing of theta-e surfaces and some weak northern stream entrance region jet support. These conditions will be sufficient to hold borderline numerous to widespread coverage of showers and storms in the forecast. Locally heavy rainfall will also stay mentioned but with no further advancement of the message for now. Mostly shower coverage with a few thunderstorms fill in Tuesday morning south of I-69 through metro Detroit to the Ohio border as the southern stream mid level circulation and surface low move into the Ohio valley. The northern fringe of the system`s rainfall pattern reaches into southern Lower Mi while pulling the front steadily southward across the area. The potential for heavy rainfall during this time is diminished by lower rainfall intensity and the steady movement of the front. Eastward progression of the low pressure system carries showers south of the Ohio border shortly after midnight Tuesday night after rainfall averaging 0.5 inch in 12 to 18 hours. Mid week model projections have cooler and drier weather building into Lower Mi with high pressure Wednesday and Thursday. Extended range global runs then exhibit similar timing of arrival for the next low pressure system in the Great Lakes Thursday night and Friday. MARINE... Northern stream low pressure stalls over Hudson Bay this morning, slowly sinking a cold front into the Great Lakes region. The front has already been a focus for showers and embedded thunderstorms overnight, and will continue to be a favorable corridor for showers and storms throughout the day into this evening as it settles across Saginaw Bay-central Lake Huron. Meanwhile, a cutoff southern stream low lifts toward lower MI this evening in turn causing expansion of showers and a few thunderstorms from southwest lower MI into southern portions of the marine zones late tonight. Slow progression of the southern stream low maintains unsettled conditions on Tuesday, with prevailing northeast flow established by Tuesday evening as the front drifts south. Onshore component of the flow and some enhancement to the gradient provides an opportunity for Small Craft Advisory conditions later Tuesday before high pressure builds in mid-week to support drier and calmer marine conditions. HYDROLOGY... A cold front is on schedule to become the focus for an active shower and thunderstorm pattern in southeast Michigan today through Tuesday. Locally heavy rainfall is the primary concern as the front stalls across the region tonight. Showers and thunderstorms will be numerous along the front, especially tonight from I-69 northward, resulting in locally heavy rainfall totals around 1 inch by sunrise Tuesday. Predictability is greater on the overall rainfall scenario (numerous showers and some thunderstorms along the front), but still low on precisely where the rainfall axis will line up. The latest guidance data suggest the front stalls north of M59 while the rainfall axis sets up from I-69 northward. A broad area of minor flooding potential is centered on the time period from tonight through Tuesday morning when ponding of water on roads and in other prone areas will be possible. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ AVIATION.....KDK DISCUSSION...BT MARINE.......MV HYDROLOGY....BT You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.