502 FXUS63 KDTX 050403 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 1203 AM EDT Sat Apr 5 2025 .KEY MESSAGES... - Widespread rain overnight through Saturday morning. - Dry with cooler conditions for the latter half of the weekend. - Cooler conditions persist early next week with rain/snow showers likely on Monday. && .AVIATION... Fragile patches of light rain during late evening fill in with greater coverage and intensity after midnight. This is accompanied by northward advancement of MVFR ceiling as low level dry air from east wind is gradually overcome. A transition to IFR/LIFR follows later in the night as showers increase coverage intensity, and then as the surface low approaches NW Ohio. A rumble of thunder remains possible near to the south of DTW and more likely south of the Ohio border during the late night. This will be monitored as the surface low ripples along the warm front south of a TOL to CLE line early in the morning. Passage of the low brings wind around to the NW across Lower Mi leading to a slow ceiling improvement through afternoon into Saturday evening. .DTW THRESHOLD PROBABILITIES... * High for ceiling 5000 feet or less late tonight and Saturday. * Low for thunderstorms late tonight. && .PREV DISCUSSION... Issued at 957 PM EDT Fri Apr 4 2025 UPDATE... Ohio valley convective trends and potential northward extent into Lower Mi remain the forecast focus for SE Mi tonight and Saturday morning, although evening observational evidence suggests expectations for a manageable rainfall event remain intact. Upstream radar/satellite/surface observations indicate a band of showers and storms extending from the lower Ohio valley to east Texas along a broad surface frontal structure. The pattern is capitalizing on deep SW flow moisture transport consolidated east of the northern stream upper level trough and southern stream closed low that extends from central Canada to northern Mexico. New thunderstorm development is occurring east of the main line from the central Ohio valley into central Ohio as the low level jet ramps up north of the surface warm front making the surface to 925 mb frontal zone most active with new convection. This trend is expected to continue while the northern end of line extends NE toward western Lake Erie and as low pressure ripples northward from AR/MO. The surface low track is projected to reach very near the west end of Lake Erie which maintains a late night time window for elevated thunderstorms to graze the corner of SE Mi prior to sunrise. Overnight rainfall totals around 0.75 inch remain possible up to about the I-94 corridor while clusters of lighter showers activate farther north/higher up the frontal slope over most of southern Lower Mi. The initial 6 hours of the 00Z NAM and the latest runs of the RAP/HRRR concentrate this activity generally north of the I-69 corridor where totals around 0.5 inch are possible until about mid morning when the surface low exits east of Lake Erie. PREV DISCUSSION... Issued at 337 PM EDT Fri Apr 4 2025 DISCUSSION... High pressure anchored north of the region maintains cool and dry conditions through the evening period. Temperatures easing into the 40s during this time. Another widespread rainfall event then becomes the focus for the overnight period. Wave of low pressure ejecting northeast across the Ohio valley will draw an elevated warm frontal boundary into the local area during this time. This occurs in conjunction with deep northward moisture transport governed by increasing magnitude to low level southwest flow and characterized by pw in excess of 1.25 inches across southern sections. Combination of pronounced isentropic ascent along the advancing frontal slope and strengthening frontal forcing in the presence of increasing deformation effectively yields an axis of moderate to potentially brief heavy rainfall, with some probability for the northern expanse to develop across areas mainly south of M-59. Model guidance offering lower spatial predictability than desired at this stage in providing greater insight in location of heavier rainfall. Consensus with the HREF suggests convection across the warm sector will have greater influence on prospective moisture transport across the cold side of the frontal slope, maintaining a manageable qpf of generally less than 0.75" under limited mid level destabilization. Assessment of EPS membership, NAM output and local probabilistic information highlight the uncertainty, indicating greater potential with a roughly 50% chance of achieving an inch south of I-94 and a 25% chance of 1.5". Should forced ascent ultimately capitalize on greater theta-e advection and mid level instability, then a focused region of higher precipitation rates will be possible. Peak rainfall rates centered 04z-10z, with pockets of light showers lingering into Saturday morning as mid level forcing slowly peels away from west to east. Increasing deep layer stability with time heading into Saturday afternoon as emerging low level northwest flow affords greater drying throughout the column. Limited insolation potential given the lingering stratus canopy, as weak cold air advection solidifies a below average temperatures for the day. Highs capped at upper 40s north to mid 50s south. Energetic mid level southwest flow maintains a stream of shortwave energy along and north of the frontal zone easing southward across the Ohio valley. Tremendous moisture advection along the frontal slope in the presence favorable entrance region upper jet support will elicit another axis of heavy rainfall Saturday night, but expectation remains for this moist plume to mainly hold south of the region. Low end precip chances maintained across the far south to capture some uncertainty yet on the northern fringes of the qpf axis. Notably colder conditions to finish the weekend period, as a period of greater heights falls offer renewed cold air advection characterized by 850 temperatures of -5 to -7c. Highs peaking the 40s. Compact mid level wave of polar origin projected to pivot across the great lakes Monday. Potential for a narrow but pronounced axis of forced ascent to arrive tied to associated frontal forcing and dcva. Despite the daytime arrival, suppressed freezing levels afford a high probability for precipitation type of snow, particularly given the likelihood for some higher precipitation rates. Significant component of melting as surface temperature lift from lower 30s into the 40s, but some accumulation potential will exist on grassy surfaces. Another downturn in temperatures as high amplitude troughing takes control Tuesday. Inbound airmass will leave temperatures roughly 15 degrees below average, with readings struggling to climb out of the 30s. MARINE... High pressure over Lake Huron this afternoon leading to light and variable winds which will give way to light easterly this evening/tonight with a warm front lifting into southern Michigan. Widespread rain showers will develop, with embedded weak thunderstorms possible over Lake St. Clair and Lake Erie. A wave of low pressure will ride along the front Saturday morning, with increasing northwest winds following for Saturday afternoon-night. Good surge of low level cold advection, as 850 MB temps drop to around -10 C over northern Lake Huron, promoting deep mixing and wind gusts around 30 knots for a short period during early Saturday evening. A brief period of wind gusts near 25 knots over Saginaw Bay and northern tip of the Thumb region. Light winds return for Sunday before a clipper system tracks through on Monday producing a period of snow and rain showers. Even colder air will follow this system and northwest wind gusts around 30 knots appear likely over much of Lake Huron for Monday evening. HYDROLOGY... A warm front will bring widespread rain to all of SE MI late tonight through tomorrow morning. Rainfall totals are expected to range between 0.25" and 0.75" for most of the forecast area, with highest totals south of I-94. There remains potential for some repeated areas of higher intensity rainfall, particularly with any thunderstorms, to lead to locally higher rainfall totals possibly in excess of one inch. Given prior widespread rain activity and saturated soil, some ponding of water on roadways and localized flooding in low-lying and poor drainage areas may still be possible. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ AVIATION.....BT UPDATE.......BT DISCUSSION...MR MARINE.......SF HYDROLOGY....MR You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.