


Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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393 FXUS63 KDTX 020410 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 1210 AM EDT Wed Apr 2 2025 .KEY MESSAGES... - A Winter Weather Advisory is in effect along/north of M-46 late tonight through morning for minor snow and ice accumulations; periods of rain mixed with melting precipitation expected further south. - A conditional threat exists for severe weather Wednesday evening and early Wednesday night with damaging winds, hail, an isolated tornado, and localized flooding all possible. - A Flood Watch is in effect Wednesday evening through Thursday morning. - Abnormally warm conditions expected Wednesday afternoon through Thursday with highs in the 60s. && .AVIATION... A leading band of snow heads toward the MBS area for the early hours after midnight with a few bursts of higher intensity IFR visibility restriction. The snow possibly grazes FNT as a snow to freezing rain transition occurs toward sunrise. Freezing rain is also briefly possible at PTK early in the morning just prior to temperature warming above freezing. Clusters of thunderstorms, ongoing over IL at midnight, spread rapidly into SE Mi during the morning affecting all terminals through early afternoon. The active precipitation pattern leads to a rapid MVFR trending to IFR ceiling and visibility as the Ohio valley warm front moves into southern Lower Mi toward noon Wednesday. SE surface wind gusting near 30 knots is a measure of strong gradient flow with locally higher gusts possible in and around thunderstorms. A few hours of IFR/LIFR ceiling and IFR visibility is associated with the warm front as it moves south to north across the terminal corridor into northern Lower Mi by Wednesday evening. For DTW... VFR above 5000 ft transitions quickly below 5000 ft and into MVFR early in the morning as rain showers also increase from the west. The chance for thunderstorms is shifted to earlier morning timing leading into a period of IFR/LIFR ceiling and visibility as a moisture laden warm front moves through the region. .DTW THRESHOLD PROBABILITIES... * Moderate for ceiling 5000 ft or less in the morning, high in the afternoon. * Moderate for thunderstorms during mid to late morning. && .PREV DISCUSSION... Issued at 957 PM EDT Tue Apr 1 2025 UPDATE... Upstream observations indicate inbound mid level moisture transport is on schedule to reach central Lower Mi shortly after the 2 AM Advisory start time. The leading band initially works against a deep layer of low level dry air shown in the 00Z DTX sounding which is steadily saturated top down into an all snow thermal profile in model soundings. This process keeps accumulation in the 1 to 2 inch range in a few heavier bursts. ENE surface wind maintains Td in the teens and 20s for a sustained wet bulb cooling influence most pronounced along and north of M-46 to sustain sub freezing temperatures at least through early morning. A snow to showery freezing rain transition then occurs toward daybreak as warm air aloft gains ground in the profile. Road and soil temperature observations in the 30s this evening suggest just a minor obstacle for snow accumulation and icing while elevated road surfaces become most prone to hazardous conditions for the morning commute. Icing is nudged up toward 0.10 in this update due to stubborn sub freezing surface air temperature until closer to the 10 AM Advisory expiration when early April daytime warming combines with veering surface wind to lift readings above 32 F. Farther south, conditions will be monitored along the I-69 to M-59 corridors where surface air temperature wavers closer to 32 F and is vulnerable to similar wet bulb cooling influence. A shorter period of snow to wintry mix to all rain is expected in this area for now. A later onset toward metro Detroit helps readings hold above freezing there. PREV DISCUSSION... Issued at 357 PM EDT Tue Apr 1 2025 DISCUSSION... Aggregate surface ridging, supported by anticyclonic flow aloft, acts to minimize diurnal boundary-layer cloud development through the rest of today. Easterly flow prevails during the evening and early overnight hours as the ridge structure responds to potent upstream longwave trough with a rapidly evolving shortwave feature. Mid-level moisture plume moves into Lower Michigan ahead of the arrival of an elevated warm front migrating northward from the Ohio Valley. This leads to a notable isentropic response as vapor condensation occurs within a broad region of system-relative ascent along the sloped material surface. Forecast soundings reveal some precipitation type uncertainty, especially between M-59 and I-69 where the duration of cold air will be shorter. Overall QPF with this lead forcing is generally pretty limited, but light snow accumulations are anticipated along/north of I-69. Duration of sub- freezing temperatures will vary greatly between M-59 and the northern edge of the forecast area, with The Thumb holding below freezing the longest. This favors some minor snow accumulations with potential for light icing late tonight through Wednesday morning. High degree of variability exists with the 12Z NWP suite regarding temperature profiles, and therefore precipitation type/accumulations. Opted to issue an initial Winter Weather Advisory along/north of M-46 for wintry weather leading to nuisance impacts for the morning commute. Highest confidence in 2+ inches of snowfall is mainly for Midland/Bay Counties, whereas the icing threat (later in the Advisory period) favors higher accretion efficiency over the drier/colder Thumb region. A changeover to rain should be complete across all of Southeast Michigan by 16Z as the warm front becomes firmly entrenched. This reflects a quick jump in 850 mb temperatures from the minus single digits (Celsius) to positive double digits, leading to a very sharp inversion between 1.5 kft and 5 kft AGL. Meanwhile, a shortwave trough closing off through 300 mb tilts strongly negative over the Missouri River basin featuring an impressive ageostrophic response and 150 knot jet streak at 250 mb. In spite of the formidable lower column inversion layer, confluent downwind sub-2 kft winds result in 60 knot LLJ winds passing overhead until late Wednesday evening. This ties into a highly conditional convective scenario late Wednesday as tremendous ThetaE advection pumps PWATs into the 1.20 to 1.50 inch range, exceeding April 2 12Z and April 3 00Z DTX sounding climatology maxima. Instability carries the highest uncertainty in that surface-based CAPE will struggle to materialize, but elevated/MUCAPE values of 1200-1500 J/kg are possible, based near the top of the inversion layer. From a shear/helicity perspective, hodographs/hodomaps profiles are extremely broad with 0- 1 km SRH values in excess of 1000 m2/s2. Fortunately, these values occur during the midday hours, before instability has time to build up. The main convective threat window, approximately 22Z Wednesday to 04Z Thursday, does lend a considerable reduction in SRH values, but still affords some low-level rotational threat. With EBWDs of 45-55 knots and 0-6 km bulk shear of 60+ knots, storm speed should be fast. Convective organization will likely lead to squall line activity with damaging winds, hail, an isolated tornado, and localized flooding all possible. Given the later timing and multiple convective axis, integrity for the norther portion of the line carries more uncertainty than the southern areas. SPC has included a portion of Southeast Michigan within an Enhanced Risk area while the northern half to two thirds carries a Slight Risk designation. Note that the primary threat is for damaging winds, with a hatched area for wind. 991 mb surface low tracks from Lake Superior, through Ontario, and into central Quebec Thursday with a slow recovery in southwesterly gradient winds. This ensures another mild day with highs in the upper 50s to mid 60s. Gusty during the day with mixing depths to around 5 kft AGL which translates to peak gusts in the 35-40 mph gusts once the boundary-layer interfaces with 40-50 knot flow. mainly dry conditions expected through the day with a low-end shower threat Thursday night, dependent on the northward extent of induced rainfall along a wavering stationary boundary. Split-flow emerges below 700 mb Friday with a shift to light northeasterly prevailing winds. This brings highs more in line with seasonal averages to close out the work before renewed rain chances over the weekend. MARINE... Area of high pressure has slide just to our east but still well in control of the weather through this evening. Winds emerge out of the southeast tonight and ramp up quickly ahead of the next low pressure system that will affect the region on Wednesday. Winds across Lake Huron will likely reach gales tonight through Wednesday so the watch has been upgraded to a warning. Additionally, farther south across Lake St Clair and Lake Erie, winds look to hold around 30 knots with building wave heights leading to a period of Small Craft Advisories for those lakes. The cold front will sweep through late Wednesday evening which will flip the winds around to the southwest and though they will remain elevated, will top out around the mid 20s. There will also be potential for strong to severe thunderstorms across the lakes late in the day on Wednesday. The front will then stall across the Ohio River Valley through the end of the week as high pressure builds back over the Great Lakes keeping lighter westerly flow Thursday and northerly flow Friday. HYDROLOGY... Several rounds of showers and thunderstorms begin Wednesday morning and continue through late Wednesday night. Daytime rainfall is not expected to cause widespread flooding as amounts will generally hold under an inch, with highest amounts across the northern tier counties where Flash Flood Guidance is generally above 2 inches. A second wave of thunderstorms, some strong to severe, will lift into the metro Detroit area Wednesday evening and overnight ahead of a cold front. Cell motion will be nearly parallel to the cold front in a high moisture environment characterized by PWAT values near daily maximum values of 1.5 inches, conducive to training storms with heavy rainfall. Coverage ahead of the front remains a point of uncertainty in the guidance, but a high coverage scenario would lead to rainfall amounts of at least 2 inches with localized higher totals. 6-hour Flash Flood Guidance in the Detroit Metro area is generally between 1.5 to 2 inches, supporting increased flash flooding concerns especially for the urban areas of Detroit and rises in area rivers. A Flood Watch has been issued as a result. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...Winter Weather Advisory until 10 AM EDT this morning for MIZ047>049- 053>055. Flood Watch from this evening through Thursday morning for MIZ063- 069-070-075-076-082-083. Lake Huron...Gale Warning from 4 AM early this morning to 10 PM EDT this evening for LHZ361>363-421-422-441>443-462>464. Lake St Clair...Small Craft Advisory until 4 AM EDT Thursday for LCZ460. Michigan waters of Lake Erie...Small Craft Advisory until 4 AM EDT Thursday for LEZ444. && $$ AVIATION.....BT UPDATE.......BT DISCUSSION...KGK MARINE.......DRK HYDROLOGY....MV You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.