textproduct: Detroit/Pontiac

KEY MESSAGES

- Widespread showers and some embedded thunderstorms develop late tonight and continue through most of Saturday.

- Thunderstorms may be strong on Saturday, producing wind gusts of 45 to 55 mph, particularly over the eastern half of the CWA, where a marginal severe risk also exists.

- Below-normal temperatures return Sunday and persist through early next week. Low temperatures in the 20s are likely both Monday night and Tuesday night.

DTW THRESHOLD PROBABILITIES

* High for ceiling at or below 5000 ft tonight and Saturday.

* Moderate for thunderstorms overnight. Moderate Saturday afternoon.

PREV DISCUSSION

Issued at 250 PM EDT Fri Apr 3 2026

DISCUSSION...

A strong, closed 500MB low is tracking through the central/northern Plains this evening and will move through the Western Great Lakes tomorrow. An exceptional 500 MB height fall center is set to track through southern Minnesota Saturday morning and through Lake Superior Saturday evening. A strong southwest low-level jet (LLJ) of 50 - 60 knots will track through the Western Ohio Valley and southeast Michigan Saturday morning. Stellar moisture advection will take place tonight, with precipitable water (PW) values rising to at or above 1.3 inches- a record-setting level for early April per the SPC sounding climatology. Fortunately, instability will be weak; MUCAPE will struggle to reach 300 J/kg and will be mostly confined to near the southern Michigan border tonight. Furthermore, with mid- level lapse rates being average to poor, severe hail looks unlikely. There are no concerns for severe wind tonight due to a steep low- level inversion and backed surface flow from the southeast.

With the surface low tracking over eastern Iowa and into southern Wisconsin tonight, the best forcing looks to reside over western Lower Michigan, where the heaviest rainfall totals are expected. The persistent near-surface inversion will be maintained by a combination of early-morning rain and thick cloud cover as the occlusion resides over Southeast Michigan for most of the day. There appears to be a short window during the afternoon- depending on the track and intensity of the low through northern Lower Michigan- where eastern areas could enter a muddled warm sector before the cold front swings through by early evening. Strong wind fields (50 knots at 850 mb) could still support a marginal wind threat despite weak surface-based instability. We may see convective showers produce stronger wind gusts of 45 to 55 mph, with even gradient winds potentially approaching 45 mph late in the day. The eastern half of the CWA stands the best chance for stronger winds due to the timing of the cold front during peak heating. In fact, SPC even upgraded areas along a line from Monroe-Detroit-Port Huron to slight risk of severe, including 2 percent for tornado. However, expect the most favorable overlap of buoyancy and wind shear shifting east into Lake Erie basin and Southwestern Ontario by the time peak heating occurs.

Sunday through Tuesday: The departure of the low-pressure system into eastern Canada will usher in a period of strong cold-air advection as flow veers to the northwest. H850 temperatures are progged to drop significantly, falling into the -6C to -10C range by Sunday morning. This will result in a sharp contrast from Saturday's warmth, with surface highs struggling to exit the mid-40s under persistent cyclonic flow and stratocumulus cover. Model consensus, including the ECMWF and Canadian, highlights a reinforcing thermal trough as a secondary shortwave carves into the longwave trough over the Great Lakes Monday into Tuesday. Given the low freezing levels (generally below 1,500 ft AGL) and steep lapse rates, any convective- based showers on Monday could produce a rain/snow mix or even graupel, despite surface temperatures in the 40s. By late Tuesday, a strong 1030+ mb surface high is expected to build into the region, finally scouring out the lingering cloud cover. Low temperatures in the 20s appear likely for both Monday night and Tuesday night.

MARINE...

A short-lived ridge of high pressure passes over the Great Lakes this evening in between low pressure systems, allowing gusty westerly winds to subside and veer around to easterly by Saturday morning. The next low tracks from the mid-Mississippi Valley to across the Straits by Saturday evening, bringing widespread showers and thunderstorms tonight into tomorrow, some of which could be strong to severe in the south. A tightened pressure gradient produces easterly wind gusts to 30 knots across northern Lake Huron late tonight into Saturday afternoon. There is potential for brief gusts to 35 knot gales, mainly between 8am and 2pm, but confidence is too low for a Gale Warning at this time. As the system lifts north of Lake Huron late Saturday, wind will veer around to southwest and become gusty as cold advection ensues Saturday night. Gusts of 25 to 30 kt can be expected through Sunday and Small Craft Advisories will be likely. The gradient relaxes Monday causing wind magnitude to weaken. A series of clipper systems bring cooler air and chances for snow showers Monday and Tuesday.

HYDROLOGY...

The influx of high moisture content, characterized by PW values near 1.30 inches, will support high precipitation efficiency across Southeast Michigan tonight through Saturday evening. A widespread area of rain, occasionally enhanced by embedded thunderstorms, is expected to bring basin-average rainfall totals of approximately 0.75 inches to most of the region. However, given the robust low- level jet and strong moisture convergence, any stronger convective elements or training of cells could lead to higher localized amounts. In these areas, rainfall totals have the potential to reach or exceed 1.5 inches.

Fortunately, current 6-hour Flash Flood Guidance (FFG) for the Saginaw Valley and the broader CWA remains generally at or above 2.0 inches. This indicates the soil and drainage systems should be able to absorb the anticipated rainfall without significant flash flooding. Primary impacts will likely be limited to nuisance ponding or minor flooding in urban or low-lying areas and steady, near- bankfull rises on local rivers through the remainder of the weekend, with a low potential to reach flood stage.

DTX WATCHES/WARNINGS/ADVISORIES

MI...None. Lake Huron...Small Craft Advisory from 4 AM early this morning to 10 PM EDT Sunday for LHZ421-441.

Small Craft Advisory from 4 PM this afternoon to 10 PM EDT Sunday for LHZ422.

Small Craft Advisory from 10 AM this morning to 10 PM EDT Sunday for LHZ442-443.

Lake St Clair...None. Michigan waters of Lake Erie...None.