textproduct: Detroit/Pontiac

KEY MESSAGES

- Increasing clouds into this evening.

- Several rounds of showers and embedded thunderstorms are likely Saturday, Saturday night, and Sunday.

- A cool and cloudy pattern is expected through early next week.

DTW THRESHOLD PROBABILITIES

* High in ceilings aob 5000 feet Saturday and Saturday night.

* Low in thunderstorms Saturday afternoon and Saturday night.

PREV DISCUSSION

Issued at 809 PM EDT Fri Sep 18 2026

UPDATE...

A band of steady rain now extends from central Wisconsin into the Saginaw Valley and thumb. It appears that system relative frontogenesis along the 312 to 318K isentropic surfaces is the main driving mechanism for this elevated frontal rain. Regional satellite data would suggest the rain will persist well into tonight. As the low level jet develops upstream, hi res guidance still suggests development a little farther south across Wisconsin overnight, activating the lower portions of the elevated front. This is expected to cause some degree of weakening of the forcing across the north overnight while upstream activity causes the more widespread rain to become focused a little farther south across the area on Saturday. An earlier update already raised precip chances across the north tonight. If trends continue to suggest more persistence to the elevated forcing, an additional update to raise precip chances through the overnight may be needed.

PREV DISCUSSION... Issued at 342 PM EDT Fri Sep 18 2026

DISCUSSION...

Cooler north-northeasterly flow on the south end of a surface high pressure migrating across Ontario and into Quebec tonight will ensure more stable conditions locally. Limited cloud cover exists this afternoon with the flow supplying a good amount of lower level dry air. The quiet weather expected for the remainder of the afternoon with seasonal afternoon high temperatures.

Upstream over the western Great Lakes states, showers and isolated thunderstorms have developed on the leading edge of the theta-e ridge and monsoonal moisture plume and at the nose of the low level jet. Increasing cloud cover will arrive locally into the evening and tonight before greater rain chances begin to increase around 12Z tomorrow morning. Deeper moisture will be characterized by PWAT values climbing to 1.5 inches and above and will be focused along the warm frontal slope over the course of the weekend. This supports a good soaking rain and some isolated thunder potential Saturday morning with additional rounds of heavy rain potential and isolated thunder Saturday night into Sunday.

The first round moving through Saturday morning with QPF amounts generally at 0.25" to 0.75" through 00Z Saturday evening. CAPE depth will be lacking in a weak lapse rate environment with some hi-res guidance pointing toward a lull in heavier precipitation potential by mid afternoon Saturday given the showers moving across this weaker instability environment. Though, could still see scattered light shower activity continue during the afternoon. MUCAPE will be minimally supportive of embedded thunder potential with isolated to scattered coverage that becomes lesser in the afternoon. Highest QPF axis is focused across southwest portions of the CWA in the latest HREF.

The next surge of monsoonal moisture along the frontal zone is driven into the area Saturday after 00Z into Sunday morning. This presents the next chance for heavier precipitation potential with FGEN that could lead to areas of banded precipitation. Forecast QPF from 00Z Saturday to 12Z Sunday carries the highest 12 hour QPF potential with 0.75" to 1.00" or greater with the higher totals covering smaller footprints based on where any focused banding sets up along the frontal slope.

Latest NBM has trended toward a more broad area of 1+ inches of storm total precipitation over the course of Saturday and Sunday generally across the Tri-Cities east towards the Port Huron area as a camp of models have moved this direction as opposed to a focused swath of higher precipitation across southeast portions of the CWA. Still lean towards the look of the HREF with highest precipitation focused across southwest/southern portions of the CWA. Given the high end moisture and potential for repeated rounds, there will be at least a low chance for localized amounts of 2.00 to 2.50 inches over the 24 to 36 hour period. Given the spaced out nature of precipitation and weak thunderstorm activity, widespread flooding potential looks limited, but will come with the typical urban flooding potential if repeated heavier rounds of precipitation do occur over these areas.

Another high pressure moves into central Ontario and then into Quebec late Sunday into Monday. This allows northeasterly flow to push bulk of any lingering showers activity to the southern MI border or south. Cooler airmass with a tightening pressure gradient will bring breezy conditions with temperatures dropping down into the low to mid 60s for all of southeast Michigan for Monday and Tuesday. Developing trough mid-week will bring a return to more widespread rain precipitation chances early Wednesday.

MARINE...

High pressure is building southward across the Great Lakes today in the wake of a cold front that has about cleared the area to the south. Northeasterly winds behind the front gusting to around 20 knots have built waves enough to continue the current Small Craft Advisory for the southern Lake Huron nearshore zones. Weaker gradient with the incoming ridge will decrease winds and waves through the evening allowing the headline to end this evening. A low pressure system will then ride along the front on Saturday nudging the front back northward into southern MI through the day. Widespread showers and scattered thunderstorms are possible, mainly focused over the southern half of the region. Tightening of the gradient on the backside of the exiting low will ramp northeast winds back up on Sunday reaching 25 to 30 knots. These increased winds will carry into Monday as well which may necessitate additional headlines.

HYDROLOGY...

A low pressure system approaching from the Plains with increasing deep moisture will bring showers and isolated embedded thunderstorms to the area this weekend. Forecast rainfall totals have trended toward a broader area of higher total rainfall amounts across the Saginaw Valley towards Port Huron area. Relatively high confidence still exists for total rainfall ranging between a half inch to two inches, but the highest amounts are more likely to occur mainly south of a line from Lansing to Detroit. A period of light to moderate rainfall Saturday morning will may be followed by a lull in heavier precipitation potential Saturday afternoon. Then moderate rainfall rates and potential for training/repeated showers is more favored to occur from Saturday night into Sunday morning, especially for areas south of M-59. The longer duration rainfall event will mitigate widespread flooding concerns, but ponding will be possible where any repeated rounds of showers lead to localized totals in excess of 1 inch, especially in urban areas.

DTX WATCHES/WARNINGS/ADVISORIES

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