textproduct: Detroit/Pontiac

KEY MESSAGES

- Dry today before a strong cold front brings rain and a few thunderstorms late tonight into Saturday morning.

- Breezy and much colder Sunday with a few lake showers mixing with wet snowflakes at times.

- Seasonably cold Monday morning with wind chills in the low 20s and freeze conditions increasingly likely.

DTW THRESHOLD PROBABILITIES

* High for ceilings aob 5000 ft late tonight and Saturday.

* High for thunderstorms tonight between 7-10z.

PREV DISCUSSION

Issued at 348 AM EDT Fri Apr 17 2026

DISCUSSION...

Dense fog has been expanding inland overnight from both Lake Michigan and Lake Huron. Strong isentropic downglide has established a dry and statically stable airmass aloft, efficiently trapping moist boundary layer conditions characterized by dewpoints still in the low 50s. Nearly all sites are now reporting 1/4 to 1/2 mile visibility. A Dense Fog Advisory has been issued for all of SE Michigan as a result. The fog layer lifts to a stratus deck with the start of the diurnal cycle before scattering out this afternoon. Brief period of mid-level ridging/height rises affords a pleasant spring day across SE Michigan, as daytime highs climb into the upper 60s to low 70s. Should see a pronounced marine influence on highs for the east side of the cwa where east flow off the lakes keeps temperatures several degrees cooler than inland locations. Dry weather is expected amidst a much drier airmass in comparison to the last few days, as PWATs fall to around 0.5".

Quiet conditions are short-lived with the next round of rain/thunderstorms expected late tonight-Saturday. Convection initiates over WI/IA this afternoon along a strong cold front, propagating into the instability plume that spills into western lower Michigan this evening. Hi-res consensus has this line outrunning the instability axis by the time it reaches SE Michigan (after 06z/2am local) which keeps the SWODY1 risk to our west. Any instability that does advect into the area remains weak and elevated, favoring mostly showers with some embedded/decaying thunderstorms most likely west of I-75/US-23. Organized severe weather is not expected at this time. A discussion of heavy rain potential can be found in the Hydrology section. A second fine line of convection is possible Saturday morning along the cold frontal passage itself. This is a sneakier set up that lacks deep convective potential, but occurs in the backdrop of strong synoptic lift, low level wind shear, and steep low level lapse rates. Thinking this could manifest as a thunderless line of convection that could mechanically mix gusty winds (40 knot LLJ at h8) to the surface. The front will also be characterized by a sharp drop in temperatures. Highs in the mid to upper 60s occur mid-morning followed by falling temperatures through the afternoon. The cold advection increases mixing depths to continue to tap into the LLJ winds, maintaining breezy conditions for the rest of the weekend.

A much cooler airmass settles in for Sunday and Monday as the parent low deepens and sends an elongated lobe of vorticity across the Great Lakes. This draws the thermal trough even further south allowing H8 temperatures to drop into the negative single digits Sunday and the negative teens Monday morning. Highs in the 40s expected both days, while the coldest period will be Monday morning as lows dip into the 20s. Several additional shortwaves ripple across the Great Lakes with broad troughing settling in through Monday. A few showers are possible in this pattern, with potential for wet snowflakes to mix in with rain due to the cool wet bulb profiles. That said, low coverage and intensity to shower activity is expected given an overall lack of column moisture. A warm up is then expected Tuesday onward with the return of southwest flow.

MARINE...

Dense fog advisories are in effect through mid morning before fog gradually improves through the latter half of the morning and afternoon. Region holds under high pressure today maintaining a brief period of dry conditions and lighter winds. Winds eventually organize and strengthen out of the southeast this evening in response to low pressure tracking into northern Ontario. Moderate southerly winds with peak gusts in the 25-30kt range expected tonight before flipping to the west-northwest daytime Saturday with the passage of a respectable cold front. Gusts along/immediately following the front top out around 30kts. Another round of showers and thunderstorms are likely in advance of said front. Core of the colder trailing airmass arrives Sunday reinvigorating northwesterly winds supporting another period of gusts around 30kts. While a couple gusts near gales are possible, overall potential remains low (<30%). Strong high pressure then slides across the central Great Lakes for Monday.

HYDROLOGY...

A strong cold front tracks across SE Michigan late tonight into Saturday morning leading to another round of rain and embedded thunderstorms. Basin wide rainfall amounts of a half inch to localized one inch are possible between late tonight and mid-day Saturday. This additional rain will fall on already saturated soils and rising area rivers, worsening existing ponding and/or flooding. Additional rises on area rivers will be possible, with several rivers already in flood stage (Saginaw, Tittabawassee, Cass).

DTX WATCHES/WARNINGS/ADVISORIES

MI...None. Lake Huron...Small Craft Advisory from 4 AM to 10 PM EDT Saturday for LHZ421-422.

Small Craft Advisory from 4 AM to 4 PM EDT Saturday for LHZ441>443.

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