textproduct: Detroit/Pontiac

KEY MESSAGES

- A wave of low pressure will pass through portions of Indiana and Ohio late tonight and bring light rain, 40 to 70% chance, south of Detroit.

- A Frost Advisory is in effect 10 pm tonight until 8am Friday for many areas north of M 59 including the Thumb.

- Afternoon rain showers are again possible Friday afternoon.

- A Freeze Watch is in effect for all of Southeast Michigan Midnight to 9 AM Saturday for the potential of temperatures dropping below freezing.

- A slight warming trend is expected Sunday and Monday before a cold front pushes through the area Monday night.

DTW THRESHOLD PROBABILITIES

* Low for ceiling at or below 5000 feet this evening, moderate late tonight, and low Friday.

PREV DISCUSSION

Issued at 233 PM EDT Thu Apr 30 2026

DISCUSSION...

Low geopotential heights will persist over eastern North America for at least the next 7 days. Extended global deterministic solutions largely support a mean upper level trough axis from James Bay southward through portions of Lake Huron and Georgian Bay which will keep much of Southeast Michigan within northwest flow aloft. Latest progs support a very high frequency of low amplitude shortwave energy digging into the western and central Great Lakes keeping chance PoPs ubiquitous in the forecast.

Diurnal, boundary layer clouds are expected to thin out with loss of daytime heating this evening. This should allow for falling temperatures into the middle to lower 30s through midnight for much of the northern forecast before clouds thicken south. Based on the temperature forecast decided to go with a Frost Advisory for many areas along and north of the M 59 corridor particularly the Thumb.

The first of many shortwaves is forecasted to pivot around the upper level low through portions of IL/IN/OH attendant to a significant lobe of potential vorticity. With convective augmentation/strengthening later today, the absolute vorticity maximum is decently well resolved in the NWP. 850-700mb frontogenesis is now expected along the northern deformation axis that will stripe through Lenawee and Monroe counties. High resolution data is bullish on precipitation and decided to increase to likely PoPs for areas south of Detroit. Precipitation rates will aid in wetbulb cooling and possible could see few wet/melting snowflakes mix in. Ambient ground moisture with steep midlevel lapse rates will result in an environment conducive for showers Friday afternoon with afternoon forecast soundings suggesting some convective instability between 4.0 and 12.0 kft agl.

Weak surface ridging is forecasted to build out of the Mid Mississippi River Valley into Lower Michigan Friday night and Saturday. Light flow and a dry lower atmospheric column suggests better support for radiational cooling. Based on forecasted temperatures of 30-32F for much of the area decided to go with a Freeze Watch. Lower confidence exists on low temperatures for the urban heat island areas of Metro Detroit as temperatures could remain in the middle 30s.

Dampened shortwave in addition to synoptic scale warm advection will lead to precipitation chances again by late Sunday. A temporary southwest flow regime is expected to support temperatures near 60 degrees Sunday which is some 10 degrees warmer than the day before. The current forecast has PoPs during the afternoon and Sunday night which is sufficient.

Significant polar vorticity reservoir and upper level jet streak will then carve out and reestablish the troughing over the Great Lakes during the Monday and Tuesday timeframe next week. Current indications suggest a wet period along a prefrontal trough late Monday. Temperatures Monday are expected to be approximately 5 degrees above normal before a cold front leads to chilly conditions by the middle of next week.

MARINE...

The Great Lakes remains under the influence of a slow moving upper- level low pressure system. Periodic isolated to scattered showers are expected through the end of the week, along with lighter winds under a more diffuse pressure gradient. Wind direction holds northwest with stronger winds confined northern lake Huron, where gusts around 20 knots will be possible.

DTX WATCHES/WARNINGS/ADVISORIES

MI...Frost Advisory until 8 AM EDT Friday for MIZ047>049-053>055-061>063- 069-070.

Freeze Watch from late Friday night through Saturday morning for MIZ047>049-053>055-060>063-068>070-075-076-082-083.

Lake Huron...None.

Lake St Clair...None.

Michigan waters of Lake Erie...None.