Normal weather days by city › Michigan
NOAA 1991-2020 normals · Michigan
Normal weather delay days in Detroit, MI
A normal year in Detroit has about 73.5 rain days (0.10 in or more), 13.6 snow days and 119.6 freezing days. May has the most rain days and February the fewest.
These are NOAA's official 1991-2020 climate normals for DETROIT METRO AP, MI US (NOAA station USW00094847, 15.9 miles from downtown). Contractors use them as the "normal" baseline for weather days in bids, schedules and weather-delay clauses.
Weather-day calculator
From the start of October to the end of March (6 months), a normal Detroit schedule sees about:
days with 0.10 in or more of rain or melted snow
days with 0.50 in or more
days with 1 in or more of new snow
days with a low of 32°F or colder
days with a high of 90°F or hotter
These count calendar days. On a Monday to Friday schedule, about 5 in 7 of them fall on workdays (24.2 rain days). Real years vary a lot around the normal, which is why a day-by-day record of the actual weather matters when a delay is disputed.
Month by month
Average number of days per month, 1991-2020.
| Month | Rain days | Heavy rain days | Snow days | Freezing days | Hot days | Normal rain | Normal high / low |
|---|---|---|---|---|---|---|---|
| January | 5.9 | 1.1 | 4.3 | 27.2 | 0.0 | 2.23 in | 32° / 19° |
| February | 5.3 | 1.2 | 3.6 | 25.1 | 0.0 | 2.08 in | 35° / 21° |
| March | 6.1 | 1.4 | 1.9 | 21.0 | 0.0 | 2.43 in | 46° / 29° |
| April | 7.2 | 2.2 | 0.5 | 6.2 | 0.0 | 3.26 in | 59° / 39° |
| May | 7.7 | 2.4 | 0.0 | 0.3 | 0.5 | 3.72 in | 70° / 50° |
| June | 6.3 | 2.1 | 0.0 | 0.0 | 3.2 | 3.26 in | 80° / 60° |
| July | 6.4 | 2.1 | 0.0 | 0.0 | 5.3 | 3.51 in | 84° / 64° |
| August | 6.1 | 2.0 | 0.0 | 0.0 | 2.7 | 3.26 in | 81° / 63° |
| September | 5.9 | 2.0 | 0.0 | 0.0 | 1.2 | 3.22 in | 74° / 56° |
| October | 5.6 | 1.6 | 0.0 | 1.9 | 0.0 | 2.53 in | 62° / 44° |
| November | 5.6 | 1.8 | 0.6 | 13.7 | 0.0 | 2.57 in | 49° / 34° |
| December | 5.4 | 1.4 | 2.7 | 24.2 | 0.0 | 2.25 in | 37° / 25° |
| Year | 73.5 | 21.3 | 13.6 | 119.6 | 12.9 | 34.3 in |
Using these numbers
- Contract first. Your contract decides which days count: the thresholds, the baseline, the notice you must give and whether the weather actually stopped work on the critical path. Some contracts name their own table of normal weather days; use that if yours does.
- Normals are averages. A wet May can easily bring twice the normal. Comparing what actually happened, day by day, with the normal is what supports a time extension request.
- One station. These numbers come from one official airport station. Rain can differ across town.
Other Michigan cities
Keep a day-by-day weather record for your own job
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Source: NOAA NCEI U.S. Climate Normals 1991-2020, monthly normals for station USW00094847. A dash means NOAA publishes no value for that station.