Byrnes Mill, MO Weather & Growing Conditions
Local forecast, frost dates, hardiness zone and planting guidance for Byrnes Mill, a city in Jefferson County, Missouri.
Tonight
51°F
Light Rain Likely
Rain likely and a slight chance of thunderstorms before 3am, then a chance of rain showers between 3am and 4am. Cloudy, with a low around 51. South wind 5 to 9 mph, with gusts as high as 24 mph. Chance of precipitation is 70%.
7-day forecast for Byrnes Mill
| When | Temp | Forecast | Wind | Precip |
|---|---|---|---|---|
| Tonight | 51°F | Light Rain Likely | 5 to 9 mph S | 74% |
| Wednesday | 63°F | Mostly Cloudy | 5 to 9 mph W | 3% |
| Wednesday Night | 40°F | Partly Cloudy | 3 mph SW | 0% |
| Thursday | 67°F | Sunny | 2 to 7 mph W | 2% |
| Thursday Night | 41°F | Mostly Cloudy | 3 mph NW | 12% |
| Friday | 58°F | Partly Sunny | 2 to 7 mph NW | 4% |
| Friday Night | 36°F | Mostly Cloudy | 0 to 3 mph NW | 3% |
| Saturday | 57°F | Partly Sunny | 2 mph NW | 0% |
| Saturday Night | 33°F | Partly Cloudy | 0 mph | 1% |
| Sunday | 63°F | Sunny | 0 to 5 mph W | 8% |
| Sunday Night | 34°F | Mostly Clear | 2 mph W | 5% |
| Monday | 67°F | Sunny | 1 to 5 mph SW | 2% |
| Monday Night | 38°F | Mostly Clear | 2 mph SW | 1% |
| Tuesday | 70°F | Sunny | 3 mph W | 1% |
Forecast source: National Weather Service (api.weather.gov) for Byrnes Mill (38.439, -90.574). Updated through the day.
Growing snapshot for Byrnes Mill
Last spring frost
Apr 12
First fall frost
Oct 23
Growing season
193 days
Hardiness zone
7a
More local growing data for Byrnes Mill: nearby ZIP 63049 weather · frost dates · planting calendar · Missouri frost dates
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Summer Set
Climate data from the nearest NOAA station, St Louis Sprt Of S L Ap, Mo (14.2 mi from Byrnes Mill). Frost dates are 1991–2020 averages, not a forecast. Page updated Nov 4, 2026.