Byrnes Mill, MO Weather & Growing Conditions
Local forecast, frost dates, hardiness zone and planting guidance for Byrnes Mill, a city in Jefferson County, Missouri.
This Afternoon
99°F
Chance Showers And Thunderstorms
A chance of showers and thunderstorms. Sunny, with a high near 99. Heat index values as high as 104. South wind around 1 mph. Chance of precipitation is 30%.
7-day forecast for Byrnes Mill
| When | Temp | Forecast | Wind | Precip |
|---|---|---|---|---|
| This Afternoon | 99°F | Chance Showers And Thunderstorms | 1 mph S | 26% |
| Tonight | 71°F | Slight Chance Showers And Thunderstorms then Mostly Clear | 2 mph SE | 22% |
| Saturday | 98°F | Mostly Sunny | 1 to 6 mph SW | 5% |
| Saturday Night | 72°F | Partly Cloudy | 2 mph SW | 1% |
| Sunday | 93°F | Slight Chance Rain Showers then Slight Chance Showers And Thunderstorms | 5 mph W | 17% |
| Sunday Night | 66°F | Chance Showers And Thunderstorms then Showers And Thunderstorms Likely | 3 mph N | 61% |
| Monday | 80°F | Showers And Thunderstorms Likely | 5 mph N | 69% |
| Monday Night | 59°F | Showers And Thunderstorms Likely then Slight Chance Showers And Thunderstorms | 2 to 6 mph N | 69% |
| Tuesday | 72°F | Slight Chance Rain Showers then Mostly Cloudy | 6 mph N | 20% |
| Tuesday Night | 54°F | Mostly Cloudy | 2 to 6 mph N | 6% |
| Wednesday | 74°F | Mostly Sunny | 5 mph N | 1% |
| Wednesday Night | 54°F | Partly Cloudy | 0 to 3 mph N | 1% |
| Thursday | 75°F | Mostly Sunny | 1 to 5 mph N | 3% |
| Thursday Night | 56°F | Partly Cloudy | 0 to 3 mph NE | 3% |
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 Sep 19, 2026.