Byrnes Mill, MO Weather & Growing Conditions
Local forecast, frost dates, hardiness zone and planting guidance for Byrnes Mill, a city in Jefferson County, Missouri.
Today
89°F
Patchy Fog then Sunny
Patchy fog before 9am. Sunny, with a high near 89. Southeast wind around 2 mph.
7-day forecast for Byrnes Mill
| When | Temp | Forecast | Wind | Precip |
|---|---|---|---|---|
| Today | 89°F | Patchy Fog then Sunny | 2 mph SE | 0% |
| Tonight | 67°F | Mostly Clear | 3 mph SE | 0% |
| Wednesday | 90°F | Sunny | 3 mph S | 9% |
| Wednesday Night | 70°F | Slight Chance Showers And Thunderstorms | 3 mph S | 63% |
| Thursday | 87°F | Showers And Thunderstorms Likely | 3 mph S | 67% |
| Thursday Night | 69°F | Chance Showers And Thunderstorms | 2 mph S | 40% |
| Friday | 87°F | Chance Showers And Thunderstorms | 2 mph SW | 40% |
| Friday Night | 69°F | Chance Showers And Thunderstorms | 1 mph S | 32% |
| Saturday | 89°F | Chance Showers And Thunderstorms | 3 mph SW | 32% |
| Saturday Night | 71°F | Mostly Clear | 3 mph S | 6% |
| Sunday | 92°F | Sunny | 5 mph SW | 6% |
| Sunday Night | 73°F | Mostly Clear | 5 mph S | 5% |
| Monday | 93°F | Sunny | 5 mph SW | 5% |
| Monday Night | 74°F | Mostly Clear | 5 mph S | 13% |
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 Aug 4, 2026.