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Regional Calendars, Climate & DataRainfall Calendar by Region
Annual rainfall totals say little about when water arrives. A rainfall calendar that tracks timing by month helps you plan planting, irrigation and field work around what your region usually does.
Key points
- Rain timing by month matters more to crops than the annual total.
- NOAA 1991 to 2020 normals give monthly precipitation for stations across the country.
- Pair normals with your own gauge records and your log of lost field days.
- Plan for the typical year but keep a plan for wet and dry extremes.
Why does rain timing matter more than total rainfall?
Two regions can receive the same yearly total and farm very differently. One may get most of its rain in the growing season, another in the cold months. USDA Climate Hubs notes that rain may fall at the wrong times, with excess water in the off-season and shortages during critical growth periods, and that this varies by region.
A calendar built from monthly normals shows which months are typically wet, which are dry, and where irrigation or drainage has to fill the gap.
Rain also comes in different forms. Steady light rain soaks in, while a heavy downpour can run off, erode soil and leave the root zone drier than the gauge total suggests. A calendar of monthly totals should be read alongside your own notes on how storms behave on your soils.
Where do you find rainfall normals for your location?
NOAA's NCEI publishes U.S. Climate Normals: 30-year averages for the 1991 to 2020 period, with monthly, daily and seasonal precipitation totals, plus statistics such as days with precipitation. They are updated every ten years. Regional climate centers and state climatologists often provide station and county summaries, and many extension offices publish local climate pages.
Pick the station nearest to your land and similar in elevation, since rainfall can change over short distances in hilly or coastal terrain.
How do you build a simple rainfall calendar?
List the twelve months, then add the normal precipitation for each from your chosen station. Add a second row for your own rain gauge totals each year so you can see how actual years compare. Mark the months when crops have peak water needs, and mark the months when field work usually stalls from wet conditions.
For example, if your records show your wettest month usually coincides with your planned planting window, you might choose well-drained fields first, or add time to your schedule for delays.
- Row 1: normal monthly rainfall
- Row 2: your gauge totals by year
- Row 3: crop water-use peaks
- Row 4: field work and harvest windows
How do rain and field work interact?
Wet soil limits when tillage, planting, spraying and harvest can happen without compaction or rutting. Climate Hubs suggests calculating workable field days for each region and crop, which is essentially a rainfall calendar viewed through a machinery lens.
Keep a log of days you could not work and why. After a few seasons, you will see how many days to build into your plan.
Snowmelt matters in places where winter precipitation is a major source of spring soil moisture. If that describes your area, add a row for snow and melt timing, and ask extension how local growers account for it.
How should irrigation fit with the rainfall calendar?
Compare crop water use with typical rainfall month by month. Where the normal rain falls short during peak crop demand, irrigation is likely to matter. Where rain is reliable, the question may be drainage or timing instead. Local water rules apply to wells, surface water and districts, so check them before planning around any source.
Scheduling by soil moisture and crop stage is more precise than by calendar alone. See the irrigation guide on this site for the logic.
What are the common mistakes?
Treating a normal as a forecast. A 30-year average hides large swings, including wet springs and dry summers in the same station record. Another mistake is using a rain gauge reading from a different microclimate. Place a gauge in an open area away from trees and buildings, and read it at a consistent time.
Use the calendar to plan the typical year, and keep a backup plan for the wet and dry extremes.
How do drought and wet-year records fit in?
The U.S. Drought Monitor offers a weekly picture of dryness across the country, and it is a useful companion to a rainfall calendar because it shows how a given year compares with what is normal. Check it during the season when you decide whether to adjust irrigation, planting depth or crop choice.
Keep your own notes on the driest and wettest years you have farmed and what you did about them. Those notes will tell you how much slack your calendar needs.
Sources and further reading
Last reviewed: November 2026. Educational information, ranges only. Confirm timing with your county extension office.