Rainfall by Zip Code: Average Rainfall and Design Storms for Your Yard
Enter a zip to see its 1991–2020 average rainfall by month (NOAA climate normals) and the one-day storms drainage is built for (NOAA Atlas 14). The typical US zip averages 43 inches a year. Raleigh averages 48.5 — 5.2 in its wettest month — and its 10-year storm drops 5.1 inches in one day.
Updated October 23, 2026 · NOAA NCEI 1991–2020 normals for 33,702 zips · NOAA Atlas 14 for 3,144 counties · How we built it
Example · enter your zip above
Zip 27601 · Wake County, NC
- Average year
- 48.5 in
- Wettest month
- Sep · 5.20 in
- 2-year storm, 1 day
- 3.48 in
- 10-year storm, 1 day
- 5.06 in
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 3.60 | 2.99 | 4.16 | 3.68 | 3.83 | 4.52 | 4.99 | 4.90 | 5.20 | 3.61 | 3.47 | 3.56 |
| 6.6 | 6.0 | 6.8 | 5.8 | 6.3 | 7.0 | 7.1 | 6.7 | 5.9 | 4.6 | 5.0 | 5.9 |
Top row: average inches. Second row: average days with 0.1 in or more (nearest NOAA station). Driest month: February (2.99 in).
Design storms for Wake County (NOAA Atlas 14)
| Storm | 1 day | Peak 5 min | Peak hour |
|---|---|---|---|
| 1-year | 2.88 in | — | — |
| 2-year | 3.48 in | 5.66 in/hr | 1.64 in |
| 10-year | 5.06 in | 7.24 in/hr | 2.3 in |
| 25-year | 6.00 in | 7.98 in/hr | — |
| 100-year | 7.54 in | 9.02 in/hr | 3.19 in |
Average: NOAA NCEI 1991–2020 gridded normals (about a 5 km cell) at the zip's centre point.
Design storms: NOAA Atlas 14 point estimates at Wake County's population centre (partial-duration series). For an exact address, use NOAA's precipitation frequency server.
What this rainfall means for a yard
For the example zip 27601. Each point below is worked out from the numbers above. They describe tendencies, not a diagnosis of a particular yard.
Plan storage fixes for about 3.48 inches in a day
A hard day of rain that arrives every year or two here drops about 3.48 inches in 24 hours (the 2-year storm). On every 1,000 sq ft of roof that is roughly 2,150 gallons, and it is the figure dry wells, rain gardens and rain barrels fill against — not the yearly total.
A rare day brings 97% of your wettest month
The 10-year storm here is 5.06 inches in 24 hours; September, the wettest month, averages 5.2 inches. Drainage problems come from these concentrated days, which is why monthly averages alone can't size a drain.
Downpours here are intense: 7.2 in/hr for five minutes
The 10-year five-minute burst is what overflows gutters, grates and small pipes. At 7.2 in/hr, 1,000 sq ft of roof or paving sends about 75 gallons per minute toward its outlet for those minutes.
Wettest stretch: Jul–Sep (31% of the year's rain)
Rain is spread fairly evenly through the year (driest month February, 2.99 in), so soil rarely gets a long dry spell to recover between storms. Slow-draining clay shows up year-round.
Use a zip's numbers in a calculator
Each calculator opens with the zip you look up filled in and picks the figure it needs: storage fixes take a one-day depth, anything that has to keep up with a downpour takes a peak rate.
- Roof runoff calculator →Uses the gallons your roof sheds in your 2- and 10-year storms
- Gutter size calculator →Uses the 10-year 5-minute intensity
- Dry well calculator →Uses the 2-year 24-hour depth
- Rain garden calculator →Uses the 2-year 24-hour depth for the overflow
- Catch basin calculator →Uses the 10-year 5-minute intensity
- Yard French drain sizing calculator →Uses the 10-year 1-hour rate
- Rainwater harvesting calculator →Uses the monthly averages and the 2-year storm
Average rainfall vs a design storm
The yearly total tells you how wet a place is. It doesn't size anything. A drain, dry well or rain garden fails on one bad day, and those days are far bigger than an average month suggests: in Raleigh, NC the wettest month, September, averages 5.2 inches, while a 10-year storm drops 5.1 inches in 24 hours. NOAA Atlas 14 publishes those storms by “recurrence interval” — the chance of a storm that size in any one year.
| Storm | In any one year | Over 10 years | Over 30 years |
|---|---|---|---|
| 1-year | ≈100% | ≈100% | ≈100% |
| 2-year | 50% | ≈100% | ≈100% |
| 10-year | 10% | 65% | 96% |
| 25-year | 4% | 34% | 71% |
| 100-year | 1% | 10% | 26% |
Chance of at least one storm that size, assuming each year is independent: 1 − (1 − 1/T)ⁿ.
Five zips side by side
A dry average doesn't mean small storms, and a wet one doesn't mean big ones. Seattle averages about 5 times Phoenix's yearly rain, much of it as long, light rain. Phoenix gets far less, yet its 10-year five-minute burst still reaches 4.86 in/hr — 67% of Raleigh's. Seattle's design storms aren't in Atlas 14 at all.
| Zip | Average year | Wettest month | 2-year day | 10-year day |
|---|---|---|---|---|
| 27601 Raleigh, NC | 48.5 in | Sep · 5.20 in | 3.48 in | 5.06 in |
| 33130 Miami, FL | 60.6 in | Jun · 8.87 in | 5.50 in | 8.54 in |
| 77002 Houston, TX | 53.9 in | Jun · 5.79 in | 5.09 in | 8.66 in |
| 85004 Phoenix, AZ | 7.4 in | Feb · 0.97 in | 1.46 in | 2.23 in |
| 98101 Seattle, WA | 38.0 in | Nov · 5.80 in | no Atlas 14 | no Atlas 14 |
Rainfall by state: map and table
Switch the map between the average year and the two storms. They are different maps: the Gulf Coast ranks high on all three; the Pacific Northwest coast is among the wettest on average but grey on the storm maps, which Atlas 14 doesn't cover; the Plains are dry on average yet still get intense bursts. Tap a county for its numbers; the table gives each state's median and range.
Tap or click a county for its full set of values.
| State | Average year, in | 2-year day, in | 10-year burst, in/hr |
|---|---|---|---|
| Alabama | 56.6 (49.6–65.8) | 4.18 (3.94–6.00) | 8.3 (7.9–11.7) |
| Alaska | 19.7 (4.7–245.7) | 1.45 (0.67–7.10) | 2.6 (1.5–4.6) |
| Arizona | 9.9 (2.8–28.5) | 1.58 (1.15–2.93) | 5.1 (3.9–7.7) |
| Arkansas | 52.0 (45.7–59.5) | 4.13 (3.70–4.75) | 8.0 (7.1–9.3) |
| California | 17.1 (2.2–79.5) | 2.40 (0.98–4.68) | 2.9 (1.6–4.7) |
| Colorado | 15.9 (7.7–47.1) | 1.75 (0.91–2.28) | 5.0 (2.6–7.8) |
| Connecticut | 48.5 (44.6–53.5) | 3.45 (3.14–3.58) | 7.3 (7.1–7.6) |
| Delaware | 46.2 (44.5–48.2) | 3.31 (3.24–3.43) | 6.6 (6.4–6.7) |
| District of Columbia | 44.3 (44.1–44.9) | 3.14 (3.14–3.14) | 6.8 (6.8–6.8) |
| Florida | 53.0 (38.7–64.9) | 4.63 (3.94–5.95) | 9.9 (8.7–11.0) |
| Georgia | 50.7 (45.1–79.8) | 3.86 (3.50–4.80) | 8.4 (6.6–10.4) |
| Hawaii | 46.2 (8.5–229.1) | 5.06 (3.70–6.82) | 8.8 (6.8–10.1) |
| Idaho | 18.7 (6.0–61.1) | 1.17 (0.91–2.11) | 3.7 (3.1–4.5) |
| Illinois | 38.8 (35.5–50.1) | 3.05 (2.64–3.77) | 7.7 (6.9–8.1) |
| Indiana | 42.9 (36.8–51.0) | 2.95 (2.57–3.29) | 7.3 (6.7–7.8) |
| Iowa | 36.3 (28.6–39.7) | 3.07 (2.76–3.31) | 8.0 (7.4–8.4) |
| Kansas | 34.5 (16.5–46.0) | 3.07 (2.26–3.98) | 7.9 (6.7–8.6) |
| Kentucky | 50.1 (41.6–57.6) | 3.12 (2.62–3.86) | 6.7 (5.8–7.6) |
| Louisiana | 61.0 (51.6–65.7) | 5.11 (4.25–5.54) | 10.1 (8.3–11.0) |
| Maine | 47.9 (38.7–56.5) | 3.09 (2.28–3.65) | 6.2 (4.9–6.7) |
| Maryland | 45.3 (39.3–51.6) | 3.24 (2.45–3.48) | 6.6 (5.8–7.0) |
| Massachusetts | 48.0 (43.6–53.8) | 3.24 (2.90–3.43) | 6.9 (6.3–7.3) |
| Michigan | 33.9 (28.2–39.8) | 2.35 (2.06–2.71) | 6.0 (5.1–7.1) |
| Minnesota | 29.8 (21.7–37.8) | 2.71 (2.23–3.07) | 7.5 (6.2–8.3) |
| Mississippi | 57.6 (53.2–66.0) | 4.37 (4.01–5.90) | 8.8 (8.0–11.2) |
| Missouri | 42.5 (33.7–51.1) | 3.46 (3.12–3.91) | 7.9 (7.2–8.7) |
| Montana | 15.0 (9.0–60.3) | 1.65 (1.08–1.94) | 5.3 (3.4–8.1) |
| Nebraska | 28.3 (13.4–34.7) | 2.71 (1.80–3.34) | 7.5 (6.0–8.7) |
| Nevada | 7.0 (3.4–38.7) | 1.13 (0.84–1.78) | 2.4 (2.0–3.9) |
| New Hampshire | 47.4 (38.5–74.9) | 2.86 (2.71–3.31) | 6.2 (5.7–6.7) |
| New Jersey | 47.6 (44.9–52.0) | 3.31 (3.24–3.55) | 6.5 (6.2–6.7) |
| New Mexico | 13.5 (6.5–36.6) | 1.66 (1.06–2.69) | 5.4 (3.7–8.6) |
| New York | 44.9 (32.9–61.3) | 2.50 (2.18–3.65) | 6.5 (5.8–8.0) |
| North Carolina | 48.4 (43.0–82.5) | 3.65 (2.64–4.70) | 7.4 (6.2–9.7) |
| North Dakota | 19.2 (14.2–24.5) | 2.09 (1.80–2.45) | 6.5 (5.4–7.3) |
| Ohio | 41.2 (33.1–46.9) | 2.54 (2.30–2.93) | 6.6 (6.0–7.2) |
| Oklahoma | 38.4 (15.9–55.9) | 3.82 (2.28–4.51) | 8.4 (7.5–9.3) |
| Oregon | 42.7 (7.6–111.5) | Not in NOAA Atlas 14 (still Atlas 2, 1973) | |
| Pennsylvania | 45.0 (36.4–55.3) | 2.66 (2.35–3.41) | 6.2 (5.2–6.8) |
| Puerto Rico | 64.8 (32.5–108.7) | 5.10 (3.77–6.46) | 8.4 (6.5–11.1) |
| Rhode Island | 49.3 (42.8–51.3) | 3.41 (3.38–3.46) | 7.2 (7.2–7.2) |
| South Carolina | 48.1 (41.6–71.8) | 3.62 (3.50–4.56) | 8.0 (7.2–9.3) |
| South Dakota | 23.6 (14.8–29.1) | 2.35 (1.87–2.86) | 7.2 (5.6–7.9) |
| Tennessee | 54.9 (44.7–65.4) | 3.67 (2.45–4.01) | 7.0 (5.4–7.8) |
| Texas | 36.7 (8.7–61.5) | 3.74 (1.54–5.64) | 8.3 (5.8–10.7) |
| Utah | 14.5 (5.5–44.0) | 1.27 (0.91–1.80) | 3.2 (2.6–4.0) |
| Vermont | 44.8 (35.4–60.1) | 2.42 (2.18–3.00) | 6.0 (5.7–6.5) |
| Virginia | 45.6 (38.8–57.0) | 3.26 (2.35–4.03) | 6.7 (5.4–8.0) |
| Washington | 38.5 (6.9–135.4) | Not in NOAA Atlas 14 (still Atlas 2, 1973) | |
| West Virginia | 46.9 (36.5–61.2) | 2.57 (2.33–2.88) | 6.3 (5.3–6.9) |
| Wisconsin | 34.0 (30.0–39.0) | 2.69 (2.33–3.07) | 7.0 (5.9–8.2) |
| Wyoming | 13.9 (6.1–60.7) | 1.58 (1.08–2.02) | 5.4 (3.3–8.2) |
Median, with the lowest and highest in brackets: across the state's zips for the average year, across its counties for the storms.
Looking for how much rain fell recently?
This page is about what to plan for, not what fell yesterday. For recent totals, the National Weather Service's precipitation maps on water.noaa.gov estimate daily rainfall from radar and gauges, and CoCoRaHS maps readings from volunteer rain gauges, sometimes within a mile or two of you. To compare a wet month with normal, use the monthly averages above.
Methodology
Average rainfall. In the lower 48 states each zip gets the NOAA NCEI 1991–2020 gridded monthly precipitation normal (built on nClimGrid, a grid of 1/24° — about 4–5 km) at the grid cell holding the zip's Census 2020 internal point; where that cell is empty, at a coast or lake edge, the nearest filled cell within 3 cells. 851 zips in the Census zip-to-county file have no Gazetteer point, so they are read at their county's population centre. Alaska, Hawaii and Puerto Rico, which the grid doesn't cover, take the nearest station in NCEI's 1991–2020 station normals whose monthly values are complete and flagged standard, representative or provisional (estimated normals are left out), within 100 km; the result names the station and its distance. 72 remote Alaska zips have no such station and show no average. The year is the sum of the months, as NOAA defines it. Rain days — the average number of days a month with at least 0.1 inch — come from the nearest station with complete counts in the same station normals (within 50 km, or 150 km where stations are sparse).
Cross-check. For the 15,622 zips with a qualifying station within 10 km, the grid's annual figure and the station's differ by a median of 3.5%, and by 10% or less for 87.2% of them — a station measures one spot, the grid averages a 4–5 km cell.
Design storms. NOAA Atlas 14 point precipitation-frequency estimates (partial-duration series), read from NOAA's Precipitation Frequency Data Server at each county's 2020 Census centre of population, for 3,144 counties. A zip takes the county holding most of its land (Census 2020 ZCTA-to-county file). Atlas 14 doesn't cover Oregon or Washington, and a few remote Alaska boroughs have no value at their centre.
Open data (CSV)
- rainfall-normals-by-zip.csv — one row per zip: state, county, the point read, the source (grid or station, with station ID and distance), January–December and annual normals in inches.
- design-rainfall-by-county.csv — one row per county: FIPS, the point read, the Atlas 14 volume, 5-minute intensities at 2-, 10-, 25- and 100-year recurrence, the 15-minute 10-year and 1-hour 2-, 10- and 100-year intensities (in/hr), and 24-hour depths at 1-, 2-, 10-, 25- and 100-year recurrence.
Both are licensed CC BY 4.0: use them for anything, including commercially, with credit to Yard Drainage Fixes and a link to this page. See the terms. Normals built October 23, 2026; Atlas 14 values read September 27, 2026.
What this page does not tell you
Every figure is read at one point — a zip's centre, a county's population centre or a station — so a particular yard can differ, most of all in hills and mountains. Averages describe 1991–2020; individual years swing well above and below them. Atlas 14 values are the federal reference for design storms but not a permit number: where a stormwater permit or engineered plan is involved, use the figures your local authority specifies. And none of it says how your soil, slope or downspouts handle the water — that is what the calculators above and the rest of this site are for.
Frequently asked questions
How do I find the average rainfall for my zip code?
How can I find out how much rain fell in my area yesterday or this week?
How much rain is a lot in one day?
What is a 10-year or 100-year storm?
Which rainfall number should I use to size a drain, dry well or rain garden?
Is there a rainfall calculator for how much water lands on my roof or yard?
Why is there no design storm for Oregon or Washington?
Sources
- NOAA National Centers for Environmental Information, U.S. Monthly Gridded Precipitation and Temperature Climate Normals for 1991–2020 (NCEI Accession 0245564, precipitation file v1.0).
- NOAA NCEI, U.S. Climate Normals 1991–2020, monthly precipitation normals by station (v1.0.1) and station inventory.
- NOAA Hydrometeorological Design Studies Center, NOAA Atlas 14 Precipitation-Frequency Atlas of the United States, via the Precipitation Frequency Data Server.
- US Census Bureau, 2020 ZCTA Gazetteer, 2020 ZCTA-to-county relationship file and 2020 county centres of population.
Related
- Rainwater harvesting calculator — how much of this rain a roof and barrel can keep, month by month
- Roof runoff calculator — gallons per storm and per downspout
- Rainwater collection laws by state — whether and how much you can store
- North Carolina rainfall design storms — design storms for 18 NC cities
- Standing water in the yard — when the rain has nowhere to go