# Climate Design Data Workflow for Washington, DC

> A source-first workflow for retrieving and recording building-design climate conditions for Washington, DC without mixing climate normals, code zones, and HVAC design percentiles.

- Canonical: https://harth.build/resources/climate-data/climate-design-data-workflow-washington-dc/
- Last updated: 2026-08-31
- Data source: Licensed ASHRAE Climatic Design Information / Standard 169 station data plus the locally adopted energy code. Coordinates 38.9072° N (America/New_York) are approximate routing references. Figures are illustrative — confirm the representative station and current edition. Climate screening data from the [NASA POWER Climatology API documentation](https://power.larc.nasa.gov/docs/services/api/temporal/climatology/) and [exact point response](https://power.larc.nasa.gov/api/temporal/climatology/point?parameters=T2M%2CT2M_MAX%2CT2M_MIN%2CRH2M%2CPRECTOTCORR%2CWS10M&community=SB&longitude=-77.0369&latitude=38.9072&format=JSON), retrieved 2026-08-31; source period: 20-year Meteorological and Solar Monthly & Annual Climatologies (January 2001 - December 2020). NASA POWER values are gridded screening statistics, not code design conditions or guaranteed local observations.

## Key facts

| Fact | Value |
| --- | --- |
| NASA POWER climatology | 20-year Meteorological and Solar Monthly & Annual Climatologies (January 2001 - December 2020) (API v2.9.7; LST) |
| Annual mean temperature | 13.2 °C (2 m gridded climatology; not a design percentile) |
| Highest monthly maximum | 40.2 °C (July) (monthly climatological statistic) |
| Lowest monthly minimum | -18.7 °C (February) (monthly climatological statistic) |
| Annual relative humidity | 76.5% (2 m gridded climatology) |
| Annual corrected precipitation | 3.16 mm/day (climatological daily rate) |
| Annual wind speed | 3.97 m/s (10 m gridded climatology; not a structural design wind speed) |

## Direct answer

NASA POWER's 2001–2020 climatology at the Washington, DC reference point reports an annual mean 2 m temperature of 13.2 °C and relative humidity of 76.5%. The highest monthly maximum is 40.2 °C in July, while the lowest monthly minimum is -18.7 °C in February; these are screening statistics, not code design temperatures. The point response uses LST and the 20-year Meteorological and Solar Monthly & Annual Climatologies (January 2001 - December 2020); its annual corrected precipitation is 3.16 mm/day and annual 10 m wind speed is 3.97 m/s. Use the monthly series to screen source selection before applying project design conditions. NASA POWER is gridded climatology: verify elevation, microclimate, urban exposure, station or weather-file suitability, current code edition and the authority's required source before design use.

*Content and cited inputs reviewed by [Harth team](https://www.linkedin.com/company/harth-build) · Published 2026-08-17 · Updated 2026-08-31.*

## Which climate inputs control the design?

1. Confirm the project jurisdiction and adopted energy-code edition.
2. Select the authoritative station and record why it applies.
3. Record heating dry-bulb percentiles and cooling dry-bulb with coincident moisture conditions.
4. Keep IP/SI units, edition, observation period and retrieval date with every value.
5. Separate climate-zone envelope requirements from HVAC sizing conditions.

| Field | Required record |
| --- | --- |
| Station | Name, ID, coordinates and elevation |
| Source | Publisher, edition and licensed/public status |
| Heating | 99.6% and 99% dry-bulb |
| Cooling | 0.4%, 1% and 2% dry-bulb plus coincident wet-bulb |
| Moisture | Dew-point or humidity design condition used |
| Code | Adopted edition, amendments and effective date |

## Washington, DC NASA POWER monthly climate screening table

| Month | Mean °C | Monthly max °C | Monthly min °C | RH % | Precipitation mm/day | Wind at 10 m m/s |
| --- | ---: | ---: | ---: | ---: | ---: | ---: |
| January | 0.11 | 20.55 | -16.49 | 81.79 | 2.16 | 4.65 |
| February | 1.30 | 23.35 | -18.73 | 80.45 | 2.49 | 4.72 |
| March | 5.83 | 25.08 | -16.83 | 78.53 | 2.70 | 4.76 |
| April | 12.16 | 32.97 | -3.82 | 76.40 | 3.07 | 4.52 |
| May | 17.64 | 32.86 | 0.39 | 77.95 | 3.53 | 3.74 |
| June | 22.84 | 36.34 | 7.67 | 74.41 | 3.94 | 3.34 |
| July | 25.79 | 40.24 | 12.56 | 69.41 | 3.75 | 2.98 |
| August | 25.13 | 37.79 | 13.22 | 69.68 | 3.53 | 2.96 |
| September | 21.31 | 36.25 | 6.64 | 71.61 | 3.57 | 3.49 |
| October | 14.40 | 35.64 | -1.13 | 76.28 | 3.38 | 4.00 |
| November | 7.85 | 25.27 | -5.68 | 78.83 | 2.67 | 4.23 |
| December | 2.75 | 22.37 | -11.19 | 83.15 | 3.06 | 4.30 |

![Monthly mean, maximum and minimum air temperature for Climate Design Data Workflow for Washington, DC](https://efwwel0vyt9vy5so.public.blob.vercel-storage.com/images/climate-data/climate-design-data-workflow-washington-dc/chart-temperature-1344.webp)

*Monthly air temperature for Climate Design Data Workflow for Washington, DC, plotted from the table above.*

![Mean daily precipitation by month for Climate Design Data Workflow for Washington, DC](https://efwwel0vyt9vy5so.public.blob.vercel-storage.com/images/climate-data/climate-design-data-workflow-washington-dc/chart-precipitation-1344.webp)

*Mean daily precipitation for Climate Design Data Workflow for Washington, DC, plotted from the table above.*

## Month-by-month climate interpretation

- **January:** mean temperature 0.11 °C is 13.04 °C below the annual mean; the monthly max–min span is 37.04 °C. Relative humidity is 81.79% (5.27 points above annual), while corrected precipitation at 2.16 mm/day is 1.00 mm/day drier than the annual daily rate.
- **February:** mean temperature 1.30 °C is 11.85 °C below the annual mean; the monthly max–min span is 42.08 °C. Relative humidity is 80.45% (3.93 points above annual), while corrected precipitation at 2.49 mm/day is 0.67 mm/day drier than the annual daily rate.
- **March:** mean temperature 5.83 °C is 7.32 °C below the annual mean; the monthly max–min span is 41.91 °C. Relative humidity is 78.53% (2.01 points above annual), while corrected precipitation at 2.70 mm/day is 0.46 mm/day drier than the annual daily rate.
- **April:** mean temperature 12.16 °C is 0.99 °C below the annual mean; the monthly max–min span is 36.79 °C. Relative humidity is 76.40% (0.12 points below annual), while corrected precipitation at 3.07 mm/day is 0.09 mm/day drier than the annual daily rate.
- **May:** mean temperature 17.64 °C is 4.49 °C above the annual mean; the monthly max–min span is 32.47 °C. Relative humidity is 77.95% (1.43 points above annual), while corrected precipitation at 3.53 mm/day is 0.37 mm/day wetter than the annual daily rate.
- **June:** mean temperature 22.84 °C is 9.69 °C above the annual mean; the monthly max–min span is 28.67 °C. Relative humidity is 74.41% (2.11 points below annual), while corrected precipitation at 3.94 mm/day is 0.78 mm/day wetter than the annual daily rate.
- **July:** mean temperature 25.79 °C is 12.64 °C above the annual mean; the monthly max–min span is 27.68 °C. Relative humidity is 69.41% (7.11 points below annual), while corrected precipitation at 3.75 mm/day is 0.59 mm/day wetter than the annual daily rate.
- **August:** mean temperature 25.13 °C is 11.98 °C above the annual mean; the monthly max–min span is 24.57 °C. Relative humidity is 69.68% (6.84 points below annual), while corrected precipitation at 3.53 mm/day is 0.37 mm/day wetter than the annual daily rate.
- **September:** mean temperature 21.31 °C is 8.16 °C above the annual mean; the monthly max–min span is 29.61 °C. Relative humidity is 71.61% (4.91 points below annual), while corrected precipitation at 3.57 mm/day is 0.41 mm/day wetter than the annual daily rate.
- **October:** mean temperature 14.40 °C is 1.25 °C above the annual mean; the monthly max–min span is 36.77 °C. Relative humidity is 76.28% (0.24 points below annual), while corrected precipitation at 3.38 mm/day is 0.22 mm/day wetter than the annual daily rate.
- **November:** mean temperature 7.85 °C is 5.30 °C below the annual mean; the monthly max–min span is 30.95 °C. Relative humidity is 78.83% (2.31 points above annual), while corrected precipitation at 2.67 mm/day is 0.49 mm/day drier than the annual daily rate.
- **December:** mean temperature 2.75 °C is 10.40 °C below the annual mean; the monthly max–min span is 33.56 °C. Relative humidity is 83.15% (6.63 points above annual), while corrected precipitation at 3.06 mm/day is 0.10 mm/day drier than the annual daily rate.

Harth retrieved this point climatology from NASA POWER API v2.9.7 for location record us:washington-dc. It is a reproducible screening dataset, not an hourly weather file, forecast, code design condition or substitute for local professional review.

## Where can you explore related guidance?

- [Explore all climate data guidance](https://harth.build/resources/climate-data.md)
- [ASHRAE / IECC Climate Zones Explained (Zones 1–8, A/B/C)](https://harth.build/resources/climate-data/ashrae-climate-zones-explained.md)
- [Heating & Cooling Design Temperatures (99%, 1% / 0.4%)](https://harth.build/resources/climate-data/heating-and-cooling-design-temperatures.md)
- [Climate Design Data Workflow for New York, NY](https://harth.build/resources/climate-data/climate-design-data-workflow-new-york-ny.md)
- [Climate Design Data Workflow for Boston, MA](https://harth.build/resources/climate-data/climate-design-data-workflow-boston-ma.md)
- [Sun Path & Solar Angles for Washington, DC](https://harth.build/resources/solar-data/sun-path-and-solar-angles-washington-dc.md)

## Sources and method

Licensed ASHRAE Climatic Design Information / Standard 169 station data plus the locally adopted energy code. Coordinates 38.9072° N (America/New_York) are approximate routing references. Figures are illustrative — confirm the representative station and current edition. Climate screening data from the [NASA POWER Climatology API documentation](https://power.larc.nasa.gov/docs/services/api/temporal/climatology/) and [exact point response](https://power.larc.nasa.gov/api/temporal/climatology/point?parameters=T2M%2CT2M_MAX%2CT2M_MIN%2CRH2M%2CPRECTOTCORR%2CWS10M&community=SB&longitude=-77.0369&latitude=38.9072&format=JSON), retrieved 2026-08-31; source period: 20-year Meteorological and Solar Monthly & Annual Climatologies (January 2001 - December 2020). NASA POWER values are gridded screening statistics, not code design conditions or guaranteed local observations.

### Source links

- [power.larc.nasa.gov](https://power.larc.nasa.gov/docs/services/api/temporal/climatology/)

- [power.larc.nasa.gov](https://power.larc.nasa.gov/api/temporal/climatology/point?parameters=T2M%2CT2M_MAX%2CT2M_MIN%2CRH2M%2CPRECTOTCORR%2CWS10M&community=SB&longitude=-77.0369&latitude=38.9072&format=JSON)

## Frequently asked questions

### What does NASA POWER climatology show for Washington, DC?

For the Washington, DC reference point, the 2001–2020 NASA POWER climatology reports 13.2 °C annual mean temperature, 76.5% relative humidity and 3.16 mm/day corrected precipitation. The monthly maximum peaks at 40.2 °C in July.

### Can the Washington, DC climatology replace project design temperatures or an hourly weather file?

No. The Washington, DC response is gridded monthly climatology; its lowest monthly minimum of -18.7 °C in February is not a code percentile or observed site extreme. Verify elevation, local exposure, the required weather file or design-condition source and the current adopted code.

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