Back-to-Back Pacific Storms to Impact the West Coast; Heavy Snow in the Central Appalachians

Back-to-back powerful Pacific storm systems to impact the Pacific Northwest and northern California through the end of this week with heavy rain, flooding, strong winds, and higher elevation mountain snow. A strong, long-duration atmospheric river will accompany the Pacific storms, bringing excessive rainfall and flash flooding to southwest Oregon and northwest California through the week. Read More >

Rainfall and Temperature Maps for Puerto Rico and U.S. Virgin Islands

1991-2020 Monthly Normals

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Frequently Asked Questions

What are normals?

In a general sense, a "normal" is the expected value (e.g., temperature, precipitation amount, etc.) for a particular location during a particular time of year. Normals help describe a location's climate by quantifying certain elements, such as precipitation seasonality. For monthly and annual values, normals are typically the average values during the 30-year period. Distinctly different from averages, daily normals (1991-2020) were computed using a harmonic fit, a statistical method which dampens the effects of outliers, creating a smooth transition between adjacent days.

Why does NOAA produce normals?

NOAA's computation of climate normals is in accordance with the recommendation of the World Meteorological Organization (WMO), of which the United States is a member. While the WMO mandates each member nation to compute 30-year averages of meteorological quantities at least every 30 years (1931-1960, 1961-1990, 1991-2020, etc.), the WMO recommends a decadal update, in part to incorporate newer weather stations.

For what purposes are normals used?

Meteorologists and climatologists regularly use normals for placing recent climate conditions into a historical context. NOAA's normals are commonly seen on local weather news segments for comparisons with the day's weather conditions. In addition to weather and climate comparisons, normals are utilized in seemingly countless applications across a variety of sectors. These include: regulation of power companies, energy load forecasting, crop selection and planting times, construction planning, building design, and many others.

Is our climate becoming warmer and wetter?

The climate of a particular location changes over time, but climate normals were not designed to be metrics of climate change. They may capture recent trends, giving a better perspective of the current state of the climate, but changes between sets of normals do not necessarily confirm a trend. Because of the rigidity of the 30-year time period, a trend on shorter or longer time scales may not be represented.