Climate and Average Weather Year Round in Lewiston United States

In Lewiston, the summers are hot, dry, and mostly clear and the winters are very cold, wet, and partly cloudy. Over the course of the year, the temperature typically varies from 28°F to 93°F and is rarely below 21°F or above 101°F.

Based on the tourism score, the best time of year to visit Lewiston for warm-weather activities is from early July to mid August.

The hot season lasts for 3.0 months, from June 17 to September 19, with an average daily high temperature above 83°F. The hottest month of the year in Lewiston is July, with an average high of 91°F and low of 53°F.

The cold season lasts for 3.4 months, from November 13 to February 24, with an average daily high temperature below 55°F. The coldest month of the year in Lewiston is December, with an average low of 29°F and high of 47°F.

In Lewiston, the average percentage of the sky covered by clouds experiences extreme seasonal variation over the course of the year.

The clearer part of the year in Lewiston begins around May 28 and lasts for 4.7 months, ending around October 18.

The clearest month of the year in Lewiston is August, during which on average the sky is clear, mostly clear, or partly cloudy 88% of the time.

The cloudier part of the year begins around October 18 and lasts for 7.3 months, ending around May 28.

The cloudiest month of the year in Lewiston is January, during which on average the sky is overcast or mostly cloudy 64% of the time.

A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. The chance of wet days in Lewiston varies significantly throughout the year.

The wetter season lasts 6.1 months, from October 25 to April 28, with a greater than 22% chance of a given day being a wet day. The month with the most wet days in Lewiston is February, with an average of 11.5 days with at least 0.04 inches of precipitation.

The drier season lasts 5.9 months, from April 28 to October 25. The month with the fewest wet days in Lewiston is August, with an average of 0.8 days with at least 0.04 inches of precipitation.

Among wet days, we distinguish between those that experience rain alone, snow alone, or a mixture of the two. The month with the most days of rain alone in Lewiston is February, with an average of 9.8 days. Based on this categorization, the most common form of precipitation throughout the year is rain alone, with a peak probability of 36% on February 27.

Rainfall

To show variation within the months and not just the monthly totals, we show the rainfall accumulated over a sliding 31-day period centered around each day of the year. Lewiston experiences extreme seasonal variation in monthly rainfall.

The rainy period of the year lasts for 9.5 months, from September 8 to June 23, with a sliding 31-day rainfall of at least 0.5 inches. The month with the most rain in Lewiston is December, with an average rainfall of 6.8 inches.

The rainless period of the year lasts for 2.5 months, from June 23 to September 8. The month with the least rain in Lewiston is August, with an average rainfall of 0.1 inches.

Snowfall

As with rainfall, we consider the snowfall accumulated over a sliding 31-day period centered around each day of the year. Lewiston experiences significant seasonal variation in monthly snowfall.

The snowy period of the year lasts for 4.5 months, from November 13 to March 29, with a sliding 31-day snowfall of at least 1.0 inches. The month with the most snow in Lewiston is December, with an average snowfall of 6.0 inches.

The snowless period of the year lasts for 7.5 months, from March 29 to November 13. The least snow falls around July 26, with an average total accumulation of 0.0 inches.

The length of the day in Lewiston varies significantly over the course of the year. In 2024, the shortest day is December 21, with 9 hours, 15 minutes of daylight; the longest day is June 20, with 15 hours, 6 minutes of daylight.

The earliest sunrise is at 5:39 AM on June 13, and the latest sunrise is 2 hours, 4 minutes later at 7:43 AM on November 2. The earliest sunset is at 4:43 PM on December 8, and the latest sunset is 4 hours, 3 minutes later at 8:46 PM on June 26.

Daylight saving time (DST) is observed in Lewiston during 2024, starting in the spring on March 10, lasting 7.8 months, and ending in the fall on November 3.

The figure below presents a compact representation of key lunar data for 2024. The horizontal axis is the day, the vertical axis is the hour of the day, and the colored areas indicate when the moon is above the horizon. The vertical gray bars (new Moons) and blue bars (full Moons) indicate key Moon phases.

We base the humidity comfort level on the dew point, as it determines whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid. Unlike temperature, which typically varies significantly between night and day, dew point tends to change more slowly, so while the temperature may drop at night, a muggy day is typically followed by a muggy night.

The perceived humidity level in Lewiston, as measured by the percentage of time in which the humidity comfort level is muggy, oppressive, or miserable, does not vary significantly over the course of the year, remaining a virtually constant 0% throughout.

This section discusses the wide-area hourly average wind vector (speed and direction) at 10 meters above the ground. The wind experienced at any given location is highly dependent on local topography and other factors, and instantaneous wind speed and direction vary more widely than hourly averages.

The average hourly wind speed in Lewiston does not vary significantly over the course of the year, remaining within 0.4 miles per hour of 3.6 miles per hour throughout.

The predominant average hourly wind direction in Lewiston varies throughout the year.

The wind is most often from the south for 3.6 weeks, from February 19 to March 15 and for 1.1 months, from July 18 to August 20, with a peak percentage of 35% on August 5. The wind is most often from the north for 4.1 months, from March 15 to July 18 and for 6.0 months, from August 20 to February 19, with a peak percentage of 42% on June 8.

To characterize how pleasant the weather is in Lewiston throughout the year, we compute two travel scores.

The tourism score favors clear, rainless days with perceived temperatures between 65°F and 80°F. Based on this score, the best time of year to visit Lewiston for general outdoor tourist activities is from early July to mid August, with a peak score in the last week of July.

The beach/pool score favors clear, rainless days with perceived temperatures between 75°F and 90°F. Based on this score, the best time of year to visit Lewiston for hot-weather activities is from early July to mid August, with a peak score in the last week of July.

Methodology

For each hour between 8:00 AM and 9:00 PM of each day in the analysis period (1980 to 2016), independent scores are computed for perceived temperature, cloud cover, and total precipitation. Those scores are combined into a single hourly composite score, which is then aggregated into days, averaged over all the years in the analysis period, and smoothed.

Our cloud cover score is 10 for fully clear skies, falling linearly to 9 for mostly clear skies, and to 1 for fully overcast skies.

Our precipitation score, which is based on the three-hour precipitation centered on the hour in question, is 10 for no precipitation, falling linearly to 9 for trace precipitation, and to 0 for 0.04 inches of precipitation or more.

Our tourism temperature score is 0 for perceived temperatures below 50°F, rising linearly to 9 for 65°F, to 10 for 75°F, falling linearly to 9 for 80°F, and to 1 for 90°F or hotter.

Our beach/pool temperature score is 0 for perceived temperatures below 65°F, rising linearly to 9 for 75°F, to 10 for 82°F, falling linearly to 9 for 90°F, and to 1 for 100°F or hotter.

Definitions of the growing season vary throughout the world, but for the purposes of this report, we define it as the longest continuous period of non-freezing temperatures (≥ 32°F) in the year (the calendar year in the Northern Hemisphere, or from July 1 until June 30 in the Southern Hemisphere).

The growing season in Lewiston typically lasts for 5.7 months (176 days), from around May 2 to around October 25, rarely starting before April 10 or after May 30, and rarely ending before October 3 or after November 14.

Growing degree days are a measure of yearly heat accumulation used to predict plant and animal development, and defined as the integral of warmth above a base temperature, discarding any excess above a maximum temperature. In this report, we use a base of 50°F and a cap of 86°F.

Based on growing degree days alone, the first spring blooms in Lewiston should appear around March 30, only rarely appearing before March 13 or after April 21.

This section discusses the total daily incident shortwave solar energy reaching the surface of the ground over a wide area, taking full account of seasonal variations in the length of the day, the elevation of the Sun above the horizon, and absorption by clouds and other atmospheric constituents. Shortwave radiation includes visible light and ultraviolet radiation.

The average daily incident shortwave solar energy experiences extreme seasonal variation over the course of the year.

The brighter period of the year lasts for 3.4 months, from May 13 to August 24, with an average daily incident shortwave energy per square meter above 7.0 kWh. The brightest month of the year in Lewiston is July, with an average of 8.2 kWh.

The darker period of the year lasts for 3.8 months, from October 31 to February 21, with an average daily incident shortwave energy per square meter below 3.0 kWh. The darkest month of the year in Lewiston is December, with an average of 1.7 kWh.

For the purposes of this report, the geographical coordinates of Lewiston are 40.707 deg latitude, -122.808 deg longitude, and 1,811 ft elevation.

The topography within 2 miles of Lewiston contains very significant variations in elevation, with a maximum elevation change of 1,493 feet and an average elevation above sea level of 2,260 feet. Within 10 miles contains very significant variations in elevation (4,760 feet). Within 50 miles also contains extreme variations in elevation (8,737 feet).

The area within 2 miles of Lewiston is covered by shrubs (62%) and trees (38%), within 10 miles by shrubs (50%) and trees (48%), and within 50 miles by trees (49%) and shrubs (36%).