Current Weather

at Pasco, WA

(21 km [13 miles] east of W Richland)


Other General Weather Data



(40 km [25 miles] NW of W Richland)

Graphs are based on data from Hanford Site Climatological Data Summary 1997, with Historical Data


D J Hoitink and K W Burk, March 1998, PNNL-11794, Richland WA






In 1995 the recorded rainfall was 12.31 in. (31.27 cm) and in 1996, 12.19 in. (30.96 cm), both nearly double the average of 6.26 in. (15.90 cm). The low rainfall of record was in 1976 with 2.99 in. (7.59 cm). 1997 had 6.39 in (16.2 cm) of precipitation, measured at Hanford.

Calendar year 1996 also had the record snowfall of 57.5 in. (146.1 cm); the previous record was 37.1 in. (94.2 cm) in 1985. Normal is about 15 inches (38 cm).

The winter of 1998/1999 was been different. The average temperature, December through February, was 37.7°F, compared to an average of 33.6°. Our coldest day was December 21 with a temperature of -1°F (-18.3°C). As of March 1, we have only had less than one inch of snow and only 2.03 inches of rain. These are not extremes, but the snowfall and temperatures have been unusual. Winter departed leaving February with a record average wind speed of 11.1 mph (17.9 kph). Our highest wind speed was 65 mph with 10 days over 40 mph. (This paragraph was abstracted from an article on March 3, 1999, in the Tri-City Herald.) On the other hand, the mountains of Washington received record amounts of snow.

December 1999 was warm and the windiest (on average, not peak velocity) on record with an average speed of 8.8 mph (14.2 kph). (January 4, 2000, in the Tri-City Herald.) Only 0.6 inches (1.5 cm) of snow fell during the year compared to normal. Only 3.75 inches of rain fell during the year compared to the average of 6.26.






Wind Speed


(Note: These peak gusts are historical values, not something that occurs every year.)

The following climate information and data were taken from the July, 1971, "Soil Survey - Benton County Area, Washington," the most recent issue published by the US Department of Agriculture, Soil Conservation Service:

The climate of the Benton County Area has both marine and continental characteristics. It is influenced by moist air moving in from the Pacific Ocean and by cold air moving southward from Canada. The weather systems are modified by the Rocky Mountains to the east and north and by the Cascade Mountains to the west.

The Summers are hot, and the winters are clear, dry, and cold. Occasional cold snaps late in spring or early in fall cause extensive damage to crops.

In the summer, the afternoon temperature reaches the nineties (mid-30's celcius), and the nighttime temperature falls to about 60°F (about 15°C). In an average summer (based on data from about 1930 to 1960), the temperature exceeds 90°F (about 32°C) on 50 to 60 days and 100°F (about 38°C) on 8 to 12 days. The relative humidity ranges from approximately 50% at sunrise to about 25% in the afternoon.

In the winter, the afternoon temperature reaches the thirties (around 0°C), and the nighttime temperature falls to about 20°F (-7°C). The relative humidity ranges from approximately 85% at night to abut 75% in the afternoon. In an average winter, the maximum temperature is below freezing on 20 to 30 days, and the minimum is below 0°F (-18°C) on two to five nights. In some of the colder winters, the temperature falls below zero on 10 to 20 nights. In January, normally the coldest month, the temperature can be expected to drop to zero or below on one or more nights in three out of ten winters, to -10°F (-23°C) or lower in two out of ten winters, and to -20°F (-29°C) in one out of ten winters. On clear, calm nights, the minimum temperature in the valleys is frequently 5° to 10°F (3 to 5°C) below that on adjacent hills. Occasionally, a chinook wind brings a rapid rise in temperature.

The lower elevations of Benton County are in the driest part of eastern Washington. Moist air moving inland from the Pacific cools as it rises over the western slopes of the Cascade Mountains and becomes warmer and drier as it descends along the eastern slopes. These weather systems bring heavy precipitation along the windward slopes, but lighter precipitation along the lee slopes. At the lower elevations, the annual precipitation is 7 or 8 in. (18 or 20 cm); it gradually increases to 10 in (25 cm) or moreover the Horse Heaven Hills and the Rattlesnake Hills.

Thunderstorms can be expected on one to three days each month from March through September. Occasionally severe thunderstorms develop over the ridges and move across the valleys.

Snow seldom accumulates to a depth of more than 6 to 10 in. (15 to 25 cm) or stays on the ground longer than two to four weeks. In unusually severe winters, snow is on the ground most of the time from late in December until early in February. Frost penetrates to a depth of 10 to 15 in. (25 to 38 cm) nearly every winter and twice that in extremely cold winters.

The prevailing winds are from the west and northwest, but the strongest are from the southwest. In the winter there is very little diurnal variation in windspeed, but late in summer there is a noticeable increase in wind velocity late in the afternoon. At 30 ft (9 m) above the ground, wind velocities can be expected to reach 50 mph (80 kph) at least once in two years, 60 to 75 mph (96 to 120 kph) once in 50 years, and 80 mph (129 kph) once in 100 years.