The weather in Prosser, WA is mostly temperate, and ranges from the high-eighties to the mid-twenties through the year. The highest recorded temperature was 111 degrees in 2002, and the lowest temperature was negative 20 degrees in 1950. In general, though, the weather does not dip nearly so low as that.
Spring in Prosser is a beautiful time, and the weather reflects this. The average precipitation for the months of March, April, and May is only a little more than 1.9 inches total, with the most rainfall in March (.67 inches), then May (.65 inches) and finally April (.64 inches). The average highs for these months climb from a 58 in March to 66 in April and then to a warm 75 in May. The lows are 34 in March, 39 in April, and then a climb to 45 in May for the summer warm-up. The records for each month are: a high of 81 and a low of 6 in March, a high of 91 and a low of 14 in April, and a high of 100 and a low of 26 in May.
Summer warms things up a little and dries out as well, with precipitation averaging just above one inch. Precipitation for June has been recorded at an average of .56 inches, July (the warmest month of the year in Prosser) at .24 inches, and in August at .35 inches. The average highs for the months of summer climb from a toasty 82 degrees in June to 89 in July and maintains the 89 degree average through August. The lows for these months range from an average of 51 in June to 55 in July, and drops slightly to 54 degrees in August. The record highs and lows for the summer were 105 degrees in June down to a record low of 32 degrees, a record breaking 111 degree high summer in July with a 37 degree July low, and 106 in August, with lows for that month reaching a recorded 37 degrees.
Things cool down in the fall with an 80 degree high in September on average, followed by 68 degree highs in October and a chilly 51 degrees in November on average. The average lows for the fall season are 47 degrees on average in September, 38 in October, and a 32 degree average in November. The record highs for the season are 99 in September, 90 in October, and 76 in November. The lows on record fall from 28 degrees in September to 11 degrees in October, and plunge to negative 7 degrees in November. Precipitation for September is averaged at .48 inches, with .65 in October and an average of 1.03 inches in November.
The winter climate in Prosser ranges from highs of 41 degrees in December and January to 48 in February on average, with average lows falling from 26 to 25 in December and January, and rising back to 29 in February. Records indicate that the highest temperature recorded in December was 66 degrees, with record highs of 69 in January and February. Lows range from the negative 14 degree record of December to the negative 18 degrees recorded in January, and finally the record shattering low of negative 20 degrees in February. Precipitation drops off from 1.18 inches in December (making this the wettest month of the year), to an average of .96 in January, and falls to a mere .70 inch average in February.