Weather conditions at Brooks Camp, the most visited spot within Katmai National Park and Preserve, is characterized by overcast skies and frequent rain storms or drizzle during most of the summer. Heavy storms accompanied by intense winds known as williwaws occur and may persist for several days. Summer high temperatures average 63º F. and low temperatures average 44º F. The sky is clear or partly cloudy about 20% of the summer. During late spring and early autumn, skies are usually clear about 40% of the time and winds are generally moderate. During this time, high temperatures average 56º F. and low temperatures average 36º F.

Winter weather at Brooks Lake from October through April is variable, average maximum daily temperatures from 18.5º to 47.5º F., and minimum temperatures between -2.8º and 39.2º F. All months usually have individual daily highs exceeding 40º F. and less than one-third of the days had maximum temperatures below freezing.

Total annual precipitation varies from year to year but can average from 20 to 40 inches. Snowfall can average 1 to 14 inches per month from October to March.

Spring, summer, and fall temperatures at King Salmon are similar to those at Brooks Camp. The average winter temperature at King Salmon ranges from a high of 21º F to a low of 6º F. Annual precipitation is about 60 inches along the Shelikof Strait, 25 inches in the lake region, and 19 inches at King Salmon. About 60% of the precipitation at King Salmon occurs from May through September as rain.

Cool temperatures, frequent rains, and occasional strong winds comprise a controlling factor in visitor use of Katmai, making reliable equipment and clothing a necessity for any recreational activity.