Average Weather On September 21 For Yellowstone National Park, Wyoming, USA

Location

This report describes the typical weather at the Yellowstone Lake (Yellowstone National Park, Wyoming, United States) weather station over the course of an average September 21. It is based on the historical records from 2001 to 2012. Earlier records are either unavailable or unreliable.

Yellowstone National Park, Wyoming has a humid subarctic continental climate with cool summers and no dry season. The area within 25 mi of this station is covered by forests (90%) and lakes and rivers (7%).

Temperature

The temperature typically varies from 31°F to 57°F and is rarely below 26°F or above 67°F.

Temperature

Average hourly temperature (black) with percentil bands (inner band from 25th to 75th percentile, outer band from 10th to 90th percentile).

The coolest hours of the day are from 1am to 9am with the coldest at 7am, at which time the temperature is below 33°F three days out of four.

The warmest hours of the day are from noon to 7pm with the hottest at 4pm, at which time the temperature is above 51°F three days out of four.

The day has gained half its heat by 10am and lost it again by 9pm.

Temperature Bands

The average fraction of time spent in various temperature bands: frigid (below 15°F), freezing (15°F to 32°F), cold (32°F to 50°F), cool (50°F to 65°F), comfortable (65°F to 75°F), warm (75°F to 85°F), hot (85°F to 100°F) and sweltering (above 100°F).

Sun

On September 21 the Sun rises at 7:08am and sets at 7:20pm.

Solar noon is at 1:14pm.

For reference, on the longest day of the year the Sun rises at 5:36am and sets at 9:10pm, while on the shortest day of the year it rises at 7:55am and sets at 4:44pm.

Astronomical twilight begins and ends 98 minutes before sunrise and after sunset at 5:29am and 8:58pm, respectively.

Nautical twilight begins and ends 63 minutes before sunrise and after sunset at 6:05am and 8:23pm, respectively.

Civil twilight begins and ends 28 minutes before sunrise and after sunset at 6:39am and 7:48pm, respectively.

Solar twilight begins and ends 38 minutes after sunrise and before sunset at 7:46am and 6:42pm, respectively.

Solar Elevation

Elevation of the Sun above (positive) or below (negative) the horizon (black line). Yellow and gray fills indicate day and night, respectively. Light gray lines are the corresponding curves for the winter and summer equinoxes.

Clouds

This weather station does not reliably report sky cover.

Precipitation

There is either very little precipitation at this location on September 21, or the weather station does not reliably report the conditions.

Snow

Either snow is exceptionally unlikely to fall at this location on September 21 or this station does not reliably report precipitation types.

Humidity

The relative humidity typically ranges from 42% (comfortable) to 84% (humid), rarely dropping below 23% (dry), or exceeding 93% (very humid).

The air is driest at 4pm, at which time the relative humidity is less than 54% (mildly humid) three days out of four; it is most humid at 6am, exceeding 80% (humid) three days out of four.

Relative Humidity

Average hourly humidity (black line) with percentile bands (inner bands from 25th to 75th percentile, outer bands from 10th to 90th percentile).

Dew Point

The dew point ranges from 27°F to 33°F with an average of 29°F.

For reference, comfortable indoor conditions should have a relative humidity between 30% and 50% with a dew point of less than 65°F.

Dew Point

Average hourly dew point (black line) with percentile bands (inner bands from 25th to 75th percentile, outer bands from 10th to 90th percentile).

Wind

Sustained wind speeds typically vary from 1 mph to 6 mph (light air to light breeze) over the course of the day.

The peak sustained wind speed typically occurs around 2pm and is rarely outside the range 3 mph to 10 mph (light air to gentle breeze).

The wind is most calm around 9am, rarely exceeding 3 mph (light air).

Wind Speed

Average hourly wind speed (black line) with percentile bands (inner bands from 25th to 75th percentile, outer bands from 10th to 90th percentile).

The wind is most often out of the west (15% of the time). The wind is least often out of the north east (0% of the time), south (0% of the time), south east (1% of the time), south west (2% of the time), north (3% of the time), and east (3% of the time).

Wind Directions

The fraction of time spent with the wind blowing from the various directions over the entire day. Values do not sum to 100% because the wind direction is undefined when the wind speed is zero.

Wind Directions Over Day

The fraction of time spent with the wind blowing from the various directions on an hourly basis. Values do not sum to 100% because the wind direction is undefined when the wind speed is zero.