Climate Insights for Hartley

Mellette County, California, United States

Hottest
July
35°C peak
Coldest
December
6°C low
Wettest
January
161mm rain
Best to Visit
April, May, June
Mild temps & low rain

Climate Overview

The climate in Hartley is temperate. The average annual temperature is 18°C and approximately 573mm of precipitation falls per year. January is the wettest month, receiving around 161mm of rainfall. Hartley is in the Northern Hemisphere. Summer begins at the end of June and lasts through September. The summer months are: July, August, June. The coldest months are December, January, February, when temperatures can drop to 6°C.

Temperature

10° 20° 30° 40° Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Max: 15° Average: 10° Min: 6° Feb Max: 18° Average: 12° Min: 7° Mar Max: 19° Average: 13° Min: 8° Apr Max: 24° Average: 17° Min: 11° May Max: 28° Average: 20° Min: 13° Jun Max: 34° Average: 24° Min: 17° Jul Max: 35° Average: 25° Min: 17° Aug Max: 35° Average: 25° Min: 17° Sep Max: 33° Average: 23° Min: 15° Oct Max: 28° Average: 19° Min: 12° Nov Max: 20° Average: 13° Min: 8° Dec Max: 16° Average: 10° Min: 6°
Max
Average
Min

Temperatures in Hartley vary considerably across the year, with a 29°C difference between the coldest and warmest months. July is the hottest month, with daytime highs reaching 35°C and an average of 25°C. December is the coolest month, with minimum temperatures around 6°C and an average of 10°C. On average, daily temperatures fluctuate by about 14°C between overnight lows and afternoon highs. The sharpest temperature change occurs between October and November, with a 6°C shift in average temperatures.

Precipitation

0mm 50mm 100mm 150mm 200mm Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Precipitation: 161mm Feb Precipitation: 107mm Mar Precipitation: 104mm Apr Precipitation: 35mm May Precipitation: 26mm Jun Precipitation: 3mm Jul Precipitation: 0mm Aug Precipitation: 0mm Sep Precipitation: 1mm Oct Precipitation: 24mm Nov Precipitation: 45mm Dec Precipitation: 67mm
Precipitation

Hartley is a relatively dry area, receiving approximately 573mm of precipitation annually, which averages out to around 48mm per month. The wettest month is January, averaging 161mm of rainfall. February and March also tend to see above-average precipitation. The driest month is July, with just 0mm. That's 161mm less than January, the wettest month. Rainfall is heavily concentrated in certain months, creating a distinct wet and dry season. Visitors should plan around these patterns, as the difference between peak and low months is dramatic.

Wind

0km/h 5km/h Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Wind Speed: 2km/h Feb Wind Speed: 2km/h Mar Wind Speed: 2km/h Apr Wind Speed: 2km/h May Wind Speed: 2km/h Jun Wind Speed: 2km/h Jul Wind Speed: 2km/h Aug Wind Speed: 2km/h Sep Wind Speed: 2km/h Oct Wind Speed: 2km/h Nov Wind Speed: 2km/h Dec Wind Speed: 2km/h
Wind Speed

Hartley is relatively calm, with an average annual wind speed of 2km/h. For context, sustained winds below 12km/h are generally light, while anything above 25km/h is considered strong. The windiest month is February, averaging 2km/h, though still comfortable for most outdoor activities. The calmest conditions occur in November, with average winds dropping to 2km/h, making it an ideal period for wind-sensitive activities. Wind conditions are fairly consistent throughout the year, varying by only 0km/h between the calmest and windiest months.

Seasons

Winter
Dec 21
Spring
Mar 20
Summer
Jun 21
Autumn
Sep 23

6 days until Summer

It is currently spring in Hartley, which began on March 20, 2026. Hartley is in the Northern Hemisphere, where spring begins in March, summer in June, autumn in September, and winter in December. The warmest period peaks in July at around 35°C, while the coldest stretch bottoms out in December near 6°C. Summer is next, beginning on June 21, 2026 — 6 days from now.

Spring

Temperatures range from 8 to 28°C. Precipitation is moderate at around 166mm for the season, averaging 55mm per month. Winds are generally light, averaging 2km/h. Light layers work well as temperatures warm through the season — a great time to be outdoors.

Summer

Temperatures range from 17 to 35°C. Precipitation is minimal, with only around 3mm for the entire season. Winds are generally light, averaging 2km/h. Light, breathable clothing is ideal — perfect conditions for outdoor activities.

Autumn

Temperatures range from 8 to 33°C. Rainfall is relatively light, with around 70mm over the season and a monthly average of 23mm. Winds are generally light, averaging 2km/h. Layered clothing works best as temperatures gradually cool — enjoy the crisp air and changing scenery.

Winter

Temperatures range from 6 to 18°C. Rainfall is heavy, totalling around 334mm across the season with a monthly average of 111mm. Winds are generally light, averaging 2km/h. A light jacket or sweater is usually sufficient, though cooler evenings may call for an extra layer.

Best Time to Visit

Jan 10°
Feb 12°
Mar 13°
Apr 17°
May 20°
Jun 24°
Jul 25°
Aug 25°
Sep 23°
Oct 19°
Nov 13°
Dec 10°

The best time to visit Hartley is during April, May, June, August, September and October, when the weather is most comfortable for travellers. During these months, average temperatures hover around 21°C with modest rainfall averaging 15mm per month. By contrast, July can be uncomfortably hot with highs reaching 35°C, while December is the coldest period with lows dropping to 6°C. With minimal rainfall expected, you can pack light and plan outdoor activities with confidence.

Monthly Climate Data

The table below shows monthly climate averages for Hartley based on historical weather data. Min and max temperatures represent typical overnight lows and afternoon highs for each month, shown in degrees Celsius (°C). Precipitation is measured in millimetres (mm) and indicates the average total rainfall per month. Wind speed is the average sustained speed in kilometres per hour (km/h). All values are based on averages from over 10 years of historical weather data. The current month is highlighted for quick reference.

Month
Min Temperature
Max Temperature
Wind Speed
Precipitation
Snow
Jan
6 °C
15 °C
2 km/h
161 mm
0 cm
Feb
7 °C
18 °C
2 km/h
107 mm
0 cm
Mar
8 °C
19 °C
2 km/h
104 mm
0 cm
Apr
11 °C
24 °C
2 km/h
35 mm
0 cm
May
13 °C
28 °C
2 km/h
26 mm
0 cm
Jun Current
17 °C
34 °C
2 km/h
3 mm
0 cm
Jul
17 °C
35 °C
2 km/h
0 mm
0 cm
Aug
17 °C
35 °C
2 km/h
0 mm
0 cm
Sep
15 °C
33 °C
2 km/h
1 mm
0 cm
Oct
12 °C
28 °C
2 km/h
24 mm
0 cm
Nov
8 °C
20 °C
2 km/h
45 mm
0 cm
Dec
6 °C
16 °C
2 km/h
67 mm
0 cm
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