May weather forecast
Johnston, IA

Weather in May

May, the last month of the spring, in Johnston, is a pleasant month, with temperature in the range of an average high of 69.6°F (20.9°C) and an average low of 52.9°F (11.6°C).

Temperature

In May, the average high-temperature increases, from a mild 59.4°F (15.2°C) in April, to a pleasant 69.6°F (20.9°C). The average low-temperature, in May, is 52.9°F (11.6°C).

Humidity

The average relative humidity in Johnston is 77%.

Rainfall

The wettest months in Johnston are May and June, with an average 2.52" (64mm) of rainfall.

Snowfall

Months with snowfall are January through May, October through December. May is the last month it regularly snows. During 0.2 snowfall days, Johnston aggregates 0.08" (2mm) of snow. In Johnston, during the entire year, snow falls for 29.6 days, and aggregates up to 6.77" (172mm) of snow.

Daylight

The average length of the day in May is 14.6h.

Sunshine

In May, the average sunshine is 8.8h.

UV index

The average daily maximum UV index in Johnston is 5. A UV Index reading of 3 to 5 represents a moderate threat to health from unsafe exposure to the UV radiation for the average person.
Note: The daily maximum UV index of 5 in May interpret into the following advice:
Take precautions - Protection against the skin and eye damage is obliged. The solar radiation is most powerful near the mid-day, so the exposure to the direct Sun should be reduced accordingly. On bright days sunglasses that block both UVA and UVB rays should be worn. A hat with a wide brim is extremely helpful, as it can prevent roughly 50% of UV radiation from reaching the eyes. Caution! The reflection of snow can nearly double the intensity of the Sun's UV radiation.
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FAQ

What is the average humidity in May in Johnston?

In Johnston, Iowa, the average relative humidity in May is 77%.

What is the wettest month in Johnston?

Months with the most rainfall in Johnston, Iowa, are May and June, with an average 2.52" (64mm) of precipitation.

How many days does it rain in May in Johnston?

In Johnston, Iowa, during May, the rain falls for 16.3 days and regularly aggregates up to 2.52" (64mm) of precipitation.

What is the last month it snows in Johnston?

May is the last month it regularly snows in Johnston. During 0.2 snowfall days, in May, Johnston aggregates 0.08" (2mm) of snow.

How many hours of daylight does Johnston have in May?

In Johnston, the average length of the day in May is 14.6h.

How long on average sun shines in May in Johnston?

In Johnston, Iowa, the average sunshine in May is 8.8h.

How high is the UV index in May in Johnston?

In Johnston, the average daily maximum UV index in May is 5. A UV Index reading of 3 to 5 represents a medium health risk from the exposure to the Sun's UV rays.

Average temperature in May
Johnston, IA

Average temperature in May - Johnston, IA
  • Average high temperature in May: 69.6°F

The warmest month (with the highest average high temperature) is July (82.4°F).
The month with the lowest average high temperature is January (27.9°F).

  • Average low temperature in May: 52.9°F

The month with the highest average low temperature is July (65.1°F).
The coldest month (with the lowest average low temperature) is January (14.4°F).

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Average pressure in May
Johnston, IA

Average pressure in May - Johnston, IA
  • Average pressure in May: 29.93"

The month with the highest atmospheric pressure is January (30.16").
The month with the lowest atmospheric pressure is June (29.88").

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Average wind speed in May
Johnston, IA

Average wind speed in May - Johnston, IA
  • Average wind speed in May: 8.8mph

The windiest month (with the highest average wind speed) is April (10.4mph).
The calmest months (with the lowest average wind speed) are July and August (7mph).

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Average humidity in May
Johnston, IA

Average humidity in May - Johnston, IA
  • Average humidity in May: 77%

The month with the highest relative humidity is January (83%).
The month with the lowest relative humidity is October (70%).

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Average rainfall in May
Johnston, IA

Average rainfall in May - Johnston, IA
  • Average rainfall in May: 2.52"

The wettest months (with the highest rainfall) are May and June (2.52").
The driest month (with the least rainfall) is January (0.47").

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Average rainfall days in May
Johnston, IA

Average rainfall days in May - Johnston, IA
  • Average rainfall days in May: 16.3 days

The month with the highest number of rainy days is May (16.3 days).
The month with the least rainy days is February (3.5 days).

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Average snowfall in May
Johnston, IA

Average snowfall in May - Johnston, IA
  • Average snowfall in May: 0.08"

The month with the highest snowfall is January (2.2").
Months with the least snowfall are June, July, August and September (0").

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Average snowfall days in May
Johnston, IA

Average snowfall days in May - Johnston, IA
  • Average snowfall days in May: 0.2 days

The month with the highest number of snowfall days is January (8.4 days).
Months with the least snowfall days are June, July, August and September (0 days).

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Average daylight in May /
Average sunshine in May
Johnston, IA

Average daylight in May / Average sunshine in May - Johnston, IA
  • Average daylight in May: 14.6h

The month with the longest days is June (Average daylight: 15.2h).
The month with the shortest days is December (Average daylight: 9.2h).

  • Average sunshine in May: 8.8h

The month with the most sunshine is July (Average sunshine: 10.4h).
The month with the least sunshine is January (Average sunshine: 4.3h).

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Average sunshine days in May
Johnston, IA

Average sunshine days in May - Johnston, IA
  • Average sunshine days in May: 12.5 days

The month with the most sunshine days is December (22.8 days).
The month with the least sunshine days is June (11.2 days).

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Average UV index in May
Johnston, IA

Average UV index in May - Johnston, IA
  • Average UV index in May: 5

Months with the highest UV index are June and July (UV index 6).
The month with the lowest UV index is January (UV index 1).

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Average cloud cover in May
Johnston, IA

Average cloud cover in May - Johnston, IA
  • Average cloud cover in May: 40

The month with the most cloud cover is January (Cloud cover 53).
The month with the least cloud cover is September (Cloud cover 28).

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Average visibility in May
Johnston, IA

Average visibility in May - Johnston, IA
  • Average visibility in May: 6mi

Months with the highest visibility are January, February, March, April, May, June, August, September, October, November and December (6mi).
The month with the lowest visibility is July (5mi).

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