Climate and monthly weather forecastJohnston, IA
Climate and monthly weather forecast
The climate of Johnston
Johnston, found in the state of Iowa, USA, has a climate generally defined by the Köppen climate classification as Dfa, which translates to a humid continental climate with no dry season and hot summers. The geographical position of Johnston adds to this definition with its location in the interior of the continent intensifying temperature swings between seasons.Throughout the year, temperature variations are significant in Johnston. The cold winter months, from December through February, experience average high temperatures ranging from 27.9°F (-2.3°C) in December to 31.5°F (-0.3°C) in February, with lows dropping to a chilling 14.4°F (-9.8°C) in December and rising slightly to 18°F (-7.8°C) by February. The summer months of June to August, on the other hand, enjoy much warmer averages with temperature highs reaching 79.3°F (26.3°C) in June and peaking at 82.4°F (28°C) in July. Correspondingly, nights during these months remain considerably warmer as well, with lows between 62.4°F (16.9°C) and 65.1°F (18.4°C).
Johnston's weather parameters exhibit a noticeable cycle. The prevailing wind speed tends to slightly increase during the spring, hitting an average of 10.4mph (16.7km/h) in April before gradually dropping to a yearly minimum of 7mph (11.3km/h) by August. Cloud coverage also follows a certain trend, minimizing in the autumn months of September and October at 28% and 35% respectively, while peaking during winter, reaching 53% in December.
Rainfall and snowfall patterns are distinctly different, with snowfall being experienced mainly in winter and rainfall more evenly spread throughout the year but peaking in late spring and early summer. Interestingly, even during the warmest months of June and July, Johnston receives an average rainfall amounting to 2.52" (64mm) each. The maximum monthly rainfall, however, is witnessed in May with 2.52" (64mm). Snowfall is almost exclusively a winter phenomenon, essentially ceasing from May to September.
The best time to visit Johnston
When assessing the best time for a visit to Johnston, numerous factors come into play and the ideal timing largely depends on the visitor's preference and planned activities. Generally, the months of May to September are preferable for outdoor activities due to the warmer temperatures, plentiful sunshine, and moderately reduced wind speeds. During these months, temperatures average high between 69.6°F (20.9°C) and 81.3°F (27.4°C), while the sun shines for an average duration of 8.8 to 10.4 hours per day. The average wind speeds are also relatively low, resting between 7mph (11.3km/h) and 8.8mph (14.2km/h).The worst time to visit Johnston
Contrarily, the months of December, January, and February are considered the least favorable for a visit to Johnston. The bitterly cold winter temperatures dip low, resulting in average highs between 27.9°F (-2.3°C) and 31.5°F (-0.3°C) and average lows between 14.4°F (-9.8°C) and 18°F (-7.8°C). Concurrently, the average daylight hours reduce to between 9.2 hours and 9.6 hours as cloud coverage increases to over 50%.Spring weather in Johnston
Spring in Johnston witnesses a rapid change in weather conditions. March kick-starts the season with an average high temperature of 46.9°F (8.3°C) and a low of 31.8°F (-0.1°C), but by May, these averages have boosted to a high of 69.6°F (20.9°C) and a low of 52.9°F (11.6°C). Rainfall also picks up, reaching its annual peak in May with 2.52" (64mm) falling over an average of 16.3 days.Summer weather in Johnston
Summer in Johnston tends to be humid and hot with temperatures peaking in July at an average high of 82.4°F (28°C). The nights remain moderate with lows hovering from 62.4°F (16.9°C) to 65.1°F (18.4°C). Rainfall decreases slightly from spring with an average of 2.52" (64mm) in June and 1.42" (36mm) in July.Autumn weather in Johnston
With the arrival of autumn, temperatures in Johnston start to drop from 75.6°F (24.2°C) in September to 46.9°F (8.3°C) by November. Corresponding night temperatures fall in the range of 44.6°F (7°C) to 55.9°F (13.3°C). Rainfall decreases, with October reporting an average precipitation of 1.06" (27mm).Winter weather in Johnston
Winter in Johnston is marked by freezing temperatures and snow. December sets the stage with an average high of 27.9°F (-2.3°C) and a low of 14.4°F (-9.8°C). Snowfall is also prevalent during these months, with an average of 2.2" (56mm) in December and 0.83" (21mm) in February.Weather in January
Johnston, Iowa greets the New Year amid the shivers of winter. January is the coldest month, with temperatures plummeting from 27.9°F (-2.3°C) to 14.4°F (-9.8°C). Outdoor enthusiasts and commuters bundle up to battle the low temperatures and biting winds. Weather in January »Weather in February
Moving from January to February, Johnston sees the winter's grip begin to slightly ease. Despite February being the tail end of winter, it is not devoid of its own frosty appeal. The temperatures, while still hovering in the low range, are beginning to climb, melting snow, and paving the way for spring. Weather in February »Weather in March
With the arrival of March, spring begins to set up residence in Johnston. Warmth begins to seep into the air and the snow starts to disappear, leaving only 0.94" (24mm) on the ground. This shift in weather is welcomed by both nature and Johnston's residents, who start to engage more actively in outdoor activities. Weather in March »Weather in April
April in Johnston offers the full bloom of spring. After the thaw of March, the city basks in longer daylight hours and diminishing snowfall. Nature unfolds in an array of colors, and people step out more frequently to soak up the milder temperature. Weather in April »Weather in May
The vibrancy of May in Johnston is palpable as the city transitions into full-blown spring. Temperatures elevate as winter's remnants fade completely, highlighting green landscapes within the city. However, this is also a month that sees considerable precipitation with an increase from 1.3" (33mm) of rain in April to 2.52" (64mm). Weather in May »Weather in June
June in Johnston signifies the arrival of summer with sun-soaked daylight and temperatures nudging towards the high range. While the rain eases a bit from the previous month, humidity begins to rise, creating a relatively warm but bearable atmosphere. Weather in June »Weather in July
July in Johnston brings in the hottest summer month, with temperatures soaring from 65.1°F (18.4°C) to 82.4°F (28°C). Despite the heat, residents find respite in local water bodies providing breeding grounds for water sports and swimming. Weather in July »Weather in August
August brings closeness to the close of summer in Johnston. Despite this transition, the weather remains warm, with mild winds adding an enjoyable rhythmic pattern to the days. The rain starts to increase slightly again, preparing the ground for the upcoming autumnal season. Weather in August »Weather in September
September commences the fall season in Johnston, providing a bridge between the hot summer and the crisp fall. The characteristic heat begins to recede, offering a gentle respite from the summer's climax. While continuing the declining trend in rainfall, this month provides a distinct palette of red and orange hues, transforming the landscapes into mesmerizing sites. Weather in September »Weather in October
Fall moves into its full swing in October, painting Johnston in vibrant autumnal hues. Temperatures begin to descend significantly as the city gives way for the upcoming winter. The landscape transforms to offer a colorful backdrop for nature photography while the clear, crisp air makes walking and hiking particularly pleasant. Weather in October »Weather in November
November in Johnston marks a noticeable plunge in temperatures as the city prepares for winter. A cold wind takes over as the fall colors begin to disappear. This transitional month sees a decline in rainfall with only 0.67" (17mm) coming down. Weather in November »Weather in December
Wrapping up the year, December in Johnston brings back the chills of winter in full force. The bare trees welcome the first flutters of snow as Christmas spirit begins to swirl in the air. A dusting of white covers the ground gently, creating postcard-perfect views across the city. Weather in December »Updated: Jul 11, 2024
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate
Frequently asked questions
Johnston's coldest month, January, generally records average temperatures ranging from a high of 27.9°F (-2.3°C) to a low of 14.4°F (-9.8°C).
With an average relative humidity of 83%, January is the most humid month.
The month with the least rainfall is January, when the rain falls for 3.8 days and typically collects 0.47" (12mm) of precipitation.
Throughout the year, there are 114.6 rainfall days, and 15.51" (394mm) of precipitation is accumulated.
January through May, October through December are months with snowfall.
January is the month with the most snowfall. Snow falls for 8.4 days and accumulates 2.2" (56mm) of snow.
In Johnston, during the entire year, snow falls for 29.6 days and aggregates up to 6.77" (172mm) of snow.
The month with the least sunshine is January, with an average of 4.3h of sunshine.
January is the month with the lowest UV index in Johnston, with an average maximum UV index of 1.
On Sunday, March 10. 2024, at 2:00 am, Daylight Saving Time starts, and the time zone changes from CST to CDT. Daylight Saving Time ends Sunday, November 3. 2024, at 2:00 am, and the time zone reverts from CDT to CST.
The months with the most rainfall are May and June, with an average 2.52" (64mm) of precipitation.
June through September are months without snowfall.
June has the longest days of the year, with an average of 15h and 12min of daylight.
June and July, with an average maximum UV index of 6, are months with the highest UV index.
July stands out as Johnston's warmest month, with temperatures ranging between an average high of 82.4°F (28°C) and a low of 65.1°F (18.4°C).
With an average of 10.4h of sunshine, July has the most sunshine of the year.
The least humid month is October, with an average relative humidity of 70%.
December has the shortest days of the year, with an average of 9h and 12min of daylight.
Average temperature
Johnston, IA
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).
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).
Average pressure
Johnston, IA
- Average pressure in January:
30.16"Hg - Average pressure in February:
30.14"Hg - Average pressure in March:
30.07"Hg - Average pressure in April:
29.93"Hg - Average pressure in May:
29.93"Hg - Average pressure in June:
29.88"Hg
- Average pressure in July:
29.96"Hg - Average pressure in August:
29.96"Hg - Average pressure in September:
30.01"Hg - Average pressure in October:
30.01"Hg - Average pressure in November:
30.09"Hg - Average pressure in December:
30.12"Hg
The month with the highest atmospheric pressure is January (30.16"Hg).
The month with the lowest atmospheric pressure is June (29.88"Hg).
Average wind speed
Johnston, IA
- Average wind speed in January:
10.3mph - Average wind speed in February:
10.3mph - Average wind speed in March:
10.3mph - Average wind speed in April:
10.4mph - Average wind speed in May:
8.8mph - Average wind speed in June:
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).
Average humidity
Johnston, IA
The month with the highest relative humidity is January (83%).
The month with the lowest relative humidity is October (70%).
Average rainfall
Johnston, IA
- Average rainfall in January:
0.47" - Average rainfall in February:
0.51" - Average rainfall in March:
0.94" - Average rainfall in April:
1.3" - Average rainfall in May:
2.52" - Average rainfall in June:
2.52"
- Average rainfall in July:
1.42" - Average rainfall in August:
1.81" - Average rainfall in September:
1.73" - Average rainfall in October:
1.06" - Average rainfall in November:
0.67" - Average rainfall in December:
0.55"
The wettest months (with the highest rainfall) are May and June (2.52").
The driest month (with the least rainfall) is January (0.47").
Average rainfall days
Johnston, IA
- Average rainfall days in January:
3.8 days - Average rainfall days in February:
3.5 days - Average rainfall days in March:
9.3 days - Average rainfall days in April:
13.1 days - Average rainfall days in May:
16.3 days - Average rainfall days in June:
15.8 days
- Average rainfall days in July:
12.8 days - Average rainfall days in August:
12.3 days - Average rainfall days in September:
9.7 days - Average rainfall days in October:
8.1 days - Average rainfall days in November:
6.1 days - Average rainfall days in December:
3.8 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).
Average snowfall
Johnston, IA
- Average snowfall in January:
2.2" - Average snowfall in February:
1.93" - Average snowfall in March:
0.94" - Average snowfall in April:
0.24" - Average snowfall in May:
0.08" - Average snowfall in June:
0"
The month with the highest snowfall is January (2.2").
The months with the least snowfall are June, July, August and September (0").
Average snowfall days
Johnston, IA
- Average snowfall days in January:
8.4 days - Average snowfall days in February:
7.7 days - Average snowfall days in March:
4.4 days - Average snowfall days in April:
0.8 days - Average snowfall days in May:
0.2 days - Average snowfall days in June:
0 days
- Average snowfall days in July:
0 days - Average snowfall days in August:
0 days - Average snowfall days in September:
0 days - Average snowfall days in October:
0.6 days - Average snowfall days in November:
2 days - Average snowfall days in December:
5.5 days
The month with the highest number of snowfall days is January (8.4 days).
The months with the least snowfall days are June, July, August and September (0 days).
Average daylight / Average sunshine
Johnston, IA
- Average daylight in January:
9h and 36min - Average daylight in February:
10h and 36min - Average daylight in March:
12h and 0min - Average daylight in April:
13h and 24min - Average daylight in May:
14h and 36min - Average daylight in June:
15h and 12min
- Average daylight in July:
14h and 48min - Average daylight in August:
13h and 48min - Average daylight in September:
12h and 30min - Average daylight in October:
11h and 6min - Average daylight in November:
9h and 48min - Average daylight in December:
9h and 12min
The month with the longest days is June (Average daylight: 15h and 12min).
The month with the shortest days is December (Average daylight: 9h and 12min).
- Average sunshine in January:
4h and 18min - Average sunshine in February:
4h and 54min - Average sunshine in March:
6h and 12min - Average sunshine in April:
8h and 6min - Average sunshine in May:
8h and 48min - Average sunshine in June:
9h and 48min
- Average sunshine in July:
10h and 24min - Average sunshine in August:
9h and 54min - Average sunshine in September:
9h and 24min - Average sunshine in October:
5h and 42min - Average sunshine in November:
5h and 36min - Average sunshine in December:
4h and 48min
The month with the most sunshine is July (Average sunshine: 10h and 24min).
The month with the least sunshine is January (Average sunshine: 4h and 18min).
Average sunshine days
Johnston, IA
- Average sunshine days in January:
20.6 days - Average sunshine days in February:
17.8 days - Average sunshine days in March:
17.6 days - Average sunshine days in April:
14.8 days - Average sunshine days in May:
12.5 days - Average sunshine days in June:
11.2 days
- Average sunshine days in July:
14.8 days - Average sunshine days in August:
15.6 days - Average sunshine days in September:
17.8 days - Average sunshine days in October:
21 days - Average sunshine days in November:
22 days - Average sunshine days in December:
22.8 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).
Average UV index
Johnston, IA
The 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).
Average cloud cover
Johnston, IA
The month with the most cloud cover is January (Cloud cover 53).
The month with the least cloud cover is September (Cloud cover 28).
Average visibility
Johnston, IA
The 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).
