Climate and monthly weather forecastO'Fallon, MO

The climate of O'Fallon

In the cordial town of O'Fallon, Missouri, USA, the climate generally adheres to the Köppen classification of a humid subtropical one with no distinct dry spell. This climate classification indicates that the area typically experiences mild winters, hot and muggy summers, significant rainfall year-round, and occasional snowfall during winter months.

Temperatures fluctuate throughout the year, with warmer conditions prevalent from late May through to early September featuring temperatures soaring to 87.1°F (30.6°C) in July. Winter months, between late November and February, usher in a noticeable drop in temperatures, where average lows can dip down to 23.7°F (-4.6°C) in January. A remarkable aspect of O'Fallon's climate is the humidity levels. It exhibits little variation from month to month, hovering between 70 to 79% all year round, contributing to the humid conditions characteristic of this region.

Rainfall follows a similar pattern, distributed fairly evenly throughout the year, with a peak in May of 2.76" (70mm) and a minimum in December of 0.91" (23mm). Indeed, snowfall is rare except for the colder months, primarily November to February, peaking at 1.61" (41mm) in February.

The best time to visit O'Fallon

Given O'Fallon's humid subtropical climate, the period from late April through to mid-October is considered most suitable for visiting. During this time, the town enjoys pleasant weather typified by warm temperatures ranging between 65.3°F (18.5°C) to 85.5°F (29.7°C) and ample sunshine, with daylight hours hovering around 13.2 hours in April and peaking at 14.9 hours in June. A highlight of this period is the typically low wind speeds, ranging from 5.5mph (8.9km/h) to 7.2mph (11.6km/h), ensuring a calm and comfortable outdoor experience.

The worst time to visit O'Fallon

Winter season in O'Fallon, beginning in late November through to February, may not be conducive for outdoor activities due to the lower temperatures typically ranging from 23.7°F (-4.6°C) to 41.9°F (5.5°C), and the higher chances of snow, particularly in the months of January and February. The daylight hours are low as well, ranging from 9.5 hours in December to 10.8 hours in February, thus leading to shorter days and fewer daylight hours for outdoor exploration.

Spring weather in O'Fallon

The spring season in O'Fallon, from March through May, greets residents and visitors with steadily rising temperatures ranging from a low of 54.1°F (12.3°C) in March to a high of 74.5°F (23.6°C) in May. Rainfall increases during this time with April and May receiving 2.48" (63mm) and 2.76" (70mm), respectively, making them the wettest months of the year. The amount of daylight also increases significantly during this period, reaching up to 14.3 hours in May, giving plenty of daylight hours to enjoy the warming temperatures.

Summer weather in O'Fallon

O'Fallon's summer months from June to August are typified by high temperatures, abundant sunshine, and moderate rainfall. Temperatures during this period range from 79.5°F (26.4°C) to 87.1°F (30.6°C). Despite these high temperatures, frequent showers are expected with rainfall measuring between 2.13" (54mm) to 2.48" (63mm) per month. However, wind speeds are at their lowest during this time of the year, averaging from 5.5mph (8.9km/h) to 6.4mph (10.3km/h), providing a respite from the heat.

Autumn weather in O'Fallon

In autumn, from September to November, O'Fallon experiences a gradual decrease in temperature and daylight hours. The average high temperature drops from 79.5°F (26.4°C) in September to 53.2°F (11.8°C) in November, while daylight decreases from 12.4 hours in September to 10.1 hours in November. Rainfall during this season is moderate, ranging from 0.98" (25mm) in November to 1.73" (44mm) in October, making it a pleasant period to experience the changing colors of the foliage.

Winter weather in O'Fallon

Winter months in O'Fallon from December through February bring frigid temperatures, sporadic snowfall, and shorter daylight hours. Average high temperatures decrease to 41.9°F (5.5°C) in December and drop to their lowest at 37.4°F (3°C) in January, while lowest temperatures can go down to 23.7°F (-4.6°C). Snowfall, though not heavy, peaks at 1.61" (41mm) in February adding to the chilly ambiance of the town. The daylight lasts for less than 10.8 hours in these months, with December having the shortest day of 9.5 hours.

Weather in January

January in O'Fallon, Missouri is characterized by a blanket of white courtesy of the snowfall and colder temperatures playing peek-a-boo. Though a smidge warmer than the anticipated starkness of winter, it poses a significant dip from the milder climes of December. Weather in January »

Weather in February

February brings a slightly more inviting atmosphere if you are willing to endure the lingering chills from January. A slightly warmer weather pattern establishes itself, as the city starts to witness the transition into the early onset of Spring. Weather in February »

Weather in March

March signals the true arrival of Spring, as overnight lows hover around 37.9°F (3.3°C). A substantial increase in temperature is evident, showing a stark contrast to its predecessor and paving the way for the warmer weather approaching in April. Weather in March »

Weather in April

April embodies Spring fully, with a bloom in temperature noticeable from 37.9°F (3.3°C) to a welcoming 47.3°F (8.5°C). The climate becomes milder and the strength of the sun's rays, as indicated by the UV index, further escalates. Weather in April »

Weather in May

The month of May escorts in a significantly warmer atmosphere, with temperatures making a considerable leap from April. As one might expect, the UV index value increases to 6, being the month with long sunlight exposure, indicating the imminent arrival of summer. Weather in May »

Weather in June

By June, summer is unmistakably in full swing, bringing with it the delight of sun-soaked days. The transition from May is notable with a climb in day and night temperatures. A definite decrease in wind speed as we move into June ensures that no gusty winds interrupt a perfect outing. Weather in June »

Weather in July

July represents the middle of summer and is, noticeably, the month with the highest day and night temperatures. As the heat peaks, days are now longer with approximately 14.6 hours of daylight. The number of sunshine hours, however, remains consistent with the previous month. Weather in July »

Weather in August

Though August shares a similar profile with July, it holds a relief with slightly lower temperatures. August could be seen as a transition phase where the intensity of the summer heat starts decelerating, ushering a slow but comfortable segue into autumn. Weather in August »

Weather in September

As we venture into September, a decline in temperature clearly signifies the arrival of the autumn season. Even though the weather cools down considerably from August, the midday sun offers a warm respite, making it pleasant for outdoor activities. Weather in September »

Weather in October

The highlight of October is the unmistakable autumn coolness, as temperatures take a significant downward plunge from its September counterpart. October, being an autumn month, enjoys a generous amount of daylight hours and adequate sunshine that adds to the crispiness of fall. Weather in October »

Weather in November

November brings O'Fallon, Missouri closer to winter, with temperatures seeing a notable drop from October. The transition from autumn to winter is most prominent this month, preparing everyone for the chilling December ahead. It stands out with the lowest recorded rainfall measuring 0.98" (25mm), which marks it as the driest month of the year. Weather in November »

Weather in December

December declares the onset of winter as O'Fallon, Missouri grapples with a sharp decline in temperature compared to November. The shortened daylight hours and reduced sunshine hours cast a wintry ambiance over the city. Rainfall maintains a low figure at 0.91" (23mm) with only 7 rainy days recorded on average in the month. Weather in December »