Map from Google - Monchengladbach

In Mönchengladbach, a city located in Western Germany, in the state of North Rhine-Westphalia, a short distance from the border with Holland, the climate is sub-oceanic, humid and rainy, influenced by the Atlantic Ocean, so it has cold (but not freezing) winters, and mild summers. In fact in winter that of Mönchengladbach and Düsseldorf is the mildest area of whole Germany, given the proximity to the ocean, from which the currents blow much of the year.
Mönchengladbach is located in the metropolitan region called Rhine-Ruhr, which includes, in addition to those of the Ruhr, cities such as Düsseldorf, the same Mönchengladbach, Wuppertal, Leverkusen, Cologne and Bonn.
The average temperature in January is 3 °C (37.5 °F), while in July it's 19 °C (66 °F).
Here are the average temperatures.
Average temperatures - Monchengl.
Monchengl.JanFebMarAprMayJunJulAugSepOctNovDec
Monchengl.JFMAMJJASOND
Min (°C)0035912141411841
Max (°C)671115192224242015106
Min (°F)323237414854575752463934
Max (°F)434552596672757568595043

Precipitation is relatively abundant, about 800 millimetres (31.5 inches) per year, but above all it is common and well distributed over the seasons; however, the rainiest season (at least in quantity) is summer, the least rainy is spring. Rainfall often occurs in the form of short showers or drizzle, whereas during the summer, thunderstorms can break out in the afternoon.
Here is the average precipitation.
Average precipitation - Monchengl.
Monchengl.JanFebMarAprMayJunJulAugSepOctNovDecYear
Monchengl.JFMAMJJASONDY
Prec. (mm)655565507075757065657070795
Prec. (in)2.62.22.622.8332.82.62.62.82.831.3
Days12101210111111911111212132

The wind blows frequently, and can be intense, especially from November to March.

Winter, from December to February, is cold: temperatures are on average a few degrees above freezing (0 °C or 32 °F) during the day, while at night they stay around freezing; wind and humidity often exacerbate the feeling of cold.
However, different weather situations can occur.
When the westerlies blow, the temperature can be quite mild, and can reach 10/12 °C (50/54 °F), but there can be wind and rain.
On the contrary, when the city is reached by cold air masses from Russia, the temperature drops below freezing, for longer or shorter periods, even during the day. The temperature rarely drops below -15 °C (5 °F), however, it can do it in the coldest periods.
Snowfalls in Mönchengladbach are quite frequent, though usually not abundant, and occur in the form of sleet or light snow, sometimes, however, snow can accumulate on the ground, and last for many days, if it occurs during cold waves.

Spring, from March to May, is initially cold, with possible snowfalls still in March, and then it gradually becomes milder in April and May, although some cold days, with highs around 10 °C (50 °F), can occur also in May, especially in the first half of the month. However, April and May are, albeit slightly, the least rainy and least cloudy months.
Typically, in the second half of May the temperature becomes permanently acceptable, and there can be the first pleasantly warm days, with highs around 25 °C (77 °F) or even above.

Summer, from June to August, is mild; the flow of Atlantic fronts does not cease even in this season. The wind blows quite often from the North Sea, which is not far, and rainfall is quite frequent as well.
However, there are pleasant periods, in which daytime temperatures are between 20 °C and 25 °C (68 °F and 77 °F), but also cooler periods, in which the temperature remains below 20 °C (68 °F) even during the day. At night it can be a bit cold, in fact the temperature can drop below 10 °C (50 °F) even in July and August. Sometimes there can be hot days, in which the temperature can reach 30/32 °C (86/90 °F). The highest records are around 37 °C (99 °F).

Autumn, from September to November, is initially pleasant, ie in the first half of September, then it gradually becomes more cold, dull, wet and windy. The first night frosts usually occur in November, but sometimes also in October.

Mönchengladbach

The amount of sunshine in Mönchengladbach is not high: the sun rarely shines from November to February, while it goes a bit better from May to August, when the weather is variable, and between a disturbance and the other the sun can come out. There are on average 6/7 hours of sunshine per day from May to August, as can be seen from the data of nearby Düsseldorf.
Sunshine - Dusseldorf
DusseldorfJanFebMarAprMayJunJulAugSepOctNovDec
DusseldorfJFMAMJJASOND
Sun (hours)234666765421

When to go

The best time to visit Mönchengladbach runs from mid-May to mid-September, being the mildest of the year. July and August are the warmest months; however, it's better to bring a sweatshirt or sweater, a light jacket and an umbrella, for cool and rainy days.