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In the part of the country where Dallas is located the weather can change rapidly, but the most obvious characteristic of the local climate is long, hot summers, strong sunshine and frequent spring thunderstorms. Dallas has over the years suffered both extreme summer heat and freezing winter outbreaks, which is why the weather plays an important role in everyday life in North Texas.
Dallas is in North Central Texas and is part of the Dallas–Fort Worth metropolitan area. The region is situated on the southern boundary of the Great Plains and consists of rolling hills, prairie and oak woodland. Elevations in the wider Dallas–Fort Worth area usually vary from about 500 to over 800 feet. The Trinity River and its tributaries also have an important role in the area's geography.
It is because of its position that certain of Dallas's weather patterns can be understood. The city is situated far enough inland to have large changes in temperature, and moisture moving north from the Gulf of Mexico can lead to high humidity, thunderstorms and extremely warm summer nights.
Dallas possesses one of the longest climate records in the state of Texas. Continuous records of the Dallas–Fort Worth climate start from 1898, which provides more than a century of weather observations for comparison with current conditions. Although the official site of observations has been altered over the years, the present record is based at the Dallas/Fort Worth International Airport since 1985.
The long-term figures clearly indicate how warm Dallas can get. Using the 1991–2020 climate normals, the average annual temperature is approximately 66.6°F (19.2°C) and the normal annual precipitation amounts to about 37 inches, whilst Dallas experiences around 20 days each year when the temperature reaches 100°F or higher.
The season which receives the most attention is summer. In July and August the average high temperatures are generally about 96°F (36°C). Overnight temperatures may stay in the mid-70s and, during especially hot periods, night temperatures can remain abnormally high. According to the National Weather Service, July and August are the two sunniest months and temperatures in them often reach or go above 100°F.
Dallas has also come across some remarkable extremes; the official record high temperature in the Dallas–Fort Worth climate record is 113°F, which occurred in June 1980, and the historical records show exceptionally cold winter temperatures, illustrating just how dramatically conditions can vary from one season to another.
Spring is usually one of the busiest times of the year since warm and humid air comes into contact with moving weather systems, leading to thunderstorms and at times severe weather. During the severe-weather seasons, the Dallas–Fort Worth area experiences large hail, damaging winds, flooding and tornadoes.
In general the temperatures become more pleasant, though in September it is still possible to feel as though it is summer. In October there is usually a noticeable change with the normal maximum temperatures falling to about 78°F (26°C) and by November the average highs have moved to around 67°F (19°C).
Although winter is fairly mild, Dallas may still have sudden periods of cold weather. In January the usual highest temperature is around 57°F (14°C) and the usual lowest temperature is about 36°F (2°C). Compared to the northern states, snow and freezing conditions are not very common, but winter weather can at times become important.
Temperature makes up only one aspect of the outdoor weather situation; the UV Index in Dallas is likewise important, especially between spring and summer.
Dallas has strong sunshine for a large part of the year and the level of UV exposure usually rises as the sun gets higher in the sky in the spring and summer months. The most intense UV conditions generally happen at midday during the hotter months.
Just because the temperature is high doesn't mean the UV Index is high, and a cooler day doesn't necessarily mean that there's low UV exposure. The two figures refer to different things. Temperature shows you how hot the air is, whereas the UV Index shows the strength of the ultraviolet radiation from the sun.
In Dallas this difference is especially useful in the spring season, since a pleasant day in March, April or May can cause considerable UV exposure even though the temperature is comfortable.
By summer time, the combination of strong sunlight and extremely high temperatures means that it becomes more important to plan outdoor activities. People who are going to be outside for several hours should look at the daily UV Index and think about using sunscreen, wearing sunglasses, putting on protective clothing and seeking shade, particularly around midday.
If you look over the years, Dallas has shown a great deal of variation from year to year, but the longer climate record does offer some useful background. According to the National Weather Service's 1991–2020 normals, the average annual temperature is 66.6°F, whereas it was 66.3°F according to the earlier 1981–2010 normals. The more recent normals also indicate around 20 days each year when the temperature reaches 100°F or higher, which is two days more than during the previous 30-year period.
It doesn't mean that each year is becoming successively hotter. There is natural year-to-year variation in weather, and Dallas has had its share of unusually cool, wet, hot and dry periods over the course of its historical record. Climate normals are more useful for understanding the general pattern than they are for predicting a specific year.
For anyone who lives in Dallas or is visiting the city, the best method is to consider the weather and the UV levels together. In the summer, afternoons can be very hot, with intense sunshine and possibly hazardous conditions outside. During spring the main worry is the quick development of thunderstorms. In the fall the temperature may shift rapidly from summer-like afternoons to cooler evenings. Although winter is generally more comfortable it can on occasion have freezing weather.
The variety in Dallas is due to its geography. The city's position in North Central Texas, the fact that it is relatively inland, and its exposure to moisture from the Gulf all lead to its unique weather patterns.
The weather in Dallas over the years shows that the city has experienced hot summers, powerful storms, some winter extremes and a lot of strong sunshine. When you include the UV Index, you get a fuller understanding of what the outdoor conditions actually imply. For ordinary planning, it is usually more helpful to check the current Dallas forecast along with the UV Index than to depend solely on historical averages.