The following is a list of weather events that occurred on Earth in the year 2003. The most common weather events to have a significant impact are blizzards, cold waves, droughts, heat waves, wildfires, floods, tornadoes, and tropical cyclones. The deadliest event of the year was a European heatwave that killed 72,210 people, which broke several nationwide temperature records.

The year began with El Niño conditions, which meant that sea surface temperatures over the equator over the eastern Pacific Ocean were anomalously warm.

The following listed different types of special weather conditions worldwide.

On January 24, an arctic air mass made it into central Florida, causing widespread wind chills in the 20s °F. Winds that helped bring in the colder air also caused wind chill readings to drop in the teens. Those winds also brought in moisture off the Atlantic coast, resulting in snow flurries and ocean effect snow along the coastlines of Volusia and Brevard counties. Daytona Beach set the record for the coldest minimum and maximum temperature, at 25 °F (−4 °C), and at 37 °F (3 °C), respectively. In February, a historic blizzard dumped unusually heavy snowfall across New England and the Northeastern United States on Presidents' Day weekend. Many locations saw over 2 feet (61 cm) of snow. Nearly the entire state of Massachusetts, southern New England and southern New York saw 1 foot (30.5 cm) of snow. Central Park received 19.8 inches (50.3 cm) from the storm, making February 2003 the fourth snowiest February in the park, with the entire month seeing 26.1 inches (66.3 cm). Boston received 27.5 inches (69.8 cm), the largest total for the city. 10 deaths were attributed to the storm. From March 17–19, a powerful blizzard affected Colorado, which is the second biggest snowstorm ever to hit Denver. 3 feet (91 cm) of snow fell in Denver and more than 7 feet (210 cm) fell in the foothills. Other snow reports include 87.5 inches (222 cm) at Rollinsville, 77.5 inches (197 cm) at Winter Park, 50 inches (130 cm) near Golden, and 40.3 inches (102 cm) in Aurora. Denver International Airport shut down, stranding 4,000 passengers, and Colorado traffic was shut down as roads and interstates were shut down. Building collapses were also reported due to the weight of the heavy snow.

A low pressure system combined with the remnants of a tropical storm brought plenty of moisture to cause heavy rain over central Indiana on September 1. In a period of 24 hours, 6–8 inches (150–200 mm) of rain fell, causing widespread flash flooding across the region. There were widespread evacuations from homes, rescues from vehicles, and many schools had to close. The National Guard was activated to assist with road closings and rescues in Indianapolis. The White River came up 15 ft (4.6 m) in 18 hours after the rain ended. Flood damage was estimated in excess of $20 million.

In the summer of 2003, there was a severe heatwave across Europe, considered the warmest summer on the continent since 1540. The heat and drought killed 72,210 people across 15 countries, making it the sixth deadliest disaster worldwide in the first two decades of the 21st century. Most of the deaths occurred in Italy and France. Several nationwide temperature records were broken during the heatwave, with a peak temperature of 44.1 °C (111.4 °F) recorded in France on August 12.

There was also a heat wave across the United States from March through November that killed 35 people.

Throughout the year, there were 1,374 tornadoes in the United States. In a one week period in May, a severe weather outbreak produced 335 tornadoes across 26 U.S. states, which set the record for the most twisters in a single week. There were 51 deaths related to the event.