Month by month
Las Vegas weather in September
Still hot early, with the first real break from summer heat by the end of the month.
At a glance
September starts out feeling like summer and ends noticeably cooler. The NWS says the monsoon typically wanes by September, bringing the first break from the intense summer heat. The monsoon period itself runs through September 30, so storms and flash floods are still possible, and 100°F days still happen, mostly early in the month.
By NOAA’s 1991–2020 normals for Harry Reid International Airport, September days peak around 95°F and nights bottom out near 72°F. An average September has 7.9 days at 100°F or hotter and 24.1 days at 90°F or hotter. Normal rainfall is 0.32 inches, with 1.8 days getting at least a hundredth of an inch and 0.7 days getting a tenth of an inch or more. The median September total is 0.05 inches, so in a typical year it is drier than the average suggests: a few wet years pull the average up.
Through the day
Mornings are the sweet spot. It averages 80°F at 9 a.m. and 93°F at the 4 p.m. peak, so hikes and runs go best before noon. Evenings are pleasant too, averaging 85°F at 9 p.m.
| Time (PDT) | Normal | Cool day | Hot day |
|---|---|---|---|
| 6 a.m. | 73°F | 66°F | 80°F |
| 9 a.m. | 80°F | 72°F | 87°F |
| Noon | 89°F | 79°F | 96°F |
| 3 p.m. | 93°F | 83°F | 101°F |
| 6 p.m. | 92°F | 82°F | 99°F |
| 9 p.m. | 85°F | 76°F | 92°F |
| Midnight | 80°F | 72°F | 87°F |
"Cool day" and "hot day" are NOAA’s 10th and 90th percentiles for that hour: one September day in ten is cooler or hotter than shown. NOAA publishes hourly normals in standard time; we shifted them to clock time for daylight saving time. Hourly averages run a little below the normal daily high because the hottest moment doesn’t land on the same hour every day.
The air is dry: the average dew point across the day is about 38°F. Wind averages 7.6 mph over the day and is usually strongest around 5 p.m. (9.7 mph on average).
Over the month
September isn’t one temperature. The normal high falls from 100.1°F on September 1 to 88.6°F on September 30, and the normal low goes from 77.6°F to 66.4°F. That 11.5° change is big enough that the start and end of the month feel different, so check the dates of your trip, not just the month.
For a specific date, the live National Weather Service forecast on our home page is more useful than any average once you are within a week of your trip.
What to pack
- Summer clothing for the afternoons
- Sunscreen, sunglasses and water
- A light layer for later in the month and for indoor air conditioning
- A rain shell just in case of a late monsoon storm
Staying safe
Heat. Heat is the deadliest weather hazard in the Southwest, according to the NWS. Drink water before you feel thirsty, avoid strenuous activity in the afternoon, and know the warning signs: heavy sweating, cramps, dizziness and nausea point to heat exhaustion, while confusion and hot skin can mean heat stroke, which is a 911 emergency. Our heat-safety guide has the NWS first-aid steps and where to find cooling stations.
Monsoon storms and flash floods. Storms often start over the mountains and send water into the valley’s washes and low streets, sometimes miles from where the rain fell. Never drive into a flooded road: the NWS says about a foot or two of moving water can float most vehicles. Stay out of washes and tunnels during and after storms, and when thunder roars, go indoors.
For current watches and warnings, follow the NWS Las Vegas office. Our resources page lists the other agencies worth knowing. In an emergency, call 911.
September records
| Record | Temperature | Date |
|---|---|---|
| Hottest | 114°F | Sep 6, 2020 |
| Coldest | 43°F | Sep 27, 1948 |
| Warmest night | 87°F | Sep 7, 2022 |
| Coolest day | 67°F | Sep 18, 1965 |
NWS Las Vegas records since January 1, 1937. Where a record has been tied, we show the most recent date. See every month on our records page.