I'll be making a 3 week holiday trip (San Francisco, Las Vegas, Los Angeles) in September.
Organized trip by touring car in a 18-20 person group with guide.
Couple of days in those 3 cities. Visiting the National Parks in between.
(Among others: Grand Canyon, Joshua Tree, Death Valley, the usual stuff.)

As I am European I don't have a good idea of Southwest USA weather during that month.
I'm wondering what sort of clothes to bring.
What sort of temperatures can I expect? Should I expect serious rain-fall?

  • 1
    "Southwest USA" is a huge place, and encompasses many different temperate zones. Even the state of California is vast, with different weather conditions. Your best bet is to look up historical weather data for the city(ies) where you will be visiting.
    – Flimzy
    Commented Jun 24, 2014 at 20:14
  • 2
    @Flimzy I've given the itinerary of the trip. Roughly the triangle SF, Vegas, LA. I'm not looking for 1-mile precision. I did some research, but it is very hard to judge from numbers. An indication what if feels like, from people, is much more useful.
    – Tonny
    Commented Jun 24, 2014 at 21:06

2 Answers 2


Temperature: the hottest place you've listed is Death Valley: expect temperatures as high as 120°F (49°C) in the shade! Next highest would be Las Vegas between 90°F (32°C) and 100°F (43°C). California will mostly be between 80°F (30°C) and 100°F (43°C) except for parts of coast and the San Francisco bay, which can be down below 70°F (24°C) in fog! The joke is that you can spot tourists walking the Golden Gate Bridge in San Francisco sweatshirts (which they just bought) and shorts! Note that although the temperatures are high during the day, the humidity is quite low (except when foggy) and so can be more comfortable than it sounds. Never the less, places like Death Valley can easily kill you if you're not careful!

You can expect the nights to be 10-20°F (6-12°C) cooler.

Rainfall: for the most part, California and Nevada get no rainfall from sometime in May through October! However, it is possible to have thunderstorms create flash floods in the desert.

FYI, I'm a California native and have lived here my entire life (59 years).

  • Thank you very much. A little bit hotter than I expected.
    – Tonny
    Commented Jun 25, 2014 at 10:57
  • There's a reason Death Valley is called that. You don't live long out there without water. Commented Jun 25, 2014 at 17:35

I would like to offer a more generic answer, that is perhaps helpful for future visitors of this question.

Weathersparkno affiliation aggregates weather trends (temperature, rainfall, humidity, etc...) for a very large number of locations.

For example, if you look up Las Vegas temperature in September it will show you a nice graph of the spread and average of the max/min temperatures (in Celsius in this case):

enter image description here

Image attribution: © WeatherSpark.com

It also has info on cloud coverage, rainfall, humidity and a range of other meteorological properties.

Obviously these are all objective numbers that don't tell you subjectively if it was "nice weather", "comfortable" or a "bit chilly" (as people tend to do). However, the site does have an indicator on the humidity comfort levels. By comparing it to a place you've been to in the past, you can gauge how you might experience that climate.

enter image description here

Image attribution: © WeatherSpark.com

Finally, the site also offers tourism and beach "scores" that might help interpret the measured numbers.

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