Weather tables are full of similar-looking numbers — average high, average low, mean, record. Confusing them can lead to packing for an 85°F afternoon and shivering through a 50°F night. Here is what each statistic means and how to use it.
The answer first
The average high is the typical warmest part of the day; the average low is the typical overnight minimum. The mean temperature sits roughly between them. The bigger the gap between high and low, the more the temperature swings between afternoon and night — large in deserts and at altitude, small near coasts. To plan well, read both the high and the low for your month.
The four numbers you’ll see
| Statistic | What it is | Use it for |
|---|---|---|
| Average (mean) high | Typical daytime peak, averaged over 30 years | What it feels like in the afternoon |
| Average (mean) low | Typical overnight minimum | What to pack for evenings/early mornings |
| Mean temperature | Midpoint of high and low | Comparing overall warmth of cities |
| Record high/low | The single hottest/coldest ever measured | Curiosity — not planning |
WeatherNormal’s city pages show the average high, average low and precipitation for all 12 months. We use NOAA’s 1991–2020 normals — see what climate normals are.
Worked example: the high–low gap
Look at two cities in July:
| City | Avg July high | Avg July low | Gap |
|---|---|---|---|
| Phoenix, AZ | 106°F | 84°F | 22°F |
| San Diego, CA | 75°F | 66°F | 9°F |
Both are in the Southwest, but Phoenix swings 22°F between afternoon and night, while coastal San Diego barely moves. The lesson: a desert “cools off” after dark far more than a coast does, even though the afternoon is much hotter. In spring, that same Phoenix gap means a pleasant 78°F day can follow a chilly 54°F dawn — pack layers.
Why the gap varies
- Dry air (deserts, high desert, altitude) loses heat fast after sunset, so nights are much cooler than days — a big gap.
- Humid or coastal air holds heat, keeping nights warm — a small gap. Notice how Miami stays in the upper-70s even overnight in summer.
- Season matters too: the gap is usually largest in spring and autumn under clear skies.
How to use highs and lows for travel
- Check the average high for your month to picture the afternoon. Our packing & comfort tool turns it into a Cold–to–Very-hot band automatically.
- Check the average low to know how cold evenings get — this is what catches people out.
- Glance at precipitation in the same row so you’re not surprised by a wet month.
- Remember it’s an average. A normal high of 75°F can hide both 85°F and 65°F days.
Don’t plan around records
A record high tells you the hottest day ever recorded — once, possibly decades ago. It says nothing about a typical visit. Stick to the averages for planning and treat records as trivia. For comparing cities by warmth, the rankings sort by exactly these average figures, such as the hottest cities in summer.
All figures here are NOAA 1991–2020 normals — 30-year averages, not forecasts. Check a live forecast before you travel.