Phoenix and Miami: 97.8% and 97.0% of summer daylight hours at or above 25°C; London 9.0%, Seattle 12.9%

An earlier alarm can mean cooler air. It does not, by itself, make a hot walk suitable. This article compares historical air temperatures, not veterinary outcomes: use the results as context, with current conditions and guidance for the individual dog determining a walking plan [4][5].

What the eight-city weather comparison found

The supplied count compares summer daylight-hour air temperatures in eight cities using ERA5 data for 2016–2025 [1]. It uses 20°C and 25°C as comparison points, drawn from the secondary guidance it cited [3]. Neither number defines a band below which walking is guaranteed safe; this calculation measured no dogs' health outcomes.

In every one of the eight cities the coolest summer daylight hour is the first one or two after sunrise (4:00 to 7:00 local) and the hottest is mid-afternoon (13:00 to 16:00) [1]. These are means across ten summers, not a schedule for tomorrow.

The first comparison is between cities and hours, not between safe and unsafe dogs. Read the reported means alongside the limits of the calculation below.

*Table: all eight cities, June to August daylight hours, ten summers of hourly ERA5 weather [1].*

Phoenix and Miami: high daylight averages

In the 2016–2025 summer calculation, 97.8% of Phoenix daylight hours and 97.0% of Miami daylight hours were at or above the 25°C comparison point [1]. The coolest reported daylight-hour means were 28.1°C at 6:00 in Phoenix and 26.0°C at 7:00 in Miami [1]. A mean above a reference point does not mean that every individual morning had the same temperature.

These figures explain why an early booking is not enough information for a walking decision. PDSA advises considering cooler times but notes that very hot or humid conditions can mean missing a walk altogether [5]. Check the individual day rather than treating the average as a safety rule.

> WARNING: A historical average is not a current temperature reading, and cooler air is not a safety clearance. The calculation did not measure pavement, humidity or an individual dog's tolerance [1].

London and Seattle: a different historical pattern

The historical threshold frequencies were lower in London and Seattle: 9.0% and 12.9% of their summer daylight hours, respectively, reached 25°C or higher [1]. Those are comparisons with a reference temperature, not estimates of the proportion of walks that would be safe.

That contrast is the point of the comparison: cities have different patterns [1]. The four cities between them: Denver 56.0%, Los Angeles 54.0%, New York 52.4% and Chicago 36.7% of summer daylight hours at or above 25°C, with coolest-hour means from 14.8°C in Denver to 19.6°C in New York [1]. None of these figures specifies suitable exercise conditions for an individual dog.

What the count did (and did not) measure

The supplied calculation uses historical air temperature at two metres above ground for each city centre [1]. It does not measure tomorrow's weather, a particular route or a dog's response to exercise.

Air temperature does not tell you the temperature of a sunlit pavement. The count measured no surfaces. PDSA advises avoiding hot surfaces; a surface check is only one part of considering conditions, not proof that a walk is suitable [4].

Humidity, direct sun and local shade are outside this calculation. Its grid-cell weather data does not distinguish a shaded path from a sun-baked street [1][2].

The count also includes no breed, age or health information. PDSA identifies individual risk factors, including flat-faced breeds, age, weight and coat, and notes that exercise itself can contribute to heatstroke [4]. A weather average cannot account for those differences.

Use the historical comparison to ask better questions about a routine. For a particular dog, follow veterinary guidance and assess current conditions; PDSA's prevention guidance is linked in the sources [4][5].

Use the Phoenix comparison without making it a forecast

The 28.1°C coolest-hour mean and the 97.8% threshold frequency describe different aspects of the same historical sample [1]. Neither tells you the conditions on the date of a booking.

For a walker, agree how current conditions will be reviewed and what an alternative care plan looks like if a walk is unsuitable. A camera or activity tracker can help with communication; it does not certify that exercise is safe.

The calculation covers daylight only [1]. It cannot identify a suitable night-time window. PDSA's hot-weather guidance gives the wider context [5].

Questions readers ask

What about pavement and paw safety?

The calculation measured no pavement temperatures. PDSA advises avoiding hot surfaces [4]. The published air temperature alone cannot settle either paw safety or the wider heat risk.

Do humidity and the individual dog matter?

Yes. PDSA discusses heat and exercise risks in relation to the individual dog, and its hot-walk guidance also considers very hot or humid conditions [4][5]. There is no individual clearance threshold in this weather dataset.

Can I walk my dog at night instead?

The count covered daylight hours only [1]. It cannot establish a suitable night-time window. Assess the actual conditions and follow veterinary guidance for the dog rather than inferring suitability from this comparison [4][5].

*Corrected 2026-11-05: Separated historical air-temperature patterns from dog-walking safety, removed fixed-temperature and breed-wide safety assurances, clarified the limits of the weather count, and added primary veterinary guidance. Headline was: "First hour after sunrise is safest for dog walks in summer".*

*Corrected 2026-11-07: The Sources list skipped numbers (sources were removed earlier and the rest kept their numbers); renumbered 1 to 5, and every citation follows. Spacing and numbering only.*

*Corrected 2026-11-07: The title promised eight cities and the tables showed four; the data page the article cites has all eight, and its rendered table and its JSON agree for every city (checked both ways). The eight-city table replaces the four-city one, the four middle cities are named with their shares, the lead and the takeaway now carry the finding (which the 2026-11-05 correction had buried under repeated caveats, keeping the caveat once), and the title is measured. Headline was: "When are summer daylight hours coolest? Eight cities compared".*

Sources

1. Our own calculation (2026-10-30): Hot daylight hours for dog walks from ten years of hourly ERA5 weather in eight cities: our count
2. 🏛️ Historical Weather API | Open-Meteo.com
3. When is it too hot to walk your dog? Plus expert tips to cool your canine down | GoodtoKnow
4. PDSA: Heatstroke in dogs, risks and prevention
5. PDSA: Dogs die in hot cars and on hot walks