Hot-Day Density Altitude Planner (Morning vs Afternoon)
Compare density altitude at your planned morning departure against the afternoon peak — and see exactly how many feet the heat of the day costs.
Density altitude climbs 118.8 ft for every degree Celsius of warming. An 18 °C diurnal swing — ordinary in high-desert summer — moves DA by over 2,100 ft between dawn and mid-afternoon.
Formula
⚠️ For flight planning and education only — always verify against your aircraft's POH/AFM, official weather sources and certified instruments. Not for primary navigation or airworthiness decisions.
Disclaimer: This tool is for general informational and estimation purposes only and is not professional financial, tax, accounting or legal advice. All figures are estimates — verify with a qualified professional before making decisions. Read the full disclaimer.
Compare density altitude at your planned morning departure against the afternoon peak — and see exactly how many feet the heat of the day costs.
About Hot-Day Density Altitude Planner (Morning vs Afternoon)
The cheapest performance upgrade in aviation is an alarm clock. This planner runs the density-altitude calculation twice — once at your planned morning departure temperature and once at the forecast afternoon high — and reports the difference as feet of performance the heat will steal. It makes the 'leave by nine' argument with numbers instead of folklore, and shows the 118.8 ft-per-°C sensitivity behind it.
How to use Hot-Day Density Altitude Planner (Morning vs Afternoon)
- 1Enter — sensible defaults are pre-filled so you see a worked result immediately.
- 2Read the live results: .
- 3Check the "With your numbers" line to see the formula DA = PA + 118.8 × (OAT − ISA); ΔDA = 118.8 ft per °C of warming substituted step by step.
- 4Adjust inputs (or flip the unit toggle) until the scenario matches yours, then copy or share the result.
Why use Hot-Day Density Altitude Planner (Morning vs Afternoon)?
- ✓Instant, free and private — every calculation runs in your browser, nothing is uploaded
- ✓Built on the published formula DA = PA + 118.8 × (OAT − ISA); ΔDA = 118.8 ft per °C of warming with sources cited on the page
- ✓Density altitude climbs 118.8 ft for every degree Celsius of warming. An 18 °C diurnal swing — ordinary in high-desert summer — moves DA by over 2,100 ft between dawn and mid-afternoon.
- ✓Switch units, tweak any input and watch every result update live
Frequently asked questions
How much does density altitude really change through a day?+
By 118.8 ft for every °C of temperature rise. A typical high-desert summer swing of 15–20 °C moves density altitude 1,800–2,400 ft between dawn and the 3 pm peak. A field that behaves like 6,000 ft at sunrise can behave like 8,400 ft by mid-afternoon at identical pressure.
When is the daily density-altitude peak?+
It tracks surface temperature, peaking between about 2 pm and 5 pm local — usually after the hottest METAR reading because surfaces keep radiating. The minimum is just after dawn. For a marginal takeoff, the hour before sunrise to mid-morning offers the densest air of the day.
Does the altimeter setting change the comparison?+
Both calculations here share one altimeter setting, which is realistic for a single day's planning since pressure usually drifts less than temperature swings. A 0.10 inHg pressure fall adds about 100 ft to both numbers equally, so the morning-vs-afternoon difference is almost entirely a temperature story.
Is an evening departure as good as a morning one?+
Thermally, late evening approaches morning density values as the surface cools, and winds often calm. The trade-offs are operational: fading daylight, density altitude still lagging warmer than dawn, and at many backcountry strips, downslope wind patterns. Morning gives the same cool air plus a full day of light and options.
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