Atmospheric data at cruise altitudes • Schmidt-Appleman criterion • Updated 2026-06-30 14:15 UTC
Each pixel = 1 hour. Hover for time + status.
T = temperature at pressure level • RH = relative humidity w.r.t. ice • [N/3] = persistent level count
| Time (UTC) | 200 hPa (FL387) | 250 hPa (FL344) | 300 hPa (FL295) | Status |
|---|---|---|---|---|
| 06-30 00:00 UTC | -54.5°C / 38% RH_ice | -45.0°C / 64% RH_ice | -34.0°C / 61% RH_ice | Ephemeral |
| 06-30 01:00 UTC | -54.0°C / 21% RH_ice | -44.5°C / 55% RH_ice | -34.5°C / 58% RH_ice | Ephemeral |
| 06-30 02:00 UTC | -54.0°C / 21% RH_ice | -45.0°C / 41% RH_ice | -34.5°C / 50% RH_ice | Ephemeral |
| 06-30 03:00 UTC | -54.0°C / 25% RH_ice | -44.5°C / 50% RH_ice | -34.5°C / 47% RH_ice | Ephemeral |
| 06-30 04:00 UTC | -54.0°C / 25% RH_ice | -45.0°C / 75% RH_ice | -34.5°C / 56% RH_ice | Ephemeral |
| 06-30 05:00 UTC | -53.5°C / 30% RH_ice | -45.0°C / 75% RH_ice | -35.0°C / 67% RH_ice | Ephemeral |
| 06-30 06:00 UTC | -53.0°C / 24% RH_ice | -44.5°C / 67% RH_ice | -34.5°C / 67% RH_ice | Ephemeral |
| 06-30 07:00 UTC | -52.0°C / 16% RH_ice | -44.0°C / 64% RH_ice | -34.5°C / 72% RH_ice | Ephemeral |
| 06-30 08:00 UTC | -52.0°C / 16% RH_ice | -44.0°C / 50% RH_ice | -34.0°C / 66% RH_ice | Ephemeral |
| 06-30 09:00 UTC | -53.0°C / 29% RH_ice | -44.0°C / 41% RH_ice | -34.5°C / 61% RH_ice | Ephemeral |
| 06-30 10:00 UTC | -52.5°C / 29% RH_ice | -43.0°C / 33% RH_ice | -34.5°C / 58% RH_ice | Ephemeral |
| 06-30 11:00 UTC | -53.5°C / 38% RH_ice | -42.5°C / 16% RH_ice | -35.0°C / 42% RH_ice | Ephemeral |
| 06-30 12:00 UTC | -53.5°C / 38% RH_ice | -41.5°C / 13% RH_ice | -35.0°C / 31% RH_ice | Ephemeral |
| 06-30 13:00 UTC | -53.5°C / 38% RH_ice | -41.0°C / 10% RH_ice | -35.0°C / 28% RH_ice | Ephemeral |
| 06-30 14:00 UTC | -53.5°C / 38% RH_ice | -41.0°C / 10% RH_ice | -35.5°C / 45% RH_ice | Ephemeral |
| 06-30 15:00 UTC | -53.5°C / 38% RH_ice | -41.0°C / 10% RH_ice | -35.0°C / 34% RH_ice | Ephemeral |
| 06-30 16:00 UTC | -53.5°C / 33% RH_ice | -41.0°C / 10% RH_ice | -34.0°C / 22% RH_ice | Ephemeral |
| 06-30 17:00 UTC | -53.5°C / 33% RH_ice | -41.0°C / 6% RH_ice | -33.5°C / 22% RH_ice | Ephemeral |
| 06-30 18:00 UTC | -53.5°C / 33% RH_ice | -41.5°C / 6% RH_ice | -33.5°C / 19% RH_ice | Ephemeral |
| 06-30 19:00 UTC | -54.0°C / 33% RH_ice | -41.5°C / 6% RH_ice | -33.0°C / 25% RH_ice | Ephemeral |
| 06-30 20:00 UTC | -54.0°C / 33% RH_ice | -41.5°C / 6% RH_ice | -33.0°C / 33% RH_ice | Ephemeral |
| 06-30 21:00 UTC | -54.5°C / 33% RH_ice | -42.0°C / 13% RH_ice | -33.0°C / 41% RH_ice | Ephemeral |
| 06-30 22:00 UTC | -54.5°C / 33% RH_ice | -42.0°C / 19% RH_ice | -33.0°C / 44% RH_ice | Ephemeral |
| 06-30 23:00 UTC | -54.0°C / 30% RH_ice | -42.5°C / 27% RH_ice | -33.0°C / 44% RH_ice | Ephemeral |
| 07-01 00:00 UTC | -54.0°C / 30% RH_ice | -43.0°C / 36% RH_ice | -33.0°C / 44% RH_ice | Ephemeral |
| 07-01 01:00 UTC | -54.0°C / 25% RH_ice | -43.0°C / 44% RH_ice | -33.0°C / 41% RH_ice | Ephemeral |
| 07-01 02:00 UTC | -53.5°C / 30% RH_ice | -43.0°C / 54% RH_ice | -33.0°C / 41% RH_ice | Ephemeral |
| 07-01 03:00 UTC | -53.5°C / 25% RH_ice | -43.0°C / 54% RH_ice | -33.0°C / 38% RH_ice | Ephemeral |
| 07-01 04:00 UTC | -53.5°C / 25% RH_ice | -43.0°C / 57% RH_ice | -32.5°C / 36% RH_ice | Ephemeral |
| 07-01 05:00 UTC | -53.5°C / 25% RH_ice | -43.0°C / 63% RH_ice | -33.0°C / 33% RH_ice | Ephemeral |
| 07-01 06:00 UTC | -53.0°C / 24% RH_ice | -42.5°C / 49% RH_ice | -32.5°C / 30% RH_ice | Ephemeral |
| 07-01 07:00 UTC | -53.5°C / 25% RH_ice | -42.5°C / 46% RH_ice | -32.5°C / 27% RH_ice | Ephemeral |
| 07-01 08:00 UTC | -53.5°C / 30% RH_ice | -42.5°C / 54% RH_ice | -32.5°C / 30% RH_ice | Ephemeral |
| 07-01 09:00 UTC | -54.0°C / 30% RH_ice | -42.5°C / 46% RH_ice | -32.5°C / 27% RH_ice | Ephemeral |
| 07-01 10:00 UTC | -54.0°C / 30% RH_ice | -42.5°C / 46% RH_ice | -32.5°C / 27% RH_ice | Ephemeral |
| 07-01 11:00 UTC | -54.0°C / 30% RH_ice | -42.5°C / 46% RH_ice | -32.5°C / 27% RH_ice | Ephemeral |
| 07-01 12:00 UTC | -54.0°C / 30% RH_ice | -42.5°C / 49% RH_ice | -32.5°C / 30% RH_ice | Ephemeral |
| 07-01 13:00 UTC | -54.0°C / 33% RH_ice | -42.5°C / 46% RH_ice | -32.5°C / 30% RH_ice | Ephemeral |
| 07-01 14:00 UTC | -54.0°C / 30% RH_ice | -42.5°C / 49% RH_ice | -33.0°C / 30% RH_ice | Ephemeral |
| 07-01 15:00 UTC | -54.5°C / 25% RH_ice | -43.0°C / 54% RH_ice | -33.0°C / 30% RH_ice | Ephemeral |
| 07-01 16:00 UTC | -54.5°C / 30% RH_ice | -43.0°C / 54% RH_ice | -33.5°C / 30% RH_ice | Ephemeral |
| 07-01 17:00 UTC | -54.5°C / 30% RH_ice | -42.5°C / 40% RH_ice | -33.0°C / 30% RH_ice | Ephemeral |
| 07-01 18:00 UTC | -54.0°C / 33% RH_ice | -42.5°C / 30% RH_ice | -33.0°C / 30% RH_ice | Ephemeral |
| 07-01 19:00 UTC | -53.5°C / 33% RH_ice | -42.5°C / 27% RH_ice | -33.5°C / 30% RH_ice | Ephemeral |
| 07-01 20:00 UTC | -53.5°C / 33% RH_ice | -42.0°C / 24% RH_ice | -33.0°C / 30% RH_ice | Ephemeral |
| 07-01 21:00 UTC | -53.5°C / 33% RH_ice | -42.5°C / 24% RH_ice | -33.0°C / 30% RH_ice | Ephemeral |
| 07-01 22:00 UTC | -53.5°C / 33% RH_ice | -42.0°C / 16% RH_ice | -33.0°C / 30% RH_ice | Ephemeral |
| 07-01 23:00 UTC | -53.5°C / 30% RH_ice | -41.5°C / 13% RH_ice | -33.0°C / 30% RH_ice | Ephemeral |
Method: 15-day hindcast via Open-Meteo + IEM ASOS hourly sky conditions. High cloud = any sky layer ≥ 20,000 ft (FEW/SCT/BKN/OVC) in the METAR report of the nearest major airport. The table shows: when we predict PERSISTENT or EPHEMERAL, how often does the METAR show high-altitude cloudiness?
Note: METAR high cloud ≠ contrail observation. Natural cirrus and contrail cirrus are indistinguishable. London EGLL uses automated ceilometers (NCD = No Cloud Detected) that cannot detect thin cirrus — excluded from aggregate. Miami shows equal high-cloud rates for both classes due to tropical convective cirrus (not sensitive to upper-tropospheric humidity). This is a directional sanity check, not a precision/recall measurement.
| City | Predicted | Hours | High Cloud When Predicted |
|---|---|---|---|
| Columbus, OH | PERSISTENT | 61 | 62% |
| Columbus, OH | EPHEMERAL | 287 | 40% |
| Denver, CO | PERSISTENT | 36 | 86% |
| Denver, CO | EPHEMERAL | 312 | 56% |
| Seattle, WA | PERSISTENT | 74 | 78% |
| Seattle, WA | EPHEMERAL | 274 | 36% |
| Chicago, IL | PERSISTENT | 40 | 70% |
| Chicago, IL | EPHEMERAL | 308 | 59% |
| New York, NY | PERSISTENT | 41 | 85% |
| New York, NY | EPHEMERAL | 307 | 70% |
| Miami, FL | PERSISTENT | 86 | 85% |
| Miami, FL | EPHEMERAL | 262 | 85% |
| Los Angeles, CA | PERSISTENT | 30 | 20% |
| Los Angeles, CA | EPHEMERAL | 318 | 1% |
| London, UK | PERSISTENT | 187 | — (63% NCD — ceilometer blind to thin cirrus) |
| London, UK | EPHEMERAL | 173 | — (87% NCD — ceilometer blind to thin cirrus) |
| All US cities | PERSISTENT | 368 | 73% |
| All US cities | EPHEMERAL | 2068 | 49% |
6/7 US cities show higher high-cloud agreement for PERSISTENT than EPHEMERAL. Aggregate: PERSISTENT = 73% vs EPHEMERAL = 49% (Δ = +24pp, ex-London). Miami is a special case: tropical convective cirrus saturates both classes at ~85%. Full satellite validation (Google OpenContrails dataset) pending Kaggle API access.
Contrails form when the mixing line between hot engine exhaust and cold ambient air passes through or above the ice saturation curve — the Schmidt-Appleman criterion.
The critical temperature Tc is the ambient temperature below which contrails must form. Whether they persist depends on whether the air is supersaturated with respect to ice (RHice ≥ 100%). Open-Meteo reports RH w.r.t. liquid water, so we convert: RHice = RHliq × (esat,liq / esat,ice). At −45°C this factor is ~1.53 — meaning 65% RH (liquid) is already supersaturated w.r.t. ice.
Engine parameters used: EIH₂O = 1.25 kg/kg • LHV = 43.2 MJ/kg • η = 0.30
| Pressure | Altitude | G (Pa/K) | Tc (contrails form below) |
|---|---|---|---|
| 200 hPa | ~11.8 km / FL387 | 1.334 Pa/K | -44.1°C |
| 250 hPa | ~10.5 km / FL344 | 1.668 Pa/K | -41.8°C |
| 300 hPa | ~9.0 km / FL295 | 2.002 Pa/K | -39.9°C |
| 350 hPa | ~7.9 km / FL259 | 2.335 Pa/K | -38.2°C |