KHYI — San Marcos Regional Airport
fog forecast & climatology · San Marcos city page · full 10-year analysis →
Fog unlikely through Saturday (peak 4%). September typically brings about 2 hours of dense fog here.forecast cycle 2026-09-04T13:00:00Z · page rebuilt daily · live layers below update hourly
- Fog hours per year
- 58 h below CAT I minima (2016–2026 average)
- Fog season
- February and January
- Typical fog event
- ~1 h once it forms (middle half 1–3 h, n=237)
- Data through
- 2026-08-15 · machine-readable data.json
When this airport fogs in
In a typical year San Marcos Regional Airport spends 58 hours below CAT I approach minima (visibility under ~½ mile or ceiling under 200 ft), concentrated in February and January. The strip above shows the hour-by-hour pattern for the current month from ten years of weather observations.
Fog season
Fog season runs October through May, peaking in January; fog is mostly a 6 AM–8 AM phenomenon; typically thinning out by 10 AM; a typical event lasts about 1 hour once it forms local time · 10-yr average
Runway infrastructure
| end | approach lights | best approach | length | RVR |
|---|---|---|---|---|
| 08 | — | LPV | 6,330 ft | — |
| 26 | — | LPV | 6,330 ft | — |
| 13 | MALS | CAT I | 5,601 ft | — |
| 31 | — | LPV | 5,601 ft | — |
| 17 | — | LPV | 5,214 ft | — |
| 35 | — | LPV | 5,214 ft | — |
From FAA NASR / curated AIP Canada research. Approach-light class and minima tier drive how low an approach can be flown — details in the chase board.
For flight operations
EFVS crews: the CHASE board ranks airports by live fog status, approach lighting, go-around height and flight time from your base. Forecast probabilities publish here per-airport once the calibrated model beats climatology on live verification — receipts on the scorecard. Methodology.
Sources: NOAA/NWS National Blend of Models guidance · METAR observations 2016–2026 (Iowa Environmental Mesonet) · FAA NASR. Machine access: data.json · llms.txt. Not for operational use.