How to read a meteogram

A meteogram is a time-series forecast for one location — it tells you what the weather at an airfield looks like hour by hour for the next 2–5 days. ClearToFly's meteograms are optimised for VFR go/no-go decisions.

The GAFOR strip (top)

The top strip colour-codes each hour as a GAFOR category, derived from the forecast ceiling and visibility:

• Oscar / Delta (green) — clear VFR, ≥ 5,000 ft ceiling and ≥ 8 km visibility.
• Charlie (yellow) — 1,000–3,000 ft ceiling or 5–8 km visibility. Legal VFR but marginal.
• Mike / X-Ray (red/pink) — below 1,000 ft ceiling or below 1.5 km visibility. Not VFR.

Use this row to find the flyable windows at a glance before drilling into detail.

Ceiling and visibility rows

Below the GAFOR strip, two rows show the raw numbers:

• Ceiling in feet AGL — the raw driver of the GAFOR colour above.
• Visibility in km.

Skim these next. A green GAFOR block with a ceiling right at 5,001 ft is less reassuring than one with 8,000 ft — always look at the number.

Cloud structure

ClearToFly's meteograms show vertical cloud cover on 28 levels up to 10,000 ft — you can see the layers, not just the base. Broken layers at 3,500 ft with clear air above versus a solid overcast up to 6,000 ft are two very different scenarios that a simple ceiling number can't distinguish.

Wind and crosswind

Surface wind is shown with direction and speed. If the airfield has runway data, a crosswind row is computed for each runway — so you don't have to do the trigonometry mid-briefing.

Precipitation and significant weather

A bar plot shows precipitation rate; an emoji strip surfaces the significant weather code (fog, drizzle, rain, snow, thunderstorm, freezing precipitation). Look here for icing risk (snow / freezing precip) and thunderstorm windows.

Reading the horizon

Hours 0–48 come from the high-resolution ICON-D2 model. Hours 49–120 are extended via ICON-EU (~7 km). The lower resolution is honest — a Day-4 forecast has meaningfully more uncertainty than a Day-1 one; use the extended horizon to spot trends, not to decide takeoff windows.

A worked example

Suppose you're planning EDAZ → EDML tomorrow morning at 09:00Z. On the meteogram:

• GAFOR strip at 09:00 is yellow (Charlie). Two rows down: ceiling 2,400 ft, visibility 6 km. Marginal but legal.
• Cloud structure: broken layer at 2,400 ft, clear above 4,500 ft. If terrain along the route is below 1,500 ft AGL, the layer isn't a hard blocker.
• Wind: 240° at 12 kt. Crosswind row for runway 07/25 shows 8 kt max — fine for the aircraft.
• Precipitation: light rain until 10:00Z, then dry. The GAFOR-yellow is a moisture / visibility issue, clearing after 10:00.

Decision: delay to 10:30Z and cross-check METAR before start-up.