Temperature alert
A discreet cue on the raw METAR only (TAFs carry no temperature) highlights the temperature/dewpoint group when it's hot, or when conditions favour fog — and picks up a light surface wind alongside it when the wind is part of what fired.
The cue highlights the TT/DD token, e.g. 28/19. The two cues mean different things and fire independently:
- Orange — hot. The group turns orange when the temperature is +27 °C or higher, a heads-up for conditions that reduce helicopter performance. This fires regardless of the wind: heat raises density altitude whether the air is moving or not.
- Underline — fog potential. The group is underlined when the temperature and dewpoint are within 2 °C of each other and the sustained wind is under 5 kt (e.g.
00000KT,27003KT,VRB02KT). Both halves are required. Air near saturation with nothing to mix it out is a classic fog and stagnation setup — but a close spread with a real wind is not, and is deliberately left unmarked. - When it's hot and the fog condition is met, the group appears orange and underlined.
When an alert fires and the surface wind is light, the wind group is highlighted too, carrying the same cue as the condition it belongs to:
- Fog condition (close spread + light wind) → the wind is underlined, alongside the temperature/dewpoint group.
- Hot + light wind → the wind turns orange. Heat raises density altitude, and with no wind there is no translational lift to help — both work against performance. If it's hot but the wind is not light, only the temperature is marked.
- Both → the wind is orange and underlined, matching the temperature/dewpoint group.
A gusty wind is never treated as light, whatever the lull reads — gusty air is not stagnant. If the report carries no readable wind group at all, the wind is not assumed calm, so the underline will not appear. A light wind on its own, with neither trigger firing, is never highlighted.
Only the temperature/dewpoint group (and, when it applies, a light-wind group) changes; the rest of the raw report is unchanged. This is a visual cue, not a substitute for evaluating density altitude, performance charts, or the full weather picture. For strong winds (20 kt+), see the Wind alert; for heat-driven performance loss, see Density altitude.