ObserveVirga
vir · Special · 9 October 2026 · By · Hazard
Virga: rain that never lands
Virga is precipitation falling from a cloud that evaporates before it reaches the ground. It is not a cloud genus — it is a supplementary feature, a suffix attached to whatever cloud is producing it. It is also one of the most common sources of a false weather report, because from a distance it looks exactly like rain.
Virga
Virga
- Band
- Special
- Altitude
- 1 km – 6 km
- Code
- vir
- Seasonal window
- Most common in dry continental and high-altitude regions year-round, and in temperate regions in spring and early summer when surface humidity is lowest relative to cloud-base humidity. (Jan–Dec)
- Published
- 9 October 2026
- By
Weather clue
Virga under a developing cumulus or altocumulus means the sub-cloud layer is dry and the shower will not reach you. Virga under a mature cumulonimbus anvil with a fast-growing shaft is a gust-front warning.
How to observe it
- Always check the ground beneath a shaft before recording rain; a wet patch spreading outward is the only reliable confirmation.
- Watch a single shaft for five minutes: shortening means the sub-cloud air is drying, lengthening means it is moistening.
- Feel for a cool gust with no rain — that is the evaporatively cooled downdraught arriving ahead of any precipitation.
- In fire weather, log virga with lightning as a distinct hazard category rather than as 'no precipitation'.
Hazard. This genus is associated with thunderstorms, downbursts, hail or severe gusts. Apply the 30-30 rule: a flash-to-thunder interval of 30 seconds or less puts you within about 10 km. Observe from substantial shelter, never from under an isolated tall tree, on a ridge or in the open.
How to tell virga from rain that is landing
The single most reliable test needs no equipment: look at the ground beneath the shaft. If the ground is dry, or if there is no visible change in the surface in the last ten minutes, it is virga.
| Feature | Virga | Reaching precipitation |
|---|---|---|
| Shaft bottom | Ends abruptly in mid-air with a ragged, fading tip | Continues to the horizon or to the ground |
| Ground beneath | Dry; no splash, no wet patch, no darkening | Wet patch spreads; you can see the impact line |
| Shaft shape | Often curved or hooked downwind | Straight, vertical or slanted with the wind |
| Distance cue | Ground between you and the shaft is clearly visible | The horizon behind the shaft is obscured |
| Time behaviour | Shaft shortens as the air dries | Shaft persists or lengthens |
The dry-air column underneath
Virga requires a cloud base that is high enough and a sub-cloud layer that is dry enough. As the raindrops fall out of the cloud they enter unsaturated air and begin to evaporate, and the smaller drops evaporate first. If the sub-cloud layer is deep and dry enough, only the largest drops survive to any depth, and if it is drier still, none do.
The evaporation cools the sub-cloud air, which makes it denser and causes it to sink. This is why virga is often accompanied by a cool, gusty outflow at the surface even though no rain has landed — a genuinely surprising experience if you are standing underneath and expecting nothing.
Why virga matters beyond curiosity
Virga has three practical consequences that are worth knowing about.
Fire weather. In dry regions, a virga-producing thunderstorm produces lightning without rain. The lightning starts the fire and there is no rain to put it out, which is why dry thunderstorms are one of the most dangerous fire-weather patterns in the western United States and Australia.
Aviation. Virga below a cloud base means the air beneath is descending and cooling, which produces strong, localised downdraughts and wind shear near the surface with no accompanying rain to warn the pilot.
Microbursts. A particularly intense downdraught beneath virga can reach the ground and spread out as a microburst — a burst of wind that can exceed 40 m/s and reverse direction within a few hundred metres. There are well-documented cases of aircraft being flown into the ground by a microburst on final approach.
Where to see it
Virga is most common in dry, continental and high-altitude regions, where the sub-cloud layer is deep and the relative humidity low. It is a routine feature of skies over the American Southwest, the Middle East, central Australia, the Sahel and the high plateaus of Asia.
It is also common in temperate regions in spring and early summer, when the surface is warm and dry and the first convective showers of the season are falling from bases that are still high.
Rules of thumb
- Virga is precipitation that evaporates before reaching the ground; it is a feature, not a genus.
- The ground beneath is the test: dry ground under a rain shaft means virga.
- Evaporation cools and sinks the sub-cloud air, producing cool gusty outflow with no rain.
- Dry thunderstorms with virga are a major wildfire ignition source and a microburst hazard to aircraft.
| The other cloud | Comparison — Virga |
|---|---|
| 落到地面的降水 · Precipitation reaching the ground | The decisive test is the ground beneath: a wet patch spreading on the surface means the rain is landing, dry ground means virga. |
| 穿洞云的下落尾迹 · Fallstreak hole trails | A fallstreak trail is a single narrow streamer of ice crystals inside a thin cloud layer, quite unlike the broad multiple shafts of virga. |
The two or three genera this one is most often confused with, and the single feature that separates them.
Observation questions
How do I distinguish virga from distant rain?
Look at the ground beneath the shaft and at the horizon behind it. If the ground under the shaft is dry and the horizon behind is clearly visible, the streaks are evaporating in mid-air. Rain that is landing hides the horizon behind it and leaves a wet patch.
Why do dry thunderstorms start so many fires?
Because the lightning strikes the ground while the rain evaporates before it gets there. You get the ignition without the extinguishing, which is why dry thunderstorms are one of the most dangerous fire-weather patterns in the western United States, Australia and the Mediterranean.