A sky completely covered by cloud — eight oktas out of eight. The default sky of a monsoon spell on the Konkan coast and of a winter western disturbance over Punjab.
BasicsWhat is Overcast?
Overcast is the sky condition in which cloud covers the whole of the visible sky with no break — the maximum value on the cloud-cover scale. Meteorologists count sky cover in oktas, or eighths: zero oktas is a completely clear sky, four is half covered, and eight oktas is overcast. In the WMO weather codes used by this site and by most forecast providers, code 0 is clear sky, 1 is mainly clear, 2 is partly cloudy and code 3 is overcast.
It is a description of coverage, not of rain. An overcast sky may be dropping steady monsoon rain, or it may be a dry grey lid that produces nothing at all — a distinction that matters a great deal to anyone deciding whether to move a crop under cover. What overcast reliably means is that the direct beam of the sun is gone. The light becomes soft and shadowless, because everything is lit by diffuse radiation scattered through the cloud layer rather than by a point source.
For South Asia, overcast is the signature sky of the monsoon. Along the Konkan and Malabar coasts and across the northeastern hills, a continuous deck can sit overhead for days at a time in July and August. It is also the sky of a winter western disturbance over Punjab, Haryana and northern Pakistan, and of the low stratus and smog layer that caps the Indo-Gangetic plain in December and January.
How overcast is recorded
By human observer. A trained observer at a manned station divides the visible sky into eighths and reports the fraction covered. Eight oktas is reported only when no gap is visible; if the sky is almost but not entirely covered, the code used is “broken” rather than overcast. Aviation reports use a compact set of abbreviations for these bands — FEW for one to two oktas, SCT (scattered) for three to four, BKN (broken) for five to seven and OVC (overcast) for eight.
By instrument. Automatic stations use a ceilometer, which fires a pulse of light straight up and times the reflection from the cloud base to measure cloud height. Because the instrument only samples the narrow column directly overhead, the station derives sky cover from how often cloud is detected over a period of minutes rather than from a single look.
From above. Geostationary weather satellites — India’s INSAT series among them — see the cloud field from the top, which is how forecasters judge whether an overcast layer covers a district or a whole state.
From models. Numerical forecast models output total cloud cover as a percentage, usually split into low, mid and high layers. A forecast approaching 100 per cent total cloud is what a consumer app displays as overcast.
For aviation, the term also feeds a critical number: the ceiling is the height of the base of the lowest broken or overcast layer, and it is one of the values that decides whether an aircraft can approach a runway.
Overcast skies in South Asia
- Monsoon cloud decks (June to September). The windward Western Ghats, the Konkan and Malabar coasts, coastal Karnataka and Kerala see the most persistent overcast in the region. Assam, Meghalaya and the rest of the northeast are similar, and coastal Bangladesh sits under long overcast spells through July and August.
- Monsoon depressions. When a depression tracks inland from the Bay of Bengal across Odisha, Chhattisgarh and central India, it drags a wide overcast shield with it, often several hundred kilometres across.
- Western disturbances (December to March). These eastward-moving systems bring layered cloud, rain and hill snow to Kashmir, Himachal Pradesh, Punjab on both sides of the border, Haryana and Delhi. The sky goes overcast a day or more before the rain begins.
- Winter stratus and smog. In the Indo-Gangetic plain a shallow, persistent layer of low cloud and trapped pollution can turn the whole day grey from Lahore through Delhi and Lucknow to Patna and Dhaka — sometimes without a drop of rain.
- Northeast monsoon (October to December). Tamil Nadu, coastal Andhra Pradesh and Sri Lanka get their own overcast season while much of the rest of the subcontinent is clear.
What an overcast sky does
It flattens the temperature curve. Cloud blocks incoming solar radiation by day, so the afternoon maximum stays lower than a clear day would produce. At night the same cloud layer absorbs and re-emits the longwave radiation the ground is trying to release, so the minimum stays higher. The result is a narrow diurnal range — overcast days are cooler than clear days and overcast nights are warmer than clear nights. This is why frost in the northern plains needs clear, calm nights, and why an overcast night during a heatwave offers less relief than it sounds like it should.
It collapses solar generation. Rooftop and utility solar output falls steeply under a thick overcast deck, because the direct beam that panels convert most efficiently is gone entirely. Grid operators across the region plan for this seasonally.
It stalls drying. Paddy, chillies, turmeric and pulses spread out to dry in open yards, and washing on a line, all depend on the direct sun and on the low humidity that comes with it. A multi-day overcast spell after harvest causes real losses — one reason the post-monsoon clear season is so important agriculturally.
It changes visibility and safety. Overcast by itself does not cut horizontal visibility, but the conditions that produce winter overcast in the plains often come bundled with fog and haze, which do. Low ceilings also disrupt flights and delay hill-road travel.
Frequently asked questions
Does overcast mean it is going to rain? No. Overcast describes how much of the sky is covered, not whether precipitation is falling. Monsoon overcast usually does produce rain, but a winter stratus layer over the northern plains can be completely dry. Check the rain probability separately from the sky condition.
What is the difference between overcast and cloudy? “Cloudy” is loose everyday language. In forecasting, overcast means specifically eight oktas — total cover with no visible break. A sky at five to seven oktas is classed as broken, and three to four as scattered or partly cloudy.
Why is an overcast night warmer than a clear night? The ground radiates heat away after dark. A cloud layer absorbs that outgoing radiation and sends much of it back down, so the surface cools far more slowly. Clear, still nights produce the lowest minimum temperatures, which is why they bring frost risk in the northern plains and hills.
Can you get sunburnt when it is overcast? Thick overcast substantially reduces ultraviolet, but it does not eliminate it, and in the tropics the underlying UV load is high enough that a long exposure under a thin grey sky can still burn. The UV index, not the brightness of the sky, is the value to check.
Where can I see current cloud conditions for my city? Each Mausam Online city page reports the current sky condition, hourly cloud cover and the seven-day outlook. See Mumbai, Kochi, Kolkata, Guwahati, Lahore or Chittagong.