Types of forecast Description
Nowcasting A short range forecast having a lead time/validity
of less than 24 hrs
Short range forecasts Forecasts having a lead time / validity period of 1
to 3 days
Forecasts having a lead time /validity period of 4
to 10 days
Long range /Extended
Forecasts having a lead time /validity period
beyond 10 days. Usually this is being issued for
a season. IMD issues Long Range Forecast for
southwest Monsoon rainfall and onset date for
Kerala, Northeast Monsoon Rainfall and Winter
precipitation over Northwest India.
Local Forecast In local forecast, whenever any weather
phenomenon is expected, its intensity, frequency
and time of occurrence is indicated. In the
absence of a weather phenomenon, the local
forecast describes anticipated sky conditions.
The other parameters for which the local forecast
issued include maximum temperature and/or
minimum temperature, rainfall, wind and special
It is valid for a radius of 50 km around the station
and is updated 4 times in a day.
Pre Monsoon Season
Southwest Monsoon Season
Northeast Monsoon Season
January – February
March – May
June - September
October - December
Reported in terms of Octa wherein the sky is divided into 8 equal parts
Clear sky 0 Octa
Mainly clear 1-2 Octa of sky covered
Partly cloudy 3-4 Octa of sky covered
Generally cloudy 5-7 Octa of sky covered
Cloudy > 7 Octa of sky covered
One or two spells of
In a 24 hrs time, rainfall occurring with a frequency of 1-2
A few spells of rain In a 24 hrs time, rainfall occurring with a frequency of
more than 2 spells but with well defined dry spells in
Intermittent rain In a 24 hrs time, rainfall occurring with a frequency more
than that defined in "A Few Spells" but is discontinuous
and without presenting the character of a shower.
Drizzle Liquid precipitation in the form of water drops of very
small size (by convention, with radius of water drops
between about 100 and 500 μm).
Rain Liquid precipitation in the form of water drops of radius between about 500 and 2500 μm.
Shower Solid or liquid precipitation from a vertically developed
cloud is designated a shower and is distinguished from
the precipitation, intermittent or continuous, from layer
clouds. Showers are often characterized by short
duration and rapid fluctuations of intensity (by
convention, with radius of water drops more than
Hail Solid precipitation in the form of balls or pieces of ice
(hailstones) with diameters ranging from 5 to 50 mm or
Thunderstorm One or more sudden electrical discharges manifested by
a flash of light (Lightning) and a sharp rumbling sound
Duststorm An ensemble of particles of dust or sand energetically
lifted to great heights by a strong and turbulent wind.
Surface visibility is reduced to low limits; the qualification
for a synoptic report is visibility below 1000 m.
Mist Mist is a phenomenon of small droplets suspended in air
Dew Condensation of water vapour on a surface whose
temperature is reduced by radiational cooling to below
the DEW-POINT of the air in contact with it
Fog Fog is a phenomenon of small droplets suspended in air
and the visibility is one kilometer or less
Frost Frost occurs when the temperature of the air in contact
with the ground, or at thermometer-screen level, is below
the freezing-point of water ('ground frost' or 'air frost',
respectively). The term is also used of the icy deposits
which may form on the ground and on objects in such
temperature conditions (glaze, hoar-frost).
Haze Haze is traditionally an atmospheric phenomenon where
dust, smoke and other dry particles obscure the clarity of
Smog Smoke and fog together reduce the visibility
Squally weather Squally weather is meant to cover occasional or frequent
squalls with rain or persistent type of strong gusty winds
(mean wind speed not less than 20 knot) accompanied
by rain. Such conditions are associated with low pressure
systems or onset and strengthening of monsoon.
Visibility The greatest distance that prominent object can be seen
and identified by unaided, normal eyes.