No Snow January in Himachal Pradesh

Why in news?

Records from the India Meteorological Department (IMD) suggest Himachal Pradesh has registered its driest January since 1901, with a 99.7% shortfall in January rain compared to what is normal.

What is snow?

• Snow - Snow is precipitation that falls in the form of ice crystals.
• The ice crystals are formed individually in clouds, but when they fall, they stick together in clusters of snowflakes.
• Snowflakes develop different patterns, depending on the temperature and humidity of the air.
• Snow requires temperatures at the ground to be near or below freezing—less than 0 degrees C (32-degrees Fahrenheit).

Precipitation is any type of water that forms in the Earth's atmosphere and then drops onto the surface of the Earth.

• Formation of snow - Water vapor, droplets of water suspended in the air, builds up in the Earth's atmosphere.
• Water vapor collects with other materials, such as dust, in clouds.
• Precipitation condenses, or forms, around these tiny pieces of material, called cloud condensation nuclei (CCN).
• Clouds eventually get too full of water vapor, and the precipitation turns into a liquid (rain) or a solid (snow).

What is the reason for the lack of snowfall?

• Fall in the number of Western Disturbances - Western Disturbances (WDs) are storms that originate in the mid-latitude regions and travel thousands of kilometres to bring rains across northern India.
• This is a non-monsoonal precipitation pattern driven by the Westerlies.
• When the temperatures are low, they result in snowfall and water being available as snow melt.
• Usually, 5 to 7 WDs affect Northwest India in the period from December to January, but this winter, there have been none.
• As a result, the Western Himalayan Region received 80% less rain than normal.
• El Niño conditions over the equatorial Pacific Ocean - El Niño is the warming of sea waters in Central-east Equatorial Pacific that occurs every few years (Warm phase off the coast of Peru).
• During El Niño, surface temperatures in the equatorial Pacific rise and this weakens the trade winds that blow near the Equator.
• In India, an El Nino event is strongly linked to suppressed rainfall.
• Absence of a strong jet stream - Jet streams are relatively narrow bands of strong wind (250 to 320 km/hr) in the upper levels of the atmosphere (about 12 km above mean sea level).
• Within jet streams, the winds blow from west to east, but the band often shifts north and south because jet streams follow the boundaries between hot and cold air.
• The western cyclonic disturbances which enter the Indian subcontinent from the west and the northwest during the winter months, originate over the Mediterranean Sea and are brought into India by the westerly jet stream.
• The arrival of these disturbances is often indicated by a rise in the night temperature.

References

1. National Geographic | Snow formation
2. The Hindu | Himachal Pradesh’s rainless January