Behind the Forecast: The true ‘calm before the storm’

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Science Behind the Forecast: The Calm Before the Storm (6/7)

LOUISVILLE, Ky. (WAVE) - Most of us have heard the adage "the calm before the storm." How much meteorological truth lies within that phrase? Quite a bit actually.

To form and thrive, storms need warm, moist air that they suck in from their surrounding environment. This warm, humid air rises from the surface, cooling and condensing into water droplets which in turn become clouds. The rising warm air actually creates a partial vacuum with sucks colder, drier air from higher in the atmosphere towards the ground. This actually helps to push the rain towards the surface. With the more air being sucked in from all around the storms, the air moving away from the storm actually gets pulled back towards the storm creating calm ahead of it.

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Warm dry air is more stable than moist air. So if the more unstable, warm, moist air is being sucked into a storm system, for example a hurricane, this leaves the drier more stable air behind. This is what grants us the calm before the storm. Stable air is associated with calmer weather conditions but it doesn’t always mean clear skies. Stable air masses are marked by a lack of convection (think thunderstorms) and calm conditions. Planes flying through stable air don’t experience turbulence when flying through stable air. Stratiform clouds (clouds that look like sheets or blankets) and fog can accompany stable air. Stratiform clouds can stretch horizontally for hundreds of miles while only climbing vertically for a few hundred feet. There can be precipitation within a stable air mass. Nimbostratus clouds bring steady light rain and/or drizzle to an area. Fog typically forms when winds are calm or light.

Not every storm system is preceded by calm weather. The atmosphere is filled with complex wind, moisture, pressure and temperature patterns. All of these things factor into the type of conditions seen before a storm moves through.

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