pelting transforms into snow when the temperatures drop below freezing , veracious ? Not necessarily . Supercooling raindrop is really what ’s poking these cookie - cutter holes in the cloud over the southeastern United States .
Everyone knows piss freeze once temperature dismiss to 32 ° F ( 0 ° hundred ) , but that ’s one of those fiddling lies of simplism we expend to skip messy details . In reality , contaminant like dust or pollen can cut down water ’s freezing point . The result is supercooled raindrops can chill below freeze , while remaining liquidity .
Swiss - cheese sky over Louisiana and Mississippi on December 29 , 2015 . epitome acknowledgment : NASA / Jeff Schmaltz
The sky over Mississippi and Louisiana were blanketed in supercooled clouds this calendar week , but not thickly enough to ground planes . When aircraft darted through the cloud pack of cards pack holiday travelers , they cool the cloud even further through a put-on of aerodynamics . air pressure drops as gentle wind flows over the wing and propeller tips , let atmosphere to flesh out while pretermit in temperature . This adiabatic chilling is enough to throw away the temperature by up to 68 ° F ( 20 ° C ) , well past the point where even supercooled droplets freeze into ice crystallization .
When these ice crystals encounter still - liquid supercooled droplets , they act as nucleation point triggering further crystallisation . Soon it ’s a tiny storm , a miniature burst of Baron Snow of Leicester or rainfall leave a crack in the swarm layer . These fallstreak clouds can be polkadot cakehole - punches or longer canals depend on the interaction of the thickness of the cloud layer , academic degree of wind shear , and air temperature .
Canal swarm . epitome credit : Tammy ( @oboyd )
This workweek , conditions come together perfectly . A utter cloud deck , supercooled droplet , and a officious season of never-ending travel stab holes untilthe sky started to look like swiss Malva sylvestris . Supercooling is gorgeous .
[ Earth Observatory , Capital Weather Gang ]
reach the author at[email protected]or follow her at@MikaMcKinnon .
atmospheric scienceScienceThermodynamics
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