Cold front

<p>
A cold front is the leading edge of a cooler mass of air at ground level that replaces a warmer mass of air and lies within a pronounced surface <a href="/facts/Trough_(meteorology)/wKKKxBuh">trough</a> of <a href="/facts/Low-pressure_area/rphmr6qP">low pressure</a>. It often forms behind an <a href="/facts/Extratropical_cyclone/4c5Y4hoJ">extratropical cyclone</a> (to the west in the <a href="/facts/Northern_Hemisphere/EFwyqL25">Northern Hemisphere</a>, to the east in the <a href="/facts/Southern_Hemisphere/QfJ4z9L5">Southern</a>), at the leading edge of its cold air <a href="/facts/Advection/3rn50V2r">advection</a> pattern—known as the <a href="/facts/Cyclone/T8IEU0aP">cyclone</a>'s dry "conveyor belt" flow. Temperature differences across the boundary can exceed 30 °C (54 °F) from one side to the other. When enough moisture is present, rain can occur along the boundary. If there is significant <a href="/facts/Convective_instability/SPuoTHLj">instability</a> along the boundary, a <a href="/facts/Squall_line/vn1lU2uY">narrow line of thunderstorms</a> can form along the frontal zone. If instability is weak, a broad shield of rain can move in behind the <a href="/facts/Weather_front/n4PXdp1f">front</a>, and evaporative cooling of the rain can increase the temperature difference across the front. Cold fronts are stronger in the fall and spring transition seasons and are weakest during the summer.</p>

Cold front open-in-new

Cold front