<P> If the cold front is highly unstable, cumulonimbus clouds producing thunderstorms commonly form along the front . Anvil cirrus clouds may spread a considerable distance downwind from the thunderstorms . The other cloud types associated with a cold front depend on atmospheric conditions such as air mass stability and wind shear . As the front approaches, middle - étage gives way to altostratus and low - level stratocumulus with intermittent light precipitation if the warm airmass being displaced by the cold front is mostly stable . With significant airmass instability, vertically developed cumulus or cumulonimbus with showers and thunderstorms will form along the front . </P> <P> After the passage of the cold front, the sky usually clears as high pressure builds in behind the system, although significant amounts of cumulus or stratocumulus, often in the form of long bands called cloud streets may persist if the air mass behind the front remains humid . Small and unchanging amounts of cumulus or cirrus clouds in an otherwise clear sky are usually indications of continuing fair weather as long as the barometric pressure remains comparatively high . </P> <P> A cold front commonly brings a narrow band of precipitation that follows along the leading edge of the cold front . These bands of precipitation are often very strong in nature, and can bring severe thunderstorms, hailstorms and / or tornadoes . In the spring, these cold fronts can be very strong, and can bring strong winds when the pressure gradient is tighter than normal . During the winter months, cold fronts sometimes come through an area with little or no precipitation . Wider rain bands can occur behind cold fronts which tend to have more stratiform, and less convective, precipitation . These rainstorms sometimes bring flooding, and can move very slowly when the storm steering it is strong and embedded within a meridional flow pattern (with more pole to equator motion rather than west to east motion). In the winter, cold fronts can bring cold spells, and occasionally snow . In the spring or summer in temperate latitudes, hail may occasionally fall along with the rain . If moisture is not sufficient, such as when a system has previously moved across a mountain barrier, cold fronts can pass without cloudiness . </P> <P> The idea that cold air wedges, or undercuts, the warm air is often used to depict how advancing cold fronts force warm air to rise along the sloping cold air, much like a snow shovel scooping up snow, creating instability . Provided with sufficient moisture, the rising air would thus condense, creating storms, clouds, and / or rain . While this concept is used to generally describe frontal precipitation patterns, it is technically incorrect . </P>

A cold front is currently over which of the following states