Cold front known as veering, and in the southern hemisphere a shift from northwest to southwest (anticlockwise, backing). Normally, cold fronts can be marked by these characteristics: <nowiki>*provided there is sufficient moisture.</nowiki> 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
Tornado outbreak of May 15–17, 2013 severe thunderstorms early that morning over northwestern Texas, for a threat of large hail and damaging winds. A low-pressure area associated with the trough moved over Oklahoma that day, producing light to moderate rainfall and non-severe thunderstorms across that state into parts of North Texas. Later forecasts expanded the slight risk further into northern and central Texas, and later into far southern Oklahoma, and indicated an enhanced risk of a few isolated tornadoes in north Texas. The atmosphere began to destabilize due to a decrease in cloud cover over western and central Texas; the sunshine and heating, combined with sufficient