This calculator requires the use of Javascript enabled and capable browsers. This script calculates the Lifted Index from the difference of an 500 millibar parcel (air mass) temperature and the 500 millibar environmental temperature. The Lifted Index is a standard and common measure of the local static stability of the atmosphere. Positive values indicate the lifted parcel is colder than its new environment, and thus the atmosphere is stable. Negative values indicate instability; the more negative, the more unstable the air is, and the stronger the updrafts are likely to be with any developing thunderstorms. However, unlike the Showalter Index, there are no "magic numbers" or threshold LI values below which severe weather becomes imminent. Thunderstorms are likely to develop in regions where the stability indices are at critical levels AND an initial lifting mechanism exists. The lifting mechanism can be solar heating or air flow patterns. The value is obtained by computing the temperature that air near the ground would have if it were lifted to some higher level (usually 500 mb) and comparing that temperature to the actual temperature at that level. It is a stability index used to gage the severity of potential storms given that the initial lifted parcel begins at 500 mb. 500 mb is roughly 18,000 feet in altitude but is always changing, higher or lower in altitude, as it is not a standard factor.
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