- Moves with mean environmental wind over 5-7 km.
- 30- 60 minute duration.
- Rainfall can be moderate to heavy, small hail is possible.
- Vertical wind shear is small.
- Series of evolving cells, forming on right or right rear flank
about every 15 minutes.
- New cells eventually dominate.
- Motion may deviate from mean winds.
- Precipitation is moderate to heavy; hail is usually present;
short-lived tornadoes along the gust front or in rapidly developing
updrafts are possible.
- An MCS, or mesoscale convective system, is a
cluster of thunderstorms that persist and evolve like multicells.
MCS's generally move with the mean 700-500 mb layer wind.
Mesoscale Convective Complexes
||A: Cloud shield with continuously low IR temperature -32°C must have an area 100,000 km2.
B: Interior cold cloud reqion with temperature of -52°C must have an area 50,000 km2.
||Size definitions A and B must be met for a period of 6 hours.
||Contiguous cold-cloud shield (IR temperature -32°C) reaches maximum size.
||Eccentricity (minor axis/major axis) 0.7 at time of maximum extent.
Definition of MCC
based on analyses of enhanced IR satellite imagery (from Maddox,
* Initiation occurs when size definitions A and B are first satisfied.
Termination occurs when size definitions A and B are no longer
- An interesting thunderstorm sub-section is the mesoscale convective
complex, or MCC. Smaller mesoscale convective systems are more
common than the larger MCC. (Bartels et al., 1984)
- MCC's account for a significant portion of growing season
rain over U.S. corn and wheat belts. (Fritsch et al., 1981)
- Almost one of every four MCC's results in injuries or deaths.
- Once formed, the MCC tends to move with mean 700 - 500 mb
- 52°C tops range in size from 50,000 to 200,00 km².
Under this area the majority of rain falls.
- MCCs are relatively rare along the East Coast and west of
the Rocky Mountains.
- Dirks (1969) and Wetzel et al., (1983) noted that many
storms originated over the Rockies or eastern slopes and became
nocturnal storm over the plains. Regardless of where they form,
they have their roots in thunderstorms that occur in the late
afternoon. Under favorable conditions, these MCCs reach their
maximum size around midnight.
- The typical MCC occurs downwind of a mid-level trough in a
region of upward vertical motion. Warm advection is strong at
low levels when the nocturnal low level jet increases in speed
and also veers.
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