Mesoscale convective complex

Short description: Type of mesoscale convective system

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A mesoscale convective complex moving through the Great Lakes region

A mesoscale convective complex (MCC) is a unique kind of thunderstorm mesoscale convective system which is defined by characteristics observed in infrared satellite imagery. They are long-lived, often form nocturnally, and commonly contain heavy rainfall, wind, hail, lightning, and possibly tornadoes.[1]

## Contents

* 1 Size
* 2 Development
* 3 Structure
* 4 Effects and climatology
* 5 Notable MCCs
* 6 See also
* 7 References
* 8 External links and sources

## Size

A mesoscale convective complex has either an area of cloud top of 100,000 km2 or greater with temperature less than or equal to −32 °C, or an area of cloud top of 50,000 km2 with temperature less than or equal to −52 °C. Size definitions must be met for 6 hours or greater. Its maximum extent is defined as when cloud shield reaches maximum area. Its eccentricity (minor axis/major axis) is greater than or equal to 0.7 at maximum extent.[2]

## Development

MCCs commonly develop from the merging of thunderstorms into a squall line which eventually meet the MCC criteria. Furthermore, some MCC formation can be tracked from the plains in Colorado back to the Rocky Mountains. These are called "orogenic" complexes.[3] The characteristics of the meteorological environment that MCCs form in are strong warm air advection into the formation environment by a southerly low-level jet stream (wind maximum), strong moisture advection which increases the relative humidity of the formation environment, convergence of air near the surface, and divergence of air aloft. These conditions are most prominent in the region ahead of an upper level trough.

1. The systems begin in the afternoon as scattered thunderstorms which organize overnight in the presence of wind shear (wind speed and direction changes with height).
2. The probability for severe weather is highest in the early stages of formation, during the afternoon.
3. The MCC persists at its mature and strongest stage overnight and into the early morning in which the rainfall is characterized as stratiform rainfall (rather than convective rainfall which occurs with thunderstorms).
4. Dissipation of the MCC commonly occurs during the morning.

After dissipation, a remnant mid-level circulation known as a mesoscale convective vortex can initiate another round of thunderstorms later in the day.

## Structure

The structure of an MCC can be separated into three layers. The low-levels of the MCC near the surface, the mid-levels in the middle of the troposphere, and the upper-levels in the upper-troposphere. Near the surface, the MCC exhibits high pressure, with an outflow boundary, or mesoscale cold front, at its leading edge. This high pressure is caused by the cooling of the air from the evaporation of rainfall (commonly referred to as a cold pool). In the mid-levels (mid-troposphere), the MCC exhibits a cyclonic (counterclockwise in the Northern Hemisphere) rotating low pressure which is warm compared to the surrounding environment (referred to as a warm core). This mid-level circulation is referred to as a Mesoscale Convective Vortex. The upper-levels contain an anti-cyclonic (clockwise in the Northern Hemisphere) rotating high pressure which is a sign of divergence of air. This high pressure is colder relative to its surrounding environment. This divergence at upper-levels and convergence of air at the surface along the cool pool's outflow boundary results in rising motion which aids maintenance of the MCC.

## Effects and climatology

MCCs produce heavy rainfall which can lead to flooding and other hydrological impacts. MCCs are found in the United States during the spring and summer months (warm season), the Indian monsoon region, the West Pacific and throughout Africa and South America. In particular, the heavy rainfall from MCCs accounts for a significant portion of the precipitation during the warm season in the United States.[4] As the warm season progresses, the favorable regions for MCC formation shift from the southern plains of the United States northward. By July and August, the north-central states become the most favorable.[5] The mid-level low pressure areas of MCCs have also been tracked to the origin of some tropical cyclones, and on rare occasions, tropical cyclones can generate MCCs.

## Notable MCCs

One of the most notable MCCs occurred overnight on 19 July 1977, in western Pennsylvania. The MCC resulted in heavy rainfall which led to the disastrous flooding of Johnstown, Pennsylvania. The complex was tracked 96 hours back to South Dakota and produced copious amounts of rain throughout the northern United States before producing up to 12 inches (300 mm) of rain in Johnstown.

A second notable MCC brought destructive straight-line winds to southern Ontario, Upstate New York, Vermont, Massachusetts, Connecticut, and Rhode Island on the morning of 15 July 1995. The MCC produced winds in excess of 160 km/h (100 mph) and was responsible for seven deaths, widespread destruction of forests in the Adirondack and Berkshire Mountains, and over $500 million in property damage.[6]

A significant mesoscale convective complex, containing the remnant mid-level circulation of Atlantic Tropical Storm Barry, along with tropical east Pacific remnant moisture, caused catastrophic and deadly flooding in July 2025 in the Texas Hill Country.[7][8] Over 130 died as a result, including many children attending Camp Mystic along the Guadalupe River.[9][10]

## See also

* Mesoscale convective system
* Supercell
* Tropical cyclone
* Convective storm detection
* Mesoscale convective vortex
* Derecho

## References

1. ↑ Maddox, R. A., 1980: Mesoscale convective complexes. Bulletin of the American Meteorological Society, Vol. 61, 1374–1387.
2. ↑ "Mesoscale convective complex". https://forecast.weather.gov/glossary.php?word=mcc#:~:text=NOAA's National Weather Service - Glossary&text=Mesoscale Convective Complex.,major axis at least 0.7.
3. ↑ Wetzel, P. J., W. R. Cotton, and R. L. McAnelly, 1983: A long-lived mesoscale convective complex, Part II: Evolution and structure of the mature complex. Monthly Weather Review, Vol. 105, 1919–1937.
4. ↑ Fritsch, J. M., R. A. Maddox, and A. G. Barnston, 1981: The character of mesoscale convective complex precipitation and its contribution to warm season rainfall in the United States. Preprints, 4th Conference on Hydrometeorology, Reno, Nev., American Meteorological Society, Boston, 94–99.
5. ↑ Maddox, R. A., K. W. Howard, D. L. Bartels, and D. M. Rogers: Chapter 17: Mesoscale Convective Complexes in the Middle Latitudes. Mesoscale Meteorology and Forecasting, American Meteorological Society, 1986.
6. ↑ Stephen F. Corfidi, Jeffry S. Evans, and Robert H. Johns, 2015: JULY 1995 DERECHO SERIES. Retrieved on 2015-02-18.
7. ↑ Otto, Richard (July 4, 2025). ﻿Mesoscale Precipitation Discussion 0584﻿ (Report). College Park, Maryland: Weather Prediction Center. https://www.wpc.ncep.noaa.gov/metwatch/metwatch_mpd_multi.php?md=584&yr=2025. Retrieved July 14, 2025.
8. ↑ Masters, Jeff; Henson, Bob (July 5, 2025). "Devastating flash floods slam Texas Hill Country; Tropical Storm Chantal heads for Carolinas". New Haven, Connecticut: Yale Climate Connection. https://yaleclimateconnections.org/2025/07/devastating-flash-floods-slam-texas-hill-country-tropical-storm-chantal-heads-for-carolinas/.
9. ↑ Riess, Taylor Romine, Dalia Faheid, Hanna Park, Laura Sharman, Alaa Elassar, Tori B. Powell, Rebekah (July 5, 2025). "Live updates: Rescuers search for over 20 girls from Texas camp as flooding death toll rises to 32". https://www.cnn.com/weather/live-news/texas-flooding-07-05-2025-hnk.
10. ↑ Mistry, Ishani (July 7, 2025). "Weather tracker: supercharged storms hit Texas's 'Flash Flood Alley'". The Guardian. https://www.theguardian.com/environment/2025/jul/07/weather-tracker-texas-flash-floods-storm-barry.

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Cyclones and anticyclones of the world (Centers of action)

Concepts|

* Anticyclonic storm
* Storm
* High-pressure area
* Low-pressure area
* Rapid intensification
* Central dense overcast
* Annular tropical cyclone
* Bar (tropical cyclone)
* Superstorm
* Hypercane

Anticyclone|

| Northern Hemisphere|

* North Polar High
* Siberian High
* Azores High
* North American High
* North Pacific High
* Ridiculously Resilient Ridge
* Subtropical ridge

|

Southern Hemisphere|

* South Polar High
* South Atlantic High
* South Pacific High
* Kalahari High
* Subtropical ridge

Cyclone|

| Synoptic scale|

| Surface-based|

| Polar|

* North Polar low
* South Polar low

|

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* e

Extratropical cyclones

Concepts|

* Anticyclonic storm
* Storm
* Cyclone
* Post-tropical cyclone
* Low-pressure area
* Weather bomb
* Sting jet
* List
* Rainband

Northern Hemisphere|

| North America|

| Continental|

| Lee Cyclone|

* Alberta clipper
* Colorado low
* Great basin low

|

Other|

* Panhandle hook
* Witch of November

Oceanic|

* Aleutian Low
* Hatteras low
* Nor'easter
* Gulf low
* Pacific Northwest windstorm

Europe|

* v
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* e

European windstorms

Historical|

* Grote Mandrenke
* Burchardi flood
* Great Storm of 1703
* Great Storm of 1824
* Night of the Big Wind
* Moray Firth fishing disaster
* Tay Bridge disaster
* Eyemouth disaster

20th century|

* Iberia 1941
* North Sea flood of 1953
* Hurricane Debbie 1961
* North Sea flood of 1962
* 1968 Scotland storm
* Quimburga 1972
* Gale of January 1976
* December 1981 windstorm
* Ex-Hurricane Charley 1986
* Great Storm of 1987
* Burns' Day storm 1990
* New Year's Day Storm 1992
* Braer Storm of January 1993
* Christmas Eve storm 1997
* Boxing Day Storm of 1998
* Anatol 1999
* Lothar and Martin 1999

2000s|

* Oratia 2000
* Jeanett 2002
* Gudrun 2005
* Per 2007
* Kyrill 2007
* Emma 2008
* Klaus 2009
* Xynthia 2010
* Berit 2011
* Friedhelm/Bawbag 2011
* Joachim 2011
* Dagmar 2011
* Andrea 2012
* St Jude 2013
* Xaver 2013
* Dirk 2013
* Tini 2014
* Elon and Felix 2015
* Niklas 2015
* Egon 2017
* Thomas (Doris) 2017
* Zeus 2017
* Xavier 2017
* Ophelia 2017
* Herwart 2017
* Eleanor (Burglind) 2018
* Friederike (David) 2018

2015–present|

* 2015–16
* 2016–17
* 2017–18
* 2018–19
* 2019–20

See also|

* List of European windstorms
* List of atmospheric pressure records in Europe

Other|

* Black Sea storms
* Icelandic Low
* Genoa low

Asia|

* Western Disturbance
* Continental North Asian storms
* East Asian-northwest Pacific storms

Other areas|

* Arctic
* Kona storm

Southern Hemisphere|

| Australia|

* Australian east coast low
* Black nor'easter

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Other areas|

* Southern Ocean cyclone
* Sudestada

Subtropical|

* Kona storm
* Australian east coast Low
* Lake Huron cyclone
* Mediterranean tropical-like cyclone
* Thermal

Tropical
(List)|

| Northern Hemisphere|

* Atlantic hurricane
* Cape Verde hurricane
* Pacific hurricane
* Typhoon
* North Indian Ocean tropical cyclone
* Mediterranean tropical-like cyclone

|

Southern Hemisphere|

* South-West Indian Ocean tropical cyclone
* Australian region tropical cyclone
* South Pacific tropical cyclone
* South Atlantic tropical cyclone

Upper level|

* Cold-core low
* Polar vortex
* Upper tropospheric cyclonic vortex

Mesoscale|

| Mesoscale ocean eddies|

* Catalina eddy
* Haida Eddies

|

Mesoscale convective system|

* Wake Low
* Mesohigh
* Mesoscale convective vortex
* Line echo wave pattern

Whirlwind|

| Major|

* Mesocyclone
* Supercell
* Low-topped supercell
* Wall cloud
* Funnel cloud
* Tornado
* Multiple-vortex tornado
* Satellite tornado
* Anticyclonic tornado
* Landspout
* Waterspout

|

Minor|

* Gustnado
* Dust devil
* Steam devil
* Fire whirl

## External links and sources

* Forecasting MCC's - Hydrometeorological Prediction Center
* MCC description - Pennsylvania State University
* MCC description - University of Illinois
* MCC page - UCAR
* NOAA Glossary

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