Land-based mesoscale tempest

A land-based mesoscale tempest is a land-based convective system defined by rapid formation, a central dense overcast-type structure at the centre with significantly more intense convection and rainfall than the outer portions, and intensity ranging from near-unnoticeable light rain with virtually no wind to Category 5 hurricane intensity, and forward speeds ranging from virtually zero to more than 50 MPH.

Formation
On hypothetical planets with different atmospheric systems to Earth, LBMTs form during the formation stage of a cumulonimbus cloud or formation stage MCSes (excluding tropical cyclones and polar lows).

During the formation stage, wind shear forcing on a cumulonimbus cloud or formation stage thunderstorm can cause the system's convection to be pushed into a circular shape, which then causes the thunderstorm's convection to mostly dissipate.

After this, given enough moisture in the air, a very weak mesocyclone may form. This causes the cloud top temperatures and atmospheric pressures to slowly drop in the system as the mesocyclone starts to rotate faster. The most intense convection forms under the mesocyclone, creating the centre, while shallower convection surrounds the MCS and potentially in the spiral bands of the proto-LBMT, which are formed by the mesocyclone not being a perfect cyclone.

Once the system is strong enough to meet the classifications outlined below it is declared an LBMT.

Properties and Structure
The average LBMT has a wind speed of 17 mph (27 kph), an average rain rate of 0.22 in/hr (5.58 mph) at the centre, a forward speed of 30 mph, and a lifespan of approximately ten hours.

LBMTs have a low atmospheric pressure (with the pressure gradient tightening as the centre is reached), rainfall, and cold cloud tops. Stronger systems can have lightning, hail, and rarely tornadoes. Some of the strongest systems ever recorded have extremely small eye-like features, sometimes as small as 30 metres, although wind speeds of Category 5 hurricane caliber are often only reached for 10 to 30 minutes at a time.

The average weak LBMT is 1 to 3 miles (1.6 to 4.8 km) wide, although systems as large as 100 mi (160 km) and as small as 300 metres (984 ft; 0.3 km; 0.18 mi) have been recorded. LBMTs grow as they strengthen, although systems wider than 15 miles (24.1 km) are rare,

A typical LBMT is consisted of an exterior region of shallow convection, potentially with spiral bands harboring somewhat deeper convection, with a centre region of moderate or deeper convection located in the centre, spinning at anywhere from 6-8 MPH to over 250 MPH.

A system is only considered an LBMT if:

- The system has developed from either a cumulonimbus cloud system or a MCS, usually formation stage mutlicell or supercell thunderstorms and/or squall lines

- The convective core is spinning faster than 5 mph (8 km/h)

- The lowest cloud top temperature is lower than 0°C (32°F)

- At least 1 mm per hour (0.04 inches per hour) of rain is falling in the centre, per radar or ground observer measurement.

LBMTs can last for a very long time if sufficient moisture is present to power the convection. Some systems have even persisted over water for some time, although they almost exclusively form over land. Persistence times have been recorded from as low as two hours to several weeks, the average time being around six hours in non-tropical climates and two days in subtropical and tropical climates, with systems reaching wind speeds above 25 mph (40 km/h) having a far longer average lifespan of three days in non-tropical climates and five days in subtropical or tropical climates. LBMTs can strengthen and weaken extremely quickly if the conditions surrounding it change.

Effects
Effects can range from none to extreme, depending on the LBMT's intensity. Intense systems can have winds in excess of 60 mph (100 km/h) or more, drop rain at violent rates, cause flash flooding, drop hen-egg-size (2 inches; 5.08 cm) or more hail, and in rare instances spawn weak (EF0-low-end EF1) tornadoes. They can be absorbed by landfalling hurricanes and tropical storms if they are near water, which under very rare conditions can spawn a supercell thunderstorm inside one of the spiral bands of the hurricane, potentially causing extremely strong tornadoes.

Damages from LBMT's have ranged from $0 to $2.7 billion.

Radar values
LBMT : Whereever the system is an LBMT. Negative = is not, Positive = is.

W: Local wind speed at the centre of the LBMT.

EW: Environmental wind speed outside of the LBMT.

Pressure: Local pressure in the LBMT. Generally relative to the environmental pressure, unless the system is strong, where it is absolute.

Lightn/Lightning = Is lightning present

If Lightning is present:

Amount: The estimated amount of lightning, in strikes/minute.

Hail: If hail is dropping and if so the observed size.

Torn: If a tornado is present.

WS: Wind strength. x (W - EW) is the first number, with y (the difference between W and W - EW) as the second, in the format x/y.

ERR = Estimated rain rate in in/hr or mm/hr.

Max DBZ = Maximum reflectivity of the system.

Min CTT = Minimum CTTs of the system.