Mesoscale Analysis

A very important part of severe thunderstorm forecasting is analyzing the mesoscale, which is a step smaller than the synoptic scale features in the previous lessons. While the previous lessons have focused on large-scale features such as the jet stream, this lesson will focus on more of a regional view of meteorological variables relating to severe weather. This scale includes most convective systems, including complexes of thunderstorms and individual thunderstorms.

Environmental Assessment

The Storm Prediction Center (SPC) operates an excellent mesoanalysis page displaying dozens of meteorological variables in a semi-regional view. Below is an example of SPC mesoanalysis during a severe weather outbreak in the central United States.

The mesoanalysis above shows a surface low pressure system along the border between Colorado and Kansas, where there is a minimum in pressure below 992 millibars. The surface winds can also show surface boundaries, which may provide the lift for severe weather to initiate. Notice how the wind barbs in far western Kansas are from the south-southwest while the wind barbs in central Kansas are from the south-southeast. This means that air will converge along the surface in far western Kansas as the air from both sides runs into each other. This will force air upwards and create the initial updrafts, which will become thunderstorms. This process is often referred to as convective initiation, and it’s something that forecasters look for to determine where severe weather outbreaks are imminently about to occur. Most of the time, convective initiation can be seen on satellite products before radar products as clouds often do not reflect the radar beam. The radar beam is reflected by precipitation and other objects of a similar size, and by this point thunderstorms may be mature enough to already be producing severe weather. This stresses the importance of using satellite imagery to recognize convective initiation and understand the ongoing severe weather threat.

In the video in the above tweet, the ongoing thunderstorm in eastern Oklahoma can be seen by satellite and radar, whereas the developing thunderstorm in north-central Oklahoma may not be resolved by radar at the time of this satellite imagery.

Many other variables at different heights can be assessed by using mesoscale analysis. For example, instability can be measured by CAPE, and mesoanalysis can reveal the largest CAPE values, which may be more supportive of severe weather. In addition, the level at which condensation forms into clouds (referred to as the LCL or lifted condensation level) can be shown on mesoanalysis. Lower LCL values may indicate a region more favorable for tornadoes to form as it is easier for them to reach the ground.

Mesoanalysis Resources

The best resource for mesoscale analysis is operated by the SPC. You can find their mesoanalysis page here: spc.noaa.gov/exper/mesoanalysis/. At that link, you can click on a region to get real-time mesoanalysis for any area of interest within the United States. During or just before severe weather outbreaks, the SPC will publish their own mesoscale discussions with expert commentary at this page here: spc.noaa.gov/products/md/.