Diagnosis

Once you have confidently identified a "Hook Echo" signature, this section will help you estimate the storm severity associated with it. Generally, the spatial and temporal scales of a signature are loosely related to the updraft strength. In other words, the larger and/or more long–lived the signature, the stronger the updraft that produced it. In velocity-based signatures, updraft severity can usually also be gauged by the magnitude of the measured radial velocities. Examining a storm's overall temporal evolution will suggest whether the storm is becoming more or less severe. Radar signatures and associated storm developments can also be time-shifted relative to each other, as is the case in supercell tornadoes that occur during the collapse of the parent storm.

When comparing signatures to diagnose relative severity, keep in mind that it is assumed that signatures are sampled at equal ranges from the radar. Otherwise, a storm sampled at greater range (with a wider beam) can appear to be weak and/or weakening, while a storm sampled at a closer range (with a narrower beam) can appear to be strong and/or strengthening.

Degree of Severity

Longevity of the Hook Echo

  • A persistent Hook Echo is a proxy for thunderstorm severity.

Time Evolution of Hook Echo Curvature

  • Radar scans with high time resolution show that some Hook Echoes can complete part of or more than a full revolution around the low-level mesoscyclone, indicative of stronger low-level rotation in the presence of a supply of falling precipitation.

Considering all these aspects of a Hook Echo signature will help to determine overall whether you are dealing with a significant signature. A Hook Echo is one of the few signatures that could influence you directly into issuing a severe thunderstorm warning, based on the tight connection to a supercellular thunderstorm. Generally, radar information should never be used in isolation and should always be considered in conjunction with the near storm environment and any reports.

Most Likely Convective Hazards

If a thunderstorm has been determined to be severe and possesses a Hook Echo of significance, the following severe weather should be considered to be included in the severe thunderstorm warning:

  • Damaging winds - A Hook Echo is a representation of a strong updraft, with potential to produce a strong downdraft. Destructive winds should be considered over damaging winds due to the supercellular classification.
  • Large hail - A strong updraft has the potential to produce large hail as it is likely to supply plenty of supercooled liquid to the -10°C to -30°C hail growth layer.
  • Heavy rainfall resulting in flash flooding - A particularly strong updraft has the potential to produce large amounts of precipitation, accumulating and falling as heavy rainfall resulting in flash flooding. For supercells, slower-moving and larger storms are more likely to produce flash flooding
  • Tornado - Due to the indication the thunderstorm is supercellular, tornadoes are possible and therefore should be at least considered, especially in environments that combine high low-level relative humidity with strong 0-1km shear.

See Conceptual Models for more details on why particular severe weather should be included.