Products built from many radars

One grid instead of many radars

Every product so far has been from one radar, with that radar's cone of silenceThe column of sky directly above a radar that it cannot see into, because the antenna cannot tilt straight up. A storm passing overhead is in the worst possible place to be observed., its blockages and its range limits. MRMSMulti-Radar Multi-SensorThe system that merges every radar in the network, plus gauges, satellite and model data, onto one grid and derives products from it including rainfall rate and accumulated precipitation estimates every two minutes., the multi-radar multi-sensor system, merges the whole network plus Canadian radars, gauges, satellite and model data onto a single national grid and updates it about every two minutes.

MESHMaximum Estimated Size of HailA radar-derived estimate of the largest hail a storm is producing. It describes hail in the cloud, so it can disagree with what actually reaches the ground., and the bias you must carry with it

Module 5 introduced the maximum estimated size of hail as a radar proxy. Here is the operational picture, and the caveat is the important half.

• It is an estimate derived from the reflectivityHow much of the radar pulse bounced back from whatever the beam was passing through on that tilt. It is the familiar green-to-red precipitation picture, and it describes what is up in the beam, not what is reaching the ground. profile above the freezing levelThe height at which the air reaches 0 °C. A hailstone has to survive the fall from there to the ground, so a high freezing level means more melting and smaller hail at the surface.. It is not a measurement of a stone and nobody claims it is.
• It underestimates the largest hail, and this is documented rather than suspected. Skill falls away badly for the very biggest stones, partly because hail bigger than the radar wavelength scatters in ways the relationship does not capture.
• It has known failure modes: highly tilted storms in strong deep-layer shearChange of wind with height, measured as the difference between the wind at the top and bottom of a layer. It is not needed to make a thunderstorm and it decides almost everything about what kind you get., left-moving supercells, and storms with a very large bounded weak echo region.
• Around 29 to 30 mm is about the most skillful threshold for separating severe from sub-severe hail, which is a different and more achievable task than sizing a stone.

Azimuthal shearA calculated measure of how sharply velocity changes across the beam, used to find rotation automatically. A diagnostic rather than a tornado observation, and it is artificially inflated very close to the radar. and rotation tracks

Azimuthal shear

A calculated measure of how sharply velocityThe radar product showing how fast the rain, hail and debris in the beam are moving toward or away from the radar. Only motion along the beam is measured, and rotation shows up here as inbound and outbound speeds side by side. changes across the beam, computed in near-surface and mid-level layers. It is a way of finding rotation automatically rather than by eye.

Rotation tracks

Azimuthal shear accumulated over time and painted as a swath on a map. Extremely useful after the fact: it shows where rotation went and how it varied, and because it is built on the merged grid it partly compensates for cones of silence, beam broadening and terrain blockage.

Probabilistic products

You may hear ProbSevereA model fusing radar, satellite, lightning and model data into a probability that a storm will produce severe weather shortly. A forecaster tool, and a probability that does not verify was not wrong. mentioned on a net. It is a model that fuses radar, satellite, lightning and model data into a probability that a storm will produce severe weather in the near future, now in its third version. It is a forecaster tool and this course prints no thresholds from it.

What this platform does with all of it

This is the same principle modules 5, 6 and 7 each arrived at, and this lesson is where the machinery behind it becomes visible. Reports submitted here are checked for plausibility, not exactness, against these products.

• A convective reflectivity gate, so a severe report during obvious convection is corroborated.
• A hail estimate gate, using a MESH threshold around the severe discrimination figure above, because that is the task MESH is actually good at.
• A rotation gate, using azimuthal shear, for reports of rotation.