Using Alerua

How to use the Alerua radar map

Every control on the radar page, and what the tilts, color styles and clutter filter do to the picture.

AleruaOctober 25, 20262 min read

The radar page is at alerua.com/map.

The controls

Product. Picks the view: reflectivity, velocity, correlation coefficient and seven more.
Style. Classic, Twilight, Frosted or Stormy colors, and the base map.
Flat or 3D. The flat map, or the scan as a 3D volume (3D opens in the app).
Share. Shares the loop as an animated picture.
Settings. Tilt, loop length and speed, the clutter filter, warnings, storm tracks and wind.

Tilts: what the beam can and can’t see

A radar can’t look along the ground. The beam leaves the dish tilted slightly upward and the Earth curves away beneath it, so the farther the beam travels, the higher it is. It also spreads: one degree wide is about 0.7 mile across at 40 miles. In Alerua, Settings, Elevation steps through the tilts, starting at the lowest.

Here is the El Reno storm, about 41 miles from the Norman radar, at three tilts within three minutes of each other.

Reflectivity of the El Reno storm at the 0.5 degree tilt, with the hook echo visible — The hook shows.

Reflectivity of the El Reno storm at the 3.2 degree tilt, about 13,000 feet up — The middle of the storm. The hook is fading.

Reflectivity of the El Reno storm at the 6.5 degree tilt, about 25,000 feet up, a rounded core with a weaker center — High in the storm: no hook, and the strongest echo gathers into a rounded core with a weaker center.

Where the lowest beam (0.5°) is, by distance from the radar
Distance	Beam height	Beam width
25 km (16 mi)	0.25 km (840 ft)	0.4 km (0.3 mi)
50 km (31 mi)	0.58 km (1,900 ft)	0.9 km (0.5 mi)
100 km (62 mi)	1.5 km (4,800 ft)	1.8 km (1.1 mi)
150 km (93 mi)	2.6 km (8,600 ft)	2.6 km (1.6 mi)
200 km (124 mi)	4.1 km (13,400 ft)	3.5 km (2.2 mi)
230 km (143 mi)	5.1 km (16,800 ft)	4.0 km (2.5 mi)

So a far storm is seen from higher up: low features such as hooks get hard to see at long range, and shallow rain can pass under the lowest beam. Far storms are also blurrier, because the beam is wider than what you are looking for. Right over the radar is a blind cone, because the highest tilt, 19.5°, can’t look straight up. That is why forecasters use the radar closest to a storm.

Flat or 3D

Stack all the tilts and you get the storm as a volume. That is what Alerua’s 3D view draws, in the iPhone and Mac apps.

3D radar volume of the El Reno supercell built from 14 tilts, with Norman and Oklahoma City labeled — Heights are stretched so the layers are easier to see.

Radar color styles: why the same storm can look different

Every radar app picks its own palette, so read the scale before trusting a color. Alerua has four; three are shown here on the same scan.

The El Reno hook in Alerua’s Classic colors — **Reflectivity** dBZ520355065
The familiar rainbow. Green is moderate rain, red is the core.

The El Reno hook in Alerua’s Twilight colors, dark blue through white to violet — **Reflectivity** dBZ520355065
Alerua’s own palette. Faint echoes are dark, moderate rain brightens toward white at about 45 dBZ, and the strongest cores turn violet.

The El Reno hook in Alerua’s Stormy look, in gray — **Reflectivity** dBZ · grey1025405059+
Gray, like cloud. Darker and denser means stronger.

Settings

Elevation picks the tilt.
Filter ground clutter, on by default, hides gates with a correlation coefficient under 0.8. That clears birds, insects and clutter, and it also hides tornado debris.
Warnings draws the National Weather Service’s tornado and severe thunderstorm polygons over the radar.
Loop length and speed, storm tracks and wind are here too.