Where to stand
- View
The safe viewing quadrant of a classic supercell, why core-punching is prohibited, and what is inside the notch that looks so inviting.
In this lesson you will
- Identify the safe viewing quadrant of a classic supercell and explain why it is that one.
- Define core-punching and state the hazards that prohibit it.
- Describe the RFD, the hook and notch, and the bear's cage.
- Account for right-moving supercell motion when positioning.
The quadrant
For a classic Northern Hemisphere supercell, the position the NWS field guide describes is to the south or south-east of the updraft base. Three reasons, and they are worth knowing separately because in a given storm one of them may not hold.
- Contrast. A developing tornado is dark against lighter sky from this side. From the other side it is a silhouette inside rain, which is no view at all.
- Out of the hail. The precipitation and hail core sits on the other flank. Being under it is lesson 6 and a broken windshield.
- An escape route that leads away. South, generally, away from a storm that is generally moving north-east. An escape route pointing into the storm is decoration.
Lightning. The field guide says so directly, and lesson 3 is why. The safe viewing position is safe from the hail and the circulation, and it is fully exposed to the hazard that is second on the list in lesson 1. The quadrant is not a safe place to stand outside a vehicle.
The storm may not go where you think
A supercell frequently moves to the right of the mean winds aloft, sometimes well to the right, because its rotation makes it propagate rather than simply drift. Module 2 covers the mechanism. What it means here is that your safe quadrant is defined relative to the storm and the storm is allowed to turn.
The field guide notes that a quickly increasing east or south-east wind can signal tornado development. You are standing in the inflow. If the air going into the storm suddenly gets a lot stronger, the storm is getting a lot better at drawing it in, and you are in the part of the storm that feeds it.
Core-punching
Driving through the precipitation and hail core to get to the other side of a storm. It is the fastest way between two points and it is prohibited here for four reasons that all arrive at once.
- Very large hail, which takes out a windshield and leaves you immobilised inside a severe storm with no glass.
- Zero visibility, on a road that is wet or covered in hail, at whatever speed you were doing when it closed in.
- You can drive out of the rain directly into the tornado, because the thing on the other side of a core is often the circulation.
- You cannot see what is coming the other way, and other people are doing the same thing.
You can enter a core without meaning to. The instruction is specific: if rain turns to hail and the hail is increasing in size, stop, back up, and get out. Back the way you came, which you know is passable. Do not push forward hoping it is nearly over, because increasing hail size means you are heading further in rather than out.
The RFD and the bear's cage
- Rear-flank downdraft
- Dry or wet air descending on the back of the storm and wrapping around the circulation. A wet RFD may carry sustained winds over 100 mph and hail larger than baseballs, and it obscures any tornado inside it. The RFD can do more damage than the tornado does.
- The bear's cage
- The notch between the precipitation core and the updraft, where the hook echo shows on radar. It is where the circulation is, wrapped in rain and hail, with no visibility and frequently no way out. On radar it looks like the most interesting place on the storm. On the ground it is the worst place you can be.
Do not attempt to drive through a wet RFD for a better view. There is no better view inside it, which is the entire point: it is opaque. What is in there is wind that will move your vehicle and hail that will blind it, and possibly a tornado you will not see until it is on you.
Which brings back the distance argument
Every hazard in this lesson is a hazard of proximity, and the temptation behind all of them is the belief that a closer look produces a better report. It does not. Lesson 1 covered why, and this is where it becomes operational: the report does not improve, and distance is free accuracy insurance.
Check yourself
You are south-east of a classic supercell with a good view of the updraft base. The inflow wind at your back increases sharply and the storm appears to be turning right, toward you. What now?
- Leave along your pre-planned escape route now, and re-establish position from further away
- Hold position. South-east is the safe quadrant for a classic supercell
- Move north through the precipitation to get ahead of the turn
- Move into the notch for a clearer view of the developing circulation
Hint
The quadrant is defined relative to the storm, not to the compass.
Answer
Leave along your pre-planned escape route now, and re-establish position from further away
The safe quadrant moves when the storm does, and a right turn plus sharply increasing inflow is both a positioning problem and a possible tornado cue. Option three is a core punch. Option four is the bear's cage. Leaving early costs you a view and nothing else.