Severe Weather Watcher Handbook

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Thunder and lightning are good severe indicators when combined with other observations. An active core will have the most intense lightning on the updraft side of the core,with multiple flashes and deep booms.With rain this is not unusual, but if vicious lightning occurs without any precipitation or only a few hailstones, a very dark, low cloud deck,and no wind - beware! You are under the explosive main updraft and could face a tornado without warning.

A soft, roaring sound can sometimes be heard near severe storms. This is usually caused by large hailstones hitting the ground and/or colliding in mid-air a short distance away. A similar "windy roar" can occur with a tornado,especially if swirling debris is involved. These situations will be quite rare,but should always be reported as a precaution.

How you can tell what's coming

If you're not sure what kind of a storm is approaching or cannot easily tell what you are looking at, there is another way you can understand the event. What you experience can usually be divided into one of two opposite descriptions of the storm's effect on you as it moves in. In a worst-first storm, the worst weather (heaviest rain, hail, lightning and wind) will be concentrated along the gust front near the beginning of what you experience. This storm complex regenerates on its forward side, along the gust front. By comparison, a worst-last storm begins slowly but becomes worse with time, culminating in large hail or even a tornado just before the end. Here, the storm regenerates along the flanking line at the back, as most storms do. The first-last distinction, based entirely on what you experience as a storm moves overhead, can help you decide where and when the greatest severe risks will be. Many of the damaging straight-line wind events occur with worst-first storms, while most of the large hail and strong tornadoes happen with worst - last storms. In most cases the severe version of either one is a supercell storm type.

When worst comes first

Worst-first storms are much more common, especially farther east and in mid-summer. When they approach, the sky darkens quickly as an ominous black cloud bank (the gust front) races toward you. Lightning bolts are common along it, or just behind it in the heavy rain curtain. The largest hail, when there is any, occurs near the beginning of the storm. Winds are breezy southerly, and then become briefly calm. As the gust front passes overhead, the temperature drops abruptly and a cold W-NW wind sweeps in. When the gust front is separated from the rainwall, very strong winds may occur before the rest of the storm gets to you. At other times the strongest winds accompany the arrival of the heavy rain and the greatest risk for damage occurs within the deluge. After a short period of severe conditions, the storm diminishes gradually and will pose no further risk to you.

Quick-thinking checklist

It's easy to talk about ideal conditions and typical examples,but reality has a way of muddying the picture.Exceptions abound:in the location of expected features,in their appearance (they may be only partially formed)or in the timing of the changes you witness.So,once you see a storm and know which way it is moving,your simplest strategy for making sense of the confusing scene before you is to check out these things first:
- The motion of scud tells you what the surface wind is doing.Horizontal motion is with outflow, upward motion is into new updrafts,and scud gathering below or attaching to the rainfree base is a developing lowering (if rotating,then it is a wall cloud).Very low scud advancing quickly below a dark cloud bank is a sharp gust front with strong winds.
- Check the temperature and wind .If it is warm and windy,look west (storm still coming);if it is calm out,look overhead for rotation;and if it is cool and windy . and persists (not just a brief gust or shower). the storm . s area of concern has passed or is to your south and moving by.
- Find the dark and light areasin the sky.All updraft locations will have dark bases while lighter areas are thinner clouds or precipitation indicating downdrafts of no concern.
- Check where the most frequent lightning bolts are .They occur just ahead of the strongest updraft core.

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