Summer severe weather can sneak up unexpectedly, but in many cases there are clues. Days that are forecast to have extremely high temperatures and high humidities can be days when pulse thunderstorms will develop. These are tough situations for you and the forecaster. These are days when the forecaster knows that the airmass can explode into clusters of small to medium thunderstorm cells which develop individually, but at times merge into larger storms. Where they pop up is the big question. We like to use the following analogy to describe this situation. Imagine putting a pot of water on the stove and turning the burner to high. We know that eventually the pot will begin to bubble but determining where the first bubble will occur in the pot is almost impossible. Watches for these types of storms have shorter lead times 1-3 hours.

Pay attention to forecasts and weather statements. Listen to evening forecasts for clues on next day weather.

In other situations, the clues are much more definite. These might be days where we know areas upstream, (sometimes the previous day from American soil) have had severe weather outbreaks. They quite often are associated with low pressure systems that move across our region. In some cases we may see lengthy outbreaks of thunderstorms ahead, along and behind the warm front. Followed in many cases is the cold front which often produces more thunderstorms. These systems are usually easier to track using satellite, radar, spotters and weather watchers. Once again, pay attention to forecasts, special statements and watches and warnings. On days like these, watches are usually issued with a lead time of 1-6 hours giving most people ample time to prepare.

Most storms in Ontario are HP (high precipitation) super-cells which produce a lot of rain and hail. They can be particularly dangerous because Environment Canada can't see what is really happening on the ground. Also, storm spotting in Ontario presents some challenges. Many of the most active days will be hot, hazy, and humid, making it hard to see in hilly terrain, areas with a tree line, and heavily built up areas.

Look at the special weather statements which are issued from May to September and are available under the weather “Warnings” link at www.weatheroffice.gc.ca. This section of Environment Canada's Web site discusses the potential for severe thunderstorms for the coming day and the next day in Ontario. The Warnings battle-board refreshes automatically every 10 minutes.

When the Ontario Storm Prediction Centre (OSPC) issues a Severe Storm Watch, it typically gives a 3-6 hrs lead time. Environment Canada will try to issue a Watch by 11 AM. Observe and monitor cloud formations over the course of the day and check radar and satellite information. Storms generally move in a west to east direction and Environment Canada adds storm movement speed to the wind speed.

When a Severe Storm Warning is issued, it gives enough time to put a plan into action.

Remember, no two thunderstorms are alike and experience comes from watching skies.

Spotting is best done from a distance, as safety is always a primary concern. Whether with the naked eye or binoculars, the distance also offers a better overall view of the immediate conditions. It is important to get the whole picture, something you can't do when too close to a storm.

Three basic ingredients of a Storm:

• Good supply of low level moisture (fuel)
• Unstable atmosphere
• Kicker, such as a cold front (could be from cooler lake air) meeting day time heating

Elements of a Severe Storm:

• Large hail, 2cm or larger
• Very heavy rain (flooding potential)
• Damaging winds with gusts of 90km/hr or more
• Tornadoes

Click here to see what to look for in a storm.

Looking at a storm, the hail shaft can look milky beside the dark, rainy area. Look for striations (banding or barber pole effect) in a thunderstorm flow. If you see wall clouds, or scud, look for slow rotation. Watch for spiraling into cloud base. Clouds that seem to form out of thin air then move upward, these are only signs of rotation, not a tornado.

Knowing where the action is, such as up front or in the rear of the formation, is important as a spotter. The front of a storm has the dark area, rainfall, a downward motion, and possibly hail. Lowering beneath the base of a cloud in the rain-free area could have dropping of cloud occurring, creating a wall cloud.

Funnel vs. tornado

A tornado is a tightly spinning column of air in contact with the ground beneath a thunderstorm cloud. The rotating column is physically connected to the cloud base or wall cloud and is often visible as a cloud-filled "condensation funnel". If the air is dry enough, the tornado may only appear as a swirl of dirt on the ground without a visible connection to the cloud above.

In contrast, a funnel cloud spins in mid-air without touching the ground. To tell the difference between a funnel cloud and a tornado, look for swirling dust or debris near the ground under the funnel. If present, then a tornado is occurring. Most tornadoes and funnel clouds are preceded by and form approximately in the middle of an accompanying rotating wall cloud.

Sometimes there are false funnels, they are cloud formations that look suspicious but after watching them they may just be just clouds. Check to see if it is in the right area of the storm. Tornadoes are not on leading edge but gustnadoes are, that is where they are born.

To learn more about the different parts of a storm and what to look for, click here to read our Weather Glossary.