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2011 Severe Weather Awareness Week in Maine


May 2nd through May 6th is Severe Weather Awareness Week in New England. The week has been divided into specialized topics each day. These topics appear on this page, for your convenience.

Follow these links for more weather safety and educational material. A variety of brochures can be found here. For example, their color brochure, titled Thunderstorms, Tornadoes, Lightning—Nature's Most Violent Storms, includes the topic "Tornado Safety Information for Schools." There are many more valuable goodies on that page, including info tailored for kids and families. Please check it out!

Table of Contents

 
Severe Weather Terminology

With severe weather season rapidly approaching, it is a good idea to refresh your memory in regard to severe weather terminology. In Maine, severe weather season generally runs from May through August. In northern Maine, mid-June to around August 1 is the most active period for severe local storms.

The term watch, when used in conjunction with tornado or severe thunderstorms, means that tornadoes or severe thunderstorms are possible. Watches are usually in effect for several hours and indicate that atmospheric conditions are favorable for severe storms to develop. When a watch is in effect, you should keep your eye to the sky and make plans for what you need to do if severe weather occurs.

The term warning means that either a severe thunderstorm or tornado is imminent or is already occurring. Warnings are usually in effect for 1 hour or less. If a warning is issued for your area, take action immediately.

A severe thunderstorm is any thunderstorm that produces winds of 58 mph or more and/or hail of 1inch in diameter or greater. Severe thunderstorms can produce damaging straight line winds that affect a relatively large area. These are usually associated with rapidly moving squall lines. Severe thunderstorms can also produce microbursts, which are damaging straight line winds that affect a relatively small area. In both cases, winds can exceed 100 mph.

A tornado is a violently rotating column of air in contact with the ground. The funnel usually descends from the base of a severe thunderstorm. They are usually wedge shaped with the narrowest end at the ground. Tornado witnesses have heard a "roaring" sound similar to a freight train. Tornadoes vary in intensity. Weak tornadoes have winds less than 100 mph while violent tornadoes have winds in excess of 200 mph.

A funnel cloud is a violently rotating column of air that descends from the base of a thunderstorm but does not make contact with the ground. A tornado usually passes through the funnel cloud stage during its development and dissipation. Not all funnel clouds become tornadoes, but you should still take cover if one approaches.

 
Severe Thunderstorms

By definition, a severe thunderstorm is one which produces wind gusts of 58 mph or more, or hail 1 inch in diameter or greater. Severe thunderstorms can also produce tornadoes.

In New England, severe thunderstorms are not uncommon during the summer.  Every year, the National Weather Service gets numerous reports of wind and hail damage throughout Maine. Severe thunderstorm winds down trees and branches onto homes, buildings, vehicles, and power lines.  Scattered power outages are often the result of lightning or wind-fallen trees and branches.  Also, wind-driven hail from thunderstorms flattens and/or damages crops.  On rare occasions, large hailstones damage homes, buildings, and vehicles. In addition to the falling trees and large hail, lightning also poses a significant threat to people, as well.

THUNDERSTORM WINDS, DOWNDRAFTS, DOWNBURSTS, AND MICROBURSTS

During the development of a thunderstorm, warm air rises upward in the atmosphere (an updraft) causing the formation of clouds and precipitation.  As a thunderstorm matures, cool, precipitation-laden air sinks downward through the atmosphere (a DOWNDRAFT).  When a downdraft reaches the ground it spreads out causing the cool, gusty wind that often accompanies a thunderstorm.

In some thunderstorms, intense downdrafts develop.  When these downdrafts reach the ground, they spread out very quickly causing strong and often damaging winds at the ground.  These intense downdrafts are called DOWNBURSTS and can cause significant wind damage over large areas.  In the case of downbursts, the damage is generally referred to as straight-line wind damage since fallen trees generally line up in the same direction.  In Maine and New Hampshire, most thunderstorm wind damage is caused by downbursts.

A special type of downburst is the MICROBURST.  Microbursts get their name because they generally affect a much smaller geographical area, but the winds in a microburst can be very intense.  Like the general downburst, most of the damage with microbursts lines up in one direction, although, there may be a tendency for the damage to radiate outward.  Microbursts are usually accompanied by heavy rain and/or hail and can have winds as strong as those in a small tornado.

Under certain atmospheric conditions, thunderstorms can begin to develop a circulation within the thunderstorm cloud.  These storms are often called MESO-CYCLONES because of the counter-clockwise circulation that develops within the storm.  The updrafts and downdrafts in these storms can persist for hours as the storm moves along its path.  Severe winds and hail are also more likely with meso-cyclones, and if the rotation within the storm becomes more intense, there is an increasing possibility that the storm might produce a tornado.  National Weather Service Doppler RADAR allows meteorologists to monitor air movement within these storms and to see the development and strength of any circulation within the storm.

HAIL

The circulation that accompanies a meso-cyclone is also a factor in HAIL formation.  Hail initially forms when liquid water droplets are carried upward by the updraft to a level where the droplets freeze.  Eventually, the small hail stone may begin to fall downward, only to be caught once again by the persistent updraft of a meso-cyclone.  Each time the hailstone goes through this process, it gets larger and heavier.  Eventually, the hailstone will be blown away from the updraft or will become too heavy for the updraft to support and the hailstone will fall to the ground.

In Maine, hail is fairly common during well-developed summertime thunderstorms.  Although most hail that reaches the ground in northern New England is an inch or less in diameter, occasionally hailstones over 2 inches in diameter will fall.  Large hailstones can fall at speeds faster than 100 mph and can do considerable damage to cars, homes, and buildings, and can be a significant threat to people, as well.

For both severe winds (58 mph or greater) and large hail (1 inch diameter or greater), the National Weather Service issues SEVERE THUNDERSTORM WATCHES and WARNINGS. A WATCH indicates that atmospheric conditions are favorable for the development of severe weather in and near the WATCH area. A WARNING indicates that severe weather is imminent or is already occurring. If you hear a WARNING for your area, be prepared to seek a safe shelter if you are in the path of the storm.

 

Severe Weather Preparedness and Safety

How to Prepare Your Family for Severe Weather

Severe weather will happen, and eventually it will affect you in some way, so the best you can do is to be prepared. In some cases, there are no easy answers to the many questions and problems that can arise. You simply have to prepare for your situation with the resources you have available. The first thing to do is develop a preparedness plan. But before you get into the details of your plan, there are some initial steps you should take.

Severe thunderstorms are a fact of life. These storms can produce tornadoes, damaging wind gusts, large hail, and heavy rain that can produce flash flooding. At some point in your life, you will likely be faced with at least one of these hazards.

Step 1: Set up your plan.

Everyone should have a severe weather plan for their home. Likewise, businesses need to have a plan for the workplace. There will be similarities, but there will also be differences between the two. Following are some ideas that can be applied to both.

1. Establish who is responsible for the plan. Someone needs to be in charge. For a large workplace that runs several shifts, you may have several people responsible for the plan.

2. How will you receive weather warnings? NOAA Weather Radio is a great way to receive severe weather warnings from the National Weather Service. You can also get information from the commercial media, such as radio and television. The Internet is also a great way to get information. However, do not depend solely on one method. Have multiple ways to receive critical weather information.

3. If you receive a weather warning such that you need to activate your plan, how will you inform the people you are responsible for? In a home that should not be a problem, but in a large workplace you have to have a method for communicating the severe weather information to everyone present.

4. Establish shelters area in your home or workplace. Depending on the amount of people who need to be sheltered, multiple areas may be needed. If your home or building is in an area prone to flooding, you need to have an evacuation plan in place.

Step 2: Practice your plan!

Conduct drills and then review the drill to find strengths and weaknesses and make improvements where necessary. It is hard to foresee every circumstance, but drills can often bring out problems that were not previously seen.

Some things you can do to protect your family include:

• Have a family disaster plan. A plan will cover what to do, where to meet, and how to contact family members in the event of a fire or severe weather. Make sure all family members know about the family emergency plan. Give emergency information to babysitters and other caregivers.

• Put together an emergency supply kit for your home, for your office, your car, and one for your child at school. A kit should have bottled water, a radio with extra batteries, a flashlight, prescription medicine and first aid supplies.

• Purchase a generator for your home or business. A generator will provide heat during a power outage in cold weather. It will also keep your food from spoiling, and the lights on. A generator can keep life/safety/health equipment functioning (ventilators, oxygen, monitors, or insulin cooling) during a power outage. Remenber though to always follow the instructions when using a generator. For example, never use a generator in a closed structure. The engine gives off deadly carbon monoxide gas . Always place the generator outside.

• Make sure all family members know all possible ways to exit your home and where to meet outside the house. Keep all exits clear.

• Conduct a tornado, fire and earthquake drill once every six months.

• Choose a place for your family to meet after a disaster in case you are at work or school when the disaster happens.

• Know how to contact your children at their school or daycare and where you can pick them up after a disaster. Designate a specific person to pick up your child if you cannot. Make sure the school or daycare has the most current emergency release information.

• Have a tone-alert weather radio to receive severe weather warnings. Also have a portable radio with extra batteries in case there are power outages. This allows you to get the most current weather and emergency information quickly.

• Learn first aid and CPR.

• In the event of a flood, tornado or earthquake, learn how to shut off your water, gas and electricity. Know where to find the shut-off valves and switches.

• Keep a small amount of cash on hand. If the power is out, ATM machines won't work.

 

TORNADO SAFETY

IN HOMES OR SMALL BUILDINGS: Go to the basement (if available) or to an interior room on the lowest floor, such as a closet or bathroom. Upper floors are unsafe. If there is no time to descend, go to a closet, a small room with strong walls, or an inside hallway. Wrap yourself in overcoats or blankets to protect yourself from flying debris.

IN SCHOOLS, HOSPITALS, FACTORIES, OR SHOPPING CENTERS: Go to interior rooms and halls on the lowest floor. Stay away from glass enclosed places or areas with wide-span roofs such as auditoriums and warehouses. Crouch down and cover your head. Don't take shelter in halls that open to the south or the west. Centrally-located stairwells are good shelter.

IN HIGH-RISE BUILDINGS: Go to interior small rooms or halls. Stay away from exterior walls or glassy areas.

IN MOBILE HOMES: ABANDON THEM IMMEDIATELY! Most deaths occur in cars and mobile homes. If you are in either of those locations, leave them and go to a substantial structure or designated tornado shelter.

IN VEHICLES: IF POSSIBLE, DRIVE AWAY! If not, get into a sturdy shelter (building). As a last resort, you need to make a personal decision whether to ride it out in your car hunched down below the windows with your SEATBELT ON, or to lie flat in the nearest ditch or depression with your hands covering your head.

IF NO SUITABLE STRUCTURE IS NEARBY: Lie flat in the nearest ditch or depression and use your hands to cover your head. Be alert for flash floods.

DURING A TORNADO: Absolutely avoid buildings with large free-span roofs. Stay away from west and south walls. Remember, seek shelter on the lowest level, go to the smallest room, and center part of the building.

No matter where you are, do some advance planning, if possible. Identify protective areas you can get to in a hurry. Obtain a NOAA Weather Radio that will provide an alarm if a tornado watch or warning is in effect for your county. The key to tornado survival is to be prepared and to take immediate action when a warning is issued or when you spot a tornado. Remember, the actions you take during a tornado may save your life and the lives of your family.

 

HAIL SAFETY

Hail remains one of the most costly severe weather phenomena observed in the United States every year. Damage from hail not only occurs to crops, but also to homes, vehicles and businesses.

Hailstorms produce around $2 billion worth of property damage each year. Damaging hail the size of golf balls or larger occur with the strongest of all thunderstorms, and hail will usually accompany tornadic thunderstorms. Remain alert for severe thunderstorm warnings from the National Weather Service, and use this valuable information to protect your property from the threat of hail.

If caught outdoors during a hailstorm, seek shelter in a reinforced building as quickly as possible. The key to personal safety in a hailstorm is to protect yourself from the falling hailstones. Hail rarely kills people, but it can become a killer if precautions are not taken. In China in May of 1986, intense hail killed 100 people, injured 9000, and destroyed 35,000 homes.

 

DAMAGING WIND SAFETY

Damaging winds come in many forms, sometimes from squall lines of thunderstorms and other times in the form of downburst winds. The most frequently encountered type of damaging straight-line wind in a thunderstorm is that associated with the leading edge of the rain-cooled outflow, known as the gust front. Although most thunderstorm outflow winds range from 30 to 50 mph, on occasion these winds can exceed 60 mph. These outflow winds typically last 5 to 15 minutes. Sometimes, the strongest winds are not associated with the gust front, but rather occur behind the gust front in close proximity to the area of heaviest rain.

When these winds are potentially damaging to structures on the ground, or to aircraft in flight, these winds are referred to as downbursts. Dr. Theodore Fujita of the University of Chicago, is credited with discovering downbursts in the mid 1970s, following investigation of the crash of Eastern Airlines Flight 66 in New York. There are two types of downbursts: microbursts produce strong winds less than 2.5 miles in diameter, while macrobursts result in strong winds over an area 2.5 miles in diameter or larger. Downbursts occur with all types of thunderstorms, from single cells to supercells. In fact, the most damaging downbursts often are produced by weaker, benign-looking storms. Downburst-producing storms often give little advance indications of the imminent danger on weather radar or to the spotter, so warnings are difficult to issue. Once the strong winds reach the ground, Doppler Radar can frequently detect the stronger winds, but the threat of additional damaging winds may be over.

While downbursts are typically produced within a single thunderstorm cell, occasionally many storms will organize into a squall line and produce damaging winds over a much larger area for a period of an hour or longer. Damaging winds of this type are known as Bow Echoes, since a portion of the squall line accelerates, or "bows" out in an easterly direction. Supercell storms also occasionally develop into Bow Echoes. In extreme cases, straight-line winds in a Bow Echo can approach 150 mph, stronger than about 80% of all tornadoes! Since Bow Echoes produce distinctive radar echoes and last 1 to 3 hours (sometimes longer), National Weather Service meteorologists can often provide considerable advance warning.

All severe thunderstorms have the potential to produce damaging winds and large hail. Count on your local National Weather Service office for the latest information regarding these weather hazards.

 

LIGHTNING SAFETY

All thunderstorms go through various stages of growth and develop­ment. As a thunderstorm cloud continues to grow, snow and ice begin to form in the middle and higher levels of the cloud where temperatures are below freezing, and electrical charges start to build up within the cloud.  Negative electrical charges near the middle of the thunderstorm cloud cause a positive charge to build up on the ground under and near the thunderstorm.  Finally, when the difference between these charges becomes too great, a giant atmospheric spark we call lightning occurs.

Lightning is an underrated killer, usually claiming its victims one at a time.  Lightning also leaves many victims with life-long serious injuries.  Lightning can strike as far as 10 miles from the side of the thunder­storm cloud.  In fact, many lightning victims are struck before the rain arrives or after the rain has ended.  Many victims also report that at least a portion of the sky was blue when they were struck.  Although Maine has less lightning than most states east of the Rocky Mountains, Maine ranks 8th highest in the country in terms of lightning casualties (per capita).

This summer, the National Weather Service will conduct a nationwide awareness campaign to reduce the number of deaths and injuries from lightning.  Although more information on lightning and lightning safety will be provided during Lightning Safety Awareness Week which will be during the week of June 19-25, here are some basic tips to help keep you and your family safe this summer.

WHILE INSIDE A HOME OR BUILDING
1. Avoid any contact with corded phones.
2. Avoid any contact with electrical or electronic equipment or cords that are plugged into the electrical system.
3. Avoid any contact with the plumbing system.  Do not wash your hands, do not wash the dishes, do not take a shower, or do not do laundry.
4. Do not stand next to a concrete wall and do not lie on a concrete floor.
5. Stay away from windows, outside doorways, and porches.

TIPS WHILE OUTDOORS
1. There is no safe place outside in a thunderstorm.  To be safe,
you must get inside a substantial building or hard-topped metal
vehicle.
2. Plan outside activities so that you minimize the risk of being caught outside in a thunderstorm.
3. If you hear thunder, move inside a safe shelter immedi­ately.  Generally, if you can hear the thunder, you're within striking distance of the storm.
4. If the sky looks threatening, move inside immediately.  Don't wait for the first flash of lightning.  It could occur anywhere under or near the storm.
5. Stay inside a safe shelter for at least 30 minutes after the last rumble of thunder was heard.  Many lightning victims are struck after the worst part of the storm has passed.

 

Remember, when it comes to thunderstorm safety, it's your own actions that will determine your personal risk of being killed or seriously injured by the hazards that accompany thunderstorms.

 

Tornadoes

Tornadoes are nature's most violent storm. By definition, a tornado is a violently rotating column of air that extends from the base of the thunderstorm cloud to the ground.

Usually, prior to the development of a tornado, a pre-tornadic thunderstorm develops a circulation, that is, it starts rotating (a meso-cyclone). As this rotation becomes stronger, the chance that a tornado may develop also increases. Although the National Weather Service's Doppler RADAR generally can not see the actual tornado, the RADAR does detect rotation of the thunderstorm cloud, and thereby gives some indication of the possibility that a tornado may be forming or has formed.

The scale used to measure tornado damage is the Enhanced Fujita scale (named after Theodore Fujita, a famous tornado damage expert). This scale is commonly referred to as the E-F scale. Based on scientific studies of tornado damage, the original Fujita scale was modified and the new "Enhanced Fujita Scale" was officially implemented in 2007.

EF-0 - Light damage (winds 65 to 85 mph)
EF-1 - Moderate damage (winds 86 to 110 mph)
EF-2 - Considerable damage (winds 111 to 135 mph)
EF-3 - Severe damage (winds 136 to 165 mph)
EF-4 - Devastating damage (winds 166 to 200 mph)

Peak tornado activity in northern New England occurs between June and August, but tornadoes have occurred as early as May and as late as November (as was seen in 2005). Most tornadoes occur between 3 and 9 pm and have an average forward speed of about 30 mph. For the 40 year period between 1950 and 1990, 74 tornadoes occurred in Maine. Based on this, Maine averages about two tornadoes per year. During this period, the average path length of the tornadoes was 1.08 miles. The strongest tornado observed in Maine was an F2.

To alert the public to the threat of tornadoes, the National Weather Service issues TORNADO WATCHES and WARNINGS. A TORNADO WATCH indicates that atmospheric conditions are favorable for the development of tornadoes. A TORNADO WARNING indicates that a tornado is imminent or is already occurring. If you hear that a TORNADO WARNING has been issued for your area, seek safe shelter immediately if you are in the path of the storm.

Due to the usual short life-span of tornadoes in northern New England, there is often little, if any, advance warning. Tornadoes in New England generally touch down and then lift off the ground very quickly. Many of the tornadoes that have occurred in the past, have occurred while severe thunderstorm warnings have been in effect. If you hear that a severe thunderstorm warning is in effect for your area, be alert for the possibility of a tornado. A low rotating cloud, large hail,
and/or a load roar are all signs that may precede the touchdown of a tornado.

Here are some tornado facts and safety tips.

* Flying debris causes most deaths and injuries in tornadoes.
* The safest place in your home during a tornado is your basement.
* Stay away from windows.
* Get out of vehicles or mobile homes, they offer little protection.
* Seek shelter in a substantial building.
* Do NOT seek shelter under a bridge overpass. Bridge overpasses offer little, if any, protection from wind-driven debris.

 

Flood / Flash Flood Terminology

Flooding has overtaken lightning nationally in weather related fatalities. Heavy rain can turn a usually tranquil stream into a life threatening torrent.

General river flooding occurs most often in the winter months, as heavy rain combines with snow melt; however, flash flooding can also occur in these months due to ice jams on rivers and streams.

Flash floods are most common in the warm season of the year when thunderstorms drop large amounts of rain in a short period of time. Hilly and mountainous terrains are especially prone to flash floods.

A flood watch is issued when flooding and/or flash flooding is possible but not imminent. Watches are can be issued up to 36 hours in advance of a flood/flash flood event.

A flash flood warning is issued when imminent flooding requires immediate action to protect lives and property. The flooding may arise from events such as short-term excessive rainfall, the sudden release of water held by an ice jam, or a dam failure. Your immediate action is required if you are in the path of the waters.

A flood warning is issued for actual flood situations not covered by the flash flood warning. The urgency for protection of life and property is lessened only by the longer term of the warning. Your action is still required; flooding is imminent.

All three can be issued for counties, parts of counties, river basins, rivers or specific points on rivers, depending on how widespread the flooding is expected to be. The two warnings can also cover general small stream or urban area flooding.

Often times flooding develops quickly, so it is important to know where you need to go to find safety. Sometimes only minutes or seconds are available to get out of harm's way in a flash flood situation.

 




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Caribou Weather Forecast Office
810 Main St
Caribou ME 04736
(207) 492-0170
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Page last modified: April 23, 2007
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