RainTan

Severe Rain
Kate W. & Juliana L. Tan Cla ﻿ ss

Introduction Severe rain is exactly what it sounds like--very heavy rain. Severe rain is usually the result of massive thunderstorms and can cause hazardous flash floods. This phenomenon derives solely from cumulonimbus clouds, whereas normal precipitation can form from nimbostratus clouds as well.

Dangers  Severe rain can range from unpleasant to extremely hazardous. In the worst cases, flash flooding may occur. Flash flooding results within minutes of excessive rainfall, causing dam failure or sudden release of ice jams (1). This is extremely dangerous because just six inches of fast-moving water can knock a person over, and two feet of water can float and sweep away cars and buses. (1) 

Click [|here] to read more about the dangers of flash flooding.

Conditions of Formation Severe rain only forms under very specific conditions, which is why this occurance is uncommon. Localized convective lifting is what starts the process--warm, very moist air rising (2). The air reaches its dewpoint and forms clouds, which is normal (2). However, since the air is so moist, updrafts from latent heat produced by the condensation keep the parcel of air rising, forming cumulonimbus clouds (2). These type of clouds are so large that updrafts and downdrafts (wind in different directions) occur side-by-side, which produces large rain drops and ice crystals, and therefore extremely heavy rain and strong wind (2). The most important differences between a normal thunderstorm and severe rain-causing thunderstorms are that thunderstorms with severe rain have more rapid motion, have air that is upturned violently (which causes very unstable air), and have much more moisture-saturated air (2).Typically, severe rain can be associated with squall lines, which are several thunderstorms banded together and can extend over 600 miles (4). Squall lines usually form between warm fronts and cold fronts, and are accountable for the majority of precipitation (4). It has also been known to result from supercell storms, which are huge, rotating storms made of cumulonimbus clouds (4).

Historical Examples

 On June 14th, 1903, a strong storm of about 50 square miles and accompanied by severe rain/hail moved near the town of Heppner, Oregon (3). The rain fell heavily down, and within minutes created a severe flash flood along the Willow Creek (3). One- third of all buildings disappeared in seconds, including at least 150 homes (3). As the thunderstorm rains began to approach, a 40 ft wall of water engulfed in the town, raging through for more than an hour (3). This wall of water was a result of run-off from the rocky hills, where precipitation had fallen hard (3). The results were brutal: 247 people found dead, their bodies more than 40 miles downstream to the Columbia River (3). The people of lone, just 20 miles downstream, almost met a similar fate; however, prompt telephoned warnings allowed for an immediate evacuation of the town (3). There are no known rainfall recordings for the storm (3).

Click [|here] to read about some other historic examples of major flash floods.

Safety If there is a flash flood watch in your area, you should make sure to have a few things: canned food, a flashlight, a battery-powered radio, a first-aid kit, and weather gear (1). Families, especially with young children, are advised to form a disaster plan and go over things such as telephone numbers, places to meet each other, basic medical procedures, etc. (6). If you are caught in the middle of a flood, get to high ground as quickly as possible, avoid flooded and low areas, and get out of your car! (1) Areas subject to flooding include dips, canyons, low spots, etc. (6). After a flood, always boil water before using it for anything and be careful when using electral instruments (1).

Sources <span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;">1) Wicker, Crystal. "Rain and Floods." Weather Wiz Kids . N.p., n.d. Web. 20 Nov. 2010. <span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;"><http://www.weatherwizkids.com/weather-rain.htm>. <span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;"> 2) "Severe Thunderstorms." Earth Science Australia. N.p., n.d. Web. 18 Nov. 2010. <span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;"><http://earthsci.org/flooding/unit1/u1-03-00.html>. <span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;"> 3) "Floods and Flash Floods." National Weather Service Forecast Office: Portland, <span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;">OR. National Oceanic and Atmospheric Administration, n.d. Web. 29 Nov. <span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;">2010. <span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;"><http://www.wrh.noaa.gov/pqr/seasonal/springmon.php> <span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;">4) "Supercell Thunderstorms and Squall Lines." Windows to the Universe. National <span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;">Earth Science Teachers Association, 27 May 2010. Web. 29 Nov. 2010. <span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;"><http://www.windows2universe.org/earth/Atmosphere/tstorm/severe.html>. <span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;"> 5) Bath, Michael, and Jimmy Deguara. "Weather Photo Catalogue." Australian Severe <span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;">Weather. N.p., 22 May 2008. Web. 29 Nov. 2010. <span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;"><http://australiasevereweather.com/photography/photos/2000/jd20000305.html>. <span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;"> 6) Flash Floods and Floods...The Awesome Power! National Oceanic and Atmospheric <span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;">Administration, July 1992. Web. 29 Nov. 2010. <span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;"><[]>. <span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;"> 7) "Noaa National Weather Service and FEMA Offer Flood Safety Tips for Flood Safety Awareness Week". NOAA, Mar. 2009. Web. 30 Nov. 2010. <span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;">[] <span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;">8) "Flood Safety Awareness Week." National Weather Forecast Service Office: Newport / <span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;"> Morehead CIty, NC. National Oceanic and Atmospheric Administration, 14 Mar. <span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;"> 2010. Web. 30 Nov. 2010. <span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;"> <http://www.erh.noaa.gov/mhx/FAWWeek.php>.