Featured Research

from universities, journals, and other organizations

New Insight On The Plains' Biggest Rains -- Rocky Mountains Affect Midwest Flooding

June 16, 1999
National Center For Atmospheric Research (NCAR)
Until now scientists have found it hard to predict which summer days would produce giant, flood-prone storm systems in the nation's midsection. Now they may have found two keys: the strength of intense downdrafts from mountain storms upstream, and the formation of small- scale low-pressure areas that can help trigger flooding rains for days.

BOULDER--Until now scientists have found it hard to predict which summerstorms forming over the Rocky Mountains would produce giant, flood-pronestorm systems in the Great Plains to the east. Now Andrew Crook(National Center for Atmospheric Research, or NCAR) and Donna Tucker(University of Kansas) may have found the key: the strength of intensedowndrafts that emerge from the mountain storms and stir up severeweather downstream. Computer modeling to track these downdrafts and thecloud-level ice crystals that help produce them may eventually giveforecasters the edge in predicting severe storm systems, and possiblyflooding, over the plains. Crook and Tucker (the lead author) arepublishing their results in the June issue of Monthly Weather Review.NCAR's primary sponsor is the National Science Foundation.

Related Articles

Most summertime floods across the Great Plains are caused by mesoscaleconvective systems (MCSs). These giant complexes often emerge fromshowers and thunderstorms that form over the Rocky Mountains. Tucker andCrook used the Pennsylvania State University/NCAR mesoscale model tosimulate convection (showers and thunderstorms) and to test howdifferent modes of mountain convection affect the likelihood of MCSformation downstream. In the model, they found that an MCS was mostlikely to form when a mass of rain-cooled air descended from themountains, colliding with moist air on the plains and forcing it upward.

Although forecasters have seen this process unfold many times, it isstill unclear whether a given day's mountain storms will be the rightkind to trigger an MCS. Sometimes the initial storms lead to an MCS thatcan travel as far as Illinois; other times, the storms dissipate shortlyafter they move off the mountains. Tucker and Crook's modeling suggeststhat the strength of the rain-cooled outflow from the mountain storms iscritical to downstream MCS development. Several factors play into theoutflow strength, including the fall speed of ice crystals within themountain storms.

Fine-scale modeling for better prediction

Even today's most sophisticated forecast models cannot peg mountainconvection well enough to assess how it might trigger storm complexesdownstream. However, under a new NSF grant, Tucker and Crook are using afiner-scale model built by NCAR scientist Terry Clark to look moreclosely at mountain convection and how it relates to the larger-scaleatmospheric flow. Since the large-scale flow is routinely forecast bycomputer models, this new work could allow forecasters to betterpinpoint a given day's mountain convection and where it might triggerlarge storm complexes on the plains. Tucker and Crook's work issupported by the University of Kansas and NSF.

One downpour leads to another: NCAR team pinpoints culprit

A typical MCS peaks in strength during the overnight hours anddissipates the next day. However, it may be followed by a second MCS thefollowing night. Sometimes a slow-moving sequence of MCSs will extendover several days, causing torrential rains over a large area. If such amultiday sequence could be forecast, valuable lead time might be gainedon flooding threats.

NCAR scientists Christopher Davis, Stanley Trier, and colleagues havegained new insight on a type of low-pressure center that connects oneMCS to the next. This low is called a mesoscale convective vortex (MCV).With a core only 30 to 60 miles wide and 1 to 3 miles deep, an MCV isoften overlooked in standard weather analyses. But Davis and Trier havefound that MCVs play a key role in helping storms regenerate over two ormore days.

Looking closely at satellite, upper-air, and radar observations from1998, Davis and Trier found evidence of 17 separate MCVs over thecentral and eastern United States. Previous studies had found only twoor three MCVs per year. The vortices appear most likely to persist whenlower- and upper-level winds are relatively light. This allows thecirculation to maintain its integrity for up to 12 hours after thestorms dissipate. If other conditions are favorable, a new round ofstorms may cluster around the vortex. For example, one MCV triggeredheavy rains in Texas on May 27, 1998; flooding in Arkansas early on the28th; and additional flooding the following night in Mississippi. An MCVthat moves into tropical waters, such as the Gulf of Mexico, can serveas the nucleus for a tropical storm or hurricane.

Currently, it's difficult to spot and track mesoscale convectivevortices from upper wind observations alone, due to their small size.However, a technique developed by NCAR's John Tuttle calculates windsusing cloud movements observed by satellite in order to spot MCVs andother features. This promising technique, along with better observationsand models, could make it practical for forecasters to use MCVs as aguide to predict locations of heavy rain. Davis and Trier's work issupported by NASA and the U.S. Weather Research Program, which isexamining forecast tools for heavy precipitation.

NCAR is managed by the University Corporation for Atmospheric Research,a consortium of more than 60 universities offering Ph.D.s in atmosphericand related sciences.

-The End-

Writer: Bob HensonNote to Editors:Visuals: Images are available at ftp://ftp.ucar.edu/communications.Filename(s): mcsradar.tif, downdraft.tif, sat.tif, satwind.tif. Captionsare at the Web address below.

UCAR and NCAR news: http://www.ucar.edu/publications/newsreleases/1999.To subscribe via e-mail send name, title, affiliation, postal address,fax, and phone number to butterwo@ucar.edu.

Story Source:

The above story is based on materials provided by National Center For Atmospheric Research (NCAR). Note: Materials may be edited for content and length.

Cite This Page:

National Center For Atmospheric Research (NCAR). "New Insight On The Plains' Biggest Rains -- Rocky Mountains Affect Midwest Flooding." ScienceDaily. ScienceDaily, 16 June 1999. <www.sciencedaily.com/releases/1999/06/990615174218.htm>.
National Center For Atmospheric Research (NCAR). (1999, June 16). New Insight On The Plains' Biggest Rains -- Rocky Mountains Affect Midwest Flooding. ScienceDaily. Retrieved April 24, 2015 from www.sciencedaily.com/releases/1999/06/990615174218.htm
National Center For Atmospheric Research (NCAR). "New Insight On The Plains' Biggest Rains -- Rocky Mountains Affect Midwest Flooding." ScienceDaily. www.sciencedaily.com/releases/1999/06/990615174218.htm (accessed April 24, 2015).

Share This

More From ScienceDaily

More Earth & Climate News

Friday, April 24, 2015

Featured Research

from universities, journals, and other organizations

Featured Videos

from AP, Reuters, AFP, and other news services

Dispute Flares Over Controversial Thai Temple Tigers

Dispute Flares Over Controversial Thai Temple Tigers

AFP (Apr. 24, 2015) Thai wildlife officials begin a headcount of nearly 150 tigers kept by monks at a temple which has become the centre of a dispute over the welfare of the animals. Video provided by AFP
Powered by NewsLook.com
Chile Volcano Cloud Spreads

Chile Volcano Cloud Spreads

Reuters - News Video Online (Apr. 24, 2015) Southern Argentina struggles to cope with a blanket of ash after the eruption of the Calbuco volcano in Chile. Rough cut (no reporter narration). Video provided by Reuters
Powered by NewsLook.com
Thousands Evacuate As Chile Volcano Erupts Twice In 24 Hours

Thousands Evacuate As Chile Volcano Erupts Twice In 24 Hours

Newsy (Apr. 23, 2015) Chile&apos;s Calbuco volcano erupted twice in a span of 24 hours, once Wednesday evening and again early Thursday morning. Video provided by Newsy
Powered by NewsLook.com
Newest Pesticide Research Wades Into Debate Over Bee Decline

Newest Pesticide Research Wades Into Debate Over Bee Decline

Newsy (Apr. 23, 2015) New research supports the claim that a popular pesticide hurts bees, but it only adds to the debate about how to handle those pesticides. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.


Breaking News:

Strange & Offbeat Stories

Plants & Animals

Earth & Climate

Fossils & Ruins

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News


Free Subscriptions

Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile

Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?

Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins