Outflow Boundaries

It is that time of year, when organized storm systems are few and far between.  Therefore, we often have to rely on thunderstorms to help generate other storms from day to day.  They accomplish this task by producing outflow boundaries.  An outflow boundary is produced by the cool air flowing away from a thunderstorm, interacting with the warmer surrounding air.  They act like mini-cold fronts, and can be very effective triggers for new thunderstorm development.  Below is a classic example of a storm producing a substantial outflow boundary:

That narrow blue arc-line surrounding the storm is the outflow boundary.  As it moves away from the storm, it could devleop additional storms.  Many times when two outflow boundaries intersect or a mature storm intersects with an outflow boundary, intensification of existing storms can occur or other big storms can develop.  The boundary can act as a mechanism to enhance low level shear, and cause an already severe storm to become even stronger and possibly become tornadic.  It can also cause a storm that has tornadic characteristics but hasn't produced a tornado, to produce a tornado.  Sometimes however, they won't do anything but produce a gust of wind when they pass through your area.  So yes, sometimes they are pretty harmless.  This is usually the case when moisture is lacking, and there is no fuel to get storms started.  However this time of year, we have our eyes on the radar screen tracking these boundaries as they roam through Southern Colorado.  They occur almost every afternoon until we get into the later part of the Summer and storm season winds down.

Chief Meteorologist Brian Bledsoe

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  • by ryan Location: monument on Jul 3, 2008 at 02:05 PM
    Brian What the heak there is something wrong with our weather in colorado we just get the worst weather in colorado in the winter we get fast moving snow storms and in the summer we get slow moving severe thunderstorms do you think it is global warming that is causing this my step dad is not a beliver in global warming but I really think that global warming is distorying our earth that also means flooding in the midwest and also fires in california, arizona, orgon, and also in wasington state
  • by Brian Location: Weather Center on Jul 2, 2008 at 06:35 PM
    Thanks for posting Tim. As you know, High Plains convection this time of year is largely dependent on outflow boundaries. With dew points being so low lately, many of the boundaries haven't had the fuel to generate additional convection. Let's hope that changes for the latter part of the Summer...
  • by Tim Location: Colorado Springs on Jul 1, 2008 at 08:53 PM
    I was going to say you must have been looking at the radar earlier this evening when an outflow boundary was evident on radar, but then I realized it's your job :) The outflow produced by the storm to our northeast is the first one I've seen in quite sometime that reacted with such a "widespread" effect. Usually we see more discrete cells form, but as I peeked at the radar occasionally this evening you could see a broken line as it progressed southward. Great post, as the past couple of weeks we've seen several pass through the area. Some benign, and others touching off smaller cells. Thanks for taking the time to post!
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