NWS Burlington Severe Weather Awareness: Flash Flooding


Welcome to the National Weather Service in
Burlington, Vermont’s presentation on Flash Flooding for Severe Weather Awareness Week. Flooding is one of the most deadly and damaging
weather hazards to affects the US every year. From 1995-2011, Flooding caused more fatalities
than tornadoes. Of those fatalities, the majority occurred while the person was driving into
flooded areas, especially at night. The northeast is vulnerable to flash flooding
from thunderstorms during the warm season, especially in areas of complex mountainous
terrain. It’s important to know where flooding is likely to occur, what evacuation routes
are available, where to find the most up to date information and what it means. So what is warm season flash flooding?
Flash flooding is a rapid rise in water levels which causes flooding that occurs very quickly…usually
within 6 hours of the causative event. And warm season refers to April through October. During the warm season in the northeast, flash
flooding is usually caused by thunderstorms that are slow moving or stationary, or training
over the same area. Training means that multiple thunderstorms continue to follow one another
over the same area. In all cases, slow moving, stationary or training thunderstorms, heavy
precipitation falls over a specific area. Tropical Cyclones can also bring very heavy
rainfall…precipitating multiple inches of rain, as was the case with Hurricane Irene
over portions of Vermont and New York receiving 6-8 inches of rain. Lastly Dam breaks can
also cause flash flooding. Areas that can be particularly vulnerable
to Flash Flooding are locations that have had recent rainfall, leaving the ground moist
and unable to absorb as much precipitation; Urban areas; and valley locations in mountainous
terrain that allow rainfall and runoff to reach rivers faster. Flash Flooding can lead to significant infrastructure
damage, such as road washouts, crop & property damage, and death. Flash flooding is especially
dangerous at night, when it’s harder to see the water. You can see on the pie chart of
the right, that a majority of flood victims perished while driving. If you come to an area that is covered with
water, you will not know the depth of the water or the condition of the ground under
the water. This is especially true at night, when your vision is more limited.
A mere six inches of fast-moving flood water can knock over an adult. It takes only two
feet of rushing water to carry away most vehicles. This includes pickups and SUVs. To alert the public, media and emergency management
community to these dangers, the National weather Service issues Flash Flood Warnings when rapid
rises in water level over a short period of time will result in flooding. Here we have
an excerpt of a Flash Flood Warning stating… The type of warning, For what areas, Timing
of the warning, Reason for the warning…in this case heavy rain has fallen and more is
expected. And hazardous conditions expected. Thank you for watching this presentation on
Warm Season Flash Flooding during the National Weather Service Burlington’s Severe Weather
Awareness Week. For more information, visit on the web at www.weather.gov/btv, Like us
on Facebook, or Follow us on Twitter.

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