national weather service introduction to flooding jason elliott senior service hydrologist nws...
TRANSCRIPT
![Page 1: National Weather Service Introduction to Flooding Jason Elliott Senior Service Hydrologist NWS Baltimore/Washington Open House September 22, 2012](https://reader035.vdocuments.net/reader035/viewer/2022062715/56649d8c5503460f94a739ec/html5/thumbnails/1.jpg)
National Weather ServiceIntroduction to Flooding
Jason ElliottSenior Service Hydrologist
NWS Baltimore/Washington Open HouseSeptember 22, 2012
![Page 2: National Weather Service Introduction to Flooding Jason Elliott Senior Service Hydrologist NWS Baltimore/Washington Open House September 22, 2012](https://reader035.vdocuments.net/reader035/viewer/2022062715/56649d8c5503460f94a739ec/html5/thumbnails/2.jpg)
Area of Responsibility Flood Forecasting / Meteorology Types of Flooding Flooding Facts / Safety NWS Flood Products
Today’s Topics
![Page 3: National Weather Service Introduction to Flooding Jason Elliott Senior Service Hydrologist NWS Baltimore/Washington Open House September 22, 2012](https://reader035.vdocuments.net/reader035/viewer/2022062715/56649d8c5503460f94a739ec/html5/thumbnails/3.jpg)
County WarningArea (CWA)Flash Flood◦ 43 Counties in 3 states◦ District of Columbia◦ 12 Independent Cities◦ MD Chesapeake Bay
Hydrologic ServiceArea (HSA)River Flood◦ Potomac Basin◦ Shenandoah Basin◦ Rappahannock Basin◦ West Chesapeake
Areas of Responsibility
![Page 4: National Weather Service Introduction to Flooding Jason Elliott Senior Service Hydrologist NWS Baltimore/Washington Open House September 22, 2012](https://reader035.vdocuments.net/reader035/viewer/2022062715/56649d8c5503460f94a739ec/html5/thumbnails/4.jpg)
13 RFCs Nationwide Focus on river forecasting & modeling
River Forecast Centers (RFCs)
![Page 5: National Weather Service Introduction to Flooding Jason Elliott Senior Service Hydrologist NWS Baltimore/Washington Open House September 22, 2012](https://reader035.vdocuments.net/reader035/viewer/2022062715/56649d8c5503460f94a739ec/html5/thumbnails/5.jpg)
River Gauges
![Page 6: National Weather Service Introduction to Flooding Jason Elliott Senior Service Hydrologist NWS Baltimore/Washington Open House September 22, 2012](https://reader035.vdocuments.net/reader035/viewer/2022062715/56649d8c5503460f94a739ec/html5/thumbnails/6.jpg)
Precipitation Monitoring
![Page 7: National Weather Service Introduction to Flooding Jason Elliott Senior Service Hydrologist NWS Baltimore/Washington Open House September 22, 2012](https://reader035.vdocuments.net/reader035/viewer/2022062715/56649d8c5503460f94a739ec/html5/thumbnails/7.jpg)
Pre-event assessment Forecast expected rainfall Consider areas more prone to flooding Put it all together!
How do we forecast flood potential?
![Page 8: National Weather Service Introduction to Flooding Jason Elliott Senior Service Hydrologist NWS Baltimore/Washington Open House September 22, 2012](https://reader035.vdocuments.net/reader035/viewer/2022062715/56649d8c5503460f94a739ec/html5/thumbnails/8.jpg)
Items to consider: Wet ground Current water levels Rainfall intensity and duration Topography Soil (type, moisture, frozen) Time of year (vegetation, snow cover)
Pre-event assessment
![Page 9: National Weather Service Introduction to Flooding Jason Elliott Senior Service Hydrologist NWS Baltimore/Washington Open House September 22, 2012](https://reader035.vdocuments.net/reader035/viewer/2022062715/56649d8c5503460f94a739ec/html5/thumbnails/9.jpg)
Slow-moving or Stationary Fronts
Favorable Weather Patterns
![Page 10: National Weather Service Introduction to Flooding Jason Elliott Senior Service Hydrologist NWS Baltimore/Washington Open House September 22, 2012](https://reader035.vdocuments.net/reader035/viewer/2022062715/56649d8c5503460f94a739ec/html5/thumbnails/10.jpg)
High Moisture Content◦ Dewpoints & Precipitable Water
Slow-moving & Training (Repeating) Thunderstorms
Favorable Weather Patterns
![Page 11: National Weather Service Introduction to Flooding Jason Elliott Senior Service Hydrologist NWS Baltimore/Washington Open House September 22, 2012](https://reader035.vdocuments.net/reader035/viewer/2022062715/56649d8c5503460f94a739ec/html5/thumbnails/11.jpg)
Automated observations◦ Near-real time, but…
Not perfect (could clog or freeze, etc.) No measurement of how much of the fallen rain is being soaked
into the ground, and how much is running into streams
Observations during heavy rain
![Page 12: National Weather Service Introduction to Flooding Jason Elliott Senior Service Hydrologist NWS Baltimore/Washington Open House September 22, 2012](https://reader035.vdocuments.net/reader035/viewer/2022062715/56649d8c5503460f94a739ec/html5/thumbnails/12.jpg)
Remote Sensing◦ Radar◦ Satellite
Precipitation Estimates
![Page 13: National Weather Service Introduction to Flooding Jason Elliott Senior Service Hydrologist NWS Baltimore/Washington Open House September 22, 2012](https://reader035.vdocuments.net/reader035/viewer/2022062715/56649d8c5503460f94a739ec/html5/thumbnails/13.jpg)
Ground truth◦ A picture really is worth a thousand words!◦ Rainfall measurement / flood report / stream measurement
Observations during heavy rain
US 301 / MD 4Upper Marlboro, MD
Photo courtesy Prince Georges County EMS
![Page 14: National Weather Service Introduction to Flooding Jason Elliott Senior Service Hydrologist NWS Baltimore/Washington Open House September 22, 2012](https://reader035.vdocuments.net/reader035/viewer/2022062715/56649d8c5503460f94a739ec/html5/thumbnails/14.jpg)
Flash Flood – A flood which follows within 6 hours of heavy or excessive rainfall, a dam or levee failure, or ice jam break.
(Areal) Flood – A flood which lasts beyond 6 hours after the heavy or excessive rainfall event. Includes small stream flooding.
Coastal Flooding – the inundation of land areas caused by sea waters over and above the level of normal tidal action.
Types of Flooding
![Page 15: National Weather Service Introduction to Flooding Jason Elliott Senior Service Hydrologist NWS Baltimore/Washington Open House September 22, 2012](https://reader035.vdocuments.net/reader035/viewer/2022062715/56649d8c5503460f94a739ec/html5/thumbnails/15.jpg)
Typical Flash Flood Characteristics◦ Caused by convection (thunderstorms or intense showers)◦More isolated compared to flooding◦ Response time is short, usually 1-2 hours, but as little as 15
mins. in urban areas (compared to 6-12 hours for flooding)◦ Swift Water Rescues, road closures (especially major roads),
creeks and streams flood within an hour or two of the causative event
◦Occurs more frequently in urban areas and in terrain
What makes a flash flood?
Flash Flood debris flownear Front Royal, VA – 2011
![Page 16: National Weather Service Introduction to Flooding Jason Elliott Senior Service Hydrologist NWS Baltimore/Washington Open House September 22, 2012](https://reader035.vdocuments.net/reader035/viewer/2022062715/56649d8c5503460f94a739ec/html5/thumbnails/16.jpg)
Can occur anytime – day or night. Approximately two-thirds of all flash flooding occurs at
the night. Most flash flood
fatalities occur at night! Flash Flooding is NOT
restricted to only mountainous areas.
When does flash flooding occur?
Berkeley Springs, WV flash flood – September 1, 2012
![Page 17: National Weather Service Introduction to Flooding Jason Elliott Senior Service Hydrologist NWS Baltimore/Washington Open House September 22, 2012](https://reader035.vdocuments.net/reader035/viewer/2022062715/56649d8c5503460f94a739ec/html5/thumbnails/17.jpg)
River Flood Forecast Points
![Page 18: National Weather Service Introduction to Flooding Jason Elliott Senior Service Hydrologist NWS Baltimore/Washington Open House September 22, 2012](https://reader035.vdocuments.net/reader035/viewer/2022062715/56649d8c5503460f94a739ec/html5/thumbnails/18.jpg)
Travel Times (in hours)
2
616
32
33 4447 36
56 45
6
17
30
![Page 19: National Weather Service Introduction to Flooding Jason Elliott Senior Service Hydrologist NWS Baltimore/Washington Open House September 22, 2012](https://reader035.vdocuments.net/reader035/viewer/2022062715/56649d8c5503460f94a739ec/html5/thumbnails/19.jpg)
Prolonged onshore flow
Storm Surge from Tropical Systems
Spring Tides: the highest tides in a lunar month, around new moon when the Earth, Moon and Sun are aligned
Coastal Flooding
Annapolis, MD – 2003
![Page 20: National Weather Service Introduction to Flooding Jason Elliott Senior Service Hydrologist NWS Baltimore/Washington Open House September 22, 2012](https://reader035.vdocuments.net/reader035/viewer/2022062715/56649d8c5503460f94a739ec/html5/thumbnails/20.jpg)
Two distinct peaks for positive anomaliesJanuary/February & September/October
September stands out due to tropical systems
Coastal Flooding
Coastal Flooding at the US Naval Academy June 2005
![Page 21: National Weather Service Introduction to Flooding Jason Elliott Senior Service Hydrologist NWS Baltimore/Washington Open House September 22, 2012](https://reader035.vdocuments.net/reader035/viewer/2022062715/56649d8c5503460f94a739ec/html5/thumbnails/21.jpg)
Other than heat, floods are the #1 weather killer! Most flood fatalities occur in cars Most flood fatalities occur at night
Most flood fatalities can be avoided!!!
Floods – a major weather killer
![Page 22: National Weather Service Introduction to Flooding Jason Elliott Senior Service Hydrologist NWS Baltimore/Washington Open House September 22, 2012](https://reader035.vdocuments.net/reader035/viewer/2022062715/56649d8c5503460f94a739ec/html5/thumbnails/22.jpg)
Take Appropriate Action! Better forecasts and earlier warnings won’t help prevent
loss of life and property unless people act. Know your area’s flood risk! Plan ahead – Identify where to go if told to evacuate.
Choose several places (a friend’s home or a motel, or a designated shelter)
Never try to drive, swim, walk, or run through a flooded area
Children should not play in flooded areas
Flood Safety
River Road, Falmouth, VAMarch 2011
![Page 23: National Weather Service Introduction to Flooding Jason Elliott Senior Service Hydrologist NWS Baltimore/Washington Open House September 22, 2012](https://reader035.vdocuments.net/reader035/viewer/2022062715/56649d8c5503460f94a739ec/html5/thumbnails/23.jpg)
If you come upon flood waters, STOP! TURN AROUND AND GO ANOTHER WAY!
Only 6 inches of fast-moving water can knock you off your feet
2 feet of water will float an average size car…less water for smaller cars
Bottom line: never assume there is a safe way to drive through water
Turn Around, Don’t Drown!
![Page 24: National Weather Service Introduction to Flooding Jason Elliott Senior Service Hydrologist NWS Baltimore/Washington Open House September 22, 2012](https://reader035.vdocuments.net/reader035/viewer/2022062715/56649d8c5503460f94a739ec/html5/thumbnails/24.jpg)
Average: $7.6 billion per year! 2010: $5 billion In 2011, 75% of all Presidentially-declared disasters
were at least in part flood-related◦ (plus three
tsunamideclarations, a different typeof flood)
Flood Damages
Great Falls, MD1996
![Page 25: National Weather Service Introduction to Flooding Jason Elliott Senior Service Hydrologist NWS Baltimore/Washington Open House September 22, 2012](https://reader035.vdocuments.net/reader035/viewer/2022062715/56649d8c5503460f94a739ec/html5/thumbnails/25.jpg)
Flood Fatalities
![Page 26: National Weather Service Introduction to Flooding Jason Elliott Senior Service Hydrologist NWS Baltimore/Washington Open House September 22, 2012](https://reader035.vdocuments.net/reader035/viewer/2022062715/56649d8c5503460f94a739ec/html5/thumbnails/26.jpg)
Flood Fatalities
![Page 27: National Weather Service Introduction to Flooding Jason Elliott Senior Service Hydrologist NWS Baltimore/Washington Open House September 22, 2012](https://reader035.vdocuments.net/reader035/viewer/2022062715/56649d8c5503460f94a739ec/html5/thumbnails/27.jpg)
Our ProductsOutlook •Hazardous Weather Outlook
•Days 3 - 7
Watch •Flood/Flash Flood/River Flood Watch•Up to 48 hours (up to 72 for rivers)
Warning •Flood/Flash Flood/River Flood Warning•Occurring or imminent
![Page 28: National Weather Service Introduction to Flooding Jason Elliott Senior Service Hydrologist NWS Baltimore/Washington Open House September 22, 2012](https://reader035.vdocuments.net/reader035/viewer/2022062715/56649d8c5503460f94a739ec/html5/thumbnails/28.jpg)
WATCH: Conditions are favorable for flooding to occur (>50% chance). Be alert for possible flooding during the watch period.
WARNING: Flooding is occurring or is extremely likely to occur (>75% chance). Stay out of low areas and seek higher ground if necessary!
Note: A watch does not necessarily precede a warning, especially for river flooding.
Watch vs. Warning
![Page 29: National Weather Service Introduction to Flooding Jason Elliott Senior Service Hydrologist NWS Baltimore/Washington Open House September 22, 2012](https://reader035.vdocuments.net/reader035/viewer/2022062715/56649d8c5503460f94a739ec/html5/thumbnails/29.jpg)
Our goal is to warn for:◦Where the rain is going to go◦Where the water is going to flow
This meanswe may warnfor placeswhere it willnot even rain!
Basin-Based Warnings
![Page 30: National Weather Service Introduction to Flooding Jason Elliott Senior Service Hydrologist NWS Baltimore/Washington Open House September 22, 2012](https://reader035.vdocuments.net/reader035/viewer/2022062715/56649d8c5503460f94a739ec/html5/thumbnails/30.jpg)
Assessing flood threat at all local stream gauges Began in September 2011 About 70% complete
Local River Assessment
![Page 31: National Weather Service Introduction to Flooding Jason Elliott Senior Service Hydrologist NWS Baltimore/Washington Open House September 22, 2012](https://reader035.vdocuments.net/reader035/viewer/2022062715/56649d8c5503460f94a739ec/html5/thumbnails/31.jpg)
http://water.weather.gov
Advanced Hydrologic Prediction Service (AHPS)