Water Predictions for Life Decisions Sarah Jamison, Service Hydrologist National Weather Service Cleveland sarah.jamison@noaa.gov

Overview Flood History Flood Prediction Flood Warning Process Future Communication

Flood of 1913 The greatest known flood in Youngstown occurred on the lower Mahoning River on Wednesday, March 26, 1913. 16.5 feet above the current flood stage and seven feet higher than the previous record set in 1904.  Many industries suffered extensive damage, major bridges were washed away, and electric power and water services were out.

January 1959 Rains of 3 to 6 inches fell on snow covered frozen ground, producing the most destructive flooding in Ohio since March 1913.  Industries were closed by floodwaters in Youngstown and Canton.  During the flood of January 1959, the flood peak on the Mahoning River at Lowellville did not occur until 30 hours after the flood rise began. This flood rose at a maximum rate of 1.5 feet per hour; and remained out of its banks 77 hours.

FEMA FIS Lowville 1990

Flood Prediction Knowledge of vulnerable locations

Flood Prediction Antecedent conditions

Flood Prediction Antecedent conditions

Flood Prediction Measure falling rainfall

Flood Prediction Measure fallen rainfall

Flood Prediction Predict future rainfall

NWS Flood Products

Flood Terms Urban and Small Stream Advisory —issued when flooding of small streams, streets and low-lying areas, such as railroad underpasses and urban storm drains, is occurring or is imminent. Advisories are issued when such events warrant notification of the public in a product less urgent than a warning. Flood Watch — issued when flooding is possible – typically within a 6 to 48 hour time frame before the event. Flood Warning — issued when flooding conditions are actually occurring or are imminent. Flash Flood Watch — issued when flash flooding is possible. Flash Flood Watches are generally issued for flooding that is expected to occur within 6 hours of the event, which could be heavy rainfall or a dam or levee failure. Flash Flood Warning — issued when flash flooding is actually occurring or imminent. Flash flood warnings tend to be fairly localized areas such as a county or small group of counties, and the specific locations threatened within those areas are often highlighted. Flash Flood Warnings are issued for short-term events, which require immediate action to protect lives and property, such as dangerous small stream flooding or urban flooding and dam or levee failures.

Flash Floods Flash flooding is one of the most hazardous natural events, and it is frequently responsible for loss of life and severe damage to infrastructure and the environment. Over the past decade flash flood forecast lead-time has expanded up to six hours due to improved rainfall forecasts. However the largest source of uncertainty of flash flood forecasts remains unknown future precipitation.

River Flooding NWS prepares hydrologic forecasts for… the time and height of flood crests the time when a river is expected to exceed flood stage the time when a river is anticipated to return within its banks. This is critical information for saving lives and reducing property damage during high waters.

River Flooding How are river forecast points selected? Why does the NWS issue forecasts for some towns and not others? Several factors go into providing river forecasts: The existence of a stream gage at the location. A history of data collection at the location. Rating Curves developed at many different river flows. The river model calibrated for the river response during many different past precipitation events and seasons. The size of the basin – too small basins will respond to rain much quicker than current hydrologic models can forecast. These are best served by flash flood areal watches and warnings. The community needs forecast information – if the river floods, but does not harm any person or property forecast services would not be needed.

Flood Impacts Nationally

Communicate Flood Risk NWS is striving to improve our communication to the public Simplify flash flood messaging is a goal of the NWS The current watch/warning/advisory system is confusing Too many flood products Improved funnel of information from communities to the NWS

Communicate Flood Risk Flood impact matrix

Communicate Flood Risk Flood Likelihood vs. Potential Impacts

Public Advice Key Very low Low Medium High No action required Keep an eye on the weather and flood forecasts Flooding possible – BE AWARE Remain alert and ensure you access the latest weather forecast for up to date information Be aware of conditions and drive accordingly Check weather and flood warnings Flooding is expected BE PREPARED Remain vigilant Consider re-scheduling your journey. Don’t drive or walk through flood water Think about preparing for flooding and take precautions where possible Check flood warnings Significant risk to life TAKE ACTION Remain extra vigilant and ensure you access the latest weather and flood forecasts Avoid all non-essential travel to postpone journeys if at all possible Follow advice given by authorities under all circumstances, and be prepared for extraordinary measures

Resources Your National Weather Service website www.weather.gov/cle Radar Forecasts Watches and Warnings River Forecast Center www.weather.gov/ohrfc Observed and Forecasted Rainfall River Observations and Forecasts