1

Historic Spring FloodingOhio River Valley and Mississippi River

Ernie WellsHydrologic Services Division

2

Snow Water Equivalent

Substantial stored water in the snow pack represents significant flooding potential in the North Central and Northeast as the spring thaw begins

March 18, 2011

3

National Hydrologic Assessment Spring 2011 – Issued March 17, 2011

4

River ObservationsMay 3

Observations of major to record crest levels in the Ohio River Valley along the Mississippi River

http://water.weather.gov

5

Observed PrecipitationApril 18, 2011 – May 2, 2011

During the previous 2 weeks, a broad area of Central US received 10-20+ inches of precipitation; 600% of normal precipitation

6

Forecasted PrecipitationMay 2, 2011 – May 7, 2011

During the next 5 days, a broad area of Central US received 0.5 - 2 inches additional rain (much has already fallen)

7

Extended Range Forecasts

6-10 Day Forecasts

Precipitation (May 8-12) Precipitation (May 10-16)

8-14 Day Forecasts

8

Hydrologic “Perfect Storm”WFO Paducah, KY

Confluence of Ohio River and Mississippi River

9

Hydrologic “Perfect Storm”Cairo, IL - Confluence of Ohio River and Mississippi

Historic levee break at New Madrid relieving flood crest at Cairo

10

Hydrologic “Perfect Storm”WFO - Memphis

Crest Moving downstream – expect flooding through June

11

River ForecastsMay 3 – next 48 hours

Short-term streamflow forecasts predict minor to major crest levels in the Northeast, Ohio River Valley, and Alabama and Mississippi

http://water.weather.gov