National Weather Service Flood Forecast Needs: Improved Rainfall Estimates

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1 National Weather Service Flood Forecast Needs: Improved Rainfall Estimates Weather Forecast Offices Cleveland and Northern Indiana Ohio River Forecast Center Presenter: Sarah Jamison, Service Hydrologist NWS CLE

2 Flood Forecasting In a Nutshell River Rises and Discharges 1. Produce Runoff by: Measuring observed basin rainfall Predict future 48 hour rainfall Place it over modelled ground conditions (wet/dry/urban/ag ) 2. Model river reaction to added runoff Flash Flood Warnings Radar estimated rainfall If we are lucky, ground truth from a rain gage Place it over modelled ground conditions (wet/dry/urban/ag )

3 Gathering Observed Rainfall Doppler Radar Our Doppler radar continually scans the skies up to 250 miles in every direction from our office and beams back information on the intensity of the storms it detects. Radars are known for their ability to obtain a wealth of information about spatial storm field characteristics. Unfortunately, rainfall estimates obtained by this instrument are known to be affected by multiple sources of error.

4 Doppler Radar Limitations Radar often underestimates (blue areas) due to distance from radar

5 Gathering Observed Weather Information Daily Rainfall Reports Climate stations across the country. Report normally around 7-9 am daily. 24-hour rainfall reports used for monthly, seasonal, and long term climatology. Not useful for river and flash flood forecasting. Real Time Rain Gages Measure in increments of an hour or less with data collected via telemetry or satellite. Provides users with information on rainfall rates/intensity. Used for calibrating NWS Radar rainfall estimates.

6 Rain Gage Networks Cooperators Ohio STORMS Gages *Not all gages listed here are ingested at the NWS due to dissemination methods

7 Real Time Rain Gage Network Ohio Sparse observations can lead to poor rainfall estimates This can result in: Less reliable river forecasts Reduced lead times for flash floods Poor climatology

8 July 13, 2017 Flood Event Flash and River Flooding NWS Building Radar a Estimated Weather-Ready Rainfall Nation (in)

9 Filling in the Gaps Non-Standard Rain Gage Networks Cooperator with 32 new gages soon to be added to NWS ingest. Are there other mesonets out there?

10 Estimated Rainfall Climatology and Research Implications NWS Annual Estimated Rainfall Daily rainfall maps are produced by the River Forecast Centers These daily maps are used to produce weekly, seasonal, and annual datasets. Based on radar estimates and rain gage measurements. Do biases, driven primarily by radar limitations, accumulate over time? 2017

11 Next Steps. Where should gages go for the most impact? It isn t so much a question of the best rain gage location. It is a matter of availability, access, and cost. Whose going to contribute? NWS would like to work with partners to expand the real-time rain gage network for Ohio

12 Measuring Observed Rainfall CoCoRaHS A nationwide volunteer rain gauge observer network.

13 Measuring Observed Rainfall CoCoRaHS Observations on a specific day Reports alert on NWS work stations when they arrive, and are sent daily out to all of our users (media, river forecast center, public, etc.) Observations in Hancock County on July 13, 2017

14 What it means to be a CoCoRaHS observer? You report your precipitation daily between 7 and 9 am Supplemental reports are recommended for change in precipitation and torrential rain events Measuring Observed Rainfall CoCoRaHS The data is archived and available to the public and NWS Data is used by NWS to: Calibrate the radar rainfall estimates Estimate runoff in the river forecast models Can support decisions to issue flash flood warnings

15 Measuring Observed Rainfall CoCoRaHS -A completed application form that is available online at - Gages can be purchased for $31.50 from their website -A unique station number and a station name (assigned automatically as you register) Station Number : OH-CN-6 Station Name : Wilmington 3.6 W

16 Questions? Sarah Jamison Service Hydrologist EXT 234