Post on 18-Dec-2015
Jeff Dobur, NWS Peachtree City, GA
Michael Moneypenny, NWS Raleigh, NC
Rainfall and River Forecasts
The Processes and Products
River Forecast Centers
River Gages and Forecasts
River Forecasts – How are they created?River Forecasts – How are they created?
Basic Forecast ProcessBasic Forecast Process
Observed PrecipitationObserved
PrecipitationFuture
PrecipitationFuture
Precipitation
SAC-SMA ModelRain to Runoff
SAC-SMA ModelRain to Runoff
Basin
Watershed
Rating CurveStages to FlowsRating Curve
Stages to Flows
Unit HydrographRunoff to Flow
Unit HydrographRunoff to Flow
Upstream FlowUpstream Flow
River GageBasin Local FlowBasin Local Flow Total Flow
(cfs)Total Flow
(cfs)
ForecasterModificationForecaster
Modification
ForecastTo WFO
ForecastTo WFO
River Forecast Points
The U.S. Geological Survey Performs Flow Measurements at Each Forecast Point
To Produce Rating Curves
Volume of Flow is Converted to Stage
River Forecast Points
The NWS Surveys Each Site
to DetermineImpacts
NWS Inundation Mapping
NC Flood Inundation Mapping Network
http://fiman.nc.gov
• Available for sites other than NWS Forecast
Points
• Need to request a Login & Password
FIMAN
Observed Rainfall
Forecast Rainfall
Factors Impacting Rainfall Distribution in Landfalling and Evolving Tropical
Cyclones
• Storm track and location
• Time of day – core rainfall overnight/ outer band rainfall during day
• Storm size – the bigger the storm, the more it rains at any given spot
• Storm motion – slower moving storms typically produce more rain at any given spot
• Nearby synoptic-scale features (i.e. fronts)
• Heaviest rainfall usually occurs along and 75 miles either side of the storm track
• Different with every system
Tropical Storm Alberto
It’s all about interactions!Forecasting Schematic for Heavy Events
Hanna interacted with a cold front and upper
level disturbance shifting the rainfall swath left of
track.
72
83
Tropical Storm Hanna
Hurricane Fran – Along Track Heavy Rainfall
Ernesto Example
Crest to Crest Relationships
MMEFSMulti Meteorological Model Ensemble Forecast System
What is MMEFS?Short-term Hydrologic Ensemble Forecasts generated from using the QPF values from the associated meteorological model ensemble data.
MMEFSMulti Meteorological Model Ensemble Forecast System
How does MMEFS work?
METEOROLOGICAL PRECIPITATION (QPF) ENSEMBLES
Hydrologic Model
No Forecaster Intervention
FORECASTSTREAMFLOW ENSEMBLES
MMEFSMulti Meteorological Model Ensemble Forecast System
Why do we have MMEFS
?
Uncertainty- our inability to know for sure- risk
MMEFSMulti Meteorological Model Ensemble Forecast System
Why do we have MMEFS?
Future Rainfall?
Esti mati ng Past Rainfall?Reservoirs?
Stage to Flow Relati onship?
River Gage Observati ons? What ’s Upstream?
Extreme Forecasts?
Uncertainty in River Forecasting
MMEFSMulti Meteorological Model Ensemble Forecast System
Why do we have MMEFS?
Future Rainfall?
Esti mati ng Past Rainfall?Reservoirs?
Stage to Flow Relati onship?
River Gage Observati ons? What ’s Upstream?
Extreme Forecasts?
Uncertainty in River Forecasting
MMEFSMulti Meteorological Model Ensemble Forecast System
Why do we have MMEFS?
Future Rainfall?
Uncertainty in River Forecasting
MMEFS attempts to capture the uncertainty in both time and magnitude of the future precipitation and its influence on hydrologic response.
http://www.srh.noaa.gov/serfc/?n=mmefsfaq