Rvrfcsting

National Oceanic and Atmospheric Administration’s
National Weather Service 1 Missouri Basin River Forecast Center
Pleasant Hill, MO
Scott Dummer
Development and Operations Hydrologist
Managing a River Forecast Scheme
Missouri Basin River Forecast Center
National Weather Service Pleasant Hill, MO

Pleasant Hill, MO
 Provide a good forecast in a timely manner
 Keep your model properly balanced in a way
that is representative of the hydro-
meteorological conditions
 Keep model modifications representative, yet
understandable for the next forecaster so they
understand what deviations from the model you
made and why
What is the goal of managing a river
forecasting scheme?

Pleasant Hill, MO
 Model limited to 6-hr time step and mean areal
values
 Use instantaneous and gridded areal data to
Make proper adjustments to model based on
this and other data
Factors to consider when managing a
well balanced well calibrated
forecasting scheme

Pleasant Hill, MO
 Need maintain good data as input – i.e.;
Garbage in, Garbage Out
 Need to develop and maintain well calibrated
models
 Need to have a good forecaster judgement to
modify input & model states as needed to
overcome model limitations and assumptions
so that the model is well balanced
forecasting scheme

Pleasant Hill, MO
 Soil moisture needs to reflect the current
conditions.
 Limitation is evapotranspiration is calculated
using mean monthly values.
 Weather could be warmer, colder, sunnier,
cloudier, windier, less windy, more humid,
less humid than ‘normal’
forecasting scheme

Pleasant Hill, MO
 Snow water equivalents and snow cover need
to reflect current conditions
 Reservoir outflows, diversions, and return flows
need to represent the current conditions
 Observed river flows reflect the current
conditions
forecasting scheme

Pleasant Hill, MO
 To make educated changes to the input or
model states, look at all available data
 Not all data is input to the model
forecasting scheme

Pleasant Hill, MO
 Precipitation Data
 View 24-hr precip or 1-hr PC data and 1-hr to 24-hr radar data in
XNAV
 View areal extent and timing of radar precip in relation to basin in
XNAV
 View 24-hr and PC data in XDAT
 View 24-hr and PC data in XDAT
 View 24-hr precip in with View Precip By Magnitude in SLOD Toolbox
 View 6-hr MAP and MAPX in CHPS Spatial Data Viewer
 View comparisons of PC data to surrounding 24-hr precip with “DCP
Reports by State” in Support Toolbox
 View radar composite loops in D2D
Managing a well balanced, well calibrated
forecasting scheme

Pleasant Hill, MO
 Stage Data
 View all received in XDAT
 View selected stations observed and forecast stages in
graphical form in AWIPS Timeseries Plot & CHPS Stage Plots
 View 6-hr data in CHPS flow plot and all data in CHPS Stage
Plots
 View USGS sites on USGS homepage to compare with stages
we receive
 View Bureau of Reclamation sites on Bureau homepage
forecasting scheme

Pleasant Hill, MO
 Snow Data
 View observed Snow Fall (SF), Snow Depth (SD) and Snow Water
Equivalent Data in XNAV and CHPS Spatial Data Viewer and Time series
Plot
 View Snow Fall (SF), Snow Depth (SD) and Snow Water Equivalent Data in
time series form with XDAT, or with CHPS Plots
 View all Snow Depth and Snow Water Equivalent Data by state with
“SnowData” in Support toolbox
 View SWE from NOHRSC in text product MSPSWEKRF or for selected
stations in CHPS Snow Plots
 View Snowpack sublimation in text product MSPSCVKRF
 View snow cover on clear data from Satellite imagery
 View snowpack from NRCS and snotel data from Climate Center using
Snowdata link on MBRFC web page
 View NOHRSC snow Data on interactive web page
forecasting scheme

Pleasant Hill, MO
 Flow Data
 View observed and blended flow in CHPSView reported diversions
and outflows in XDAT, or in CHPS plots
 View Bureau of Reclamation diversions and flows on USBR web page
 View State of Nebraska diversions and flows on NE DWR web page
 View State of Colorado diversions and flows on CO DWR web page
 View USGS flows and measurements on USGS web page
 View USGS flows plotted in the CHPS flow plot
 Review Missouri River flow measurements in NWSChat
mbrfcagencieschat chatroom
 View Missouri River measurements on USACE web page
forecasting scheme

Pleasant Hill, MO
 Soil Moisture Data
 View SAC-SMA contents or deficits in XNAV, CHPS Spatial
Data Viewer, or for particular locations in the CHPS SACSMA
Plots
 Soil Moisture Link on MBRFC web page
 High Plains Climate Center’s ET estimates
 Palmer Drought Severity Index
 Crop Moisture Index
 Standardized Precipitation Index
forecasting scheme

Pleasant Hill, MO
 The river forecast model (CHPS) has numerous
limitations
 The Forecaster must make modifications (MODS) to
account for those limitations
forecasting scheme

Pleasant Hill, MO
River Model Assumptions:
 Static and accurate Stage-Discharge Relationships
 Rainfall distributed evenly over basin
 Rainfall distributed evenly over 6 hour period
 Runoff not a function of intensity within the 6 hour period
 Snowmelt accurately defined with Snow-17 parameters
 Rainfall/runoff accurately defined with SAC-SMA parameter
 Static and accurate Unit Hydrographs
 Static and accurate routings
forecasting scheme

Pleasant Hill, MO
Modify input based on available data not in the model
 QC data that is input to the model and analyze data not
input to model
 Modifications to input should be reasonable
Modify model states based on the response of the model to
changes in input
 Based on hydrologic philosophy
 Modifications to model states should be reasonable
forecasting scheme

Pleasant Hill, MO
 Could be an input data (Meteorological Forcing,
precip/temperature) problem
 Could be a model states problem (Soil Moisture)
 Could be model parameters not defined correctly
(routing, UH, etc)
forecasting scheme

Pleasant Hill, MO
Stage Data:
 Bad stage value – check all values
 Shifted rating not current—check shift log and recent
plotted measurements
 Check USGS stages and flows
 Check to see if station is rated or has a poor rating
 Check to see if station has a looped rating/backwater
affected
forecasting scheme

Pleasant Hill, MO
Precipitation Data:
 Check areal distribution of precipitation—May need to
adjust unit hydrograph or precipitation
 Check temporal distribution of precipitation—May want to
shift distribution –May also want to consider MAP (rain
gage only)
 Check timing of precipitation in CHPS precip plot– Could
adjust if precipitation occurred near beginning or end of
6-hour period
forecasting scheme

Pleasant Hill, MO
Precipitation Data:
 Check precipitation intensity—High intensity may cause
runoff prior to saturation and give reason to increase
runoff
 Check whether precipitation is rain or snow
 Compare MAPX to MAP. Default (excluding Mountains)
is MAPX, may want to see how MAP performs using a
SWITCHTS Mod in CHPS
forecasting scheme

Pleasant Hill, MO
Flow Data
 Check Reservoir Outflows– Call other agency if needed
 Check Diversions
Snow Data
 Check snow depths, snow water equivalents (SWE) and
areal extent of snow cover
forecasting scheme

Pleasant Hill, MO
Snow-17 –Adjust to match observed data, or NOHRSC
Estimates if they make sense
 Modify Melt Factor or lower Temperatures to delay or
initiate melt if confident in saturation of UZTW
 Modify Areal Extent (ASECCHNG) of Snow Cover if
confident in SWE and UZTW data after melt has started.
forecasting scheme

Pleasant Hill, MO
SAC-SMA
 Check Soil Moisture
 Timing of filling of UZTW should coincide with initiation of
runoff
 Adjust contents of UZTW accordingly
 Compare SAC-SMA states of surrounding basins
Adjustments reasonable based neighbors and recent
precipitation events in the area
 IF UZTW saturated and not enough RO, increase
contents of LZTW to reduce percolation demand.
forecasting scheme

Pleasant Hill, MO
SAC-SMA (Cont.)
 Adjust contents of UZTW accordingly (Cont.)
 Is there reason to believe actual ET varied from
computed? (Remember ET calculation is a
climatological normal) —Adjust accordingly
 Wetter, colder, cloudier than normal
 Hotter, drier, winder than normal
 Be aware of basins that include impervious areas
 ADIMC (where used) = UZTW + LZTWC
forecasting scheme

Pleasant Hill, MO
Check type of runoff
 Adjust states (UZTWC, LZTWC) with reason to make
runoff another type
 If total runoff correct but too much interflow– adjust runoff
by placing total for a number of periods of interflow into
the period of rainfall
 If too much percolation going to base flow reduce
contents of LZTW if saturated
 Modify base flow (LZFP, LZFS)
forecasting scheme

Pleasant Hill, MO
Unit Hydrograph/Unitgraph—1 inch (unit) runoff per unit time
 Check applicability of unitgraph
 1st option Modify unitgraph UNITHG to adjust timing of
runoff
 2nd option Adjust precip TSCHNG_MAP_MAT, or RRICHNG
to adjust timing of runoff
 3rd option Adjust timing of runoff itself using ROCHNG
(bypasses SAC-SMA Model)
forecasting scheme

Pleasant Hill, MO
Backwater Affected Areas
 Be aware of locations that are backwater affected.
 These are areas that do not have stable stage-discharge
relationship due water backing up to location from to
downstream reservoir, or river
 Watch for hydrographs that appear to be cresting then
rise some more.
forecasting scheme

Pleasant Hill, MO
 Communicate with WFO about river, soil and snow
conditions
 Keep aware of and Check SAC-SMA states in CHPS
Plots
 Monitor recent weather and possible variations to climate
base ET – make adjustments to SAC-SMA parameters
as necessary
 Where confident, use model and data to adjust model
locations where there is little confidence or data
 Only adjust data and model states to reasonable values
forecasting scheme

Pleasant Hill, MO
 Document reasons to adjust model
 Conduct verification analysis on your performance
 Wait for upstream groups to be finished before
forecasting downstream group
 Make major tributary runs before 8am
 Save mainstem run shortly before 8am
 Understand the model so that you can note why the
model doesn’t work correctly
 Only with your help can we improve the model
forecasting scheme

Pleasant Hill, MO
 Scarcity of observed precipitation and/or temperature data
 Inaccurate WSR-88D precipitation estimates
 The duration of precipitation was inconsistent with model
intervals
 Non-uniform spatial distribution of precipitation
 The snow model performed poorly
 The Sacramento Model performed poorly
 The unit hydrograph was in error
 Deficiencies in the channel routing procedures
forecasting scheme
Top 15 Reasons Why I Blew My Forecast

Pleasant Hill, MO
 The stage-discharge relationship was in error due to such
occurrences as backwater, ice action, log jams, etc
 Scarcity of river/reservoir/diversion data
 The QPF did not verify
 Erroneous precipitation reports were input to the models
 Erroneous stage reports were input into the forecast system
 The forecast temperatures were in error
 Drainages assumed to be “non-contributing” actually
contributed
forecasting scheme
Top 15 Reasons Why I Blew My Forecast

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