iAdvanced Hydrologic Prediction System (AHPS)


	AHPS provides new information and products through the infusion of new science and technology. This service improves flood warnings and water resource forecasts to meet diverse and changing customer needs.

General Information: The Advanced Hydrologic Prediction System is a National Inititive undetaken, by the NOAA and the National Weather Service, to provide enhanced hydrologic services, in support of protrecting life, property, and economic well being of this nation. For complete service inititive information, link to the National Weather Service, Office of Hydrologic Development.

Plot Descriptions
1. Flow Exceedance Plot: Displays inflow or discharge on the Y-axis and date on the X-axis. The traces represent daily probability exceedance values. These probabilities are calculated using over 50+ forecast ensembles. The colors of each trace represents probability of exceedance level of the trace information.

2. Flow Accumulation Exceedance Plot: Displays inflow or discharge accumulative volumes on the Y-axis and date on the X-axis. The traces represent daily accumulated probability of exceedence volumes. These probabilities are calculated using over 50+ forecast ensembles. The colors of each trace represents probability of exceedance level of the trace information.

3. Monthly Volume Plot: Displays inflow or discharge volumes on the Y-axis and date on the X-axis. The bars represent exceedance probability of monthly volumes. These probabilities are calculated using over 50+ forecast ensembles. The colors of each bar represents probability of exceeding that volume level for the month. At the bottom of the plot you will find the summary of the probability of exceedance for the total period of the plot.

4. Trace Ensemble Plot: This trace is often refered to as the 'spaghetti' plot. It displays all the traces ploted on the same time scale. This plot does not contain explicit probabilistic information but does show the variability of the forecast data. The Y-axis is the selected hydrologic parameter and the X-axis is date of the analysis selected at forecast time. The trace color code represents the year.

5. Exceedance Probability Plot: The exceedance probability plot presents the results of a frequency analysis of a given output variable for a speified time window. Values of the output variable and/or the fitted probability distribution are plotted against the exceedance probability.

6. Expected Value Plot: This line bar plot represents the mean, standard deviation, and max/min values of the probability distribution. There is bar for each select time scale interval in the total forecast analysis window. They can represent any hydrologic parameter provided for in the ensemble forecast program.

7. Probability Histogram Plot: The probability histogram plot depictes exceedance probability ranges associated with values of an hydrologic output variable. The plot includes a series of stacked bars, one fore each analysis interval within an analysis window. Each segment of a stacked bar represents an exceedance probability range and is plotted against the associated values values of the hydrologic output variable. The example below is a two week of mean flow at this forecast point.

US Dept of Commerce
National Oceanic and Atmospheric Administration
National Weather Service
Northwest River Forecast Center (NWRFC)
5241 NE 122nd Avenue
Portland, Oregon 97230-1089
Telephone: 503-326-7401

Last Modified: December 9, 2005

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