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This is a web-based version of the Extreme Precipitation Forecasting Table. This version focuses on the global models and ensembles. It compares their 6-h and 24-h QPF forecasts to the 6-h or 24-h precipitation Average Recurrence Intervals (ARIs) from the NOAA Atlas 14 dataset.

How to navigate:

On the main table:   Click a value (e.g., '35.0') to plot an image of QPF and QPF ARI values for that time and model. Click a model (e.g., 'GFS') to create a loop of QPF and QPF ARI values for that model at all available times.

For a different table:   Select the desired Model Run, Table/Plot Region, Duration, and ARI from the drop-down menus above, and click View Table

About the NOAA Atlas 14 Average Recurrence Intervals:  
The NOAA Atlas 14 contains precipitation frequency estimates for Average Recurrence Intervals (ARIs) from 1-1000 years. An ARI for a point location is defined as the average amount of time (i.e., years) that passes between precipitation depth exceedances (i.e., inches) for a given duration. For example, the 100-yr ARI of rainfall for a 24-hr duration in New Orleans, LA is 14.5 inches. It is expected that this depth of rainfall should occur, on average, once every 100 years. However, each rainfall event is statistically independent from one to the next. Even though the ARI represents the expected amount of time that should pass before a similar rain event occurs again, it is possible for a location to experience several 100-yr ARI rain events within the period of a few years or less.

The precipitation depth associated with an ARI varies widely across the country and is dependent on the local climatology. For a 24-hr duration in Las Vegas, the 100-yr ARI is 3.3 inches. This precipitation depth is significantly less compared to New Orleans, yet if either precipitation threshold is exceeded for their respective locations, the event would be considered "extreme" and depending on the underlying ground conditions, could lead to flooding that threaten both life and property.

ARIs are approximately inversely proportional to the Annual Exceedance Probability (AEP), which describes the probability of a particular event occurring at any one location in any given year. Precipitation thresholds that have a 100-yr ARI also have a 1% AEP, or 1-in-100 chance of occurring in any given year. In this table, quantitative precipitation forecasts (QPF) from a suite of global models are compared to the 100-yr ARI precipitation estimate at each point in the contiguous US to alert the user to when a where a top 1% precipitation event could occur. The maximum ratio of QPF to ARI found at a point in the selected domain is converted to a percentage and displayed in the table.

Global deterministic models and ensemble means generally underproduce QPF associated with extreme events. If the table highlights a value exceeding 75% of the 100-yr ARI threshold, the user should be alerted to the possibility of an extreme precipitation event occurring.

For more information:  
WDTD eLearning Webinar (~20 min) describing tool

Contributors:
Diana Stovern (Weather Prediction Center - DTB)
Bill Lamberson (Weather Prediction Center - DTB)