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# New Web Images:LAMP Uncertainty and Threshold Plots

LAMP Uncertainty and Threshold Plots

February 02, 2009

## 1. Introduction

The LAMP Uncertainty and Threshold Plots are visual depictions of many of the LAMP probabilities and their associated thresholds. The elements featured on this site include :

• Ceiling Height
• Conditional Ceiling Height
• Visibility
• Conditional Visibility
• Probability of Precipitation on the Hour
• Probability of Freezing
• Probability of Freezing or Snow

The probabilities and thresholds for the above elements are depicted in two visual schemes:

1. Color-coded bar plots displaying whether a given probability exceeds the threshold required to make a forecast and the certainty of that forecast.
2. Line graphs of the probabilities and thresholds, with the ability to display multiple categories for the same element in one plot.

This page will be accessible from the GFS-LAMP Realtime Products page, or by one of the following links:

 http://weather.gov/mdl/gfslamp/uncertform.php (Uncertainty plots - station selection page) http://weather.gov/mdl/gfslamp/uncertplots.php (Uncertainty plots - direct access) http://weather.gov/mdl/gfslamp/threshplots.php (Threshold plots - direct access)

Note: If you use the second or third link to access this product, you must first input and submit a four letter station ID or select a station using the drop down menus to display the plot graphic.

## 2. FAQ

Q:  How are the thresholds determined?
A:  The thresholds are statistically derived as part of the LAMP developmental process. They vary by element, element category, cycle, projection, region, and season.

Q:  What do the different categories mean on the Uncertainty Plots?
A:  The "uncertainty categories" convey whether or not a probability exceeds its corresponding threshold and its proximity (whether above or below) to that threshold. For a specific explanation of each category, see the table below:

 No Probability is below the threshold by ≥ 10% Chnc Probability is below the threshold by < 10% Lkly Probability exceeds the threshold by < 10% Yes Probability exceeds the threshold by ≥ 10%

Q:  Why are some categories missing for ceiling height and visibility?
A:  The ceiling height and visibility categories displayed on these sites were chosen in correspondence with the MVFR, IFR, and LIFR flight categories. Not every category for ceiling height and visibility is displayed, but only those relating to these specific flight categories. To determine the best category forecast, LAMP considers all categories, beginning with the most rare. To see the official LAMP categorical forecast, please refer to the text bulletin page.

## 3. Additional Help and Information

For additional help with understanding and using the Uncertainty and Threshold plots, please see the following link:

PowerPoint Tutorial

Scott Scallion
NWS/OST/MDL/LAMP

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