# AVIATION WEATHER CENTER

## N O A AN A T I O N A L   W E A T H E R   S E R V I C E

Gate Forecast Help

### Gate Forecast Overview

There is a need for forecasts of significant weather in arrival and departure sectors for the top airports. These sectors, also called gates, are polygonal regions which roughly follow ARTCC low level sectors where arrivals and departures to these airports will be routed. It is important to know whether significant weather, such as thunderstorms, could affect large portions of the sectors so that traffic can be rerouted, if needed, to other sectors.

### Decision Support Algorithm

A three tiered approach to the display is used:

• Green - no significant weather
• Yellow - some significant weather that might affect some portions of the gate
• Red - significant weather that could affect large portions of the gate

The algorithm now uses the HRRR model to determine whether there is the potential for thunderstorm activity in the gate. It starts with the HRRR composite reflectivity forecasts and the does a time lag ensemble for the last three HRRR runs. It creates a grid with the maximum composite reflectivity at each gridpoint from the three runs (for example, the 1 hr forecast from the 18UTC run plus the 2 hr forecast from the 17 UTC run and the 3 hr forecast from the 16 UTC run). From that grid, a probability factor is computed. Low composite relectivities map to low probability. High reflectivity maps to high probability.

The algorithm then computes the gate sector coverage of these probabilities. If more than 1% of the sector is covered in low probability (.25 chance), the gate is colored yellow. If more than 4% of the sector is covered in high probability (.60 chance), then it is colored red. These are then computed for each forecast time from the HRRR.

### Gate Forecast Display

The gate forecast display shows an interactive map for the region around the airport (see Fig. 1).

Figure 1. Sample gate forecast display for Atlanta

The gate sectors are shown. Typically an airport will have 6 to as many as 10 sectors. Each are colored with the current gate status (green, yellow, or red). Around each gate is an icon with the gate name and the forecasts for the next nine hours. Clicking on the icon will bring up a dialog with more information on the forecast (see Fig. 2).

Figure 2. Gate popup display for West gate at ATL

The popup shows the percent coverage of low (TS25>1) and high (TS60>4), the three HRRR runs used in the forecast (16, 15, and 14 UTC) and the time of the last update.

#### URL Options

Here is a list of the URL options:

• id=site - This selects the specific site to display. For example "KATL" for Atlanta".
• date=yyyymmddhhnn - This selects a specific date and time to display. HRRR forecasts are updated every hour. The default is current.

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