any associated with lesser rates of precipitation. Turbulence should be expected to occur near convective activity, even in clear air. Thunderstorms are a form of convective activity that imply severe or greater turbulence. Operation within 20 miles of thunderstorms should be approached with great caution, as the severity of turbulence can be much greater than the precipitation intensity might indicate. 

## Weather Avoidance Assistance 

To the extent possible, controllers will issue pertinent information on weather and assist pilots in avoiding such areas when requested. Pilots should respond to a weather advisory by either acknowledging the advisory or by acknowledging the advisory and requesting an alternative course of action as follows: 

• Request to deviate off course by stating the number of miles and the direction of the requested deviation. 

• Request a new route to avoid the affected area. 

• Request a change of altitude. 

• Request radar vectors around the affected areas. 

The controller’s primary function is to provide safe separation between aircraft. Any additional service, such as weather avoidance assistance, can only be provided to the extent that it does not detract from the primary function. It’s also worth noting that the separation workload is generally greater than normal when weather disrupts the usual flow of traffic. ATC radar limitations and frequency congestion may also be a factor in limiting the controller’s capability to provide additional service. 

## Electronic Flight Displays (EFD) /Multi- Function Display (MFD) Weather 

Many aircraft manufacturers now include data link weather services with new electronic flight display (EFD) systems. EFDs give a pilot access to many of the data link weather services available. 

Products available to a pilot on the display pictured in Figure 13-15  are listed as follows. The letters in parentheses indicate the soft key to press in order to access the data. 

• Graphical NEXRAD data (NEXRAD) 

• Graphical METAR data (METAR) 

• Textual METAR data 

• Textual terminal aerodrome forecasts (TAF) 

• City forecast data 

• Graphical wind data (WIND) 

• Graphical echo tops (ECHO T,,,OPS) 

• Graphical cloud tops (CLD TOPS) 

• Graphical lightning strikes (LTNG) 

• Graphical storm cell movement (CELL MOV) 

• NEXRAD radar coverage (information displayed with the NEXRAD data) 

• SIGMETs/AIRMETs (SIG/AIR) 

• Surface analysis to include city forecasts (SFC) 

• County warnings (COUNTY) 

• Freezing levels (FRZ LVL) 

• Hurricane track (CYCLONE) 

• Temporary flight restrictions (TFR) 

Pilots must be familiar with any EFD or MFD used and the data link weather products available on the display. 

## Weather Products Age and Expiration 

The information displayed using a data link weather link is near real time but should not be thought of as instantaneous, up-to-date information. Each type of weather display is stamped with the age information on the MFD. The time is referenced from Zulu when the information was assembled at the ground station. The age should not be assumed to be the time when the FIS received the information from the data link. 

Two types of weather are displayed on the screen: “current” weather and forecast data. Current information is displayed by an age while the forecast data has a data stamp in the form of “__ / __ __ : __.” [Figure 13-16] 

## The Next Generation Weather Radar System (NEXRAD) 

The NEXRAD system is comprised of a series of 159 Weather Surveillance Radar–1988 Doppler (WSR-88D) sites situated throughout the United States, as well as selected overseas sites. The NEXRAD system is a joint venture between the United States Department of Commerce (DOC), the United States DOD, as well as the United States Department of Transportation (DOT). The individual agencies that have control over the system are the NWS, Air Force Weather Agency (AFWA) and the FAA. [Figure 13-17] 

NEXRAD data for up to a 2,000 mile range can be displayed. It is important to realize that the radar image is not real time and can be up to 5 minutes old. The NTSB has reported on 2 fatal accidents where in-cockpit NEXRAD mosaic imagery was available to pilots operating near quickly-developing and fast-moving convective weather. In one of these accidents, the images were from 6 to 8 minutes old. In some cases, NEXRAD data can age significantly by the time the mosaic image is created. In some extreme latency cases, the actual 

