Narrative:

A developing line of thunderstorms was located east of iad running north to south. ATC (potomac approach) cleared us direct to druzz to cross at 11000 and 250 knots and advised us to expect continuous moderate turbulence fl 240 to 11000. The line of thunderstorms was developing rapidly to the south and soon extended to druzz. I informed ATC that we were unable druzz due to weather; and we were cleared to deviate as necessary south; direct aml when able; descend to 8000. We flew a 140 heading to get around the weather to the south. ATC advised us that there were level 5 thunderstorms north and south of our position but his radar showed a hole in the line at a heading of 120; and once through the hole; he would vector us for an east downwind to iad; cleared to 4000 feet. Unfortunately the weather was developing so quickly the hole between the cells closed up before we could penetrate the line. I informed ATC and told them that we needed a heading of 180-200. He cleared us deviations as necessary; fly heading 090 when able. Passing approximately 4300 feet at the aml 210/030 we received an egpws 'caution terrain; caution terrain' warning. The copilot executed the escape maneuver; and passing 5000 feet in the climb ATC called and directed a climb to 8000. We continued to work our way through the level 5 cells and eventually cleared the line of weather for an east downwind to 19L. Throughout this incident we were experiencing continuous moderate turbulence; bordering on severe; and heavy rain. It is my assumption that the ATC controller cleared us to 4000 feet anticipating that we would be able to maintain a 120 heading to clear the weather; and then turn to a 090 heading. When the thunderstorms closed in front of us and we forced to deviate to a 180-200 heading; we flew into a sector with higher terrain. I believe that the ATC controller was doing a good job of working several aircraft in an extremely dynamic and deteriorating weather situation. It was the co-pilots leg; and he did an outstanding job.

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Original NASA ASRS Text

Title: An air carrier Flight Crew responded to an EGPWS TERRAIN warning while being vectored by Approach Control to avoid thunderstorms in the vicinity of the airport of intended landing.

Narrative: A developing line of thunderstorms was located east of IAD running north to south. ATC (Potomac Approach) cleared us direct to DRUZZ to cross at 11000 and 250 knots and advised us to expect continuous moderate turbulence FL 240 to 11000. The line of thunderstorms was developing rapidly to the south and soon extended to DRUZZ. I informed ATC that we were unable DRUZZ due to weather; and we were cleared to deviate as necessary south; direct AML when able; descend to 8000. We flew a 140 heading to get around the weather to the south. ATC advised us that there were level 5 thunderstorms north and south of our position but his radar showed a hole in the line at a heading of 120; and once through the hole; he would vector us for an east downwind to IAD; cleared to 4000 feet. Unfortunately the weather was developing so quickly the hole between the cells closed up before we could penetrate the line. I informed ATC and told them that we needed a heading of 180-200. He cleared us deviations as necessary; fly heading 090 when able. Passing approximately 4300 feet at the AML 210/030 we received an EGPWS 'CAUTION TERRAIN; CAUTION TERRAIN' warning. The copilot executed the escape maneuver; and passing 5000 feet in the climb ATC called and directed a climb to 8000. We continued to work our way through the level 5 cells and eventually cleared the line of weather for an east downwind to 19L. Throughout this incident we were experiencing continuous moderate turbulence; bordering on severe; and heavy rain. It is my assumption that the ATC controller cleared us to 4000 feet anticipating that we would be able to maintain a 120 heading to clear the weather; and then turn to a 090 heading. When the thunderstorms closed in front of us and we forced to deviate to a 180-200 heading; we flew into a sector with higher terrain. I believe that the ATC controller was doing a good job of working several aircraft in an extremely dynamic and deteriorating weather situation. It was the co-pilots leg; and he did an outstanding job.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.