Narrative:

What appeared to be a rain shower was approaching the field from the southeast as we lined up for takeoff on runway 10. The shower activity was several miles and did not appear to be the least bit threatening; either visually or on our weather radar. Since the departure procedure called for a climb to 520 ft MSL with an immediate left turn away from the shower; with the captain's concurrence I began the takeoff roll. Several seconds later; the predictive windshear system (pws) gave the aural warning 'windshear ahead!' captain immediately rejected the takeoff at approximately 90 KTS. Looking outside it appeared that it might have been a false warning. However; as we turned off the runway at the mid-field taxiway; the aircraft began to be buffeted by gusting winds. Within two to three minutes; as captain parked the aircraft for a brake and wheel inspection by maintenance; very heavy rain began; reducing visibility to no more than 100 ft. There is absolutely no doubt that the pws worked as advertised -- predicting that we would have been in a very real windshear (possibly microburst) event had we continued that takeoff. It is very likely that the timely and decisive action taken by the captain in rejecting the takeoff saved an aircraft and 76 precious lives. It is worth noting that two other airlines had aircraft ready to taxi out for departure when they heard all of this occur on tower frequency. Neither one of them asked for taxi until more than half an hour later.

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Original NASA ASRS Text

Title: A B737-800 Captain rejected a takeoff for a predictive windshear warning in apparent clear weather. After clearing the runway severe weather hampered subsequent flight operations.

Narrative: What appeared to be a rain shower was approaching the field from the southeast as we lined up for takeoff on Runway 10. The shower activity was several miles and did not appear to be the least bit threatening; either visually or on our weather radar. Since the departure procedure called for a climb to 520 FT MSL with an immediate left turn away from the shower; with the Captain's concurrence I began the takeoff roll. Several seconds later; the predictive windshear system (PWS) gave the aural warning 'WINDSHEAR AHEAD!' Captain immediately rejected the takeoff at approximately 90 KTS. Looking outside it appeared that it might have been a false warning. However; as we turned off the runway at the mid-field taxiway; the aircraft began to be buffeted by gusting winds. Within two to three minutes; as Captain parked the aircraft for a brake and wheel inspection by maintenance; very heavy rain began; reducing visibility to no more than 100 FT. There is absolutely no doubt that the PWS worked as advertised -- predicting that we would have been in a very real windshear (possibly microburst) event had we continued that takeoff. It is very likely that the timely and decisive action taken by the Captain in rejecting the takeoff saved an aircraft and 76 precious lives. It is worth noting that two other airlines had aircraft ready to taxi out for departure when they heard all of this occur on Tower frequency. Neither one of them asked for taxi until more than half an hour later.

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.