Map of the St. Louis area showing the position and track of the aircraft described in the post.

🇺🇸 N13720 - Boeing 737NG 724/W - United Airlines UAL8126/UA8126 (RDU-ORD-SNA) - 4.7 mi away @ 40075 ft, heading SW at 504 mph. Spotted 21x before! [10:03:30 AM CDT] #A097E9 #N13720 #B737 #UNITED #UAL8126 #UA8126 #ADSB #ADSBbot