As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
IN CRUISE FLT AT FL400, RADAR SHOWS SIGNIFICANT WX 70 -100+ NM LEFT AND AHEAD OF AIRCRAFT WITH NO ACTUAL WX PRESENT WHEN IN "AUTO". GROUNDED-YES. REMOVED & REPLACED WEATHER RADAR ANTENNA PLATE, REF B737-900 AMM 34-43-11. ACCOMPLISHED WXR SYSTEM OPERATIONAL TEST AMM 34-43-00-710-802-001. ALL TESTS PASS. ACCOMPLISHED GVI OF RADOME. NO DEFECTS NOTED.