Summer Branch Drop Advisory: Although the fall webworms and some early foliage (and the calendar) say fall, with the light east wind fighting daily breezes and high temperatures in the forecast it's time for another summer branch drop advisory. Summer branch drop is a widely-observed, poorly-understood phenomenon where large horizontal or leaning limbs or stems suddenly break and fall. It seems to occur more on hot, calm afternoons of late summer, and may be associated with heavy foliage and/or heavy seed crops. Recommendations on hot, still, late summer afternoons.
Practice situational awareness; don't leave immobile people (infants, elderly, etc.) directly under large oak trees; do run away if you hear a sharp crack in an overhead oak tree. -NPS Yosemite