The obvious hazard of showery precipitation is the reduced visibility that it causes and that a VFR flight can quickly become an IFR flight. What is not so obvious is the severe turbulence that can also be created by a sudden intense rain shower. We as pilots need to understand that as rain falls it cools the air around it due to evaporation. This causes the cooler air to begin to descend in respect to the nearby warmer air. This creates down drafts and microbursts that can be quickly sheared by rising updrafts caused by both advection and convection. As a general rule its best to avoid any areas that are considered moderate to severe precipitation especially at low altitudes such as during takeoffs or landings. Areas that are experiencing virga (rain that evaporates prior to reaching the ground) should also be treated with the same caution and should also be avoided.
It’s probably obvious that thunderstorms are dangerous. A typical thunderstorm will release as much energy as a 20-kiloton nuclear bomb (the bomb dropped on Hiroshima was rated up to 18 kilotons), with larger storms producing as much as 100 times more energy than that. What isn’t so obvious is where the real danger of thunderstorms comes from.
We all know thunderstorms as imposing clouds with streaks of lightning and deafening thunder, but the lightning and thunder are largely not a threat to aircraft. The great thing about electricity is that it will always take the path of least resistance. Good thing for us is that our aircraft skin has a lot less electrical resistance than we do and the energy from a lightning strike (while likely blinding) will flow around the aircraft, defuse off our static wicks, and likely leave us unscathed. Thunder is just the cold air rushing in to meet where the superheated air of the lightning strike is and is basically clapping against itself. It poses no risk to flying other than the possibility of making the pilot jump in their seat.
The real danger of thunderstorms comes from the incredibly powerful up and downdrafts that are associated with the storms. These storms can have extreme updrafts that are immediately sheared by devastating downdrafts. These shears can be so strong that no aircraft can safely pass through them. Imagine being pulled upward by a 2000ft/min updraft and then immediately slammed back down by a downdraft in excess of 6000ft/min. The structural integrity and performance of your aircraft will be put to the test and I promise it will not be a smooth ride! These intense downdrafts can cause incredibly powerful microbursts near the ground and are one of the most dangerous hazards to aircraft. Flying through or under a thunderstorm of any size should be avoided at all cost!