Why winter weather is the most detrimental for flying.

 The cold temperatures of places like Colorado are often accompanied by strong weather patterns that carry high winds. Alongside the winds can be freezing rain or large snowflakes, both of which can be difficult to deal with in an aircraft.

For aircraft, two things are very important, being able to generate lift, and having a way, either visually or by instrument, to navigate the aircraft safely. Winter weather can inhibit both of these along with other undesired conditions. 

To start off, freezing rain and snow are both water, which can introduce a variety of situations. This means that two dangerous conditions can occur during flight, flameout and icing. A flameout can occur when an engine ingests too much water or when sufficient icing in the engine occurs during operation, this "puts out" the engine and requires a restart, which may or may not be successful. Depending on when this occurs it can be very dangerous as an aircraft is very limited on what it can perform during the loss of 1 or more engines as that is a severe loss of power to a heavy vehicle. Aircraft have had dual flameouts occur while the aircraft was flying a low pattern on approach, this can easily into a deadly situation. Ice buildup has caused a number of these alongside rain. If you were to add that risk to the cold temperatures which introduce icing to the aircraft body as well, you now can lose lift while adding the ice weight to the aircraft body due to ice buildup. Ice makes an airfoil dirty by disrupting the intended air pathing around the wing, it also doesn't freeze in a smooth shape but rather an angular and jagged pattern further increasing drag and ruining the airfoil shape.

Icing can also cause other issues based of an aircraft's design. It can freeze pitot holes closed or disrupt the performance of various instruments on an aircraft. Ice just doesn't get along with aircraft and instruments which is why avoiding icing conditions without deicing equipment is crucial. Even with deicing they are only temporary fixes and need to be avoided when possible.

Other issues cold weather provides are prominent on takeoff and landing. These are a combination of runway conditions and visibility. Ice and standing water or snow on runways is generally not beneficial to aircraft as they exacerbate the difficulty of controlling an aircraft. When you add the poor visibility produced by rain or snow it can become even worse. Cold weather in Washington also brought with it dense and low sitting cloud layers and fog which are both still unhelpful when trying to takeoff. 

Pilots Handbook of Aeronautical Knowledge (2016, August 24) FAA

Pilot’s Handbook of Aeronautical Knowledge (faa.gov)

Dead-stick landing (September 2008) Mark Lacagnina

Dead-Stick Landing (flightsafety.org)