Professional Pilot, February 2019

The combination of greatly reduced visibility and potential backscatter of aircraft lights means that a pilots ability to see other aircraft or obstacles before they become a danger is substantially diminished in blizzard conditions Blizzard winds also are strong and frequently gusty This often produces unmanageable crosswinds on takeoff and landing and may create momentary upsets at critical points such as when the aircraft is low and slow in ground effect Pilots should remember to include gusts in their crosswind calculations as a strong gust can push an aircraft off the glidepath before the pilot has time to respond with rudder or aileron Additionally strong sustained winds mobilize snow especially freshly fallen snow These ground blizzard conditions may extend several hundred feet above the surface And though a pilot may be on final in clear air and be able to see the runway that snow can rob visibility during the last few feet of the descent If the sun is shining above the reflection off millions of ice crystals can be blinding Polarized sun glasses are a good idea in these situations Snowfall during blizzards can be copious and may overwhelm the ability of airport crews to remove it from runways and taxiways The wind can quickly rearrange fallen snow into drifts that may extend into the runway pavement Should a tire hit one of these drifts at high speed 60 PROFESSIONAL PILOT February 2019 it is likely that the aircraft may lose control or even suffer landing gear damage Drifting and blowing snow can also adhere to airport signage making navigation at an unfamiliar airport a challenge Pilots should be aware that visiting aircraft may accidentally turn onto an incorrect taxiway or runway in these conditions While many blizzards are accompanied by subfreezing temperatures this is not a requirement and these winter storms sometimes occur in temperatures near freezing In these situations icing becomes a danger both on aircraft and on the runway Conversely winter storms may begin in warmer air and as the low passes by the airport surface temperatures drop precipitously Chemical ice melt applied to the runways to keep them clear in the early phases of the storm may not be effective in the super cold air accompanying the blizzard and standing pools of water can gradually refreeze to form slick spots on the runway and taxiways Additionally blowing snow in the blizzard can mask these slick spots as well as create a thin film of snow in spots that acts as slippery as ice Forecasting blizzards At a general scale blizzards are not difficult to forecast Meteorologists and weather models are able to track winter cyclone development with a great degree of accuracy several days in advance However some of the remaining difficulties in blizzard forecasting are the strength of the winds quantity and type of precipitation and the expected duration of blizzard conditions The reason for this level of uncertainty is that while the track and development of a winter cyclone is based on larger scale patterns and well understood atmospheric dynamics the intensity magnitude or duration of the individual conditions depend far more on smaller scale dynamics in which even small inputs can aggregate into substantial changes in outcome For example a few percent difference in humidity and a 1 or 2 degree error in temperature in the middle level of the troposphere can mean the difference between snow falling at a rate of 2 and 6 inches per hour Forecasts of snowfall totals and estimates of peak wind speeds may continue to change even just a few hours ahead of the storm However the variability of the estimates decreases dramatically as the storm nears Pilots facing a forecast blizzard or strong winter storm should simply assume the worst of the possible forecast conditions and plan accordingly If it is possible to adjust flight departures or arrivals to avoid the worst of the storm that is the best option Planning for blizzard conditions Significant winter storms are normally tracked closely by meteorologists several days to even weeks before they may impact a location Because these storms frequently occur beneath and follow the larger ridge and trough pattern of the polar jet pilots can anticipate which part of the storm is most likely to affect their route of flight or the airports from which they are operating If the track of the storms center is poleward of the airport the blizzard conditions which normally only occur in the upper rear quadrant of the system poleward and behind the low are far less likely to strike On the other hand if the low is tracking equatorward of the airport then that may place the blizzard zone right over you Of course this does not mean that pilots should take any part of a winter storm system lightly All parts of the storm contain adverse fly Bombardier Global Express kicks up a cloud of snow on departure from MDW Chicago IL Snow is just one challenge pilots face as part of winter weather operations