Professional Pilot, January 2018

Mt St Helens erupts on May 18 1980 One of several major shield volcanoes in the Pacific Northwest Mt St Helens represents the potential for a major volcanic ash event over the region are normally advection or precipitation types forming during the winter months they can become thick and persistent Additionally despite winter months having an average monthly temperature above freezing daily temperatures can and do drop several degrees below freezing Fog in connection with subfreezing temperatures is a recipe for freezing fog so operators often need to deice before flight Though the coasts with a good chance of rainfall through the year may not present ideal flying weather most of the region experiences periods of excellent weather during the summer months With less than 1 inch of rain falling during some summer months skies are frequently clear and temperatures are high enough to require substantial weight adjustments to account for departures under increased density altitudes However the much drier weather during the summer can lead to a different weather hazard Fire weather As recent summers have demonstrated the lack of rain during the summer has been coupled with far above average temperatures often climbing into the 30 40 C or 86 104 F range This combination of hot and dry has contributed to active wildfire seasons in the heavily for 58 PROFESSIONAL PILOT January 2018 ested region Though the prevailing westerlies move much of the smoke eastward over the mountains at low levels the southerly flow has produced greatly reduced visibility at many of the area airports and forced a number of airspace closures to facilitate firefighting activity The Pacific NW is also a geologically active region with several major volcanoes Most of these volcanoes are dormant but as Mt St Helens reminded us in 1980 they are far from extinct Over the past decade or so volcanic activity has been minimal in the area but pilots should recognize this can change quickly The region may be faced with a volcanic ash advisory grounding a lot of air traffic based in the region and diverting transiting aircraft The mountains also present another potential flying hazard for the region Steady winds flowing over the Cascades and other ranges there will frequently produce standing mountain waves The height of the mountains ensures that these waves will affect much of the lower atmosphere Even an isolated peak can create a standing wave and strong mechanical shear downwind Whenever you are faced with winds blowing toward you over a mountain or range you should expect to be in a region of mountain waves and possibly encounter moderate to strong turbulence Karsten Shein is a climatologist with NOAA in Asheville NC He formerly served as an assistant professor at Shippensburg University Shein holds a commercial license with instrument rating Photo by Richard Bowen Another risk of flying in the mountainous terrain of the Pacific NW is that the frequent and low cloud decks can easily obscure terrain and other obstacles The region has seen its share of CFIT accidents as pilots misjudged their position relative to the mountains Unfortunately many of these accidents have occurred in remote areas during winter At higher elevations these mountains can build an impressive snow pack that can quickly bury a downed aircraft and make the rescue of survivors difficult if not impossible When flying across or near the mountains it is important to pay extra attention to your position and maintaining minimum safe altitudes rather than depending on any outside cues if ceilings or visibility are issues Oregon Washington and British Columbia have over 500 public use airports with a majority of them in the more heavily populated Cascadia portion of the Pacific Northwest In fact for many communities especially in the northern part of the region aviation is often the only viable transportation option The region also boasts 3 major hubs for trans Pacific travel SEA PDX and YVR Because of the importance of aviation to the region Boeing still maintains a facility north of Seattle there is a robust weather observing and forecasting network in place This provides a level of coverage that ensures pilots throughout the region have access to reliable weather info However given the many remote community airports scattered through the region and the highly variable nature of the weather as one goes between mountain and coastal climates it is easy to recognize the importance of frequent weather reporting by pilots In many parts of the Pacific Northwest pireps may be the only information available to meteorologists and your fellow pilots