Page 27 - February 2016

Primerby John Loughmillerremains in Canada the whole time. But, when the polar jet is making a deep intrusion into the U.S. midsection, the clipper can pay a visit to southern parts of the upper Midwest, including Illinois, Indiana and Ohio, before heading northeast towards New England.Alberta Clippers have very little moisture to work with, so 2 to 4 inches of snow on the northern side of their path is the norm. Strong and bitterly-cold north winds are their hallmark and pilots operating from east-west runways would do well to practice their crosswind techniques late in the autumn to be ready for these visitors from the Canadian prairies. Of all the winter storms, these are generally the most benign but turbulence can be intense and white-out conditions can create havoc on an approach (along with a 45+ degree crab angle, particularly if you’re flying an airplane with low mass like a light twin).Colorado Lows and Panhandle HooksAs an Aleutian Low (or its offspring) hits the Rocky Mountains, it generally loses its moisture as the circulation is forced up and over the high terrain. Once on the eastern side of the mountain range, what happens next depends on where the remnant of the low ends up.Depleted Pacific storms often reform around Colorado or a bit farther south. When the polar front’s jet stream loops south, it captures the Colorado Low (or its cousin, the Texas “Panhandle Hook” Low) and heads off towards the northeast. These low pressure areas will deepen as they follow the polar front’s jet stream, picking up moisture from the Gulf of Mexico maritime airmass and drawing it north into the Low’s circulation. As the low deepens, it will frequently cause a central plains event called a “Blue Norther” which drives very strong winds, biting cold and significant snowfall into the southern plains states, complicating life for pilots in Oklahoma, Texas and even eastern New Mexico.If a winter storm’s genesis is in this area, from west Texas up into eastern Colorado, watch out! Next to Nor’easter, these storms are the most likely ones to cause problems over a large area of the United States and southern Canada. (See the “A Winter Storms Journey” below.)Ohio Valley StormsOhio River Valley storms typically begin life in Arkansas and move through Southern Illinois, Indiana, Ohio, Pennsylvania and into New England. Almost as nasty as the Colorado and Panhandle Hook storms, the saving grace (if there is such a thing with a winter storm) is this type of storm will usually be forecast well in advance and, except for path variations +/- a few hundred miles, the forecast tracks are normally quite accurate. Ice is going to be a problem along and to the south of the track for a few hundred miles. Don’t be fooled into thinking you won’t need a FIKI (Flight into Known Icing) approved airplane just because you’re staying a couple of hundred miles to the south of the storm track – good advice for all winter storms, actually.East Coast StormsThe path of these storms depends on where they originate and the synoptic set up (large scale weather features). They can move along thewestern margin of the Appalachians, along the coastal plain, or anywhere within a few hundred miles off shore. The worst place for an aviator to be – especially at low altitude - is to the west of the storm’s center when it’s just offshore.Normally, the storm’s genesis is somewhere in an arc from the Gulf of Mexico to near Cape Hatteras. When it is still down in Dixie, thunderstorms typically break out but, once it is offshore and north of Cape Hatteras, snow is likely to fall to the left of the storm’s track, with rain more likely to the right.If a Colorado Low or Panhandle Hook storm runs into a Nor’easter moving north up the coast, the two lows will merge and the storm will “bomb out”, meaning it will become a very powerful storm, very rapidly. The result is the closing of airports all along the eastern seaboard and flying conditions that are impossible for light aircraft (and many heavy ones as well).An example of a merger of two powerful storms was documented in the movie “A Perfect Storm” which accurately depicted Hurricane Grace merging with an enormous Nor’easter, resulting in the loss of the fishing vessel Andrea Gail as well as a National Guard helicopter. But you don’t need a hurricane to merge with a nor’easter to have virtually un-flyable weather; a potent winter storm will work just as well.Winter storms come in several flavors but the one thing all have in common is the bad taste they leave in the mouth of a pilot who attempts to fly through them.A Winter Storm’s JourneyThe progenitor for most severe winter storms is a remnant from a piece of energy thrown off by our old friend the Aleutian Low. After it plagues the Northwest, it crosses the Rocky Mountains and, a mere shadow of its former self, it frequently meanders into Texas, where it regenerates.FEBRUARY 2016TWIN & TURBINE • 25