Seldom does a single weather event prompt such a sudden and habitual consumption of Tylenol and Motrin for both meteorologist and viewer simultaneously. The meteorologist- whose knowledge and wisdom for his craft are often overshadowed by guessing abilities and number of four leaf clovers shoved in a back pocket in moments of success, and the viewer- accustomed to taking what the meteorologist says with one very large grain of salt. The paper thin trust that exists between the two often flutters as effortlessly as the very flakes that broke the trust in the first place. The cause? Countless tiny snowflakes and one big lake. Lake-effect snow has been a forecaster's nightmare from when maps were drawn by hand to the current days of computer predicted models. But no one computer can accurately predict the magnitude or severity of a lake- effect event with the same success as a synoptic event. To describe lake effect snow as temperamental would be a gross understatement. Often arranging itself in rogue bands of heavy snow, lake- effect can stop and start on a dime, and it can dump a foot of snow on one neighborhood and leave the residents of another wondering why the idiot meteorologist keeps breaking into Oprah about some kind of Lake Effect Snow Warning. And in its unpredictable nature comes its beauty. One of natures precious wintertime treats, just the prospect of lake- effect snow strikes both fear and awe in the hearts of a forecaster. There are, however, trends. Subtle nuances that fade in the background to the untrained eye, but trends nonetheless. If nothing else, these trends offer a faint possibility that maybe, just maybe, Mother Nature may be following a game plan all along. The conditions that must be in place for lake- effect snow to form are not easy to come by. Cleveland Meteorologist Dick Goddard likes to refer to the junction of such conditions as "ducks all lined up". Actually, I don't think the ducks like lake- effect snow, but that's beside the point. His point is accurate, although potentially offensive to ducks. In fact, these conditions are so difficult to achieve in one given place that lake effect only occurs in four locations on the entire planet: the southeast shoreline of the Hudson Bay, areas just east of the Great Salt Lake in Utah, the northernmost Japanese island of Hokkaido, and of course, the Great Lakes. Lake snows generate downwind of the Lakes. Sure, lots of people live near a Great Lake, but only a few lucky ones live downwind. Downwind though, is very much a relative term. One day, it takes a west wind. Another, a north wind. But that's just one piece of the puzzle. Pace yourself. Meteorology follows from this point on. As I stated, the dynamics necessary for significant lake snows don't happen everyday. While there are exceptions, lake- effect is most prevalent from late fall to early winter, when the combination of warm lake waters and increasingly cold intrusions of arctic air coincide to play out one of weather's most fundamental rules right in front of our eyes. Warm air is less dense than cold air. When an Alberta Clipper (the most common source of cold air in winter here in Ohio) passes over the warm open waters of Lake Erie, cold NW winds in its wake spread over a warm lake surface. That warm surface air is less dense than the ambient environment and tends to rise. Abundant moisture from the body of water saturates this rising air, which condenses, forming the clouds. This phenomenon in itself is often barely sufficient enough for flurries. Several other things must happen for significant snows to occur, and these mechanisms are the basis for this paper. Those familiar with northeast Ohio know the difference between the words primary and secondary better than anyone. Often, one means flurries and the other blizzard. But this is not always the case. In fact, even though the primary snow belt will almost always exceed the secondary snow belt in terms of seasonal accumulations, there is still an interesting trend that exists solely in the secondary. When a forecaster looks back on the seasonal accumulation map for a given year, a strange discontinuity exists. The snowfall amounts are not evenly spread out everywhere. There is one spot, almost a bulls eye in south-central Cuyahoga County, where snowfall amounts are just a bit higher. This isn't just a one time thing either. The data is consistent. That one spot in Cuyahoga County consistently beats out all other spots in the secondary snow belt every year. The fun part comes when you try to figure out why. Lake- effect snow occurs in most of Northeast Ohio anytime from late fall through early spring, provided the air is cold enough and the lake warm enough. The trick is being able to forecast areas that may be more prone to receiving heavier amounts. Unfortunately, the method of throwing darts at a map of northeast Ohio counties provides much more fun than it does accuracy to a forecast. One of the first things a meteorologist looks at when a lake- effect event already appears likely is elevation. When air streaming off Lake Erie, or any other lake for that matter, runs into the elevated coastline several processes occur. First, friction with the coast slows air down, causing it to pile up. More importantly though, the increase in elevation encountered by this air forces it upward, similar to when air runs into a mountain range and is forced upward. This orographic lift increases the tendency for the air to rise vertically, and when coupled by an already unstable atmosphere, compliments of a warm lake and cold air aloft, rather explosive lifting can occur. Entire cities can literally shut down and yard sticks prove their worth in some of the more impressive storms. Next to wind direction, otherwise known as fetch, elevation is the common denominator when it comes to knowing where the heavy snow is likely to fall. In fact, it is elevation that separates the primary from the secondary snow belt. Smack dab in the middle of the secondary snow belt lies Cuyahoga County, home to the Rock and Roll Hall of Fame, the Cleveland Indians, and one of the more fascinating occurrences with regards to lake effect. In terms of elevation, Cuyahoga County is very volatile. It is virtually littered with peaks and valleys that in some cases are only a few miles apart. The city of Cleveland itself, which hugs the lakeshore in the north central part of the county, is about 600 feet above sea level. Head 15 miles south toward the south-central part of the county toward the bulls eye of snowfall and it quickly becomes obvious why the snowfall maximum exists where it does. Within a 5-10 mile radius, elevation increases dramatically. North Royalton lies at 850 feet. Parma at 879 feet. Strongsville at 945 feet, and the king of the county, Broadview Heights, at 1050 feet. Such a sudden increase in elevation over such a small space rapidly forces the saturated air off Lake Erie upwards. This enhances the depth of the clouds, where tops can reach anywhere between 10,000-15,000 feet. While not all that impressive when compared to something like a thunderstorm, when the notion of slantwise convection is considered, these heights are more than potent enough for blinding snow. With elevation considered, it is not surprising that Broadview Heights can receive several feet of snow more a year that it's close neighbor to the north, Cleveland. While the city of Cleveland is closer to the source of the snow, it's relatively low elevation provides a bit less lift as clouds roll onshore. These clouds often drop the heaviest squalls right on that bulls eye centered over Broadview Heights. Picture the air running into a brick wall. It has nowhere to go but up, and up it goes. It is well-known that the greater the area air moves over the warm lakes, the more time it has to pick up crucial moisture, which in turn can lead to increased coverage and intensity of snow showers. Lake Erie is oriented in such a fashion that a west wind has much more lake, and thus juice, from one end to the other. A north wind, while potentially bringing in colder air, has much less water to cover from the time it hits the shoreline in Canada to the time it reaches the coast of northeast Ohio. Unfortunately for snow lovers in the secondary snow belt, a west wind ( which again is favored for lake effect because it has more water to cover), tends to keep snow bands offshore just to the north, before they move onshore off to the east in the primary snow belt. One might wonder then how the secondary snow belt still receives so much snow, and how that bulls eye in the south central part of the county can eclipse even parts of the primary snow belt. While uncommon, a north wind does occur, especially in the wake of low pressure passing to our northeast. Counter-clockwise flow around the low can generate these rare north winds in certain situations. North winds blow snow bands right onshore into both the primary and secondary. Now I know what you're thinking, I just told you the a north winds will not produce as heavy lake snows because there is less water to pick up moisture from. Now the catch. Our good buddy, Lake Huron lies directly north of Cuyahoga County, and as luck would have it is oriented in such a fashion that a north wind picks up more juice than a west wind. Bands of heavy snow can form from Huron, make the treck over the brief area of Canadian land, and receive a reinforcing shot of moisture from Erie before dumping over the secondary snow belt. While two lakes don't necessarily make for twice as heavy snow, it certainly helps. Once these double-lake bands move onshore, most anyone in the secondary can receive snow, but those areas like Broadview Heights who sit just a little higher than everyone else get that extra bump from orographic lift which can account for the increase in yearly snowfall totals that we see. Today, forecasters have several tools at their disposal, but none of them are guarantees. Intrusions of dry air which, even with a lake full of potential moisture can kill snow bands, can be analyzed on water vapor imagery. Visible and infrared imagery can show where lake snows may be falling upwind which can help determine where individual bands may set up. Radar is vital, but tends to only be of use when bands have already formed. Because cloud tops tend to be rather shallow, even radars using the lowest tilt angle can overshoot the tops of the clouds, which is why it appears on radar that snow showers are only present within close proximity to the radar site even though they may be present well over the lake. While it can be easy to figure out wind direction and elevation, the fact of the matter is lake effect snow can at times still be darn near impossible to predict. While the conditions, whether it be dynamic or orographic in nature, mentioned above certainly enhance the likelihood of organized snow bands, mother nature has a way of deviating from what we perceive as the norm every once in a while. It is far from uncommon for the low-sitting Cleveland to get two feet of snow and Broadview Heights to remain sunny. There are so many intangibles that play into each lake- effect event that it is impossible for both model and forecaster to know when and where a snow band will form and persist. While the atmosphere can occasionally follow patterns that appear somewhat repetitive, where separate storms in the same month looked eerily similar in form and intensity, most lake effect events can produce completely different results even when the same conditions appear to be in place. A wind from 280 degrees can produce a much different result than a wind from 290 degrees. In the meantime, a forecaster can rely on the only occasionally accurate models, but it is experience that proves to be vital to success in the lake- effect prone region. Knowledge is power, and having years worth of past lake effect events replaying in the back of your mind certainly doesn't hurt. Until models figure out this mystery, forecasters may forever find that bottle of Tylenol or Motrin their most useful meteorological tool. References Haby, Jeff: Professor, Mississippi State University http://www.theweatherprediction.com/winterwx/lesnow/ Goddard, Dick. Dick Goddard's Weather Guide for Northeast Ohio. 2nd ed. Cleveland: Gray & Company, 1998. Images obtained from following site: http://www.erh.noaa.gov All other information compliments of the fine education from Mississippi State University! |