On the Road: WI - Annual NIFC Predictive Services Workshop Ghana - WMO International Workshop on Rescue and Digitization of Climate Records for Countries in West Africa
Lake-Effect Snow in the Upper Ohio Valley
Will Kubina, Senior Forecaster, NWS Cleveland
The weather across the Upper Ohio Valley is known for being diverse, especially during the colder months of the year. Lake Erie, he smallest and shallowest of the five Great Lakes, dominates the weather across the region during the winter months. Frequent rounds of lake-effect or lake-enhanced snow occur from northern Ohio eastward into western New York. Annual snowfall totals are often in excess of 150 inches and sometimes exceed 200 inches downwind of the lake. The primary Lake Erie snowbelt stretches from Cleveland across northeastern Ohio and into Erie and Crawford counties of western Pennsylvania (Figure 1). The National Weather Service Office in Cleveland serves this area and issues dozens of Lake-Effect Snow Watches, Warnings and Advisories each winter. Lake-effect snow occurs downwind of all of the Great Lakes but the Lake Erie snowbelt is differentiated from the others by its population density. Approximately 3.2 million people live in the counties that make up the primary snowbelt. The secondary snowbelt, which stretches west and south from Cleveland and encompasses much of north-central Ohio, is populated by another million people.
Lake-effect snowstorms can cause millions of dollars of damage. Prolonged lake-effect snow events often produce two to three feet of snow accumulation, with tree damage, power outages, vehicle accidents and roof damage common during these events. Early or late season snows are extremely dangerous and often result in widespread power outages, especially if the trees have leaves. In November 1996, as much as five feet of snow accumulated in portions of northeastern Ohio during the first few days of the month and on April 23-25, 2006, over two feet of snow fell on much of the Cleveland Metropolitan area. Damage to trees was significant and widespread power outages occurred during both storms.
Lake-Effect Snow Basics
So what is lake-effect snow and what causes it? Lake-effect snow is caused by the interaction of cold air moving across the relatively warm waters of a body of water, in this case Lake Erie. Latent heat release from the lake moistens and warms the lower atmosphere. This interaction causes condensation which leads to cloud formation, and eventually to precipitation if moisture is sufficient. If temperatures are cold enough, the precipitation will fall as snow (Figure 2). The larger the temperature difference between the surface of the lake and the lower atmosphere, the more intense the precipitation can be. Meteorologists commonly use temperatures at the 850-millibar pressure level (approximately 5,000 feet) to forecast the likelihood of precipitation. If the difference in temperature from the lake surface to 850 millibars exceeds 13°C, the likelihood of lake-effect precipitation is enhanced. If the difference in temperature from the lake surface to 500 millibars (approximately 18,000 feet) reaches 40°C, then thunder and lightning become possible. Snowfall rates greater than 2 to 4 inches per hour can occur during these episodes of extreme instability.
Other factors influence the onset of lake-effect precipitation. The distance that an airmass is over a body of water is called a fetch (Figure 3). Larger fetches result in an increased likelihood of significant precipitation. On Lake Erie, the best fetches for heavy snow in northeast Ohio are from the northwest. Northwestern Pennsylvania receives its heaviest snow from a more westerly fetch across Lake Erie.
Orography, or the terrain surrounding the lake, also plays a role in the development of lake-effect precipitation. Forced orographic ascent effectively squeezes precipitation out of the cloud deck resulting in increased precipitation totals. The surface of Lake Erie lies around 570 feet above mean sea level. The terrain rises around 700 feet from the shoreline to northern Geauga County, where peak snowfall totals in Ohio are often reported. In northwestern Pennsylvania, up to 1,200 feet of ascent occurs from the lake to the eastern ends of Erie and Crawford Counties (Figure 4).
The most common limiting factor to lake-effect precipitation is a lack of low-level moisture in the atmosphere. Cold air masses originating from well upstream of Lake Erie are often very dry and it is tough for the atmosphere to overcome this lack of moisture. During lake-effect snow events with northerly wind regimes, Lake Huron can act as a supplemental source of moisture for snow falling in northern Ohio.
Lake Erie Climatology
The water in Lake Erie typically experiences about a 40° temperature variation over the course of a year. Temperatures peak in early August and then steadily fall through the autumn months. Temperatures usually reach a minimum value in late January and then vary no more than a degree or two into early March (Figure 5).
Even though Lake Erie is the shallowest, smallest and southernmost of the five Great Lakes, it has the highest average peak ice coverage (Figure 6). However, the ice coverage on Lake Erie is highly variable from year to year. During cold winters, ice coverage on the lake can peak at nearly 100% while in mild winters, it can be as low as 5% to 10%. The winter of 2011-2012 was extremely mild and resulted in little ice cover on Lake Erie.
The National Weather Service in Cleveland relies on a network of volunteer snow spotters that report twice a day during the winter months. This data is augmented by trained observers at all of the major climate sites. Peak normal values in Ohio are around 120 inches of snow per season with upwards of 180 inches in portions of inland Erie County, Pennsylvania (Figure 7). Normal snowfall totals vary considerably across the area. For example, a nearly 60-inch range in normal snowfall totals exists across Cuyahoga County, which includes the City of Cleveland. Six of the past ten years have seen peak snowfall totals in northwest Pennsylvania in excess of 200 inches. During this same period, northeast Ohio saw peak totals exceed 200 inches once and 170 inches six times.
Locations in the snowbelt can expect to see about 40 to 50 days of measurable snowfall each winter. By comparison, Columbus in the central part of Ohio and away from the lake-effect snowbelt, sees an average of 21 days of measurable snowfall each winter. Lake-effect snowfall contributes a large percentage to the annual precipitation totals. Locations on the periphery of the snowbelt get about 20% of their annual precipitation during the months of December, January and February. During especially snowy seasons, some areas can see more than a third of their annual precipitation during these same three months.
Lake Erie is responsible for the dynamic winter weather across the Upper Ohio Valley. Lake-effect snow remains very challenging to forecast given the variety of factors that affect its development. It is also challenging for the residents that deal with it on a frequent basis. Can you imagine yourself living in an area that gets 20 feet of snow each winter? That’s the reality of living downwind of Lake Erie.
The fall colors were abundant during the Midwestern Regional Climate Center’s (MRCC) final regional road trip of 2012 (Figure 1). With the headquarters of the MRCC being in the heart of some of the flattest farmland in the US, it was breathtaking to get out and see all of the wonderful autumn colors, forests, and diverse landscapes within the MRCC region! There were several storms that were chasing us on our way east, but we managed to dodge all of those raindrops. It was only on our last day, back to Champaign, that we encountered any rain – as if to mark the sadness of seeing the regional road trip come to a close.
Like all the MRCC regional road trips, there were several National Weather Service offices that hosted us so we could learn more about each other’s climate service needs. The first stop was Indianapolis (Figure 2); then Wilmington, OH (between Cincinnati and Columbus); Louisville, KY; and finally Paducah, KY. Each office has great personality and varying levels of climate data needs. Topics such as the 2012 drought, the need for better drought tools such as evapotranspiration and soil moisture, and the concern over the potential loss of thousands of surface weather observation stations throughout the country were common among all offices. Indianapolis NWS is involved with the preparations for the 100th anniversary of the 1913 flood along with the MRCC, Wilmington NWS, and Cleveland NWS. The Louisville NWS provided us great feedback on how we could improve our online climate products and website historical resources. Finally, Paducah NWS kept us laughing throughout the entire visit due to their great attitudes and enthusiasm toward climate and weather.
The Wilmington NWS was combined with the Ohio River Forecast Center (RFC) (Figure 3). Being co-located, they could offer us a lot of insight into the myriad of hydrological products they have either developed or consult with regularly. Some of the key topics from that visit included looking at downscaled future climate scenarios and a strong interest in any sort of gridded precipitation that might be available to them to help with both forecasts and future planning.
While in the Cincinnati region, the MRCC dropped in on the regional Army Corps of Engineers office to learn more about the sorts of data they use for their decision-making efforts. We also met with the Ohio River Valley Water Sanitation Commission (ORSANCO). After a recent climate service request, we thought we’d take the opportunity to stop by and introduce ourselves to them in person. They were great hosts and asked lots of questions about the MRCC and how we might be able to collaborate.
In addition to the NWS offices in Kentucky, the MRCC also got to meet with the University of Kentucky’s Agricultural Meteorology Department led by Tom Priddy, and the Kentucky State Climate Office led by Stuart Foster at Western Kentucky University (Figure 4). Both of these universities enlightened us on all the great climate products and online tools that have been developed for the state – particularly in terms of agriculture and energy. With the Kentucky Mesonet providing copious amounts of data, the opportunities for climate information when the spatial density is high is truly enviable. The MRCC looks forward to working with both universities in the future to find out how we can not only collaborate with transferring several state products to a regional scale, but also utilize their mesonet data as much as possible!
As with past road trips, the MRCC wanted to mix things up a bit by reaching out to some new climate partners. Foresters from the Morgan-Monroe State Forest in Indiana (Figure 5) and the Shawnee National Forest in Illinois invited us to stop by for a few hours each to learn more about climate needs from a forest and wildfire perspective. The information was enlightening and the MRCC hopes to be able to provide several forest/wildfire-relevant climate products within the next year in addition to exploring ways in which the MRCC can form a stronger partnership with those protecting our state and national forests.
The MRCC was excited to visit 8 of the 9 states within its region in 2012. Unfortunately, we were not able to visit Missouri this year. However, the 2013 Annual Meeting for the American Association of State Climatologists will be held in St. Louis in July, so Missouri will definitely be the itinerary for the summer/July MRCC Regional Road Trip! If you are located within a 3-5 hour drive around the St. Louis/Missouri region, and would like the MRCC to stop by for a visit, please let us know!
The month of October brought near to above normal precipitation to much of the Midwest. The highest precipitation totals of 6” to 10” in northeastern Ohio resulted from Hurricane Sandy making landfall on the East Coast of the United States at the end of the month. While the impacts of Sandy were greatest on the East Coast, the storm system also brought significant rainfall and snowfall to the eastern Midwest, as well as damage from the very high wind gusts and rough, high waves on Lake Erie.
For the second month in a row, below normal average temperatures were widespread across the Midwest. All nine Midwest states experienced average statewide temperatures that were below normal, with many states at least 1.5°F to 2°F below normal. In addition, Lake Michigan-Huron and Lake Superior were near their record low levels for October this past month, which resulted from the lack of snowfall last winter and the hot, dry summer experienced throughout the region. Read more...
First Snow Climatology maps:
Ever wonder when the first snow typically occurs where you live? You can now find out using the new MRCC First Snow Climatology maps! The first snow climatology maps show the median date of the first measurable snowfall (the median date is determined such that half of the years fall before and half fall after) for stations across the central United States. In addition to the median date map, there are also maps showing the earliest and the latest date for first measurable snowfall across the region. The first measurable snowfall is defined as the first time a station reports snowfall greater than or equal to 0.1” and all information on the maps are based on data from 1981-2010.
The Great Lakes Water Level Dashboard, developed by NOAA’s Great Lakes Environmental Research Laboratory (GLERL) with support from the Great Lakes Restoration Initiative and in cooperation with the Cooperative Institute for Limnology and Ecosystem Research, is an interactive tool designed to facilitate visualization, analysis and downloading of Great Lakes water levels and forecasts on a variety of time scales. The dashboard has been available on the NOAA GLERL website since June 2012. A new release of the dashboard (version 1.5) will make additional data products available, extending the existing data set into both the past and the future. Several paleological reconstruction data sets using submerged tree stumps and tree ring data to draw conclusions about past lake levels have been added to the dashboard. In addition, lake level projection data sets from some recent regional climate modeling studies were made available. Both of these types of data sets can add context to our understanding of current lake level fluctuations as well as our attempts to project how future climates will impact these levels.
Milwaukee, WI (Nov. 12-15) - Annual NIFC Predictive Services Workshop
Beth Hall will be participating in the National Interagency Fire Center's (NIFC) annual Predictive Services Workshop that brings partners and agencies together to better predict and plan for the potential of wildfire outbreaks across the U.S.
Accra, Ghana (Nov. 19-23) - WMO International Workshop on Rescue and Digitization of Climate Records for Countries in West Africa
Dr. Nancy Westcott will be attending the workshop as the representative from North America. This workshop kicks off the West Africa Data Rescue initiative, and will be attended by more than sixteen African countries, as well as representatives and participants from many international climatology and data management agencies.