LAKE EFFECT SNOW: COLD WINDS BLOWING ACROSS WARM WATER BREW
INTENSE FORECASTING AT NOAA’S NATIONAL WEATHER SERVICE
Meteorologists Must Discern Where Narrow Bands Will Leave Residents Buried

March 2, 2007 — Having to deal with the large scale winter snowstorms that blanket much of the northern United States every winter is a big challenge. But those living in the Great Lakes area must also contend with lake effect snows. These snows often generate enormous amounts of snowfall over localized, and sometimes heavily populated, regions downwind of the Great Lakes. (Click NOAA image for a larger view of satellite image showing lake effect snow. Please credit “NOAA.”)

Fortunately, the NOAA National Weather Service is just as skilled at forecasting and tracking localized lake effect snow as it is with larger scale snow storms. The forecasters at the NOAA National Weather Service Forecast Office in Buffalo, N.Y., pride themselves on making accurate lake effect snow forecasts. In fact, thanks to the Buffalo office, residents were warned more than 24 hours in advance of the tremendous lake effect snows that buried much of the Great Lakes region earlier this month. This advance warning is significant considering these snows occur on the same scale as a summertime thunderstorm. Of course, it also helps that those living in this area are well prepared for and equipped to handle heavy snowfall.

The lake effect storms that buried many parts of New York state with near-record breaking snow in February 2007 were unusual in terms of its duration, but such storms are not uncommon at this time of the year, according to Tom Niziol, Buffalo native and meteorologist-in-charge of the Buffalo forecast office.

“Most lake effect snows last a day or two, but this episode lasted more than a week,” said Niziol. “The only other time this has happened recently was Christmas 2001 when a similar weather pattern in the Great lakes region brought a five-day total of 81.6 inches of snow to Buffalo and a total of 127 inches of snow to the town of Montague, N.Y. — just east of Lake Ontario. Such storms reinforce this region’s reputation as one of the snowiest regions east of the Rockies.”

Niziol also explained that lake effect snow is one of the most difficult challenges facing weather forecasters in the Great Lakes region. Snowfall amounts are often referred to in feet rather than inches. Although lake effect snows generally result in less death and destruction than other types of severe weather (i.e., tornados and hurricanes), they often produce significant impacts on travel, commerce and industry.

NOAA National Weather Service Forecast Office in Buffalo
The NOAA National Weather Service Forecast Office in Buffalo, N.Y., provides forecasts for the two largest snow belts in the Great Lakes region (i.e., Lake Erie and Lake Ontario) and has been involved in lake effect snow research and forecasting for decades. The office is “located in one of the best natural laboratories for [winter] weather and the recent lake effect snowfall confirms this,” said Niziol. El Niño-induced above normal temperatures hampered lake effect snows earlier this winter. However, now that El Niño has dissipated and temperatures have dropped back to normal levels, the Great Lakes region has seen the return of lake effect snows.

What Makes Lake Effect Snows so Unique?
Lake effect snows are extremely localized snow storms that occur downwind of the Great Lakes in the late fall and winter. Lake effect snows typically form discrete, narrow bands of snow, which are often characterized by intense snowfall and limited visibility. The bands occur throughout the Great Lakes region, both in the United States and Canada.

The main difference between a lake effect snow and a “standard” snowstorm is the area that is blanketed by such events. In a large scale snowstorm, such as a Nor’easter, snow may cover several states at one time. In a lake effect storm, the snowfall may be confined to only a portion of a county.

Lake effect snow occurs when cold air, often originating from Canada, moves across the open waters of the Great Lakes. As the cold air passes over its unfrozen, relatively warm waters of the Great Lakes, its warmth and moisture are transferred into the lowest portion of the atmosphere. As this warm air rises and cools, its moisture condenses, leading to cloud formation and ultimately snow on the downwind (or leeward) sides of the Great Lakes. The wind direction determines where the snowband will occur. Because winds accompanying arctic air masses generally originate from a westerly direction, lake effect snow typically falls on the east or southeast sides of the Great Lakes. (Click NOAA image above for a larger view of diagram showing lake effect snow event. Please credit “NOAA.”)

While a typical winter storm lasts a few hours to a few days, lake effect snow often produces snow continuously for up to 48 hours in a particular area. Snowfall rates from a single intense band of lake effect snow can approach six inches per hour at times. As long as the wind remains steady and out of the same direction, a single band of lake effect snow can remain stationary for several hours or, in rare instances, several days at a time.

"Another unique aspect of lake effect snows is the extreme variability that can occur in space and time," said Niziol. "It is not uncommon for sunny skies at a particular location to be quickly replaced by blinding, wind-driven snowfall in a matter of minutes." Similarly, snowfall accumulations can vary from trace amounts to a couple feet over a very short distance (i.e., several miles). One of the more challenging aspects of forecasting lake effect snow is pinpointing exactly where the heaviest snow will occur because even small changes in wind direction can significantly alter the areas to be impacted.

When heavy lake effect snow is expected, a variety of Lake Effect Snow Watches, Warnings and Advisories can be issued by the NOAA National Weather Service. Exact snowfall criteria differ across geographic regions in the Great Lakes. The following criteria apply to areas of the eastern Great Lakes:

• Lake Effect Snow Watches mean that conditions in the atmosphere are primed to produce lake effect snow. Watches are issued from 24 to 36 hours in advance of an anticipated event.
• Lake Effect Snow Warnings mean that more than seven inches of snow are expected in a 12 hour period or more than nine inches of snow in a 24 hour period.
• Lake Effect Snow Advisories mean that four to seven inches of snow are expected in a 12-hour period.

How does the NOAA National Weather Service Forecast Lake Effect Snow?
Because lake effect snows impact such a small geographic region, it was only recently that they could be predicted by NOAA’s regional and national scale computer models. Forecasters also rely on locally developed methods to predict such events. Forecasters at the Buffalo office for example, used lessons learned from years of operational experience and rules of thumb to develop their own forecast tool called BUFKIT.

BUFKIT is a computer application that uses high-resolution numerical weather prediction data to enhance forecasts for local scale snowstorms near the Great Lakes. The local scale data sets are interpolated from hourly forecast data from one of NOAA’s National Centers for Environmental Prediction models. The data is collaborated by voluntary local snow spotters. BUFKIT quickly and easily streamlines the process of assimilating these data sets for operational use in the real-time forecast environment. The data sets are extremely well-tailored for the prediction of lake-effect snow because they provide the high degree of temporal and vertical resolution necessary to evaluate these local scale events.

Originally designed in the early 1990s to help predict lake effect snow, BUFKIT is so successful and user friendly that its use has been expanded to include other local scale weather predictions, including floods, thunderstorms and high winds. Today, BUFKIT is being used at more than one hundred locations throughout the United States and Canada.

To more accurately measure the snow that fell from such localized storms, the office trained hundreds of volunteers from across the region to call in snowfall measurements. The network provides forecasters with real-time updates on conditions and snowfall accumulations.

What is NOAA doing to improve Lake Effect Snow forecasts in the future?
NOAA continues working to improve lake effect snow forecasts using satellite data, advanced high resolution computer models and collaborative partnerships:

• Satellites: NOAA is using satellites to help track and forecast lake effect snow. NOAA geostationary operational environmental satellites (GOES) are being used to monitor the location and movement of lake effect snow bands both during the day and night using infrared satellite technologies. NOAA also uses its polar-orbiting environmental satellites (POES) to obtain accurate lake surface temperatures — an important factor in determining the potential for lake effect snow — using Advanced Very High Resolution Radiometer (or AVHRR) remote sensing technology. The NOAA Great Lakes Environmental Research Laboratory then uses this data in combination with ice cover data from the NOAA National Ice Center to compile digital maps known as the daily Great Lakes Surface Environmental Analysis (or GLSEA). This information is then fed into computer models to predict snowfall in the Great Lakes region.
• Models: Over the past 10 years, new and improved numerical models and forecast techniques have greatly improved lake effect snow forecasts. For example, because of increased spatial and temporal resolution in NOAA’s regional and national scale models, many meteorological parameters associated with the Great Lakes can now be incorporated into these models, including Great Lakes surface temperatures. NOAA’s research efforts are also concentrating on real-time mesoscale numerical models that will predict not only the location and movement of lake effect snow, but accurate snowfall amounts as well.
• Collaborative Partnerships: NOAA’s National Weather Service Forecast Office in Buffalo, N.Y., is involved in a NOAA-funded Cooperative Program for Operational Meteorology, Education and Training (COMET) project wiith the State University of New York at Oswego to evaluate computer models designed to help further improve Lake Effect Snow forecasts. The Buffalo Weather Forecast Office, located near the Canadian border, also coordinates the Great Lakes Workshop on Operational Meteorology, an annual conference dedicated to share new forecast techniques and technology to improve the prediction of all types of weather associated with the Great Lakes region.

Lake Effect Snow Monitoring
One of the best ways to monitor and track lake effect snow during the winter season is to go to the Buffalo Weather Forecast Office Web page (or other NOAA National Weather Service forecast offices across the Great Lakes region) and use the Buffalo local weather radars to track the movement of the lake effect snow bands in near real time. If you want to learn more about the topic or look back at lake effect snow storms on the eastern Great Lakes, go to the NWS Buffalo Lake Effect Snow Page.

Relevant Web Sites
NOR’EASTER TO DELIVER COLD-HEARTED VALENTINE: Persistent February Chill Supporting Array of Winter Weather Woes

NOAA National Weather Service Eastern Region—Latest Winter Weather Watches and Warnings Issued

NOAA Weather Safety

Winter Storms: The Deceptive Killers (PDF)

Lake-Effect Snow Summary

NOAA Storm Watch

NOAAWatch—Storms and Hazards

Media Contact:
NOAA National Weather Service, (301) 713-0622