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What is “Lake-Effect” SnowWhat is “Lake-Effect” SnowWSHS Environmental Biology

Lake effect snow is caused when very cold air flows over the relatively warmer water of a large lake. Intense evaporation from the lake surface forms convective clouds that can not contain all of this water, and some of it falls back to the surface as snow.

WHAT CAUSES LAKE EFFECT SNOW?

Lake effect snow showers often form into bands, with abrupt edges to the falling snow. One location can receive a foot of snow, while another location just a few miles away receives only flurries. Once the lake surface cools to near 32oF, the lake effect snow slows considerably. When the lake freezes, the snow stops altogether.

The Greater Cleveland area is the largest population center that is routinely impacted by heavy lake-effect snowfall (LES) within the Great Lakes region. Cleveland Hopkins airport receives about 50" of snow annually, and about 40% can be attributed to LES from Lake Erie.

Some 35 miles due east, Chardon is known as the snow capital of northeast Ohio and receives over 100" annually - the majority as a result of LES. http://ww2010.atmos.uiuc.edu/(Gh)/arch/cases/961109/adv/bk.rxml

WOW

http://ww2010.atmos.uiuc.edu/(Gh)/arch/cases/961109/adv/bk.rxml

Radar observations

Satellite visible imagery

These are the mechanisms to make Lake Effect Snow,

ranked in usual order of importance

HEATING: The water in the Great Lakes does not cool off as quickly as the atmosphere in the fall and early winter. This warmer water heating the cooler air results in instability, especially during early cold outbreaks. The warmer air rises and quickly reaches saturation, and the result is shallow cumuliform clouds, often aligned in bands parallel to the low-level wind.

By January, ice covers most lakes, at least in part, cutting off or reducing the heat supply. Lake Erie often freezes entirely because it is more shallow than the other Great Lakes.

MOISTURE: The lake surface evaporates, which is very effective when the wind is strong and the air dry The cold air from Canada has a very low pressure. Also, strong winds cause spray, facilitating evaporation.

WIND FETCH: The greater the distance that wind blows over the warm water, the greater the snow fall. Three of the five lakes are relatively long and narrow. Winds blowing the length of these lakes have a long route over water and will produce a lot of snow, but a 30 degree wind shift brings the winds across the lake. The shorter routes will produce less lake-effect snow and move the snow to a different site.

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Click on Map

FRICTIONAL DIFFERENCE:

The effect of the land surface on the moving air is much greater over rough land than it is over relatively smooth lake water. The rougher land slows the surface wind, causing more surface convergence and lifting. This effect is much greater with stronger winds.

UPSLOPE LIFT:

In some localities, wind blowing from a lake onshore is forced to climb up hills. As the air rises, it cools and precipitates.

Orography/ Topography

Annual snowfall increases by 8-12 inches per 100 ft increase in elevation

LARGE-SCALE FORCING: The general cyclonic nature of an air mass supports development of precipitation anywhere, and may also enhance lake-effect snow.

What Is Snow? When falling from the sky, snow is in the form of crystalline ice, and ice crystallizes into six-sided objects. After reaching the ground, snow loses it's crystalline shape and becomes granular. So falling snow and snow on the ground should be considered two different forms.

                                                                                                              

Formation of Snow Crystals

Snow crystals are crystals of ice formed within the atmosphere at temperatures below freezing. They form due to condensation of water vapor on a very small ice crystal or dust particle. Typical Snow crystals are see through like glass, and are typically from .02 to .5 inches in diameter.

                                                      

Lower levels of cumulonimbus clouds consist mostly of water droplets while at higher

elevations, where temperatures are well below 0 degrees Celsius, ice crystals dominate.

http://ww2010.atmos.uiuc.edu/(Gh)/arch/cases/961109/adv/bk.rxml

Even though it is the rarest of storm types, the supercell is the most dangerous because of the extreme weather generated. This storm was producing baseball hail

http://ww2010.atmos.uiuc.edu/(Gh)/arch/cases/961109/adv/bk.rxml

Thundersnow viewed from space

Ground Snow Once snow hits the ground, it cannot keep its crystalline shape. The shape changes into more of a rounded form, even if the temperature remains below freezing. The ground snow will eventually become ice granules.

Can You Look Cross-Eyed???

Cross your eyes and stare at the next 3 Slides.

You will be able to see a 3-Dimension image in the center.

http://emu.arsusda.gov/snowsite/selected/select2.html

http://emu.arsusda.gov/snowsite/selected/select2.html

http://emu.arsusda.gov/snowsite/selected/select2.html

After several days in a snow pack

http://emu.arsusda.gov/snowsite/selected/select2.html

From a melting snow pack

http://emu.arsusda.gov/snowsite/selected/select2.html

Hexagonal snow crystal with broad branches, composed of 2 offset 3 branched snow crystals.

http://emu.arsusda.gov/snowsite/selected/select1.html

Hexagonal snow crystal with broad branches, composed of 2 offset 3 branched snow

crystals.

The needle crystal is often associated with heavy snowfall in the Northeastern United States.

Overview of the Lake-Effect Process

• Occurs to the lee of the Great Lakes during the cool season.

• Polar/ arctic air travels across a lake, picks up heat and moisture, and is destabilized.

• Cloud formation is enhanced by thermal and frictional convergence and upslope along lee shore.

Fetch

• Small changes in wind direction can significantly change the fetch.

• Lake Erie: 250 deg wind--225 mi fetch 230 deg wind-- 80 mi fetch

Upstream Lakes

Upstream lakes impact snowfall to the lee side of downwind lakes. For example, with a northwest flow, Lake Huron snowbands re-form and intensify over Lake Ontario and Lake Erie.

Snow/ Ice Cover on the Great Lakes

Lake freeze-over reduces, or completely ends the lake-effect snow season.

The Lake Erie snow season often ends late in J anuary or early February.

The Lake Ontario lake-effect snow season continues on into March because Lake Ontario doesn’t freeze completely.

Satellite Applications

Data from satellite channels can be used in combination with other data sources for diagnostic studies and now-casting or short-term forecasting applications.

See next slide

Water Vapor Imagery

Water vapor imagery may be used to map weather patterns.

Infra-Red Cloud Top Temperatures

Cloud top temperatures can be used to measure lake-effect intensity. Temperatures colder than -15 C imply efficient precipitation.

References

Byrd, G. P. , R. A. Anstett, J. E. Heim, and D. M. Usinski, 1991: Mobile sounding observations of lake-effect snowbands in western and central New York. Mon. Wea. Rev., 119, 2323-2332.

Byrd, G. P. and R. S. Penc, 1992: The Lake Ontario snow event of 11-14 January 1990.Proc. Fifth Conf. on Mesoscale Processes, Atlanta, GA, Amer. Meteor. Soc, J59-J66.

Byrd, G. P., D.E. Bikos, D.L. Schleede, and R.J. Ballentine, 1995: The influence of upwind lakes on snowfall to the lee of Lake Ontario. Preprints, 14th Conf. on Weather Analysis and Forecasting, Dallas, TX, Amer. Meteor. Soc., 204-206.

Eichenlaub, V. L., 1979: Weather and Climate of the Great Lakes Region, University ofNotre Dame Press, 335 pp.

Kelly, R. D., 1984: Horizontal roll and boundary layer interrelationships observed over Lake Michigan. J. Atmos. Sci., 41, 1816-1826.

LaDue, J., 1996: COMET course notes and satellite meteorology modules.

Niziol, T. A., 1987: Operational forecasting of lake-effect snow in western and central New York. Wea. Forecasting, 1, 311-321.

Niziol, T.A., W.R. Snyder, and J. S. Waldstreicher, 1995: Winter weather forecasting throughout the eastern United States. Part IV: Lake effect snow. Wea Forecasting, 10, 61-77.

NWS/Buffalo, various forecast products.

NWS/Marquette, 1996: Web homepage.

Reinking, R. et al., 1993: Lake Ontario winter storms (LOWS) project final report. NOAA Tech. Memo. ERL WPL-216, 147 pp.