Transcript Lake Effect Snow2

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What is “Lake-Effect” Snow
WSHS
Environmental Biology
WHAT CAUSES LAKE EFFECT SNOW?
 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.
 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.
WOW
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
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.
Click on Map
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.
O rography/ Topography
A nnual snowfall increases by 8 -1 2
inches per 1 0 0 ft increase in elevat ion
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
CrossEyed???
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.ht
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.
O verview of t he Lak e-Effect Process
• O ccurs t o t he lee of t he Great Lak es
during t he cool season.
• Polar/ arct ic air t ravels across a lak e,
pick s up heat and moist ure, and is
dest abilized.
• Cloud format ion is enhanced by
t hermal and frict ional convergence and
upslope along lee shore.
Fet ch
• Small changes in wind direct ion can
significant ly change t he fet ch.
• Lak e Erie:
2 5 0 deg wind--2 2 5 mi fet ch
2 3 0 deg wind-- 8 0 mi fet ch
Upst ream Lak es
Upst ream lak es i mpact snowfall
t o t he lee side of downwind
lak es. For ex ample, wit h a
nort hwest flow, Lak e Huron
snowbands re-form and int ensify
over Lak e O nt ario and Lak e Erie.
Snow/ I ce Cover on t he Great Lak es
Lak e freeze-over reduces, or complet ely
ends t he lak e-effect snow season.
The Lak e Erie snow season oft en ends lat e
in January or early February.
The Lak e O nt ario lak e-effect snow season
cont inues on int o M arch because Lak e
O nt ario doesn’ t freeze complet ely.
Sat ellit e A pplicat ions
Dat a from sat ellit e channels can be used
in combinat ion wit h ot her dat a sources
for diagnost ic st udies and now-cast ing
or short -t erm forecast ing applicat ions.
See nex t slide
Wat er Vapor I magery
Wat er vapor imagery may be used t o map weat her pat t erns.
I nfra-Red Cloud Top Temperat ures
Cloud t op t emperat ures can be used t o measure
lak e-effect int ensit y. Temperat ures colder t han 1 5 C imply efficient precipit at ion.
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 of
Notre 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.