Snow and Winter
Weather
Download Winter
Weather Safety Guide (PDF)
Snowflakes form when water
vapor freezes into ice crystals in cold clouds. The ice
crystals attract cooled water droplets to form various
shapes. They get heavy and fall. If the air is
cold enough, the snow falls all the way to the earth without
melting. If the ground is freezing, the snowflakes stick
to the ground.
No Two Alike?
Have
you noticed that there are many different shapes of
snowflakes? That is because a snowflake is usually made
of many different kinds of snow crystals, and the shape of a
snow crystal depends a lot on the temperature at which it
forms. For example, at temperatures from 25 to 32
degrees F, the crystals are shaped like thin plates. At
temperatures between 20 and 25 degrees F they look more like
needles and at 15-20 degrees F they resemble hollow columns.
Usually the colder the temperature, the smaller the
crystals.
As
the crystals fall from the cold clouds, they bump into other
crystals and freeze together, making even more shapes.
This is one reason why it's so hard to have two snowflakes
exactly alike. In fact, in air right at the freezing
mark, several snowflakes may stick together, forming large
clumps of flakes that may melt as they hit the
ground.
Winter Weather Terms
NOAA'S NATIONAL WEATHER SERVICE SAYS:
KNOW YOUR WINTER WEATHER TERMS
NOAA's National Weather
Service
urges residents to keep abreast of local forecasts and
warnings and familiarize themselves with key weather
terminology.
Winter Storm Warning: Issued when
hazardous winter weather in the form of heavy snow, heavy
freezing rain, or heavy sleet is imminent or occurring. Winter
Storm Warnings are usually issued 12 to 24 hours before the
event is expected to begin.
Winter Storm Watch: Alerts the public to
the possibility of a blizzard, heavy snow, heavy freezing
rain, or heavy sleet. Winter Storm Watches are usually issued
12 to 48 hours before the beginning of a Winter
Storm.
Winter Storm Outlook: Issued prior to a
Winter Storm Watch. The Outlook is given when forecasters
believe winter storm conditions are possible and are usually
issued 3 to 5 days in advance of a winter
storm.
Blizzard Warning: Issued for sustained or
gusty winds of 35 mph or more, and falling or blowing snow
creating visibilities at or below ¼ mile; these conditions
should persist for at least three
hours.
Lake
Effect Snow Warning: Issued when heavy lake effect snow is
imminent or occurring.
Lake
Effect Snow Advisory: Issued when accumulation of lake
effect snow will cause significant
inconvenience.
Wind
Chill Warning: Issued when wind chill temperatures are
expected to be hazardous to life within several minutes of
exposure.
Wind
Chill Advisory: Issued when wind chill temperatures are
expected to be a significant inconvenience to life with
prolonged exposure, and, if caution is not exercised, could
lead to hazardous exposure.
Winter Weather Advisories: Issued for
accumulations of snow, freezing rain, freezing drizzle, and
sleet which will cause significant inconveniences and, if
caution is not exercised, could lead to life-threatening
situations.
Dense
Fog Advisory: Issued when fog will reduce visibility to ¼
mile or less over a widespread area.
Snow
Flurries: Light snow falling for short durations. No
accumulation or light dusting is all that is
expected.
Snow
Showers: Snow falling at varying intensities for brief
periods of time. Some accumulation is
possible.
Snow
Squalls: Brief, intense snow showers accompanied by
strong, gusty winds. Accumulation may be significant. Snow
squalls are best known in the Great Lakes
region.
Blowing Snow: Wind-driven snow that
reduces visibility and causes significant drifting. Blowing
snow may be snow that is falling and/or loose snow on the
ground picked up by the wind.
Sleet: Rain drops that freeze into ice
pellets before reaching the ground. Sleet usually bounces when
hitting a surface and does not stick to objects. However, it
can accumulate like snow and cause a hazard to
motorists.
Freezing Rain: Rain that falls onto a
surface with a temperature below freezing. This causes it to
freeze to surfaces, such as trees, cars, and roads, forming a
coating or glaze of ice. Even small accumulations of ice can
cause a significant hazard.
Winter
Weather Tips
A
Major Winter Storm is Moving Up the East Coast- How is it
Monitored and Forecast?
Have you ever wondered how the National
Weather Service can tell a major winter storm is brewing and
will impact your area in the coming days or hours? How can
meteorologists tell if a storm is intensifying and where it
will bring the most snow? It's a highly sophisticated process.
It all starts with observing the current situation. The
National Weather Service operates a widespread network of
observing systems such as geostationary satellites. Doppler
radars, and automated surface observing systems that
constantly monitor the current state-of-the-art numerical
computer models to provide a glimpse of what will happen next
- ranging from hours to days. The models are then analyzed by
NWS meteorologists who use their experience and expertise to
write and disseminate forecasts. Want to learn more about the
technologies? Visit the following web page:
www.nws.noaa.gov
Winter Weather Watches, Warnings
and Advisories- What do they all Mean?
The National Weather Service uses specific
winter weather terms to ensure that people know what to expect
in the coming days and hours . A Winter Storm
Watch means that severe
winter conditions, such as heavy snow and/or ice, may affect
your area, but its occurrence, location and timing are still
uncertain. A winter storm watch is issued to provide 12 to 36
hours notice of the possibility of severe winter weather. A
winter storm watch is intended to provide enough lead time so
those who need to set plans in motion can do so. A watch is
upgraded to a Winter Storm
Warning when 4
or more inches of snow or sleet is expected in the next 12
hours, or 6 or more inches in 24 hours, or 1/4 inch or more of
ice accretion is expected. Winter Weather
Advisories inform you
that winter weather conditions are expected to cause
significant inconveniences that may be hazardous. If caution
is exercised, advisory situations should not become
life-threatening. A Blizzard
Warning means
that snow and strong winds will combine to produce a blinding
snow (near zero visibility), deep drifts, and life-threatening
wind chill. Be sure to listen carefully to the radio,
television, and NOAA Weather Radio for the latest winter storm
watches, warnings, and advisories.
Why is Predicting the Exact Amount
of Snowfall So Challenging?
Snow forecasts continue to improve, but
they remain a challenging task for meteorologists. Heavy snow
often falls in small bands that are hard to discern on larger
resolution computer models. In addition, extremely small
temperature differences define the boundary line between rain
and snow.
Will the approaching
storm bring heavy snowfall to your area?
Each winter, meteorologists at the Storm
Prediction Center in Norman, Okla., monitor weather data from
across the nation for developing bands of heavy snow and
freezing precipitation, as well as lightning, within weather
systems. Their ability to provide additional information about
developing situations enhances winter storm warnings and helps
National Weather Service field offices, private industry and
local governments improve preparedness. For instance, a
prediction of eight inches of snow carries much greater
consequences for a city's rush hour than four inches. Want to
learn more about the Storm Prediction Center's operations?
Are you Prepared for Winter
Weather?
Winter weather too often catches people
unprepared. Researchers say that 70 percent of the fatalities
related to ice and snow occur in automobiles, and about 25
percent of all winter related fatalities are people that are
caught off guard, out in the storm. What winter weather
preparations are being made in your area, and what are the
appropriate steps to take that will ensure your winter weather
safety? Help your readers, viewers and listeners make sure
their homes and cars are ready for the worst winter has to
offer.
Getting the Latest Winter Weather
Information
There is no better way to keep ahead of a
winter storm than with NOAA Weather Radio (NWR), a small
receiver device that can be purchased at many electronic
stores. As the "Voice of the National Weather Service," it
provides continuous broadcasts of the latest weather
information from local National Weather Service offices. The
NWR network has more than 425 stations, covering all 50
states, adjacent coastal waters, Puerto Rico, the U.S. Virgin
Islands, and U.S. Pacific Territories. Weather radios come in
many sizes, with a variety of functions and costs. The NWR
network has been further advanced by the implementation of
Specific Area Message Encoding (SAME) technology. The SAME
allows the user to receive warnings only for their specific
location. SAME receivers are a live-saving tool, providing
audible alert tones for any weather warnings. A NOAA Weather
Radio is a useful and potentially life-saving gift idea this
holiday season.
What is Wind
Chill?
One of the gravest dangers of winter
weather is wind chill. The wind chill is based on the rate of
heat loss from exposed skin by combined effects of wind and
cold. As the wind increases, heat is carried away from the
body at an accelerated rate, driving down the body
temperature. Animals are also effected by wind chill. Check
out the wind chill chart on the Internet at
http://www.nws.noaa.gov/er/iln/tables.htm#wind
NOAA's Snow and Ice
Center
The National Snow and Ice Data Center
(NSIDC) serves as the national information center that
supports research in glaciers and freezing weather phenomenon.
The NSIDC archives snow and ice data, and maintains
information about everything from avalanches to icebergs. The
NSIDC web site contains a
fascinating list of Questions and Answers about snow that are
sure to be of interest to anyone experiencing winter weather.
Hard At Work When the Storm
Hits
While most of us stay home from work or
school during severe winter weather, National Weather Service
meteorologists are hard at work. Twenty-four hours a day, 365
days a year, NWS meteorologists staff local offices across the
country to make sure the latest forecasts, watches and
warnings get out to emergency managers, the media, and the
public. What's it like at a forecast office? Don't wait for a
major winter storm; contact your local office and ask to spend
the day with them, and observe the exciting, day-to-day
process of forecasting the snow before it hits.
Learning
Activities
Try these learning activities about Snow and
Winter Weather
Catch a Falling Flake
When it
is snowing, catch a snowflake on a piece of black construction
paper. Look at it through a magnifying glass. What
shape is it? What does that tell you about how cold the
air is?
Play
a version of charades. Act out a favorite activity to do
in the snow, whether it's making snowmen, making snow angels,
having snowball fights, sledding, etc. Have others guess
what you're acting out.
Cut out a snowflake shape from a
piece of paper. If you are with other students, go around and
see if you can find another one like yours.
Make
two columns on the blackboard. In one column, list ways
that snow can be good. In the other, list how it can be
bad.
