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Please help the NWS spread these messages on social media! Everyone is welcome to use the text and images provided below to help the NWS build a Weather-Ready Nation.

What Causes Winter?

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Did you know that, in the northern hemisphere, winter actually occurs when the Earth is closest to the Sun? This is possible because of the way the Earth tilts on its axis. During winter, the northern hemisphere is tilting away from the Sun, causing the Sun’s rays to hit the northern hemisphere at a lower angle, and resulting in far lower temperatures. Learn more at scijinks.gov/earths-seasons/

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In the northern hemisphere, winter actually occurs when the Earth is closest to the Sun. Learn more scijinks.gov/earths-seasons/

What Causes Winter? In the northern hemisphere, winter actually occurs when the Earth is closest to the Sun. This is because the northern hemisphere is tilting on its axis away from the Sun.

 

Weird Weather (Video)

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Haboob. Funny name, dangerous weather phenomenon. Learn about haboobs and other examples of weird weather in this short video: youtu.be/vuk6gvq7Nwk #wxscience

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Haboob. Funny name, dangerous weather phenomenon. Learn about haboobs and other examples of weird weather in this short video: youtu.be/vuk6gvq7Nwk #wxscience

 

What is a 500-year flood? (video)

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The term 500-year flood doesn’t necessarily mean that it’s only going to happen one time every 500 years. Rather, it’s a reference to the probability of occurrence. youtu.be/eQFyaXDH42U #FloodScience

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The term 500-year flood doesn’t necessarily mean that it’s only going to happen one time every 500 years. Rather, it’s a reference to the probability of occurrence. youtu.be/eQFyaXDH42U #FloodScience

 

Science of Debris Flow

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Water is essential for life on Earth. However, in large enough quantities, the very substance we drink and use to grow crops can destroy homes and businesses, and can also cause fatalities. Learn all about the science of river flooding in the infographic below, and visit weather.gov/jetstream/flood for more flood science.

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Learn all about the science of river flooding with this graphic, and visit weather.gov/jetstream/flood for more flood science. #WeatherReady

Flood Science - Debris Flows 
	Debris Flows: Dangerous land and water flow caused by rainfall, terrain and loose-bare soil. Flash flooding and debris flows are common in or near burn scars.  
	Debris flows carry everything: A debris flow is a moving mass of loose mud, sand, soil, rock, water and air that travels down a slope under the influence of gravity. To be considered a debris flow, the moving material must be loose and capable of 'flow', and at least 50% of the material must be sand-size particles or larger. In areas of very steep slopes they can reach speeds of over 100 mph.  
	Burn scars are notorious for debris flows: Burned soil can be as water repellant as pavement. When vegetation is burned at high intensity, water repellent compounds are vaporized, and condense on the soil layers below, which prevents soil from absorbing water. As a result, much less rainfall is required to produce a flash flood.  
	Rainfall and gravity take over: As water runs downhill through burned areas it can create major erosion and pick up large amounts of ash, sand, silt, trees and boulders. The force of the rushing water and debris can damage or destroy culverts, bridges, roadways, and buildings even miles away from the burned area. 
	The risk of debris flow could last years: Most burn areas will be prone to this activity for at least two years. Each wildfire burn area poses its own unique risk of flash flooding due to many factors including proximity to population centers, burn severity, steepness of terrain, and size of the burned area. 
	www.weather.gov/flood 

 

Science of Snowmelt Processes

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At certain times of the year, water from melting snow can be responsible for almost all of the streamflow in a river. The processes of snowmelt are crucial in forming accurate river flood forecasts. Learn more about flood science at weather.gov/jetstream/flood.

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At certain times of the year, water from melting snow can be responsible for almost all of the streamflow in a river. The processes of snowmelt are crucial in forming accurate river flood forecasts. Learn more about flood science at weather.gov/jetstream/flood.

Flood Science - Snowmelt Process 
	Snowmelt Processes: During certain times of the year, water from snowmelt can be responsible for almost all of the streamflow in a river. It's important for hydrologists to understand these processes in order to accurately forecast river floods. 
	Snow Distribution: The path that weather systems take is the most important factor in determining snowpack, but terrain and vegetation also influence how snow accumulates on the ground. 
	Snowpack Characterisitcs: The temperature and the amount of water (snow water equivalent) in the snowpack and important to the melting process. Before rapid melting can occur, the snowpack as a whole needs to be warmed to 32 degress F. 
	Snow Energy Exchanges: Incoming solar radiation, emitted longwave radiation, turbulent transfer of heat, ground conduction, and heat transferred during rainfall are all important factors in heating or cooling the snowpack. 
	Weather Factors: Strong winds and high dew point temperatures aid in melting by limiting the effects of evaporative cooling and allow the layer directly above the snowpack to remain warm due to turbulent mixing. Rain falling on a snowpack can accelerate the melt process as well. 
	Where the Water Goes: Once rapid melting begins, the water will either infiltrate into the soil, run off into streams and other bodies of water, pool in place and potentially refreeze as ice, or a combination. Ice jam floding can occur if the river channel has excessive ice cover. 
	www.weather.gov/flood 

 

Streamflow Routing

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Even without rain or snowmelt, floods can happen along any rivers, creeks, and streams. This is because of something called streamflow routing, which occurs when water volume in a river moves from upstream to downstream. Learn more about flood science at weather.gov/jetstream/flood.

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Even without rain or snowmelt, floods can happen along any rivers, creeks, and streams. This is because of something called streamflow routing, which occurs when water volume in a river moves from upstream to downstream. Learn more about flood science at weather.gov/jetstream/flood.

Flood Science - Streamflow Routing 
	Streamflow Routing: Describes the movement of water volume from one point to another along a river. Hydrologists use this to predict flood peaks. 
	Hydrologic Routing Techniques: Advanced formulas are used to determine the behavior of flow from point A to point B in a stream, creek or river. 
	Streamflow Characteristics: The geometry of the channel may vary at different points along a stream or river and will affect the amount of discharge for a given volume of water. 
	Watershed Characteristics: Additional inflows to a stream between point A and point B further complicate the predictability of the flow. 
	Rating Curve: A rating curve is a relationship between stage and discharge at a cross section of a river. The output from a hydrologic modle is a discharge or flow, which can then be converted stage - a measure of the water level at a given point on the river.
	Floodplains: These are lowland areas adjacent to the river or stream that are prone to flooding due to increases in streamflow on the channel -- which may result from water that is routed downstream. 
	www.weather.gov/flood 

 

Science of River Flooding

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Water is essential for life on Earth. However, in large enough quantities, the very substance we drink and use to grow crops can destroy homes and businesses, and can also cause fatalities. Learn all about the science of river flooding in the infographic below, and visit weather.gov/jetstream/flood for more information on river flooding.

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Learn all about the science of river flooding with this graphic, and visit weather.gov/jetstream/flood for more flood science. #WeatherReady

SCIENCE OF RIVER FLOODING -
Water is essential for life on Earth. But in large enough quantities, the very substance we drink and use to grow crops can destroy homes, businesses and cause fatalities.

River flooding occurs when river levels rise & overflow their banks or the edges of their main channel and inundate normally dry areas.

River flooding can be caused by heavy rainfall, dam failures, rapid snowmelt and ice jams.

Six Steps to Create a River Model
Hydrologic Cycle: Hydrologists try to understand and simulate the natural hydrologic cycle, which is the intricate combination of many processes such as evaporation, transpiration, precipitation, infiltration, interflow, groundwater storage, and runoff.

Precipitation: Precipitation is the primary input to basin hydrologic processes and serves as the primary driver of hydrologic models. Accurate representation of precipitation input is an important intial step. Small river channel systems are very sensitive to rainfall.

Runoff: The next step is to compute the amount of precipitation that appears in surface water within a relatively short time from the onset of a storm event. This is runoff. Runoff consists of 3 components: 
overland flow, rain falling directly on surface water bodies, and interflow.

Unit Hydrograph: After computing basin runoff, the next step is to calculate a forecast hydrograph in units
of discharge. A hydrograph is a plot of the change of stage or discharge with respect to time. Discharge is the volume of water flowing past a location per unit time and is usually expressed in cubic feet per second (cfs).

Streamflow Data: Scientists use streamflow measurements to capture the vital relationship between discharge (volume flow rate) and stage (height) for a given location. This can only be done by taking streamflow measurements at different river levels and noting the corresponding stages. This relation is called a rating curve.

Routing: Hydrologists analyze and interpret how the water moves once it’s in the river and how a flood wave is modified due to the effects of storage and friction as it moves downstream. So, what happens upstream affects the entire downstream community. 

 

Lake Effect Snow

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Lake Effect snow occurs when cold air moves across warmer water. Warmth and moisture rise into the air, condensing into clouds that can produce 2 to 3 inches of snow per hour or more. Learn more weather science at weather.gov/jetstream

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Lake Effect snow occurs when cold air moves across warmer water. Warmth and moisture rise into the air, condensing into clouds that can produce 2 to 3 inches of snow per hour or more. Learn more weather science at weather.gov/jetstream

What is lake effect snow? Lake effect snow occurs when cold air, often originating from Canada, moves across the open waters. As the cold air passes over the unfrozen and relatively warm waters, warmth and moisture are transferred into the lowest portion of the atmosphere. The air rises and clouds form and grow into narrows bands that produce 2 to 3 inches of snow per hour or more.

 

What's a Blizzard?

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Did you know not all blizzards involve falling snow? By definition, a blizzard includes 35+ mph winds that cause blowing snow, reducing visibility to 1/4 mile or less for at least 3 hours. If the visibility reduction comes from snow that has already fallen, it is called a ground blizzard. Whether or not the snow falls during the time of the blizzard, dangerous conditions can result. Make sure you’re prepared! weather.gov/winter

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Did you know that not all blizzards involve falling snow? Whether or not the snow falls during the blizzard, dangerous conditions can result. weather.gov/winter Be #WeatherReady!

What's a Blizzard? Blowing snow, 35+ mph winds, less than 1/4 mile visibility, for 3+ hours.  Did you know that falling snow isn't necessary for a blizzard?  A blizzard that results from previously fallend snow is called a ground blizzard.

 

Upslope Snow

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Have you wondered why the windward side of mountains or large hills receives so much more snow than surrounding areas? This is due to upslope snow. When moist wind blows against the side of mountains/hills, the air is forced to rise (called orographic lift). As the air rises and cools, water vapor condenses, resulting in clouds and precipitation over the windward region. Conversely, the leeward side often receives less snow due to descending air.

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Why does the windward side of mountains or large hills receive so much more snow than surrounding areas? It’s because of the upslope effect. When you’re in one of these windward areas, make sure you’re #WeatherReady

Upslope Snow: 1) When wind blows against mountains or hills, it is forced to rise. This is called orographic lift. 2) As moist air rises and cools, water vapor condenses, resulting in clouds and precipitation. 3) This results in the windward sides of mountains and hills receiving more snow than surrounding areas in the winter.

 

Snow Water Cycle

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During winter months, falling snow serves as an important source of fresh water across the world. When spring arrives, melting snow helps replenish rivers, lakes, and reservoirs. The melting snow adds much-needed moisture to the soil and helps refill underground aquifers, which are vital for growing crops and for drinking water. weather.gov/jetstream/hydro

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During winter months, falling snow serves as an important source of fresh water. weather.gov/jetstream/hydro

Snow Water Cycle: The hydrologic cycle involves the continuous circulation of water in the Earth-Atmosphere system. At its core, the water cycle is the motion of the water from the ground to the atmosphere and back again. During the winter months, falling snow serves as an important source of fresh water across the world. When spring arrives, melting snow helps replenish rivers, lakes and reservoirs. The melting snow adds much needed moisture to the soil and helps refill underground aquifers, which are vital for growing crops and for drinking water.

 

Science of Snowflakes

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Did you know that, while no two snowflakes are exactly the same, they are all six-sided? Snowflakes’ hexagonal shapes are due to the molecular structure of ice. Learn more about the science behind snowflakes: noaa.gov/stories/how-do-snowflakes-form-science-behind-snow

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Did you know that no two snowflakes are alike, but they are all 6-sided? noaa.gov/stories/how-do-snowflakes-form-science-behind-snow #SnowflakeScience

Science of Snowflakes: No two snowflakes are the same, but they are all six-sided. Their shapes are due to the molecular structure of ice.

 

Aurora Colors

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The aurora borealis is usually green in color, although it can also appear to be a range of other colors like red, blue, pink, and purple. The color of the aurora is determined by the altitude in which it appears. Different atmosphere compounds, like nitrogen and oxygen, are found at different altitudes. When charged particles from the Sun enter our atmosphere, they interact with those compounds, and the aurora is the visible result. Depending on which compounds are being excited by the Sun’s charged particles, different colors will appear. Learn more at pwg.gsfc.nasa.gov/polar/telecons/archive/PR_E-PO/Aurora_flyer/aurora-flyer_p2.doc.pdf

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Changing colors of the aurora? It’s elemental, my dear Watson!! The color of the aurora is determined by the altitude in which it appears, as different atmospheric compounds (like nitrogen and oxygen) are found at different altitudes. More here: pwg.gsfc.nasa.gov/polar/telecons/archive/PR_E-PO/Aurora_flyer/aurora-flyer_p2.doc.pdf #SpaceWeather

Why does the aurora change colors? The aurora is usually green, but it can be other colors too. The color is determined by the altitude of the aurora. Atmospheric compounds influence the color.

 

Science of Frost Formation (Video)

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Did you know that frost can form when the official low is above freezing? The official temperature is recorded around 6ft above the ground. In a strong temperature inversion on a clear night, ground temps can be 5-10℉ cooler than the air below that. youtu.be/HBn1oSWu2nE

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Did you know that frost can form when the official low is above freezing? The official temperature is recorded around 6ft above the ground, and in a strong temperature inversion on a clear night, ground temps can be 5-10℉ cooler than the air below that. youtu.be/HBn1oSWu2nE

 

Science of Valley Fog

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Why do we see fog in valleys more often than other spots? First, air at higher elevations cools down, which then drains downslope into the valley. From there, a cool, stable layer forms near the ground, limiting turbulent mixing and trapping the cool, moist air. Finally, the air near the ground continues to cool until water vapor molecules are changed into small droplets of liquid water. weather.gov/safety/fog-mountain-valley

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Looking down on the clouds? Do you know how valley fog is created? weather.gov/safety/fog-mountain-valley #FogScience

1. Air cools at higher elevations as the ground radiates heat into the atmosphere and space. 2. Cooler air drains downslope into the valley. 3. A cool, stable layer forms the ground, which limits turbulent mixing and traps the cool, moist air.  4. The air near the ground continues to cool until water vapor moleculesd are changed into small droplets of liquid water.

 

Science of Fog Formation (video)

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Fog limits visibility, delays air travel, brings danger to the roads, and makes things generally spooky. But, how does it form? Watch this short video: youtu.be/QkRqjcO1ROk

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Fog limits visibility, delays air travel, brings danger to the roads, and makes things generally spooky. But, how does it form? Watch this short video: youtu.be/QkRqjcO1ROk #FogScience

 

Science of Wind (Video)

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Wind is just air moving somewhere else...but WHERE is it going, and WHY? Check out this short video for a primer. youtu.be/kb9oRYUzlwQ

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Wind is just air moving somewhere else...but WHERE is it going, and WHY? Check out this short video for a primer. youtu.be/kb9oRYUzlwQ #WindScience

 

Science of Wind Chill

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In calm winds, our body is able to keep a thin layer of warmer air near it. Once the wind picks up, that layer is quickly disrupted, exposing any unprotected body parts to the full brunt of the cold.
Arctic air + brisk winds = dangerously cold wind chills.
weather.gov/safety/cold weather.gov/safety/cold

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In calm winds, our body is able to keep a thin layer of warmer air near it. Once the wind picks up, that layer is quickly disrupted, exposing any unprotected body parts to the full brunt of the cold.
Arctic air + brisk winds = dangerously cold wind chills.
weather.gov/safety/cold weather.gov/safety/cold

Infographic - The Science of Wind Chill. The average temperature of the human body is 98.6 degrees fahrenheit. Under calm conditions, the body radiates heat, creating a layer of warmth between or skin and the cold surroundings.  But when it's windy, the moving air breaks up this insulating layer. It speeds up heat loss by whisking away the warmth from our skin. Hypothermia begins when our body temperature drops two to four degrees.

 

Science of Santa Ana Winds

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Santa Ana winds are strong downslope winds that blow through the mountain passes in Southern California. They are created over the Great Basin region from high-pressure air masses, which then blow down towards sea level. These winds, which can easily exceed 40 miles per hour (18 m/s), are warm and dry and can severely exacerbate brush or forest fires, especially under drought conditions. For more info, visit earthobservatory.nasa.gov/NaturalHazards/view.php?id=10727.

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Santa Ana winds are notorious for creating dangerous fire conditions. Learn how here: earthobservatory.nasa.gov/NaturalHazards/view.php?id=10727 #WindScience

What are Santa Ana Winds? Strong downslope winds. Created over the Great Basin from high-pressure air masses. They are warm, dry, and can worsen forest fires.

 

Skywarn

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Do you know what to watch for when severe weather threatens? Check out NWS Skywarn. Help keep your community safe by volunteering to become a trained storm spotter for NOAA's National Weather Service. Potential volunteers should visit nws.noaa.gov/skywarn/ and contact their local NWS office. #CitizenScience

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Let’s learn about #NWSCitizenScience opportunities! Become a trained Skywarn storm spotter and help keep your community safe! nws.noaa.gov/skywarn/ #CitizenScience

NWS Skywarn: National Weather Service Citizen Science

 

CoCoRaHS

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Ever wanted to take rain or snow measurements? Join CoCoRaHS or the Community Collaborative Rain, Hail, and Snow Network. This volunteer network of observers measures precipitation from their backyards. Any age can volunteer. Data is used by NWS meteorologists to help with forecasts. www.cocorahs.org

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Ever wanted to take rain or snow measurements? Learn more about #NWSCitizenScience and join CoCoRaHS today! Cocorahs.org #CitizenScience

CoCoRaHS: National Weather Service Citizen Science

 

mPING

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Check out the mPING (Meteorological Phenomena Identification Near the Ground) project. Weird name, cool app! You can report the type of precipitation you see where you are. No need to measure! Use the free mobile app to send reports anonymously. Reports are automatically recorded into a database, which improves weather computer models. The information is even used by road maintenance operations and the aviation industry to diagnose areas of icing. mping.nssl.noaa.gov #CitizenScience

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Check out mPING! Weird name, cool app for #CitizenScience! Report weather types via the mPing app and help improve weather model forecasts! mping.nssl.noaa.gov #NWSCitizenScience

mPING: National Weather Service Citizen Science

 

COOP

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The NWS Cooperative Observer Program (COOP) is truly the nation's weather and climate observing network of, by, and for the people. With over 8,700 volunteer observers, this program has existed since 1890 and is one of the few programs that measures snowfall and its water equivalent. Help #NWSCitizenScience and become a COOP! You can help support warnings and forecasts, and contribute to building a climatological database! For more information, visit weather.gov/coop/Overview

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Join NWS COOP! The NWS Cooperative Observer Program (COOP) is truly the nation's weather and climate observing network of, by, and for the people. Help support warnings, forecasts & build a climatological database! weather.gov/coop/Overview #NWSCitizenScience

NWS Cooperative Observer: National Weather Service Citizen Science