How Do We Predict Weather? How Do We Predict Weather? General Weather Information General Weather Information Clouds, rain, thunderstorms, etc.

What is the National Weather Service??

Organizational Structure… U. S. Department of Commerce (International Trade, US Business Growth, Aid in Technological Advancement) National Oceanic and Atmospheric Administration (NOAA) (Climate, Ocean Life, Satellites, Research) National Weather Service (Forecasts, Warnings, River Data, Weather Safety)

Produce Weather, Water and Produce Weather, Water and Climate Forecasts and Warnings Climate Forecasts and Warnings -For All Americans -For All Americans -To Protect Life and Property -To Protect Life and Property -To Enhance the National Economy -To Enhance the National Economy Data and Products: Data and Products: -Government Agencies -Government Agencies -Private Sector -Private Sector -The Public -The Public -Global Communities -Global Communities Weather and data are becoming more important to the economy and business decisions What We Do

National Weather Service The protection of lives and property Watches, warnings, and advisories for: -Tornados -Flash Floods -Severe Thunderstorms -Floods -Winter Storms Our Primary Mission:

Advisory: Just so you know… Watch: Stay Alert! Warning: Take Cover NOW!

National Weather Service 122 Weather Forecast Offices (CONUS, AK, HI, Guam and Puerto Rico) 122 Weather Forecast Offices (CONUS, AK, HI, Guam and Puerto Rico)

Austin/San Antonio, TX National Weather Service Forecast Office

WEATHER FORECASTING This problem has two parts... Analyze: What’s going on right now? Forecast: What’s going to happen?

Surface Observations... mostly at airports... can be taken by people Or by machines such as the ASOS - Automated Automated Surface Surface Observing Observing System System Analyzing the Weather

COOPERATIVE OBSERVERS Volunteer weather observers Volunteer weather observers Daily temperature and precipitation reports Daily temperature and precipitation reports River level reports River level reports Important for ground truth Important for ground truth

It can see father - with greater detail and more power than any other weather radar in the world!! So sensitive... it can detect birds... bats... bugs and pollen in the air... and leaves rustling on nearby trees. Of course, we can’t forget radar!

But observations are not limited to surface conditions. Aircraft reports of winds and weather are important. And observations from upper air balloons launched twice a day at around 120 sites are the basis of upper air analysis.

Dozens of satellites keep a constant watch over the earth each day. Some are geosynchronous (stay in the same position over the earth) while others orbit around the earth.

FORECASTING Persistence Persistence Experience Experience Computer Modeling Computer Modeling There are 3 basic methods of forecasting:

Not much is going to change. Not much is going to change. Tomorrow will be like today. Tomorrow will be like today. Works great in summer. Works great in summer. Not so good the rest of the year. Not so good the rest of the year. PERSISTENCE:

Forecast what was seen before to repeat. Forecast what was seen before to repeat. This is good for 1 to 2 day forecasts. This is good for 1 to 2 day forecasts. Works great a lot of the time. Works great a lot of the time. Problem when something new happens. Problem when something new happens. EXPERIENCE:

They are better than people past 3 days. They are better than people past 3 days. Works great most of the time. Works great most of the time. Problem when bad data gets put in or if something really new occurs. Problem when bad data gets put in or if something really new occurs. MODELS:

Let’s start with a question... Why do we have weather? The Earth rotates on a tilted axis. Due to the tilt, the equator is always heated more than either pole.

The Result... Part of Earth’s atmosphere is too cold and dense and part of the atmosphere is much too warm and light Somehow... this must all be balanced out.

Not just temperature differences… Air which stays over water for long periods of time absorbs some of the moisture through evaporation. Air which stays over water for long periods of time absorbs some of the moisture through evaporation.

How do clouds form?

CLOUDS Cirrus Cirrus Stratus Stratus Cumulus Cumulus Nimbus Nimbus

Cirrus Clouds High-level clouds High-level clouds Usually only ice crystals Usually only ice crystals Generally in fair weather Generally in fair weather

Stratus Clouds Base is usually only a few hundred feet above the ground Base is usually only a few hundred feet above the ground Little to no vertical development Little to no vertical development Can cover entire sky Can cover entire sky

Cumulus Clouds Base is at low level, but tops can reach 60,000 feet (11 miles) high Base is at low level, but tops can reach 60,000 feet (11 miles) high Made of both ice and water droplets Made of both ice and water droplets Puffy like cotton balls Puffy like cotton balls

Nimbus Clouds Generally form 7,000 to 15,000 feet (1 to 3 miles) above ground Generally form 7,000 to 15,000 feet (1 to 3 miles) above ground Steady precipitation Steady precipitation

PRECIPITATION Two basic ways precipitation forms: Two basic ways precipitation forms: “Collision” process (warm clouds)“Collision” process (warm clouds) “Ice Crystal” process (cold clouds)“Ice Crystal” process (cold clouds)

“Collision” Process

“Ice Crystal” Process Easier for water vapor to deposit directly onto ice crystals. Crystals then grow heavy enough to start falling. Easier for water vapor to deposit directly onto ice crystals. Crystals then grow heavy enough to start falling.

Rain or Snow??

THUNDERSTORMS Moisture Moisture Instability Instability Lifting Lifting In order to form, thunderstorms need:

Low-level moisture comes from the Gulf of Mexico. Mid and upper-level moisture can arrive from the Pacific.

INSTABILITY If air is stable, it will try to go back to where it was If air is stable, it will try to go back to where it was If air is unstable, it will continue in the direction it was pushed If air is unstable, it will continue in the direction it was pushed

LIFT Differences in heating Differences in heating Terrain Terrain Fronts, boundaries, drylines Fronts, boundaries, drylines

The three stages in a thunderstorm’s life:

Thunderstorm Hazards Hail Hail Damaging Winds Damaging Winds Tornados Tornados Flash Floods Flash Floods

HAIL

DAMAGING WINDS Damage from a downburst Damage from a tornado

TORNADOS F-Scale Named after its creator, Dr. FujitaNamed after its creator, Dr. Fujita Used to describe how fast winds in a tornado areUsed to describe how fast winds in a tornado are Actually goes all the way to F12, which is the speed of soundActually goes all the way to F12, which is the speed of sound

- F0, F1 - F0, F1 - 67% of S.C. TX Tornadoes - 67% of S.C. TX Tornadoes - Causes 5% of all deaths - Causes 5% of all deaths - Life span 1 to 2 minutes - Life span 1 to 2 minutes - Path length less than 1 mile - Path length less than 1 mile - Path width less than 100 yards - Path width less than 100 yards - Wind speeds up to 110 mph - Wind speeds up to 110 mph Minimal Tornado

- F2, F3 - 30% of S.C. TX Tornadoes - Causes 30% of all deaths - Life span 15 to 20 minutes - Path up to 15 miles - Path width up to 500 yards - Wind speeds up to 200 mph Strong Tornado

- F4, F5 - F4, F5 - 3% of S.C. TX Tornadoes - 3% of S.C. TX Tornadoes - Causes 65% of all deaths - Causes 65% of all deaths - Life span to several hours - Life span to several hours - Path length dozens of miles - Path length dozens of miles - Path width to 1 1/ 2 miles - Path width to 1 1/ 2 miles - Wind speeds over 300 mph - Wind speeds over 300 mph Violent Tornado

Jarrell, TX — May 27, 1997

FLASH FLOODING

For each foot of rising water, a car weighs 1500 pounds less! As little as 18 inches of water can float a truck! It takes only 12 to 14 inches of water to float a car!

Tire 8” wide, 30” diameter floats 816 lbs of car weight Tire 12” wide, 30” diameter floats 1225 lbs of car weight

NOAA Weather Radio Or: For Current Weather Information: Clickable map of the entire U.S. NWS Austin/San Antonio’s Homepage

QUESTIONS? Marianne National Weather Service Austin/San Antonio 2090 Airport Road New Braunfels, TX 78130