•How Do We Predict Weather?

•General Weather InformationClouds, rain, thunderstorms, etc.

What is the National Weather

Service??

Organizational Structure…

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 Climate Forecasts and

Warnings -For All Americans -To Protect Life and Property -To Enhance the National

Economy

Data and Products: -Government Agencies -Private Sector -The Public -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 ServiceNational Weather Service

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

Austin/San Antonio, TXAustin/San Antonio, TX

National Weather Service Forecast Office

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 peopleOr by machines such as the ASOS - Automated Surface Observing System

Analyzing the Weather

COOPERATIVE OBSERVERS

• Volunteer weather observers

• Daily temperature and precipitation reports

• River level reports

• 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

• Experience• Computer

Modeling

There are 3 basic methods of forecasting:

•Not much is going to change.

•Tomorrow will be like today.

•Works great in summer.

•Not so good the rest of the year.

PERSISTENCE:

•Forecast what was seen before to repeat.

•This is good for 1 to 2 day forecasts.

•Works great a lot of the time.

•Problem when something new happens.

EXPERIENCE:

•They are better than people past 3 days.

•Works great most of the time.

•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.

How do clouds form?

CLOUDS

•Cirrus•Stratus•Cumulus•Nimbus

Cirrus Clouds

• High-level clouds

• Usually only ice crystals

• Generally in fair weather

Stratus Clouds

• Base is usually only a few hundred feet above the ground

• Little to no vertical development

• Can cover entire sky

Cumulus Clouds

• Base is at low level, but tops can reach 60,000 feet (11 miles) high

• Made of both ice and water droplets

• Puffy like cotton balls

Nimbus Clouds

• Generally form 7,000 to 15,000 feet (1 to 3 miles) above ground

• Steady precipitation

PRECIPITATION

Two basic ways precipitation forms:

•“Collision” process (warm 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.

Rain or Snow??

THUNDERSTORMS

•Moisture• Instability•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 unstable, it will continue in the direction it was pushed

LIFT

•Differences in heating

• Terrain

• Fronts, boundaries, drylines

The three stages in a thunderstorm’s life:

Thunderstorm Hazards

•Hail•Damaging Winds• Tornados• Flash Floods

HAIL

DAMAGING WINDS

Damage from a downburst

Damage from a tornado

TORNADOSF-Scale

•Named after its creator, Dr. Fujita

•Used to describe how fast winds in a tornado are

•Actually goes all the way to F12, which is the speed of sound

- F0, F1

- 67% of S.C. TX Tornadoes

- Causes 5% of all deaths

- Life span 1 to 2 minutes

- Path length less than 1 mile

- Path width less than 100 yards

- 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

- 3% of S.C. TX Tornadoes

- Causes 65% of all deaths

- Life span to several hours

- Path length dozens of miles

- Path width to 1 1/ 2 miles

- 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” diameterfloats 1225 lbs of car

weight

NOAA Weather RadioOr:

For Current Weather Information:

www.weather.govClickable map of the entire U.S.

www.srh.noaa.gov/ewx

NWS Austin/San Antonio’s Homepage

QUESTIONS?

Marianne Sutton@noaa.gov

National Weather Service

Austin/San Antonio

2090 Airport Road

New Braunfels, TX 78130