# Presentation: 084134

## Slide 1

## How Do We Predict Weather?

General Weather Information
Clouds, rain, thunderstorms, etc.

- 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)

## What We Do

-                               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 Service

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

## 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?

## Slide 11

## Analyzing the Weather

- mostly at airports . . .
- can be taken by people

- Or by machines such as the ASOS -
-       _A_utomated
-       _S_urface
-       _O_bserving
-       _S_ystem

## COOPERATIVE OBSERVERS

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

## Of course, we can’t forget radar!

- 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.

## 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:

## PERSISTENCE:

- Tomorrow will be like today.
- Works great in summer.
- Not so good the rest of the year.

## EXPERIENCE:

- This is good for 1 to 2 day forecasts.
- Works great a lot of the time.
- Problem when something new happens.

## MODELS:

- Works great most of the time.
- Problem when bad data gets put in or if something really new occurs.

## 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.

## Slide 23

## Not just temperature differences...

-    Air which stays over water for long periods of time absorbs some of the moisture through evaporation.

## Slide 25

## 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.

**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

## TORNADOS

- F-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

## Slide 46

## Minimal Tornado

-  - 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

## Strong Tornado

- - 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

## Violent 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

## Jarrell, TX — May 27, 1997

## FLASH FLOODING

## Slide 52

## For each foot of rising water, a car weighs 1500 pounds less!

- 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!**

## floats 816 lbs 

- Tire 8” wide,
- 30” diameter
- floats **816 lbs**
- of car weight

- Tire 12” wide,
- 30” diameter
- floats **1225 lbs** of car weight

## Slide 55

## NOAA Weather Radio
Or:

- Or:

- For Current Weather Information:

- www.weather.gov
- Clickable 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