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

3. What is the National Weather Service??

4. 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)

5. What We Do Climate Forecasts and Warnings Produce Weather, Water and
-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

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

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

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

9. National Weather Service Forecast Office
Austin/San Antonio, TX

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

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

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

14. 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.

15. But observations are not limited to surface conditions
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.

16. Dozens of satellites keep a constant watch over the earth each day
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.

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

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

19. EXPERIENCE: 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.

20. MODELS: 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.

21. 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.

22. 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.

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

26. How do clouds form?

27. Cloud Formation (Cont’d)
Warm air rises (less dense), and will gradually cool. The air will begin condensing (when the temperature and dewpoint become closer together), and water droplets bond onto condensation nuclei. These nuclei will collide with other nuclei, eventually forming a cloud.
Air can reach saturation in a number of ways. The most common way is through lifting. As a bubble or parcel of air rises it moves into an area of lower pressure (pressure decreases with height). As this occurs the parcel expands. This requires energy, or work, which takes heat away from the parcel. So as air rises it cools. This is called an adiabatic process. Since cold air can hold less water vapor than warm air, some of the vapor will condense onto tiny clay and salt particles called condensation nuclei. The reverse is also true. As a parcel of air sinks it encounters increasing pressure so it is squeezed inward. This adds heat to the parcel so it warms as it sinks. Warm air can hold more water vapor than cold air, so clouds tend to evaporate as air sinks.

28. CLOUDS
Cirrus
Stratus
Cumulus
Nimbus

29. Types of Clouds
Low clouds: Consist of stratoform (flat) clouds, or cumuloform (puffy) clouds, lying on or just above the surface (up to ~10,000 ft).
Stratus: Cumulus:
Stratus clouds consist of a feature-less low layer that can cover the entire sky like a blanket, bringing generally gray and dull weather. The cloud bases are usually only a few hundred feet above the ground. Over hills and mountains they can reach ground level when they may be called fog. Also, as fog "lifts" off the ground due to daytime heating, the fog forms a layer of low stratus clouds.
Cumulus clouds are of small vertical development with flat bases and rounded tops. These types of clouds indicate fair weather.

30. Types of Clouds (Cont’d)
Middle Clouds: Consist of altoform (meaning a middle cloud) type clouds, extending from 10,000 – 20,000 feet above the surface.
Altostratus: Altocumulus:
These clouds typically form between 7,000 and 15,000 feet (2,100 to 4,600 m) and bring steady precipitation. As the clouds thicken and precipitation begins to fall, the bases of the clouds tend to lower toward the ground.

31. Types of Clouds (Cont’d)
High Clouds: Consists of mainly ice crystals suspended above 20,000 feet from the surface. These clouds are wispy/crisp/featherlike in appearance, and do not produce precipitation.
Cirrus: Cirrostratus: Cirrocumulus:
High-level clouds which form above 20,000 feet and are usually composed of ice crystals. High-level clouds are typically thin and white in appearance, but can create an array of colors when the sun is low on the horizon. Cirrus generally occur in fair weather and point in the direction of air movement at their elevation.

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

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

34. 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

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

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

37. “Collision” Process

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

39. Rain or Snow??

40. In order to form, thunderstorms need:
Moisture
Instability
Lifting

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

42. 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

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

44. The three stages in a thunderstorm’s life:

45. Thunderstorm Hazards Hail Damaging Winds Tornados Flash Floods
Lightening

46. HAIL

47. DAMAGING WINDS
Damage from
a tornado
Damage from
a downburst

48. 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

51. 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

52. Strong 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

53. 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

54. Jarrell, TX — May 27, 1997

55. FLASH FLOODING

57. 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!

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

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

61. QUESTIONS? Marianne Sutton@noaa.gov National Weather Service
Austin/San Antonio
2090 Airport Road
New Braunfels, TX 78130