Transcript Austin/San Antonio, TX National Weather Service Forecast Office

•How Do We Predict Weather?
•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
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
National Weather Service
Our Primary Mission:
The protection of lives and property
Watches, warnings, and advisories for:
-Severe Thunderstorms
-Tornados
-Floods
-Flash Floods
-Winter Storms
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
Austin/San Antonio, TX
WEATHER FORECASTING
This problem has two parts . . .
Analyze: What’s going on right now?
Forecast: What’s going to happen?
Analyzing the Weather
Surface Observations . . .
mostly at airports . . .
can be taken by people
Or by machines such as the
ASOS Automated
Surface
Observing
System
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
There are 3 basic methods of
forecasting:
• Persistence
• Experience
• Computer Modeling
PERSISTENCE:
•Not much is going to change.
•Tomorrow will be like today.
•Works great in summer.
•Not so good the rest of the year.
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.
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.
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
In order to form, thunderstorms need:
•Moisture
•Instability
•Lifting
Mid and upper-level
moisture can arrive
from the Pacific.
Low-level moisture
comes from the
Gulf of Mexico.
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
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
- 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
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
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
For Current Weather Information:
NOAA Weather Radio
Or:
www.weather.gov
Clickable map of the entire U.S.
www.srh.noaa.gov/ewx
NWS Austin/San Antonio’s Homepage
QUESTIONS?
Marianne [email protected]
National Weather Service
Austin/San Antonio
2090 Airport Road
New Braunfels, TX 78130