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mP. cP. mT. cT. Review questions:. Describe the movement of water through the hydrologic cycle. . Most water evaporates from the oceans. Some of the water is transported considerable distances, condenses to form clouds, and eventually falls to earth’s surface as precipitation.
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Describe the movement of water through the hydrologic cycle.
How does stable air differ from unstable air?
Why are high clouds always thin in comparison to
low or middle clouds?
Explain why air pressure decreases with an increase
-The Weather Business
-Long Range Forecasts
-Tools in Weather Forecasting
In the United States, the governmental agency responsible for
gathering and disseminating weather related information is the
National Weather Service (NWS).
The most important services provided by the NWS are forecasts
and warnings of hazardous weather information including:
thunderstorms, flooding, hurricanes, tornadoes, winter weather
and extreme heat.
Weather forecasting is the process, (science, art) by which, from
current weather patterns, various methods are used to determine
the state of the atmosphere.
The National Weather Service is responsible for issuing forecasts and
warnings of hazardous weather including thunderstorms, flooding,
Large Rivers are monitored at several key locations to assess changes in
By using automated equipment in the gaging station, river stage can be continuously monitored and reported to an accuracy of 1/8 of an inch. Linking battery-powered stage recorders with satellite radios enables transmission of stage data to computers in USGS and NWS facilities even when extreme high waters and strong winds disrupt normal telephone and power services. In this way, USGS and NWS hydrologists know the river stage at remote sites and how fast the water is rising or falling.
To produce the image shown above is very complicated, labor intensive undertaking.
To produce even a short range forecast involves numerous steps, including collecting weather data, compiling it on a global scale, and
The NWS is not responsible for the plethora of animated
weather images we see on TV. It is not part of the mission of the
NWS to provide these data. Private enterprises, using “raw data”
from the NWS, undertake this task.
It is a unique joint venture between the NWS and the private weather sector. The NWS is the official voice, and therefore
is ultimately responsible in the United States for issuing warnings.
Before issuing a forecasting, the forecaster must have an
accurate picture of the atmospheric conditions; this project
is called the weather analysis.
Because the atmosphere is always changing, time is of the
essence when analyzing the weather. Clearly, high speed
computers have revolutionized the weather analysis process.
First introduced in 1985, this system had a peak
performance of 1.9 gigaflops. At the time, the
CRAY-2 system had the world's largest central
memory with the possibility of 2048 megaBytes,
which is still considered large today.
A critical mass of information is needed to generate a useful
weather chart for even a short range forecast.
The World Meteorological Organizationwhich
includes more than 130 nations, was formed to address this problem.
It is their responsibility for gathering the needed data and for
producing numerous weather maps and upper-level charts that
describe the current state of the atmosphere.
then transmitted to three World
Meteorological Centers. From there
the world centers send data to the
meteorological center in each office.
Once weather data has been collected, the analyst displays it on
a number of different synoptic weather maps which are used
to produce weather forecasts.
Synoptic means coincident in time. (syn- same, optic – to look at)
(Of or relating to data obtained nearly simultaneously over a large area of the atmosphere)
Over 200 surface maps and charts are produced by the NWS
and its forecast centers.
As we already know, different levels in the atmosphere are used
to study different processes important to weather forecasting….
Surface maps show the location of major pressure centers, fronts, weather conditions at several locations.
850-mb maps are useful to analyze temperature advection and
observe surface features.
700-mb maps are useful to track the movement of air-mass thunderstorms.
500-mb maps are useful to predict the movement of upper level cyclones. Prior to high-speed computing 500-millibar maps were heavily relied on.
300 (200mb) maps show jet stream location. Recall the jet stream
associated with areas of upper level divergence and convergence.
Imagine a system on a rotating sphere that is 8000 miles wide,
consisting of different materials, different gases that have different
properties (one of the most important of which is water which is
exists in different concentrations), heated by a nuclear reactor
93 million miles away.Then just to make life interesting, this sphere
is oriented such that as it revolves around the reactor it is heated
differently at different locations at different times of the year:
Then someone is asked to watch the mixture of gases, a fluid only
20 miles deep, that covers an area of 250 million square miles,
and to predict the state of that fluid at one point on a sphere 2 days
This is the problem forecaster have to face. (Bob Ryan WRC-TV)
The persistence method assumes that the conditions at the time of the forecast will
not change. For example, if it is sunny and 87 degrees today, the persistence method
predicts that it will be sunny and 87 degrees tomorrow. If two inches of rain fell
today, the persistence method would predict two inches of rain for tomorrow.
The trends method involves determining the speed and direction of movement for fronts, high and low pressure centers, and areas of clouds and precipitation.
Numerical weather prediction relies on the fact that the gases of
the atmosphere obey a number of known physical principles.
(PV=nRT for example)
Numerical weather prediction employs a number of highly
refined computer models to attempt to mimic the behavior of the
Using numerical models, the National Weather Service produces
a number of prognostic charts whichpredict the state of the
atmosphere in the future (temperature, winds, moisture, clouds,
The ENIAC machine occupied a room thirty by fifty feet. The controls are at the left, and a small part of the output device is seen at the right.
The number and distribution of vertical layers in the operational Eta Model has changed throughout the years
Implemented in 1993 (0-48hrs) 80km resolution
Oct 1995 Eta -48km w/EDAS
Feb 1998 Eta –32km (0000, 1200 UT) 48 hr forecast 3D var
Mar 1995 Eta –29km (meso Eta) (0300 and 1500 UT)
Feb 1998 Eta –32km (0300 + 1800UT) 45 levels
2001 Eta –12km 60 layers
Eta Model Vertical Resolution Characteristics/Layer Distribution
A model’s vertical structure is as important in defining the model’s behavior as the horizontal configuration and model type. Proper depiction of the vertical structure requires selection of an appropriate vertical coordinate and sufficient vertical resolution.
Two Common Vertical Coordinates:
Sigma Vertical Coordinate
(NGM, AVN/GFS, ECMWF, NOGAPS and UKMET, MM5, COAMPS, RAMS)
Eta (or Step) Vertical Coordinate
p is the pressure on a forecast level within the model and ps is the pressure at the earth’s surface, not mean sea level pressure.
The lowest coordinate surface ( = 1) follows a smoothed version of the actual terrain.
To address the problem of discontinuous forecast surfaces, Phillips (1957) developed a terrain-following coordinate called the sigma ( ) coordinate, illustrated below. The sigma coordinate or variants are used in the NGM, AVN/MRF, ECMWF, NOGAPS, and UKMET models and appear in some meso-scale models, such as AFWA MM5, COAMPS, and RAMS.
1) Model wind forecasts depend on accurate calculation of the pressure gradient force (PGF). When sigma surfaces slope, the PGF must be expanded from its simple pressure coordiante form account for the slope. This can introduce errors because the lapse rate must be expanded approximated at points that lie between the pressure surfaces. With steep slopes the errors can be significant. 2) Because the actual and often abrupt steepness of mountain slopes is smoothed in sigma coordinate models, they often misrepresent the true surface elevation. This can cause forecasts for locations immediately adjacent to mountain ranges to severely misrepresent the surface pressure and thus the temperature and moisture (PGF as well).
Limitations of the Sigma Vertical Coordinate
The eta coordinate system allows the bottom atmospheric layer to be represented within each grid box as a flat “step”, rather than a sloping sigma terrain. For this reason it is sometimes called the step mountain coordinate system.
Eta models do not need to perform the vertical interpolations that are necessary to calculate the PGF in sigma. This reduces the error in PGF calculation and improves the forecast of wind and temperature and moisture changes in areas of steeply sloping terrain.
Although the numerical formulation near the surface is more complex, the low-level convergence in areas of steep terrain are far more representative of real atmospheric conditions than sigma models. The improved forecasts of low-level convergence result in better precipitation forecasts in these areas that out way the extra computer time needed.
The step nature of the eta coordinate makes it difficult to retain detailed vertical structure in the boundary layer over the entire model domain (elevated terrain). Because the depth of the layers typically increases with height from sea level, the eta coordinate system can have difficulty representing boundary layer processes over elevated terrain.
Eta models do not accurately depict gradually sloping terrain. Since all terrain is represented in discrete steps, gradual slopes that extend over large distances can be concentrated within as few as one step.
This model is the primary weather prediction model for forecasting for the United States. The model is under active development and is therefore frequently being improved.
The model uses a limited-area domain, centered over North America and including much of the surrounding oceans. It has the finest horizontal and vertical resolution of all the models currently in use at NCEP, and thus has the potential of forecasting the weather with the greatest accuracy. However, it is also the newest model, and is therefore not as sophisticated in some aspects as the other models.
Giving that many time steps are needed to produce a forecast, the
problem of “propagation of errors” is a constraint on weather
Small errors may make
little difference in the
early stages of prediction,
can amplify dramatically
Yt = (a x Yt+1) – Y2t
Geostationary satellites were placed in orbit over the equator; they remain fixed over a point. To keep the satellite in place over Earth the satellite must orbit at a farther distance than
polar orbiters (35,000 km). Some resolution is lost but very powerful satellites.
Polar orbiting satellites orbit the globe
at low altitudes (a few hundred km)
which allows them to complete one
pass in 100 minutes. With such a
quick orbit the satellite can capture
two sweeps of the globe in 24 hours.
The TIROS Program (Television Infrared Observation Satellite) was NASA's first experimental step to determine if satellites could be useful in the study of the Earth.
The images above show the stark contrast between the first image beamed down from
TIROS-1 on April 1, 1960 and the full-color full-Earth images that GOES-8 produces every
three hours. But, if it hadn't been for TIROS and the TIROS experiment, there would
be no GOES images today.
NOAA's National Environmental Satellite,Data and Information Service
NESDIS operates the satellites and manages the processing and distribution
of millions of bits of data and images these satellites produce daily. The
prime customer for the satellite data is NOAA's National Weather Service,
which uses satellite data to create forecasts for television, radio, and weather
NOAA's operational environmental satellite system is composed of:
geostationary operational environmental satellites (GOES) for short-range
warning and "nowcasting," and polar-orbiting environmental satellites (POES)
for longer term forecasting. Both kinds of satellites are necessary for
providing a complete global weather monitoring system. The satellites carry
search and rescue instruments, and have helped save the lives of about
10,000 people to date. The satellites are also used to support aviation safety
and maritime/shipping safety (ice monitoring and prediction).
Around the world...around the clock...NOAA proudly stands watch. As an integral part of worldwide search and rescue, NOAA operates the Search & Rescue Satellite Aided Tracking (SARSAT) System to locate those in distress almost anywhere in the world at anytime and in most conditions.The SARSAT system uses NOAA satellites in low-earth and geostationary orbits to detect and locate aviators, mariners, and land-based users in distress. The satellites relay distress signals from emergency beacons to a network of ground stations and ultimately to the U.S. Mission Control Center (USMCC) in Suitland, Maryland. The USMCC processes the distress signal and alerts the appropriate search and rescue authorities to who is in distress and, more importantly, where they are located. Truly, SARSAT takes the "search" out of search and rescue.