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Transcript
Weather Forecasting
GEOL 1350: Introduction To Meteorology
1
Overview
• Weather Forecasting Tools
• Weather Forecasting Methods
• Weather Forecasting Using Surface Charts
2
Weather Forecasting Tools
To help forecasters handle all the available charts
and maps, high-speed data modeling systems
using computers are employed by the National
Weather Service.
Advanced Weather Interactive Processing System
(AWIPS) has data communications, storage,
processing, and display capabilities to better help
the individual forecaster extract and assimilate
information from available data.
3
Weather Forecasting Tools
AWIPS computer work station provides various weather
maps and overlays on different screens.
AWIPS gathers data from Doppler radar system, satellite
imagery, and the automated surface observing system that
are operational at selected airports and other sites through
4
out the United States.
Weather Forecasting Tools
•  Doppler radar detects
severe weather size,
movement, and
intensity
  A forecaster can project
the movement of the
storm and warn those
areas in the path of
severe weather.
Doppler radar data from Melbourne, Florida, on Mar 25, 1992, during the time of a
severe hailstorm. The hail algorithm determined that there was 100% probability
that the storm was producing hail. It also estimated that maximum size of the 5
hailstones to be greater than 3 inches.
Weather Forecasting Tools
•  It is essential that the data can
be easily accessible for the
forecasters and in a format that
allows several weather variables
to be viewed at one time.
• Meteogram is a chart that shows
how one or more weather
variables has changed at a station
over a given period of time.
• Meteogram may represent how
air temperature, dew point, and
pressure change over five days.
Meteogram illustrates predicted weather
elements at Buffalo from 1 pm Jan 18 to 7 pm
Jan 20.
At 7 am on Jan 19:
P = 1007 mb, Cloud height = 2000 ft,
Visibility=10 miles, Wind=15 knots, T=33F,
6
Dew Point=24F, Minimum T=30F.
Weather Forecasting Tools
•  Radiosonde instruments can be
used to measure the vertical
profiles of temperature, dew point,
and winds.
•  Saturated air extends up to
about 820 mb.
• Below-freezing temperatures
only exist in a shallow layer near
the surface and the freezing rain
would continue or possibly
change to rain, as cold easterly
surface winds are swinging
around to warmer southwesterly
winds aloft.
A sounding of air temperature, dew point,
and winds at Pittsburgh, PA on Jan 14, 1999.
7
Weather Forecasting Tools
•  Another valuable tool utilized to forecast the
weather is the satellite.
•  Satellites provide extremely valuable cloud
images of areas where there are no ground-based
observations.
•  Before weather satellites were in use, tropical
storms often went undetected until they moved
8
dangerously near inhabited areas.
Weather Forecasting Tools
NASA Satellites
9
Weather Forecasting Tools
•  Occultation Method
•  One of the most recent and promising
atmospheric remote sensing technique is
the Radio Occultation applied to GPS
measurements.
•  Its importance has been increasing
during the last decade, since the first
related
mission
highlighted
its
possibilities.
•  It has better vertical resolution.
Observation Geometry
10
Weather Forecasting Tools
•  Nadir observations allow to probe the global tropospheric
composition, in particular boundary layer:
•  Location of most sources and sinks of greenhouse gases and air
pollutants
•  Nadir observation satellites include SBUV, TOMS, GOME,
MISR, MODIS, TES, AIRS, SCIAMACHY, OMI
11
Weather Forecasting Methods
•  Probability Forecasts
•  Climate records, often 30 years of data, are used to generate
probability forecasts for a given event.
•  In this case, most of Texas has a less than 5% chance of snow on
Dec 25, while northern Minnesota has more than 90% chance of
snow on Dec 25.
12
Weather Forecasting Methods
•  Several methods are used to forecast weather
•  Persistence Forecast: a prediction that future weather will be the
same as present weather.
•  Trend Forecast: Surface weather systems tend to move in the
same direction and at approximately the same speed as they have
been moving.
•  Analogue Forecast: The future will be like weather that
historically occurred when similar conditions were present.
•  Statistical Forecast: Made routinely of weather elements based
on the past performance of computer models.
13
Weather Forecasting Methods
•  Weekly & Monthly Forecasts
•  Stationary weather systems often allow for trend based extended
weather forecasts, while multiple runs of numerical weather
models, known as ensemble forecasts, allow for 30 to 90 day
outlooks.
The 90-day outlook for (a) precipitation and (b) temperature for Feb, Mar, and Apr, 1999. For
precipitation (a), the darker the green color the greater the probability of precipitation being
above normal, whereas the deeper the red color the greater the probability of precipitation
being below normal. For temperature (b), the darker the orange/red colors the greater the
probability of temperatures being above normal, whereas the darker the blue color, the14greater
the probability of temperatures being below normal.
Weather Forecasting Methods
•  Short-time Forecasting with Surface Charts
•  Simplified 6 AM Tuesday surface weather map is useful for short
time interval predictions of fronts and associated weather.
Surface weather map for 6 AM. Dashed lines indicate positions of weather features six
hours ago. Areas shaded green are receiving rain, while areas shaded white are
receiving snow, and those shaded pink, freezing rain or sleet.
15
Weather Forecasting Methods
•  Short-time Forecasting with Surface Charts
•  Simplified 6 AM Tuesday surface weather map is useful for short time interval
predictions of fronts and associated weather.
•  For short-time intervals, mid-latitude cyclonic storms and fronts tend to move
in the same direction and at approximately the same speed as they did during
the pervious six hours.
Surface weather map for 6 AM. Dashed lines indicate positions of weather features six
hours ago. Areas shaded green are receiving rain, while areas shaded white are
receiving snow, and those shaded pink, freezing rain or sleet.
16
Weather Forecasting Methods
•  Surface Chart Predictions
•  3-hour pressure tendencies plotted on isobar maps help predict the movement
of highs and lows and indicate how rapidly pressure systems are changing.
•  Lows tend to move toward the region of greatest pressure fall, while highs
move toward the region of greatest rise.
•  The low from the previous map will likely move to the NE, while the high will
move to the SE.
17
Weather Forecasting Methods
•  Upper Level Charts
•  Upper level winds, particularly those at 5500 m, which is a common elevation
for the 500 mb surface, often guide the path of surface pressure systems.
•  These upper level winds, however, travel at nearly twice the speed as the
surface systems.
•  Low will head to the NE, while the high will head SE.
18
Weather Forecasting Methods
•  Observed Movement of Fronts
•  Surface weather observations from 6 PM Tuesday and 6 AM Wednesday show
how the fronts, pressure systems, and precipitation have moved as predicted.
19
Weather Forecasting Methods
•  Observed Movement of Fronts
•  Surface weather observations for 6 AM Wednesday
20
Weather Forecasting Methods
•  Surface Weather Map for 4 PM Monday
21
Weather Forecasting Methods
•  Visible Satellite Image for 9 AM Tuesday
22