Part 5. Human Activities
Chapter 13
Weather Forecasting and Analysis
Introduction
Weather Forecasting – Both Art and Science
National Weather Service
• Began as Army Signal Corps, then National Weather Bureau
• Part of the National Oceanic and Atmospheric Agency (NOAA)
• National Centers for Environmental Prediction (NCEP)
– Automated Surface Observing Systems (ASOS)
Data acquisition and dissemination
• World Meteorological Organization (WMO)
– 170 member nations with 10,000 land stations, 7000 ships,
300 buoys, weather satellites, and 1000 weather balloons
(twice daily)
A National Weather Service Office
Advanced Weather Interactive Processing System (AWIPS)
An automated weather recording station
– Upper atmosphere
– Radiosondes, rawinsondes
A radiosonde launch
Forecasting methods
• Climatological forecasts
• Persistence forecasts
• Analog approach
• Numerical weather forecasting
Types of forecasts
• Qualitative forecasts
• Probability (PoP) forecasts
• Quantitative forecasts
Numerical Modeling and Weather Forecasting
(supercomputer-based forecasts)
Analysis phase -- create or update a computer code of a
numerical model of the atmosphere
• Numerical model -- mathematical model of
atmospheric circulation and moisture; includes
equations of motion, continuity, energy, etc.
Prediction phase
– Start by inputting current and recent atmospheric
conditions into the model/computer program
– Solve equations to obtain prediction of future
atmospheric conditions
– Output maps and other prediction products
– After some time elapses (hours or days), repeat
the process with the latest current data
(a)-(c) = Three numerical models, (d) = Final forecast, (e) = Observed
Forecast
represents some
type of weighted
average of the
individual
forecast maps
Precipitation forecast
Observed precipitation
24-hr forecast skill for various NCEP models
Forecast results
from 1995.
Forecasts of
heavy
precipitation
were less
accurate than
forecast of light
precipitation.
Here, the
EDAS model
was most
consistently
accurate.
24-hr, 1-in. NCEP precipitation forecast skill average
Forecast skill
from 1983-1993
for manual
forecasts. Winter
precipitation
forecasts were
better than
summer forecasts.
MOS Example
Forecast skill
is steadily
improving
with time.
Medium range forecasts (MRF) -- 72 hours to a
few weeks
• Several different numerical models are used
to make medium range forecasts
– Ensemble forecasting is a forecast in
which the predictions from several
different computer model forecasts are
combined to form an ensemble average
A 10-day ensemble forecast of the 500 mb layer
Lower
forecast
reliability is
expected
where the
model
forecasts
disagree.
Higher forecast
reliability is
expected where the
model forecasts all
agree.
Long range forecasts cover times from several
weeks to several months or more
• Use climatology, statistics, numerical modes,
and subjective judgment
• Usually involve coupled ocean-atmosphere
models
• Are produced in the USGS by NOAA’s
Climate Prediction Center (CPC)
Weather Maps and Images
• Forecasting done by experienced
meteorologist
– Examination and analysis of many
weather charts and models
Surface maps
• Large-scale features depicted
• Pressure cells, winds, station models
Weather maps are an important part of weather forecasting
Early morning 850 mb maps can be used to predict surface high air
temperatures; the surface high temperature is usually about 27° higher
than the early morning air temperature at 850 mb in summer (22° in
spring and fall, 16° in winter).
700 mb maps can be used to help forecast cyclogensis and
thunderstorm movement
500 mb maps help with forecasts of cyclone development
and movement
An omega high on a 500 mb map
300 mb and 200 mb maps show the locations of the jet
stream and strong jets; these help determine Rossby wave
movements
Convergence/divergence associated with jet streaks
Slower moving air
Faster moving air
Slower moving air
Visible satellite image
Infrared image
Water vapor image
Thermodynamic diagrams
• Temperature and humidity values plotted
• Indicates stability
A Stuve diagram
Sounding plotted on a Stuve diagram
Stability as indicated on a Stuve diagram
Lifted index
• Thunderstorm potential
• Negative values indicative of thunderstorms
K-index
• Indicates air mass thunderstorm potential
• High positive values (> 15) indicate
thunderstorm potential
End of Chapter 13
Understanding Weather and
Climate
4th Edition
Edward Aguado and James E. Burt