Weather Forecasting

who employs meteorologists?

• primarily the National Weather Service (NWS)

• aviation industry

• military; air force and navy

• nasa for satellites + rocket launches

• colleges + universities

• national center for atmospheric research (NCAR)

• private companies (AccuWeather + weather channel) + television stations

national weather service (NWS)

• branch of national oceanic + atmospheric administration (NOAA)

• mission statement: provide weather + climate forecasts and warning to US, territories, + waters for protection of life + property + enhancement of economy

national centers for environmental predication

• branch of NWS collects weather data from all over the world

• info disseminated to all regional weather forecast offices, which prepare local forecasts

world metoerological organization (WMO)

• part of UN responsible for international exchange of weather data

• responsible for naming + retiring hurricanes

surface observations

• NWS + federal aviation administration (FAA) operate 900 automated surface observation systems (ASOS)

• worldwide, about 18,000 weather stations

weather balloons

• launched twice daily at midnight + noon Greenwich mean time (7pm + 7am our time)

• contain radiosondes - lightweight instrument packs measuring temp, humidity, + pressure

weather maps

• pictures of atmosphere

• info placed on synoptic weather maps which means coincident in time

• generated twice daily

• drawn at 850-. 700-. 500-, 300-, + 200-mb levels

850-mb maps

about 4800ft

finds areas of cold-air + warm-air advection

700-mb maps

• about 1000ft

• predict movement of weather producers

500-mb maps

• about 18000ft

• show upper level lows best

300- + 200-mb maps

• represent zones near the top of the troposphere

• jet stream is best observed at these levels

zonal patterns

depict quickly moving westerlies (w - e)

• quick moving storms every few days

• no wild swings in temp

• straight line

meridional patterns

consist of slow-moving n-s flows

• heavy precipitation

• not a straight line

numerical weather prediction

• technique uses mathematical models

• begins by entering temp, wind speed + direction, pressure + humidity

  • prognostic charts(progs) - generalized forecast maps produced by NWS

model output stats(mos)

statistical analysis of progs corrects accuracy of previous forecasts

• corrects model biases, such as too much precipitation, temps too warm

• localized weather (such as sea breezes)

north american mesoscale (NAM)

• short range

• forecasts out to 3.5 days

• updates every 6hrs

• used for thunderstorm/frontal forecasting

global forecast system (GFS)

• long range

• forecasts out to 16 days

• updates every 6hrs

high resolution rapid refresh

• short range

• forecasts out to 18hrs

• updates every hr

• used just prior to + during weather events such as snowstorms or severe weather

European center for medium range weather forecasts (ECMWF)

• viewed as most accurate computer model

• forecasts out to 10 days

canadian meteorological center

• temp + precipitation forecasts out 10 days

ICON (German)

• newer computer model

• one of the more accurate forecasting models

• forecasts out to 7 days

ensemble forecasting

• produces # of forecasts using same computer model

• alters conditions while remaining within error range of observational instruments

persistence forecasting

• technique based on tendency of weather to remain unchanged for hrs or days

• weather occurring upstream will most likely affect other areas in a similar way in path

climatological forecasting

method uses climate data (average weather stats over many years)

analog method

• based on assumption that weather repeats itself

• forecasters attempt to find weather patterns

• helps to improve short-range, computer-generated forecasts

trend forecasting

• determines speed + direction of fronts, cyclones, clouds, + precipitation

TIROS 1 satellite

• launched in 1960, 1st weather satellite

• since then, more than 30 versions have been launched

polar orbiting satellite

orbit over the poles

geostationary satellite

• orbit w - e over equator

• track large weather systems

• provide visible, infrared + water-vapor images

• Visible light imagery records the intensity of light reflected from
  cloud tops and other surfaces, to help define shapes, patterns,
  and thicknesses

• infrared images determine which clouds are likely to produce heavy precipitation

visible

• only during day

• higher resolution

• no temps

infrared

• day or night

• shows temp of cloud tops

• lower clouds-warmer

• higher clouds-cooler

water-vapor images

Most of Earth’s radiation with a wavelength of micrometers is emitted by water vapor.

qualitative forecast

• Observable but hard to measure

• Easy for the public

• Example: Partly cloudy skies this morning, followed by
  clearing this afternoon.

quantitative forecast

• measurable weather data

• ex: QPF forecast map

what does a 40% chance of rain really mean?

there’s a probability of at least 0.01” of
precipitation occurring at any particular location within a forecast area and time.

short-range forecasts

up to 48hrs in the future

medium-range forecasts

between 3 + 7 days in the future

long-range forecasts

• beyond 7 days in the future

• Climate Prediction Center, branch of NWS, produces 30 + 90 day outloooks

storm prediction center (SPC)

primary responsibility for forecasting severe thunderstorms, hail, + lighting

national hurricane center (NHC)

monitors + tracks storms in the atlantic, carribean, + east pacific

false weather reports

It is actually illegal to relay watches or warnings to the
public if not issued by the National Weather Service

roles of the forecaster

• blend info with local conditions, progs, + regional weather to produce site-specific forecasts

• use knowledge + judgments based on experience

• account for local microclimates

• only use computer models as guidance