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XC Meteorology
And other bullshit
(c) Jim White 2014
Why do Met?
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Choose whether to turn up
Choose best task for day
Choose glider configuration
Choose pilot configuration!
Avoid being in wrong place
– Achieve good speed
– Reduce risk of land out
What do we want to know?
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Height of thermals?
Strength of thermals?
When will they start being useable?
How much cloud will there be?
How long is the soaring window?
Wind strength and direction?
How hot / cold
What changes during the day?
What tools do we have?
• Internet
– Observations: temperature, pressure, wind
– Synoptics: surface, thickness, and geopotential
– Meteograms: various models
– Tephigrams: Measured and forecast
– Model based forecast charts
• Eyes and Experience
– Does it feel and look right?
Sources of Information
• UK Met Office
• US Met Office
• ECMWF
• Soundings
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XC Weather
RASP
Meteoblue
Charts
• Satellite
www.meto.gov.uk
www.noaa.gov
ready.arl.noaa.gov/READY_animations.php
www.ecmwf.int
weather.uwyo.edu/upperair/sounding.html
rucsoundings.noaa.gov/plot_soundings.cgi
www.xcweather.co.uk
rasp.inn.leedsmet.ac.uk
www.meteoblue.com
www.weathercharts.org
www.weatheronline.co.uk/cgi-bin/expertcharts
www.sat24.com/en/gb
Whither our Weather?
Character of Air Masses
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Cold air is dry and heavy
Warm air is less dense and therefore light
Warm air can hold more water than dry
Wet air is less dense and therefore lightest
• Cold air = high pressure
• Warm air = low pressure
• Warm wet air = lowest pressure
Character of Air Masses
• Cold Air Sinks
• Sinking air increases pressure
• Sinking air enhances stability
• Warm Air Rises (when there is cold air about)
• Rising air reduces pressure
• Rising air encourages instability
Coriolis Effect
Coriolis Magic
Why us?
Single Cell Model
Multi-cell model
The Polar Front
High Pressure
High Pressure
Low Pressure
Low Pressure
Rossby Waves
Rossby Waves
Birth of a Depression
Cold and Dry
Wet and Warm
More Depressed!
Frontal Weather
Character of Depressions
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Wind blows around it due to Coriolis effect
Wind speed dependent on pressure gradient
Depressions move W to NE at 10-30kts
Cold front moves 50% faster than warm
Warm sector is unstable and wet because it is
being squeezed and is rising
• Following cold sector is conditionally unstable
because it is cold and contains some moisture
Approaching Warm Front
Warm Sector
Post Cold Front
What’s on a synoptic chart?
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Isobars – lines of equal pressure
Geopotential height contours (or thickness)
Isotherms – lines of equal temperature
Weather system centres
Weather system tracks
Fronts – cold, warm, and occluded
Troughs and ridges
MSLP, Geopotential, & Thickness
What can a synoptic tell us?
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Locations of highs and lows
Pressure and gradient
Wind direction and strength
Location of fronts, troughs, ridges
Source and character of airmass
Some also plot temperature / dew point
Te-phi-grams!
Environmental Lapse Rate
Lapse Rates
12000
10000
Altitude
8000
ELR
6000
DALR
4000
2000
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Dry Adiabatic Lapse Rate
Lapse Rates
12000
10000
Altitude
8000
ELR
6000
DALR
4000
2000
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Saturation Mixing Ratio
Lapse Rates
12000
10000
Altitude
8000
ELR
6000
DALR
SMR
4000
2000
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SkewT log P
Larkhill Ascent
Larkhill 15C
Larkhill 20C
BOB FRO EVE BOO 300K
What can a tephigram tell us?
• Atmospheric profile at a single location and
point in time
– Environmental lapse rate
– Moisture content
– Predicted ascent of a parcel or warm air
– Cloud base, top, and amount
– Thermal strength and start time
– Cloud amount, likelihood of convective showers
– Wind profile and other useful indices
What can a meteogram tell us?
• Forecast parameters for a single location
– Temperature
– Humidity
– Pressure
– Wind
– Cloud / Rain
– Radiation
• Changes over time
Temperature and Dew Point
Atmosphere
Cloud and Precipitation
Surface Pressure Wind and Radiation
Parameter Charts
Regional Atmospheric Soaring Prediction (RASP)
XC-Weather
More Information and
Acknowledgements
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Met Office - www.metoffice.gov.uk
Scott Haby – theweatherprediction.com
Wikipedia – surprisingly useful
ww2010.atmos.uiuc.edu/(Gh)/guides/home.rxml