XC Meteorology And other bullshit (c) Jim White 2014
Why do Met? 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? 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 www.meto.gov.uk US Met Office www.noaa.gov ready.arl.noaa.gov/ready_animations.php ECMWF www.ecmwf.int Soundings weather.uwyo.edu/upperair/sounding.html rucsoundings.noaa.gov/plot_soundings.cgi XC Weather www.xcweather.co.uk RASP rasp.inn.leedsmet.ac.uk Meteoblue www.meteoblue.com Charts www.weathercharts.org www.weatheronline.co.uk/cgi-bin/expertcharts Satellite www.sat24.com/en/gb
Whither our Weather?
Character of Air Masses 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 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? 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? 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!
Altitude Environmental Lapse Rate 12000 Lapse Rates 10000 8000 6000 ELR DALR 4000 2000 0 0 2 4 6 8 10 12 14 16 18 20 22 24 26
Altitude Dry Adiabatic Lapse Rate 12000 Lapse Rates 10000 8000 6000 ELR DALR 4000 2000 0 0 2 4 6 8 10 12 14 16 18 20 22 24 26
Altitude Saturation Mixing Ratio 12000 Lapse Rates 10000 8000 6000 ELR DALR SMR 4000 2000 0 0 2 4 6 8 10 12 14 16 18 20 22 24 26
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 Met Office - www.metoffice.gov.uk Scott Haby theweatherprediction.com Wikipedia surprisingly useful ww2010.atmos.uiuc.edu/(gh)/guides/home.rxml