The document discusses the club pilot theory of weather and how it impacts gliding. It explains that the uneven heating of the Earth's surface by the sun causes large air circulation cells and differences in air pressure that drive weather patterns around the world. Weather phenomena like high and low pressure systems, fronts, wind direction and speed, and cloud formation are described. The effects of these conditions on thermal development and glider flying are also covered.

1. CLUB PILOT THEORY

3. THE SUN IS RESPONSIBLE FOR EVERYTHING!
THE SUN HEATS THE EARTH AT DIFFERENT RATES
ANGLE AT WHICH THE SUN’S RAYS STRIKES THE EARTH’S SURFACE
STRONGEST AT EQUATOR AND WEAKEST AT THE POLES
CAUSES HUGE CELLS OF MOVING AIR CIRCULATING AROUND
THE MOVEMENT OF AIR MASSES CAUSE HIGH & LOW PRESSURES
THE HIGH AND LOW PRESSURE ZONES ARE UNIFORMLY PLACED
IT CAUSES THE MOVEMENT OF AIR ON MASSIVE SCALES
IT CAUSES THE WEATHER WE EXPERIENCE AROUND THE WORLD
IT CAUSES THE JET STREAMS AND MORE LOCALISED WEATHER
KNOWING HOW THIS IMPACTS ON A MICRO LEVEL IS KEY TO MAKING
SAFE DECISIONS ON WHEN AND WHERE TO FLY

4. THE FLOW OF AIR IN THESE SUPER CELLS CAUSE HIGH AND LOW
PRESSURE ZONES
THESE AREAS OF HIGH AND LOW PRESSURE FORM IN BELTS AROUND
THE WORLD
THEY TEND TO BE WARMER AT THE EQUATOR AND COOLER AT THE
POLES
THEY CAUSE THE JET STREAMS AND OTHER HUGE WEATHER TRENDS
THE SPINNING OF THE EARTH CAUSES THE GENERAL AIRFLOW TO
DEFLECT
THE SPINNING OF THE EARTH CAUSES THE CORIOLIS EFFECT AND
CAUSES THE LOW AND HIGH PRESSURE ZONES TO ROTATE
HIGH PRESSURE ROTATE IN A CLOCKWISE DIRECTION
LOW PRESSURE ROTATE IN A ANTI CLOCKWISE DIRECTION
THIS IS REVERSED IN THE SOUTHERN HEMISPHERE

5. WEATHER FRONTS
COLD MOVE QUICKLY / WARM SLOWLY
COLD HEAVY SHORT RAIN / WARM LIGHT LONG RAIN
BEST XC DAYS AFTER COLD FRONTS – UNSTABLE
OCCLUDED FRONTS CAN MEAN DAYS OF LIGHT RAIN
HIGH = CLOCKWISE / LOW = ANTICLOCKWISE
PRESSURE DIFFERENCES AND WINDS
THE HIGH AND LOW PRESSURE AREAS TURN IN
OPPOSITE DIRECTIONS.
THIS TELLS US THE DIRECTION OF THE WIND
THE STRENGTH IS SHOWN BY HOW CLOSE THE
ISOBARS ARE TO EACH OTHER
WIND DIRECTION AND PRESSURE FRONTS

6. CHANGES OF WIND DIRECTION
ABOVE 2000FT THE EFFECT OF THE EARTH’S ROTATION STOPS
THE WIND FOLLOWS THE NORMAL DIRECTION OF TURN CAUSED BY
THE PRESSURE GRADIENT FORCE
CLOCKWISE AROUND A HIGH
ANTI CLOCKWISE AROUND A LOW
CLOSER TO THE GROUND THEY GET SKEWED BY THE CORIOLIS
EFFECT GIVING A DIFFERENT WIND DIRECTION:
INWARDS IN LOW PRESSURE ZONES
OUTWARDS IN HIGH PRESSURE ZONES
IN THE NORTHERN HEMISPHERE THE WIND VEERS AS YOU GAIN
HEIGHT (CLOCK WISE DIRECTION)
BUY BALLOTS LAW:
IN THE NORTHERN HEMISPHERE WITH YOUR BACK TO THE WIND THE
DEPRESSION OR LOW PRESSURE IS ON YOUR LEFT HAND SIDE
WIND AT
ALTITUDE
WIND AT
GROUND
H
L
H
L

7. WIND SPEED FROM SYNOPTIC CHARTS
WIND FLOWS FROM HIGH TO LOW PRESSURE ZONES TO
BALANCE THE PRESSURE
THIS CAUSES THE WIND WE FEEL AT GROUND LEVEL
AND HIGHER UP IN THE ATMOSPHERE
THE DIRECTION OF THE WIND IS SLIGHTLY SKEWED BY
THE ROTATION OF THE EARTH
THE GROUND LEVEL WIND IS NORMALLY SKEWED
COMPARED TO HIGHER LEVEL WIND
THIS BALANCE BETWEEN THE PRESSURE GRADIENT
WIND AND THE CORIOLIS EFFECT GIVES US OUR
GROUND LEVEL DIRECTION
TIGHTLY PACKED ISOBAR LINES = STRONG WINDS
MORE SPREAD OUT LINES = WEAKER WINDS

8. A COLD FRONT DISPLAYED BY A
PURPLE LINE WITH TRIANGLES
ON
THE TRIANGLES INDICATE THE
DIRECTION OF TRAVEL
A WARM FRONT DISPLAYED BY A
RED LINE WITH SEMI CIRCLES ON
THE SEMI CIRCLES INDICATE THE
DIRECTION OF TRAVEL
AN OCCLUDED FRONT COMBINES
THE TWO LINES AND MERGES
THE SYMBOLS
DIRECTION OF TRAVEL IS
INDICATED IN THE USUAL WAY

9. A COLD FRONT MOVES IN QUICKLY, WEDGING THE
WARM AIR UPWARDS AND CREATING DRAMATIC
WEATHER CONDITIONS
POST COLD FRONTS CAN BE VERY UNSTABLE BUT
LEAD TO GOOD XC FLYING CONDITIONS
A WARM FRONT MOVES IN SLOWLY AND IS WEDGED
UPWARDS. IT STARTS WITH HIGH CLOUD FOLLOWED
BY LOTS OF DRIZZLE THAT CAN LAST FOR DAYS
NOT VERY GOOD FOR FLYING
AN OCCLUDED FRONT IS WHERE A WARM AIR MASS
IS WEDGED UP BETWEEN TWO COLD AIR MASSES.
THIS NORMALLY MEANS LONG SPELLS OF LIGHT
RAIN AND LOTS OF CLOUD COVER
NOT VERY GOOD FLYING CONDITIONS

10. CLOUD TYPES AND HEIGHT

11. HIGH PRESSURE DAYS
ANTI CYCLONE OR HIGH PRESSURE
AIR DESCENDING DOWN / STABLE AIRMASS
STABLE AIRMASS LESS CUMULOUS CLOUDS
HIGH CHANCE OF INVERSION & BLUE THERMALS
THERMALS CAN BE WEAKER BUT BIGGER
LOW PRESSURE DAYS
CYCLONE OR LOW PRESSURE
AIR RISING / UNSTABLE AIRMASS
HIGHER CHANCE OF CUMULOUS CLOUDS
STRONGER SMALLER THERMALS
CHANCE OF OVER DEVELOPMENT (DANGEROUS)
HOW HIGH AND LOW PRESSURE IMPACTS ON OUR FLYING

12. THERMAL DEVELOPMENT
THE IMAGE SHOWS HOW A WARMED AIRMASS RISES AND COOLS
THE AIRMASS WILL RISE UNTIL ITS TEMPERATURE MATCHES THAT OF THE
SURROUNDING AIR
COLD DRY AIR IS MORE UNSTABLE THAN WARM MOIST AIR
CLOUDS FORM AT THE DEW POINT UNLESS THEY HIT AN INVERSION GIVING
US BLUE THERMAL DAYS
LARGER TEMPERATURE GRADIENTS MEANS A MORE UNSTABLE AIRMASS
IN SPRING WE HAVE THE MOST UNSTABLE AIRMASSES
SPRING IS THE MOST DANGEROUS TIME AND ACCIDENTS ARE COMMON
SUMMER IS NORMALLY MORE STABLE CAUSED BY HIGHER PRESSURE
AUTUMN AND WINTER ARE THE MOST STABLE WITH SMALLER
TEMPERATURE GRADIENTS

13. THE SUN HEATS THE GROUND AND THE GROUND HEATS THE AIR IN
CONTACT WITH IT
THIS WARM BUBBLE OF AIR RISES AND BREAKS FREE FROM THE
GROUND. IT STARTS TO RISE THROUGH THE ATMOSPHERE AND IF THE
AIRMASS GETS TO IT’S DEW POINT A CUMULOUS CLOUD IS FORMED
THE CLOUD MAY BE FED BY THE THERMAL FOR A WHILE AND THEN
START TO DECAY
STORED ENERGY IS RELEASED WHEN CLOUDS ARE FORMED AND THIS
GIVES THEM A BOOST. OFTEN THIS IS ENOUGH TO SUSTAIN THE CLOUD
WITHOUT A GROUND SOURCE FEEDING IT
IF THE AIRMASS IS VERY UNSTABLE
OVERDEVELOPMENT IS POSSIBLE
CUMULOUS NIMBUS CLOUDS ARE
FORMED LEADING TO VERY
DANGEROUS FLYING CONDITIONS
IF YOU SEE ANYTHING LIKE THIS IN
THE SKY THEN LAND
CU-NIMS CAN FORM VERY QUICKLY
AND AFFECT A LARGE AREA

14. CUMULOUS NIMBUS CLOUDS ARE THE HUGE ANVIL TYPE CLOUDS
THESE CLOUDS MAY BRING A MULTITUDE OF DANGERS
HUGE INFLUX OF AIR INTO THE CLOUD MAY BE STRONGER THAN YOU
CAN EVER GET AWAY FROM
IF YOU GET DRAWN INTO ONE THEN YOU ARE LIKELY TO DIE
THEY FREQUENTLY BRING SUDDEN DOWNPOURS OF RAIN AND GUST
FRONTS
JUMBO JETS AVOID THESE AND SO SHOULD YOU!
WHEN THEY DUMP THEIR WATER IT CAUSES A HUGE DOWN DRAFT OF
AIR WHICH SPREADS OUT AS IT HITS THE GROUND
THIS AIR RUSHES OUT IN ALL DIRECTIONS AS GUST FRONTS AND CAN
BE VERY STRONG - 50KPH OR MORE
THEY BRING VERY TURBULENT AIR, THEY HAVE CAUGHT OUT MANY
PILOTS AND CAUSE MANY ACCIDENTS EACH YEAR
IF YOU SEE A CU-NIM FORMING GET OUT OF THE AIR

15. INVERSION L AYERS
A LAYER OF WARM AIR ABOVE A COOLER AIR CLOSER TO GROUND
ALSO KNOWN AS AN ISOTHERM
STOPS AIR RISING FROM THE GROUND & CAUSES A HAZY LAYER
THE HAZE IS ALL THE TRAPPED DUST & POLLUTANTS
IF CAN BE GET QUITE DARK & IF IT DOESN’T BREAK CAN CAUSE SMOG
SMOKE OR RISING AIR WILL HIT IT & SPREAD OUT ALONG IT’S BASE
IF A THERMAL IS STRONG ENOUGH TO BREAK THROUGH THEN IT RUSHES
INTO THE COLDER AIR ABOVE IT
THIS SUDDEN ESCAPE CAN CAUSE OVER DEVELOPMENT
INVERSION LAYERS CAN BE BE BUMPY WHEN YOU REACH THEM AND
RESTRICT THE HEIGHT YOU CAN CLIMB TO

16. OROGRAPHIC CLOUDS
IF AN AIRMASS IS FORCED UP OVER A MOUNTAIN RANGE OR RIDGE IT CAN
REACH IT’S DEW POINT ALTITUDE AND FORM CLOUDS
THE LIFTING OF THE AIRMASS GIVES US OROGRAPHIC CLOUDS AND CAN
HAPPEN ON SMALL OR LARGE SCALES
THE CLOUD STARTS OFF AS WHISPS IN THE SKY BUT CAN QUICKLY TURN INTO
THICK CLOUD. THEY CAN GROW SURPRISINGLY FAST AND HAVE CAUGHT
PEOPLE OUT SO KEEP AN EYE OUT FOR THEIR FORMATION
IN SOME CONDITIONS THE WIND CAN CAUSE PHASE CLOUDS OR WAVE
CLOUDS BEHIND RIDGES AS THE AIRMASS IS FORCED UP AND DOWN
WAVE CAN BE GREAT SOURCES OF LIFT FOR GLIDERS BUT OFTEN BRING
LARGE AREAS OF STRONG SINK OR TURBULENCE
THE BOUNDARY AREAS CAN BE VERY ROUGH SO IT IS ADVISED TO STAY AWAY
FROM SUCH CLOUDS
THEY ARE NORMALLY QUITE HIGH SO DIFFICULT FOR US TO UTILISE BUT IT IS
NOT IMPOSSIBLE TO HAVE THEM LOWER DOWN

17. THE SEA BREEZE
WE GET TAUGHT THAT THE WARM AIR RISES OVER THE LAND
AND IT DRAWS IN AIR FROM THE COAST TO REPLACE IT.
THIS IS A VERY SIMPLISTIC WAY OF EXPLAINING IT
BEING AWARE AND CAUTIOUS OF THE SEA BREEZE EFFECT IS
ENOUGH BUT KNOWING WHAT IS HAPPENING CAN HELP YOUR
FLYING
IF WE THINK MORE ABOUT A BALANCE OF PRESSURE, WE GET
A BETTER PICTURE OF WHAT IS HAPPENING
THE HIGH PRESSURE OVER THE WATER MOVES TOWARDS
THE LOW PRESSURE OVER THE LAND IN A ‘FRONT’
THE TWO AIR MASSES DO NOT MIX AND THE WARMER LOW
PRESSURE AIR IS PUSHED UPWARDS
OFTEN AT NIGHT THE REVERSE HAPPENS, GIVING US AN
OFFSHORE BREEZE

18. THE SUN HEATS THE GROUND WHICH IN TURNS HEATS THE
AIR CAUSING THERMALS AND LOWER PRESSURE ZONES
INLAND
EVENTUALLY THIS PRESSURE DIFFERENCE CAUSES HIGHER
PRESSURE AIR OVER THE SEA TO MOVE INLAND FROM THE
COAST
AT FIRST THE INFLUX OF COLD SEA AIR CAN BE VERY GENTLE
BUT IT CAN INCREASE IN STRENGTH AND THE BORDERS CAN
BE QUITE ROUGH
THE COLD DAMP SEA BREEZE UNDERCUTS THE WARMER
LAND AIR, SPILLING INTO THE VALLEYS AND EVENTUALLY
OVER THE BACK OF OUR SITES
IF YOU STAY IN THE WARM AIRMASS YOU CAN STAY UP ABOVE
THE SEA BREEZE IN A FORM OF CONVERGENCE
WATCH OUT FOR SIGNS OF THE SEA BREEZE IF YOU PLAN ON
TOP LANDING
CHECK THE WIND SOCK AND GLIDERS BEING KITED

19. CONVERGENCE IS WHERE TWO AIRMASSES MEET & ONE OR BOTH
ARE PUSHED UPWARDS
THIS CAN LEAD TO HUGE AREAS OF LIFT
“EVERYTHING WAS GOING” & “I STRUGGLED TO GET DOWN”
SOMETIMES THE CONVERGENCE CAN BE VERY STRONG & GETTING
DOWN CAN BE TRICKY
A SEA BREEZE CAN BE FELT BY A DROP IN AIR TEMPERATURE & RISE
IN HUMIDITY AS YOU ENTER IT QUICKLY FOLLOWED BY SINK
CONVERGENCE CAN LEAD TO UNSTABLE AIR WHERE THE TWO AIR
MASSES MEET
CONVERGENCE CAN OCCUR ANYWHERE. IT IS COMMON ON THE
SOUTHERN SITES BECAUSE WE FREQUENTLY HAVE DIFFERENT
AIRMASSES MOVING AROUND
NOT BEING ABLE TO COME DOWN CAN BE QUITE SCARY – DON’T
PANIC!
WHAT IS CONVERGENCE AND HOW DO WE USE
IT?

20. DURING THE DAY THE SIDES OF VALLEYS WARMS UP AND AIR
FLOWS UP THEIR SIDES TO THE PEAKS AND TOPS OF RIDGES
THIS MOVEMENTS OF AIR IS ANABATIC
IN THE MIDDLE OF THE VALLEY WE WOULD EXPECT SINK AS SOME
AIR IS DRAWN IN TO REPLACE THIS MOVEMENT OF AIR FROM THE
VALLEY FLOOR
BETTER LIFT MAY BE FOUND CLOSE TO THE SIDE OF THE VALLEY
AT NIGHT THE SIDES OF THE VALLEY COOL DOWN CAUSING A
KATABATIC WIND FLOW DOWN INTO THE VALLEY
THIS WIND IS NORMALLY COOLER AND HEAVIER
IN THE LATE EVENING THE MIDDLE OF THE VALLEY CAN BE LIFTY
KEEP AN EYE OUT FOR A KATABATIC WIND ON TAKE OFF BECAUSE
THIS WILL MAKE LAUNCHING HARDER AND POSSIBLY DANGEROUS
SOME ALPINE SITES REGULARLY HAVE LIGHT KATABATIC WINDS SO
A GOOD FORWARD LAUNCH IS ESSENTIAL
KATABATIC AND ANABATIC WINDS

21. AS THE VALLEYS AND MOUNTAINS HEAT UP THEY DRAW AIR IN FROM THE
SURROUNDING FLAT LANDS
ON A LARGER SCALE THE AMOUNT OF AIR BEING PULLED IN CAN BE
HUGE
IT IS SQUEEZED THROUGH THE SMALL VALLEYS AND CAN CAUSE VERY
STRONG LOCALISED VALLEY WINDS
THESE WINDS TEND TO BE LOW DOWN AND KEEP SEPARATE FROM THE
WINDS ABOVE
HIGH IN THE VALLEY THERE COULD BE VERY LITTLE WIND BUT CLOSE TO
THE VALLEY FLOOR THERE MAY BE +30KPH WINDS
THIS WILL MAKE GETTING TO LANDING VERY HARD SO ALWAYS
APPROACH THE LANDING FIELD FROM AN UPWIND LOCATION
LOOSING YOUR HEIGHT HERE ALLOWS YOU TO GET TO YOUR LANDING
FIELD IF THE WIND SUDDENLY PICKS UP LOWER DOWN
VALLEY WINDS ARE NORMALLY OPPOSITE TO THE WAY WATER FLOWS
OUT!
AT NIGHT THIS IS NORMALLY REVERSED AND THE AIR TENDS TO FLOW
OUT OF THE VALLEY
VALLEY WINDS

22. TYPES OF LIFT
WE HAVE TWO MAIN TYPES OF LIFT
DYNAMIC = RIDGE LIFT, CONVERGENCE AND WAVE
THERMIC = THERMALS
THERE ARE MANY SUBSECTIONS OF THE ABOVE
IN ENGLAND WE ARE NORMALLY FLYING WINDY RIDGES LOOKING
FOR THE THERMIC CYCLES THAT COME THROUGH
RIDGE LIFT
WHEN WIND BLOWS UP THE FACE OF A RIDGE OR HILL SOME OF IT IS
DEFLECTED UP BEFORE BEING BLOWN OVER THE TOP
THIS CREATES A LIFT BAND MADE OF RISING AIR OR LIFT
IF THE RISING AIR IS EQUAL TO OUR SINK RATE THEN WE CAN
SUSTAIN OUR HEIGHT
IF THE RISING AIR IS GREATER THAN OUR SINK RATE WE CAN CLIMB
HIGHER THAN TAKE OFF