Soaring Weather

Presented by Jim Martin 2015

Basic Principles• Obtain the basic weather data 1st

• Is it Dangerous / Soarable ?

• Understand How the atmosphere works– Its Our Engine!– Calculations to see if soaring is possible

• Graphs and Maps improve understanding

• Continue throughout the flight to Analyze & Update

Obtaining Weather Data• Look Outside – Gain Personal Experience

– …Yet Airport may be 60 miles away!

• Consult Online Weather Sources – 1st– 1800WxBrief.com (Lockheed Martin off. Site)– National Weather Service / Duat / DUATS– Call Flight Service Station (1-800-WXBrief)

• ASOS /AWOS /ATIS – Phone #s in AFD

• Make a Local Sounding

• Cell Phone / NEXRAD Sites

Weather Briefing• Online Http\\www.1800WxBrief.com

• FSS call 1-800-992-7433 (1800WXBrief)– Identify yourself as a glider pilot

• Give Aircraft ‘N’ number

• type of flight and location

– Ask for;• standard briefing / forecast

• surface reports

• winds aloft forecast

• Soaring forecast – including LI, overcast, turbulence

• other pertinent data (Notams, TFR’s)

Same Charts as Briefer Uses

ADDS METAR/TAF Data

VansAirForceWeather

• Better Site - Yet Not Official

• All Charts come from Official Sites

• Logically Grouped Together

• Typical Order Pilot’s are interested in

• Can be Customized to your location or likes

VansAirForceWeather.com

Decision Making

• Be realistic!– Are Storms forecast for later in the day/evening– Strong x-winds later in day? (not often forecast)– Local vs Long X-C flight– Your experience level– Precipitation?– How Soarable is the Weather?

Continue Your Weather Analysis throughout Flight

• Enroute weather data– Flight Watch (122.0 MHz)– Airport automated weather services –

ATIS/ASOS/AWOS

• Smart Phone / Cell Phone Updates• End-of-flight weather data

– Wind direction for landing – ATIS / ASOS– Current Altimeter setting

• Other Pilots 122.8 / 122.9 / CTAF• 123.5MHz glider ground crew

En Route Flight Advisory Service (Flight Watch) 122.0

• AIM section 7-1-5

• Real-time weather advisories

• National coverage above 5000 ft on 122.0

• Available 6:00 am to 10:00 pm

• State ARTCC facility, N number, & nearest VOR name

• Eg. “Buffalo Flight Watch, this is..”

Hazardous Weather

• Fronts

• Winds

• Airmass Changes

• Precipitation

• Overcast

Src: Aviation Weather AC 00-6A

Cold Front

Cold Frontal Weather• Cold Front Passage - Cumulus then Cumulonimbus

• Overcast / High Cirrus 2 Days Prior

• May Superheat air in front of airmass if fast moving

• Squall lines 50 - 300 miles ahead – Gusty day prior

• Frontal Passage = Wind Shift

+ Day after is typically Super Adiabatic (Chopped Up)+ Ground has to Dry Out

+ Good Soaring conditions - 2 days after+ Typically Clear, Good Visibility, Higher Cloudbase

Src: Aviation Weather AC 00-6A

Warm Front

Warm Frontal Weather• Warm Airmass – High Stratus Increasingly Lowers

– Deep temperature inversion – Increasingly Stable– lowering cloudbases– broad overcast cloud system precedes front

– + Stable Air = Ridge Soaring

• Occluded = Generally Not Soarable– both warm & cold cloud patterns

Src: Aviation Weather AC 00-6A

Colder Overtaking Occlusion Front Warm Air Aloft

Src: Aviation Weather AC 00-6A

Warm-Occlusion FrontCool Air overtaking Colder

Airmass Changes

Mount a Sensitive Thermometer (measures .10 deg change)Able to detect airmass changes

Watch for significant Cloud changes throughout the dayCan signal approaching Front / Airmass change

Winds: Shifting or Speed Significant changes

Atmospheric Facts

• WEIGHT: A cubic inch of air near the ground at sea level has about 14.7 pounds of air sitting on top of it, pushing it down

• Pressure Decreases with Altitude • 1” hg (Mercury) = 1000 ft difference

• 14.7” @ Sea Level (Density)

• @ 18,000 ft Density / Pressure is ½ of sea level

Air Facts

• Air holds Water: Water Vapor REDUCES Density of Air – 10C Warmer Air can Absorb TWICE amount of

Water Vapor…..– 10C Colder Air can only hold ½ the water

Water Vapor Content

• Air always holds water, but only up to a certain amount of it--more than that and you get condensation

• The higher the dew point temperature, the more water is in the air

• When Dewpoint and Temperature are equal = 100% Saturated = Clouds /Fog

Bouyancy• Warm Air Rises through Cooler Air Aloft

– Bigger the Difference = Faster Ascent Rate !– Larger Heated Area = More Inertia &

Momentum (Rises Higher)

• It takes a lot of sunshine to evaporate any water on the ground

• Moist Air (Saturated) Rises ½ as Fast as Dry

Lifting Rate Assumptions• Any ground water has to evaporate 1st

– 440 calories / gram of water / 1 deg C– A lot of heat to evaporate a small amount of

H20

• Air rises at the DRY Lapse rate 1st from the ground ~3-5C/1000ft (It’s not Saturated)

• As it cools, the parcel humidity increases until it reaches the condensation level (cloudbase) where it’s 100% saturated– Rises at the WET Lapse Rate ~2C/1000ft

What are SOUNDINGS?• Temperature and Dewpoint

and Wind Directions and Speed plottedvs. increasing Altitude (Pressure)

– Done at 6AM and 6 PM with weather balloons

– Now done by Satellites with Computer modelling

• Plot is called a “Sounding” and Chart is called a “Skew-T”

• It displays the characteristics of the airmass

Skew-T / Sounding

Constant Temperature “Skewed”.. Angled Up & to the Right

Vs. Altitude

Constant Temp

NOAA Chart NOAA Chart ColorsColors

• Mixing Ratio = Constant Water Content (Gray)

• Temp (Red)

• Alt. (Blue)

Pressure / Feet

All those Lines !!Actually calculations

Dry Adiabat Line from Surface

Temp at Surface (1200 ft MSL) = 25C

Rises along DRY Adiabatic Line to 7500 ft where it has cooled to 08C

Cloudbase

Project Up from Surface Dewpoint Temp (10C)Along Constant Mixing Line to where it intersects the Dry Adiabat drawn from the Surface Temp (of 25C)

= 7000 ft.

Lapse RatesRate at which the Temp

Decreases as the Air Ascends• DRY Adiabatic = 3-5C (5-7F) / 1000ft

• WET Adiabatic = 2C (3.5F)/ 1000ft

• So… Dry air is Better!

• Rough Estimation …

Cloud base = (max surface temp - dewpoint)/2C = (in 1000’s of ft)

Thermal Lifting

• If Air Above is cooler and not saturated…– Rises and cools at the DRY LAPSE Rate (5F /

1000ft)– Once it cools to the Dewpoint …

it rises at the WET (Saturated) LAPSE Rate

(3.5F / 1000ft) ==== Slower

Airmass Stability

• Stable = Doesn’t Want to Go Up ?!

• Unstable = Wants to Go Up!

• Thermal Index (TI) / Lifted Index (LI) = How Fast it wants to Go Up!

Cloudbase Estimate

• Dry adiabatic lapse rate 5.4o (3C)/1000 ft– Wet adiabatic lapse rate less than dry– Dew point decreases 2Co / 1000 ft

• Therefore if air is unsaturated….– Surface Temp – Dewpoint Temp ÷ 2C =

Cloudbase

• eg. 20C (surf.)–10C (dewpoint) = 10 ÷2 = 5000 ft Cloudbase

Conclusions

• Drier & Cooler Air aloft means Stronger Thermals

• Drier ground means thermals start earlier

• As Surface Dewpoint Spread increases…. Cloudbase goes UP

• Higher elevations (at same temp) trigger thermals earlier and stay later

Airmass Stability• Stable = Temp increases (Inversion)/Stays the same, or

same as std lapse rate as altitude increases {pos stabilty number}

• Unstable = Temp decreases more rapidly than standard lapse rate {minus number)

• Thermal Index (TI) / Lifted Index (LI) is comparison between 5000ft (850mb) temp and 10000 ft (700mb) temp

Typical FSS Soaring Forecast(6AM Sounding)

• Morning Low* 50F 10C• Max Expected Temp 89F 35C• T.I. at 5000 ft -5• T.I. at 10,000 ft +2• Height of -3 TI 7200’• Top of Lift 8500’

• (They assume a 3C lapse Rate / 1000ft)

• Note: Their Skew-T Looks Different !

Step 1, draw the adiabatic line

35C

Step 2, add the Sounding

Step 3 Draw the sounding

Src: Soaring Flight Manual

Step 4: Calculate the Difference between the Dry Lapse Rate Line and the Sounding at the Altitude you Select

= Thermal Index

Src: Soaring Flight Manual

Thermal IndexTI = +6

TI = -10

Dewpoint Plots

• Wherever the Dewpoint Touches or is close to the plotted temperature = Clouds will form

• If the Dewpoint is close at other levels… cloud layers will exist at that level

Internet Sources

• Kevin Ford - http://www.soarforecast.com

• NOAA-FSL, Forecast Systems Laboratory - http://www-frd.fsl.noaa.gov/mab/soundings/java/

• Aviation Digital Data Service - http://adds.aviationweather.noaa.gov

• Dr Jack BLIPMAP - http://www.drjack.info/BLIP/index.html

Kevin Ford Plots

• === Interpolations (temps in deg. F, altitudes in feet MSL) ===• MSL *TI* Wdir@kts trig VirT 1.2 degrees/division ("`": Dry Adiabatic)• ----- ---- -------- ---- . ---- -----------------------------------------• 10000 12.4 40 | -9.8 ` :• 9500 11.6 39 | -8.6 ` :• 9000 10.7 280 27 37 | -7.5 ` :• 8500 9.8 35 | -6.5 ` :• 8000 8.8 290 25 34 | -5.5 ` :• 7500 7.9 32 | -4.5 ` :• 7000 6.9 295 24 30 | -3.5 ` :• 6500 6.0 29 | -2.6 ` :• 6000 3.7 300 27 25 | -4.0 ` :• 5500 3.6 24 | -1.5 ` :• 5000 3.5 24 | 0.9 ` :• 4500 3.3 24 | 3.3 ` :• 4000 2.1 22 | 3.7 ` :• 3500 0.8 19 | 4.1 `:• 3000 -0.5 18 | 4.4 :`• 2500 -1.8 16 | 4.8 : `• 2000 -2.1 15 | 7.0 : `• 1500 -2.1 15 | 9.7 : `• 1000 -2.1 15 | 12.3 : `

NOAA Forecast Plot

Cloud Layer1000 to 7500 ft

Cloud Layer30,000 ft

Noaa Skew T’s• Temperature Plot vs Altitude

– If Temp increasing = Stable Air (Inversion)

• Dewpoint Plot vs Altitude– If Temp Plot touches or is close to Dewpoint =– Predicts where Clouds and Layers will form

• Winds Aloft

• Knowing Forecast Max Temperature = – Predicts Height of Thermals– If Significant Heating = Excess Energy is Hatched

Evaporation• Evaporation take 7.5 times as much energy as

melting or freezing. ( 440 cal. / deg C)

• Condensation at Cloudbase Gives Off that Energy and the parcel continues to rise unless an inversion is above it.

• Avoid Rain Soaked Areas

• It May take a day or more to dry the ground after rainfall

Definitions• LCL (Lifted Condensation Level)

– Cloudbase = altitude where air is 100% saturated

• CCL (Convective Condensation Level)– Height predicted a parcel will reach based upon

max temp {above the LCL}

• LI (Lifted Index) negative indicates unstable = Thermals

• KI (K Index / Showalter) amount of water in parcel if >400 TStms likely

Best Sites

Interactive Skew T (Moninger/ NOAA)

• http://www-frd.fsl.noaa.gov/mab/soundings/java/

Bad Winter DayMassive Inversion………

If it Got to 75F.. Could Soar to 30,000 ft

.. Yet Clouds from Surf to….. 15,000 ft !!

Best Book

•Understanding the Sky

•By Dennis Pagen

Clouds & Thermals

Condensation releases latent heat. This causes the temperature of a cloud to be warmer than it otherwise would have been if it did not release latent heat. Anytime a cloud is warmer than the surrounding environmental air, it will continue to rise and develop. The more moisture a cloud contains, the more potential it has to release latent heat.

Dr Jack’s BLIPMAPS

BLIPMAP Assumptions

• Your Sailplane Sinkrate must be subtracted from the predicted Climbrate

• Must Subtract the Terrain Height from the Thermal / Cloudbase Height (is MSL Alt.)

• Assumes NO Overcast unless Stippling added• Is Based on Atmospheric Models forecast for

6 AM –is NOT Updated throughout day

Blipmaps

• Does Not predict or use any Precipitation on the ground

Local Effects

• Terrain features– Ridges– Mountains– Rivers– Lakes– Towns

Local factors

• Ridge conditions– Calculations– Predictions

• 90O +/- 30O to ridge line

• 10 - 15 kts

– Ridges• Lift extends 2 – 3 times the ridge height

• Ridge length should be several miles

Ridge Weather

• Stable Lower Level Airmass

• Wind within 30 deg of perpendicular to Ridge

• Wind increasing with altitude

• Wind > 5K, better the faster, upto 30K

• Beware of Sink behind ANY ridge

Ridge Lift ZonesGradual Slope Sharp Slope

Eddy formation

Local factors

• Wave conditions– Calculations– Predictions

• Wind at peak– 15 – 20 kts

• Wind 2000 m above peak– Same direction

– 20 – 25 kts higher

Wave Weather

• Lower Stable Layer / Unstable / Stable Aloft

• Winds > 15K / Increasing with Altitude

• Significant geographic elevation change

• 90 deg is optimum

• Strength increases if amplified by another terrain feature in phase with primary

Mountain Wave System

04/21/23

Transition pilot wave sketch

Lenticularcular

Rotor

04/21/23

Some rotor research in progress

04/21/23

Some rotor research in progress

Thermal Predictors/Indicators• Negative Thermal Index values at alt.

• Forecast plots

• Clouds

• Birds – Eagles & Hawks see in the Infrared

• Gliders circling – Most expensive Variometer ever invented (another sailplane)

• Dirt, crops, houses, animals rising before your eyes

Seasonal Weather Operations

• Density Altitude Increases with Temp

• Thunderstorms – Spring & Fall• Temperature extremes

• Wind shear

• Microbursts

• Foliage & Ground Cover– Ground Temperature at start of day

• Frost, Snow Ice

Determining When to Land

• What effect does the wind have on landing?

• Why Fly a Pattern?

• Unplanned for Crosswinds account for over 30% of landing accidents

Effect of 20 Kt wind

27

9

Time on Downwind: More, Less, no Change?Altitude loss: More, Less, no Change?

20 Kts

Effect of 20 Kt wind

27

9

Time on base: More, Less, no Change?Altitude loss: More, Less, no Change?

20 Kts

Effect of 20 Kt wind

27

9

Time on Final: More, Less, no Change?Altitude loss: More, Less, no Change?

20 Kts

Effect of 20 Kt wind

27

9

Which path is your student likely to fly?Which path do you want them to fly?

20 Kts1

2

3

4

Final Approach(No wind)

2400

200

60 kts @ 500 ft/m decent rate12:1 glide slope

24 seconds

Final Approach(20 Kt Head Wind)

2400

20060 kts @ 500 ft/m decent rate

8:1 glide slope24 seconds

1600

Final Approach(20 kt wind shear)

2400

200

60 kts @ 500 ft/m decent rateMaintain constant speed during approach

How much time remains?

1600

X Y

20 kts

0 kts

Decision Time

• With a 20 kt shear, are you likely to – overshoot (into area Y) – undershoot (into area X)

• Said another way, what actions do you need to take to reach your intended touchdown point– close the spoilers to extend (when undershooting)– open the spoilers to sink faster (overshooting)

• Another variation, what will the aim spot do?– move up on the canopy (undershooting)– move down on the canopy (overshooting)

Glide Distance

L/D Height distance

8 100 800

12 67 800

20 40 800

27 30 800

With 20K Headwind

How much Altitude does it take to regain original airspeed?

?

Transition through Wind Shear Line

Speed (kts)

Time(s)

Alt Remaining(ft)

Distance(ft)

60 0 100 800

50 1 89 867

40 2 70 934

Final Approach(20 Kt Wind Shear)

2400

200

2 seconds for the glider to stabilize at the new sink rateAOA increases from 0.5o to 5.0o

1600

20 kts

0 kts

934

Distance & Altitudeduring recovery phase

Speed (kts)

Time (s)

Alt Remaining (ft)

Distance (ft)

40 0 70 934

47 1 56 1012

53 2 31 1110

60 3 -5 1230

Final Approach(20 Kt Wind Shear)

2400

200

3 seconds to accelerate back to 60 KtsGlider nose is 20o below the horizon

1600

20 kts

0 kts

1230

Final Approach(Likely outcome in 3 cases?)

2400

200

16001230

No WindConstant headwind 20 Kt Wind Shear

Shear Encounters

• When can this happen?– Landing in gusty conditions– Landing area shielded by obstructions– During good thermal conditions (backside of a

passing thermal)

Recommendations

• Plan for this loss of energy– Pick an approach speed that will allow for some

loss– Move base leg closer to runway edge– Be higher turning Final– Be prepared to close the spoilers– Be prepared to pitch forward to

maintain/recover airspeed

Conclusions

• Shear line causes loss of Total Energy

• Large Pitch change required to rapidly recover lost energy

• Large amount of Time ‘lost’ while total energy changes

• Immediate action is required to reach original touchdown point!

Effects on Landing

• Steady wind requires more energy– 800 feet closer or 100 ft higher for 20 kt wind

• Changing wind requires more energy

• Sink requires more energy

• Ask yourself “Are you more likely to wind up getting low or high on final?”

SO … What have you Learned?