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;
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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
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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!
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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
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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
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Fronts
Winds
Airmass Changes
Precipitation
Overcast
Cold Front
Src: Aviation Weather AC 00-6A
Cold Frontal Weather
• Cold Front Passage - Cumulus then Cumulonimbus
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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
Warm Front
Src: Aviation Weather AC 00-6A
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
Colder Overtaking Occlusion
Front Warm Air Aloft
Src: Aviation Weather AC 00-6A
Warm-Occlusion Front
Cool Air overtaking Colder
Src: Aviation Weather AC 00-6A
Airmass Changes
Mount a Sensitive Thermometer (measures .10 deg change)
Able to detect airmass changes
Watch for significant Cloud changes throughout the day
Can 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 plotted
vs. 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
All those Lines !!
Actually calculations
• Mixing Ratio = Constant Water Content (Gray)
• Temp (Red)
• Alt. (Blue)
Pressure / Feet
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 Rates
Rate 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
– Dew point decreases
less than dry
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)
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Morning Low*
Max Expected Temp
T.I. at 5000 ft
T.I. at 10,000 ft
Height of -3 TI
Top of Lift
50F 10C
89F 35C
-5
+2
7200’
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
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 Index
TI = +6
TI = -10
Src: Soaring Flight Manual
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
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=== Interpolations (temps
MSL *TI* Wdir@kts trig
----- ---- -------- ---10000 12.4
40
9500 11.6
39
9000 10.7 280 27
37
8500
9.8
35
8000
8.8 290 25
34
7500
7.9
32
7000
6.9 295 24
30
6500
6.0
29
6000
3.7 300 27
25
5500
3.6
24
5000
3.5
24
4500
3.3
24
4000
2.1
22
3500
0.8
19
3000 -0.5
18
2500 -1.8
16
2000 -2.1
15
1500 -2.1
15
1000 -2.1
15
in deg. F, altitudes in feet MSL) ===
VirT 1.2 degrees/division ("`": Dry Adiabatic)
. ---- ----------------------------------------| -9.8 `
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| -8.6
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| -7.5
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| -6.5
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:
| -5.5
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:
| -4.5
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:
| -3.5
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| -2.6
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| -4.0
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| -1.5
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:
| 0.9
`
:
| 3.3
`
:
| 3.7
` :
| 4.1
`:
| 4.4
:`
| 4.8
: `
| 7.0
: `
| 9.7
: `
| 12.3
:
`
NOAA Forecast Plot
Cloud Layer
30,000 ft
Cloud Layer
1000 to 7500 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 Day
Massive
Inversion………
.. Yet Clouds
from Surf to…..
15,000 ft !!
If it Got to
75F.. Could
Soar to 30,000
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
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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 Zones
Gradual 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
Transition pilot wave sketch
Lenticularcular
Rotor
3/19/2016
W o r k a b l e
Some rotor research in progress
3/19/2016
Some rotor research in progress
3/19/2016
Thermal Predictors/Indicators
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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
9
27
Time on Downwind: More, Less, no Change?
Altitude loss: More, Less, no Change?
20 Kts
Effect of 20 Kt wind
9
27
Time on base: More, Less, no Change?
Altitude loss: More, Less, no Change?
20 Kts
Effect of 20 Kt wind
9
27
Time on Final: More, Less, no Change?
Altitude loss: More, Less, no Change?
20 Kts
Effect of 20 Kt wind
9
27
Which path is your student likely to fly?
Which path do you want them to fly?
4
20 Kts
3
1
2
Final Approach
(No wind)
200
60 kts @ 500 ft/m decent rate
12:1 glide slope
24 seconds
2400
Final Approach
(20 Kt Head Wind)
200
60 kts @ 500 ft/m decent rate
8:1 glide slope
24 seconds
1600
2400
Final Approach
(20 kt wind shear)
200
60 kts @ 500 ft/m decent rate
Maintain constant speed during approach
How much time remains?
20 kts
0 kts
X
Y
1600
2400
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
8
12
Height
100
67
distance
800
800
20
27
40
30
800
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)
200
2 seconds for the glider to stabilize at the new sink rate
AOA increases from 0.5o to 5.0o
20 kts
0 kts
934
1600
2400
Distance & Altitude
during 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)
200
3 seconds to accelerate back to 60 Kts
Glider nose is 20o below the horizon
20 kts
0 kts
1230
1600
2400
Final Approach
(Likely outcome in 3 cases?)
200
No Wind
Constant headwind
20 Kt Wind Shear
1230
1600
2400
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?