Lift & Instability


BLIPMAP = Map of Boundary Layer Information Predictions by Dr. John W. (Jack) Glendening, Meteorologist. Boundary Layer Information Prediction MAPs give thermal soaring parameters over a geographic region. They take so many critical factors into consideration that these are the most useful tool for forecasting.

Univiewer is one of the best interfaces to view ajoining regions, RAP & NAM as well as different forecast times.

Links To Example BLIPMAP Regions (follow main link for other regions and a full explaination):

SouthCentral region BLIPMAPS for GA-AR-AL-KY-LA-MO-MS-TN

SouthEast region BLIPMAPS for FL-GA-NC-SC-VA

Mini-Blipspot @ Near Warm Springs RAP, NAM, Cordele RAP, NAM

**** XC Skies

XC Skies Soaring Forecast Maps & Tools. Interactive soaring forecast maps and tools for virtually every flyable location on planet Earth. Our goal is to provide timely and highly useful soaring forecasts to allow pilots to make better decisions on when and where to fly.

**** Thermal Index (TI) reports

Kevin's Ford's Thermal Report Generator, is based on RAOB sounding and is very useful. A TI of 0 is the max height a thermal will reach, a TI of -3 is an estimate of how high a sailplane can fly. The 12Z sounding is useful for predicting soaring conditions (available as soon as 1245Z-1330Z [7:45EST/8:45EDT - 8:30EST/9:30EDT] and until 2359Z). The 0Z sounding is useful to review the conditions after a day. See Kevin's full instructions for further details. When forecast high is missing, you can input your own # based on another forecast source (TWC...). Choose an upper air station that is upwind of your soaring location, and a surface station that is close enough to have the same forecast high temperature.

A few examples:

Peachtree City GA Upper Air Sounding & Forecast high from:Albany, GA Montgomery, AL, Atlanta, Athens Macon
Birmingham AL Upper Air Sounding & Forecast high from: Columbus, GA good for prevailing winds for LaGrange
Nashville TN Upper Air Sounding & Forecast high from: Chattanooga
Tallahassee FL Upper Air Sounding & Forecast high from: Columbus, GA, Albany, GA
Valparaiso/Elgin AFB FL Upper Air Sounding & Forecast high from: Columbus, GA, Albany, GA, Destin, FL, Pensacola, FL
Greensboro NC Upper Air Sounding & Forecast high from: Greensboro, NC
Reno NV Upper Air Sounding & Forecast high from: Reno

**** Interactive SkewT soundings

This resouce shows you how the read the vertical profile of the atmosphere, it is a very key point in knowing how the thermals will be generated based on the stacking of layers of air, you can determine where the inversion is and if a small temperature change is significant to changing the thermal heights or not, and if clouds will form etc.
An excellent source for SkewT soundings derived from the many models rather than only the balloon soundings are are in just a few specific locations. This is one of the best sources of Upper Air Forecasts, this way you can see what the conditions will be while you plan to fly instead of hours old data. This model is run hourly (instead of just twice daily with the balloons). The analyses include many types of data sources besides radiosondes (only every 12hrs).. including NEXRAD winds, radar wind profilers and aircraft ascent/descent winds from ACARS data links. The 3d analyses of temp and winds is very good, allowing excellent estimates of local soundings interpolated for your airport at any hour. Model forecasts of sounding data reach out 12hours. See the instructions, and useful if you learn how to zoom into the lower part of the atmosphere where we fly.

Interactive SkewT soundings NonJava HTML5 - works on Ipads etc, Interactive SkewT soundings java version

NonInteractive (but still good) Sounding plots RAPS/RUC

*Ready FORECAST RAOB plots for specific locations
Ready Forecast Soundings This gives you a forecast sounding for any location in the world, not just the few RAOB balloon locations. This site is excellent because you can specify:
1. Any location, (use 3 letter airport ID such as ffc, lgc or cha, or Lat/Long)
2. Future time, since you are more likely to be soaring at 18Z instead of 12Z,
3. Model source - choose AVN, RUC or ETA etc (base your choice on daily guidance from the local NOAA weather office as to which computer model they feel is most accurate in their Forecast Discussion. Find your Forecast Discussion in this List).
4. Zoom in on the altitudes below 400mb to see the convective area that we usually fly in. Choose the Skew-T Log-P only up to 400 mb
5. You can even Plot 1 time period OR an animated GIF loop, with your choice of number of forecast hours for the animation. This is a good way to see how the sounding will change throughout the day.

*Forecast Model Soundings Machine
Forecast Soundings This gives you a forecast sounding from the National Centers for Environmental Prediction (NCEP)'s operational RUC, ETA, NGM, Aviation (AVN) or MRF models for any site that produces a METAR. The advantage of the other models is that their forecasts extend further into the future. Generally the best model to use (out to 48 hour prediction) is the ETA model, since it uses a more highly resolved grid. The Aviation model has the advantage of providing 72 hour forecasts (if one believes a weather model that far ahead!). Part of the Storm Machine

** Skew-T Diagrams
Skew-T Thermodynamic Diagram Based on balloon soundings at 0Z & 12Z, has many lift/instability indexes too. ... Examples: Peachtree City GA ... Birmingham AL

NOAA Soaring Forecasts for specific locations

Reno, NV
Spokane, WA, as well as Salem OR, Seattle WA and Boise ID
Denver/Boulder, CO
Fort Worth, TX, Decatur
Little Rock, AR
Pittsburgh, PA, Buffalo, Detroit, Wilmington OH

Roab GIF images

Called a "RAOB" (Radiosonde Observation), these images show both a diagram of the upper air sounding as well as some lift/instability indexes at the top. Examples:
FFC Peachtree City GA . . . BMX Birmingham Shelby County . . . GSO Greensboro NC . . . BNA Nashville, TN . . .TLH Tallahassee FL ... REV Reno, NV

Source: Real-Time Weather Data: Upper-Air Page
also available: Stuve Thermodynamic Diagrams ... and ... Atmospheric Thermodynamic Diagrams

** Other sources of RAOB data
Archived RAOB data
NOAA Weather Balloon Data

Formula for Calculating Cloudbase Height
This formula is based tells you at what point the temperature and dewpoint converge, which is the point of condensation = clouds.
(Surface Temperature - Dewpoint) / 4.4° F . . . 400ft per ° C.
Temp minus Dewpoint Difference F° Cumulus Cloudbase in feet   Temp minus Dewpoint Difference C° Cumulus Cloudbase in feet
5 1,100   2 800
10 2,300   4 1,600
15 3,400   6 2,500
20 4,500   8 3,300
25 5,700   10 4,100
30 6,800   12 4,900
40 9,100   15 6,100
50 11,400   20 8,200
60 13,600   25 10,200
70 15,900   30 12,300
80 18,200   35 14,300

Bradbury Rule for Thermal Height & Strength
From the UK, the "Bradbury rule" estimates that the afternoon cumulus cloudbase will be 400' for every 1C (222'/1F) between max and min temperature for a day. In General terms, UK average climb rates in knots are equivalent to cloudbase (or thermal height in blue weather) in thousands of feet -1. For example: 4,000' cloudbase/1000=4-1=3 knots. This rule should vary in the different climates of the Eastern & Western US. However, this is a very crude method to predict lift because it totally ignores the stability of the atmosphere.
Temp Difference F°
Cumulus Cloudbase in Feet
Climb Rate knots

Relationship between Thermal Height, Strength and Cloudcover

Click on the graph to see a larger version and explanation for Strength of Thermals and the relationship to cloud height and cover.

* K index
K index Unisys- An index of moisture and instability - see table below. For Soaring K values in the mid 20's to low 30's are optimal. -5 is the lower threshold, Overdevelopment at +28. Please email me to help fill data into the Eastern US column. After a flight try to correlate performance to the K value.
Unisys' K Index Stability Contour is a contour plot of K index with a contour interval of 4. The KI field shows instability in the atmosphere as it relates to the development of air mass thunderstorms. It is based on the 850 to 500 mb lapse rate plus 850 mb dewpoint minus the 700 mb dewpoint depression. Strong Springtime thunderstorms often require dry air at mid levels to cap the convection. On the other hand, summer air mass thunderstorms need a very moist atmosphere at mid levels to prevent evaporation through entrainment. Where KIs are greater than 35, air mass thunderstorms are likely. the higher the number, the higher the probability. Values less than 10 indicate areas of stable weather where skies are generally clear. (Purdue University) Basically double the KI value to calculate the chance of thunderstorms.
Some of the feedback I have gotten is that the K Index is a more reliable predictor of thunderstorms (which it was invented for) than lift, so your mileage may vary. So this is just one of the many indicators.
General Soaring Lift Performance
"K" value Convective Activity
Western US
Eastern US
<-10 None
< 300 fpm
-10 to +5 Blue Thermals*
300-600 fpm
+5 to +10 Increasing Convection
500-700 fpm
+10 to +15 Isolated strong vertical extent
600-800 fpm
+15 to +20 20% coverage thunderstorms
700-900 fpm
17.5=300-500fpm in July LaGrange
+20 to +25 20% to 40% coverage thunderstorms
800-1000 fpm
+25 to +30 40% to 60% coverage thunderstorms
900-1100 fpm
+30 to +35 60% to 80% coverage thunderstorms
1000-1200 fpm
31.8=500-700fpm w/ hi pressure system in June LaGrange
33.1=400-600fpm, July LaGrange
+35 and higher Greater than 80% coverage thunderstorms
1100-1300 fpm
*Blue thermal conditions can deliver strong lift rates at times, especially with unusually clear skies intensifying heating for thermals. . . . Above K value data from "Soar Sierra" edited by John Joss Copyright John Joss 1976, the Soaring Press. Chapter 1 "Mountain Meteorology, know before you go!" by Doug Armstrong & Chris Hill. An excellent book available from the SSA.

* Relative Humidity/Lifted Index
The Relative Humidity/Lifted Index (4 panel NAM Forecast) RAP chart depicts two fields:

1 Lifted Index (in white line contours). The LI field shows instability in the atmosphere. where LIs are <0 (also highlighted in a gray shading), thunderstorms are possible. the lower the number, the more unstable the atmosphere is and as a result, the stronger the thunderstorms (and Thermals) could become. Values of -4 or lower indicate areas where severe thunderstorms are possible. Values >10 indicate areas of stable weather where skies are generally clear.

2 Integrated Relative Humidity (in color contours) from 850 to 500 mb The RH field is a good predictor of cloud location and thickness. Areas of RH <60% generally are clear or have partly cloud skies. areas of 60-80% are generally overcast or mostly cloudy. areas greater than 80% are overcast with a high likelihood of precipitation as rh approaches 100%. This can show you if the thermal is likely to be capped by a cloud.

Lifted Index
Current Lifted Index (Unisys) Contour plot with a contour interval of 2 degrees Celsius. The LI field shows instability in the atmosphere by lifting a parcel of air from the surface to 500 mb and comparing its temperature to that of the environment. Where LIs are less than 0, thunderstorms are possible. The lower the number, the more unstable the atmosphere is and as a result, the stronger the thunderstorms (lift) could become. Values > 10 indicate areas of stable weather where skies are generally clear.
     LI > 2    No significant activity
 0 < LI < 2    Showers probable, isolated thunderstorms possible
-2 < LI < 0    Thunderstorms probable
-4 < LI < -2   Severe thunderstorms possible
     LI < -4   Severe thunderstorms probable, tornadoes possible 
Lifted Index - is calculated by lifting (frontal, orographic, upper air dynamics, etc.) a parcel of air dry adiabatically while conserving moisture until it reaches saturation. At that point the parcel is lifted moist adiabatically up to 500 mb. The Lifted Index is the ambient air temperature minus the lifted parcel temperature at 500 mb. If the parcel is warmer than the environment (negative L.I.), it has positive buoyancy, and will tend to continue to rise, favoring convection. L.I. values less than -5 C indicate very unstable conditions. A positive L.I. value indicates negative parcel buoyancy, and the parcel will tend to sink. This is representative of stable conditions where convection is unlikely. Increasingly negative numbers correspond to increasing instability and likelihood of severe weather. At times, very high (stable) lifted index values in cold air are indicative of frozen precipitation verses rain during warm advection events. The extreme stability results in cold air "damming", which restricts the advance of warm air at the surface. .. Forecast Product Development Team (FPDT) NOAA

Showalter Index
The Showalter Index (link2) is a good indicator of Air Mass thunderstorms. Derived from the Skew-T upper air soundings. It is a parcel-based index, calculated in the same manner as the Lifted Index, using a parcel at 850mb. That is, the 850mb parcel is lifted to saturation, then moist adiabatically to 500mb. The difference between the parcel and environment at 500mb is the Showalter Index. Again, the calculation is environment minus parcel, so negative numbers indicate instability. The SHOW values are similar to the LI values as far as references for severe weather (negative is unstable, values -2 and below indicate possible severe t-storms, below about -5C is highly unstable).

Total Totals Index

Unisys TT. This is a contour plot of total totals index with a contour interval of 2. The TT field shows instability in the atmosphere based on the lapse rate from 850 to 500 mb plus dewpoint at 850 mb. Where TTs are greater than 45, thunderstorms are possible. The higher the number, the more unstable the atmosphere is and as a result, the stronger the thunderstorms could become. Values of 52 or higher indicate areas where severe thunderstorms are possible. Values < 40 indicate areas of stable weather where skies are generally clear.

Indices definition

Mountain WAVE and RIDGE forecasts

for those lucky enough to be close to mountains:

Wave forecasts from Dr Jack:

Latest WINDIP upper-level wind and mt. wave forecasts

Mountain Wave Project, ostiv link

Mountain Wave Activity Over the Southern Rockies reference material by Alberta Vieira

COMAP 1999 Downslope Wind Lab - Wave Research.

also see the SkewTs

"Not everything that can be counted counts, and not everything that counts can be counted." - Albert Einstein (1879-1955)

Plan your own Record & Badge Tasks to be flown at SES.

Comments & Suggestions are welcome gmail read carefully Last modified June 4, 2014