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Vertical Weather – Skew-T Log-P Charts

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Use Skew-T Log-P Diagrams to see the current temperature, relative humidity, and winds at each altitude,
what altitudes are likely to form clouds, storms, whether temperatures will cause rain, sleet, or snow, freezing levels, etc.

See also our Aviation Weather, IFR, Ceilings, Icing, Turbulence, Dew Point webpage.
Skew-T Log-P Diagrams Shown Below
(38 of 70 available)

from the NOAA Skew-T Log-P website

A great pilot's app for iPad and iPhone.  Get a copy on each.
Note that these Skew-T Log-P charts are actual values
obtained via weather-balloon soundings
recorded daily at 0600, 1200, 1800, and 2400 GMT
Note that these Skew-T Log-P charts are forecasts
calculated hourly, averaged for each 20km x 20km square,
including any airport or any location contained within.
Note dates and times on each chart
format is "yymmdd/hhmm" GMT
See two videos below explaining "Weather in the Vertical"

Detailed explanation of Skew-T Log-P chart meanings and interpretation

Other webpages with Skew-T Log-P information
    Explanation of Skew-T Log-P Diagrams including blank charts in 2 sizes
    Vertical Motion of Air and Stability
    AOPA - Skew-T Basics
    Thermo and Skew-T Education
    Mathematical Algorithms
    NOAA GOES Image Viewer
    General Information: GOES Atmospheric Soundings Display
        Click here for a good description of Skew-T-graphic plotting.

Additional sources for Soundings data
    NOAA-20 NUCAPS Global Map
    Pivotal Weather – US weather and Skew-T Log-P charts
    Earth System Research Laboratory - Model Soundings
    Model Analysis and Guidance - Forecast Soundings
    SPC Experimental Sounding Analysis System
    Hourly Mesoscale Analysis
    Skew-T Log-P charts source data

Definitions
    Adiabatic – occurring without loss or gain of heat
    Adiabatic Temperature – especially with regard to a lifting parcel of air
    Atmospheric Stability
    CAPE - Convective Available Potential Energy
    Convective Inhibition
    Determining Air Parcel Temperature:
        Rising air parcels and adiabatic cooling
    EL - Equilibrium Level
    Lapse Rate
    LFC - Level of Free Convection
    Saturated Adiabatic Lapse Rate
    Wind Barbs detailed description
Al - Birmingham
Az - Flagstaff
Az - Tucson
Ca - Los Angeles
Ca - San Diego
Ca - San Francisco
Canada - Ottawa
DC - Washington
Fl - Jacksonville
Fl - Key West
Fl - Tampa Bay
Ga - Atlanta
Ia - Des Moines
Id - Boise
Il - Lincoln
La - Baton Rouge
La - Shreveport
Me - Portland
Mi - Detroit
Mn - Minneapolis
Mo - Springfield
Ms - Jackson
Mt - Great Falls
NC - Greensboro
NM - Albuquerque
NY - Albany
Or - Portland
Pa - Pittsburgh
SC - Charleston
SD - Rapid City
Tn - Nashville
Tx - Dallas - Ft. Worth
Tx - El Paso
Ut - Salt Lake City
Va - Roanoke - Blacksburg
Wa - Seattle
Wi - Green Bay
Wy - Riverton
Understanding Skew-T Log-P Charts

See these videos explaining Skew-T Log-P charts:
        Current Doppler Radar
        "Weather in the Vertical"

See the PDF Making Sense of the Weather,
a copy of the handout for a presentation on Skew-T Log-P charts given at the Triple Tree Aerodrome's 2021 Annual Fly-In, on Saturday, 25 September.
Inches Hg   to   Millibars   to   Altitude   conversion   (standard pressure)
29.92" = 1013 mb = 0000'       23.98" = 0812 mb = 6000'       14.76" = 0500 mb = FL 180
28.85" = 0977 mb = 1000' 23.09" = 0782 mb = 7000' 11.81" = 0400 mb = FL 240
27.82" = 0942 mb = 2000' 22.24" = 0753 mb = 8000' 8.86" = 0300 mb = FL 300
26.81" = 0908 mb = 3000' 21.38" = 0724 mb = 9000' 6.64" = 0225 mb = FL 360
25.84" = 0875 mb = 4000' 20.58" = 0697 mb = 10,000' 5.17" = 0175 mb = FL 420
24.89" = 0843 mb = 5000' 19.19" = 0650 mb = 12,000' 3.69" = 0125 mb = FL 480
Skew-T Log-P chart showing standard temperatures vs. altitude

Standard atmospheric temperatures
Skew-T Log-P Charts  –  General Description
Vertical Weather
The primary feature in each of the charts below is the large graph and its associated elements in the upper left rectangle.  Most of the remaining components of the chart are derived from the same data used to build that graph.
The graph's vertical axis is altitude, given in millibars.  See the table above for translation into altitude in feet.  It is shown on a logarithmic scale; hence the "Log-P" in the term "Skew-T Log-P chart".
The graph's horizontal axis is temperature, in degrees Centigrade.  Note that on the graph itself, the vertical lines to indicate temperature slant to the right; hence the "Skew-T" in the term "Skew-T Log-P chart".  The skewing is due to the fact that the atmospheric temperature declines about two degrees per thousand feet increase.  For any given temperature on the X axis, look vertically for the corresponding expected temerature at any given altitude:  if it is 20 degrees Centigrade at 1000 feet, expect the temperature at 10,000 feet to be 2 degrees.
The Chart's Contents
The red line indicates the temperature at each altitude for that location.
The green line indicates the dew point at each altitude for that location.
Note that the bottom ends of the red and green lines stop at a particular altitude, not at the bottom of the graph itself.  That particular altitude reflects the ground level at that location.
The closer the green line is to the red line, the higher the relative humidity at that altitude.  If they overlap, that indicates 100% relative humidity.
At that altitude there will be clouds (at ground level, fog).  If the two lines are far apart, clear skies will be present at that altitude.
SkewTLogPro forecast charts indicate conditions for a 20-kilometer by 20-kilometer (13-mile by 13-mile) square.  Obviously, variations of the conditions within that square will occur.
The closer together the red and green lines are, the more clouds will form, transitioning from clear skies when the lines are far apart, to scattered clouds to broken clouds to overcast as the lines converge.
Freezing Level
The dotted blue lines at 0 degrees and -20 degrees indicate the freezing level, which is very important for aviation.
If clouds are present where the temperature line crosses the 0 degree line, and is within the 0-degree to -20-degree range, expect super-cooled water droplets, and subsequent icing.  That possibility progressively declines with the drop in temperature away from 0 degrees.
The likelihood of icing also drops depending on air movement.  In very calm air, water can remain liquid to a much colder temperature.  But air movement, whether due to the flight of an airplane or due to natural causes, such as flow over mountains or the movement of a front, causes disturbance and air movement which will result in the freezing of those liquid droplets.  Once frozen (i.e., as snow), that moisture is no longer of concern regarding icing on wing surfaces.  As snow however, it can clog air intakes.
Winds Aloft
The wind barbs to the right of the main chart indicate direction and speed of the winds at each altitude.
Of primary interest are high winds, which result in turbulence, or changes in wind direction and speed with altitude, which indicates wind shear.  Progressive, minimal changes indicates smoother flying.  Rapid, more radical changes indicate turbulence and wind shear.
CAPE and Cumulonimbus Clouds
The thin dotted brown line that typically lies between the red and green lines indicates Convective Available Potential Energy:  CAPE.
When the dotted brown CAPE line is to the right of the red Temperature line, convective activity can be expected.
Cumulus clouds will build to altitudes above what the areas of convergence of the red Temperature line and the green Dew Point line would indicate, forming cumulonimbus clouds.  Turbulence in such clouds is likely to be severe.
For further description and greater detail, see the NOAA Sounding Analysis Help Page and Mesoscale Analysis Overview webpage.
Related Notes of Interest to Pilots
Levels of Turbulence
Light – Small, correctable deviations from position and altitude.  Aircraft control is maintained.
Moderate – Significant deviations from position and altitude.  Momentary losses of control of aircraft.
Severe – Uncontrollable deviations from position and altitude.  Loss of control of aircraft; possible deformation and destruction of aircraft.
Boundaries Between Air Masses
Cloud bases or tops will often indicate boundaries between two air masses.  If all cloud bases or (more rarely) all cloud tops are at the same altitude, that is the dividing line between two air masses with differing wind speed, direction, temperature, and relative humidity.

Ground Thermals
On clear, sunny days, the heating of the earth will cause ground thermals – rising columns of air that late in the afternoon can reach up to 4,000' above ground level (AGL) and be a bit bumpy.  Cloud bases will often form at that level as ground humidity reaches the cooler air above the thermals.
More generally, on Skew-T Log-P charts this is called the Lifting Condensation Level (LCL), defined as the level at which a lifted parcel of air becomes saturated (i.e., due to cooling bringing the temperature down to be equal to the dew point).  The LCL is a reasonable estimate of cloud base height when air parcels experience forced ascent.
Multiple Cloud Layers
If clouds are indicated at two levels – for example, a layer at 30,000 feet and another below 5,000 feet – then the upper cloud layer will typically block the sun's warmth from reaching the lower layer of clouds.  Flying through the lower layer should be fairly smooth (assuming no turbulence due to winds).
Without a shielding cloud layer, the sun's warmth typically makes that lower level of clouds increasingly more turbulent as the daytime hours progress.
Daily Atmospheric Changes
The day's weather is most calm from about 3:00am until sunrise.  The heat of the previous day has radiated away, and with sunrise the clouds and ground begin to warm again, creating atmospheric changes.
Obviously, strong fronts, hurricanes, etc., continue througout the night with enough force not to be significantly abated.  The movement of air masses across the earth's surface is not affected as much by the sun's radiation; their substantial mass has substantial inertia, and does not stop.


Current SkewT-LogP charts



Al - Brimingham

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Az - Flagstaff

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Az - Tucson

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Ca - Los Angeles

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Ca - San Diego

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Ca - San Francisco

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DC - Washington

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Fl - Jacksonville

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Fl - Key West

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Fl - Tampa Bay

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Canada - Ottawa

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Ga - Atlanta

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Ia - Des Moines

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Id - Boise

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Il - Lincoln

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La - Baton Rouge

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La - Shreveport

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Me - Portland

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Mi - Detroit

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Mn - Minneapolis

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Mo - Springfield

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Ms - Jackson

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Mt - Great Falls

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NC - Greensboro

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NM - Albuquerque

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NY - Albany

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Or - Portland

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Pa - Pittsburgh

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SC - Charleston

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SD - Rapid City

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Tn - Nashville

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Tx - Dallas Ft. Worth

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Tx - El Paso

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Ut - Salt Lake City

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Va - Roanoke-Blacksburg

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Wa - Seattle

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Wi - Greenbay

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Wy - Riverton

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Current Doppler Radar

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Videos explaining SkewT-LogP charts

Weather in the Vertical – part 1


Weather in the Vertical – part 2


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