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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 and relative humidity at each altitude,
what altitudes are likely to form clouds, storms,   whether temperatures will cause rain, snow,   freezing levels,   etc.

See also our Aviation Weather, IFR, Ceilings, Icing, Turbulence, Dew Point webpage.
Skew-T Log-P Diagrams Shown Below NOAA Skew-T Log-P home page
Note dates and times on each chart
(format is "yymmdd/hhmm" GMT)

    A great pilot's app for iPad and iPhone.  Get a copy on each.
    Chart data is updated hourly, for any airport or any location.

See two videos 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
    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
    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
Co - Denver
DC - Washington
Fl - Cape Canaveral
Fl - Jacksonville
Fl - Key West
Fl - Tallahassee
Fl - Tampa Bay
Ga - Atlanta
Ia - Des Moines
Id - Boise
Il - Lincoln
La - Baton Rouge
La - Shreveport
Me - Portland
Mn - Minneapolis
Mo - Springfield
Ms - Jackson
Mt - Great Falls
NC - Greensboro
NM - Albuquerque
NY - Albany
Oh - Wilmington
Or - Portland
Pa - Pittsburgh
SC - Charleston
SD - Rapid City
Tn - Nashville
Tx - Dallas - Ft. Worth
Ut - Salt Lake City
Va - Roanoke - Blacksburg
Wa - Seattle
Wi - Green Bay
Wy - Riverton

 
Also shown:  Current Doppler Radar              
                      "Weather in the Vertical" videos
 
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

Standard atmospheric temperatures, from Geology Cafe

Skew-T Log-P Charts    General Description and Notes of Interest to Pilots
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 reduces the graph's width and also makes it easier to understand at a glance.

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.

Skew-T Log-P 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.  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 block 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.  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

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, 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 equal 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.

Current SkewT-LogP charts



Al - Brimingham



Az - Flagstaff



Az - Tucson



Ca - Los Angeles



Ca - San Diego



Ca - San Francisco



DC - Washington



Fl - Cape Canaveral



Fl - Jacksonville



Fl - Key West



Fl - Tallahassee



Fl - Tampa Bay



Canada - Ottawa



Co - Denver



Ga - Atlanta



Ia - Des Moines



Id - Boise



Il - Lincoln



La - Baton Rouge



La - Shreveport



Me - Portland



Mn - Minneapolis



Mo - Springfield



Ms - Jackson



Mt - Great Falls



NC - Greensboro



NM - Albuquerque



NY - Albany



Oh - Wilmington



Or - Portland



Pa - Pittsburgh



SC - Charleston



SD - Rapid City



Tn - Nashville



Tx - Dallas Ft. Worth



Ut - Salt Lake City



Va - Roanoke-Blacksburg



Wa - Seattle



Wi - Greenbay



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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