Upper Air Sounding Tutorial For TheWxPage.Com

These Images are Called ‘Soundings’ and are achieved by releasing a weather balloon 2 times a day at 0Z and 12Z. (Special Launches Can also Occur, Mostly During Severe Weather Season)

The Idea behind this tutorial is to help identify features on Upper Air charts that are most common so that you, the user may be able to interpret more information from these great resources.

This is a VERY BASIC description of what a SKEW-T Sounding Chart Shows.

Below is a SAMPLE Upper Air Image Meant to Help Identify SOME of the Features Mentioned Below.

upperairtutorial

KMPX (72649) Sounding:

The Sounding is for station KMPX K followed by the three letter identifier MPX (Minneapolis, MN). 72469 is the 5 digit code for KMPX.

0000Z 23 JUL 07:

The Sounding was taken at 0000Z on July 23, 2007

validtime

Pressure:

The SKEW-T Sounding shows Pressure in millibars (mb) on the left side of the Sounding.  Note the Red, Green and Blue lines All Start at the SLP (Sea Level Pressure) That was taken at that time. [You can’t have a weather balloon underground, right?]

pressure

Heights:

Alongside the Pressure in Millibars, a Height in Meters (M) is shown to correspond with a particular pressure level.

heights

Mixing Ratio:

The ratio of the mass of a variable atmospheric constituent to the mass dry air. Typically This is Used to Find LCL (Lifted Condensation Level) Heights and is used in calculating Theta (Blue Line).

mixratio

Temperature:

The Temperature on a SKEW-T is measured in Degrees Centigrade ( ºC ).

tempc

Wind:

Wind is Measure in the SKEW-T and shown at various heights.  follow the wind barb all the way to the left to get the height at which the wind value (Speed/Direction) was achieved.

wind

Temperature, Dew point, Theta

The SKEW-T Diagram shows A temperature Profile in Red, The Dew point Profile in Green and Theta in Blue.  All Values are in ºC.  Theta is calculated through the mixing ration, and adiabatic lines.

threelines

Index Values:

The MOST useful tool of the SKEW-T Chart is the ability to directly measure atmospheric Values from all levels of the atmosphere.  Many years of research went into calculating certain indices and how they may relate to various weather Conditions.  Below is a Brief overview of what Each Abbreviation Stands for, and if available a set of parameters as to what Each value might indicate.

indexvalues

WMO: The 5 Digit Station Identifier (This on is for KMPX – Minneapolis, MN)

TP: Tropopause Level in millibars

FRZ: The Freezing Level ( 0º, 32º) in millibars.

WBO: Wet Bulb Zero. When the Sounding Reaches 0ºC due to evaporational cooling.

PW: Precipitable Water in inches.

RH: Average Relative Humidity between the Surface and 500mb (millibars)

MAXT: Forecasted Maximum Temperature (Best used at 12Z launch)

L57: 700 to 500mb Lapse Rate (Lapse Rate shows how much colder it is getting between the 2 levels in ºC)

LCL: Lifted Condensation Level is the height in Millibars that the base of the clouds will form at should clouds start to form.

LI: Lifted Index is the difference between the environmental and parcel (Blue Line Theta) temperatures at 500mb

SI: Showalter Index is conceptually the same as LI except the parcel is lifted from 850mb (Thus lower in the atmosphere)

TT: Total Totals are as <44 convection not likely, 44 to 50 convection likely, 51- 52 isolated severe storms, 53- 56 widely scattered severe storms, Greater than 56 scattered severe storms.

KI: K-Index shows Lapse Rate with Available Moisture. If Values Indicate Less than 15, Convection is NOT Likely. 15-25 Small Chance for Convection, 26-39 Moderate Potential, 40 and Above a High Potential for Convection.

SW: SWEAT (Severe Weather Threat Index) 150-300 Slight Severe, 300-400 Severe Storms are possible, 400+ Tornadic Severe Storms Possible.

CAPE: Convective Available Potential Energy, Shows How Much Energy is Available in J/kg (Joules per Kilogram). Values above 1000 J/kg are enough for thunderstorms. 2000+ indicates moderate instability and 3000+ Indicates Extreme Instability.

CINH: Convective Inhibition, Shows The Negative Energy, if Too Large Storms Will NOT Initiate.

LCL: Lifted Condensation Level is the height in Millibars that the base of the clouds will form at should clouds start to form.

CAP: Cap Strength in ºC Values of Greater than 2 Indicate a Strong Cap, Values of Less than 2 indicate a weakening CAP.

LFC: Level of Free Convection, when parcels reach this level they will move vertically without any negative energy.

EL: Equilibrium Level, The Level in MB at which the Parcel will not rise any Further.

MPL: Maximum Parcel Level in millibars

STM: Direction in degrees (0-360) and speed in Knots.

HEL: Helicity Value 150-300 possible supercell, 300-400 Supercell Thunderstorms, 400+ Tornadic Supercells

SHR: Shear 0-3000m AGL (Above Ground Level) 0-3 weak, 4-5 moderate, 6-8 Large, 9+ Incredible.

SRDS: Storm Relative Directional Shear

EHI: Energy Helicity Index >1 Supercells Likely, 1-5 EF2-EF3 Tornadoes Likely, 5+ EF4-EF5 Tornadoes possible

BRN: Bulk Richardson Number Less than 45 = Supercells, 13-19 Perfect for Supercells, Less than 10 Too much Shear.

BSHR: Bulk Shear Value.