Unit 5 of 12 · 1 of 4 lessons published
Soundings
A sounding is a profile of the atmosphere from the ground up: temperature, dew point and wind at every level a weather balloon passes through. It is the most direct measurement of whether air will rise on its own, how high it will go, what the wind will do to the storm that forms, and what kind of precipitation will reach the ground.
The National Weather Service launches radiosondes from 92 stations, twice a day, up to an hour before 00 and 12 UTC (NWS radiosonde fact sheet), and forecast models produce the same profile for any place and hour. This unit teaches the two charts used to read them, the skew-T diagram for temperature and moisture and the hodograph for wind, and then the severe weather parameters computed from both.
Read the lessons in order. The skew-T lesson assumes only dew point and lapse rate, both defined in the glossary.
- How to read a skew-T diagram
Every line on the chart, how to lift a parcel, CAPE and CIN, and the sounding shapes behind storms, snow, ice and fog.
- How to read a hodograph
The wind profile as one curve: shear, turning, storm motion and helicity.
- Severe weather parameters
What STP, SCP, SRH and effective shear measure, and what their thresholds mean.
- Forecast soundings from models
Reading model soundings, and where they are most often wrong.