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Thanks for the explanation of the wind shear. What does "mixing down" mean? Is it that conditions move further away from the dew point as … read more one comes closer to the the surface? Well, it's correlated, but not caused by that. A well-mixed portion of an upper-level sounding has an "inverted-v" shape to it. This is a result of the mixing, mainly mixing down. As unsaturated air descends, it warms at a specific rate, about 10 Celsius degrees per kilometer. Conversely, rising air cools at that same rate. A parcel (blob) of unsaturated air will keep the same amount of moisture within it. Graphically, the unsaturated parcel's temperature increases (decreases) with height, its potential temperature stays the same. (The potential temperature is the temperature the parcel would have if it were brought to 1000 mb). The amount of moisture in that parcel stays the same, and there are many ways of measuring it, but the moist convenient is the dewpoint (the temperature to which you must cool a parcel with no change in pressure to reach saturation). One can convert this dewpoint into a mixing ratio (the derivation of which I seem to have forgotten). But this mixing ratio stays constant as you raise (lower) an unsaturated parcel. Why all this emphasis on an unsaturated parcel? It's because heat released (captured) by the condensing (evaporating) moisture changes the heat balance in the parcel. The equations still work, but it's not as simple. Anyway, if you can imagine a saturated parcel (temperature = dewpoint) descending (ascending), it's temperature increases (decreases) at a rate of 10 deg C per kilometer, and its mixing ratio stays the same. So you get this "spreading" ("converging") of the temperature and moisture lines from that level to a lower (higher) level. By the way, the rate at which temperature decreases with height is called the "lapse rate." It's almost always a positive number, indicating a decreasing with height. If the temperature increases with height, the lapse rate is negative, and that condition is known as an inversion. Anyway, along with this mixing of blobs of temperature is a mixing of blobs of wind speed. For example, the winds a couple of kilometers off the ground are moving at, say 50 mi/hr. The wind speed is often faster at higher elevations because there's little friction (with the ground) to slow it. A parcel of that air is mixed downward (because air is being mixed upward - we need some kind of compensation or we'd run out of air down here!), and you have some fast air near the surface. It's not 50 mi/hr because as it mixes down, it mixes with slower air , so you might end up with 20 to 30 mi/hr. Conversely, 10 to 20 mi/hr air at the surface is brought upward with parcels and mixes with the 50 mi/hr air and gives you about, say, 40 mi/hr (again, taking into account friction at the ground). This mixing is made more likely when the air is more "unstable", at term which means that air is more likely to move vertically. We had very unstable conditions, so air was pretty free to move up (and down), thus mixing higher wind speeds at higher altitudes to the surface, and giving a well-mixed temperature/dewpoint profile.