METEOROLOGIST JEFF HABY
The change in wind direction and wind speed with height gives clues to the synoptic
temperature advection. A clockwise
turning of the wind with height is termed
veering. Winds turn from
southeasterly at the surface to westerly aloft in a veering case. A veering wind is associated with warm air advection.
of the warm air advection will depend on the strength of the wind and the amount of veering with height. If winds are
strong and southerly at the surface and from the west at 700 mb, through time the low levels of the atmosphere will
warm while the upper levels may stay near the same temperature. This will cause
instability. The amount of
instability in the low levels will depend on the amount of thermal advection and the amount of veering from the
surface to the mid-levels. A veering profile is common in the warm sector of a mid-latitude cyclone. The wind
will veer with height in the vicinity of a warm front. Before warm front passage it is common for winds to be
light northerly, shift to the east, then finally shift to a southerly direction.
Winds that turn counterclockwise with height are termed a
backing wind. A backing wind is associated with cold
fronts. Behind a cold front, wind will be from a northerly direction, then shift counter-clockwise to a westerly
direction with height. Keep in mind that the winds in the mid and upper levels usually have a more westerly
component than an easterly component due to the prevailing planetary scale westerlies. A backing wind is
cold air advection. A backing wind in the low levels of the atmosphere is favorable for synoptic
scale sinking motion. Most rain and thunderstorms are out ahead of cold fronts. Precipitation behind cold fronts
is generally lighter or lacking all together in most situations.
A hodograph displays the wind speed and direction with height. Veering and backing of wind can be figured very
easily through the diagram.
A hodograph can be used to determine most likely thunderstorm type.
The low level of the atmosphere is from the surface to 850 mb, the mid-levels from 850 to 500 mb, and the upper
levels 500 to 150 mb. These hodograph types are described below:
*Strong veering of wind in low levels, extending into mid-levels
*Wind speed greater than 20 knots in low levels and preferably greater than 100 knots from 500 to 300 millibars
*The stronger the wind, generally the more favorable
*Wind speed very high in upper levels, greater than 100 knots, the higher the better
*Hodograph curved sharply with height
*Wind veers with height, but not as pronounced as
*Wind direction remains fairly unidirectional from lower mid-levels into upper levels (850 to 300 mb)
*Speed shear is present (increase of wind speed with height)
AIR MASS STORMS
*Wind speed change with height is relatively small
*Wind direction is fairly constant with height or unorganized
*Upper level winds are much weaker than supercell or multicell case
The link below has current online hodographs
CURRENT HODOGRAPHS WITH SKEW-T