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 INTERPRETATION OF UVV ON SYNOPTIC MODELS

METEOROLOGIST JEFF HABY

Upward vertical velocity is traditionally displayed on the 700-millibar model progs. One location of this prog as well as for the other progs is available at:

http://weather.unisys.com/nam/700.php

Upward vertical velocity is the compilation of all lifting and sinking mechanisms over a fixed point. Some important points are as follows:

a) UVV is used to assess synoptic scale lift. The value of vertical velocity by itself only tells if the air is rising or sinking on the synoptic scale. The vertical velocity value does not tell the forecaster what is causing the upward vertical velocity. An analysis of all the progs is needed in order to determine the cause of synoptic scale lift.

b) The synoptic scale UVV is not associated with the UVV in thunderstorms. Synoptic scale UVV is only on the order of a few centimeters per second (more specifically called microbars per second) due to gradual large-scale uplift. Convective UVV occurs on a much smaller scale than the synoptic scale, is much faster and occurs due to the release of CAPE.

c) Synoptic UVV over a region does not guarantee precipitation. The precipitation may evaporate before reaching the ground or the UVV may be large enough to produce clouds but lacks the upward motion to produce precipitation. On the other hand, synoptic DVV over a region does not guarantee a lack of precipitation. Convective UVV can occur and often does within a mT air mass when the synoptic scale vertical velocity is near zero or sinking.

d) The units of UVV or DVV are microbars per second. The math conveniently works out such that a microbar per second is very close to a centimeter per second. A DVV of 5 means the air is sinking at a rate of 5 centimeters per second at 700 millibars. Given an hour time, a 5 cm/s descent produces a total descent of 18,000 cm or 180 meters (found by multiplying 5 by 3,600 seconds in an hour).