WMOD00378

• Title: Physical Investigations of Winter Orographic Clouds in Utah
• Date: 3/1/1984
• State: UT
• Weather Modification - Doc Type: Report

is due to their great depth. No water would be expected in the colder,

upper parts of these PETs (T < -16C) if the aircraft observations of

STORM 9 are representative.

Thus water content in the lower parts of

A PETs may be higher than the quoted figure. The low average liquid water

content in C PETs is due to the azimuthally localized nature of the

liquid. Higher contents would be expected in the vicinity of the cells.

Aircraft observations in STORM 14 showed significant amounts of super-

cooled liquid' water in small 'cumulus clouds at temperatures as cold as

-20C. NP PETs are shallow but contain substantial total amounts of liquid

water. Their liquid water contents are thus relatively high.

At the detector on the upper slope of the Tushar Mtns supercooled

liquld water was. observe.d a small fraction of the,~!.'!I,e.
------------'-""-"-" -"~..

NP PETs were

responsible for most (45%) of the observations and for the highest con-

tents (- 0.56 g m-3).

C PETs made the next highest contribution.

Supercooled liquid water at the surface appears to occur only when there

is direct or inferred evidence of a precipitation echo aloft. Comparison

of the flux of supercooled liquid water at the detector integrated over a

STORM to that of precipitation shows that the ratio is largest for

NP PETs. NP PETs may thus provide a significant precipitation augmen-

tat ion potential.

c.

Spatial distribution of supercooled liquid water.

The spatial

distribution of supercooled liquid water has a strong orographic depen-

dence. I ntegrated liquid water for C or NP PETs increases by a factor of

2.0 or 1.7, respectively, from 5-10 km west of the radiometer site to

5-10 km east. The orographic increase for A PETs is only a factor of 1.3.

There is no reason to expect these orographic increases not to continue

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