WMOD00378

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

valley locations. The NP PET has the lowest (~ 2630 m AGL) and war"mest

(~-14C) tops. "No echo" appears in its name only because it lies below

the C-band radar beam. Average and maximum Ku-band radar reflectivities

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are nevertheless significant and, in ..fc:l_c:.tJu ar:e similar to those of C PETs.
---------'-....-.....'..'.... . ~

Maximum reflectivities are concentrated over a narrow range of heights

near cloud base. NP PETs are relatively similar to each other in terms of

height and reflectivity.

They are variable producers of precipitation

particles.

Relative frequency in 1983 of these major PETs was: A-11%, C-20%,. and

NP-44%. Precipitation amounts during STORMS were in rough proportion to

the frequency of the various PETs. NP PETs contributed about 45% of the

precipita_ti?_~ .

A and C PETs each contributed 15-25% of the precipita-

tion.

The Tushar Mtns have an orographic effect on precipitation.

Precipitation amounts increase by a factor of 2.5 from the base of the

mountains to a point halfway up the slopes, and there is a fUlrther

doubling from there to the snowfields at the highest elevations.

Precipitation amounts increase largely because of an increase of prE!cipi-
" -.-.-. -~~-- --.-

tation duration.

Precipitation rates increase relatively little up the

mountain slopes.

b. Dependence of supercooled liquid water on PE T . Liquid water

varies with PET. Radiometric measurements at all azimuths point to mledian
-.----..----

integrated liquid water depths for A, C, and NP PETs of 0.29, 0.175..,. and

0.26 mm.

Estimated cloud depths for A, C, and NP PETs of 3.4, 2.12" and

1 .45 km yield average liquid water contents of 0.085, 0.083 and

0.18 g m-3, respectively. The low average liquid water content in A PETs

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