WMOD00537

• Title: Remote and In Situ Observations of Sierra Nevada Winter Mountain Clouds: Relationsips between Mesoscale Structure, Precipitation and Liquid Water
• Date: 2/2/1988
• Weather Modification - Doc Type: Report

FEBRUARY 1988

DA VID W. REYNOLDS AND ARUNAS P. KUC1AUSKAS

151

Relative Humidity (%) and Temperature (DC)

9

20

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7

6

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40 60
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80
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Distance (km)

fiG. 10. Horizontal cross section ofrelative humidity (solid) and
temperature (dashed) as derived from the Sheridan, Blue Canyon
and Kingvale soundings for 2100 UTC 24 March 1985. Terrain profile
is annotated at the bottom.

frontal passage, which delayed the onset of SL W until
these clouds moved east.

,.
"

c. 26-27 March 1985

;

Although the organization of the two previous pre-
cipitation events were substantially different, similar
frontal characteristics could be identified. Both storms
had low-level fronts characteristic of cold katafronts
and each were preceded by an upper-level jet streak
and accompanying cold surge/humidity front. Each of
these storms was in the decaying stage, especially the
one of 24-25 March, substantiating Sansorn's (1951)
theory .
This next and last case study is more typical of a
classic cold anafront. As Browning (1985) describes for
similar cases, the warm conveyer belt undergoes rear-
ward sloping ascent above the low-level frontal zone
with cold air descending behind it. This will usually

r

produce a distinct narrow cold frontal rainband asso-
ciated with the cold anafront passage.
The Sheridan time-height profile shown in Fig. lla
illustrates the important frontal features. A well-defined
warm front could be observed, producing 8 to 9 h of
warm overrunning precipitation having fairly high
precipitation rates (Fig. lid) and high radar reflectiv-
ities (Fig. II c). In this particular instance, no substantial
liquid water preceded the onset of precipitation. Be-
tween the passage of the warm front and cold anafront,
a low-level jet developed in response to the passage of
the main upper-level jet. The speed of this low-level
jet may have been enhanced by the barrier jet mech-
anism (Parish, 1982). The speed of the upper jet was
estimated from the CP-4 real time Doppler radar ob-
served winds since the Sheridan sounding terminated
early due to the excessive speed of the low-level jet.
The main frontal precipitation came as a series of
three fairly intense bands. The three bands can be ob-
served passing Kingvale between 0000-0100, 0300-
0400, and 0400-0500 in the radar time-height over
Kingvale (Fig. llc). Each band produced a corre-
sponding increase in precipitation rate. The first of
these bands was closely associated temporally with the
passage of the upper jet. The satellite sequence in Fig.

26- 27 MAR 1985

325
TROP
320

315

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-290

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250. CSR 2.12 1.76 .62 1.30 4.64 6.29 6.29 4.17 3.06 1.56 .19
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15 12 09 06 03 00 21 18 15 12 09
TIME IUTC)

fiG. 11. As in Fig. 2 but for 26-27 March 1985. Numbers under
radar time-height refer to' rainbands discussed in text; WF = warm
front.