WMOD00290 ‎(3)‎

• Title: Automated Objective Analysis and Prediction of Mesoscale Convective Systems
• Prepared By: David A. Matthews, Leon Osborne
• Date: 6/6/1983
• Weather Modification - Doc Type: Report

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at 300 mb were str~ong, rangi ng from 64 to
90 mis, which produced very strong vertical
shear clearly visible in satellite imagery
as convective towers were sheared toward the
north. Fig. 6 shows a schematic of the flow and
radar echo structure derived from the three-
dimensional vectors, Qe analyses and total
wind field analyses. The conditional insta-
bility from 900 to 300 mb levels combined with
the vertical motion fields to produce strong
mesoscale triggering in this case.

Radar echoes developed from an unorgan-
ized field of scattered echoes at 1500 to
1900 GMT into a more organized series of north-
east to southwest ori ented 1 i nes from 2000 to
0004 GMT. The strongest region of lifting
occurred in the southwestern part of the network
and extended from the surface to 300 mb levels.
This area had the most intense radar echoes from
2205 to 2305 GMT along a northeast to southwest
line that developed from echo-free skies at 1900
to 2000 GMT, as shown in Fig. 7.

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Figure 7: Radar echo PPI showing maximum echo
top heights (km MSL) at 2205 GMT,
June 8, 1979.

Cross sections at 1800 GMT clearly
showed the most intense lifting in the south-
western part of the grid 3 h before deep con-
vection developed. The weak vertical motion at
330 N. produced only scattered echoes; however,
at 32.6 and 32.20 N., a region of deep lifting
extended to 200 mb, as shown in Fig. 8. At
1020 W., the north-south cross sect i on showed
the transition from subsidence in the north to
lifting in the south which correctly predicted
the subsequent clear regions and region of deep
convection from 2200 to 2300 GMT.

At 2100 GMT, the mesoscale circulations
intensified, producing a line of confluence of
easterly and southerly flow across the network
from southeast to northwest. This resulted in
a distinct zone of convergence that reached
-26 x 1O-5/s at 1010 W. and 32.60 N. This
maximum convergence and lifting core was at
0.40 1 at itude south of a 1 arge echo ce 11 385,
which developed at 2200 to 2300 GMT and had

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Figure 8:

East-west cross section at 330 N. (a)
and 32.60 N. (b) from 102.2 to 101.80
W. s howi ng 30-mi n wi nd vectors, Qe,
and vertical moisture flux and MESOCU
predictions of cloud-top heights.
Radar echo cross section at 2205 GMT,
June 8, 1979.

echo tops of '12 to 15 km shown in Fig. 8. The
vertical moisture flux reached 15 (g/m2)/h at
900 mb and 7.5 (g/m2)/h at 700 mb. These
large values correlated well with the evolution
of llarge echoes (385, 147, 476 and 605) from
210~i to 2205 GMT when the grid is shifted
0.40 N. in order to fit the 700 mb motion at
2100 GMT.

Cross sections at 330 N. show a good
correlation between low-level (900 to 700 mb)
lifting and vertical moisture flux and the
echoes observed at 2200 to 2300 GMT. The
evolution of cell 385 clearly matched the
vertical moisture flux shown in Fig. 8. The
region of most intense lifting and vertical
moisture flux, shown in the east-west cross
section at 32.60 N., demonstrates an excellent
correlation with radar echo-top heights observed
from 2205 to 0004 GMT when the grid is shifted
0.40 N. to match the 700-mb flow.

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