WMOD00400

• Contract/Permit #: 14-06-D-6801
• Title: Structure and Seedability of San Juan Storms
• Date: 11/1/1976
• Weather Modification - Doc Type: Report

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26

Details of the structure of the liquid water region over the mountain

appear in the discussions of V.A.3.e, V.C.3.c, V.D.3.c, and V.H.3.e. The

region is generally rather smooth, without significant turbulence or varia-

tions in state parameters. However, in unstable cases the liquid \vater con-

tent is quite variable, perhaps indicating that the liquid water originates

in the convective region ahead of the mountains.

b. Associated \vi th the up\vind rise in the terrain

Liquid water regions were often found just following the rise in the

terrain dO\vl1\vind from Navaj 0 Reservoir. This rise is followed by a rela-

tively flat region, and in the absence of continued lifting the liquid water

produced here \vas rapidly glaciated. Often, the cloud first fanned in this

region, and a liquid Hater region \vas found at the leading edge of the cloud.

In cases where the flow was relatively smooth into the clouds, this liquid

water Has rapidly glaciated by the developing ice crystals. The result was

that the cloud approaching the mountains was generally a glaciated cloud.

c. Associated Hith convection

The third region in which liquid \vater was frequently observed was about

15 km up\vind of the mountains, above the surface convergence zone \vhich formed

over Pagosa and which was discussed in section IILA. A particularly good ex-

ample was observed on 29 December 1974, flight 1. Liquid water contents of

0.3-0.5 g/m3 were found in the convective elements, which had dimensions of

1-3 km and were spaced about 3-5 km apart. This convective zone is highly

significant for the seeding of these storms, for the following reasons:

(1) Supercooled water is probably required for seeding to be effective.

This convection provides a source of supercooled \\"ater at relatively] ow'

altitudes upwind of the mountain range, in a hiGhly seeclable ]oc~tion.

Furthermore, the convection apparently extends the liquid water region further