WMOD00176

• Project Name: Annual Report
• Title: Seeding Operations & Atmospheric Research, 2005 Annual Report
• Prepared By: Duncan Axisia
• Date: 12/31/2005
• Weather Modification - Doc Type: Report

pattern of a high-pressure ridge over the desert
southwest. A prolonged east to west flow in
the lower levels of the atmosphere increases
the moisture from the eastem plains to the
Continental Divide. Most of the convection
remains confined to the mountainous areas of
southwest Texas and southeastern New
Mexico due to upslope low-level winds and
upslope flow. Other areas rely on diurnal
heating and humid conditions with some upper
air support from disturbances rotating in the
periphery of the high pressure for convection.
When an upper level low pressure develops in
the northern Pacific, the ridge breaks down and
a trough pushes an occasional cool front,
bringing some temporary relief from the heat in
the Mid West and the Great Plains. However,
these fronts usually stall to the north of the
region due to a strong southerly flow.

The latter part of the growing season is
characterized by the onset of the Mexican
Monsoon in southern and southeastern New
Mexico. The main synoptic feature is a
persistent broad high-pressure ridge at the
upper levels meandering over the southern
plains and the desert southwest. This feature
increases the convective inhibition due to
synoptic scale subsidence over the region.
The convective energy is weak and convection
is hard to forecast due to the lack of a surface
feature. The sea level pressure of the
southwestern United States decreases
significantly and leads to the development of a
thermally induced trough in the desert
southwest. Surges of tropical continental air
with convection along this trough are very
common. Tropical maritime influences from
the Gulf of Mexico are also observed even
though most of this moisture remains to the
southeast. During this period the ridge over
the western United States weakens as the
monsoon high retreats southward and Mexican
Monsoon precipitation diminishes. The decay
phase is also accompanied by an increase in
rainfall over much of the surrounding region
(Okabe, 1995).

Meteorological summary for the
Southern Ogallala target area

For the purpose of this summary, monthly
rainfall data is analyzed from 106 rain gauges

scattered across the counties in Yoakum, Terry
and Gaines (1 rain gauge every 19320 acres).
Each rain gauge is read once a month from
April through September. These rain gauges
consist of a fence-post rain gauge having
tubing to individual, sealed, subterranean
collector reservoirs. These rain gauges do not
measure rainfall in real time, and the density of
rain gauges is very low which makes them
unsuitable for cloud seeding evaluation
purposes. This data is presented in contour
plots attached in this section of the report. No
rain gauge data has been made available in
the New Mexico target.

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April 2005

April began with an exiting low pressure over
Oklahoma, which gave west Texas a
southwesterly flow and above average temps
in the mid 70's to low 80's. This pattern also
helped maintain strong winds as a high
pressure was established to the east. By April
6th another low moving out of the southern
Rockies finally shifted the winds out of the
north, relieving the area of the strong
southwesterly winds. An upper level ridge
moved in behind the exiting system to the
north, again providing the Southern Ogallala
target with above average temperatures,
continued light and variable winds and a few
high clouds across the region. As the ridge
translated east, a series of low-level short wave
systems moved out of the Rockies again
driving a southwesterly flow and causing high
winds in the area. To the south, the National
Weather Service issued several high wind
advisories for the Big Bend area.

Finally by the 10th an impressive upper level
low over the 'Four Corners' region of the
country broke the pattem and moved through
the northern panhandle of Texas northeast
through Oklahoma and in to the central plains.
The winds shifted and became northerly and
weakened significantly but temperatures still
remained in the mid 70's cooling down in to the
mid 40's during the nighttime hours. The
Southern Ogallala target area remained in a
dry pattem as an upper level ridge and surface
high pressure dominated until finally on April
15th the ridge moved east and provided strong
southeasterly wind accompanied by a Gulf

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