WMOD00259

• Applicant: Western Kansas Groundwater Management
• Project Name: Western Kansas Weather Modification Program
• Date: 1/1/1999
• Weather Modification - Doc Type: Report

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VI. RAINFALL DISTRIBUTION

Seasonal rainfall in Western Kansas in 1999 turned out to be a normal, to above normal,
for most areas with few exceptions. Storm activity the first half of the season---into early.July,
. tended to be more severe than one would normally expect in large part due to the greater than
unusually high number of days in which the Jet Stream layover the region while having an
abundance ofabnorma1ly high dew-point moisture in the low-levels of the atmosphere. Storms
developing under these circumstances are usually persistent and often produce voluminous
amounts of moisture in a short period of time.

Moisture maps have been produced at the NOAAlUSDA Joint Weather Facility in
Washington, D.C. showing the short-term Crop Moisture index and the long-term Palmer
Drought Severity index for the USA. Figs. 8-19, on pages 39 - 44, show the short and long-term
changes during the 1999 season. The short-term Crop Moisture index is released every week
while the long-term Drought Severity index is released every second week. The periodical,
"Weekly Weather and Crop Bulletin" present them as they become available and they are available
on the Internet at the Joint Agricultural Weather Facility (JAWF) website.

The Crop Moisture index is a measure of the more rapid response to rainfall over a short-
term period, almost from week to week. The figures show the changes valid at the dates given
for it. Not all months periods are presented.

The Palmer long-term Drought Severity Index shows USA soil moisture conditions for
the period of time which nearly parallels our WKWi\1P season and is not prone to short-term
moisture changes. The index is developed from official measurements made at second-order
weather observing sites, around 30 - 40 miles apart in our area. Normally, this index takes periods
of weeks or months to change, not days. While not perfect at the smallest geographical locations,
the areaSshown generally tend to exhibit the a near, real-world crop moisture pattern existing in
the region.

As the crop-year began, crop moisture was generally sufficient around Western Kansas.
Figures 8 through 15 show the short term moisture conditions in Kansas and the larger pattern
around the USA. The reader can see how widespread the moisture, or the lack of it, was
distributed in all directions. Moisture by May 1st was rated "Favorably Moist" to "Abnormally
Moist" over all of Western Kansas. From then until late June, except in extreme NW Kansas,
short-term moisture continued to be rated "Favorably Moist" in the rest of Western Kansas. In
NW Kansas there was a short dry spell beginning in early to mid-May that ran into early June.
However, by late June to early July, drier conditions developed in Western Kansas including NW
Kansas, however, conditions were rated only as "Slightly Dry." The slightly dry region was
generally a triangular-shaped area appearing from near Hamilton Cou.nty to the NE through
Rawlins County and thence west toward the Colorado State line. Moisture tended to be on and
off for Western Kansas for the remainder of the growing season such that when the WKWMP

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