WMOD00079

• Contract/Permit #: #98-1
• Applicant: Western Kansas Groundwater
• Project Name: Kansas Weather Modification
• Date: 1/1/1998
• Weather Modification - Doc Type: Report

VI. RAINFALL DISTRIBUTION

1998 was an interesting year for precipitation. In late fall of 1997 moisture was becoming
scarce in Western Kansas but was interrupted by a blizzard hitting in October, dumping around 12"
of snow and providing widespread moisture to the region. Thereafter, it was mostly dry until a couple
of blizzards hit us again this March, the month most usually associated with blizzards in this area.
Again, moisture was widespread and contributed considerably to improving the overall conditions of
the wheat crop so that by the time the program began in late April, general moisture conditions
generally were favorable.

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. Pages 34 - 38 (Figs. 7 - 16) show the approximate monthly changes as
the 1998 progressed. The shdrt-teirn 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.

The Crop Moisture index is a measure of the more rapid response to rainfall over a shorter
period, or lack of it, almost from week to week. The figures show the changes valid at the dates given
for that index this season. Not all months are presented.

The Palmer long-term Drought Severity Index shows USA soil moisture conditions for the
period of time which nearly parallels our WKWMP 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 scales, the categorized areas shown generally
tend to exhibit the real-world crop moisture pattern.

Seasonal rainfall began becoming more prevalent in May, however, by late May we entered
a period of generally much drier conditions with June being a hot and very dry month until the last the
very last part of it. By July 4th (Figs. 10, 11), the WKWMP was abnormally dry in short-term
moisture but the long-term was still good. As we moved into July it became just the opposite. Some
areas in Logan and Wichita counties recorded 12" to 13" of rainfall for the month. August I st (Figs.
12, 13) show the WKWMP again Favorably Moist to Abnormally Moist on the short-term index and
looked above average in the long-term. Moisture tapered off again becoming mostly dry through
August and very much drier through September. Figs. 15 and 16, near the time the program ended,
show that short-term moisture had turned Slightly Dry to Severely Dry; the driest being in SW Kansas.
Even drier conditions existed further southwest across large areas of New Mexico, Oklahoma, Texas,
Arizona and Colorado. The long-term drought severity was about normal for Western Kansas,
however, conditions had turned Extremely Dry to Severely Dry over large areas of Texas, Oklahoma'
and New Mexico. Fortunately for Western Kansas, on the evening of Sept. 30th, rain was widespread
with many areas receiving around an inch of rain.

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