Ag Weather Forum

Too Much, Enough, or Too Little?

Bryce Anderson
By  Bryce Anderson , Ag Meteorologist Emeritus
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"Flooding rains in southern Nebraska and northern Kansas illustrate extreme precipitation in central U.S. storms the week of May 3-9." (NOAA graphic by Nick Scalise)

The past week was indeed one of precipitation extremes across the U.S. Storm and situation reports bear that out. At the end of the week, there were areas which had over-the-top excessive rainfall, the more-or-less right amount to heal some dryness, or measurements which serve to reinforce a long-term calamity.

First, the "excessives". As the illustration for this entry shows, a swath of outsize rain amounts ran from southeastern Nebraska to north-central Kansas in a heavy rain outbreak Wednesday, May 6. Rainfall totals topped 11 inches. Flooding was widespread in this area. Crop loss is possible, of course, with this kind of heavy rain, and there was significant damage to homes and businesses. The heavy rain was called a "one in a thousand years" event in Lincoln, Nebraska.

Central Oklahoma also was the scene of very heavy rain along with tornado damage. Tornado development is of course not a rare occurrence in the southern Plains. But the rainfall was unprecedented. Oklahoma City took in more than seven inches of rain in one day on Wednesday, May 6, with some area communities totaling more than eight inches. For the first time ever, Oklahoma City had a flash flood emergency issued.

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These two headline features illustrate--again--one of the key points regarding climate change effects that scientists have noted in their research, which is that rainfall in the central U.S. is likely to more and more show up heavy amounts at one time. This facet, over a period of years, is unfavorable for soil moisture supplies, because such heavy precipitation either runs off or evaporates.

Not all the rainfall was too much of a good thing. Take Lubbock, Texas for example. On Monday and Tuesday, May 4 and 5, Lubbock had rainfall totaling 4.5 inches. For the year through Thursday, May 7, Lubbock has had 8.6 inches of precipitation, more than four inches above normal, and far more than the .90 inches for the year at this same time in 2014. Moisture fortunes have indeed improved in the southern Texas Panhandle.

More detail on rainfall totals is here: http://water.weather.gov/…

Now to the ongoing calamity--more dryness in the western U.S. This week's fifth 2015 snowpack forecast for the western U.S. issued by the USDA Natural Resources Conservation Service (NRCS) said that west-wide snowpack has mostly melted. NRCS hydrologist David Garen said that "Across most of the West, snowpack isn't just low--it's gone. With some exceptions, this year's snowmelt streamflow has already occurred." For much of the western U.S., the snowpack at many stations is at or near the lowest on record. Months of unusually warm temperatures hindered snowpack growth and accelerated its melt. The only areas with some snowpack still left are northern Colorado, western Montana and southern Wyoming.

A detailed look at the NRCS snowpack (or lack of) forecast is here: http://www.wcc.nrcs.usda.gov/…

Bryce

Twitter @BAndersonDTN

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