Tuesday, 9 January 2018: 2:00 PM
616 AB (Hilton) (Austin, Texas)
Monthly precipitation totals over the western Great Plains peak from April to August, but most of these warm season totals are delivered in a few extreme daily events. Tree-ring chronologies of annual ring width tend to be highly correlated with the long-term soil moisture balance, but the last formed latewood cells that terminate the growth rings are very distinctive in High Plains ponderosa pine. These latewood growth cells can be exactly dated, separately measured, and adjusted to remove the biological memory of prior earlywood growth. Adjusted latewood chronologies from the northern and central Great Plains were developed from ponderosa pine and are significantly correlated with monthly July precipitation (r = 0.68 for both regions). But these latewood chronologies appear to be most sensitive to meteorological timescale rainfall, and higher correlations are computed for accumulated 10-day totals within the month of July using the Climate Prediction Center’s 0.25 x 0.25° Unified Range Gauge Dataset (r = 0.75 and 0.79 for the northern and central Great Plains study areas). In fact, most of the variance in these adjusted latewood chronologies can be explained by annual time series based only on the wettest single day within the optimal 10-day July window, with correlations of r = 0.64 and 0.70 calculated for the northern and central Plains from 1948 to 1990 and 1948-1997. Spatially, the Northern Plains chronologies are highly correlated with 10-day precipitation totals across a broad area of the northern United States (Montana to Iowa), apparently reflecting the NW-SE propagation of mesoscale convective systems tracking upper-level airflow. The Central Plains chronologies are correlated with precipitation in east-central Colorado and western Kansas, often representing convective precipitation that develops along the Front Range and propagates eastward during the evening and nighttime hours, usually associated with an enhanced North American monsoon.
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