NCDC added Alaska climate divisions to its nClimDiv dataset on Friday, March 6, 2015, coincident with the release of the February 2015 monthly monitoring report. For more information on this data, please visit the Alaska Climate Divisions FAQ.
- A file containing the national monthly percent area severely
dry and wet from 1900 to present is available for the severe to extreme and moderate to extreme categories.
- Historical temperature, precipitation, and Palmer drought data
from 1895 to present for climate divisions, states, and regions in
the contiguous U.S. are available at the Climate Division:
Temperature-Precipitation-Drought Data page in files having
names that start with "drd964x" and ending with "txt" (without the
|Dryness was observed in
June over much
of the country west of the Appalachians. The Southwest, western
Texas, western High Plains and the south Atlantic states have
experienced very dry conditions for the last
several months. The most severe conditions at the end of June
were in the Desert Southwest and
western Plains, and along parts of the western Gulf coast.
About 9 percent of the contiguous U.S. was very
dry (i.e., precipitation in the bottom 10th percentile of the
Coupled with the very dry conditions were continuing high
temperatures in the Southwest
and western Plains. The combination of high temperatures and
very little precipitation led to extreme drought as defined by the
Palmer Z Index.
Heavy rain near the end of the month in the mid-Atlantic States
alleviated dry conditions, but dryness continued in most of the
The June precipitation pattern at the primary stations in Alaska
was below normal in most of the southeast part of the state. Across
the precipitation pattern remained dry in the Northwest and became
progressively drier towards the Southeast. In Puerto
Rico, the month was predominantly dry in the central and
western interior areas and along the northeast coast, based on
Weather Service radar estimates of precipitation.
Some regional highlights:
- Several states had the tenth driest, or drier, multi-month
soil moisture conditions, based on model computations (CPC-1,
MRCC), were drier than normal across a broad swath from the
Southwest and central Plains to the Atlantic coast. At depth, soil
eastern Nebraska and Kansas continued much below normal.
- Low streamflows,
as computed by models and based on USGS observations,
continued in the Southeast westward and northward into the
Southwest and northern Plains.
State/Regional/National Moisture Status
June 2006 Paleoclimatic Analysis for Southern
|The past year has seen
a deepening of the long-term drought conditions that have persisted
since late 1999 in southern Wyoming. Since July 2005, precipitation
in Wyoming Division
10 (Upper Platte basin) has been below normal in 10 of 12
months, totaling only 73% of normal during the period. Both the
Palmer Hydrological Drought Index (PHDI) and Palmer Drought
Severity Index (PDSI) for Division 10 have values below -4 for late
June 2006, indicating "extreme drought".
|The graph below
(annual values in light blue, 5-year weighted average in dark blue)
shows the annual (July-June) precipitation, 1896-2006, for Wyoming
Division 10. The value for 2006 (8.55 inches) is the 5th lowest
since 1896. The most persistent multi-year drought, with five
consecutive years of below-normal precipitation, was 2000-2004.
There were also several four-year droughts, including 1933-1936
(the Dust Bowl) and 1953-1956. The 1950s drought (indicated with
the orange arrow) is similar to the present one in that several
below-normal years were followed by an average year (1957, 2005),
and then a return to drought conditions, which in the 1950s lasted
for four more years. The 1950s drought and the 2000-2004 drought
were also similar in overall severity.
large image (50 KB)
larger image (220
|The graph to the left
also shows a 481-year tree-ring record (1520-2000; annual values in
light red; 5-year smoothed values in dark red) that corresponds
well to the variability in July-June precipitation. This record is
the average of four tree-ring chronologies (Douglas-fir and pinyon
pine) from Wyoming and Colorado. The correlation between the annual
values of the tree-ring record and July-June precipitation is
0.633, indicating a high degree of shared variance. The tree-ring
record captures the multi-year variability of the observed
precipitation record particularly well.
|The tree-ring record,
as a proxy for precipitation, can put the annual precipitation
variability of the last century in southern Wyoming into a much
longer perspective. The tree rings indicate that about a dozen
individual years prior to 1896 had lower tree growth than any year
since then, suggesting these were years with annual precipitation
lower than the lowest values in the past century. Turning to
multi-year events, the average ring-width anomalies for the
four-year periods 1665-1668 and 1845-1848 (red arrows) are very
similar to that for 1953-1956, suggesting that those periods were
droughts of similar severity to the 1950s. There are also four
different periods before 1896 when the ring-width index was below
average for more than five years in a row, including a nine-year
period just before the start of the instrumental record (1886-1894;
- Woodhouse, C.A., S.T. Gray, and D.M. Meko, 2006. "Updated
streamflow reconstructions for the Upper Colorado River basin."
Water Resources Research 42, W05415, 11 May