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Climate of 2006 - June
U.S. Drought Watch

National Climatic Data Center, 13 July 2006

Global Analysis / Global Hazards / United States / Extremes
Use these links to access detailed analyses of Global and U.S. data.

Contents Of This Report:

National Drought Overview
Detailed Drought Discussion
State/Regional/National Moisture Status
Pre-Instrumental Perspective
Drought Indicators
Additional Contacts
Questions

National Overview

Based on the Palmer Drought Index, severe to extreme drought affected about 27 percent of the contiguous United States as of the end of June 2006, an increase of about 7 percent compared to last month. By contrast, about 8 percent of the contiguous U.S. fell in the severely to extremely wet categories.
About 45 percent of the contiguous U.S. fell in the moderate to extreme drought categories (based on the Palmer Drought Index) at the end of June.
On a broad scale, the previous two decades (1980s and 1990s) were characterized by unusual wetness with short periods of extensive droughts, whereas the 1930s and 1950s were characterized by prolonged periods of extensive droughts with little wetness (moderate to extreme drought, severe to extreme drought).

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 quotes).

Detailed Drought Discussion

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 historical record).

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 Southeast.

Map showing 3-month Standardized Precipitation Index

The June precipitation pattern at the primary stations in Alaska was below normal in most of the southeast part of the state. Across Hawaii, 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 National Weather Service radar estimates of precipitation.

Map showing June State Precipitation Ranks

Some regional highlights:

Several states had the tenth driest, or drier, multi-month seasons (April-June, January-June, July-June).
Month-averaged and end-of-month soil moisture conditions, based on model computations (CPC-1, CPC-2, MRCC), were drier than normal across a broad swath from the Southwest and central Plains to the Atlantic coast. At depth, soil moisture across 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.

Western U.S. percentage area wet and dry, 1996-2006

Drought conditions in the Southwest continued during June. About 35 percent of the western U.S. (Rockies westward) fell in the moderate to extreme drought category, and about 25 percent fell in the severe to extreme category (as defined by the Palmer Drought Index) as of the end of June. The percent of average basin precipitation at the end of the month reflected the very dry conditions in Arizona and New Mexico.
Drought impacts during June included the Governors of Nebraska, South Dakota, Texas and Alabama requesting drought declarations from USDA for many counties in their respective states. According to media sources, farmers in most of the Southwest and western Plains have been affected by drought. Dry conditions also led to dozens of large fires in the West.

State/Regional/National Moisture Status

A detailed review of drought and moisture conditions is available for all contiguous U.S. states, the nine standard regions, and the nation (contiguous U.S.):

STATES:

Alabama	Arizona	Arkansas	California	Colorado	Connecticut
Delaware	Florida	Georgia	Idaho	Illinois	Indiana
Iowa	Kansas	Kentucky	Louisiana	Maine	Maryland
Massachusetts	Michigan	Minnesota	Mississippi	Missouri	Montana
Nebraska	Nevada	New Hampshire	New Jersey	New Mexico	New York
North Carolina	North Dakota	Ohio	Oklahoma	Oregon	Pennsylvania
Rhode Island	South Carolina	South Dakota	Tennessee	Texas	Utah
Vermont	Virginia	Washington	West Virginia	Wisconsin	Wyoming*

* State page has supplemental information.

REGIONS:

Northwest	West North Central	East North Central
Northeast	Central	Southeast
South	Southwest	West

Map showing the nine U.S. standard regions

NATIONAL:

Contiguous U.S.

Pre-Instrumental Perspective

June 2006 Paleoclimatic Analysis for Southern Wyoming

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".

1996-2006 Wyoming Division 10 monthly precipitation anomaly

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Precipitation Ranks for
Wyoming Division 10, 2005-2006
Period	Rank
Jun	36^th driest
May-Jun	23^rd driest
Apr-Jun	21^st driest
Mar-Jun	15^th driest
Feb-Jun	13^th driest
Jan-Jun	8^th driest
Dec-Jun	12^th driest
Nov-Jun	10^th driest
Oct-Jun	15^th driest
Sep-Jun	7^th driest
Aug-Jun	6^th driest
Jul-Jun	5^th driest

July-June Wyoming Division 10 precipitation, 1895-2006

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Wyoming Division 10 Palmer Hydrological Drought Index, 1900-2006

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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.

Paleoclimatic tree-ring reconstruction and observed precipitation for Wyoming Division 10 for the total period 1520-2006

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larger image (220 KB)

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; yellow arrow).

Resources:

Divisional climate data, including precipitation for Wyoming Division 10 as shown above, can be obtained from NCDC.
Tree-ring data, including the chronologies for North Park Update, Big Thompson Update, and Plug Hat Butte (Colorado), and Encampment (Wyoming), can be obtained from the International Tree-Ring Data Bank (ITRDB), World Data Center for Paleoclimatology.

Reference:

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 2006.

Drought Indicators

The following indicators illustrate the drought conditions this month:

Palmer Drought Indices,
Standardized Precipitation Index,
long-term (36 to 60 month) percent of normal precipitation maps,
statewide precipitation rank maps,
Cooperative station percent of normal precipitation maps,
percent of average maps for the SNOTEL stations in the western mountains provided by the Western Regional Climate Center
- hydrologic year precipitation,
satellite-based observations of vegetative health,
National Weather Service model calculations of
National Weather Service model calculations of soil moisture using the Leaky Bucket Model,
Midwest Regional Climate Center model calculations of soil moisture,
streamflow maps maintained by the USGS.

Additional Contacts:

For all climate questions other than questions concerning this report, please contact the National Climatic Data Center's Climate Services Division:

Climate Services Division
NOAA/National Climatic Data Center
151 Patton Avenue
Asheville, NC 28801-5001
fax: 828-271-4876
phone: 828-271-4800
email: ncdc.info@noaa.gov
For further information on the historical climate perspective presented in this report, contact:

Richard Heim
NOAA/National Climatic Data Center
151 Patton Avenue
Asheville, NC 28801-5001
fax: 828-271-4328
email: Richard.Heim@noaa.gov

-or-

Ned Guttman
NOAA/National Climatic Data Center
151 Patton Avenue
Asheville, NC 28801-5001
fax: 828-271-4328
email: Ned.Guttman@noaa.gov

-or-

Jay Lawrimore
NOAA/National Climatic Data Center
151 Patton Avenue
Asheville, NC 28801-5001
fax: 828-271-4328
email: Jay.Lawrimore@noaa.gov