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HOME
> Monitoring
& Data > Drought Indicator Blends |
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Experimental
Objective Blends of Drought Indicators
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Long-Term
and Short-Term
Percentiles
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Product
Description
Comments on these new products
are encouraged and can be entered here.
|
(Click
on the maps or links below for larger images) |
![](lbfinal.gif)
Long-Term Blend at screen resolution, or
high-resolution PDF
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![](sbfinal.gif)
Short-Term Blend at screen resolution, or
high-resolution PDF
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Both
maps on one page at screen resolution, or
High-resolution PDF of both maps on one
page
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LONG-TERM
BLEND COMPONENT PERCENTILES: Modeled Soil Moisture,
Palmer Hydrologic Drought Index, 6-Month Precipitation, 1-Year
Precipitation, 2-Year Precipitation, & 5-Year
Precipitation
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SHORT-TERM
BLEND COMPONENT PERCENTILES: Z-Index, 30-Day
Precipitation,
3-Month Precipitation, Modeled
Soil Moisture, & Palmer (modified)
Drought Index
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Maps
of Long- & Short-Term Drought Indicator Percentile
Changes from previous week at screen resolution,
or
High-resolution PDF
|
Table
of drought coverage for selected severity levels (% of
contiguous U.S.)
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Map
Archive |
Long-Term
Blend |
Short-Term
Blend |
July 19, 2008
July 12, 2008
July 5, 2008
June 28, 2008
June 21, 2008
June 14, 2008
June 7, 2008
May 31, 2008
May 25, 2008
May 17, 2008
May 10, 2008
May 4, 2008
April 26, 2008
April 19, 2008
April 12, 2008
April 5, 2008
March 29, 2008
March 22, 2008
March 15, 2008
March 8, 2008
March 2, 2008
February 23, 2008
February 17, 2008
February 9, 2008
February 4, 2008
January 26, 2008
January 20, 2008
January 12, 2008
January 5, 2008
December 31, 2007
December 22, 2007
December 15, 2007
December 9, 2007
December 1, 2007
November 24, 2007
November 18, 2007
November 11, 2007
November 3, 2007
October 27, 2007
October 20, 2007
October 14, 2007
October 7, 2007
September 30, 2007
September 22, 2007
September 15, 2007
September 8, 2007
September 1, 2007
August 25, 2007
August 18, 2007
August 11, 2007
August 4, 2007
July 28, 2007
July 22, 2007
July 14, 2007
July 7, 2007
June 30, 2007
June 23, 2007
June 16, 2007
June 9, 2007
June 4, 2007
May 28, 2007
May 19, 2007
May 12, 2007
May 5, 2007
April 9, 2007
April 2, 2007
March 25, 2007
March 17, 2007
March 11, 2007
March 3, 2007
February 24, 2007
February 17, 2007
January 27, 2007
January 20, 2007
January 13, 2007
January 6, 2007
December 31, 2006
December 25, 2006
December 16, 2006
December 10, 2006
December 4, 2006
November 25, 2006
November 18, 2006
November 4, 2006
October 28, 2006
October 21, 2006
October 15, 2006
October 9, 2006
September 30, 2006
September 24, 2006
September 16, 2006
September 9, 2006
September 3, 2006
August 26, 2006
August 19, 2006
August 12, 2006
August 5, 2006
July 30, 2006
July 15, 2006
July 9, 2006
July 1, 2006
June 25, 2006
June 18, 2006
June 10, 2006
June 4, 2006
May 29, 2006
May 20, 2006
May 14, 2006
May 7, 2006
April 30, 2006
April 23, 2006
April 16, 2006
April 8, 2006
April 2, 2006
March 25, 2006
March 19, 2006
March 11, 2006
March 6, 2006
February 25, 2006
February 18, 2006
February 11, 2006
February 4, 2006
January 28, 2006
January 21, 2006
January 14, 2006
January 7, 2006
December 31, 2005
December 24, 2005
December 17, 2005
December 10, 2005
December 3, 2005
November 26, 2005
November 19, 2005
November 12, 2005
November 5, 2005
October 29, 2005
October 22, 2005
October 15, 2005
October 8, 2005
October 1, 2005
September 24, 2005
September 17, 2005
September 10, 2005
September 3, 2005
August 27, 2005
August 20, 2005
August 13, 2005
August 6, 2005
July 30, 2005
July 23, 2005
July 16, 2005
July 9, 2005
July 2, 2005
June 25, 2005
June 18, 2005
June 11, 2005
June 4, 2005
May 28, 2005
May 21, 2005
May 14, 2005
May 7, 2005
April 30, 2005
April 23, 2005
April 16, 2005
April 9, 2005
April 2, 2005
March 26, 2005
March 19, 2005
March 12, 2005
March 5, 2005
February 26, 2005
February 19, 2005
February 12, 2005
February 5, 2005
January 29, 2005
January 22, 2005
January 15, 2005
January 8, 2005
January 1, 2005
December 25, 2004
December 18, 2004
December 11, 2004
December 4, 2004
November 27, 2004
November 20, 2004
November 13, 2004
November 6, 2004
October 30, 2004
October 23, 2004
October 16, 2004
October 9, 2004
October 2, 2004
September 25, 2004
September 18, 2004
September 11, 2004
September 4, 2004
August 28, 2004
August 21, 2004
August 14, 2004
August 7, 2004
July 31, 2004
July 24, 2004
July 17, 2004
July 10, 2004
July 3, 2004
June 26, 2004
June 19, 2004
June 12, 2004
June 5, 2004
May 29, 2004
May 22, 2004
May 15, 2004
May 8, 2004
May 1, 2004
Apr. 24, 2004
Apr. 17, 2004
Apr. 10, 2004
Apr. 3, 2004
Mar. 27, 2004
Mar. 20, 2004
Mar. 13, 2004
Mar. 6, 2004
Feb. 28, 2004
Feb. 21, 2004
Feb. 14, 2004
Feb. 7, 2004
Jan. 31, 2004
Jan. 24, 2004
Jan. 17/18, 2004
Jan. 10, 2004
Jan. 3, 2004
Dec. 27, 2003
Dec. 20, 2003
Dec. 13, 2003
Dec. 6, 2003
Nov. 29, 2003
Nov. 22, 2003
Nov. 15, 2003
Nov. 8, 2003
Nov. 1, 2003
Oct. 25, 2003
Oct. 18, 2003
Oct. 11, 2003
Oct. 4, 2003
Sep. 27, 2003
Sep. 20, 2003
Sep. 13, 2003
Sep. 6, 2003
Aug. 30 / Sep. 1, 2003
August 23, 2003
August 16, 2003
August 9, 2003
August 2, 2003
July 26, 2003
July 19, 2003
July 12, 2003
July 5, 2003
June 28, 2003
June 21, 2003
June 14, 2003
June 7, 2003
May 31, 2003
May 24, 2003
May 17, 2003
May 10, 2003
May 3, 2003
April 26, 2003
April 19, 2003
April 12, 2003
April 5, 2003
March 29, 2003
March 22, 2003
March 15, 2003
March 8, 2003
March 1, 2003
February 22, 2003
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July 19, 2008
July 12, 2008
July 5, 2008
June 28, 2008
June 21, 2008
June 14, 2008
June 7, 2008
May 31, 2008
May 25, 2008
May 17, 2008
May 10, 2008
May 4, 2008
April 26, 2008
April 19, 2008
April 12, 2008
April 5, 2008
March 29, 2008
March 22, 2008
March 15, 2008
March 8, 2008
March 2, 2008
February 23, 2008
February 17, 2008
February 9, 2008
February 4, 2008
January 26, 2008
January 20, 2008
January 12, 2008
January 5, 2008
December 31, 2007
December 22, 2007
December 15, 2007
December 9, 2007
December 1, 2007
November 24, 2007
November 18, 2007
November 11, 2007
November 3, 2007
October 27, 2007
October 20, 2007
October 14, 2007
October 7, 2007
September 30, 2007
September 22, 2007
September 15, 2007
September 8, 2007
September 1, 2007
August 25, 2007
August 18, 2007
August 11, 2007
August 4, 2007
July 28, 2007
July 22, 2007
July 14, 2007
July 7, 2007
June 30, 2007
June 23, 2007
June 16, 2007
June 9, 2007
June 4, 2007
May 28, 2007
May 19, 2007
May 12, 2007
May 5, 2007
April 9, 2007
April 2, 2007
March 25, 2007
March 17, 2007
March 11, 2007
March 3, 2007
February 24, 2007
February 17, 2007
January 27, 2007
January 20, 2007
January 13, 2007
January 6, 2007
December 31, 2006
December 25, 2006
December 16, 2006
December 10, 2006
December 4, 2006
November 25, 2006
November 18, 2006
November 4, 2006
October 28, 2006
October 21, 2006
October 15, 2006
October 9, 2006
September 30, 2006
September 24, 2006
September 16, 2006
September 9, 2006
September 3, 2006
August 26, 2006
August 19, 2006
August 12, 2006
August 5, 2006
July 30, 2006
July 15, 2006
July 9, 2006
July 1, 2006
June 25, 2006
June 18, 2006
June 10, 2006
June 4, 2006
May 29, 2006
May 20, 2006
May 14, 2006
May 7, 2006
April 30, 2006
April 23, 2006
April 16, 2006
April 8, 2006
April 2, 2006
March 25, 2006
March 19, 2006
March 11, 2006
March 6, 2006
February 25, 2006
February 18, 2006
February 11, 2006
February 4, 2006
January 28, 2006
January 21, 2006
January 14, 2006
January 7, 2006
December 31, 2005
December 24, 2005
December 17, 2005
December 10, 2005
December 3, 2005
November 26, 2005
November 19, 2005
November 12, 2005
November 5, 2005
October 29, 2005
October 22, 2005
October 15, 2005
October 8, 2005
October 1, 2005
September 24, 2005
September 17, 2005
September 10, 2005
September 3, 2005
August 27, 2005
August 20, 2005
August 13, 2005
August 6, 2005
July 30, 2005
July 23, 2005
July 16, 2005
July 9, 2005
July 2, 2005
June 25, 2005
June 18, 2005
June 11, 2005
June 4, 2005
May 28, 2005
May 21, 2005
May 14, 2005
May 7, 2005
April 30, 2005
April 23, 2005
April 16, 2005
April 9, 2005
April 2, 2005
March 26, 2005
March 19, 2005
March 12, 2005
March 5, 2005
February 26, 2005
February 19, 2005
February 12, 2005
February 5, 2005
January 29, 2005
January 22, 2005
January 15, 2005
January 8, 2005
January 1, 2005
December 25, 2004
December 18, 2004
December 11, 2004
December 4, 2004
November 27, 2004
November 20, 2004
November 13, 2004
November 6, 2004
October 30, 2004
October 23, 2004
October 16, 2004
October 9, 2004
October 2, 2004
September 25, 2004
September 18, 2004
September 11, 2004
September 4, 2004
August 28, 2004
August 21, 2004
August 14, 2004
August 7, 2004
July 31, 2004
July 24, 2004
July 17, 2004
July 10, 2004
July 3, 2004
June 26, 2004
June 19, 2004
June 12, 2004
June 5, 2004
May 29, 2004
May 22, 2004
May 15, 2004
May 8, 2004
May 1, 2004
Apr. 24, 2004
Apr. 17, 2004
Apr. 10, 2004
Apr. 3, 2004
Mar. 27, 2004
Mar. 20, 2004
Mar. 13, 2004
Mar. 6, 2004
Feb. 28, 2004
Feb. 21, 2004
Feb. 14, 2004
Feb. 7, 2004
Jan. 31, 2004
Jan. 24, 2004
Jan. 17/18, 2004
Jan. 10, 2004
Jan. 3, 2004
Dec. 27, 2003
Dec. 20, 2003
Dec. 13, 2003
Dec. 6, 2003
Nov. 29, 2003
Nov. 22, 2003
Nov. 15, 2003
Nov. 8, 2003
Nov. 1, 2003
Oct. 25, 2003
Oct. 18, 2003
Oct. 11, 2003
Oct. 4, 2003
Sep. 27, 2003
Sep. 20, 2003
Sep. 13, 2003
Sep. 6, 2003
Aug. 30 / Sep. 1, 2003
August 23, 2003
August 16, 2003
August 9, 2003
August 2, 2003
July 26, 2003
July 19, 2003
July 12, 2003
July 5, 2003
June 28, 2003
June 21, 2003
June 14, 2003
June 7, 2003
May 31, 2003
May 24, 2003
May 17, 2003
May 10, 2003
May 3, 2003
April 26, 2003
April 19, 2003
April 12, 2003
April 5, 2003
March 29, 2003
March 22, 2003
March 15, 2003
March 8, 2003
March 1, 2003
February 22, 2003
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Coverage
Table Archive |
July 19, 2008
July 12, 2008
July 5, 2008
June 28, 2008
June 21, 2008
June 14, 2008
June 7, 2008
May 31, 2008
May 25, 2008
May 17, 2008
May 10, 2008
May 4, 2008
April 26, 2008
April 19, 2008
April 12, 2008
April 5, 2008
March 29, 2008
March 22, 2008
March 15, 2008
March 8, 2008
March 2, 2008
February 23, 2008
February 17, 2008
February 9, 2008
February 4, 2008
January 26, 2008
January 20, 2008
January 12, 2008
January 5, 2008
December 31, 2007
December 22, 2007
December 15, 2007
December 9, 2007
December 1, 2007
November 24, 2007
November 18, 2007
November 11, 2007
November 3, 2007
October 27, 2007
October 20, 2007
October 14, 2007
October 7, 2007
September 30, 2007
September 22, 2007
September 15, 2007
September 8, 2007
September 1, 2007
August 25, 2007
August 18, 2007
August 11, 2007
August 4, 2007
July 28, 2007
July 22, 2007
July 14, 2007
July 7, 2007
June 30, 2007
June 23, 2007
June 16, 2007
June 9, 2007
June 4, 2007
May 28, 2007
May 19, 2007
May 12, 2007
May 5, 2007
April 9, 2007
April 2, 2007
March 25, 2007
March 17, 2007
March 11, 2007
March 3, 2007
February 24, 2007
February 17, 2007
January 27, 2007
January 20, 2007
January 13, 2007
January 6, 2007
December 31, 2006
December 25, 2006
December 16, 2006
December 10, 2006
December 4, 2006
November 25, 2006
November 18, 2006
November 4, 2006
October 28, 2006
October 21, 2006
October 15, 2006
October 9, 2006
September 30, 2006
September 24, 2006
September 16, 2006
September 9, 2006
September 3, 2006
August 26, 2006
August 19, 2006
August 12, 2006
August 5, 2006
July 30, 2006
July 15, 2006
July 9, 2006
July 1, 2006
June 25, 2006
June 18, 2006
June 10, 2006
June 4, 2006
May 29, 2006
May 20, 2006
May 14, 2006
May 7, 2006
April 30, 2006
April 23, 2006
April 16, 2006
April 8, 2006
April 2, 2006
March 25, 2006
March 19, 2006
March 11, 2006
March 6, 2006
February 25, 2006
February 18, 2006
February 11, 2006
February 4, 2006
January 28, 2006
January 21, 2006
January 14, 2006
January 7, 2006
December 31, 2005
December 24, 2005
December 17, 2005
December 10, 2005
December 3, 2005
November 26, 2005
November 19, 2005
November 12, 2005
November 5, 2005
October 29, 2005
October 22, 2005
October 15, 2005
October 8, 2005
October 1, 2005
September 24, 2005
September 17, 2005
September 10, 2005
September 3, 2005
August 27, 2005
August 20, 2005
August 13, 2005
August 6, 2005
July 30, 2005
July 23, 2005
July 16, 2005
July 9, 2005
July 2, 2005
June 25, 2005
June 18, 2005
June 11, 2005
June 4, 2005
May 28, 2005
May 21, 2005
May 14, 2005
May 7, 2005
April 30, 2005
April 23, 2005
April 16, 2005
April 9, 2005
April 2, 2005
March 26, 2005
March 19, 2005
March 12, 2005
March 5, 2005
February 26, 2005
February 19, 2005
February 12, 2005
February 5, 2005
January 29, 2005
January 22, 2005
January 15, 2005
January 8, 2005
January 1, 2005
December 25, 2004
December 18, 2004
December 11, 2004
December 4, 2004
November 27, 2004
November 20, 2004
November 13, 2004
November 6, 2004
October 30, 2004
October 23, 2004
October 16, 2004
October 9, 2004
October 2, 2004
September 25, 2004
September 18, 2004
September 11, 2004
September 4, 2004
August 28, 2004
August 21, 2004
August 14, 2004
August 7, 2004
July 31, 2004
July 24, 2004
July 17, 2004
July 10, 2004
July 3, 2004
June 26, 2004
June 19, 2004
June 12, 2004
June 5, 2004
May 29, 2004
May 22, 2004
May 15, 2004
May 8, 2004
May 1, 2004
Apr. 24, 2004
Apr. 17, 2004
Apr. 10, 2004
Apr. 3, 2004
Mar. 27, 2004
Mar. 20, 2004
Mar. 13, 2004
Mar. 6, 2004
Feb. 28, 2004
Feb. 21, 2004
Feb. 14, 2004
Feb. 7, 2004
Jan. 31, 2004
Jan. 24, 2004
Jan. 17/18, 2004
Jan. 10, 2004
Jan. 3, 2004
Dec. 27, 2003
Dec. 20, 2003
Dec. 13, 2003
Dec. 6, 2003
Nov. 29, 2003
Nov. 22, 2003
Nov. 15, 2003
Nov. 8, 2003
Nov. 1, 2003
Oct. 25, 2003
Oct. 18, 2003
Oct. 11, 2003
Oct. 4, 2003
Sep. 27, 2003
Sep. 20, 2003
Sep. 13, 2003
Sep. 6, 2003
Aug. 30 / Sep. 1,
2003
August 23, 2003
August 16, 2003
August 9, 2003
August 2, 2003
July 26, 2003
July 19, 2003
July 12, 2003
July 5, 2003
June 28, 2003
June 21, 2003
June 14, 2003
June 7, 2003
May 31, 2003
May 24, 2003
May 17, 2003
May 10, 2003
May 3, 2003
April 26, 2003
April 19, 2003
April 12, 2003
April 5, 2003
March 29, 2003
March 22, 2003
March 15, 2003
March 8, 2003
March 1, 2003
February 22, 2003 |
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Comments
on these new products are encouraged and can be entered here.
Product
Description
The
Drought Monitor was
introduced as an operational weekly product in 1999 to provide
an overview of conditions averaged across a broad array of
time scales and impact indicators, leaning toward those that
seem most relevant to observed impacts. This approach has led
to an unprecedented degree of cooperation and coordination
among a variety of disparate Federal, state, and local
government agencies, in addition to many interested members of
the academic and private research communities. The result has
boiled the complex issues of drought and drought-related
impact assessment down to a single, simple, visually-intuitive
summary of conditions which has replaced the uncoordinated,
disparate, and often contradictory assortment of opinions and
data that formerly characterized responses to requests for
drought information.
While
this approach has been successful and well-received overall,
there are situations where it can be substantially misleading.
Drought and its related impacts operate on a variety of time
scales, and the Drought Monitor depiction (which usually
portrays some semblance of an "average" condition
across all time scales and impact types) cannot accurately
confer information when conditions and impacts dependent on
one time scale differ dramatically from those related to a
much longer (or shorter) time scale. Hypothetically, a region
which has received consistently and substantially inadequate
precipitation over the course of several years might
experience a day, or a few days, or even a few weeks of heavy
rain. What is the overall drought status after this occurs?
The Drought Monitor would likely depict a substantial
improvement in conditions (in deference to major short-term
relief) but maintain some indication of continuing drought (in
deference to the multi-year dryness which likely changed only
slightly in response to the heavy rains). This is all that a
single-image depiction could possibly do. In reality, however,
the degree to which drought-related impacts would continue to
be a concern would depend on what time scale a given class of
impacts responds to. Obviously, in this situation, wildfire
danger would decline sharply, at least for the immediate
future. Also, unregulated streamflows would swell from runoff
and topsoil moisture would be substantially recharged if the
precipitation lasted long enough, thereby providing at least a
temporary respite for non-irrigated agriculture. On the other
hand, reservoir stores might increase only slightly, having
been depleted by a few years of precipitation failing to keep
up with demand, and ground water levels and/or well water
depth, if they were low, might be barely (or at best
belatedly) affected by the heavy short-term rains, since much
of the water was likely dispersed by swollen streams or
absorbed by parched topsoil.
To
confer information about drought status on different time
scales to those users that need such information, two new
experimental products are being made public which will serve
as timescale-specific supplements to the Drought Monitor at a
basic level. Both assess conditions based on a blend of
several drought indicators, and are depicted relative to the
local historic record.
The
Short-Term Blend
approximates drought-related impacts that respond to
precipitation (and secondarily other factors) on time scales
ranging from a few days to a few months, such as wildfire
danger, non-irrigated agriculture, topsoil moisture, range and
pasture conditions, and unregulated streamflows.
The
Long-Term Blend
approximates drought-related impacts that respond to
precipitation on time scales ranging from several months to a
few years, such as reservoir stores,
irrigated agriculture, groundwater levels, and well water
depth.
It
should be noted that the relationship between indicators and
impacts varies, sometimes markedly, with location and season.
This is particularly true of water supplies, which are
additionally dependent on the source (or sources) tapped,
management practices, and legal mandates. Exercise caution
when attempting to relate these maps to specific impact
implications for a particular location and time of year. The
blend-to-impact correlation is not always direct, and will
vary spatially and temporally.
The
following bullets describe the composition of these
experimental blends:
-
These
products are generated using the Climate Prediction
Center's real-time daily & weekly climate division
data, and the National Climatic Data Center's monthly
climate division data archive, back to 1932.
-
The
indices used in the blends and their weights are as
follows:
-
All
parameters are first rendered as percentiles with
respect to 1932-2000 data using a percent rank method.
Most parameters are ranked relative to the National
Climatic Data Center's historic climate division data
for the current month, except for the Z-Index which is
rendered relative to all months on record (this
introduces evaporative seasonality into the short-term
blend).
-
For
each blend, the averages of the percentile inputs are
calculated, with each input weighted as described above.
This yields a "weighted raw average" of the
individual component percentiles for each blend. Then,
each raw average is compared to its historic (1932 -
2000) distribution (these have been retrospectively
generated from the climate division data archive). The
real-time data are compared to ALL retrospective months,
not just the current month, since the individual
percentile inputs were each generated (for all but the
Z-Index) relative to the history of the current month
only. This allows for a more confident estimation of the
percentile by using more data to define the historical
array (12 times as many as if we assessed the blends'
raw weighted averages relative to the current month
only).
-
The
precipitation percentile inputs are generated in a
somewhat unusual way, combining month-to-date numbers
from Climate Prediction Center with the National
Climatic Data Center's monthly totals for prior months.
As daily precipitation totals for the current month are
ingested into the x-month totals, an identical
proportion of the monthly precipitation that fell during
the first month in the x-month period is eliminated
(e.g., to determine a 6-month preciptation total, from
which a percentile will be calculated and incorporated
into the blend, for the period ending September 21,
2002, we add the daily preliminary precipitation amounts
for September 1-21 to the 6-month total for March-August
2002, then subtract 21/30 of the March total from the
result, since 21/30 of September have been added). This
process (a) emulates natural cycles by adding
precipitation as it falls but eliminating early-period
precipitation evenly over the course of a month; and (b)
ensures that the data utilized in real time are as
consistent with the historical array as possible. The
near-real-time climate division precipitation data are
biased in some areas relative to the final NCDC monthly
archive, with wet near-real-time biases in the central
and northern Rockies particularly extreme. The data are
adjusted where appropriate at the end of each month, but
the biases remain in the data for all precipitation time
scales since the end of the previous calendar month. In
addition, the biased near-real-time data are used in the
Palmer Drought Index, the Palmer Hydrologic Drought
Index, the Z-Index, and CPC's modeled soil moisture
data, and can remain in those calculations for several
weeks. For more information, a graphic
is available depicting the observed biases (a) for
the 12 most recent 3-month periods, and (b) for the last
3 years in each season.
These blends may be subject to change in
the future. Feel free to forward any questions or comments to
the Drought Monitor
authors for consideration or response.
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