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During the last 9 months, a severe drought has developed across the southern Plains, the Southwest, and northern Mexico.
Although normal October - May precipitation is rather low (under 6 inches) over much of this region, exceptionally scant totals
(less than 1 inch in some areas) were observed during this period in late 1995 - mid-1996. Furthermore, temperatures averaging
2F to 6F above normal, very low humidities, and frequent windy conditions during the period aggravated drought conditions.
Across portions of northern Mexico, long-term moisture shortages date back to autumn 1994.
As a result of this prolonged dryness, many of the region's crops and pastures have deteriorated, with the unirrigated winter wheat crop in New Mexico almost totally lost. In addition, the National Interagency Coordination Center indicated that wildfires charred nearly 1.5 million acres across areas to the south and west of the Ohio River during January 1 - June 11, 1996, compared to only 390,000 acres for the same period last year. Fortunately, reservoir, lake, and river impacts from the drought have been relatively minor, according to the National Weather Service Office of Hydrology, except for the Rio Grande River and its reservoirs, some of which are at or near record-low levels. In addition, water supplies and streamflows across northern Mexico are reported to be critically low.
During June 12 - 16, the heaviest and most widespread rains since September 1995 fell across New Mexico and adjacent
areas. Isolated locations in east-central New Mexico (near Clovis and Portales) received 2.2 to 3.7 inches of rain during this
period while 0.5 to 1.1 inches were measured across the rest of the eastern half of the state (totals ranged from a few hundredths
up to 0.5 inch farther west). These rains were connected with a transient weather system and are not believed to be indicative of
an early onset to the July/August monsoon that typically brings some of the heaviest rains of the year to the southwestern High
Plains and Southwest. Although these rainfall totals appeared large in comparison to the amounts measured during the previous
8 months, they were actually below the June monthly normals at most locations outside of east-central New Mexico.
The ongoing drought is one result of a planetary-scale circulation pattern that has influenced the weather over a large part of
the Northern Hemisphere. This pattern featured strong upper-level ridges across the Southwest and the high latitudes of the
North Atlantic and North Pacific Oceans and strong upper-level troughs over eastern North America and the mid-latitudes of
the North Atlantic and North Pacific. Two important climatic factors appeared to contribute to the development of this pattern:
1) The evolution of cold-episode (La Niņa) conditions in the tropical Pacific Ocean, and 2) The development of an extremely
persistent negative phase of the North Atlantic Oscillation (NAO), the duration of which was unparalleled since the late 1970's.
In the absence of an early onset to the Southwest monsoon, the prognosis for significant, widespread relief in the near future
is not good. Over the next 10 days (June 18 - 27), only widely-scattered thundershowers are expected across the affected region,
with temperatures averaging above normal to much-above normal.
The most realistic chance for a significant break from the long-term dryness across the Southwest is during the
summer/early autumn monsoon. The Climate Prediction Center's most recent 90-day outlook for July - September (issued in
mid-June) called for climatological precipitation probabilities; that is, equal chances for above-normal, near normal, and
below-normal rainfall throughout the region. Unfortunately, above-normal temperatures appear more likely than
below-normal readings in most areas during this period. In addition, wildfire potential will continue to be high to extreme from
the southern Plains westward to the Pacific Coast through July 10, according to a recent outlook issued by the National
Interagency Coordination Center.
Observed Climatological and Meteorological Conditions
For the past 9 months (since October 1995), well below-normal precipitation fell over much of the southwestern quarter of
the country. Most areas from the desert Southwest eastward across New Mexico and northwestern Mexico received only 0.3 to
2.5 inches during October 1995 - May 1996, compared to normals of 3 to 6 inches (Figure 1). The dryness
in northern Mexico dates back much farther, originating during the below-normal monsoonal rains of 1994. Across the southern Plains,
precipitation ranged from 2 inches in western sections of the southern High Plains to nearly 30 inches in the western lower Mississippi
Valley. Typically, totals would range from 6 to 40 inches, increasing from west to east. In addition, temperatures across most of the
aforementioned areas averaged 2F to 6F above normal throughout the period, aggravating the dryness
The following table depicts preliminary monthly and multi-monthly statewide precipitation rankings generated by the
Climate Prediction Center for October 1995 - May 1996 for states affected by the current drought, based on data since January
1895. Please note that these rankings are preliminary and experimental, and should be used with caution. They are calculated
from hundreds of first-order and thousands of River Forecast Center station reports. Months or a series of months are ranked
from driest to wettest in comparison with all other such periods on record, so that "1" means the driest such period ever observed
across a given state, and "101" (for October - December 1995) or "102" (for January - May 1996) represents the wettest such
period on record. Ranks printed in bold type were among the driest one-third of all such periods (rank < 34):
STATE OCT NOV DEC JAN FEB MAR APR MAY OCT-MAY JAN-MAYNote that across the most severely-affected states (AZ, NM, OK, TX), the only monthly statewide above-median ranking was for February in Arizona.
AZ 8 45 21 7 66 21 9 37 2 9 CO 8 36 16 90 65 37 21 60 23 50 KS 3 22 49 44 7 35 15 83 7 35 NE 79 40 11 86 1 28 26 95 47 57 NM 3 32 37 29 41 16 51 24 5 15 OK 15 15 7 33 1 36 19 19 1 4 TX 18 45 45 9 2 15 28 7 2 1
Extreme long-term drought, as determined by the Palmer Drought Index (PDI), was widespread from southeastern
California eastward through the southwestern High Plains as of June 8 (Figure 3), and also covered parts of eastern Texas.
Meanwhile, moderate to severe drought affected the central Rockies and the southern Plains. The PDI identifies long-term
moisture budget conditions on time scales from a few months to a year, and takes several parameters (including temperatures,
soil types, and evaporation) into account in addition to precipitation. It is relevant for hydrologic concerns and water-supply
applications, but is less indicative of agricultural stress, which is usually a shorter-term phenomenon. In order to bring the PDI
up to -0.5 (near normal), most areas from southern California eastward to western sections of Texas and Oklahoma must receive
4 to 8 inches plus the normal amount of rain during the next several weeks or months (Figure 4). Across the southeastern Great
Plains (where normals are higher), many areas need at least 8 inches more than normal to completely alleviate the long-term
drought, with eastern Texas requiring 12 to 15 inches more than normal.
Another index used to gauge drought conditions is the Standardized Precipitation Index, developed by McKee et al in 1993
and generated operationally by the Western Regional Climate Center and the National Drought Mitigation Center (Figure 5).
According to this index, the first five months of 1996 were extremely dry (more than 2 standard deviations below normal) over
most of Texas, western Louisiana, northern New Mexico, and parts of Oklahoma and Arkansas. This is generally consistent with
the Climate Prediction Center's statewide rankings for the period, which indicated that this was the driest January - May on
record across Texas.
Although severely dry conditions have affected all areas from the southern Great Plains westward through the desert
Southwest, conditions evolved somewhat differently in various parts of the affected region. 1) From the southwestern High
Plains westward across the Southwest and northern Mexico, where normals are low, little precipitation fell consistently through
October 1995 - May 1996. 2) Farther to the east, precipitation for the October - May period normally increases sharply from
west to east, ranging from 6 to 8 inches in the relatively-dry southern High Plains to more than 30 inches across the lower
Mississippi Valley. In the northwestern half of Texas and much of Oklahoma, well below normal October through mid-March
precipitation was measured, but amounts increased thereafter. In late April, the first significant precipitation in months fell on
west-central Texas, and widespread light to moderate rains fell on most of central and northeastern Texas and much of
Oklahoma during the latter half of May. In most areas, however, the precipitation observed from late March through May was
only near or somewhat below normal for the period, and failed to alleviate drought conditions. 3) Across southern and eastern
Texas, moderate to heavy precipitation (8 to 14 inches) fell during the last 3 months of 1995, but exceptionally low totals were
reported during January - May 1996. As a result, some locations (notably Brownsville, with 0.79 inch) reported the driest such
period on record, as did the state of Texas as a whole.
June 11 - 16 brought the heaviest, most widespread rains since September 1995 to New Mexico and adjacent areas.
Between 0.5 and 1.1 inches fell on most of the eastern half of the state while totals ranged from 2.2 to 3.7 inches near Clovis and
Portales in east-central New Mexico. Anywhere from a few hundredths up to 0.5 inch fell on western sections of the state.
Although these rains were somewhat beneficial, much more precipitation is needed. In fact, these amount were below the June
monthly normals at most locations, even though they appeared very large compared to the extremely low precipitation totals
measured over the previous 8 months. The following table compares precipitation totals at selected New Mexico sites during
October 1 - June 10 and June 11 - 16 with the June monthly normal.
SITE October 1 - June 10 Pcp. June 11 - 16 Pcp. June Monthly Normal
Alamogardo 1.14" 0.53" 0.90" Carlsbad 1.58" 0.84" 1.30" Clovis 1.25" 3.84" 2.84" Gallup 2.70" 0.50" 0.45" Roswell 0.38" 0.79" 1.61" Hobbs 1.60" 0.87" 1.91" Las Vegas 0.60" 0.96" 1.92" Raton 0.60" 0.56" 1.58"
Across parts of the drought-affected region outside of New Mexico, scattered heavy thunderstorms dropped significant
amounts of precipitation on parts of the southern Plains during the first half of June. Totals of 2 to 6 inches were widespread
across eastern Kansas, southern Oklahoma, central and northeastern Texas, and the lower Mississippi Valley, with 6 to 10 inches
reported in portions of the central Red River Valley. Farther south and west, totals were lower, with 1 to 3 inches dampening most
of southeastern Texas and the Panhandle, northern and western Oklahoma, and most of the eastern half of Kansas. Between 0.2
and 1.0 inch of rain was reported at most other locations, with little or none measured in extreme southern and western Texas and
the desert Southwest. These rains were somewhat beneficial, particularly in central Texas and across Oklahoma, but much more
rain is needed for these areas to begin experiencing significant drought relief.
The same pattern of subnormal precipitation across the southern Plains and Southwest for the October 1995 - May 1996
period was also evident during March - May 1996 (meteorological spring, and the first three months of the growing season for
most of the region's crops, except winter wheat). Most areas south of a line from central Nevada to central Kansas received less
than 75% of normal precipitation for the period, with large sections of Arizona, New Mexico, southern Texas, and northern
Mexico reporting under 25% of normal (Figure 6).
The recent rains improved topsoil conditions (which respond primarily to short-term moisture anomalies) across the
southern Plains, as indicated by the short-term (4-week) Crop Moisture Index (Figure 7), but topsoil moisture in other
drought-affected areas and subsoil moisture (which responds more slowly) throughout the southern Plains and Southwest
remained very low. According to the United States Department of Agriculture, topsoil moisture was categorized as short or very
short across 12% of Kansas and 25% of Oklahoma on June 8 (as opposed to only 2% of Kansas and none of Oklahoma in
early-June 1995) while subsoil was short or very short over 22% of Kansas and 63% of Oklahoma (compared to 6% and 0%,
respectively, at this time last year).
The winter wheat crop was severely affected by the drought, with nearly half or more than half of the crop in poor or very
poor condition across Oklahoma (49%), Texas (58%), and Kansas (60%) in early June. By contrast, the proportion of the winter
wheat crop in poor or very poor condition in early June 1995 across these states was 20%, 36%, and 21%, respectively.
Ironically, recent rains in Oklahoma have benefitted the moisture budget, but have also delayed the progress of the winter wheat
harvest, after the crop was stressed by months of drought. Farther west, unirrigated winter wheat was nearly a total loss in New
Mexico, with 99% of the crop rated very poor on June 1, 1995; however, the state's irrigated winter wheat fared better (only 30%
was rated poor or very poor). Across the nation as a whole (including those areas not affected by the drought), 40% of this year's
winter wheat crop was in poor or very poor condition on June 8, as opposed to 18% in early June 1995.
In addition to the winter wheat difficulties across New Mexico, 90% of the state's sorghum crop was in poor or very poor condition, versus only 8% at this time in 1995. Statewide, very short soil moisture covered 81% of the area on June 8, compared to 41% on June 10, 1995.
The condition of cattle, feed grain, and pastures are fair to poor throughout the region. Some cattlemen shipped cattle to non-drought affected areas, and some have been prematurely liquidating cattle so that sufficient feed will be available for the remaining herds. On June 1, feed grain and hay supplies were 45% and 42% short, respectively, across Kansas; cattle conditions in New Mexico were 42% poor or very poor, 40% fair.
Fortunately, hydrologic impacts from the drought have thus far been relatively minor since precipitation is normally quite
low over much of the affected region during October - May. According to the National Weather Service Office of Hydrology,
most of the region's rivers, most notably the Colorado, are regulated by reservoirs that recharge over the course of decades, and
are barely affected by a year-long drought. However, irrigation-water rationing has been necessary in parts of New Mexico, and
water-use reservoirs across much of Texas are below conservation levels, though not yet critically deficient. As a result, no
water rationing should be necessary in Texas through the end of the calendar year.
One significant exception to the above rule has been the Rio Grande River and its reservoirs. Streamflows are very low at many locations, and some reservoirs, notably the Choke Canyon, Amistad, and Falcon Reservoirs, have dropped to record low levels. In addition, the level at Lake Corpus Christi is only 26% above the record-low level recorded in May 1951. Farther south, reports indicate that severe drought-related impacts have affected much of northern Mexico, where water management is not as advanced, but reliable statistics are lacking. Press reports indicated that the ongoing drought in this region may be the worst in 43 years.
The combination of long-term precipitation deficits, above-normal temperatures, frequent low humidities, and occasional
gusty winds engendered prime wildfire conditions. In the area from central Texas and Oklahoma eastward to the Atlantic Coast,
nearly 1.1 million acres had been consumed by fires this year through June 11, compared to only 314,000 acres during the same
period last year. Across western Texas, the Oklahoma Panhandle, New Mexico, and Arizona, 187,000 acres were consumed by
fires during January 1 - June 11, 1996, which was 3 times as much as the 61,500 acres consumed through the same period last
year. For the southern and western sections of the country (excluding areas north of the Ohio River, the middle and upper
Mississippi Valley, North Dakota, the northern Rockies, and the Pacific Northwest), a total of 1.45 million acres were charred
through June 11, 1996, compared to just 392,000 acres during the same period last year (an increase of over 250%).
Although Alaska is not the main focus of this Special Climate Summary, it should be noted that a mild winter with abnormally little snowfall was followed by a warm and dry spring across much of the state, providing favorable conditions for wildfires similar to those in the southern Plains and Southwest. During January 1 - June 11, over 172,600 acres had been charred, compared to only 9,670 acres during this period last year (an increase of almost 1700%). Particularly dry, windy, and warm weather in early June (temperatures reached 79F in parts of the state's interior) made it difficult for firefighters to contain a large fire near Anchorage. This fire destroyed a few hundred dwellings and forced 1800 residents from their homes near Anchorage through June 7. Fortunately, somewhat moister and cooler conditions by June 10 aided containment efforts.
Global Circulation Features
The drought in the Southwest and the southern Plains has been one manifestation of an extraordinarily persistent
upper-level circulation pattern that has extended across the western North Pacific Ocean, North America, and the North
Atlantic Ocean (Figure 8). This planetary-scale pattern featured amplified ridges over the southwestern United States and the high
latitudes of both the North Atlantic and North Pacific Oceans, and amplified troughs over the eastern United States and the
central latitudes of the North Pacific and North Atlantic Oceans.
Over North America, this circulation pattern has been associated with an enhanced jet stream and enhanced storm track
across the northern half of the United States, with weakened jet stream winds and weakened storms over the Southwest. These
features produced the persistent dryness and warmth in the southern Plains and Southwest, and cool and wet conditions from the
Pacific Northwest to the mid-Atlantic states. This enhanced precipitation resulted in some localized flooding across the Ohio
Valley. Thus, the drought has been only one manifestation of an abnormal circulation pattern that has dominated large portions
of the Northern Hemisphere since October 1995.
There appear to be at least two important short-term climate factors responsible for the above circulation pattern. The first is the transition from warm-episode (El Niņo) to cold-episode (La Niņa) conditions in the tropical Pacific Ocean during the past year. A cold episode favors an upper-level ridge over the Southwest, and thus a northward displacement of the jet stream and storm track over the West, resulting in below-normal precipitation across the Southwest and above-normal precipitation in the Pacific Northwest. Farther east, a persistent upper-level trough and below-normal temperatures are favored over eastern North America during La Niņa event.
The second factor associated with the above circulation pattern is an extremely persistent negative phase of the North Atlantic Oscillation (NAO), the duration of which was unparalleled since the late 1970's. The negative phase of the NAO features anomalous upper-level ridging at high latitudes of the North Atlantic Ocean and anomalous upper-level troughing over the central latitudes of the North Atlantic Ocean and throughout eastern North America. The NAO is a naturally-occurring mode of atmospheric variability that tends to significantly influence temperature, precipitation, jet stream, and storm track patterns from eastern North America to Europe.
Thus, it appears that the circulation features associated with both the La Niņa and the negative phase of the NAO tended to reinforce each other during the last 9 months, resulting in the extremely persistent and coherent planetary-scale circulation pattern extending across much of the Northern Hemisphere.
Forecasts and Outlooks
The prognosis for significant, widespread relief from drought conditions in the near future is not good despite the recent
thundershower activity across New Mexico and adjacent areas. During June 11 - 16, a transient weather system enhanced
thunderstorm development over New Mexico and surrounding areas, but these rains are expected to decrease in intensity and
areal coverage as a hot and relatively dry high-pressure center develops across the region. Therefore, the recent thundershower
activity was, unfortunately, not indicative of an early onset to the monsoon.
The 5-day outlook valid June 18 - 22 calls for moderate precipitation across the eastern half of Kansas, eastern Arkansas,
and most of Louisiana while light rains fall on western Kansas, the Texas and Oklahoma Panhandles, and eastern Colorado.
Other areas, including much of the drought-affected region, should receive only widely-scattered thundershowers. High
temperatures are expected to continue aggravating the drought situation in many areas, with readings averaging over 4F above
normal from eastern New Mexico and southeastern Colorado eastward through the western Lower Mississippi Valley. Some
locations in the Texas and Oklahoma Panhandles and the Big Bend area of Texas could average over 8F above normal.
Through the ensuing 5 days (June 23 - 27), above-normal precipitation is expected across much of Kansas and eastern
Colorado, but considerably lower amounts are forecast farther to the south (Figure 9). Light rain is anticipated across northeastern
New Mexico, southeastern Colorado, central and northern Oklahoma, the northern half of Arkansas, and part of central and
northeastern Texas. Elsewhere, no widespread precipitation is forecast, although widely-scattered thundershowers may
dampen some areas.
The wildfire potential from the southern High Plains westward to the Pacific Coast is expected to remain high to extreme
through at least July 10, according to a recent outlook issued by the National Interagency Coordination Center (Figure 10). In
addition, the southeastern half of Alaska retains a high fire potential during this period; however, the potential should be low
across the southern Great Plains and the lower Mississippi Valley, where large fires occurred over the last 4 months.
The most realistic chance for a significant break from the long-term dryness across the Southwest would be during the summer/early autumn monsoon that typically brings increased thundershower activity to the region in July and August. In the absence of any compelling reason to forecast otherwise, the Climate Prediction Center's most recent 90-day outlook for July - September (issued in mid-June) called for climatological precipitation probabilities; that is, 1 chance in 3 for above-normal precipitation, 1 chance in 3 for near-normal precipitation, and 1 in 3 for below-normal precipitation throughout the region. Unfortunately, above-normal temperatures appear more likely than below-normal readings for the period as a whole from the southern High Plains westward to the Pacific Coast (Figure 11).