Issued July 22, 2009, Vol. 5, Issue 5

Brad Udall – WWA Director
Jeff Lukas, Kristen Averyt, Andrea Ray – Editors/Writers
Julie Malmberg – Writer
Lucia Harrop – Graphic Designer
Klaus Wolter, Gary Bates – Asst. Editors

PRINTER-FRIENDLY VERSION


July 2009 Summary

Hydrological ConditionsDry conditions have diminished throughout the region since May. Currently no part of the region is in drought status (D1–D4) for the first time since 2001. Small areas of abnormally dry conditions persist in southeast Colorado and southwest Utah.

TemperatureMonthly average temperatures in June were cooler than average across the Intermountain West region, with only scattered above-average anomalies in southern Utah and Colorado.

PrecipitationJune 2009 was a wet month overall, with all areas except southern Utah seeing above-average precipitation, and precipitation anomalies exceeding 200% in far northern Utah, northern Colorado, and much of Wyoming.

ENSOSea surface temperatures in the equatorial Pacific continued their upward trend during June, and have now exceeded the threshold for an El Niño event. El Niño conditions are forecasted to persist into winter, influencing weather in the Intermountain West.

Climate ForecastsAn increased risk of above-average temperatures is forecasted for much of Utah in August. The area of increased risk of warmer temperatures shifts to southern Utah and southern Colorado for the fall, and then expands across the region for October–December, reflecting the likelihood of continued El Niño conditions. An increased likelihood of above-average precipitation is forecasted for portions of Colorado and Wyoming in August and through the fall.

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Announcements & News

New study by WWA team members on climate change impacts on Colorado River storage

A study led by Balaji Rajagopalan (University of Colorado, CEA Engineering & WWA) looked at the effects of a range of reductions in Colorado River stream flow on future reservoir levels and the implications of different management strategies. The study, "Water Supply Risk on the Colorado River: Can Management Mitigate?", is in press in the journal Water Resources Research. Other authors included Ken Nowak (University of Colorado), James Prairie (Bureau of Reclamation), Martin Hoerling (NOAA), Andrea Ray (NOAA & WWA), Joseph Barsugli (CIRES & WWA), Brad Udall (WWA) and Benjamin Harding (AMEC Earth & Environmental Inc.) The study was conducted with support from the WWA, CADSWES, and the Bureau of Reclamation.

(Read the CIRES press release, with link to paper in 2nd paragraph)

Changes in WWA and IWCS staff

Jessica Lowrey, who has served as writer/editor for the IWCS since it began in 2005, left WWA at the end of June in preparation for starting law school at the University of Colorado this fall. Filling her role in supporting the IWCS is Jeff Lukas, who recently joined WWA as full-time staff. He comes from the University of Colorado's Institute of Arctic and Alpine Research (INSTAAR), where he conducted WWA-supported research to develop tree-ring paleohydrologies in collaboration with water managers.

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Feature Article

Continuing paths and new directions for the Western Water Assessment

By Kristen Averyt (Western Water Assessment)

The Western Water Assessment is expanding the scope of its research, complementing its continuing focus on water resources with new studies on climate adaptation, the water-energy nexus, and climate impacts on ecosystems.

(download pdf)

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Focus Article

NEW ENSO Alert System from NOAA Climate Prediction Center

By Jessica Lowrey (Western Water Assessment) and Michelle L'Heureux (NOAA Climate Prediction Center)

The NOAA Climate Prediction Center has introduced a new ENSO Alert System that more succinctly describes the onset and status of ENSO. This information can be used to plan and prepare for weather events that typically accompany El Niño or La Niña events.

(download pdf)

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Recent Climate Conditions

Throughout most of the Intermountain West, temperatures ranged between average to 4º below average through the month of June. The only exceptions were pockets in the far southern corners of Utah extending across the New Mexico border, and a few isolated areas in Colorado and Wyoming, where temperatures reached 2ºF above average. The average temperature for June exceeded 75ºF in southwest Utah and eastern Colorado; and across the Rockies the average monthly temperature ranged from below 40ºF up to 55ºF.


Figure RC-1. Average temperature for the month of June 2009 in °F. (Source: High Plains Regional Climate Center)


Figure RC-2. Departure from average temperature for the month of June 2009 in °F. (Source: High Plains Regional Climate Center)

Location

Record

New

Old

Year

June 4

Rawlins, WY

Daily Max Precipitation

0.64 inches

0.26 inches

1964

June 6

Bryce Canyon Airport, UT

Low Min Temperature

20º

27º

1951

June 9

Cheyenne, WY

Daily Max Snowfall

Trace

Trace

1979

June 22

Bryce Canyon Airport, UT

Low Min Temperature

27º

30º

1977

June 23

Denver International Airport, CO

Daily Max Precipitation

1.64 inches

0.69 inches

1906

ENTIRE MONTH

Salt Lake City, UT

Days in June w/ any precip.

17 days

17 days

1967

Salt Lake City, UT

Days in June w/ >0.1" precip.

9 days

8 days

1998

Table RC-1. Record temperature and precipitation events in the Intermountain West during June 2009. (Source: NOAA National Weather Service)


With the cool temperatures came relatively large amounts of rain and snow, with approximately half the Intermountain West receiving more than 200% of average precipitation (Figure RC-4). For the most part, precipitation was delivered in multiple, smaller events throughout the month. This is reflected by the dearth of record precipitation events (Table RC-1), given the above-average rainfall (Figure RC-4).


Figure RC-3. Precipitation for the month of June 2009 (inches). (Source: NOAA ESRL Physical Science Division)

Figure RC-4. Precipitation for the month of June 2009 as percent of average precipitation for June. (Source: NOAA ESRL Physical Science Division)

Figure RC-4b. Precipitation for water-year-to-date (October 2008–June 2009) as percent of average precipitation for that period. (Source: NOAA ESRL Physical Science Division)

 


In most climate divisions within the Intermountain West, the precipitation was sufficient to cause a shift toward wetter conditions in the 3-month SPI (Figure RC-5). In Colorado, where precipitation accumulation exceeded 4” in many parts of the state (Figure RC-3), a dramatic shift occurred in the 36-month SPI (Figure RC-6), with the western slope and the northern portions of the state are now categorized as moderately wet (+0.75 to +1.24).



Figure RC-5. 3-month Intermountain West regional Standardized Precipitation Index as of the end of June 2009 (data from 4/01/09– 6/30/09). (Source: Western Regional Climate Center)

Figure RC-6. 36-month Intermountain West regional Standardized Precipitation Index as of the end of June 2009 (data from 07/01/06–6/30/09). (Source: Western Regional Climate Center)


For the first time since February 2001, the U.S. Drought Monitor (Figure RC-7) indicates no drought (D1–D4) across the entire Intermountain West, with only a small area of abnormally dry (D0) conditions in the far southeast corner of Colorado and a small sliver of southwestern Utah. Persistent below-average temperatures (Figure RC-2) in combination with significant precipitation (Figure RC-4) provided drought relief across the entire Intermountain West.


Figure RC-7. Drought Monitor from July 14, 2009 (full size) and June 16, 2009 (inset, lower left) for comparison. (Source: National Drought Mitigation Center)


Notes & Weblinks
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Intermountain West Snowpack

May's weather across the region was generally 1–5ºF warmer than average, and aided by widespread presence of multiple dust layers in the snowpack (see the Feature article in the July 2008 IWCS), caused an unusually rapid depletion of the snowpack during May, particularly in Colorado and Utah. As a result, the SWE values for June 1 were below average across the region, with the lowest values in southern Utah and southwest Colorado. The weather in June was much cooler and wetter than average across most of the region, which conserved the remaining snowpack in those basins that still had snow.

In Colorado, statewide snowpack sank to 32% of average on June 1 from 90% of average on May 1. The southwestern basins were particularly hard-hit by the accelerated meltout caused by the dust layers and essentially melted out by June 1, despite wetter than average conditions in May across those basins. Cool and wet conditions in June, with multiple snow events, slowed the meltout in the northern and central mountains, with many observers by late June and early July noting unusually deep and extensive snowpacks remaining above treeline.

The trajectory of the snowpack in Utah was similar to Colorado, with statewide SWE dropping to just 18% of average on June 1. In the southeast and southwest basins, where the dust layers were most prevalent, the snowpack was gone by June 1. Despite cool and very wet weather in the northern part of the state in June, no sites in those basins indicated any snow remaining by the end of June.

Across Wyoming, the snowpack fared better in May than to the south, with statewide June 1 SWE at 61% of average. The June 1 snowpack was greatest in the northwestern basins (73%), and least in the northeastern basins (37%).

Figure SP-W. An extensive reddish dust layer exposed by the melting snowpack at Independence Pass in central Colorado on June 18, 2009. The deposition of multiple dust layers in the snowpack speeded up melt throughout the region. (Source: Klaus Wolter)

Notes & Weblinks
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Spring and Summer Streamflow - Forecasted and Observed

Prior to its accelerated depletion, the regional snowpack had peaked at near-average levels in most basins. Also, the conversion of snowpack to runoff appears to have been relatively efficient. As a result, the region-wide spring runoff was running near-average overall as of July 1.

With the early melt, peak runoff shifted 1–4 weeks earlier than average, so that May volumes were generally well above average around the region. Since June and July volumes were expected to be much lower than average as this early peak runoff quickly tapered off, the overall April–July flows as forecasted on June 1 indicate only minor changes from the May 1 forecasts in most basins. But cool and wet weather in June augmented the runoff and reduced evapotranspiration losses, leading to unexpectedly large June volumes. Streamflow for July was still forecasted to be below average across most of the region.

In Colorado, the June 1 forecasts for April–July volume were at least 90% of average for all basins except the San Juan, Animas, Dolores, San Miguel, the southern tributaries of the Arkansas, and the headwaters of the South Platte. The wet weather in June caused a secondary peak in runoff on several major rivers, improving the prospects for greater than forecasted April–July runoff. For example, the June 1 forecast for the Colorado River Basin (Cameo gage) April–July flow was for 2.67 MAF (110% of average), but with near-average June flows, the observed April–June volume was about 2.45 MAF, so even if July flows are much less than average (0.5 MAF), the forecast will be exceeded.

In Utah, the June 1 forecasts for April–July volume in basins across the state were mainly from 80-100% of average, with a low of 50% and a high of 110% of average. But as in Colorado, the wet June weather boosted the spring–summer runoff above forecasted levels in many basins. For example, on the Duchesne River near Duchesne, the June 1 forecast for April–July volume was 158 KAF, 84% of average, but after above average June flow, the observed April–June total was already at 210 KAF.

In Wyoming, June 1 forecasts for the April–July and June–September yields were generally below average statewide. But the very wet June weather across the state has improved the outlook for summer flows. For example, on the Green River above Fontanelle Reservoir, the June 1 forecast for April–July volume was 705 KAF, 82% of average, but after a well-above average June flow, the observed April–June total was about 720 KAF.

For the whole Upper Colorado River Basin, April–July inflows to Lake Powell were forecasted on June 1 to be 7.1 MAF, 90% of average. With precipitation in June across the upper basin estimated at 215% of average, observed June inflows were 0.4 MAF higher than forecasted, and observed April–June total inflows were 6.4 MAF. Accordingly, the Bureau of Reclamation on July 9 revised the forecasted April–July inflows upward, to 7.55 MAF (95% of average).

Notes & Weblinks
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Reservoir Supply

The “front-loading” of the spring–summer runoff due to accelerated snowmelt, plus the generally greater than expected June runoff, led to generally above-average reservoir levels across the region for the beginning of July. Lake Powell, much depleted by multi-year drought, has recovered to 66% of capacity, its highest level since spring 2002 (Figure RES-1).


 

 
RESERVOIR
current storage
(af)
capacity
(af)
% full
% of average for 6/30
COLORADO
Dillon Reservoir
256,100
254,036
101%
102%
 
Turquiose Lake
126,742
129,390
98%
109% 
 
Lake Granby
495,327
539,758
92%
116% 
 
Blue Mesa
826,302
829,500
100%
119% 
 
Pueblo
222,645
354,000
63%
139% 
 
UTAH
Strawberry
1,047,000
1,106,500
95%
147%
 
Utah Lake
909,000
870,900
104%
104%
 
Bear Lake
 509,400
1,302,000
39%
52% 
 
Lake Powell
16,060,989
24,322,000
66%
81% 
 
WYOMING
Fontenelle
329,819
344,800
96%
122% 
 
Flaming Gorge
3,342,446
3,749,000
89%
103% 
 
Seminoe
932,091
1,017,273
92%
135% 
 
Boysen
768,592
741,594
104%
128% 
 
Buffalo Bill
596,981
644,126
93%
123% 

Figure RES-1. Tea-cup diagram and table of several large reservoirs in the Intermountain West Region. The size of each “tea-cup” is proportional to the size of the reservoir, and the amount the tea-cup is relative to the current storage as a percent of capacity (% full in table). All reservoir content data is from June 30, 2009. Percent full ranges are color coded as follows: green: 80–100%; light green: 60–79%; yellow: 40–59%; orange: 20–39%; red: 0–19%


In Colorado, overall reservoir levels are at their highest point since spring 2000, with every basin above average for the end of June. Blue Mesa Reservoir in late June peaked at its highest level since 1999, nearly spilling before the Bureau of Reclamation initiated bypass operations.

In Wyoming, total storage at the end of June was also above average in most basins, except for the Belle Fourche and Cheyenne Basins, and the North Platte basin. Pathfinder Reservoir in the North Platte Basin, while still below its long-term average, improved to its highest end-of-June level since 2001.

In Utah, statewide storage at the end of June was well ahead of last year at this time, with all basins except the Bear River and Sevier storing at least 75% of capacity. Strawberry Reservoir has improved to 95% of capacity.

Notes & Weblinks
(provides explanations of graphics and additional information sources)

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ENSO Status and Forecast

NOAA scientists announced the arrival of an El Niño event in the July “ENSO Diagnostic Discussion,” as part of the new ENSO Alert System (see the Focus Page in this issue). NOAA expects this El Niño to continue developing during the next several months, with further strengthening possible. The event is expected to last through winter 2009–10. Although often associated with negative impacts, El Niño typically brings beneficial winter precipitation to the arid Southwest, can help suppress Atlantic hurricane activity, less wintry weather across the North, and a reduced risk of Florida wildfires.

Sea surface temperatures (SSTs) in the equatorial Pacific Ocean are now well above average (Figure EN-1). Subsurface water temperatures also are well above average in the upper 200 meters of the tropical Pacific, making it likely that above-average SSTs will continue into the rest of summer, fall, and winter.


Figure EN-1. Observed SST (upper) and the observed SST anomalies (lower) in the Pacific Ocean.  The Niño 3.4 region encompasses the area between 120°W–170°W and 5°N–5°S.  The graphics represent the 7-day average centered on July 15, 2009. (Source: NOAA Climate Prediction Center)


Model forecasts of SST anomalies (Figure EN-2) reflect a strong consensus for the continuation, if not strengthening, of El Niño conditions (+0.5°C or greater in the Niño-3.4 region). The dynamical and statistical models continue to generally differ on the trajectory of ENSO conditions over the next 9–12 months, with all dynamical models forecasting continuation of this El Niño into winter, while several statistical models forecast a return to ENSO-neutral conditions. (None of the statistical models in May, however, forecasted the development of El Niño conditions at any time in 2009.)

El Niño has only spatially limited influence on North American temperature and precipitation during the summer and early fall, but this influence strengthens and expands during the late fall and winter. ENSO composites (the historical influences of ENSO on climate) were consulted for the forecasts reported this month.

The outlooks for temperature and precipitation from October–December 2009 through March–May 2010 are heavily influenced by the likelihood that El Niño conditions will continue. According to the NOAA Climate Prediction Center, it is still early to predict El Niño strength for the winter months (as reflected in the spread of ENSO forecasts; Figure EN-2). The evolution of SSTs in the equatorial Pacific in the coming months will be critical to the wintertime forecasts in the U.S.


Figure EN-2. Forecasts made by dynamical and statistical models for sea surface temperatures (SST) in the Niño 3.4 region for nine overlapping 3-month periods from July–September 2009 to March–May 2010 (released July 16, 2009). (Source: International Research Institute (IRI) for Climate and Society)

Notes & Weblinks
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Temperature Outlook
August–December 2009 (Released July 16, 2009)

The latest temperature outlooks from the NOAA Climate Prediction Center indicate an enhanced risk of above-average temperatures across much of the West, including Utah and adjacent areas in Colorado and Wyoming in August 2009, and for southern Utah and Colorado in the August–October season (Figures TEMP-1 and TEMP-2). For October–December and November–January (Figures TEMP-3 and TEMP-4), there is an increased risk of above-average temperatures across the Intermountain West.

Although an El Niño event is beginning, temperature impacts over the U.S. are typically weak during the summer and early fall, and generally strengthen during the late fall and winter. ENSO composites are considered in the August and near-term forecasts, and then heavily influence the outlooks for temperature for October–December and subsequent seasons.

The August 2009 temperature forecast will be updated on July 31st on the CPC web page. This “zero-lead” monthly update will incorporate information from the short-range numerical weather prediction models and the latest monthly predictions from the Climate Forecast System models. The Seasonal Outlooks are updated on the third Thursday of the month, and the next one will be issued on August 20th.


Figure TEMP-1. Long-lead national temperature forecast for August 2009. (Source: NOAA Climate Prediction Center)

Figure TEMP-2. Long-lead national temperature forecast for August–October 2009. (Source: NOAA Climate Prediction Center)

Figure TEMP-3. Long-lead national temperature forecast for September–November 2009. (Source: NOAA Climate Prediction Center)

Figure TEMP-4. Long-lead national temperature forecast for October–December 2009. (Source: NOAA Climate Prediction Center)

Notes & Weblinks
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Precipitation Outlook
August–December 2009 (Released on July 16, 2009)

The CPC precipitation outlook for August 2009 and through the September–November season (Figures PPT-1 and PPT-2) shows an increased probability of above-median precipitation in much of Wyoming and Colorado and across the High Plains, based on the Climate Forecast System models, ENSO composites, and precipitation trends. There are no clear signals in the outlook for the October–December season, resulting in a forecast for equal chances for below, near, or above-median precipitation in the Intermountain West (PPT-3); however, there is a signal for increased precipitation across the southern tier of the U.S. that is typical of El Nino winters.

The August 2009 precipitation forecast will be updated on July 31st on the CPC web page. This “zero-lead” monthly update will incorporate information from the short range numerical weather prediction models and the latest monthly predictions from the Climate Forecast System models. The Seasonal Outlooks are updated on the third Thursday of the month, and the next one will be issued on August 20th.


Figure PPT-1. Long-lead national precipitation forecast for August 2009. (Source: NOAA Climate Prediction Center)

Figure PPT-2. Long-lead national precipitation forecast for August–October 2009. (Source: NOAA Climate Prediction Center)

Figure PPT-3. Long-lead national precipitation forecast for September–November 2009. (Source: NOAA Climate Prediction Center)

Figure PPT-4. Long-lead national precipitation forecast for October–December 2009. (Source: NOAA Climate Prediction Center)


According to the experimental SWcast discussion (early version) released on July 16th, June’s early monsoon-like pattern has been replaced in July by a drier pattern that would have been more typical of late June conditions ahead of the monsoon season, though a return to more typical monsoon-like weather is expected by the end of July.

The experimental forecast guidance for the monsoon season (July–September 2009) supports slightly enhanced precipitation chances in eastern Colorado, while northwestern Utah faces a slight risk of drier conditions (Figure PPT-5). Compared to earlier experimental forecasts for the monsoon season, precipitation odds are about the same or slightly more favorable. The weak-to-moderate El Niño conditions that have become established since June have increased the odds for a wet monsoon season in much of Colorado, especially on the eastern plains.


 

Figure PPT-5. Experimental precipitation forecast guidance. Forecasted shifts in tercile probabilities for July–September 2009. (Source: NOAA ESRL Physical Science Division)

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Seasonal Drought Outlook
through October 2009 (Released July 16, 2009)

Only two areas of the Intermountain West are categorized as abnormally dry (D0 category) as of July 16th: a small area in southwestern Utah and an area in southeastern Colorado (Figure RC-7 above). The U.S. Seasonal Drought Outlook (DO) builds on the Drought Monitor categories to project how these drought areas might change or where new drought areas might develop. No change is indicated for the two areas in the region currently categorized in D0, and no new areas of drought development are projected in the region (Figure DO-1).

Readers interested in the next 5 and 6–10 days can consult the “Looking Ahead” section of each week’s Drought Monitor for near-term drought outlook conditions. The next Seasonal Drought Outlook will be issued August 6th.


Figure DO-1. Seasonal Drought Outlook for July 16, 2009–October 2009. (Source: NOAA Climate Prediction Center)

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The Intermountain West Climate Summary is published periodically by Western Water Assessment (WWA), a joint project of the University of Colorado Cooperative Institute for Research in Environmental Sciences (CIRES) and the National Oceanic and Atmospheric Administration (NOAA) Earth System Research Laboratory (ESRL), researching water, climate, and societal interaction.

Disclaimer - This product is designed for the provision of experimental climate services. While we attempt to verify this information, we do not warrant the accuracy of any of these materials. The user assumes the entire risk related to the use of this data. WWA disclaims any and all warranties, whether expressed or implied, including (without limitation) any implied warranties of merchantability or fitness for a particular purpose. This publication was prepared by CIRES/WWA with support in part from the U.S. Department of Commerce/NOAA, under cooperative agreement NA17RJ1229 and other grants. The statements, findings, conclusions, and recommendations are those of the author(s) and do not necessarily reflect the views of NOAA.