Issued October 28, 2009, Vol. 5, Issue 6

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


October 2009 Summary

Hydrological Conditions Since July, dry conditions have been alleviated in eastern Colorado but have emerged in far southern Utah and southwestern Colorado, with some areas of moderate (D1) and severe (D2) drought.

Temperature & Precipitation— Temperature anomalies across the region during September largely reflected the precipitation anomalies, with warmer-than-average temperatures in all areas other than the eastern slope of Colorado. Most of the region was drier than average in September, with only eastern Colorado receiving above-average precipitation.

ENSO The El Niño event which began in July has recently strengthened and is now in the “moderate” category. El Niño conditions are forecasted to persist through the winter.

Climate Forecasts Seasonal outlooks indicate enhanced risk of above-average temperatures across much of the West in November 2009 and through the winter; the Intermountain West region is forecast to have "equal chances" of high or low precipitation over those periods.


Announcements & News

"Dealing with Drought" Workshops

The WWA, in conjunction with the Colorado Water Conservation Board (CWCB), presented the “Dealing with Drought-Adapting to a Changing Climate” workshop series during October in three locations around Colorado: Castle Rock, Glenwood Springs, and Durango. These workshops built on themes and information from the October 2008 Colorado Governor’s Conference on Managing Drought and Climate Risk. The 80 participants represented diverse sectors and interests affected by drought and climate, including water resource management, agriculture, land-use planning, forest and range management, watershed protection, environmental organizations, and tourism & recreation.

Participants engaged with Colorado climate scientists Joe Barsugli, Jeff Lukas, Kristen Averyt, and Imtiaz Rangwala (WWA) and Nolan Doesken (CSU-Colorado Climate Center) in instructional sessions to learn more about Colorado’s climate and climate variability, the history of past drought in Colorado, scenarios for future climate change, and implications of climate change for water and other resources. During small-group discussion sessions, participants discussed the impacts of the 2000s drought, and what information or resources would help adapt to future droughts; and what potential impacts from a changing (warming) climate most concerned them. Discussion sessions were facilitated by those named above and by Christina Alvord (WWA), Taryn Hutchins-Cabibi (CWCB), and Koren Nydick (Mountain Studies Institute). Input from these discussion sessions will be incorporated into the revised Colorado State Drought Plan scheduled for release in fall of 2010, and the Colorado Climate Action Plan. Participant surveys prior to and after the workshops assessed their climate literacy and use of climate information.

Workshop information including agenda, presentations, and discussion summaries will be posted in coming weeks on the workshop website, http://wwa.colorado.edu/drought09.php. This series of workshops was sponsored by the WWA, CWCB, and the National Integrated Drought Information System (NIDIS), along with the CSU Colorado Climate Center and the Mountain Studies Institute.

Changes in WWA and IWCS staff

Christina Alvord, who previously worked as a research associate with WWA from 2006–2008, returned to WWA in August as a research associate and will again serve as a writer and editor with the IWCS.


Feature Article

The Water Year 2009 in Review

By Christina Alvord (Western Water Assessment)


Focus Article

TreeFlow: A comprehensive web resource for tree-ring reconstructions of streamflow

By Jeff Lukas (Western Water Assessment)


Recent Climate Conditions

Temperatures throughout most of the Intermountain West were high relative to average conditions, ranging between 2ºF below average in the north to 8ºF above average in the southwest for the month of September (Figure RC-1, RC-2). Above-average temperatures occurred across northern Wyoming, transitioning to average temperatures in Utah and northwestern Colorado, which then trended toward below average temperatures in eastern Colorado (Figure RC-2). The average temperature for September exceeded 75ºF in the far reaches of southwest Utah, and typically ranged between 55ºF and 70ºF in the rest of the state. Average temperatures were relatively cooler in Wyoming and Colorado, (50ºF to 65ºF), with the coolest temperatures occurring at high elevation in the Rockies (Figure RC-1).


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

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

Location

Record

New

Old

Year

September 6

Bountiful Val Verda, UT

High Min Temperature

71ºF

66ºF

1998

Salt Lake City Airport, UT

High Min Temperature

70ºF

69ºF

2003

September 14

 

 

 

 

Alamosa, CO

Daily Max Rainfall

0.36 inch

0.25 inch

1949

September 15

 

 

 

 

Laramie Airport, WY

Daily Max Rainfall

0.49 inch

0.30 inch

1950

September 22

 

 

 

 

Grand Junction Airport, CO

Low Min Temperature

34ºF

34ºF

1995

September 25

 

 

 

 

Cedar City Airport, UT

High Max Temperature

86ºF

86ºF

1994

September 26

 

 

 

 

Cedar City Airport, UT

High Max Temperature

88ºF

87ºF

1994

Tooele, UT

High Max Temperature

86ºF

86ºF

1922

Wendover, UT

High Max Temperature

90ºF

88ºF

1928

September 27

 

 

 

 

Bryce Canyon Airport, UT

High Max Temperature

81ºF

80ºF

1963

Capitol Reef NP, UT

High Max Temperature

88ºF

86ºF

2001

Cedar City Airport, UT

High Max Temperature

88ºF

87ºF

2003

Escalante, UT

High Max Temperature

92ºF

91ºF

2003

Ferron, UT

High Max Temperature

88ºF

88ºF

2003

Hanksville, UT

High Max Temperature

95ºF

94ºF

2003

Lander, WY

High Max Temperature

87ºF

86ºF

1899

Worland, WY

High Max Temperature

89ºF

88ºF

2001

Randolph, UT

High Max Temperature

77ºF

77ºF

2003

September 29

 

 

 

 

Casper, WY

High Max Temperature

86ºF

85ºF

1957, 1992

Salt Lake City Airport, UT

High Min Temperature

68ºF

60ºF

2001

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


Wyoming, Utah, and the western slope of Colorado received less than 75% of average precipitation for September (Figure RC-4). The lack of precipitation and elevated temperatures were sufficient to cause a shift toward drier conditions in the 3-month SPI for these climate divisions (Figure RC-5). However, the 36-month SPI (Figure RC-6) suggests that the above average precipitation that occurred across this region earlier in the summer was sufficient enough to minimize drying in the region (Figure RC-7). In eastern Colorado, where precipitation was generally >100% of average in September (Figure RC-3), both the 3-month and 36-month SPI indicate near average conditions (Figure RC-6).


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

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

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


Figure RC-5. 3-month Intermountain West regional Standardized Precipitation Index as of the end of September 2009 (data from 7/01/09– 9/30/09). (Source: Western Regional Climate Center)

Figure RC-6. 36-month Intermountain West regional Standardized Precipitation Index as of the end of September 2009 (data from 10/01/06–9/30/09). (Source: Western Regional Climate Center)


The U.S. Drought Monitor (Figure RC-7) for mid-October has changed significantly since July, with abnormally dry (D0), moderate drought (D1), and severe drought (D2) conditions in southwestern Colorado and in the southern portion of Utah. A dearth of precipitation and relatively high average temperatures between July and October contributed to a worsening of drought conditions.


Figure RC-7. Drought Monitor from October 15, 2009 (full size) and July 15, 2009 (inset, lower left) for comparison. (Source: National Drought Mitigation Center)


Intermountain West Snowpack

Snowpack values during October reflect the beginning of the winter snowpack accumulation curve and are poorly correlated with late-season (e.g., April 1) snowpack values. That said, October precipitation and snowfall can be important in alleviating summertime drying of the soil (potentially improving runoff efficiency in the following spring) and in establishing the snow base at regional ski areas. As of October 12, SNOTEL snow water equivalent (SWE) percent of average values in the Intermountain West were highest across Wyoming and northern Colorado and Utah, with the majority of sites in these areas reporting 150% to >200% of average SWE (Figure SP-1). The majority of SNOTEL sites in Wyoming reported >200% of average SWE values due to above-average precipitation the state during the first half of October. Wyoming water year-to-date (since October 1, 2009) precipitation ranges from 124–181% of average according to NRCS SNOTEL sites. In comparison, inconsistent precipitation across Utah and the southern half of Colorado is reflected in varying SWE values in these areas as of October 12. In Colorado, year-to-date precipitation is near or above average, ranging from 76–158% of average with southwestern stations reporting the lowest averages. In central and southern Utah, SNOTEL stations are reporting nominal SWE amounts due to below-average precipitation in the first half of October in these areas. Year-to-date precipitation reflects a north-south gradient with the highest percentages (100% to >125% of average) reported in northern Utah and the lowest percentages (<45%) in southern basins.

Figure SP-1. Snow-water equivalent as of October 12, 2009 as percent of the long-term average, at SNOTEL sites across the Intermountain West. (Source: Natural Resources Conservation Service)


ENSO Status and Forecast

NOAA scientists announced the arrival of an El Niño event in July, and this event continues with monthly sea surface temperature (SST) anomalies remaining 0.5ºC to 1.5ºC above average across the central and east-central equatorial Pacific (Figure EN-1). There has been some waxing and waning of the strength of the anomalies over the past 6 weeks, but NOAA expects that the currently weak El Niño conditions will strengthen to a moderate event peaking in the January-March 2010 season, and extend through the March–May 2010 season. A strong event is less likely, but still possible. (Note: Since the release of the NOAA ENSO Diagnostic Discussion in early October, on which this text is based, the current El Niño has strengthened to a moderate event.) 

The impact of El Niño on the climate over North America is expected to be greatest during the winter season, although the event influences the temperature and precipitation outlooks for October–December 2009 through the March–May 2010 season. Although often associated with negative impacts, El Niño typically brings beneficial winter precipitation to the arid Southwest, can help suppress Atlantic hurricane activity, and leads to less wintry weather across the North and a reduced risk of Florida wildfires.


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 October 14, 2009. (Source: NOAA Climate Prediction Center)


According the International Research Institute for Climate and Society (IRI), which partners with NOAA on these outlooks, there is an approximately 90% probability of maintaining at least weak El Niño conditions for the October–December and November–January seasons, and a 10% probability of returning to ENSO-neutral conditions. Probabilities for continuing El Niño conditions remain above 80% through the January–March season, decreasing to 50% by March–May season and further decreasing to the 25% (the typical climatological probability) by the May–July season. Across a broad set of dynamical and statistical forecast models, nearly all indicate maintenance of at least weak El Niño conditions, or El Niño conditions of increasing strength, during the October–December season currently in progress (Figure EN-2).

The NOAA ENSO Diagnostic Discussion will be updated on the first Thursday of November 2009.


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 October–December 2009 to June–August 2010 (released October 15, 2009). (Source: International Research Institute (IRI) for Climate and Society)


Temperature Outlook
November 2009–March 2010 (Released October 15, 2009)

The latest temperature outlooks from the NOAA Climate Prediction Center indicate an enhanced risk of above-average temperatures for across much of the West, including all of the Intermountain West, in November 2009 and subsequent seasons (Figures TEMP-1 to TEMP-4).

Temperature impacts of El Niño over the U.S. are typically weak during the summer and early fall, and strengthen during the late fall and winter.  ENSO composites heavily influence the outlooks for temperature for November and subsequent seasons through the winter. There is an overall trend towards warming conditions in the southwestern U.S.

Note: These climate outlooks are intended for use prior to the start of their valid period (in this case, prior to the beginning of November).  Within any given valid period observations and NWS short- and medium-range forecasts should be consulted. The November 2009 temperature forecast will be updated on October 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 November 19th.


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

Figure TEMP-2. Long-lead national temperature forecast for November 2009–January 2010. (Source: NOAA Climate Prediction Center)

 

Figure TEMP-3. Long-lead national temperature forecast for December 2009–February 2010. (Source: NOAA Climate Prediction Center)

Figure TEMP-4. Long-lead national temperature forecast for January–March 2010. (Source: NOAA Climate Prediction Center)


Precipitation Outlook
November 2009–March 2010 (Released on October 15, 2009)

The CPC precipitation outlook for November 2009 (Figure PPT-1) shows “EC” ("Equal Chances") for most of the continental U.S., including the Intermountain West. There are no clear signals in the outlook for November or the November–January season, resulting in a forecast for equal chances for below, near, or above median precipitation (similar to climatology) in the Intermountain West (Figure PPT-1 to -4).

Areas of above- or below-median precipitation are largely due to expected El Niño impacts on climate, including the typical El Niño-influenced tilt of the odds towards above-median precipitation for some areas of the southern tier, and towards dry conditions for the Pacific Northwest and Ohio Valley.

Note: these climate outlooks are intended for use prior to the start of their valid period (in this case, prior to the beginning of November).  Within any given valid period observations and NWS short- and medium-range forecasts should be consulted. The November 2009 precipitation forecast will be updated on October 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 November 19th.


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

Figure PPT-2. Long-lead national precipitation forecast for November 2009–January 2010. (Source: NOAA Climate Prediction Center)

Figure PPT-3. Long-lead national precipitation forecast for December 2009–February 2010. (Source: NOAA Climate Prediction Center)

Figure PPT-4. Long-lead national precipitation forecast for January–March 2010. (Source: NOAA Climate Prediction Center)


As noted in the latest experimental SWcast discussion released on October 23, El Niño conditions increased in strength since the end of September. The experimental SWcast forecast guidance for the fall (October–December 2009) shows a tilt towards dry conditions for New Mexico and Arizona, but more neutral for Colorado and Utah (Figure PPT-5). El Niño fall seasons tend to be wet in all four states, so this forecast in part reflects the weak nature of El Niño conditions through September.  The new late-winter forecast guidance (January–March 2010) released on October 23, also tilts towards dry conditions for Arizona. The outlook for New Mexico is wet, consistent with El Niño expectations, while Colorado and Utah show a generally dry forecast (Figure PPT-6).


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

Figure PPT-6. Experimental precipitation forecast guidance. Forecasted shifts in tercile probabilities for January–March 2010. (Source: NOAA ESRL Physical Science Division)


Seasonal Drought Outlook
through January 2010 (Released October 15, 2009)

The October 13 U.S. Drought Monitor indicated that a portion of southwest Colorado and southeast Utah near the Four Corners is in severe (D2) and moderate (D1) drought status. Besides this area, southern Utah and central Colorado are the only other areas experiencing abnormally dry (D0) conditions, and Wyoming is reporting no drought conditions (Figure RC-7 above). The U.S. Seasonal Drought Outlook builds on the Drought Monitor categories to project how these drought areas might change or where new drought areas might develop. The Drought Outlook is reporting that some improvement is expected by the end of January 2010 in the drought conditions observed in the Four Corners area. The development of new areas of drought is not expected in the Intermountain West for the forecasted period (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 November 5th.


Figure DO-1. Seasonal Drought Outlook for October 15, 2009–January 2010. (Source: NOAA Climate Prediction Center)


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.