Greater Yellowstone Network

Transcription

1 National Park Service U.S. Department of the Interior Natural Resource Program Center Greater Yellowstone Network Climate of 2007 Natural Resource Report NPS/GRYN/NRR 2009/076

2 ON THE COVER Grand Teton National Park. National Park Service photo.

3 Greater Yellowstone Network Climate of 2007 Natural Resource Report NPS/GRYN/NRR 2009/076 Authors Stephen Gray Christopher Nicholson Thomas Dietrich Scott Laursen Wyoming State Climate Office 1000 E. University Ave. University of Wyoming Laramie, WY Editing and Design Emily Yost January 2009 U.S. Department of the Interior National Park Service Natural Resource Program Center Fort Collins, Colorado

4 The Natural Resource Publication series addresses natural resource topics that are of interest and applicability to a broad readership in the National Park Service and to others in the management of natural resources, including the scientific community, the public, and the NPS conservation and environmental constituencies. Manuscripts are peer-reviewed to ensure that the information is scientifically credible, technically accurate, appropriately written for the intended audience, and is designed and published in a professional manner. Natural Resource Reports are the designated medium for disseminating high priority, current natural resource management information with managerial application. The series targets a general, diverse audience, and may contain NPS policy considerations or address sensitive issues of management applicability. Examples of the diverse array of reports published in this series include vital signs monitoring plans; monitoring protocols; how to resource management papers; proceedings of resource management workshops or conferences; annual reports of resource programs or divisions of the Natural Resource Program Center; resource action plans; fact sheets; and regularly-published newsletters. Views, statements, findings, conclusions, recommendations, and data in this report are solely those of the author(s) and do not necessarily reflect views and policies of the U.S. Department of the Interior, National Park Service. Mention of trade names or commercial products does not constitute endorsement or recommendation for use by the National Park Service. Printed copies of reports in this series may be produced in limited quantity, and are only available as long as the supply lasts. You may send a request to: Greater Yellowstone Network AJM Johnson Hall Bozeman, MT This report is also available electronically from the Greater Yellowstone Network website, units/gryn/, and the Natural Resource Publications Management website, Please cite this publication as: Gray, S., C. Nicholson, T. Dietrich, and S. Laursen Greater Yellowstone Network: Climate of Natural Resource Technical Report NPS/GRYN/NRR 2009/076. National Park Service, Fort Collins, Colorado. NPS D-1304, January 2009 ii

5 Contents 1. Introduction Summary of GRYN Climate in Annual Regional Overview Precipitation Temperature Annual GRYN Climate Stations Precipitation Temperature Annual GRYN Snowpack Annual GRYN Region Stream Flows Annual GRYN Region Drought Status Appendix 1: National Weather Service COOP Stations Appendix 2: Natural Resource Conservation Service SNOTEL Stations Appendix 3: U.S. Geological Survey Stream Gauging Stations Contents iii

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7 Overall, 2007 represented a continuation of predominately dry conditions and a moderate-to-severe drought which began in the late 1990s. The prevalence of drought conditions in the headwaters of the Wind and Bighorn rivers, which flow into Bighorn Lake, contributed to drought conditions in Bighorn Canyon National Recreation Area. 1. Introduction This report is the first installment in an annual series detailing the climate of the Greater Yellowstone Network (GRYN). The GRYN is comprised of three National Park Service units: Yellowstone National Park, Grand Teton National Park (including the John D. Rockefeller, Jr. Memorial Parkway), and Bighorn Canyon National Recreation Area. The GRYN covers a vast area and encompasses a variety of climatic zones. For example, the Yellowstone Plateau and Teton Range represent some of the wettest and coolest areas in the Interior West while the Bighorn Canyon area is one of the driest and warmest. Factors controlling climate vary throughout the region; western portions of the GRYN are influenced by the Pacific Northwest climate, while a mid-continental or Great Plains-type climate prevails in the east. The purpose of this annual climate report is twofold: First, these reports detail recent climate events from both local (single weather stations) and park-level perspectives. Second, these reports place GRYN climate in a regional context and consider recent events in a historical context. The content is generally divided into discussions of temperature and precipitation and further sub-divided into regional- and station-level reviews. Information includes precipitation and temperature variability and is supplemented with sections on snowpack, stream flow, and regional drought status. Raw monthly temperature and precipitation data, links to all station records used in this report, and station metadata are available in the appendices. The criteria used for selecting stations in this report and discussions of data availability, data quality, and data completeness are available from the GRYN in a separate document, Report Preparation and Data Issues: Annual Climate of the Greater Yellowstone Network. Those interested in additional climate-related information for the GRYN and surrounding areas should seek: Western Regional Climate Center ( Western Water Assessment ( National Oceanic Atmospheric Administration Climate Prediction Center ( Natural Resources Conservation Service Water and Climate Program ( USGS (U.S. Geological Survey) Water Information System ( Idaho State Climate Service ( index.html) Montana Climate Office ( Wyoming State Climate Office ( wrds/wsc/wsc.html) U.S. Drought Monitor ( monitor.html) 1.1 Summary of GRYN Climate in 2007 The climate of 2007 was comprised of warmer than average temperatures throughout most of the year and drier than average conditions over the spring and summer months. The extremely warm nighttime temperatures in the months of March and July were particularly noteworthy. Warm spring temperatures contributed to an early runoff throughout the GRYN region. When combined with a lackluster snowpack, this early runoff also contributed to lower than average river levels from July through August. Abnormally dry-to-severe drought conditions prevailed throughout the summer months. Overall, 2007 represented a continuation of predominately dry conditions and a moderate-tosevere drought which began in the late 1990s. 1

8 2. Annual Regional Overview 2.1 Precipitation The year 2007 began with an unusually dry January (fig. 1). Compared to the climatological normal (the prevailing set of weather conditions calculated over a 30-year period, currently ), Yellowstone received between 50% and 75% of average precipitation, with similar conditions in Grand Teton. This January dryness is notable because snowfall is generally heaviest during mid-winter in Yellowstone and Grand Teton and this lack of moisture eventually contributed to the onset of drought conditions over the summer months. January was also quite dry within Bighorn Canyon, but precipitation at the headwaters of the Wind-Bighorn River system, which eventually flows into Bighorn Lake, was generally average to slightly above average. A mix of conditions was present in the GRYN and surrounding areas during February and March (fig. 1). February precipitation was generally average to slightly above average in Yellowstone and Grand Teton compared to , whereas March was relatively dry. Between February and May, three out of four months had below-average precipitation in the headwaters of the Wind-Bighorn River system. Moisture from April through June is critical for much of eastern Yellowstone, all of Bighorn Canyon, and the Wind-Bighorn watershed because these are historically the months of greatest precipitation, and rain or snow over this period has a large impact on forage production. As shown in figure 1, these months were relatively dry over much of the GRYN region. Of particular note is the extreme dryness (25% of average or less) in areas south of Bighorn Canyon during April. This lack of spring moisture would later contribute to low inflows into Bighorn Lake, the centerpiece of recreational activity at Bighorn Canyon. Moisture to the Wind- Bighorn watershed upstream from Bighorn Canyon in July (fig. 1) did little to ease the drought conditions that developed during the summer. A wide range of moisture conditions occurred in the fall. October was extremely wet across the region though large parts of the Wind-Bighorn watershed were extremely dry again by November. In December, near average precipitation was recorded in Yellowstone and Grand Teton, with relatively wet conditions in the watershed upstream from Bighorn Canyon and Bighorn Lake. On the whole, near average precipitation levels have prevailed since December 2007, bringing hope of some drought relief in Temperature Regional climate in 2007 was marked by unusually warm temperatures over the spring and summer months. Maximum daily temperatures for March were generally much warmer (usually 4ºF 6ºF) than averages (fig. 2). Moreover, minimum daily temperatures (fig. 3) were 6ºF to more than 8ºF above average in each park unit during March, and nighttime temperatures were similarly warm for Yellowstone and Grand Teton in February. A pattern of slightly warmer than average daytime temperatures (fig. 2) and markedly warmer than average nighttime temperatures (fig. 3) prevailed in the Yellowstone and Grand Teton areas in April. Likewise, days and nights in both May and June were generally 2ºF 6ºF above averages across the GRYN region. Early spring through early summer warmth would in turn set the stage for an early runoff and contribute to drought conditions experienced in the GRYN during the summer months. The unusual heat of July was of the greatest significance in terms of drought and ecosystem impacts. Hot daytime temperatures (fig. 2) and a reduction in nighttime cooling (fig. 3) exacerbated the effects of an early snowmelt and a dry May through June in Yellowstone and Grand Teton. When combined with an early runoff and the subsequent low stream flows this heat had major negative impacts on Yellowstone, Grand Teton, and surrounding By the beginning of June 2007, the combination of a warm, dry spring and a declining snowpack left parts of Yellowstone National Park and all of Grand Teton National Park in a state of severe drought. Mike Tercek 2

9 Legend Figure 1. Maps showing percent of average precipitation versus for each month in calendar year Maps were created using estimates from the Parameter-elevation Regressions on Independent Slopes Model (PRISM). PRISM interpolates precipitation values between actual observation stations, and corrects these interpolated estimates for changes in topography across the region. For more information, see 3

10 Legend Figure 2. Maps showing departures from average maximum daily temperatures for each month in calendar year 2007 versus Departure values are reported in degrees Fahrenheit. Maps were created using estimates from PRISM. 4

11 Legend Figure 3. Maps showing departures from average minimum daily temperatures for each month in calendar year 2007 versus Departure values are reported in degrees Fahrenheit. Maps were created using estimates from PRISM. 5

12 Table 1. Total monthly precipitation during 2007 and percentage of average monthly precipitation versus for select GRYN region stations in inches Station Name Station ID Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sep. Oct. Nov. Dec. Annual Mammoth, WY (YNP) Cooke City 2 W, MT Lake Yellowstone, WY Old Faithful, WY Snake River, WY Moose, WY Moran 5 WNW, WY Alta 1 NW, WY Driggs, ID Cody, WY Lovell, WY Shell, WY Pryor, MT Yellowtail Dam, MT (84) 1.07 (45) 0.94 (53) 1.6 (66) 2.28 b (58) 0.97 (37) 1.46 (47) 1.56 (70) 0.98 c (73) 0.33 (75) 0.08 (33) 0.2 (35) 0.22 (33) 0.83 (94) 1.1 (153) 2.12 (105) () 2.94 (130) 2.7 (84) 1.28 a (60) 2.39 (96) 1.64 (84) 0.88 c (77) 0.52 (163) 0.44 (259) 1.16 a (232) 0.26 (41) 0.96 (125) 0.36 (38) 0.64 a (33) () 0.7 (32) 0.88 (33) 0.58 (35) 0.62 (28) 0.59 (31) 0.23 (19) 1.01 (191) 0.66 (213) 0.35 a (59) 2.41 a (210) 2.52 a (184) 1.33 (114) 2.71 (138) 2.56 (164) 1.94 (90) () 1.3 (87) 1.77 (88) 1.86 (84) 1.11 (78) 1.58 (141) 1 (167) 1.03 (97) () 1.96 (92) 0.5 (26) 1.79 (65) 0.76 (34) 0.75 a (27) 0.23 a (8) 0.14 (7) 0.6 (26) 0.84 (25) 0.68 (34) 0.65 (34) 1.39 (116) 2.05 (118) () 2.41 (77) () 2.49 (85) () 0.84 b (36) 0.36 b (15) 0.37 (22) () 1.92 (86) 1.71 (129) 2.22 (138) () 0.53 b (35) 1.46 (67) 6.39 (280) 0.64 (41) 1.98 (94) 2.50 c (150) 1.21 b (72) () 0.56 (41) 0.99 (76) 1.83 (108) 1.51 (126) 0.31 (27) 0.38 (54) 0.46 a (49) 2.49 (182) 0.14 (10) 1.6 (109) () () 1.9 (122) 2.28 (130) 1.6 (107) 1.6 (119) 1.51 (92) 1.39 (120) 1.09 (110) 0.21 (33) 0.76 (107) 0 (0) 0.12 (11) 1.13 (84) () () 1.72 (114) 2.01 (118) 1.49 (108) 1.68 (120) 1.83 (102) 1.5 (129) 0.34 (31) 0.14 (18) 0.84 a (78) 0.84 (52) 1.26 (71) 1.91 (199) 3.35 (212) () 4.22 (279) 3.14 b (154) 2.82 (212) 3.87 (232) 3.18 (161) 3.17 (258) 1.47 (167) 1.97 (328) 2.08 (229) 2.84 (172) 3.68 (215) 0.46 (49) 1.35 (64) 1.4 (80) 1.86 (76) () 2.98 (135) 2.82 (101) 1.5 (71) 0.89 (70) 0.27 (540) 0.17 (63) 0.28 (500) () 0.55 (52) () 1.59 (66) 4.7 (280) () () 2.38 (92) () () () () () () 0.67 (110) 0.57 (66) 9.73 (66) (86) (71) (78) (44) (74) 17.8 (70) (72) (89) 9.79 (90) 6.44 (95) 9.74 (91) (72) (116) Note: Percentages of monthly average precipitation versus are given in parentheses. Station IDs are from National Weather Service COOP stations. Monthly statistics not reported if more than three days of data are missing. Individual months not used for annual statistics if more than five days of data are missing. a 1 day of data missing. b 2 days of data missing. c 3 days of data missing. fisheries. Likewise, hot July temperatures helped intensify local drying around Bighorn Canyon. Maximum daily temperatures (fig. 2) moderated somewhat from August through October, but minimum daily temperatures remained quite warm through November. Maximum daily temperatures for December 2007 were near average to slightly below average across the GRYN. Minimum daily temperatures were slightly warmer than average for southern Yellowstone and all of Grand Teton during December. 3. Annual GRYN Climate Stations 3.1 Precipitation Selected National Weather Service Cooperative Observer (COOP) stations show key aspects of precipitation variability within the GRYN (appendix 1). As in the regional overview provided by Parameter-elevation Regressions on Independent Slopes Model (PRISM) estimates (fig. 1), individual station records from Yellowstone and Grand Teton show the extreme dryness of January The Lake Yellowstone station in central Yellowstone and the Cooke City, Montana station near the park s northeast entrance were at 45% and 53% of average (versus ) for the month (table 1). The Moose and Moran stations represent the eastern and central half of Grand Teton where at 37% and 47% of average for January, respectively. Conditions during February varied widely across the region with stations in the Grand Teton area generally reporting below average precipitation (e.g., Moose at 60% average precipitation), and some stations in the Wind-Bighorn watershed upstream from Bighorn Canyon reporting over 200% of average (e.g., Lovell and Shell, Wyoming). Data from National Weather Service COOP Stations throughout Yellowstone and Grand Teton documented a very dry May with two sites (Snake River and Moose, Wyoming) at less than 10% of averages (table 1). In locations such as Old Faithful in the interior of Yellowstone where May is historically the wettest month of the year, this lack of late-spring precipitation would later contribute to the moderate to severe drought conditions that 6

13 Table 2. Observed average maximum daily temperatures and departures from averages of select GRYN region stations during calendar year 2007 Station Name Station ID Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sep. Oct. Nov. Dec. Annual Mammoth, WY (YNP) Cooke City 2 W, MT Lake Yellowstone, WY Old Faithful, WY Snake River, WY Moose, WY Moran 5 WNW, WY Alta 1 NW, WY Driggs, ID Cody, WY Lovell, WY Shell, WY Pryor, MT Yellowtail Dam, MT (-3.2) 24.2 (-0.2) 21.3 b (-2.0) 24.2 (-4.0) 23.6 (-2.9) 21.9 (-4.0) 21.5 (-4.5) 22.7 (-6.5) 22.2 (-7.4) 33.5 (-2.0) 29.8 (0.3) 29.7 (-2.3) () 40.9 (1.5) 34.0 (-0.3) 29.4 (-1.3) 29.2 (0.7) 29.8 (-3.5) 30.3 (-1.4) 35.3 (3.9) 33.2 (1.0) 33.2 (-0.8) 34.4 (-0.4) 39.8 (-1.0) 33.4 (-4.7) 34.5 (-6.5) ) 36.4 (-8.5) 48.3 (7.2) 43.6 (6.1) () 41.4 (1.3) () 45.6 (5.8) 45.7 (5.7) 44.4 (4.2) 46.3 (4.0) 57.4 (8.4) 55.0 (5.5) 55.4 (3.8) () 57.9 (4.7) 52.3 (2.9) 47.8 (2.8) () 47.5 (0.6) () 52.8 (3.6) 51.5 (3.3) 51.1 (2.5) 52.6 (0.2) 57.2 (0.3) 55.4 (-3.4) 56.4 (-3.6) () 57.5 (-4.8) 65.6 (6.0) 60.6 (6.1) () 59.0 (3.9) 59.8 (3.0) 66.8 (6.3) 62.5 (4.3) 64.8 (5.4) 64.9 (2.2) 71.4 (5.6) 70.5 (2.2) 72.8 (3.2) () 71.2 (-0.4) () 70.1 (5.2) () 68.7 (3.8) 70.9 (3.2) 76.6 (6.2) () 73.3 (3.7) 75.0 (2.8) 80.2 (4.2) () 82.6 (2.5) () 80.9 (-0.6) 89.1 (10.2) 82.7 (9.7) () 82.0 (8.4) () 90.2 (11.4) 86.1 (8.5) 85.9 (8.0) 85.1 (5.5) 89.7 (6.6) 90.9 (4.8) 94.5 (6.6) () 96.7 (7.1) 81.2 (2.9) 74.7 (2.9) () 74.2 (0.9) 77.0 (1.3) 81.7 (3.6) 78.8 (2.1) 79.2 (2.2) 79.6 (0.7) 84.4 (2.6) 85.3 (0.3) 88.8 (2.1) () 87.8 (-1.7) 69.4 (1.7) () () 63.2 (-0.4) 65.5 (-0.8) 70.1 (1.2) 70.4 (3.4) 67.4 (-0.3) 67.4 (-2.4) 75.5 (3.5) 74.7 (1.0) 77.0 (1.7) () 77.3 (-1.2) 51.4 (-3.2) 48.4 (-0.5) () 48.2 (-2.3) 48.7 (-3.7) 53.6 (-1.6) 52.4 (-1.1) 51.5 (-3.1) 52.7 (-4.6) 59.5 (-0.5) 59.0 (-1.2) 60.6 (-1.3) () 63.3 a (-1.8) 42.3 (5.0) 36.7 (5.2) 36.0 a (3.6) 37.0 c (2.7) () 43.4 (6.7) 41.0 (5.7) 41.9 (4.6) 42.7 (3.3) 48.6 (4.8) 48.2 (5.8) 50.0 a (6.2) () 50.8 (3.1) () 22.2 (-1.1) 19.5 (-5.0) () () 27.8 (1.7) () () () () () () () 38.9 (-1.9) 56.0 (3.3) 49.1 (1.6) () 52.3 (2.9) 53.7 (3.6) 55.5 (3.6) 54.3 (3.3) 55.9 (3.7) 56.6 (2.3) 63.4 (4.8) 60.2 (1.5) 63.8 (3.3) () 63.3 (-0.6) Note: Temperatures are given in degrees Fahrenheit. Departures from averages are given in parentheses. Station IDs are from National Weather Service COOP stations. Monthly statistics not reported if more than three days of data are missing. Individual months not used for annual statistics if more than five days of data are missing. a 1 day of data missing. b 5 days of data missing. c 19 days of data missing. affected these areas over the summer. This lack of precipitation continued in southern Yellowstone and Grand Teton during the month of June, with stations reporting between 15% and 36% of average. July was drier than average at sites around the northern and southern ends of Bighorn Canyon (i.e., Lovell and Shell, Wyoming, and Yellowtail Dam, Montana) combined with very warm temperatures would lead to deteriorating on the ground drought conditions in the mid to late summer. However, July wetness to the northwest of Bighorn Canyon (e.g., Pryor, Montana at 182%) shows the potential impact of summer thunderstorms in this area. Average to slightly above average precipitation during August and September kept drought conditions from deteriorating further in the GRYN. October was extremely wet throughout most of the GRYN. Of particular note is the greater than four inches of precipitation received at Old Faithful in Yellowstone and the >300% of historical averages recorded at Lovell, Wyoming, near the southern end of Bighorn Canyon. November was generally dry, with the exception of the Moose and Moran stations which represent eastern and central Grand Teton. Numerous station observations were missing for December 2007, but available data confirm a general pattern of near average precipitation in Yellowstone and Grand Teton for this month. General dryness during December in the area immediately surrounding Bighorn Canyon contrasts with wetter than average conditions in the Wind-Bighorn headwaters upstream from the area. 3.2 Temperature Individual National Weather Service COOP stations throughout the GRYN region (appendix 1) show fine-scale variability in annual temperatures that closely agree with the large-scale overview afforded by the PRISM analyses (figs. 2 and 3). January 2007 featured cooler than average (versus ) daytime temperatures at most Yellowstone and Grand Teton stations (table 2). Stations to the west of Grand Teton (e.g., Driggs, Idaho and Alta, Wyoming) reported the lowest maximum daily temperatures for the month at 6.5ºF 7.4ºF below average. January 7

14 Table 3. Average observed minimum daily temperatures and departures from averages for select GRYN region stations during calendar year 2007 Station Name Station ID Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sep. Oct. Nov. Dec. Annual Mammoth, WY (YNP) Cooke City 2 W, MT Lake Yellowstone, WY Old Faithful, WY Snake River, WY Moose, WY Moran 5 WNW, WY Alta 1 NW, WY Driggs, ID Cody, WY Lovell, WY Shell, WY Pryor, MT Yellowtail Dam, MT (-4.4) -3.8 (-6.9) -5.7 d (-3.3) -9.7 (-8.4) -9.1 (-7.6) -6.6 (-7.0) (-13.4) 2.6 (-6.7) -3.0 (-10.9) 12.2 (-1.4) 5.3 (0.3) 1.0 (-4.9) () 19.5 (0.8) 17.7 (4.0) 14.0 (8.5) 7.3 c (8.0) 12.3 (10.3) 8.5 (7.4) 11.8 (8.5) 5.3 (0.7) 17.8 (5.3) 18.7 (7.2) 18.3 (-0.1) 15.2 (3.2) 11.2 (-2.6) () 18.1 (-4.5) 26.3 (6.6) 19.6 (8.4) () 17.6 (8.8) () 18.3 (5.7) 13.1 (0.7) 25.7 (7.4) 25.6 (6.7) 33.4 (8.0) 27.1 (4.5) 27.5 (5.2) () 33.1 (4.0) 29.2 (2.5) 22.9 (4.3) () 22.5 (5.0) () 26.2 (4.5) 22.2 (0.8) 28.5 (3.1) 28.6 (2.4) 33.9 (1.7) 33.3 (2.1) 33.0 (3.3) () 35.9 (-1.0) 36.4 (1.6) 29.9 (2.4) () 28.3 c (0.8) 26.9 c (0.2) 32.0 (1.2) 27.2 (-3.1) 37.7 (4.6) 35.2 (1.3) 43.7 (3.1) 42.6 (1.2) 41.5 (3.8) () 46.9 (1.7) Note: Temperatures are given in degrees Fahrenheit. Departures from averages are given in parentheses. Station IDs are from National Weather Service COOP stations. Monthly statistics not reported if more than three days of data are missing. Individual months not used for annual statistics if more than five days of data are missing. a 1 day of data missing. b 2 days of data missing. c 4 days of data missing. d 5 days of data missing nighttime temperatures were even colder (table 3), with two stations (Moran, Grand Teton, and Driggs, Idaho) reporting average daily minimum temperatures more than 10ºF below average. In contrast to January, March was notable for widespread warmer than average maximum daily temperatures (table 2). Maximum daily temperature departures in March ranged from 3.9ºF above average (Shell, Wyoming, east of Bighorn Canyon) to 8.4ºF above average (Cody, Wyoming, east of Yellowstone). Nighttime temperatures were even warmer (table 3), with Old Faithful in Yellowstone at nearly 9ºF above average. Though the total departures were somewhat smaller, the general pattern of warmer than average temperatures continued from April through June. The impacts of these warmer than average temperatures can be seen in the early snowmelt, runoff, and drought conditions that mark summer July 2007 was very warm in the GRYN (tables 2 and 3). Maximum daily temperatures ranged from 4.8ºF above average near the southern end of Bighorn Canyon (Lovell, Wyoming) () 34.9 (1.2) () 35.2 (1.2) 32.3 (-0.7) 38.4 (1.6) () 44.0 (3.5) 41.6 (0.9) 52.4 (3.8) () 51.8 (4.6) () 54.5 (1.6) 55.2 (7.9) 44.4 (6.6) () 43.1 (5.1) () 49.4 (8.6) 44.3 (2.7) 53.0 (6.4) 52.0 (6.3) 62.5 (8.4) 61.0 (7.0) 63.5 (10.2) () 64.2 (6.4) 48.3 (1.9) 40.2 (3.3) () 39.2 (2.9) 37.8 (3.1) 44.2 (4.7) 40.2 (-0.1) 49.4 (4.0) 48.2 (3.7) 56.5 (3.4) 53.4 (1.9) 56.0 (5.8) () 58.0 (1.1) 40.4 (2.7) 31.2 d (1.4) () 32.1 (3.7) 30.7 (4.3) 36.1 (4.3) 32.8 (-0.1) 39.5 (1.9) 38.8 (2.3) 46.4 (2.3) 43.1 (2.2) 43.5 (3.8) () 48.4 (0.2) 30.7 (1.4) 25.1 (3.1) () 23.7 (3.7) 24.4 (5.5) 26.7 (3.8) 25.9 (1.2) 29.9 (1.3) 30.1 (2.5) 37.7 (2.8) 33.7 (3.2) 33.4 (4.3) () 40.3 a (1.2) 21.6 (2.9) 15.2 (3.7) 15.6 b (5.2) 11.2 a (3.1) () 18.0 (5.7) 14.6 (0.2) 21.3 (4.1) 20.6 (2.9) 27.7 (4.4) 22.1 (3.9) 21.2 a (4.2) () 28.3 (0.6) () 8.1 (4.8) 3.9 (2.9) () () 5.3 (3.9) () () () () () () () 22.3 (1.3) 31.2 (2.9) 23.5 (3.3) () 23.2 (5.0) 21.6 (4.0) 25.0 (3.7) 21.4 (-0.8) 31.8 (4.7) 30.6 (3.8) 38.6 (4.9) 33.7 (3.2) 34.9 (5.4) () 39.1 (1.0) to 11.4ºF above average at southern Grand Teton (Moose, Wyoming). Minimum daily temperatures were similarly warm. Heat stress to wildlife was exacerbated by the indirect effects of higher air temperatures as increased evaporation and elevated water temperatures contributed to drought conditions. Data from individual National Weather Service COOP stations documented daytime temperatures (table 2) moderating somewhat in August, and then generally dropping to average or slightly below average for September and October. However, minimum daily temperatures (table 3) generally remained 1ºF 4ºF above average through October. Of interest are stations such as Snake River, Wyoming (immediately south of Yellowstone in the parkway), where maximum daily temperatures were below average in September October, but minimum daily temperatures were as much as 5.5ºF above. Warmer than average nighttime temperatures continued through November. 8

15 A B C Figure 4. Measurements begin in October 2006 and span through winter Values from 2007 (red) and winter 2006 (yellow) are compared to the 30-year average (blue) over the normal period. A and B, daily measurements of SWE from two representative sites in the Bighorn River drainage upstream from Bighorn Canyon and Bighorn Lake; C, daily measurements of SWE from a site in the Shoshone River drainage upstream from Bighorn Canyon and Bighorn Lake. Data courtesy of the Natural Resources Conservation Service. 4. Annual GRYN Snowpack Automated snow measurement (SNOTEL) stations are operated by the Natural Resources Conservation Service throughout the GRYN region (appendix 2). These stations offer a means to track the build-up and ablation (depletion by melting and evaporation) of the winter 2007 snowpack. As measured in terms of snow water equivalent (SWE)the amount of liquid water held in a given volume of snowwinter 2007 brought near average (i.e., compared to the climatological normal) snowpack to some sites in the Bighorn River drainage upstream of Bighorn Canyon (fig. 4a and b). However, the basin as a whole had only 74% of average snowpack by the end of May The Wind and Shoshone rivers drainage above Bighorn Canyon did not fare as well. Snowpack throughout this region was lower than average, and measurement sites were often melted-out several weeks earlier than historical averages (fig. 4c). By the end of May 2007, snowpack averaged over the entire Wind and Shoshone river drainages were at 14% and 38% of historical averages. Low snowpack in these basins would eventually contribute to the very low inflows and outflows at Bighorn Lake. Individual SNOTEL sites in Yellowstone and the Yellowstone River drainage (figs. 5a and 5b) generally show a pattern of lower than average SWE from January onward. Melt-out and runoff from these sites occurred approximately four weeks earlier than historical averages. By the end of May, SWE averaged across all sites in the Yellowstone and Madison rivers drainages was only 28% of historical averages.stations in the Snake River drainage (Grand Teton and parts of southern Yellowstone) experienced lower than average SWE accumulations from the end of January onwards (figs. 5c and 5d). This low SWE was also combined with a very early melt and runoff (figs. 5c and 5d). By the end of May, the Snake River drainage was at only 9% of historic SWE. 5. Annual GRYN Region Stream Flows The USGS monitors stream flow at numerous locations throughout the GRYN. Key aspects of regional hydrology can be represented by a subset of these gauging stations (appendix 3). The Shell Creek (near Shell Creek, Wyoming) and South Fork of the Shoshone River (near Valley, Wyoming) gauges represent small, higher elevation, and relatively unregulated watersheds upstream from Bighorn Canyon and Bighorn Lake (fig. 6a and 6b). Total discharge at Shell Creek was near average for water between October 2006 and September 2007 (federal fiscal year 2007). However, peak runoff occurred one month earlier than the average from the previous 31 years. Runoff was also shifted forward by 9

16 A B C D Figure 5. Measurements begin in October 2006 and span through winter Values from 2007 (red) and winter 2006 (yellow) are compared to the 30-year average (blue) over the normal period. A and B, daily measurements of SWE from two representative sites in potions of the Yellowstone River drainage within the GRYN; C and D, daily measurements of SWE from two representative sites in portions of the Snake River drainage within the GRYN. Data courtesy of the Natural Resources Conservation Service. approximately four weeks on the South Fork of the Shoshone. In addition, mid to late summer (i.e., July through August) flows were noticeably lower than average (versus the 50-year average from 1957 to 2006). The Bighorn River at Kane, Wyoming, gauge (fig. 6c and 6d) shows that total inflows to Bighorn Canyon and Bighorn Lake were only 50% of average during water year 2007 (versus ). Though it must be noted that the Bighorn River above the Kane is regulated by several dams, this gage shows diminished flows in the July through August period. Outflows from Bighorn Lake were also low, reaching only 51% of historical averages (versus ). As represented by gauges at the Yellowstone Lake outlet and Corwin Springs, Montana, the Yellowstone River in Yellowstone showed a combination of early peak runoff and diminished summer flows in water year 2007 (fig. 6e and 6f). Total discharge at these gauges was also lower than average, with Yellowstone Lake outlet at 68% (versus ) and Corwin Springs at 71% (versus ). Flows on the Madison River near West Yellowstone in Montana (fig. 7a) depict similar patterns, though at 83% of average (versus ) relative discharge was slightly higher than for the Yellowstone River gauges. The Snake River at Flagg Ranch, Wyoming gauge represents unregulated inflows to Grand Teton and Jackson Lake. Once again, this gauge record shows an early runoff peak and lower than average summer flows (fig. 7b and 7c). Total discharge at Flagg Ranch was 74% of average (versus ). Total releases from Jackson Lake Dam were 83% of average (versus ). 6. Annual GRYN Region Drought Status The U.S. Drought Monitor tracks drought conditions across the nation on a weekly basis, and it incorporates data and expert input from a wide variety of state and federal agencies. The U.S. Drought Monitor is designed to represent a broad brush, regional perspective on drought, and therefore provides an ideal tool for tracking generalized drought conditions across the GRYN and surrounding areas. According to the U.S. Drought Monitor by the beginning of June 2007 the combination of a warm, dry spring and a declining snowpack left all of Grand Teton and parts of Yellowstone in a state of severe drought, or D2 conditions, while conditions in the remainder of Yellowstone were classified as moderate (D1) drought (fig. 8). Conditions in Bighorn Canyon were classified 10

17 A B C D E F Figure 6. Stream gauge data from points within the GRYN. Daily flows for October 2006 through September 2007 are shown versus median daily flows for the period of record. Data and graphs are courtesy of the USGS. Stream gauge date from: A and B, representative flows on relatively unregulated streams above Bighorn Canyon and Bighorn Lake; Bighorn River inflow (C) and outflow (D) for Bighorn Canyon and Bighorn Lake; E and F, Yellowstone River in Yellowstone. 11

18 A B C Figure 7. Stream gauge data from points within the GRYN. Daily flows for October 2006 through September 2007 are shown versus median daily flows for the period of record. Data and graphs are courtesy of the USGS. Stream gauge date from: A, Madison River as it leaves Yellowstone; representative flows from unregulated Snake River inflows to Grand Teton and Jackson Lake (B) and outflow from Jackson Lake dam (C). as abnormally dry (D0) for this same month. However, this optimistic assessment was largely a function of this park unit being in a transition zone between the dryness of the Yellowstone and Grand Teton areas and abnormally wet areas to the east (e.g., the Tongue River drainage). Far more relevant to the status of drought in Bighorn Canyon during 2007 was the prevalence of drought conditions in the headwaters of the Wind-Bighorn rivers which, in turn, flows into Bighorn Lake. Drought conditions remained steady through the start of July (fig. 8). However, extremely warm temperatures over the remainder of this month would eventually contribute to a general deterioration. Stream flows across most of the GRYN and surrounding areas were also in decline by this time. In response, the first U.S. Drought Monitor report of August 2007 placed parts of Grand Teton in extreme drought (D3), with the remainder under severe drought status. In addition, all of Yellowstone was classified in severe drought by the beginning of August. Bighorn Canyon was again caught between contrasting regional-scale dryness to the west and wetness to the east. By this time, a large portion of the Bighorn Lake watershed had deteriorated into extreme drought. Unusually wet conditions in October 2007 led to slight improvements in drought status for parts of the GRYN. This moisture kept conditions from deteriorating further in the remainder of the GRYN. By the end of December, most of Yellowstone had been upgraded to moderate drought (fig. 8), but the regional U.S. Drought Monitor depiction still showed the cumulative effects of warm temperatures, low snowpack, and low runoff earlier in the year. Determining the timing of drought onset or the end date for a drought period is extremely difficult. This problem stems from the fact that climatic events affect species and natural systems in different ways, and multiple factors (e.g., lack of precipitation, changes in timing of precipitation, high temperatures) can lead to moisture deficits. However, by all measures the drought of 2007 is the continuation of a multi-year dry event beginning in the late 1990s or early 2000s. The severity of individual dry years varied throughout the GRYN region and some years (e.g., 2005) featured near historic average precipitation in some parts of the GRYN. On the other hand, years like 2002 and 2003 were among some of the driest in the GRYN region for over a century. When averaged across all climate stations in the upper Yellowstone River watershed, the last year with precipitation at or above historical average levels was Clearly the impacts of this dryness will linger for years to come. 12

19 Legend Figure 8. U.S. Drought Monitor maps for the GRYN region during summer 2007 and at the year end. Drought classifications range from abnormally dry (D0) to exceptional drought (D4). 13

20 Appendix 1: National Weather Service COOP Stations Table 1. National Weather Service Cooperative Observer (COOP) stations used in report Station NWS ID Elevation (ft) Latitude Longitude Latitude DD Longitude DD State County Alta 1 NW, WY ( , WY Teton Cody, WY ( , WY Park Cooke City 2 W, MT ( , MT Park Driggs, ID ( , ID Teton Lake Yellowstone, WY Yellowstone , WY ( NP Lovell, WY ( , WY Big Horn Yellowstone Park, WY (YNP; Mammoth) Yellowstone , WY ( NP Moose, WY ( , WY Teton Moran 5 WNW, WY ( , WY Teton Old Faithful, WY Yellowstone , WY ( NP Pryor, MT ( , MT Big Horn Shell, WY ( , WY Big Horn Snake River, WY Yellowstone , WY ( NP Yellowtail Dam, MT ( , MT Big Horn Note: Station URL is given in parentheses. DD = decimal degrees. 14

21 Appendix 2: Natural Resources Conservation Service SNOTEL Stations Table 1. Natural Resources Conservation Service SNOTEL stations used in report Station NRCS ID Elevation (ft) Latitude Longitude Latitude DD Longitude DD State County Bald Mountain, WY ( pl?sitenum=309&state=wy) Canyon, WY ( pl?sitenum=384&state=wy) Fisher Creek, MT ( pl?sitenum=480&state=mt) Phillips Bench, WY ( pl?sitenum=689&state=wy) Shell Creek, WY ( pl?sitenum=751&state=wy) Snake River Station, WY ( pl?sitenum=764&state=wy) Younts Peak, WY ( pl?sitenum=878&state=wy) Note: Station URL is given in parentheses. DD = decimal degrees. 07e21s 9, WY Big Horn 10e03s 8, WY Yellowstone NP 09d06s 9, MT Park 10f23s 8, WY Teton 07e23s 9, WY Big Horn 10e12s 6, WY Park 09f18s 8, WY Park 15

22 Appendix 3: U.S. Geological Survey Stream Gauging Stations Table 1. U.S. Geological Survey (USGS) stream gauging stations used in report Station USGS ID Latitude Longitude Latitude DD Longitude DD State County Madison River near West Yellowstone, MT ( MT Gallatin Yellowstone River at Yellowstone Lake Outlet, YNP ( WY Teton Yellowstone River at Corwin Springs, MT ( MT Park Bighorn River at Kane, WY ( WY Big Horn Bighorn River near St. Xavier, MT ( MT Big Horn Shell Creek near Shell, WY ( WY Big Horn South Fork Shoshone River near Valley, WY ( WY Park Snake River AB Jackson Lake at Flagg Ranch, WY ( WY Teton Snake River at Moose, WY ( WY Teton Note: Station URL is given in parentheses. DD = decimal degrees. 16

23 The Department of the Interior protects and manages the nation s natural resources and cultural heritage; provides scientific and other information about those resources; and honors its special responsibilities to American Indians, Alaska Natives, and affiliated Island Communities. NPS D-1304, January 2009

24 National Park Service U.S. Department of the Interior Natural Resource Program Center 1201 Oak Ridge Dr., Suite 150 Fort Collins, CO EXPERIENCE YOUR AMERICA