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Wyoming Climate Summary--Water Year 2018

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Contents
Temperature
The period from 01 Oct 2017 through 30 Sep 2018 (Water Year 2018) was the 12th warmest Wyoming water year in the last 123 years. The state ranged from about 2.5°F below normal to 4°F above normal (Figure 1). The lower elevations of the Bighorn Basin and much of the northeast quarter of the state were coolest compared to normal, whereas the far eastern plains in the south, central Campbell County, and the central region (lower elevation areas of Fremont County and southern Natrona County into Converse County) were about normal. The rest of the state and the high elevation mountain ranges were above normal, especially throughout the southwest.

Looking at the Climate Divisions (CD) in the state (Figure 2), the rankings show that the warmth in the higher elevations offset the relative coolness in the basins. This is seen most vividly in CD 4, the Bighorn Basin. Parts of the basin were as much as 2.5°F below normal, but the Bighorns in the east and the Absaroka Range in the west were above normal, making the CD the 20th warmest of the last 123 years. CD 3, the Green and Bear drainages, had the warmest ranking of all ten divisions and was the 4th warmest since 1895. At the opposite corner of the state, CD 6, the Belle Fourche Drainage, was the coolest. Even this, ranking as the 50th warmest, was in the warmer half of years.


Figure 1. Wyoming Water Year 2018 Annual Temperature Departure from Normal (PRISM Climate Group, 2018)

Statewide, there was no one period in particular that drove the ranking. While all but three months of the water year (August, February, and October) were in the warmer half of their rankings, four isolated months pushed this water year to its rank of the 12 warmest. September was ranked 12th, January and November were both ranked 8th, and May was ranked as the 7th warmest.

When considering the individual months, all divisions except CD 6 (the Belle Fourche drainage) were in the bottom tercile (below normal) for average temperature in October of 2017. For maximum temperature, all climate divisions were in the middle tercile (normal) except for CD 2 and CD 9 (Snake and Wind River drainages) which were in the bottom tercile. The minimum temperature drove down the average temperature ranking for the state as all climate divisions were in the bottom tercile. CD 3 (the Green and Bear drainages), ranked as the 12th coldest October since 1895, was in the bottom 10 percent.

Figure 2. Wyoming Water Year 2018 Climate Division Temperature Rankings (NOAA National Centers for Environmental Information (NCEI), 2018)

February was the other month with a statewide ranking in the bottom third for average temperature. Like October, this was also driven more by the minimum temperature. Unlike October, though, February.s minimum temperatures were not as intense across all climate divisions, rather, the statewide ranking was influenced by extreme cold in northeast Wyoming. Minimum temperatures in Climate Divisions 5, 6, and 7 (the Powder/Tongue, Belle Fourche, and Cheyenne/Niobrara drainages) were all in the bottom 10 percent of the record from 1895 to 2018.

On the other end of the thermometer, May 2018 had monthly average temperatures in the top 10 percent of years statewide and for all climate divisions except CD 9, the Wind River drainage (Table 1). The maximum temperature was only in the top 10 percent of years in four climate divisions but, again, the minimum temperatures are what drove up the average and statewide and in all climate divisions, the minimum monthly temperatures were in the top 10 percent of year in all drainage basins without exception (Table 2).

Tables 1, 2, and 3 below show the rankings for the state and for each climate division in terms of how cold and how warm each period was ranked and compared to the last 123 years. The rankings are shown for each month and for the water year as a whole. The table below shows Average Temperature rankings and the two tables on the following page show rankings for the Minimum and Maximum Temperature.

Coldest 10%

Coldest 33%

Normal

Warmest 33%

Warmest 10%

 

Average Temperature (Coldest [C] and Warmest [W] Rankings)

Date 

Wyoming

CD 1

CD 2

CD 3

CD 4

CD 5

CD 6

CD 7

CD 8

CD 9

CD 10

 

C

W

C

W

C

W

C

W

C

W

C

W

C

W

C

W

C

W

C

W

C

W

Oct-17

35

89

39

85

30

94

30

94

41

83

41

83

44

80

40

84

36

88

37

87

33

91

Nov-17

116

8

100

24

100

24

120

4

102

22

97

27

99

25

104

20

120

4

111

13

119

5

Dec-17

96

28

92

32

103

21

115

9

78

46

55

69

50

74

49

75

90

34

94

30

111

13

Jan-18

117

8

119

6

122

3

120

5

113

12

101

24

89

36

74

51

112

13

114

11

119

6

Feb-18

27

98

30

95

66

59

70

55

16

109

14

111

9

116

12

113

36

89

33

92

56

69

Mar-18

93

32

88

37

78

47

98

27

92

33

82

43

72

53

86

39

100

25

93

32

99

26

Apr-18

73

52

80

45

85

40

91

34

62

63

53

72

31

94

40

85

70

55

77

48

89

36

May-18

118

7

119

6

117

8

116

9

119

6

116

9

117

8

117

8

120

5

111

14

119

6

Jun-18

97

28

83

42

84

41

106

19

91

34

89

36

90

35

89

36

104

21

87

38

106

19

Jul-18

98

27

107

18

105

20

115

10

96

29

85

40

68

57

56

69

84

41

97

28

105

20

Aug-18

60

65

70

55

69

56

89

36

59

66

49

76

44

81

34

91

55

70

65

60

74

51

Sep-18

113

12

101

24

108

17

120

5

102

23

92

33

85

40

106

19

121

4

110

15

121

4

2018

112

12

113

11

117

7

120

4

104

20

87

37

74

50

76

48

114

10

113

11

118

6

Table 1. Statewide and Climate Division Rankings for Average Temperature (NOAA NCEI Climate at a Glance, 2018)


Coldest 10%

Coldest 33%

Normal

Warmest 33%

Warmest 10%

 

Minimum Temperature (Coldest and Warmest Rankings)

Date

Wyoming

CD 1

CD 2

CD 3

CD 4

CD 5

CD 6

CD 7

CD 8

CD 9

CD 10

 

C

W

C

W

C

W

C

W

C

W

C

W

C

W

C

W

C

W

C

W

C

W

Oct-17

21

103

39

85

24

100

12

112

29

95

19

105

33

91

32

92

32

92

27

97

21

103

Nov-17

118

6

102

22

102

22

121

3

107

17

103

21

106

18

106

18

118

6

114

10

123

1

Dec-17

86

38

89

35

93

31

109

15

71

53

53

71

46

78

46

78

69

55

94

30

100

24

Jan-18

115

10

119

6

116

9

120

5

113

12

101

24

88

37

76

49

109

16

113

12

120

5

Feb-18

25

100

50

75

81

44

88

37

18

107

12

113

3

122

10

115

22

103

31

94

58

67

Mar-18

86

39

95

30

81

44

98

27

92

33

72

53

67

58

76

49

90

35

95

30

98

27

Apr-18

49

76

84

41

92

33

79

46

47

78

25

100

19

106

23

102

35

90

48

77

68

57

May-18

121

4

123

2

118

7

121

4

121

4

117

8

120

5

122

3

122

3

118

7

119

6

Jun-18

102

23

98

27

90

35

108

17

99

26

89

36

98

27

93

32

103

22

87

38

107

18

Jul-18

102

23

100

25

99

26

113

12

95

30

87

38

89

36

76

49

92

33

90

35

103

22

Aug-18

58

67

76

49

66

59

79

46

58

67

55

70

46

79

32

93

50

75

58

67

70

55

Sep-18

97

28

94

31

58

67

95

30

95

30

82

43

98

27

104

21

111

14

78

47

106

19

2018

110

14

115

9

115

9

120

4

96

28

75

49

72

52

73

51

107

17

109

15

118

6

Table 2. Statewide and Climate Division Rankings for Minimum Temperature (NOAA NCEI Climate at a Glance, 2018)


Coldest 10%

Coldest 33%

Normal

Warmest 33%

Warmest 10%

 

Maximum Temperature (Coldest [C] and Warmest [W] Rankings)

Date

Wyoming

CD 1

CD 2

CD 3

CD 4

CD 5

CD 6

CD 7

CD 8

CD 9

CD 10

 

C

W

C

W

C

W

C

W

C

W

C

W

C

W

C

W

C

W

C

W

C

W

Oct-17

45

79

44

80

36

88

46

78

46

78

50

74

50

74

47

77

43

81

40

84

42

82

Nov-17

107

17

96

28

94

30

112

12

98

26

97

27

95

29

100

24

120

4

103

21

117

7

Dec-17

105

19

93

31

110

14

120

4

86

38

62

62

47

77

55

69

98

26

102

22

115

9

Jan-18

116

9

119

6

121

4

120

5

110

15

107

18

90

35

76

49

112

13

116

9

120

5

Feb-18

31

94

21

104

40

85

57

68

18

107

19

106

16

109

15

110

52

73

36

89

57

68

Mar-18

94

31

87

38

74

51

98

27

93

32

81

44

70

55

91

34

107

18

94

31

100

25

Apr-18

86

39

83

42

84

41

96

29

82

43

73

52

48

77

59

66

90

35

88

37

96

29

May-18

112

13

116

9

112

13

115

10

105

20

111

14

113

12

110

15

108

17

103

22

116

9

Jun-18

97

28

77

48

82

43

102

23

91

34

90

35

87

38

86

39

105

20

87

38

105

20

Jul-18

95

30

104

21

101

24

113

12

92

33

80

45

57

68

39

86

80

45

100

25

103

22

Aug-18

67

58

68

57

73

52

95

30

64

61

50

75

38

87

42

83

54

71

70

55

76

49

Sep-18

117

8

105

20

118

7

124

1

108

17

93

32

71

54

97

28

122

3

121

4

124

1

2018

113

11

108

16

112

12

121

3

106

18

96

28

76

48

81

43

117

7

112

12

120

4

Table 3. Statewide and Climate Division Rankings for Maximum Temperature (NOAA NCEI Climate at a Glance, 2018)


Precipitation
Precipitation totals across the state ranged from about 25% to 205% of the 1981-2010 Normal for water year 2018. The Continental Divide split the state into two different precipitation regimes. To the west, an area which received less than normal precipitation and, to the east, one which had above normal precipitation (Figure 3). The higher elevation areas such as the Wind River Range, the Bighorn Mountains, the Laramie Range, and the eastern flanks of the Owl Creek mountains also had less than normal precipitation totals for the year.


Figure 3. Wyoming Water Year 2018 Annual Precipitation Percent of Normal (PRISM Climate Group, 2018)

Climate Division 7 in the east (the Cheyenne and Niobrara drainages) had the highest percentage of normal and water year 2018 ranked as the 6th wettest year for the period 1895 to 2018. Low elevation areas of the Bighorn Basin and Wind River Basin (Climate Divisions 4 and 9) also had high percentages of normal, but the basins, as a whole, ranked much higher in terms of dryness because of being offset by the relative lack of precipitation in the surrounding higher elevations. Those two divisions (4 and 9) ranked as the 44th and 52nd wettest respectively.


Figure 4. Wyoming Water Year 2018 Climate Division Temperature Rankings (NOAA National Centers for Environmental Information (NCEI), 2018)

Climate Division 6 (the Belle Fourche Drainage) had the second highest ranking in the state (12th wettest out of the last 123 years) and, for all months of the water year, had normal or above normal precipitation. Four months (December, May, June, and August) were in the upper tercile (above normal) of years and an additional three months (February, March, and July) were in the top 10 percent.

Climate Division 10 (the Upper Platte) receive the least precipitation compared to normal and ranked as the 16th driest of the last 123 years. All months ranked either normal or below normal.

Climate Division 1 (the Yellowstone Drainage) had two months (July and September) that were in the bottom 10 percent while three other months (November, February, and April) were in the top 10 percent.

Statewide, September 2018 was the driest month, ranking as the 12th driest since 1895. Four of the divisions (1, 2, 3, and 9) had totals for September that were in the bottom 10 percent (Table 4). While November ranked as the wettest (18th wettest since 1895), February had four divisions (1, 4, 5, and 6) that were in the top 10 percent. May, which had almost the same ranking as February only had one climate division (7, the Cheyenne and Niobrara drainages) that was in the top 10 percent for wetness.

Wyoming, as a whole, for water year 2018 was very close to normal and ranked as the 60th driest and 64th wettest year of the last 123. This ranking, though, is somewhat misleading given the stark differences east and west of the Continental Divide.

Driest 10%

Driest 33%

Normal

Wettest 33%

Wettest 10%

 

Precipitation (Driest [D] and Wettest [W] Rankings)

Date 

Wyoming

CD 1

CD 2

CD 3

CD 4

CD 5

CD 6

CD 7

CD 8

CD 9

CD 10

 

D

W

D

W

D

W

D

W

D

W

D

W

D

W

D

W

D

W

D

W

D

W

Oct-17

33

91

40

84

46

78

13

111

41

83

41

83

55

69

53

71

49

75

49

75

36

88

Nov-17

106

18

119

5

115

9

93

31

105

19

81

43

63

61

74

50

48

76

110

14

63

61

Dec-17

66

58

73

51

31

93

49

75

92

32

83

41

96

28

91

33

60

64

106

18

57

67

Jan-18

47

78

71

54

55

70

41

84

37

88

61

64

79

46

105

20

70

55

43

82

45

80

Feb-18

102

23

117

8

79

46

71

54

117

8

116

9

122

3

109

16

41

84

108

17

60

65

Mar-18

78

47

59

66

92

33

66

59

59

66

93

32

114

11

103

22

79

46

60

65

50

75

Apr-18

48

77

119

6

121

4

39

86

74

51

35

90

59

66

30

95

25

100

43

82

19

106

May-18

103

22

82

43

103

22

98

27

110

15

78

47

89

36

113

12

108

17

108

17

67

58

Jun-18

84

41

110

15

88

37

66

59

88

37

86

39

109

16

113

12

65

60

90

35

64

61

Jul-18

73

52

8

117

13

112

16

109

30

95

84

41

115

10

118

7

89

36

51

74

37

88

Aug-18

60

65

87

38

70

55

42

83

88

37

81

44

98

27

56

69

52

73

38

87

43

82

Sep-18

12

113

7

118

1

124

2

123

21

104

46

79

47

78

43

82

38

87

6

119

17

108

2018

60

64

111

13

81

43

20

104

80

44

65

59

112

12

118

6

52

72

72

52

16

108

Table 4. Statewide and Climate Division Rankings for Precipitation (NOAA NCEI Climate at a Glance, 2018)


Snowpack
April 1st snowpack in Wyoming, the amount which is commonly used in spring stream runoff forecasts, was above normal for much of the north and west. The Upper Bear, Lower Green, Little Snake, Upper North Platte, and Sweetwater basins were about 80% to 90% of normal. The Lower North Platte was the lowest at only 70% of normal.

    Figure 5. Basin Snow Water Equivalent Percent of Normal on the
    1st of April, 2018
  1. Belle Fourche River Basin. April snowstorms pushed Snow Water Equivalent (SWE) well above normal although the start of meltout began less than a week later than the median. Final meltout took place almost exactly at the normal date.
  2. Bighorn River Basin. Spring snows made for an above normal snowpack and meltout began about a week later than normal. The basin was melted out almost a full two weeks before normal.
  3. Lower Green River Basin. Snowpack was about two inches less than normal SWE. Meltout began about two weeks later than normal but finished about a week and a half early.
  4. Lower North Platte River Basin. A poor snowpack reached its peak about as normal but melted out close to two weeks early.
  5. Sweetwater River Basin. Peak snowpack occurred about the normal time but was about three inches below normal SWE. The basin was melted out at the beginning of a June, just a few days earlier than normal.
  6. Little Snake River Basin. Peak snowpack was a few days later than normal but close to three inches of SWE less than normal. Meltout came a little over a week earlier than normal.
  7. Laramie River Basin. This basin peaked right about on schedule compared to normal. SWE was higher than normal but melted out about two weeks earlier than normal.
  8. Cheyenne River Basin. The basin had normal snowpack until the last week in March when storms pushed the SWE up two inches above normal. The peak came a few days later than normal and meltout finished near to the normal date.
  9. Powder River Basin. The peak SWE was reached a few days early but was almost three inches above normal. The basin melted out a little less than a week before normal.
  10. Tongue River Basin. The basin was under normal up until the first part of February. Peak SWE was more than a week later than normal and the SWE, itself, above normal. Meltout came about a week earlier than normal.
  11. Shoshone River Basin. The northwest part of the state received much precipitation and the Shoshone had a peak SWE that was over 12 inches above normal. The peak came at about normal and meltout ended only a day or two early.
  12. Snake River Basin. Peak SWE was about eight inches above normal and the peak was about a week late. The meltout date was only a few days earlier than normal.
  13. Upper Bear River Basin. The peak SWE in this basin was more of a plateau that spanned the normal peak date. Meltout began about a week late and finished about a week early.
  14. Upper Green River Basin. The peak SWE was under five inches above normal and came almost two weeks late. This was one of the few basins that melted out later than normal, although only by a few days.
  15. Upper North Platte River Basin. Peak SWE was just under an inch below normal and occurred right at normal. Final meltout took place more than two weeks early, though.
  16. South Platte River Basin. While peak SWE occurred as normal and was a bit above normal, the basin melted out about two weeks early.
  17. Madison-Gallatin River Basins. This basin peaked about two weeks late with about two inches of SWE more than normal. Even so, meltout occurred close to normal.
  18. Yellowstone River Basin. The basin had above normal SWE for the entire season. It peaked right about normal and finished meltout a few days later than normal.
  19. Wind River Basin. At about two inches of SWE higher than normal, the basin peaked a few days later and melted out a few days early. Basin snowpack may be monitored using various products available at http://www.wrds.uwyo.edu/wrds/nrcs/nrcs.html


Drought
The start of the 2018 water year showed a state with three areas of drought; south central, a small portion in Goshen and Platte counties, and an area covering the far northeast part of the state (Figure 6). While the first two areas were strictly D0 (Abnormally Dry), the latter included an area of D1 (Moderate Drought) stretching across the northern parts of Campbell and Crook counties.


Figure 6. US Drought Monitor showing conditions at the start of Water Year 2018

Figure 7. US Drought Monitor showing conditions at the end of Water Year 2018
The U.S. Drought Monitor is jointly produced by the National Drought Mitigation Center at the University of Nebraska-Lincoln, the United States Department of Agriculture, and the National Oceanic and Atmospheric Administration. Map courtesy of NDMC.

After a brief expansion which saw the two eastern areas merge and cover about half of the eastern quarter of Wyoming starting in mid-December and lasting into the first part of February, only the south central drought remained by mid-April. By this time the D0 had spread all the way to the western border, covering almost all of Uinta County as well as a large portion of southern Lincoln County. Additionally, D1 formed in the central areas around the Carbon and Sweetwater county border.

High evaporative demand fueled by the warm temperatures in July and September and especially by the lack of precipitation in those months caused both the D0 and the D1 areas to continue to expand through the summer with the D1 entering southwestern Albany County by 10 July. By the end of July, D1 conditions expanded westward to the Stateline covering much of Uinta County as well as the southwest corner of Lincoln County. At the same time, D2 (Severe Drought) covered the southern two-thirds of the border area between Carbon and Sweetwater counties.

By mid-August, almost all of Sweetwater County was in D0 to D2 and D0 had spread two-thirds of the way north into Lincoln County. By the 21st of August, a swath of D0 covered the western part of the state all the way to the Montana border, although conditions quickly improved for the Yellowstone National Park area in the following weeks. In mid-September, D0 covered all of Sublette County and the far southern part of Fremont County.

Figure 8. Timeline of drought intensities and geographic extent for Water Year 2018

The end of the 2018 water year (Figure 7) saw the first D3 (Severe Drought) in Wyoming since the 6th of September 2016. D0 conditions began to emerge in the northeast part of Wyoming again during the last week of the water year.

Figure 8 shows a timeline of drought in Wyoming during the 2018 water year. The chart shows the percentage of the state in each category of drought. Over 10 percent of Wyoming was in D0 or greater for the entire year. And about two percent of the state was in D1 or worse for the same period. The increased drought levels and area in southwest and south central Wyoming can be seen starting in the first third of July as a result of above normal temperatures and below normal precipitation amounts (Tables 1-4).


Severe Weather and Natural Disasters

Avalanches


Figure 9. Mesocyclone that spawned Laramie EF3 tornado, 06 June 2018
(Photo: Tony Bergantino)
Three fatalities were reported in Wyoming resulting from avalanches. On 29 December 2017 five snowmobilers were caught with one buried and killed. On 17 February an avalanche caught and killed a skier near Wilson. On 22 April a snowmobiler was caught and killed west of Togwotee Pass.

Tornadoes
Thirteen tornadoes were reported in Wyoming between late May and the end of July. Almost three times as many warnings were issued this year compared to the average of 19 per year from 2006 to 2017. Three of the thirteen tornadoes were EF3 and two were rated at EF2. The EF3 tornadoes were the first confirmed tornadoes of that intensity since 1987 when the state.s lone F4 tornado went through Teton County. Since the start of records in 1950, Wyoming has only had a dozen EF3 or greater tornadoes. The EF3 in Laramie on the 6th of June was the strongest ever in Albany County dating back to 1950. The map in Figure 10 shows the dates and locations of confirmed tornadoes in Wyoming during the 2018 tornado season.


Figure 10. Map showing locations, intensities, and dates of tornadoes in Wyoming during the 1918 season (NWS Damage Surveys)

Hail
Numerous hail storms impacted the state in 2018 and, while most of these were on the eastern plains, Fremont, Sweetwater, Hot Springs, Park, Big Horn, Sublette, and Washakie counties were not without incidents. Lusk saw a particularly severe storm on the 24th of July when hailstones up to 1.75. in diameter caused property damage across the town. On the 26th of July severe thunderstorms hit Lovell, also producing 1.75. diameter hail, and causing extensive property damage. On the 27th of July, Buffalo was hit by golf-ball size hail which caused property damage in the form of broken windows, damaged siding, and, in the surrounding areas, crop damage. (NCDC Storm Events Database, 2018). The 29th of July saw Cheyenne pounded with damaging hail resulting in over a 1,000 insurance claims for property damage. (Casper Star Tribute, 2018).

Floods
A combination of rain and melting snowpack caused flooding along the Wind River in June while the Green River was also in flood stage. In Teton County, a mudslide that blocked an irrigation ditch caused flood damage to six homes south of Jackson. Rains also caused minor flooding along the Shoshone River in northern Wyoming. Rain and snowmelt also caused Ten Sleep Creek to overflow into a local campground. Heavy rains in late May caused Big Goose Creek near Sheridan to rise which caused street flooding as well as flooding of numerous basements. Additionally, thunderstorms and hail caused urban flooding in other locations such as Casper in late May, and Laramie in June. (NCDC Storm Events Database, 2018).


Fires
During the summer of 2018, much of Wyoming lay under smoke-filled skies which either blocked the sun completely or turned it into a distinct blood-red circle. Much of this smoke originated out of state from as far away as the Ranch and Carr fires in northern California.

Within the borders of the state, there were nearly 75 fires reported this season. Almost two-thirds of these were under 100 acres in size.

Another five fires were between 1,000 and 10,000 acres while the top seven ranged from 12,073 acres to the largest, the Roosevelt Fire in the far west part of the state, at over 62,000 acres. The fires combined had a total of almost 245,000 acres burned.

The 245,000 acres is almost twice the average annual acres burned over the last 16 years and 2018 had the highest number of burned acres since the 2012 Drought when almost 475,000 acres burned. In the last 16 years, 2018 had the third highest acreage, falling just below the number of acres burned in 2006.

The total number of fires per year is a bit less significant since there could be several small fires that burn less acreage than just one large fire. However, the 74 fires in 2018 was above the approximately 55 fire yearly average from 2003 to 2018, and 2018 ranked as the 6th highest in terms of fire-count.

At the end of the September, fire activity around the state was at a minimum and mostly constrained to mop-up operations.

Figure 11 below shows smoke from the Badger Creek fire drifting over Jelm Mountain southwest of Laramie. The photo was taken on the 12th of June, one day after the fire started.

Figure 11. Badger Creek fire seen from Laramie, 12 June 2018 (Photo: Tony Bergantino)


Fire

Date Reported

Acres Burned

 

Fire

Date Reported

Acres Burned

Roosevelt

15-Sep-2018

62,042

 

Boxelder

20-Jun-2018

36

Terek

09-Jul-2018

47,901

 

Turner Draw

15-Jul-2018

33

Britania Mountain

28-Aug-2018

32,193

 

Basin Creek

28-Sep-2018

31

Ryan

16-Sep-2018

28,784

 

Skull Creek

13-Aug-2018

29

Badger Creek

11-Jun-2018

21,404

 

Butte

08-Aug-2018

25

Laney Rim

30-Jul-2018

13,183

 

Fence Creek

09-Jul-2018

25

Marten Creek

16-Sep-2018

12,073

 

Buffalo Creek

16-Jul-2018

24

Denver Jake

14-Aug-2018

7,247

 

Mckenzie

06-Jul-2018

19

Zimmerman

30-Jul-2018

6,289

 

Horse Pasture

30-Jun-2018

15

Black Butte

29-Jul-2018

4,937

 

Patterson

09-Jul-2018

14

Black Mountain

17-Sep-2018

2,100

 

Little Missouri

31-Jul-2018

11

Weintz

15-Jun-2018

1,990

 

Sulphur Creek

05-Aug-2018

10

Yellow Mountain

29-Sep-2018

482

 

Highway 31

30-Jul-2018

10

Alkali Flats

05-Jul-2018

434

 

Jake

22-Jun-2018

10

Rattlesnake

06-Aug-2018

354

 

Buffalo North

07-Aug-2018

9

Tater Ridge

08-Aug-2018

346

 

Coal Gulch

23-Jul-2018

8

Reno

16-Jul-2018

299

 

Big Antelope Basin

06-Aug-2018

8

Baker Cabin

08-Jul-2018

250

 

Beck

11-Jun-2018

7

Bixby

01-Aug-2018

247

 

Willow Creek

12-Jul-2018

7

Big Ridge

29-Jul-2018

205

 

286

15-Aug-2018

6

Red Butte

08-Aug-2018

176

 

Chameleon

30-Aug-2018

6

Haul

16-Jul-2018

152

 

Highway 2

06-Aug-2018

5

King Draw

14-Jul-2018

151

 

Gravel Pit

05-Aug-2018

5

Shirttail Butte

10-Jul-2018

142

 

Sweet Clover

17-Jul-2018

5

Hampton

22-Jun-2018

123

 

Geary

03-Sep-2018

4

Spotted Horse Creek

17-Aug-2018

110

 

Mud Lake

27-Jul-2018

4

Olmstead Creek

02-Jul-2018

105

 

Blue Ridge

06-Jul-2018

4

Evans Draw

10-Sep-2018

90

 

Shed

04-Aug-2018

3

Brush

12-Jul-2018

89

 

Leigh Canyon

15-Sep-2018

3

Enduro

06-Aug-2018

79

 

259

12-Sep-2018

3

Lower Nowood

06-Aug-2018

78

 

Lxr Creek

31-Jul-2018

3

North Bobcat

30-Jul-2018

65

 

Ek Road

21-Aug-2018

2

Diamond

10-Sep-2018

65

 

Cabin Camp

03-Jul-2018

2

Fire Trail

12-Aug-2018

61

 

Million Creek

11-Jun-2018

1

Martin

10-Jul-2018

51

 

Spring Creek

17-Aug-2018

1

Devils Slide

22-Jun-2018

42

 

Pitch Draw

16-Jul-2018

1

Coalbank

22-Jul-2018

37

 

Schoonover Road

29-Jun-2018

1

Table 5. List of fires, dates, and acres burned during the 2018 fire season. (EcoWest, 2018)


Streamflow and Reservoirs


Figure 12. Streamflow percentiles in Wyoming at the end of Water Year
2018 (NWIS, 2018)
Streams in Wyoming ended the water year ranging from Low to Much Above Normal. Figure 12 shows USGS streamflow gauges in the state. Most of the gauges are in the 25th to 75th percentile which is the normal range although there are a number of stations, mostly in the northern half of the state that are in the 76 to 90 percentile, or above normal. There are about a dozen stations around the state in the 10th to 24th percentile, or below normal. While not an absolute, the south and southwest generally has a higher number of stations running below normal while the north and northeast have more running above normal.

Reservoirs on the 1st of June were in good shape and many had filled to over 80 percent of capacity from the spring runoff (Figure 14). Storage in the reservoir system amounted to a bit over 10 million acre-feet (Figure 13).

By the end of the water year, reservoir releases lowered storage considerably although six (Alcova, Bighorn Lake, Boysen, Flaming Gorge, Keyhole, and Kortes) were still above 80 percent of normal (Figure 16). Storage was down to just under 9 million acre-feet on the 30th of September (Figure 15). (http://www.wrds.uwyo.edu/surface_water/teacups.html)

 











Figure 13. Amount of reservoir storage in acre-feet on 01 June 2018



Figure 14. Percent of capacity for reservoirs on 01 June 2018



Figure 15. Amount of reservoir storage in acre-feet remaining at the end of water year 2018



Figure 16. Percent of capacity for reservoirs remaining at the end of water year 2018


Wind
Wind patterns for the sixteen cities for which the Water Resources Data System and State Climate Office produces wind roses for maintained the same basic signature compared to the 2006 to 2015 averages. There may be variations month-to-month but the shapes of the roses are very similar as far as dominant directions when compared on an annual basis. Where there are differences, they are mainly that the frequency of wind speed ranges from a particular direction may vary. Appendix A shows a comparison of the annual wind rose to the 10-year average for each of the sixteen cities.


Figure 17. Wind Sock at Cheyenne National Weather Service Office (Photo: Tony Bergantino)


Outlook for Water Year 2019
There is about a 70 to 75% chance of El Niño forming in the coming months and continuing into 2019. Conditions were still neutral at the end of water year 2018, but sea surface temperatures are continuing to increase across the equatorial regions of the Pacific.

El Niño events have varying influence on Wyoming given the state.s geographic location at the boundary between impacts. For example, temperature tends to be higher during El Niño conditions compared to neutral conditions when it occurs in the January through March period, while in the July through September period the temperatures tend to be less than during neutral conditions.

For precipitation, the July through September period is usually wetter than during neutral conditions. For April through June precipitation is often higher in the west and lower in the east compared to what is seen during neutral conditions.

During January through March, the northwest is usually drier while the southeast trends toward being wetter than neutral conditions. The northeast and southwest generally do not see much difference in precipitation compared to a neutral Pacific.

Currently, the three-month outlook for the January through March period is calling for higher chances of above normal temperatures statewide with those chances being better than 50% in the western third of Wyoming. The chances for below normal precipitation are greater in the northern quarter of the state, slightly better for above normal in the far southeast and indeterminate elsewhere (Figure 18).

For the second quarter of 2019 (months of April, May, and June) the temperatures are again expected to be above normal for most of the state although the chances are greatest in the southwest and diminish somewhat toward the northeast. The far northeast region of the state has equal chances for above, below, or normal temperatures. Precipitation is unknown for the entire state during this period and could be above, below, or normal.


Figure 18. Three-month temperature (left) and precipitation (right) outlook for Jan-Mar 2019. (Climate Prediction Center, 2018)

During the final quarter of the water year (July, August, and September of 2019) temperatures are, again, expected to be above normal for most of the state with some uncertainty in the far northeast corner. The odds of above normal temperatures for this period increase toward the southwest and in the far southwestern quarter the chances are better than 50% for having above normal temperatures. The signal for precipitation is a bit stronger during this three-month period and the odds slightly favor below normal precipitation in the northwest while the rest of the state still has even chances for above, below, or normal precipitation. (Climate Prediction Center, 2018).

The seasonal outlook calls for drought persisting in the south and southwest through at least the end of calendar year 2018.


References

  1. Casper Star Tribune. (2018). Cheyenne, Lovell residents clean up after major storms, published 31 July 2018, retrieved 17 October 2018 from https://trib.com/news/state-and-regional/cheyenne-lovell-residents-clean-up-after-major-storms/article_b251b823-aa0c-5418-8913-4a612db6dd92.html
  2. Climate Prediction Center. (2018). Seasonal Outlooks. National Oceanic and Atmospheric Administration, retrieved 17 October 2018 from http://www.cpc.noaa.gov
  3. EcoWest. (2018). Wildfires in Wyoming. Major Wildfires in Wyoming. Retrieved 14 October 2018 from https://vis.ecowest.org/interactive/wildfires.php#f=all&loc=WY&h=1
  4. NCDC Storm Events Database. (2018). NCDC Storm Events Database, retrieved on 16 October 2018 from a href="https://www.ncdc.noaa.gov/stormevents/ftp.jsp">https://www.ncdc.noaa.gov/stormevents/ftp.jsp
  5. NWIS. (2018). US Geological Survey, National Water Information System, retrieved on 03 October 2018 from https://waterdata.usgs.gov/wy/nwis/rt
  6. NWS Damage Survey for mm/dd/yy Tornado Event (Report). Iowa Environmental Information. National Weather Service Weather Forecast Office in Cheyenne, Wyoming. Retrieved 14 October 2018.
  7. NOAA National Centers for Environmental information, (2018). Climate at a Glance: Divisional Time Series, published October 2018, retrieved on 13 October 2018 from https://www.ncdc.noaa.gov/cag/
  8. PRISM Climate Group, (2018). 1981-2010 Temperature and Precipitation Normals. Oregon State University, http://prism.oregonstate.edu, created 11 October 2018.
  9. PRISM Climate Group, (2018). Monthly Temperature and Precipitation Grids October 2017 thru September 2018. Oregon State University, http://prism.oregonstate.edu, created 11 October 2018.


Appendix A