Fossil Butte National Monument
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fossil Butte National Monument clear sky chart from 2005-11-06 to 2024-03-18.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.
Observation TypeMinimum conditions for hour to be usableOut of hours
Clear of CloudsTransparencySeeingSky Brightness
Planetary:50%(no limit)Average(no limit)Nighttime Hours
Deep Sky:70%Average(no limit)5.9Nighttime Hours
CCD Imaging:70%Below AveragePoor(no limit)Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

PlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
Night
54%
24839
20%
80496
17%
24751
58%
24751
31%
47727

By Month

MonthDays of MonthPlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
January1st to 10thNight
44%
790
15%
4109
13%
779
49%
779
15%
2514
January11th to 20thNight
43%
758
13%
4091
13%
740
51%
740
13%
2696
January21st to endNight
42%
827
10%
4497
15%
814
47%
814
12%
3218
February1st to 10thNight
34%
760
12%
2470
10%
760
40%
760
19%
1691
February11th to 20thNight
44%
741
16%
2403
14%
740
49%
740
27%
1474
February21st to endNight
40%
628
17%
1905
13%
628
46%
628
26%
1230
March1st to 10thNight
47%
760
18%
2109
13%
760
52%
760
28%
1376
March11th to 20thNight
54%
752
19%
2068
14%
752
59%
752
36%
1236
March21st to endNight
42%
792
16%
2178
9%
792
47%
792
29%
1430
April1st to 10thNight
44%
644
16%
1904
10%
644
50%
644
28%
1191
April11th to 20thNight
42%
533
22%
1683
14%
533
50%
533
30%
968
April21st to endNight
48%
540
23%
1620
15%
540
55%
540
33%
931
May1st to 10thNight
47%
540
20%
1620
13%
540
51%
540
30%
968
May11th to 20thNight
59%
531
19%
1595
17%
531
61%
531
33%
962
May21st to endNight
55%
583
17%
1582
14%
582
57%
582
36%
969
June1st to 10thNight
62%
540
20%
1440
16%
540
66%
540
46%
792
June11th to 20thNight
56%
540
25%
1440
18%
540
63%
540
51%
759
June21st to endNight
70%
540
27%
1440
24%
540
74%
540
60%
717
July1st to 10thNight
75%
525
23%
1434
21%
525
78%
525
52%
750
July11th to 20thNight
76%
522
25%
1566
25%
522
78%
522
50%
765
July21st to endNight
81%
591
27%
1674
26%
558
83%
558
52%
807
August1st to 10thNight
74%
537
28%
1602
24%
534
75%
534
46%
840
August11th to 20thNight
78%
534
35%
1602
29%
534
79%
534
54%
767
August21st to endNight
79%
594
36%
1831
33%
594
81%
594
52%
876
September1st to 10thNight
71%
570
34%
1830
32%
570
76%
570
54%
827
September11th to 20thNight
74%
720
32%
1980
26%
720
78%
720
54%
999
September21st to endNight
69%
720
34%
1980
25%
720
74%
720
52%
1027
October1st to 10thNight
61%
720
25%
2119
20%
720
65%
720
42%
1169
October11th to 20thNight
58%
720
30%
2160
21%
720
66%
720
42%
1142
October21st to endNight
56%
792
28%
2376
22%
792
62%
792
39%
1303
November1st to 10thNight
53%
740
24%
2377
20%
740
59%
740
34%
1341
November11th to 20thNight
50%
873
21%
2583
15%
873
55%
873
34%
1504
November21st to endNight
49%
950
21%
2660
14%
950
55%
950
34%
1611
December1st to 10thNight
43%
950
13%
2660
9%
950
46%
950
26%
1775
December11th to 20thNight
42%
948
16%
3142
10%
948
44%
948
21%
2072
December21st to endNight
35%
1034
8%
4766
7%
1026
40%
1026
13%
3030

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

Occurrence of each ForecastData
Points
Cloud CoverDay
46%37%6%45%5%6%8%46%
78808
Night
36%37%6%45%5%6%8%47%
81047
TransparencyDay
33%7%14%20%18%8%
78530
Night
33%7%15%22%16%7%
80846
SeeingDay
6%13%28%30%17%5%
14535
Night
5%8%25%39%20%2
24880

By Month

Percentage Cloud Cover SW (2006-)
Color Meanings:
Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
17%5%14%12%6%7%7%6%7%28%
2803
11th to 20thDay
16%5%16%13%5%7%5%6%7%28%
2860
21st to endDay
28%6%14%11%6%9%5%7%9%23%
3146
February1st to 10thDay
210%5%11%9%5%5%6%6%9%32%
1710
11th to 20thDay
28%5%9%8%46%7%6%9%36%
1665
21st to endDay
18%5%10%10%5%7%6%6%7%34%
1546
March1st to 10thDay
27%48%7%5%7%7%7%8%38%
2071
11th to 20thDay
36%47%7%45%6%7%10%42%
2058
21st to endDay
5%9%48%7%5%7%6%7%9%35%
2178
April1st to 10thDay
5%8%37%6%47%7%7%7%41%
2056
11th to 20thDay
49%47%7%46%7%6%7%39%
2222
21st to endDay
48%38%5%46%6%6%7%43%
2340
May1st to 10thDay
8%8%36%6%45%6%7%9%40%
2340
11th to 20thDay
6%7%25%6%46%7%8%8%41%
2301
21st to endDay
8%8%37%6%46%6%7%9%37%
2693
June1st to 10thDay
44245%35%6%7%9%51%
2520
11th to 20thDay
5%42443345%8%57%
2520
21st to endDay
2213333347%68%
2520
July1st to 10thDay
33233345%5%8%62%
2480
11th to 20thDay
431442445%7%62%
2340
21st to endDay
5%21343446%8%58%
2545
August1st to 10thDay
43145%345%6%7%59%
2328
11th to 20thDay
321332345%7%66%
2299
21st to endDay
3323424446%65%
2525
September1st to 10thDay
431232335%6%68%
2126
11th to 20thDay
4313424446%64%
1980
21st to endDay
5%413433445%65%
1980
October1st to 10thDay
7%6%345%245%5%7%52%
1841
11th to 20thDay
5%5%2443445%8%56%
1800
21st to endDay
26%36%6%335%5%8%53%
1980
November1st to 10thDay
5%6%38%5%35%6%5%8%45%
1698
11th to 20thDay
310%46%6%345%6%9%44%
1577
21st to endDay
27%48%7%35%7%6%10%43%
1520
December1st to 10thDay
27%5%11%8%37%6%5%8%38%
1520
11th to 20thDay
29%5%10%9%5%7%6%8%8%31%
1926
21st to endDay
27%49%9%6%8%7%7%11%30%
2794
January1st to 10thNight
28%5%14%12%45%45%7%35%
4179
11th to 20thNight
16%5%15%13%5%6%5%6%8%29%
4110
21st to endNight
211%8%13%10%5%8%6%5%7%26%
4521
February1st to 10thNight
28%5%10%7%5%7%6%7%8%33%
2470
11th to 20thNight
26%5%9%6%46%5%6%9%41%
2402
21st to endNight
18%5%8%9%5%6%6%7%8%37%
1905
March1st to 10thNight
27%37%6%48%6%6%9%39%
2109
11th to 20thNight
26%26%5%45%6%6%9%48%
2068
21st to endNight
310%47%6%36%5%6%8%42%
2178
April1st to 10thNight
49%47%5%35%5%5%7%45%
1904
11th to 20thNight
48%36%5%45%5%7%8%45%
1683
21st to endNight
46%36%5%25%46%9%49%
1620
May1st to 10thNight
7%6%245%35%5%6%8%48%
1620
11th to 20thNight
7%5%26%5%346%7%8%48%
1594
21st to endNight
8%5%25%6%45%5%7%8%45%
1582
June1st to 10thNight
431442446%10%57%
1440
11th to 20thNight
431332435%8%64%
1440
21st to endNight
2313313346%71%
1440
July1st to 10thNight
331433446%8%61%
1476
11th to 20thNight
33133345%5%7%62%
1620
21st to endNight
221343446%8%62%
1773
August1st to 10thNight
43245%345%6%7%57%
1611
11th to 20thNight
4213423446%66%
1602
21st to endNight
2214424446%67%
1831
September1st to 10thNight
3323322346%69%
1830
11th to 20thNight
43123336%6%6%65%
1980
21st to endNight
5%31242334468%
1980
October1st to 10thNight
7%5%15%42345%6%56%
2119
11th to 20thNight
6%6%25%414446%59%
2160
21st to endNight
45%25%43446%7%55%
2376
November1st to 10thNight
38%35%5%345%6%8%51%
2377
11th to 20thNight
35%35%6%45%5%7%9%48%
2583
21st to endNight
27%37%6%45%6%7%7%47%
2660
December1st to 10thNight
37%5%9%7%5%5%6%6%8%39%
2660
11th to 20thNight
38%5%11%7%5%5%5%6%9%36%
3271
21st to endNight
27%410%9%6%7%6%8%9%32%
4873

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
42%12%23%15%7%1
2804
11th to 20thDay
45%12%22%13%7%1
2860
21st to endDay
50%12%19%12%5%2
3146
February1st to 10thDay
47%9%18%15%10%1
1710
11th to 20thDay
42%8%20%20%7%3
1674
21st to endDay
43%9%19%19%9%2
1546
March1st to 10thDay
38%10%20%22%9%1
2071
11th to 20thDay
35%9%23%21%10%1
2058
21st to endDay
43%9%20%19%8%1
2178
April1st to 10thDay
38%9%17%20%13%3
2056
11th to 20thDay
40%8%14%25%13%
2225
21st to endDay
38%6%14%27%14%1
2340
May1st to 10thDay
38%7%14%24%16%2
2340
11th to 20thDay
36%8%14%27%12%4
2304
21st to endDay
41%8%13%25%11%1
2693
June1st to 10thDay
27%6%15%25%22%4
2520
11th to 20thDay
24%5%10%20%27%14%
2520
21st to endDay
16%45%18%34%22%
2520
July1st to 10thDay
20%6%8%18%26%22%
2413
11th to 20thDay
20%5%7%15%27%27%
2271
21st to endDay
23%5%8%15%29%21%
2404
August1st to 10thDay
23%5%7%19%24%21%
2313
11th to 20thDay
17%5%7%20%31%21%
2299
21st to endDay
20%5%8%15%35%18%
2525
September1st to 10thDay
18%47%17%31%22%
2126
11th to 20thDay
21%5%7%22%30%15%
1980
21st to endDay
22%47%25%35%7%
1980
October1st to 10thDay
31%5%12%26%21%5%
1841
11th to 20thDay
26%415%31%20%4
1800
21st to endDay
29%6%18%26%20%2
1980
November1st to 10thDay
35%7%15%25%15%3
1698
11th to 20thDay
34%6%21%22%15%1
1577
21st to endDay
36%7%17%24%15%2
1520
December1st to 10thDay
40%10%23%15%9%3
1520
11th to 20thDay
45%9%19%17%10%1
1924
21st to endDay
43%14%13%14%11%6%
2794
January1st to 10thNight
40%10%17%21%11%1
4179
11th to 20thNight
44%12%21%14%7%1
4110
21st to endNight
49%12%18%14%5%2
4521
February1st to 10thNight
43%11%19%19%8%1
2470
11th to 20thNight
36%8%18%22%13%3
2403
21st to endNight
38%9%18%22%11%2
1905
March1st to 10thNight
38%8%19%24%11%1
2109
11th to 20thNight
30%7%21%26%13%2
2068
21st to endNight
38%7%20%25%8%1
2178
April1st to 10thNight
37%6%17%20%13%6%
1904
11th to 20thNight
32%7%18%28%16%
1683
21st to endNight
32%5%16%30%16%
1620
May1st to 10thNight
34%7%13%25%20%2
1620
11th to 20thNight
32%8%14%29%14%3
1595
21st to endNight
32%7%18%30%13%1
1582
June1st to 10thNight
23%6%19%23%25%4
1440
11th to 20thNight
19%5%10%25%28%14%
1440
21st to endNight
15%46%15%33%27%
1440
July1st to 10thNight
19%6%7%17%26%25%
1434
11th to 20thNight
19%46%16%25%28%
1566
21st to endNight
19%49%16%27%24%
1674
August1st to 10thNight
23%5%9%19%22%22%
1602
11th to 20thNight
18%36%20%30%22%
1602
21st to endNight
18%47%17%32%21%
1831
September1st to 10thNight
17%38%18%28%26%
1830
11th to 20thNight
18%5%11%20%29%17%
1980
21st to endNight
20%47%26%35%9%
1980
October1st to 10thNight
26%5%12%27%24%6%
2119
11th to 20thNight
26%311%32%22%5%
2160
21st to endNight
27%5%16%31%18%3
2376
November1st to 10thNight
29%7%17%24%19%3
2377
11th to 20thNight
31%5%21%27%14%2
2583
21st to endNight
33%6%16%27%15%3
2660
December1st to 10thNight
40%8%21%18%9%3
2660
11th to 20thNight
43%7%18%21%11%1
3272
21st to endNight
43%10%17%16%10%5%
4873

Seeing (when cloud cover <= 80%)
Color Meanings:
Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
9%17%22%31%16%4
270
11th to 20thDay
6%17%27%30%19%2
270
21st to endDay
311%35%32%15%3
297
February1st to 10thDay
6%27%35%25%6%1
270
11th to 20thDay
420%36%26%10%4
270
21st to endDay
323%36%30%7%1
358
March1st to 10thDay
6%17%36%29%9%2
460
11th to 20thDay
5%14%32%34%14%1
449
21st to endDay
11%21%31%29%7%1
462
April1st to 10thDay
11%20%28%25%14%2
420
11th to 20thDay
11%21%36%22%9%2
412
21st to endDay
11%25%25%19%16%4
420
May1st to 10thDay
11%19%30%25%11%3
423
11th to 20thDay
13%13%27%32%11%5%
448
21st to endDay
10%13%25%25%21%7%
648
June1st to 10thDay
6%8%25%30%24%7%
630
11th to 20thDay
5%13%31%32%17%2
630
21st to endDay
37%27%35%22%5%
630
July1st to 10thDay
3421%42%25%6%
583
11th to 20thDay
35%30%36%21%5%
444
21st to endDay
5%420%40%23%9%
487
August1st to 10thDay
5%426%35%23%6%
447
11th to 20thDay
25%27%32%26%9%
437
21st to endDay
35%27%33%22%10%
495
September1st to 10thDay
48%25%29%22%12%
450
11th to 20thDay
6%9%31%25%17%11%
450
21st to endDay
6%13%24%31%20%7%
450
October1st to 10thDay
8%11%25%23%23%11%
311
11th to 20thDay
7%19%21%27%17%9%
270
21st to endDay
9%18%30%28%13%2
297
November1st to 10thDay
9%17%28%27%13%6%
270
11th to 20thDay
10%14%26%37%10%4
270
21st to endDay
413%31%31%16%4
270
December1st to 10thDay
6%14%29%32%17%1
270
11th to 20thDay
418%30%34%12%1
270
21st to endDay
7%16%35%24%12%6%
297
January1st to 10thNight
5%11%29%34%19%2
803
11th to 20thNight
412%31%32%18%2
760
21st to endNight
5%7%32%39%14%2
836
February1st to 10thNight
5%14%36%33%11%2
760
11th to 20thNight
49%33%38%14%1
744
21st to endNight
410%36%39%10%1
628
March1st to 10thNight
6%9%31%40%13%2
760
11th to 20thNight
37%27%46%16%1
752
21st to endNight
7%8%35%36%13%1
792
April1st to 10thNight
8%10%31%37%12%1
644
11th to 20thNight
7%12%34%35%11%2
533
21st to endNight
8%10%28%35%17%2
540
May1st to 10thNight
9%9%26%37%17%1
540
11th to 20thNight
9%7%19%37%25%3
531
21st to endNight
9%6%23%32%28%3
584
June1st to 10thNight
5%7%21%37%27%3
540
11th to 20thNight
6%8%27%40%19%1
540
21st to endNight
3220%46%26%2
540
July1st to 10thNight
4112%41%39%2
525
11th to 20thNight
3214%49%30%2
522
21st to endNight
218%48%39%3
591
August1st to 10thNight
4210%48%32%3
537
11th to 20thNight
3210%47%36%2
534
21st to endNight
3111%43%37%4
594
September1st to 10thNight
4217%43%31%3
570
11th to 20thNight
4315%38%35%5%
720
21st to endNight
6%417%35%29%9%
720
October1st to 10thNight
7%5%21%37%25%4
720
11th to 20thNight
7%9%21%36%24%3
720
21st to endNight
7%7%24%39%19%3
792
November1st to 10thNight
5%7%28%37%21%3
740
11th to 20thNight
5%12%28%38%15%2
873
21st to endNight
7%10%29%35%16%3
950
December1st to 10thNight
6%12%31%39%12%1
950
11th to 20thNight
5%10%32%41%11%1
950
21st to endNight
5%14%34%34%11%2
1045
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