This page made possible by the sponsorship of: Gary D. Maupin.

Horse Heaven Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Horse Heaven Observatory clear sky chart from 2005-11-06 to 2024-01-16.

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
51%
22471
18%
74790
16%
22439
56%
22439
25%
47342

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
30%
758
7%
2646
4%
756
33%
756
9%
2131
January11th to 20thNight
37%
740
8%
2590
7%
740
40%
740
11%
1983
January21st to endNight
42%
792
9%
2772
7%
792
46%
792
13%
2086
February1st to 10thNight
41%
720
12%
2367
8%
720
47%
720
17%
1655
February11th to 20thNight
43%
700
14%
2234
12%
700
48%
700
19%
1533
February21st to endNight
40%
592
17%
1776
13%
592
47%
592
18%
1251
March1st to 10thNight
45%
720
16%
2160
14%
720
49%
720
22%
1469
March11th to 20thNight
47%
720
17%
2061
12%
720
52%
720
25%
1391
March21st to endNight
37%
792
15%
2016
7%
792
42%
792
23%
1446
April1st to 10thNight
44%
720
15%
1800
6%
720
47%
720
26%
1256
April11th to 20thNight
45%
711
21%
1779
10%
711
50%
711
33%
1158
April21st to endNight
43%
573
19%
1653
11%
573
50%
573
31%
1025
May1st to 10thNight
54%
360
25%
1440
24%
360
65%
360
31%
719
May11th to 20thNight
56%
354
20%
1416
25%
354
62%
354
25%
779
May21st to endNight
62%
388
16%
1552
22%
388
68%
388
28%
831
June1st to 10thNight
56%
360
15%
1440
19%
360
64%
360
29%
758
June11th to 20thNight
44%
360
17%
1440
16%
360
57%
360
29%
731
June21st to endNight
61%
360
19%
1440
27%
360
71%
360
40%
638
July1st to 10thNight
75%
350
22%
1400
34%
350
82%
350
54%
532
July11th to 20thNight
70%
348
28%
1392
39%
348
80%
348
57%
513
July21st to endNight
80%
394
35%
1488
47%
372
88%
372
69%
477
August1st to 10thNight
79%
358
35%
1424
43%
356
85%
356
55%
535
August11th to 20thNight
82%
516
36%
1584
31%
516
85%
516
63%
673
August21st to endNight
73%
792
36%
1980
21%
792
76%
792
63%
1012
September1st to 10thNight
75%
720
35%
1800
19%
720
78%
720
66%
888
September11th to 20thNight
71%
720
33%
1822
22%
720
74%
720
53%
994
September21st to endNight
66%
720
30%
1980
24%
720
71%
720
47%
1079
October1st to 10thNight
58%
720
22%
2160
20%
720
63%
720
37%
1230
October11th to 20thNight
57%
720
26%
2160
22%
720
63%
720
32%
1280
October21st to endNight
50%
792
23%
2566
19%
792
58%
792
27%
1556
November1st to 10thNight
45%
740
17%
2405
14%
740
50%
740
20%
1622
November11th to 20thNight
43%
760
12%
2624
10%
760
47%
760
16%
1848
November21st to endNight
48%
760
13%
2660
10%
760
53%
760
18%
1841
December1st to 10thNight
41%
760
9%
2660
7%
760
44%
760
12%
2031
December11th to 20thNight
35%
758
4%
3276
3%
758
37%
758
7%
2735
December21st to endNight
32%
823
7%
4827
6%
817
38%
817
7%
3656

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
7%7%36%6%35%5%5%7%48%
74807
Night
8%8%46%6%35%5%5%7%44%
75007
TransparencyDay
36%6%11%22%18%7%
74510
Night
40%7%12%20%15%6%
74825
SeeingDay
9%8%21%27%24%11%
13307
Night
11%7%23%34%22%3
22493

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
15%17%6%13%8%46%5%5%6%17%
1519
11th to 20thDay
13%13%6%12%10%5%6%5%45%22%
1480
21st to endDay
12%14%6%13%9%46%6%5%5%21%
1584
February1st to 10thDay
12%13%5%8%7%47%45%7%28%
1589
11th to 20thDay
11%11%47%7%46%45%7%35%
1615
21st to endDay
9%8%37%6%47%6%7%9%34%
1480
March1st to 10thDay
10%9%47%6%47%6%7%9%32%
1800
11th to 20thDay
7%8%37%8%5%7%5%6%9%35%
1898
21st to endDay
9%8%48%7%48%7%8%7%30%
2340
April1st to 10thDay
7%7%36%7%46%6%6%9%38%
2160
11th to 20thDay
6%6%36%6%36%6%5%8%44%
2129
21st to endDay
5%6%26%6%35%6%6%8%47%
2303
May1st to 10thDay
5%5%245%35%5%6%8%53%
2520
11th to 20thDay
7%5%36%6%36%5%8%9%42%
2477
21st to endDay
7%6%36%5%35%5%6%8%46%
2723
June1st to 10thDay
9%5%26%5%35%5%6%7%48%
2520
11th to 20thDay
5%5%245%345%6%8%53%
2520
21st to endDay
332332345%6%66%
2520
July1st to 10thDay
121231235%5%74%
2520
11th to 20thDay
2112212345%76%
2520
21st to endDay
111211223483%
2741
August1st to 10thDay
322213335%76%
2507
11th to 20thDay
2112222335%78%
2313
21st to endDay
3312423345%70%
2376
September1st to 10thDay
2212322347%72%
2160
11th to 20thDay
3425%4345%5%7%59%
2138
21st to endDay
5%5%2443445%7%57%
1977
October1st to 10thDay
8%5%25%43345%8%53%
1800
11th to 20thDay
6%5%25%5%36%5%6%8%49%
1800
21st to endDay
11%6%25%6%35%5%5%8%42%
1788
November1st to 10thDay
9%9%48%6%46%5%6%8%34%
1674
11th to 20thDay
11%14%5%8%8%46%46%6%30%
1554
21st to endDay
10%11%5%11%8%5%6%7%6%8%25%
1520
December1st to 10thDay
10%11%8%12%10%46%5%46%25%
1520
11th to 20thDay
13%14%8%14%11%5%5%5%5%5%14%
1928
21st to endDay
14%12%7%13%11%5%6%6%5%417%
2794
January1st to 10thNight
15%13%6%10%8%5%6%5%6%6%20%
2646
11th to 20thNight
13%12%6%11%7%5%5%45%7%24%
2590
21st to endNight
11%12%6%9%8%46%5%5%6%28%
2772
February1st to 10thNight
11%11%46%6%45%5%5%8%35%
2367
11th to 20thNight
8%9%5%7%7%46%5%6%7%36%
2232
21st to endNight
8%9%48%6%46%6%8%8%34%
1776
March1st to 10thNight
10%8%46%6%46%6%6%8%37%
2160
11th to 20thNight
8%7%37%7%46%6%7%8%38%
2061
21st to endNight
6%9%47%6%47%7%6%8%35%
2016
April1st to 10thNight
9%8%46%7%45%6%6%8%37%
1800
11th to 20thNight
6%7%37%5%36%45%6%48%
1779
21st to endNight
5%6%35%6%45%5%6%7%48%
1653
May1st to 10thNight
4424336%5%7%8%54%
1440
11th to 20thNight
7%5%25%6%35%7%6%9%45%
1416
21st to endNight
5%434446%6%7%11%46%
1552
June1st to 10thNight
7%4245%45%5%5%9%51%
1440
11th to 20thNight
8%5%2443335%6%56%
1440
21st to endNight
43143335%5%5%65%
1440
July1st to 10thNight
2212213436%73%
1440
11th to 20thNight
311221223478%
1440
21st to endNight
111111323483%
1576
August1st to 10thNight
3212212346%74%
1432
11th to 20thNight
2212212345%76%
1584
21st to endNight
2212323446%70%
1980
September1st to 10thNight
2212223335%75%
1800
11th to 20thNight
33143245%5%7%63%
1822
21st to endNight
45%1432445%8%60%
1980
October1st to 10thNight
7%6%25%5%2445%6%54%
2160
11th to 20thNight
7%5%25%5%35%5%6%6%50%
2160
21st to endNight
8%6%36%6%35%5%5%7%48%
2566
November1st to 10thNight
12%8%38%6%445%5%6%38%
2405
11th to 20thNight
10%9%47%7%5%5%6%6%6%34%
2624
21st to endNight
10%10%37%6%46%6%5%7%35%
2660
December1st to 10thNight
12%11%6%11%8%45%5%5%6%27%
2660
11th to 20thNight
14%14%7%12%10%5%5%5%6%6%16%
3276
21st to endNight
12%15%7%9%7%46%6%5%6%23%
4862

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
68%10%9%9%3
1519
11th to 20thDay
66%8%13%11%3
1480
21st to endDay
64%9%11%11%41
1584
February1st to 10thDay
56%10%15%14%41
1589
11th to 20thDay
49%7%14%21%8%1
1624
21st to endDay
44%9%17%19%9%1
1480
March1st to 10thDay
47%8%13%22%10%
1800
11th to 20thDay
44%8%13%26%9%
1898
21st to endDay
47%10%15%20%7%1
2340
April1st to 10thDay
40%8%14%22%15%1
2160
11th to 20thDay
37%5%14%24%17%4
2132
21st to endDay
32%7%13%28%17%4
2303
May1st to 10thDay
28%6%11%32%21%3
2520
11th to 20thDay
35%6%11%26%16%4
2480
21st to endDay
34%7%13%28%15%3
2724
June1st to 10thDay
34%6%10%28%19%4
2520
11th to 20thDay
27%6%11%30%22%4
2520
21st to endDay
19%38%29%29%11%
2520
July1st to 10thDay
13%35%22%36%21%
2451
11th to 20thDay
12%35%14%36%29%
2445
21st to endDay
8%2413%41%32%
2589
August1st to 10thDay
13%37%18%38%21%
2490
11th to 20thDay
12%26%23%39%19%
2313
21st to endDay
17%36%27%35%12%
2376
September1st to 10thDay
13%48%27%31%17%
2160
11th to 20thDay
23%6%10%25%26%10%
2138
21st to endDay
27%6%13%30%18%6%
1977
October1st to 10thDay
31%413%30%20%2
1800
11th to 20thDay
32%7%17%30%13%1
1800
21st to endDay
41%8%15%25%11%
1788
November1st to 10thDay
47%8%15%20%7%1
1674
11th to 20thDay
55%8%14%17%5%1
1554
21st to endDay
57%10%15%11%7%1
1520
December1st to 10thDay
61%9%10%14%5%
1520
11th to 20thDay
72%7%10%8%2
1928
21st to endDay
69%9%9%10%3
2794
January1st to 10thNight
63%9%13%10%4
2646
11th to 20thNight
59%8%14%15%4
2590
21st to endNight
57%8%16%15%41
2772
February1st to 10thNight
48%9%19%19%5%1
2367
11th to 20thNight
46%9%15%21%9%1
2234
21st to endNight
46%10%13%21%9%2
1776
March1st to 10thNight
44%8%13%23%11%2
2160
11th to 20thNight
42%7%13%26%10%1
2061
21st to endNight
45%8%15%23%9%
2016
April1st to 10thNight
43%7%14%22%13%2
1800
11th to 20thNight
35%6%11%26%17%4
1779
21st to endNight
33%8%13%23%17%5%
1653
May1st to 10thNight
25%8%9%31%22%5%
1440
11th to 20thNight
33%6%11%23%22%4
1416
21st to endNight
30%8%14%28%17%3
1552
June1st to 10thNight
30%7%9%29%20%5%
1440
11th to 20thNight
30%5%7%32%22%5%
1440
21st to endNight
21%5%7%25%28%14%
1440
July1st to 10thNight
14%35%21%31%27%
1400
11th to 20thNight
12%35%16%31%33%
1392
21st to endNight
8%2311%37%39%
1488
August1st to 10thNight
14%35%14%38%26%
1424
11th to 20thNight
13%35%20%32%28%
1584
21st to endNight
15%46%21%38%16%
1980
September1st to 10thNight
13%37%25%31%21%
1800
11th to 20thNight
20%6%9%24%26%16%
1822
21st to endNight
23%5%11%28%23%10%
1980
October1st to 10thNight
31%5%9%25%28%3
2160
11th to 20thNight
33%6%11%28%19%3
2160
21st to endNight
36%7%12%26%17%2
2566
November1st to 10thNight
46%7%13%23%10%1
2405
11th to 20thNight
48%10%16%19%7%1
2624
21st to endNight
47%9%17%19%8%1
2660
December1st to 10thNight
58%8%14%15%4
2660
11th to 20thNight
67%10%13%8%2
3276
21st to endNight
60%9%12%11%7%
4862

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
24%12%24%23%13%3
180
11th to 20thDay
19%7%21%35%13%5%
170
21st to endDay
17%7%21%31%20%3
176
February1st to 10thDay
22%8%24%27%16%3
309
11th to 20thDay
16%11%26%27%16%3
353
21st to endDay
12%15%25%28%16%3
346
March1st to 10thDay
15%12%33%22%15%3
420
11th to 20thDay
12%12%23%28%19%5%
420
21st to endDay
13%15%26%29%15%3
462
April1st to 10thDay
14%17%23%26%15%5%
420
11th to 20thDay
11%15%30%23%13%7%
412
21st to endDay
7%13%28%25%19%8%
420
May1st to 10thDay
8%9%26%27%23%7%
423
11th to 20thDay
12%8%22%25%20%13%
448
21st to endDay
12%418%28%25%13%
485
June1st to 10thDay
8%9%20%25%23%14%
450
11th to 20thDay
6%10%27%32%16%8%
450
21st to endDay
25%18%27%31%17%
450
July1st to 10thDay
1214%28%43%12%
446
11th to 20thDay
2314%29%37%15%
444
21st to endDay
1211%24%36%25%
487
August1st to 10thDay
2412%22%34%26%
447
11th to 20thDay
229%22%34%31%
437
21st to endDay
45%16%26%28%21%
495
September1st to 10thDay
3213%30%36%16%
450
11th to 20thDay
6%415%26%33%16%
450
21st to endDay
7%10%15%29%30%8%
450
October1st to 10thDay
8%8%24%23%26%11%
450
11th to 20thDay
9%11%16%28%25%11%
450
21st to endDay
14%9%26%29%14%9%
303
November1st to 10thDay
11%14%22%34%16%3
270
11th to 20thDay
17%12%28%21%16%7%
196
21st to endDay
10%7%23%29%22%8%
180
December1st to 10thDay
9%10%23%31%14%13%
180
11th to 20thDay
21%6%25%33%13%3
180
21st to endDay
19%6%26%32%14%4
198
January1st to 10thNight
22%9%23%31%13%2
760
11th to 20thNight
17%6%23%32%20%3
740
21st to endNight
17%5%19%37%19%3
792
February1st to 10thNight
17%8%25%33%15%2
720
11th to 20thNight
12%9%24%33%20%2
704
21st to endNight
12%11%26%34%14%2
592
March1st to 10thNight
12%9%25%34%18%2
720
11th to 20thNight
9%11%24%35%20%1
720
21st to endNight
10%10%34%32%13%1
792
April1st to 10thNight
12%10%26%32%17%2
720
11th to 20thNight
8%13%30%27%18%3
711
21st to endNight
7%12%31%30%18%2
573
May1st to 10thNight
49%29%34%20%4
360
11th to 20thNight
8%7%21%32%26%5%
354
21st to endNight
5%5%22%41%24%4
389
June1st to 10thNight
8%5%26%36%24%2
360
11th to 20thNight
9%8%32%35%15%1
360
21st to endNight
5%424%36%29%2
360
July1st to 10thNight
4215%47%29%3
350
11th to 20thNight
4322%45%26%1
348
21st to endNight
1214%47%33%3
394
August1st to 10thNight
3214%40%37%5%
358
11th to 20thNight
3112%34%38%12%
516
21st to endNight
2317%36%34%7%
792
September1st to 10thNight
3217%38%34%5%
720
11th to 20thNight
5%116%31%38%9%
720
21st to endNight
6%5%19%32%32%6%
720
October1st to 10thNight
11%5%19%33%29%4
720
11th to 20thNight
9%6%21%33%24%7%
720
21st to endNight
11%7%25%32%20%5%
792
November1st to 10thNight
15%7%23%37%17%1
740
11th to 20thNight
15%9%25%32%17%3
760
21st to endNight
13%6%22%36%20%3
760
December1st to 10thNight
15%5%21%36%20%2
760
11th to 20thNight
19%7%21%36%17%1
760
21st to endNight
19%8%26%34%12%1
836
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