Summit View Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Summit View Observatory clear sky chart from 2005-11-05 to 2019-07-16.

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
67%
17827
26%
54237
23%
17791
70%
17791
37%
30281

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 15thNight
57%
836
19%
2767
20%
836
60%
836
28%
1662
January16th to endNight
59%
896
23%
2912
23%
896
62%
896
27%
1790
February1st to 15thNight
56%
818
25%
2669
25%
818
62%
818
27%
1639
February16th to endNight
50%
736
22%
2207
18%
736
57%
736
29%
1377
March1st to 15thNight
53%
840
19%
2342
17%
840
55%
840
27%
1551
March16th to endNight
52%
896
20%
2435
15%
896
57%
896
32%
1556
April1st to 15thNight
50%
839
22%
2099
13%
839
54%
839
32%
1371
April16th to endNight
60%
832
24%
2080
11%
832
64%
832
44%
1201
May1st to 15thNight
69%
741
24%
2001
17%
741
71%
741
45%
1114
May16th to endNight
70%
475
21%
1790
19%
475
75%
475
32%
923
June1st to 15thNight
77%
420
28%
1680
29%
420
84%
420
41%
748
June16th to endNight
88%
420
31%
1680
40%
420
91%
420
50%
674
July1st to 15thNight
91%
465
30%
1665
35%
465
92%
465
61%
648
July16th to endNight
87%
615
28%
1746
26%
582
88%
582
44%
904
August1st to 15thNight
81%
606
28%
1751
22%
603
81%
603
43%
940
August16th to endNight
86%
828
30%
2070
20%
828
86%
828
56%
1120
September1st to 15thNight
88%
780
37%
1950
27%
780
89%
780
63%
994
September16th to endNight
82%
776
39%
2122
36%
776
85%
776
61%
1026
October1st to 15thNight
73%
780
29%
2340
32%
780
77%
780
47%
1193
October16th to endNight
75%
832
34%
2496
36%
832
79%
832
45%
1297
November1st to 15thNight
70%
820
31%
2548
32%
820
73%
820
42%
1349
November16th to endNight
64%
840
25%
2811
26%
840
67%
840
32%
1572
December1st to 15thNight
58%
840
24%
2940
23%
840
64%
840
27%
1733
December16th to endNight
50%
896
20%
3136
18%
896
56%
896
24%
1899

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
8%423323347%57%
55069
Night
8%42432345%8%53%
54426
TransparencyDay
27%49%19%23%15%
54758
Night
29%5%10%18%21%15%
54238
SeeingDay
9%8%21%32%21%6%
8404
Night
9%312%31%34%9%
17839

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 15thDay
16%5%36%32435%7%40%
1828
16th to endDay
16%6%245%24446%42%
2016
February1st to 15thDay
17%7%25%32345%6%41%
1856
16th to endDay
17%6%45%424446%39%
1839
March1st to 15thDay
16%7%25%6%345%5%8%34%
2274
16th to endDay
13%6%37%5%34446%39%
2492
April1st to 15thDay
15%7%35%324347%42%
2509
16th to endDay
7%424413337%56%
2485
May1st to 15thDay
4413313348%60%
2605
16th to endDay
5%5%25%5%2335%7%53%
3025
June1st to 15thDay
5%31321235%8%63%
2940
16th to endDay
111212336%74%
2940
July1st to 15thDay
11212337%74%
2866
16th to endDay
1111212337%74%
2679
August1st to 15thDay
112212337%72%
2450
16th to endDay
11212337%74%
2484
September1st to 15thDay
1111211226%76%
2340
16th to endDay
3212212346%70%
2165
October1st to 15thDay
4313314346%62%
1950
16th to endDay
6%312322447%60%
2080
November1st to 15thDay
8%424324447%53%
1968
16th to endDay
12%6%2342435%6%47%
1806
December1st to 15thDay
15%7%35%433445%42%
1680
16th to endDay
15%8%35%42345%7%39%
1792
January1st to 15thNight
13%5%25%5%245%6%7%40%
2767
16th to endNight
15%6%24334437%44%
2912
February1st to 15thNight
13%6%25%42445%6%42%
2657
16th to endNight
15%6%2442335%7%43%
2207
March1st to 15thNight
14%9%25%5%23447%40%
2342
16th to endNight
12%6%25%5%2435%7%43%
2435
April1st to 15thNight
11%5%25%43445%8%42%
2099
16th to endNight
5%31322345%9%56%
2080
May1st to 15thNight
231332446%10%56%
2001
16th to endNight
3314435%5%7%10%52%
1789
June1st to 15thNight
111231336%9%63%
1680
16th to endNight
111111245%6%71%
1680
July1st to 15thNight
111335%9%72%
1750
16th to endNight
1123245%6%12%59%
1854
August1st to 15thNight
11144245%5%9%59%
1760
16th to endNight
123245%6%9%63%
2070
September1st to 15thNight
112124410%68%
1950
16th to endNight
2112212248%71%
2122
October1st to 15thNight
4313323346%63%
2340
16th to endNight
4313323347%61%
2496
November1st to 15thNight
6%42332335%8%56%
2548
16th to endNight
9%425%424448%49%
2811
December1st to 15thNight
13%7%35%323347%45%
2940
16th to endNight
16%5%245%3445%6%42%
3136

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 15thDay
41%411%18%15%8%
1828
16th to endDay
41%49%14%18%11%
2016
February1st to 15thDay
41%39%18%20%7%
1856
16th to endDay
44%5%7%22%15%4
1839
March1st to 15thDay
45%5%10%19%14%5%
2274
16th to endDay
43%6%11%18%17%2
2492
April1st to 15thDay
40%412%20%19%2
2509
16th to endDay
27%412%25%22%6%
2485
May1st to 15thDay
22%49%29%27%6%
2605
16th to endDay
31%5%12%24%20%5%
3029
June1st to 15thDay
21%5%12%23%25%11%
2940
16th to endDay
13%46%17%33%24%
2940
July1st to 15thDay
12%37%10%24%41%
2722
16th to endDay
12%5%6%11%29%34%
2524
August1st to 15thDay
15%45%10%30%33%
2434
16th to endDay
12%5%6%13%33%28%
2484
September1st to 15thDay
13%36%14%31%31%
2340
16th to endDay
16%3423%30%21%
2165
October1st to 15thDay
22%28%19%25%21%
1950
16th to endDay
24%48%22%23%16%
2080
November1st to 15thDay
29%410%24%22%9%
1968
16th to endDay
36%311%18%25%5%
1806
December1st to 15thDay
41%5%9%16%17%10%
1680
16th to endDay
42%312%16%18%5%
1792
January1st to 15thNight
38%313%19%15%8%
2767
16th to endNight
38%5%10%14%15%15%
2912
February1st to 15thNight
40%38%18%20%9%
2669
16th to endNight
38%412%24%15%4
2207
March1st to 15thNight
43%411%19%15%6%
2342
16th to endNight
38%412%19%19%5%
2435
April1st to 15thNight
37%413%23%17%3
2099
16th to endNight
23%6%13%27%20%7%
2080
May1st to 15thNight
23%6%11%21%26%10%
2002
16th to endNight
25%8%16%22%21%5%
1790
June1st to 15thNight
17%8%13%22%22%15%
1680
16th to endNight
15%46%15%28%29%
1680
July1st to 15thNight
11%39%11%23%40%
1665
16th to endNight
21%7%9%9%21%29%
1746
August1st to 15thNight
23%6%8%9%22%30%
1751
16th to endNight
19%48%10%28%28%
2070
September1st to 15thNight
12%5%9%12%27%32%
1950
16th to endNight
15%3419%33%23%
2122
October1st to 15thNight
22%49%18%21%23%
2340
16th to endNight
22%5%7%21%24%19%
2496
November1st to 15thNight
25%5%11%23%23%11%
2548
16th to endNight
32%49%21%22%9%
2811
December1st to 15thNight
37%48%17%18%12%
2940
16th to endNight
39%414%15%18%6%
3136

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 15thDay
27%6%22%25%16%1
277
16th to endDay
17%9%21%27%20%3
352
February1st to 15thDay
19%14%20%25%16%3
329
16th to endDay
19%15%28%23%11%2
342
March1st to 15thDay
22%15%24%19%14%3
390
16th to endDay
14%13%30%28%11%3
416
April1st to 15thDay
20%16%28%22%10%2
389
16th to endDay
9%16%26%25%14%6%
378
May1st to 15thDay
9%10%29%30%14%4
408
16th to endDay
9%12%23%31%18%4
458
June1st to 15thDay
5%8%25%34%18%7%
435
16th to endDay
1320%42%24%7%
435
July1st to 15thDay
212%44%30%9%
425
16th to endDay
17%48%30%12%
392
August1st to 15thDay
215%39%33%8%
359
16th to endDay
12%42%29%13%
396
September1st to 15thDay
1119%43%24%9%
375
16th to endDay
4417%32%30%9%
375
October1st to 15thDay
5%6%25%34%22%5%
375
16th to endDay
7%5%19%30%25%12%
400
November1st to 15thDay
9%5%13%26%33%10%
294
16th to endDay
13%5%17%32%25%5%
156
December1st to 15thDay
15%13%14%25%22%9%
120
16th to endDay
10%15%16%19%28%9%
128
January1st to 15thNight
15%412%30%29%7%
840
16th to endNight
17%311%31%27%8%
896
February1st to 15thNight
16%6%12%29%27%7%
824
16th to endNight
17%5%19%32%19%5%
736
March1st to 15thNight
18%5%14%26%28%5%
840
16th to endNight
14%5%17%33%25%3
896
April1st to 15thNight
14%7%19%32%23%2
839
16th to endNight
7%6%20%31%25%8%
832
May1st to 15thNight
4316%35%33%7%
742
16th to endNight
3416%36%33%6%
476
June1st to 15thNight
2113%40%36%6%
420
16th to endNight
17%40%44%5%
420
July1st to 15thNight
15%26%56%11%
465
16th to endNight
421%54%18%
615
August1st to 15thNight
18%28%51%9%
606
16th to endNight
16%28%49%14%
828
September1st to 15thNight
25%29%47%15%
780
16th to endNight
219%29%42%13%
776
October1st to 15thNight
6%210%33%33%12%
780
16th to endNight
7%18%25%37%18%
832
November1st to 15thNight
8%112%31%36%9%
820
16th to endNight
11%311%32%31%9%
840
December1st to 15thNight
16%213%32%27%7%
840
16th to endNight
17%6%16%31%22%4
896
Page generated at 2019-07-17 05:53:07. Version ac04

Copyright 2019 A. Danko


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