Challis Astronomical Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Challis Astronomical Observatory clear sky chart from 2005-11-05 to 2018-01-20.

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
58%
15683
20%
48518
17%
15657
62%
15657
34%
27676

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
49%
776
14%
2716
13%
776
53%
776
22%
1699
January16th to endNight
57%
788
19%
2758
18%
788
62%
788
27%
1622
February1st to 15thNight
46%
698
11%
2273
10%
696
49%
696
25%
1423
February16th to endNight
45%
632
15%
1895
12%
632
50%
632
29%
1184
March1st to 15thNight
52%
720
15%
2106
10%
720
57%
720
33%
1260
March16th to endNight
46%
768
15%
2112
8%
768
51%
768
32%
1309
April1st to 15thNight
51%
688
15%
1769
7%
688
54%
688
31%
1173
April16th to endNight
52%
540
18%
1620
13%
540
56%
540
33%
960
May1st to 15thNight
57%
539
18%
1619
16%
539
60%
539
35%
904
May16th to endNight
59%
434
11%
1549
13%
434
61%
434
24%
968
June1st to 15thNight
64%
360
15%
1260
18%
360
68%
360
30%
725
June16th to endNight
74%
360
25%
1261
31%
360
80%
360
46%
588
July1st to 15thNight
85%
340
20%
1360
31%
340
88%
340
53%
514
July16th to endNight
88%
376
32%
1416
44%
354
91%
354
59%
508
August1st to 15thNight
78%
534
28%
1607
27%
532
80%
532
54%
751
August16th to endNight
74%
602
36%
1748
28%
602
75%
602
56%
818
September1st to 15thNight
78%
720
32%
1896
23%
720
81%
720
57%
977
September16th to endNight
71%
716
33%
1980
26%
716
75%
716
47%
1075
October1st to 15thNight
64%
720
27%
2047
21%
720
69%
720
42%
1146
October16th to endNight
62%
768
26%
2463
22%
768
68%
768
38%
1303
November1st to 15thNight
55%
760
21%
2470
20%
760
59%
760
30%
1422
November16th to endNight
50%
878
19%
2633
12%
878
57%
878
33%
1529
December1st to 15thNight
52%
975
12%
2889
9%
975
54%
975
28%
1822
December16th to endNight
44%
991
15%
3071
11%
991
49%
991
24%
1996

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
47%37%6%35%5%5%7%40%
49014
Night
25%25%5%35%6%7%9%45%
48688
Cloud CoverDay
45%26%6%35%5%6%8%44%
49015
Night
2425%435%5%7%9%49%
48690
TransparencyDay
34%6%14%22%15%6%
48687
Night
29%7%18%26%14%4
48519
SeeingDay
7%13%29%31%14%3
5971
Night
45%21%42%22%3
15695

By Month

Percentage Cloud Cover NW (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
427%10%46%7%8%9%37%
1552
16th to endDay
6%38%9%5%7%7%7%8%35%
1569
February1st to 15thDay
16%5%10%8%5%5%5%6%8%36%
1588
16th to endDay
7%7%12%13%47%5%6%7%26%
1579
March1st to 15thDay
28%5%10%8%5%7%6%7%8%28%
1854
16th to endDay
413%7%10%9%45%5%6%8%24%
2111
April1st to 15thDay
314%7%10%8%5%5%5%5%7%25%
2176
16th to endDay
6%12%5%8%7%3445%8%33%
2340
May1st to 15thDay
7%11%37%6%45%45%6%37%
2331
16th to endDay
12%15%5%8%8%35%5%46%24%
2560
June1st to 15thDay
10%8%47%6%35%6%6%7%33%
2700
16th to endDay
44245%2445%6%55%
2694
July1st to 15thDay
4414435%5%5%7%53%
2520
16th to endDay
43135%24345%60%
2657
August1st to 15thDay
5%425%5%445%6%5%50%
2343
16th to endDay
4323323446%61%
2453
September1st to 15thDay
5%5%1332335%5%60%
2064
16th to endDay
8%6%244235%46%50%
1980
October1st to 15thDay
9%9%46%5%23445%45%
1912
16th to endDay
37%26%6%35%5%6%8%43%
1758
November1st to 15thDay
28%48%6%36%6%6%8%38%
1719
16th to endDay
15%38%5%38%7%7%9%37%
1641
December1st to 15thDay
16%310%10%5%8%6%6%9%32%
1398
16th to endDay
7%5%11%10%5%7%6%8%8%27%
1515
January1st to 15thNight
436%7%36%6%8%12%40%
2716
16th to endNight
15%36%5%46%6%7%10%43%
2758
February1st to 15thNight
1448%7%47%8%8%9%35%
2262
16th to endNight
5%35%6%48%6%9%12%35%
1895
March1st to 15thNight
1425%6%47%6%10%12%35%
2106
16th to endNight
27%35%6%35%6%8%11%37%
2109
April1st to 15thNight
48%5%7%5%246%8%9%35%
1769
16th to endNight
48%35%5%345%6%7%44%
1620
May1st to 15thNight
49%244236%6%9%45%
1619
16th to endNight
9%10%35%6%26%5%6%10%34%
1549
June1st to 15thNight
8%6%24436%46%7%44%
1260
16th to endNight
344322447%61%
1261
July1st to 15thNight
12222345%8%64%
1440
16th to endNight
1112213235%73%
1512
August1st to 15thNight
22133235%5%7%62%
1615
16th to endNight
331322236%6%65%
1748
September1st to 15thNight
4212223345%66%
1896
16th to endNight
7%423313347%58%
1980
October1st to 15thNight
6%6%2332445%7%51%
2047
16th to endNight
3425%435%5%6%9%50%
2463
November1st to 15thNight
17%37%435%7%8%10%39%
2470
16th to endNight
325%6%37%8%8%11%41%
2633
December1st to 15thNight
1337%7%48%7%8%9%38%
2889
16th to endNight
16%48%8%47%7%8%10%31%
3071

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
326%7%37%6%9%13%37%
1552
16th to endDay
5%36%7%37%7%10%10%37%
1569
February1st to 15thDay
439%6%46%7%8%11%37%
1588
16th to endDay
5%5%8%9%5%8%7%9%10%29%
1579
March1st to 15thDay
16%26%6%5%8%7%9%11%34%
1854
16th to endDay
39%5%8%7%5%6%6%7%10%28%
2112
April1st to 15thDay
28%5%9%8%5%6%6%7%9%29%
2176
16th to endDay
5%8%48%6%25%5%6%8%37%
2340
May1st to 15thDay
6%8%27%6%346%5%7%40%
2331
16th to endDay
11%11%48%8%45%5%5%7%28%
2560
June1st to 15thDay
9%5%36%6%45%6%6%8%36%
2700
16th to endDay
33135%25%46%6%58%
2694
July1st to 15thDay
3314425%5%6%6%55%
2520
16th to endDay
3213334445%62%
2657
August1st to 15thDay
33135%35%6%5%6%53%
2343
16th to endDay
3213323446%63%
2453
September1st to 15thDay
4313423345%61%
2064
16th to endDay
7%413324348%54%
1980
October1st to 15thDay
8%7%245%25%446%47%
1912
16th to endDay
35%246%346%6%8%48%
1758
November1st to 15thDay
15%36%6%47%6%7%8%43%
1719
16th to endDay
1335%5%46%8%9%10%41%
1641
December1st to 15thDay
15%37%7%6%8%7%7%10%35%
1398
16th to endDay
5%39%9%49%6%9%10%31%
1515
January1st to 15thNight
1435%6%46%6%8%12%41%
2716
16th to endNight
5%36%5%35%6%7%10%43%
2758
February1st to 15thNight
1437%7%46%7%8%11%37%
2262
16th to endNight
5%36%5%26%7%7%10%43%
1895
March1st to 15thNight
4245%36%7%10%12%42%
2106
16th to endNight
36%35%5%346%7%11%43%
2112
April1st to 15thNight
48%35%5%45%6%7%9%39%
1769
16th to endNight
46%36%435%5%6%8%46%
1620
May1st to 15thNight
46%15%5%1346%9%49%
1619
16th to endNight
8%8%26%5%25%6%6%10%38%
1548
June1st to 15thNight
9%324416%5%7%8%46%
1260
16th to endNight
3313313346%64%
1261
July1st to 15thNight
1131447%8%65%
1440
16th to endNight
111213445%74%
1512
August1st to 15thNight
22231346%7%64%
1615
16th to endNight
32321235%6%67%
1748
September1st to 15thNight
3213212446%67%
1896
16th to endNight
7%312223446%61%
1980
October1st to 15thNight
5%6%1331445%7%54%
2047
16th to endNight
331433446%8%54%
2463
November1st to 15thNight
16%25%435%5%7%9%46%
2470
16th to endNight
1324425%7%8%12%46%
2633
December1st to 15thNight
1335%6%47%7%8%12%40%
2889
16th to endNight
15%47%7%47%7%10%9%35%
3071

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
33%11%25%20%6%1
1552
16th to endDay
35%9%19%26%7%2
1569
February1st to 15thDay
35%12%25%18%7%
1588
16th to endDay
41%12%18%20%6%
1579
March1st to 15thDay
35%11%26%18%7%
1854
16th to endDay
43%10%21%19%4
2112
April1st to 15thDay
45%8%17%21%5%
2176
16th to endDay
41%5%18%25%9%
2340
May1st to 15thDay
37%5%15%31%9%
2331
16th to endDay
52%5%14%19%7%1
2564
June1st to 15thDay
41%6%11%24%12%2
2700
16th to endDay
23%46%22%34%9%
2694
July1st to 15thDay
24%46%19%26%18%
2371
16th to endDay
21%3312%28%31%
2490
August1st to 15thDay
26%5%7%19%24%16%
2327
16th to endDay
20%36%22%30%16%
2453
September1st to 15thDay
23%37%20%32%12%
2064
16th to endDay
27%49%30%22%4
1980
October1st to 15thDay
35%414%30%13%2
1912
16th to endDay
30%7%17%29%15%
1758
November1st to 15thDay
35%8%19%22%11%2
1719
16th to endDay
30%8%22%25%9%2
1641
December1st to 15thDay
40%10%23%19%5%
1398
16th to endDay
43%8%21%19%5%
1515
January1st to 15thNight
34%12%22%23%6%
2716
16th to endNight
32%9%18%26%9%2
2758
February1st to 15thNight
37%8%26%21%6%
2273
16th to endNight
34%8%24%25%5%1
1895
March1st to 15thNight
28%9%26%26%8%
2106
16th to endNight
30%9%25%27%6%
2112
April1st to 15thNight
36%7%20%24%9%
1769
16th to endNight
32%6%20%29%11%
1620
May1st to 15thNight
29%5%15%38%10%
1620
16th to endNight
40%6%18%25%8%
1549
June1st to 15thNight
33%6%13%29%13%3
1260
16th to endNight
20%47%25%30%11%
1261
July1st to 15thNight
13%49%25%29%17%
1360
16th to endNight
11%3412%34%32%
1416
August1st to 15thNight
16%411%22%25%20%
1607
16th to endNight
17%26%23%31%18%
1748
September1st to 15thNight
18%38%24%32%13%
1896
16th to endNight
23%410%29%25%5%
1980
October1st to 15thNight
27%313%35%17%2
2047
16th to endNight
26%5%16%32%18%
2463
November1st to 15thNight
31%7%20%27%10%1
2470
16th to endNight
26%10%24%27%10%1
2633
December1st to 15thNight
33%10%27%21%6%
2889
16th to endNight
39%8%21%21%7%1
3071

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
121%40%22%15%
90
16th to endDay
230%38%25%2
72
February1st to 15thDay
11%33%31%17%5%
103
16th to endDay
215%36%28%14%1
238
March1st to 15thDay
416%35%35%7%
270
16th to endDay
8%24%39%21%5%
288
April1st to 15thDay
421%37%24%9%2
269
16th to endDay
10%20%31%28%6%2
270
May1st to 15thDay
13%15%28%30%9%1
288
16th to endDay
18%9%21%26%20%3
336
June1st to 15thDay
12%14%19%31%16%4
495
16th to endDay
5%13%24%32%22%2
489
July1st to 15thDay
411%26%40%14%2
305
16th to endDay
5%11%34%34%8%3
327
August1st to 15thDay
36%35%34%14%5%
315
16th to endDay
411%28%32%15%8%
332
September1st to 15thDay
7%12%26%28%15%7%
315
16th to endDay
11%11%26%29%17%3
315
October1st to 15thDay
15%13%24%25%18%2
247
16th to endDay
410%24%39%15%5%
144
November1st to 15thDay
6%9%17%42%21%2
135
16th to endDay
5%8%34%44%5%1
135
December1st to 15thDay
110%29%39%13%6%
97
16th to endDay
112%36%34%13%2
96
January1st to 15thNight
37%28%41%15%3
780
16th to endNight
2423%45%20%3
788
February1st to 15thNight
25%30%42%16%3
704
16th to endNight
35%33%38%16%3
632
March1st to 15thNight
15%32%44%13%2
720
16th to endNight
5%11%27%41%13%1
768
April1st to 15thNight
5%6%25%38%20%3
688
16th to endNight
7%5%26%40%17%2
540
May1st to 15thNight
6%8%19%35%26%2
540
16th to endNight
11%312%33%35%4
435
June1st to 15thNight
10%114%48%22%2
360
16th to endNight
3311%47%30%3
360
July1st to 15thNight
215%44%42%5%
340
16th to endNight
16%50%38%2
376
August1st to 15thNight
219%44%38%2
534
16th to endNight
4210%39%38%3
602
September1st to 15thNight
5%110%38%35%8%
720
16th to endNight
8%310%36%33%8%
716
October1st to 15thNight
9%315%43%24%3
720
16th to endNight
4421%45%18%4
768
November1st to 15thNight
47%22%46%16%1
760
16th to endNight
38%30%41%14%2
878
December1st to 15thNight
26%27%46%14%2
975
16th to endNight
37%30%41%13%2
991
Page generated at 2018-01-21 10:19:23. Version ac04

Copyright 2018 A. Danko


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