Cabin in the Sky Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cabin in the Sky Observatory clear sky chart from 2005-11-05 to 2017-09-23.

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
39%
14759
12%
46786
9%
14730
44%
14730
17%
32133

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
25%
719
7%
2506
5%
716
28%
716
8%
2003
January16th to endNight
30%
768
8%
2688
7%
768
33%
768
10%
2066
February1st to 15thNight
33%
702
8%
2377
7%
700
36%
700
12%
1775
February16th to endNight
38%
632
13%
1948
8%
632
44%
632
16%
1377
March1st to 15thNight
29%
720
9%
2160
6%
720
33%
720
13%
1641
March16th to endNight
30%
768
9%
2004
4%
768
34%
768
15%
1532
April1st to 15thNight
37%
719
11%
1799
5%
719
40%
719
19%
1328
April16th to endNight
38%
531
13%
1611
9%
531
43%
531
18%
1090
May1st to 15thNight
40%
359
15%
1440
15%
359
49%
359
18%
841
May16th to endNight
41%
374
8%
1496
10%
374
46%
374
14%
962
June1st to 15thNight
46%
360
6%
1290
3%
360
47%
360
19%
811
June16th to endNight
42%
360
10%
1148
2%
360
46%
360
23%
692
July1st to 15thNight
57%
340
10%
1339
8%
340
62%
340
34%
598
July16th to endNight
61%
376
20%
1416
24%
354
76%
354
41%
586
August1st to 15thNight
70%
360
24%
1432
31%
358
76%
358
38%
616
August16th to endNight
63%
652
28%
1798
17%
652
70%
652
45%
932
September1st to 15thNight
62%
720
26%
1800
13%
720
67%
720
47%
992
September16th to endNight
57%
688
24%
1864
16%
688
61%
688
31%
1149
October1st to 15thNight
45%
660
16%
1975
15%
660
49%
660
23%
1280
October16th to endNight
37%
704
12%
2266
8%
704
43%
704
15%
1614
November1st to 15thNight
32%
700
10%
2362
8%
700
35%
700
11%
1827
November16th to endNight
26%
750
7%
2550
5%
750
30%
750
8%
2030
December1st to 15thNight
30%
900
8%
2700
6%
900
32%
900
11%
2116
December16th to endNight
22%
897
9%
2817
4%
897
28%
897
8%
2275

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
12%8%36%5%345%5%6%38%
48123
Night
13%10%36%42445%6%37%
46953
Cloud CoverDay
12%9%36%5%35%45%6%36%
48123
Night
13%10%46%5%3445%6%36%
46957
TransparencyDay
47%6%13%19%10%1
47794
Night
47%6%13%20%9%1
46786
SeeingDay
16%21%24%23%10%2
5798
Night
16%20%15%27%17%3
14764

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
18%14%6%8%6%34345%23%
1432
16th to endDay
15%15%47%5%33347%28%
1536
February1st to 15thDay
16%14%5%7%5%35%447%25%
1486
16th to endDay
12%14%36%6%35%5%6%6%28%
1526
March1st to 15thDay
18%13%46%5%35%5%5%8%24%
1800
16th to endDay
14%12%5%9%7%35%6%6%7%21%
2220
April1st to 15thDay
11%10%410%9%46%6%5%6%24%
2149
16th to endDay
9%10%47%7%45%5%5%8%31%
2347
May1st to 15thDay
9%8%46%6%45%5%6%6%35%
2511
16th to endDay
14%7%37%8%5%6%5%5%8%28%
2615
June1st to 15thDay
16%6%36%6%45%5%5%7%33%
2667
16th to endDay
11%6%36%5%35%6%6%6%38%
2802
July1st to 15thDay
43143145%47%58%
2535
16th to endDay
421242345%6%62%
2657
August1st to 15thDay
431342345%6%60%
2520
16th to endDay
43134245%5%7%57%
2401
September1st to 15thDay
4313423337%62%
2160
16th to endDay
10%42443345%6%47%
1932
October1st to 15thDay
14%6%25%42446%6%41%
1653
16th to endDay
20%11%45%5%335%35%31%
1606
November1st to 15thDay
23%10%35%5%35%46%5%26%
1497
16th to endDay
18%13%6%7%4246%5%5%25%
1395
December1st to 15thDay
16%11%6%7%6%25%45%6%26%
1260
16th to endDay
20%16%6%8%42344423%
1416
January1st to 15thNight
23%14%5%8%5%33345%22%
2506
16th to endNight
14%17%5%9%424345%25%
2688
February1st to 15thNight
17%14%5%6%424346%29%
2365
16th to endNight
12%12%46%4345%47%34%
1948
March1st to 15thNight
15%11%48%5%25%5%6%7%27%
2160
16th to endNight
12%11%48%6%35%5%5%6%30%
2000
April1st to 15thNight
11%8%37%436%6%6%7%34%
1799
16th to endNight
7%7%35%5%37%6%5%8%39%
1611
May1st to 15thNight
8%5%25%5%3445%6%46%
1439
16th to endNight
11%7%26%5%36%6%7%8%35%
1496
June1st to 15thNight
12%5%235%36%5%7%7%39%
1290
16th to endNight
8%414435%46%7%48%
1148
July1st to 15thNight
322214347%64%
1419
16th to endNight
122223346%70%
1512
August1st to 15thNight
222222348%65%
1440
16th to endNight
321232335%7%63%
1798
September1st to 15thNight
3312223447%65%
1800
16th to endNight
8%42443345%7%50%
1864
October1st to 15thNight
14%7%25%42445%6%44%
1975
16th to endNight
19%8%36%43446%5%32%
2266
November1st to 15thNight
23%11%35%5%3445%7%26%
2362
16th to endNight
21%14%5%8%5%25%335%23%
2550
December1st to 15thNight
17%13%410%6%24446%26%
2700
16th to endNight
19%20%6%8%42233324%
2817

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
17%16%6%10%6%4444422%
1432
16th to endDay
14%16%48%5%2435%6%28%
1536
February1st to 15thDay
15%15%6%6%6%35%35%6%24%
1486
16th to endDay
12%13%47%7%35%5%6%6%27%
1526
March1st to 15thDay
16%15%47%6%25%46%7%22%
1800
16th to endDay
14%13%6%9%7%45%5%6%6%19%
2220
April1st to 15thDay
11%11%5%11%8%5%6%5%5%6%22%
2149
16th to endDay
10%12%48%7%35%46%7%29%
2347
May1st to 15thDay
10%9%27%7%37%5%47%33%
2511
16th to endDay
15%8%48%8%46%5%5%7%26%
2615
June1st to 15thDay
17%6%37%8%35%6%5%6%30%
2667
16th to endDay
12%7%36%6%35%5%6%6%36%
2802
July1st to 15thDay
5%3233245%5%7%56%
2535
16th to endDay
4213424436%62%
2657
August1st to 15thDay
4313424446%59%
2520
16th to endDay
431343445%8%55%
2401
September1st to 15thDay
5%413313346%61%
2160
16th to endDay
10%5%25%43445%6%47%
1932
October1st to 15thDay
14%7%36%42445%7%40%
1653
16th to endDay
21%12%36%5%245%45%30%
1606
November1st to 15thDay
20%12%46%5%35%46%6%25%
1497
16th to endDay
17%12%6%7%6%345%5%425%
1395
December1st to 15thDay
14%11%5%11%5%44446%26%
1260
16th to endDay
18%19%5%8%423445%23%
1416
January1st to 15thNight
21%14%6%9%6%23435%21%
2506
16th to endNight
14%17%6%9%6%2435%5%23%
2688
February1st to 15thNight
16%14%5%7%5%24445%29%
2365
16th to endNight
11%13%45%425%5%5%7%32%
1948
March1st to 15thNight
15%11%47%6%346%6%7%26%
2160
16th to endNight
12%12%48%6%35%5%5%6%28%
2004
April1st to 15thNight
10%8%47%6%36%6%5%6%33%
1799
16th to endNight
6%8%46%6%46%5%5%6%38%
1611
May1st to 15thNight
9%5%25%6%45%45%5%44%
1439
16th to endNight
12%6%36%6%45%5%6%7%34%
1496
June1st to 15thNight
13%5%145%35%46%8%38%
1290
16th to endNight
10%3246%25%5%6%6%46%
1148
July1st to 15thNight
421231336%6%63%
1419
16th to endNight
1212223347%69%
1512
August1st to 15thNight
221232335%8%64%
1440
16th to endNight
321332335%8%62%
1798
September1st to 15thNight
421232245%7%64%
1800
16th to endNight
8%424424447%49%
1864
October1st to 15thNight
13%6%35%43435%6%43%
1975
16th to endNight
19%9%35%5%35%46%5%31%
2266
November1st to 15thNight
21%11%46%5%35%446%25%
2362
16th to endNight
20%15%5%9%6%35%33423%
2550
December1st to 15thNight
16%13%5%9%5%34445%25%
2700
16th to endNight
19%19%6%8%5%2233423%
2817

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
64%6%12%11%4
1432
16th to endDay
55%7%14%15%41
1536
February1st to 15thDay
59%8%17%12%2
1486
16th to endDay
56%8%13%14%7%
1526
March1st to 15thDay
59%8%14%13%3
1800
16th to endDay
63%8%14%10%3
2220
April1st to 15thDay
61%7%13%13%3
2149
16th to endDay
52%8%14%19%41
2347
May1st to 15thDay
49%6%13%21%8%1
2511
16th to endDay
55%6%15%16%4
2619
June1st to 15thDay
54%5%11%16%8%2
2667
16th to endDay
46%5%12%21%12%
2802
July1st to 15thDay
27%5%10%25%22%8%
2386
16th to endDay
23%5%9%25%28%7%
2490
August1st to 15thDay
25%5%11%30%22%4
2503
16th to endDay
25%7%11%31%19%3
2401
September1st to 15thDay
24%413%30%24%3
2160
16th to endDay
35%8%14%25%13%2
1932
October1st to 15thDay
42%7%15%25%8%
1653
16th to endDay
55%6%13%18%5%
1606
November1st to 15thDay
58%8%14%13%31
1497
16th to endDay
58%8%12%15%4
1395
December1st to 15thDay
58%8%13%15%3
1260
16th to endDay
63%6%12%13%3
1416
January1st to 15thNight
65%5%12%10%4
2506
16th to endNight
61%5%13%12%41
2688
February1st to 15thNight
56%7%16%14%41
2377
16th to endNight
49%7%17%19%6%
1948
March1st to 15thNight
54%8%15%16%3
2160
16th to endNight
54%7%15%17%4
2004
April1st to 15thNight
47%8%15%20%6%
1799
16th to endNight
44%7%15%25%6%
1611
May1st to 15thNight
39%5%14%25%14%1
1440
16th to endNight
44%7%19%21%6%
1496
June1st to 15thNight
41%6%14%25%10%1
1290
16th to endNight
35%6%15%25%15%1
1148
July1st to 15thNight
21%412%27%24%8%
1339
16th to endNight
16%411%28%29%9%
1416
August1st to 15thNight
18%5%12%32%25%5%
1432
16th to endNight
19%5%13%33%24%3
1798
September1st to 15thNight
19%5%12%29%27%4
1800
16th to endNight
33%6%12%28%15%4
1864
October1st to 15thNight
41%6%16%24%11%1
1975
16th to endNight
51%7%13%22%4
2266
November1st to 15thNight
59%8%12%13%41
2362
16th to endNight
65%5%10%12%5%
2550
December1st to 15thNight
60%6%13%14%3
2700
16th to endNight
66%6%9%13%4
2817

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
16%6%11%33%23%8%
60
16th to endDay
39%6%17%23%9%4
64
February1st to 15thDay
23%19%26%22%7%
146
16th to endDay
18%20%21%27%9%1
229
March1st to 15thDay
31%31%25%10%1
270
16th to endDay
24%35%20%15%4
288
April1st to 15thDay
21%27%26%15%7%1
269
16th to endDay
17%33%23%15%6%3
270
May1st to 15thDay
18%29%25%20%6%
288
16th to endDay
18%19%23%20%14%5%
330
June1st to 15thDay
12%20%24%25%15%2
462
16th to endDay
12%23%24%24%13%2
597
July1st to 15thDay
7%18%26%33%11%2
320
16th to endDay
320%32%27%12%3
327
August1st to 15thDay
8%12%23%34%14%6%
315
16th to endDay
6%18%26%31%10%5%
332
September1st to 15thDay
7%21%24%26%15%4
315
16th to endDay
15%17%27%25%10%2
284
October1st to 15thDay
23%20%27%19%7%1
255
16th to endDay
40%9%17%19%11%1
118
November1st to 15thDay
30%12%25%26%5%
75
16th to endDay
25%13%23%10%18%10%
60
December1st to 15thDay
26%6%25%25%13%3
60
16th to endDay
26%7%25%23%12%4
64
January1st to 15thNight
22%23%14%25%11%2
720
16th to endNight
19%20%16%27%14%1
768
February1st to 15thNight
19%21%14%25%15%2
704
16th to endNight
16%20%16%27%16%3
632
March1st to 15thNight
19%24%18%24%11%1
720
16th to endNight
16%24%20%24%11%1
768
April1st to 15thNight
11%22%17%26%17%4
719
16th to endNight
9%24%19%29%14%3
531
May1st to 15thNight
10%24%16%29%16%2
360
16th to endNight
14%20%13%25%20%5%
375
June1st to 15thNight
10%21%15%29%20%2
360
16th to endNight
11%20%17%28%20%2
360
July1st to 15thNight
5%17%14%26%31%4
340
16th to endNight
221%11%30%30%4
376
August1st to 15thNight
212%9%26%40%8%
360
16th to endNight
413%14%31%29%5%
652
September1st to 15thNight
413%14%27%27%11%
720
16th to endNight
12%12%11%32%26%5%
688
October1st to 15thNight
18%14%16%26%21%2
660
16th to endNight
23%12%16%27%16%3
704
November1st to 15thNight
23%22%15%29%8%1
700
16th to endNight
26%24%12%21%12%3
750
December1st to 15thNight
21%23%15%30%8%1
900
16th to endNight
26%22%18%26%6%
897
Page generated at 2017-09-24 06:15:49. Version ac04

Copyright 2017 A. Danko


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