Observatory on the Ridge
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatory on the Ridge clear sky chart from 2005-11-05 to 2017-09-16.

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
28%
14880
11%
46875
7%
14842
33%
14842
13%
34812

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
8%
716
5%
2464
2%
716
12%
716
4%
2160
January16th to endNight
9%
768
5%
2496
1%
768
13%
768
4%
2143
February1st to 15thNight
11%
704
4%
2287
2%
701
15%
701
5%
1951
February16th to endNight
16%
631
7%
2003
2%
631
22%
631
7%
1650
March1st to 15thNight
20%
720
11%
1980
5%
720
25%
720
11%
1583
March16th to endNight
23%
768
16%
2112
7%
768
31%
768
16%
1544
April1st to 15thNight
23%
718
12%
1811
5%
718
27%
718
17%
1386
April16th to endNight
32%
594
18%
1674
6%
594
41%
594
22%
1120
May1st to 15thNight
35%
495
15%
1575
9%
495
41%
495
14%
1098
May16th to endNight
39%
374
16%
1497
13%
374
50%
374
18%
904
June1st to 15thNight
37%
360
13%
1440
10%
360
48%
360
15%
916
June16th to endNight
39%
360
11%
1440
12%
360
47%
360
16%
907
July1st to 15thNight
50%
340
15%
1360
20%
340
55%
340
24%
754
July16th to endNight
48%
498
14%
1530
12%
466
57%
466
26%
910
August1st to 15thNight
55%
539
15%
1609
11%
536
59%
536
27%
985
August16th to endNight
57%
645
19%
1791
11%
645
61%
645
32%
1109
September1st to 15thNight
50%
720
19%
1800
11%
720
53%
720
30%
1215
September16th to endNight
48%
658
19%
1842
13%
658
51%
658
25%
1227
October1st to 15thNight
35%
660
15%
1980
14%
660
38%
660
18%
1391
October16th to endNight
18%
704
8%
2112
4%
704
23%
704
10%
1671
November1st to 15thNight
29%
700
17%
2344
15%
700
34%
700
16%
1628
November16th to endNight
16%
720
8%
2520
5%
720
22%
720
8%
1990
December1st to 15thNight
10%
720
3%
2520
2%
720
11%
720
4%
2182
December16th to endNight
8%
768
3%
2688
0%
768
11%
768
3%
2388

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
15%9%46%5%3445%7%31%
47860
Night
17%10%47%5%3445%6%30%
47056
Cloud CoverDay
15%9%46%6%3445%7%31%
47870
Night
17%10%47%5%34446%30%
47060
TransparencyDay
51%7%12%17%9%
47559
Night
55%6%11%15%9%1
46875
SeeingDay
18%18%23%22%12%4
5393
Night
20%24%22%21%10%1
14885

By Month

Percentage Cloud Cover NE (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
19%18%6%10%8%45%345%13%
1471
16th to endDay
15%17%8%12%9%45%5%5%411%
1728
February1st to 15thDay
18%17%7%13%7%35%43413%
1575
16th to endDay
18%14%6%11%8%35%435%17%
1467
March1st to 15thDay
17%13%6%9%7%35%446%20%
1969
16th to endDay
17%12%46%5%3435%6%30%
2112
April1st to 15thDay
21%10%35%434445%31%
2137
16th to endDay
18%8%245%34445%39%
2296
May1st to 15thDay
16%6%25%5%445%5%7%35%
2373
16th to endDay
11%6%35%5%2446%7%42%
2618
June1st to 15thDay
16%6%2443446%8%37%
2520
16th to endDay
13%4244345%6%9%42%
2520
July1st to 15thDay
8%424425%5%6%9%45%
2520
16th to endDay
10%425%437%5%7%10%36%
2531
August1st to 15thDay
8%425%5%445%7%10%40%
2340
16th to endDay
11%42443446%9%43%
2399
September1st to 15thDay
15%5%35%434447%41%
2160
16th to endDay
15%5%25%3445%6%7%39%
1787
October1st to 15thDay
20%7%36%5%245%45%33%
1650
16th to endDay
24%11%47%7%34445%21%
1760
November1st to 15thDay
13%9%46%7%35%45%7%32%
1511
16th to endDay
22%12%38%6%2445%6%22%
1440
December1st to 15thDay
19%20%7%8%6%23446%15%
1440
16th to endDay
21%19%7%11%7%3434410%
1536
January1st to 15thNight
23%17%6%9%7%3434415%
2464
16th to endNight
17%19%6%11%7%34445%16%
2496
February1st to 15thNight
18%17%7%11%7%3433318%
2285
16th to endNight
18%14%5%11%8%35%445%18%
2003
March1st to 15thNight
21%12%38%6%34435%25%
1968
16th to endNight
16%11%36%5%24445%34%
2112
April1st to 15thNight
23%9%35%43444431%
1811
16th to endNight
13%6%25%5%35%45%6%41%
1674
May1st to 15thNight
16%5%36%5%35%5%6%7%33%
1575
16th to endNight
12%5%245%345%6%7%41%
1495
June1st to 15thNight
14%5%25%5%45%5%5%7%38%
1440
16th to endNight
12%4246%46%6%5%7%39%
1440
July1st to 15thNight
7%4246%2345%8%49%
1440
16th to endNight
8%324445%5%7%8%44%
1636
August1st to 15thNight
8%5%244346%6%8%46%
1620
16th to endNight
8%4145%245%6%8%48%
1791
September1st to 15thNight
15%5%2442346%6%45%
1800
16th to endNight
15%5%2442445%5%44%
1842
October1st to 15thNight
20%7%25%424446%37%
1980
16th to endNight
26%8%26%6%345%5%6%24%
2112
November1st to 15thNight
17%8%36%424446%37%
2344
16th to endNight
20%11%5%8%5%4445%7%22%
2520
December1st to 15thNight
22%20%6%7%5%24345%15%
2520
16th to endNight
23%16%7%10%7%3444412%
2688

Percentage Cloud Cover SE (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
19%18%6%11%8%34345%13%
1471
16th to endDay
15%18%7%12%9%47%44411%
1728
February1st to 15thDay
17%17%7%12%7%45%44413%
1575
16th to endDay
18%14%6%11%10%34435%17%
1467
March1st to 15thDay
17%13%7%9%8%35%346%20%
1980
16th to endDay
16%11%5%6%5%3445%6%30%
2111
April1st to 15thDay
20%11%36%434345%31%
2137
16th to endDay
18%8%25%5%23345%38%
2296
May1st to 15thDay
16%6%25%5%345%5%7%35%
2373
16th to endDay
12%6%244345%6%8%41%
2618
June1st to 15thDay
15%7%345%2446%8%37%
2520
16th to endDay
12%4244345%6%9%41%
2520
July1st to 15thDay
7%5%24425%5%6%8%45%
2520
16th to endDay
10%425%5%46%5%8%10%36%
2531
August1st to 15thDay
8%5%15%5%45%5%7%11%39%
2340
16th to endDay
11%5%144245%6%9%43%
2399
September1st to 15thDay
15%5%25%435%447%40%
2160
16th to endDay
14%6%25%435%5%6%7%38%
1787
October1st to 15thDay
20%7%36%5%345%5%5%33%
1650
16th to endDay
23%12%47%6%2445%422%
1760
November1st to 15thDay
12%11%36%7%36%447%32%
1511
16th to endDay
21%12%47%7%3345%6%22%
1440
December1st to 15thDay
20%20%7%8%5%2345%6%15%
1440
16th to endDay
21%19%7%11%7%34335%10%
1536
January1st to 15thNight
23%16%6%8%8%3444414%
2464
16th to endNight
17%18%6%11%7%34435%15%
2496
February1st to 15thNight
17%17%7%10%7%25%33418%
2278
16th to endNight
17%13%5%11%8%35%445%18%
2003
March1st to 15thNight
22%11%48%6%25%445%25%
1980
16th to endNight
16%11%46%424446%34%
2112
April1st to 15thNight
23%10%36%43345%431%
1811
16th to endNight
13%7%25%5%245%47%41%
1674
May1st to 15thNight
16%5%36%6%25%5%6%7%33%
1574
16th to endNight
12%5%24435%46%7%42%
1495
June1st to 15thNight
13%6%35%5%35%5%5%7%38%
1440
16th to endNight
11%5%245%35%6%5%6%40%
1440
July1st to 15thNight
7%5%245%3345%8%48%
1440
16th to endNight
8%4245%35%5%6%8%44%
1636
August1st to 15thNight
8%4245%25%5%6%9%45%
1620
16th to endNight
8%424435%5%5%8%48%
1791
September1st to 15thNight
15%5%2442345%7%44%
1800
16th to endNight
15%6%2442445%6%43%
1842
October1st to 15thNight
20%6%26%334345%38%
1980
16th to endNight
25%9%36%6%35%45%7%24%
2112
November1st to 15thNight
17%8%36%324446%37%
2344
16th to endNight
19%11%5%7%6%35%45%7%22%
2520
December1st to 15thNight
22%19%6%8%5%24445%16%
2520
16th to endNight
22%17%6%10%7%44345%11%
2688

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
75%5%9%7%1
1472
16th to endDay
76%7%8%5%1
1728
February1st to 15thDay
75%8%7%7%
1577
16th to endDay
68%6%11%11%3
1467
March1st to 15thDay
64%6%10%13%4
1980
16th to endDay
54%6%9%20%8%1
2112
April1st to 15thDay
54%5%10%18%10%
2137
16th to endDay
46%5%9%19%15%2
2296
May1st to 15thDay
46%7%12%21%11%
2373
16th to endDay
39%7%16%22%12%1
2622
June1st to 15thDay
43%8%13%21%11%1
2520
16th to endDay
37%9%15%24%12%
2520
July1st to 15thDay
34%8%12%24%18%1
2371
16th to endDay
39%10%17%21%11%1
2374
August1st to 15thDay
35%11%16%22%12%1
2327
16th to endDay
34%8%15%27%12%1
2399
September1st to 15thDay
42%7%14%23%11%
2160
16th to endDay
41%8%13%23%12%
1787
October1st to 15thDay
52%6%12%15%11%
1650
16th to endDay
64%6%14%10%2
1760
November1st to 15thDay
52%7%14%15%7%1
1511
16th to endDay
65%7%12%11%3
1440
December1st to 15thDay
73%8%11%5%
1440
16th to endDay
79%7%8%4
1536
January1st to 15thNight
76%5%8%5%2
2464
16th to endNight
73%5%10%7%2
2496
February1st to 15thNight
73%5%10%8%1
2287
16th to endNight
68%5%10%11%3
2003
March1st to 15thNight
62%6%10%15%4
1980
16th to endNight
51%6%9%17%12%1
2112
April1st to 15thNight
55%5%9%17%11%
1811
16th to endNight
42%5%11%20%15%3
1674
May1st to 15thNight
48%7%9%22%11%1
1575
16th to endNight
39%7%13%21%15%2
1497
June1st to 15thNight
43%7%11%21%15%
1440
16th to endNight
42%7%13%20%14%1
1440
July1st to 15thNight
34%6%13%23%19%3
1360
16th to endNight
35%6%16%23%14%3
1530
August1st to 15thNight
33%8%17%26%13%1
1609
16th to endNight
32%8%15%27%14%1
1791
September1st to 15thNight
39%6%15%23%14%1
1800
16th to endNight
40%7%11%23%16%
1842
October1st to 15thNight
49%5%11%19%14%
1980
16th to endNight
61%6%14%12%4
2112
November1st to 15thNight
49%7%12%18%10%2
2344
16th to endNight
63%7%13%12%3
2520
December1st to 15thNight
74%6%11%5%1
2520
16th to endNight
78%6%9%5%
2688

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
28%34%19%8%7%1
67
16th to endDay
31%17%33%14%3
96
February1st to 15thDay
22%35%34%7%
90
16th to endDay
21%22%38%15%1
111
March1st to 15thDay
24%26%24%18%41
270
16th to endDay
22%21%27%20%6%1
288
April1st to 15thDay
22%24%25%17%8%1
270
16th to endDay
16%23%22%21%9%5%
270
May1st to 15thDay
25%20%19%19%11%3
288
16th to endDay
13%17%26%25%11%4
331
June1st to 15thDay
20%18%20%27%13%
315
16th to endDay
15%18%26%27%11%1
315
July1st to 15thDay
9%13%21%31%20%4
305
16th to endDay
11%14%23%28%17%4
326
August1st to 15thDay
11%9%20%26%21%10%
313
16th to endDay
12%10%18%25%21%12%
332
September1st to 15thDay
11%8%21%26%24%8%
315
16th to endDay
16%12%16%20%24%9%
254
October1st to 15thDay
16%15%24%20%16%6%
255
16th to endDay
28%22%25%19%4
272
November1st to 15thDay
14%16%30%25%8%3
126
16th to endDay
26%25%16%30%1
60
December1st to 15thDay
31%33%13%15%6%
60
16th to endDay
29%42%25%3
64
January1st to 15thNight
25%35%22%13%3
720
16th to endNight
24%30%27%13%3
768
February1st to 15thNight
22%32%25%16%3
704
16th to endNight
22%28%25%21%2
631
March1st to 15thNight
25%27%23%19%5%
720
16th to endNight
20%23%28%19%7%
768
April1st to 15thNight
22%27%22%22%4
718
16th to endNight
14%24%24%24%10%1
594
May1st to 15thNight
19%22%16%28%11%1
495
16th to endNight
11%20%23%28%14%1
375
June1st to 15thNight
15%18%23%29%13%
360
16th to endNight
13%20%21%31%11%
360
July1st to 15thNight
7%13%20%37%20%
340
16th to endNight
9%17%20%28%21%2
498
August1st to 15thNight
9%12%15%36%21%3
539
16th to endNight
10%10%17%30%27%3
645
September1st to 15thNight
14%12%16%28%24%3
720
16th to endNight
16%14%15%24%23%5%
658
October1st to 15thNight
22%16%20%23%15%2
660
16th to endNight
28%24%25%16%4
704
November1st to 15thNight
19%23%25%20%9%1
700
16th to endNight
22%35%22%13%6%
720
December1st to 15thNight
33%32%18%12%2
720
16th to endNight
28%32%23%12%2
768
Page generated at 2017-09-16 17:06:58. Version ac04

Copyright 2017 A. Danko


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