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 2018-04-23.

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
28%
15747
11%
49578
7%
15709
33%
15709
13%
36834

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
9%
776
5%
2670
3%
776
13%
776
4%
2326
January16th to endNight
9%
832
5%
2704
1%
832
13%
832
5%
2295
February1st to 15thNight
11%
764
4%
2482
2%
761
14%
761
5%
2121
February16th to endNight
16%
683
7%
2169
2%
683
22%
683
8%
1777
March1st to 15thNight
20%
780
11%
2145
5%
780
25%
780
11%
1707
March16th to endNight
24%
832
17%
2288
7%
832
32%
832
17%
1659
April1st to 15thNight
23%
778
12%
1962
5%
778
26%
778
16%
1515
April16th to endNight
33%
614
19%
1728
7%
614
41%
614
22%
1153
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
51%
717
22%
2007
16%
717
54%
717
27%
1311
October1st to 15thNight
35%
720
15%
2160
14%
720
38%
720
19%
1514
October16th to endNight
20%
768
10%
2304
6%
768
25%
768
11%
1798
November1st to 15thNight
29%
760
16%
2545
14%
760
33%
760
15%
1791
November16th to endNight
17%
780
9%
2730
4%
780
23%
780
8%
2145
December1st to 15thNight
10%
780
2%
2730
1%
780
12%
780
4%
2354
December16th to endNight
8%
832
3%
2912
0%
832
11%
832
3%
2570

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
16%9%46%5%3445%7%31%
49932
Night
17%10%47%5%3445%6%30%
49759
Cloud CoverDay
15%9%46%6%3445%7%31%
49942
Night
17%10%47%6%34446%30%
49763
TransparencyDay
51%7%12%17%9%
49631
Night
55%6%11%15%9%1
49578
SeeingDay
19%18%24%21%12%4
6078
Night
20%23%22%21%10%1
15752

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%17%6%10%8%45%445%14%
1594
16th to endDay
15%17%8%12%9%45%5%5%412%
1872
February1st to 15thDay
19%17%7%12%8%35%43413%
1710
16th to endDay
19%13%6%11%8%25%435%17%
1587
March1st to 15thDay
17%15%6%9%7%35%445%20%
2134
16th to endDay
17%11%47%5%3435%6%31%
2288
April1st to 15thDay
21%11%36%433445%30%
2316
16th to endDay
18%8%245%23445%39%
2357
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
14%5%25%4445%6%7%40%
1949
October1st to 15thDay
20%8%36%6%245%45%33%
1800
16th to endDay
24%11%47%7%24445%23%
1920
November1st to 15thDay
14%10%47%7%35%45%6%31%
1640
16th to endDay
21%12%38%6%24446%24%
1560
December1st to 15thDay
18%21%6%8%6%23446%15%
1560
16th to endDay
21%18%7%12%7%3434411%
1664
January1st to 15thNight
23%16%5%9%7%34445%15%
2670
16th to endNight
17%18%5%11%7%34445%16%
2704
February1st to 15thNight
18%17%7%11%7%3434417%
2480
16th to endNight
18%13%5%11%7%35%445%19%
2169
March1st to 15thNight
20%13%38%6%34435%25%
2133
16th to endNight
16%11%36%5%34445%36%
2288
April1st to 15thNight
23%9%46%43445%430%
1962
16th to endNight
14%6%25%5%25%45%6%42%
1728
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
14%42442445%5%46%
2007
October1st to 15thNight
20%7%25%434336%38%
2160
16th to endNight
25%8%25%6%345%5%6%26%
2304
November1st to 15thNight
18%8%36%434446%36%
2545
16th to endNight
20%11%48%5%4445%7%23%
2730
December1st to 15thNight
22%20%6%7%6%24445%16%
2730
16th to endNight
23%16%7%10%7%3444412%
2912

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
18%17%6%10%9%35%445%13%
1594
16th to endDay
14%17%7%12%10%46%44412%
1872
February1st to 15thDay
18%17%7%12%7%45%44313%
1710
16th to endDay
19%14%6%11%9%34435%17%
1587
March1st to 15thDay
17%14%7%9%8%34345%20%
2145
16th to endDay
17%11%47%5%3445%6%31%
2287
April1st to 15thDay
20%11%46%424345%30%
2316
16th to endDay
18%8%245%23445%39%
2357
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
13%5%25%435%46%7%40%
1949
October1st to 15thDay
20%8%36%5%3445%5%33%
1800
16th to endDay
23%12%47%6%2445%5%23%
1920
November1st to 15thDay
13%11%36%7%36%447%30%
1640
16th to endDay
21%12%47%7%3345%6%24%
1560
December1st to 15thDay
19%20%7%8%5%3345%6%15%
1560
16th to endDay
21%18%7%11%7%34335%11%
1664
January1st to 15thNight
22%16%6%9%8%34445%14%
2670
16th to endNight
17%18%6%11%7%34445%16%
2704
February1st to 15thNight
18%17%7%10%7%25%33417%
2473
16th to endNight
18%13%5%11%8%34445%18%
2169
March1st to 15thNight
21%12%48%6%25%445%25%
2145
16th to endNight
16%10%37%434445%35%
2288
April1st to 15thNight
23%10%36%5%2345%429%
1962
16th to endNight
13%7%25%5%245%47%42%
1728
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
14%6%2442445%5%45%
2007
October1st to 15thNight
20%6%26%434345%38%
2160
16th to endNight
24%8%36%6%35%45%7%25%
2304
November1st to 15thNight
17%9%36%434446%36%
2545
16th to endNight
19%11%5%7%6%35%45%7%23%
2730
December1st to 15thNight
21%19%6%8%6%23445%16%
2730
16th to endNight
22%16%6%10%7%44345%12%
2912

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
74%5%10%8%2
1595
16th to endDay
75%7%9%5%1
1872
February1st to 15thDay
75%8%7%7%
1712
16th to endDay
68%5%10%11%3
1587
March1st to 15thDay
64%6%10%13%4
2145
16th to endDay
53%5%9%21%8%1
2288
April1st to 15thDay
55%5%10%18%9%
2316
16th to endDay
46%5%9%19%15%3
2357
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
40%8%12%24%12%
1949
October1st to 15thDay
53%6%12%16%11%
1800
16th to endDay
63%6%15%10%3
1920
November1st to 15thDay
53%8%14%14%7%1
1640
16th to endDay
63%6%13%11%4
1560
December1st to 15thDay
72%8%11%6%
1560
16th to endDay
78%7%8%5%
1664
January1st to 15thNight
75%6%8%6%2
2670
16th to endNight
72%6%11%7%2
2704
February1st to 15thNight
72%6%10%8%1
2482
16th to endNight
67%6%9%12%4
2169
March1st to 15thNight
62%5%10%15%5%
2145
16th to endNight
51%5%9%18%13%1
2288
April1st to 15thNight
56%5%9%17%10%
1962
16th to endNight
42%5%11%20%16%3
1728
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
38%7%11%23%17%
2007
October1st to 15thNight
49%5%11%18%14%
2160
16th to endNight
59%7%14%12%5%
2304
November1st to 15thNight
50%7%12%17%9%1
2545
16th to endNight
62%6%13%12%3
2730
December1st to 15thNight
74%6%12%41
2730
16th to endNight
77%6%9%5%
2912

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
24%29%25%15%6%1
100
16th to endDay
26%22%34%13%2
144
February1st to 15thDay
27%33%31%8%
135
16th to endDay
26%23%38%11%1
152
March1st to 15thDay
24%23%26%20%41
330
16th to endDay
22%18%29%21%6%1
352
April1st to 15thDay
25%24%26%15%6%1
330
16th to endDay
16%22%23%22%10%4
289
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
14%10%16%18%26%13%
314
October1st to 15thDay
19%14%23%19%15%7%
315
16th to endDay
27%23%23%18%6%
336
November1st to 15thDay
21%14%31%21%8%3
165
16th to endDay
30%24%22%21%2
90
December1st to 15thDay
34%27%16%14%6%
90
16th to endDay
27%40%27%5%
96
January1st to 15thNight
25%34%23%13%3
780
16th to endNight
24%31%27%13%3
832
February1st to 15thNight
23%32%25%15%2
764
16th to endNight
23%26%26%20%2
683
March1st to 15thNight
24%26%23%19%5%
780
16th to endNight
20%21%28%20%7%
832
April1st to 15thNight
23%26%23%22%4
778
16th to endNight
15%23%23%24%10%1
614
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
15%13%15%23%25%7%
717
October1st to 15thNight
22%15%20%23%15%2
720
16th to endNight
27%23%25%17%5%
768
November1st to 15thNight
20%22%25%20%9%1
760
16th to endNight
23%34%21%14%6%
780
December1st to 15thNight
33%32%18%12%2
780
16th to endNight
28%32%24%12%1
832
Page generated at 2018-04-24 10:03:05. Version ac04

Copyright 2018 A. Danko


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