Green Ridge Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Green Ridge Observatory 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
33%
16030
15%
49344
9%
15992
40%
15992
18%
34081

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
13%
877
10%
2622
4%
876
20%
876
10%
2052
January16th to endNight
17%
832
10%
2704
3%
832
25%
832
9%
2127
February1st to 15thNight
17%
762
9%
2482
3%
761
24%
761
9%
1914
February16th to endNight
23%
683
12%
2080
5%
683
32%
683
12%
1564
March1st to 15thNight
24%
780
14%
2197
7%
780
29%
780
16%
1603
March16th to endNight
30%
832
19%
2288
10%
832
37%
832
20%
1582
April1st to 15thNight
27%
716
14%
1988
7%
716
33%
716
19%
1438
April16th to endNight
33%
558
21%
1672
8%
558
43%
558
21%
1088
May1st to 15thNight
37%
540
15%
1620
8%
540
43%
540
18%
1125
May16th to endNight
43%
492
16%
1615
11%
492
51%
492
23%
994
June1st to 15thNight
45%
360
16%
1381
14%
360
56%
360
22%
780
June16th to endNight
50%
360
19%
1260
17%
360
60%
360
25%
712
July1st to 15thNight
60%
456
17%
1320
15%
456
64%
456
34%
775
July16th to endNight
57%
564
17%
1595
12%
531
66%
531
34%
912
August1st to 15thNight
65%
539
19%
1609
15%
536
68%
536
33%
934
August16th to endNight
62%
573
25%
1719
17%
573
67%
573
34%
985
September1st to 15thNight
56%
716
22%
1920
15%
716
59%
716
32%
1213
September16th to endNight
55%
717
25%
1980
17%
717
61%
717
33%
1221
October1st to 15thNight
45%
720
18%
2115
17%
720
48%
720
24%
1376
October16th to endNight
26%
768
16%
2337
8%
768
36%
768
16%
1667
November1st to 15thNight
34%
760
19%
2471
16%
760
40%
760
20%
1596
November16th to endNight
20%
780
13%
2711
6%
780
30%
780
12%
1930
December1st to 15thNight
15%
780
8%
2730
3%
780
21%
780
9%
2085
December16th to endNight
13%
865
7%
2928
1%
865
20%
865
7%
2408

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
14%8%36%6%35%5%5%7%33%
50135
Night
15%8%36%5%3445%6%35%
49528
Cloud CoverDay
14%8%36%6%35%5%5%7%33%
50145
Night
15%8%36%5%3445%6%35%
49532
TransparencyDay
48%7%13%19%10%1
49837
Night
48%6%12%20%11%1
49344
SeeingDay
16%13%25%23%14%5%
6358
Night
16%20%23%25%12%1
16038

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
18%13%49%8%45%445%20%
1638
16th to endDay
17%15%6%9%7%35%5%6%5%17%
1872
February1st to 15thDay
17%13%6%9%7%45%5%35%21%
1710
16th to endDay
16%11%48%8%46%5%45%24%
1677
March1st to 15thDay
18%9%6%8%7%345%4427%
2081
16th to endDay
17%9%48%6%3445%6%29%
2288
April1st to 15thDay
20%9%36%435%46%7%28%
2302
16th to endDay
16%8%35%5%24447%37%
2402
May1st to 15thDay
15%8%36%5%3446%7%33%
2331
16th to endDay
11%5%35%5%345%5%8%42%
2497
June1st to 15thDay
9%5%36%5%35%6%6%8%40%
2575
16th to endDay
9%5%25%5%36%5%7%10%38%
2700
July1st to 15thDay
8%425%4245%6%9%45%
2552
16th to endDay
7%425%5%36%5%7%10%40%
2465
August1st to 15thDay
6%426%5%36%6%8%10%39%
2340
16th to endDay
9%5%24435%6%6%9%43%
2474
September1st to 15thDay
11%5%25%435%47%8%40%
2034
16th to endDay
13%5%25%425%5%5%7%43%
1980
October1st to 15thDay
14%5%26%6%3445%6%39%
1843
16th to endDay
20%8%25%5%35%45%5%32%
1884
November1st to 15thDay
15%6%36%5%35%45%7%35%
1717
16th to endDay
17%10%49%6%335%5%7%25%
1576
December1st to 15thDay
19%12%6%7%6%34447%22%
1560
16th to endDay
22%13%7%10%7%2445%6%14%
1637
January1st to 15thNight
21%12%48%6%35%35%6%23%
2622
16th to endNight
15%14%6%9%7%45%445%21%
2704
February1st to 15thNight
16%14%5%8%6%345%46%24%
2480
16th to endNight
18%10%47%6%35%5%5%5%26%
2080
March1st to 15thNight
17%10%37%6%3445%6%30%
2185
16th to endNight
16%7%445%25%45%6%36%
2288
April1st to 15thNight
17%9%46%5%3445%5%33%
1988
16th to endNight
13%5%25%5%25%45%7%40%
1672
May1st to 15thNight
15%5%26%6%347%6%8%32%
1620
16th to endNight
11%5%245%34447%45%
1613
June1st to 15thNight
9%3344345%6%8%45%
1381
16th to endNight
9%41443447%9%45%
1260
July1st to 15thNight
6%324424447%54%
1401
16th to endNight
5%3144245%6%10%50%
1703
August1st to 15thNight
5%3134445%7%8%50%
1620
16th to endNight
8%42442345%7%52%
1719
September1st to 15thNight
10%4345%345%46%48%
1920
16th to endNight
10%5%25%4245%5%7%47%
1980
October1st to 15thNight
15%5%26%433346%43%
2115
16th to endNight
19%6%36%6%35%45%6%33%
2337
November1st to 15thNight
14%6%26%5%3445%7%39%
2471
16th to endNight
21%9%35%5%3445%7%29%
2711
December1st to 15thNight
20%12%5%7%6%24446%24%
2730
16th to endNight
21%12%6%8%7%45%45%5%17%
2928

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%13%5%9%9%45%445%19%
1638
16th to endDay
16%15%6%9%8%35%5%5%5%17%
1872
February1st to 15thDay
17%13%7%9%6%45%446%21%
1710
16th to endDay
16%11%49%8%46%45%5%23%
1677
March1st to 15thDay
18%10%5%8%7%44435%26%
2092
16th to endDay
17%9%48%6%34447%29%
2287
April1st to 15thDay
19%10%36%5%345%5%8%27%
2302
16th to endDay
17%7%35%5%33447%36%
2402
May1st to 15thDay
15%8%36%5%3446%7%33%
2331
16th to endDay
10%5%35%5%345%5%8%41%
2497
June1st to 15thDay
9%6%25%5%345%6%7%40%
2575
16th to endDay
9%5%25%6%35%5%6%10%39%
2700
July1st to 15thDay
8%5%244245%7%9%45%
2552
16th to endDay
7%425%5%45%6%7%10%39%
2465
August1st to 15thDay
7%426%6%35%6%8%11%38%
2340
16th to endDay
10%4245%35%5%7%8%42%
2474
September1st to 15thDay
11%5%25%425%47%8%40%
2034
16th to endDay
13%5%245%25%45%7%43%
1980
October1st to 15thDay
14%6%26%6%35%45%6%38%
1843
16th to endDay
20%9%25%5%345%46%31%
1884
November1st to 15thDay
15%6%35%6%35%5%5%7%35%
1717
16th to endDay
17%10%39%7%35%45%7%24%
1576
December1st to 15thDay
19%12%5%8%6%2445%7%22%
1560
16th to endDay
22%14%7%9%8%345%5%5%14%
1637
January1st to 15thNight
21%12%47%6%34445%23%
2622
16th to endNight
14%15%7%8%7%45%45%5%21%
2704
February1st to 15thNight
16%13%6%9%6%25%45%5%25%
2473
16th to endNight
18%10%47%6%45%5%5%6%26%
2080
March1st to 15thNight
18%9%46%6%34446%29%
2197
16th to endNight
15%8%35%425%45%6%37%
2288
April1st to 15thNight
17%10%35%6%2445%5%33%
1988
16th to endNight
12%6%26%5%34447%41%
1672
May1st to 15thNight
15%5%36%5%446%7%8%32%
1619
16th to endNight
11%5%25%435%446%46%
1613
June1st to 15thNight
9%434435%46%9%44%
1381
16th to endNight
9%5%143345%6%9%46%
1260
July1st to 15thNight
6%224434448%53%
1401
16th to endNight
6%3144245%7%9%50%
1703
August1st to 15thNight
5%2134445%6%9%50%
1620
16th to endNight
8%42442345%8%52%
1719
September1st to 15thNight
10%425%434446%48%
1920
16th to endNight
11%5%2432445%6%49%
1980
October1st to 15thNight
15%5%25%433346%43%
2115
16th to endNight
18%6%36%6%345%5%6%32%
2337
November1st to 15thNight
14%7%26%5%3445%7%39%
2471
16th to endNight
21%8%36%5%34347%29%
2711
December1st to 15thNight
20%12%5%8%5%25%445%25%
2730
16th to endNight
21%12%5%8%7%45%45%5%18%
2928

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
66%5%10%10%5%
1639
16th to endDay
66%6%13%9%3
1872
February1st to 15thDay
64%6%10%13%4
1712
16th to endDay
60%7%10%15%5%
1677
March1st to 15thDay
60%6%10%14%7%
2092
16th to endDay
54%5%11%19%9%
2288
April1st to 15thDay
53%7%11%17%10%
2302
16th to endDay
47%5%12%17%13%2
2402
May1st to 15thDay
48%7%11%21%10%1
2331
16th to endDay
38%8%14%23%13%1
2501
June1st to 15thDay
39%7%13%24%13%1
2575
16th to endDay
37%8%16%20%15%1
2700
July1st to 15thDay
33%7%11%26%18%2
2404
16th to endDay
36%8%15%22%13%2
2310
August1st to 15thDay
35%10%16%24%12%
2327
16th to endDay
35%9%13%26%12%2
2474
September1st to 15thDay
39%7%15%25%11%
2034
16th to endDay
38%6%14%26%13%
1980
October1st to 15thDay
44%5%14%20%13%1
1843
16th to endDay
51%7%15%17%7%
1884
November1st to 15thDay
47%7%14%19%10%1
1717
16th to endDay
57%7%14%14%5%
1576
December1st to 15thDay
60%8%14%12%4
1560
16th to endDay
69%6%11%9%2
1637
January1st to 15thNight
61%5%10%12%7%
2622
16th to endNight
63%5%13%13%4
2704
February1st to 15thNight
60%6%11%15%5%
2482
16th to endNight
57%5%10%18%6%
2080
March1st to 15thNight
54%411%19%8%1
2197
16th to endNight
46%5%11%23%11%1
2288
April1st to 15thNight
51%5%10%19%12%1
1988
16th to endNight
43%49%18%19%4
1672
May1st to 15thNight
46%6%10%20%12%3
1620
16th to endNight
38%6%12%23%16%2
1615
June1st to 15thNight
34%6%12%28%16%1
1381
16th to endNight
33%6%14%24%20%1
1260
July1st to 15thNight
29%6%8%28%22%3
1320
16th to endNight
28%7%15%26%19%3
1595
August1st to 15thNight
27%8%13%32%15%2
1609
16th to endNight
30%6%11%31%18%2
1719
September1st to 15thNight
35%5%13%26%17%2
1920
16th to endNight
34%5%11%31%16%
1980
October1st to 15thNight
41%5%11%20%19%
2115
16th to endNight
50%6%13%20%8%
2337
November1st to 15thNight
44%414%22%11%1
2471
16th to endNight
53%5%14%18%6%
2711
December1st to 15thNight
60%6%13%13%5%
2730
16th to endNight
67%7%10%10%4
2928

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
22%13%42%12%8%
135
16th to endDay
35%10%38%14%
144
February1st to 15thDay
24%17%41%14%1
135
16th to endDay
28%11%45%13%
120
March1st to 15thDay
21%21%29%19%7%
277
16th to endDay
21%16%29%24%5%1
352
April1st to 15thDay
23%17%30%18%8%1
330
16th to endDay
20%16%29%19%9%5%
289
May1st to 15thDay
21%13%30%17%14%2
288
16th to endDay
14%14%25%25%14%5%
331
June1st to 15thDay
12%14%23%32%14%2
370
16th to endDay
11%15%26%28%14%2
495
July1st to 15thDay
10%9%22%29%20%8%
458
16th to endDay
6%12%16%26%26%11%
326
August1st to 15thDay
9%7%13%32%24%12%
313
16th to endDay
10%7%14%25%25%17%
332
September1st to 15thDay
10%7%17%22%29%12%
315
16th to endDay
16%6%13%22%23%16%
314
October1st to 15thDay
18%11%19%25%18%6%
315
16th to endDay
21%16%32%22%6%1
300
November1st to 15thDay
17%13%26%25%12%4
135
16th to endDay
20%19%38%14%7%
94
December1st to 15thDay
20%25%30%16%7%
90
16th to endDay
25%29%33%9%4
100
January1st to 15thNight
21%25%30%16%4
881
16th to endNight
19%25%29%21%4
832
February1st to 15thNight
21%25%29%21%2
764
16th to endNight
20%20%27%25%5%
683
March1st to 15thNight
19%22%26%24%6%
780
16th to endNight
18%20%26%25%8%
832
April1st to 15thNight
20%21%26%26%4
716
16th to endNight
13%20%27%26%9%1
558
May1st to 15thNight
14%20%21%29%14%1
540
16th to endNight
10%19%21%30%16%1
494
June1st to 15thNight
10%18%20%38%13%
360
16th to endNight
11%17%16%35%17%1
360
July1st to 15thNight
7%11%14%36%26%3
456
16th to endNight
7%16%13%33%24%3
564
August1st to 15thNight
6%10%11%36%30%5%
539
16th to endNight
9%9%13%28%35%4
573
September1st to 15thNight
10%12%14%26%28%7%
716
16th to endNight
12%10%14%28%25%8%
717
October1st to 15thNight
16%13%19%28%18%3
720
16th to endNight
19%19%29%23%6%
768
November1st to 15thNight
15%20%23%25%12%1
760
16th to endNight
22%29%22%16%8%
780
December1st to 15thNight
24%26%27%14%6%
780
16th to endNight
22%26%31%16%2
865
Page generated at 2018-04-24 10:03:03. Version ac04

Copyright 2018 A. Danko


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