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 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
34%
15159
15%
46658
9%
15121
41%
15121
18%
32189

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
12%
809
9%
2419
4%
808
18%
808
9%
1919
January16th to endNight
18%
768
10%
2496
3%
768
26%
768
8%
1965
February1st to 15thNight
17%
702
9%
2287
3%
701
24%
701
9%
1758
February16th to endNight
24%
631
13%
1922
5%
631
33%
631
12%
1442
March1st to 15thNight
24%
720
14%
2028
7%
720
30%
720
15%
1480
March16th to endNight
30%
768
18%
2112
10%
768
36%
768
20%
1470
April1st to 15thNight
28%
661
15%
1835
7%
661
34%
661
20%
1311
April16th to endNight
32%
540
20%
1620
7%
540
42%
540
20%
1056
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
54%
658
23%
1818
16%
658
59%
658
32%
1126
October1st to 15thNight
45%
660
19%
1939
17%
660
49%
660
25%
1250
October16th to endNight
24%
704
14%
2142
6%
704
34%
704
15%
1551
November1st to 15thNight
34%
700
20%
2276
17%
700
40%
700
21%
1451
November16th to endNight
20%
720
12%
2502
6%
720
29%
720
11%
1798
December1st to 15thNight
14%
720
7%
2520
3%
720
20%
720
9%
1953
December16th to endNight
13%
798
7%
2703
1%
798
20%
798
7%
2229

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%7%36%6%35%5%5%7%33%
48047
Night
15%8%36%5%3445%7%35%
46842
Cloud CoverDay
14%8%36%6%35%5%5%7%33%
48057
Night
15%8%36%5%3445%7%35%
46846
TransparencyDay
47%7%13%19%10%1
47749
Night
47%6%12%20%11%1
46658
SeeingDay
15%13%24%24%15%6%
5662
Night
16%20%22%25%12%1
15167

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%410%8%46%445%19%
1511
16th to endDay
16%16%6%10%7%35%6%6%5%16%
1728
February1st to 15thDay
16%13%6%9%7%45%5%35%21%
1575
16th to endDay
14%10%49%9%46%5%46%24%
1549
March1st to 15thDay
19%9%5%8%7%345%45%26%
1920
16th to endDay
17%9%48%7%35%45%6%28%
2112
April1st to 15thDay
19%8%46%435%46%8%29%
2124
16th to endDay
16%8%35%5%24447%36%
2340
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%41%
1815
October1st to 15thDay
13%5%26%6%35%5%5%6%39%
1690
16th to endDay
21%8%35%5%34445%32%
1727
November1st to 15thDay
14%6%36%5%35%46%7%37%
1582
16th to endDay
18%10%410%6%3345%7%23%
1455
December1st to 15thDay
21%12%6%7%6%34447%21%
1440
16th to endDay
21%14%7%10%7%2445%6%14%
1511
January1st to 15thNight
22%12%49%6%35%35%6%21%
2419
16th to endNight
15%15%6%9%7%45%445%21%
2496
February1st to 15thNight
15%14%5%8%6%34446%25%
2285
16th to endNight
17%10%47%7%45%5%5%5%26%
1922
March1st to 15thNight
18%10%36%6%3345%6%30%
2016
16th to endNight
16%8%445%25%45%7%36%
2112
April1st to 15thNight
17%9%36%5%3445%5%35%
1835
16th to endNight
12%5%36%5%35%45%7%39%
1620
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
11%5%15%4245%5%7%47%
1818
October1st to 15thNight
14%5%26%433347%44%
1939
16th to endNight
19%6%36%6%35%45%6%32%
2142
November1st to 15thNight
12%6%26%5%3445%6%39%
2276
16th to endNight
22%9%36%5%3345%7%28%
2502
December1st to 15thNight
21%12%5%7%6%24446%23%
2520
16th to endNight
22%12%5%8%6%45%45%5%17%
2703

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%10%9%35%445%19%
1511
16th to endDay
16%16%6%9%7%35%6%6%5%16%
1728
February1st to 15thDay
15%13%7%9%6%45%5%36%21%
1575
16th to endDay
15%11%49%9%46%45%6%23%
1549
March1st to 15thDay
19%10%49%7%44435%25%
1931
16th to endDay
17%9%48%6%34447%27%
2111
April1st to 15thDay
18%9%36%43445%8%28%
2124
16th to endDay
16%7%35%5%33447%36%
2340
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
14%6%245%25%5%6%7%41%
1815
October1st to 15thDay
13%6%26%6%35%5%6%6%38%
1690
16th to endDay
21%9%25%5%345%46%31%
1727
November1st to 15thDay
14%6%35%5%35%5%5%7%36%
1582
16th to endDay
17%10%410%7%3445%7%23%
1455
December1st to 15thDay
20%12%5%8%6%2445%7%21%
1440
16th to endDay
21%14%7%9%8%345%45%14%
1511
January1st to 15thNight
22%13%47%6%34445%22%
2419
16th to endNight
14%15%7%8%6%45%45%5%21%
2496
February1st to 15thNight
15%12%6%9%6%35%45%5%25%
2278
16th to endNight
17%9%47%7%45%5%5%6%26%
1922
March1st to 15thNight
18%9%46%6%34446%29%
2028
16th to endNight
16%8%45%435%45%6%36%
2112
April1st to 15thNight
18%10%35%5%24445%35%
1835
16th to endNight
12%6%36%5%35%45%7%40%
1620
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
12%5%1432445%6%48%
1818
October1st to 15thNight
14%5%25%433346%44%
1939
16th to endNight
19%7%36%6%345%5%6%31%
2142
November1st to 15thNight
12%7%36%5%3445%7%39%
2276
16th to endNight
22%8%36%5%24347%28%
2502
December1st to 15thNight
21%12%5%8%5%24445%24%
2520
16th to endNight
22%12%5%8%6%45%45%5%17%
2703

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
68%5%10%11%4
1512
16th to endDay
67%7%12%9%4
1728
February1st to 15thDay
64%6%10%13%4
1577
16th to endDay
60%7%10%15%5%
1549
March1st to 15thDay
61%6%10%14%6%
1931
16th to endDay
55%5%11%18%8%
2112
April1st to 15thDay
52%7%11%17%10%
2124
16th to endDay
47%5%13%18%13%2
2340
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
39%6%15%26%12%
1815
October1st to 15thDay
43%5%15%20%12%1
1690
16th to endDay
52%6%16%16%7%
1727
November1st to 15thDay
45%7%15%19%11%1
1582
16th to endDay
59%6%14%14%4
1455
December1st to 15thDay
61%9%15%11%3
1440
16th to endDay
70%6%11%9%2
1511
January1st to 15thNight
63%5%10%12%6%
2419
16th to endNight
63%5%12%13%4
2496
February1st to 15thNight
60%6%11%15%5%
2287
16th to endNight
57%5%11%18%6%
1922
March1st to 15thNight
53%5%11%20%7%1
2028
16th to endNight
46%5%11%23%11%1
2112
April1st to 15thNight
49%411%20%12%1
1835
16th to endNight
43%410%19%18%3
1620
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
35%5%11%32%15%
1818
October1st to 15thNight
40%5%12%20%20%
1939
16th to endNight
51%6%12%20%7%
2142
November1st to 15thNight
43%414%23%12%1
2276
16th to endNight
54%5%14%18%6%
2502
December1st to 15thNight
62%6%13%13%4
2520
16th to endNight
67%7%10%10%3
2703

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
21%16%40%14%6%1
90
16th to endDay
38%12%34%13%1
96
February1st to 15thDay
20%22%41%15%1
90
16th to endDay
20%9%49%18%1
81
March1st to 15thDay
22%23%28%18%7%
221
16th to endDay
20%18%27%24%6%2
288
April1st to 15thDay
21%17%28%20%9%1
270
16th to endDay
20%17%29%17%9%5%
270
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
18%7%12%25%22%12%
254
October1st to 15thDay
14%12%20%27%18%6%
255
16th to endDay
23%17%31%21%5%1
239
November1st to 15thDay
10%12%25%34%13%4
90
16th to endDay
20%25%31%15%6%
63
December1st to 15thDay
23%26%31%11%6%
60
16th to endDay
25%32%32%7%1
67
January1st to 15thNight
21%27%29%16%4
813
16th to endNight
19%26%27%21%4
768
February1st to 15thNight
19%26%28%21%2
704
16th to endNight
19%21%26%26%6%
631
March1st to 15thNight
19%23%26%24%6%
720
16th to endNight
19%20%25%24%8%
768
April1st to 15thNight
20%22%25%26%4
661
16th to endNight
13%21%28%25%9%1
540
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
13%11%14%29%23%7%
658
October1st to 15thNight
15%13%20%28%19%2
660
16th to endNight
20%19%30%23%5%
704
November1st to 15thNight
13%22%24%24%13%2
700
16th to endNight
23%30%21%16%8%
720
December1st to 15thNight
24%27%28%14%5%
720
16th to endNight
22%27%30%16%2
798
Page generated at 2017-09-16 17:06:59. Version ac04

Copyright 2017 A. Danko


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