Stony Ridge Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stony Ridge Observatory clear sky chart from 2005-11-05 to 2017-09-21.

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
64%
15859
35%
46836
26%
15809
73%
15809
52%
22537

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
42%
720
29%
2485
19%
716
59%
716
36%
1217
January16th to endNight
42%
768
33%
2335
19%
768
59%
768
36%
1261
February1st to 15thNight
50%
700
33%
2105
23%
698
64%
698
42%
1096
February16th to endNight
46%
632
28%
1895
22%
632
57%
632
32%
1108
March1st to 15thNight
54%
720
28%
2160
21%
720
66%
720
43%
1103
March16th to endNight
56%
768
31%
2009
20%
768
64%
768
45%
1109
April1st to 15thNight
53%
719
30%
1799
14%
719
61%
719
48%
1002
April16th to endNight
57%
720
33%
1800
14%
720
65%
720
57%
914
May1st to 15thNight
63%
608
32%
1688
20%
608
68%
608
55%
828
May16th to endNight
67%
561
34%
1685
24%
561
73%
561
61%
724
June1st to 15thNight
80%
472
34%
1552
30%
472
84%
472
69%
595
June16th to endNight
92%
360
42%
1440
50%
360
94%
360
79%
429
July1st to 15thNight
91%
340
35%
1360
43%
340
91%
340
67%
449
July16th to endNight
88%
618
34%
1640
27%
578
89%
578
64%
749
August1st to 15thNight
92%
717
37%
1790
25%
713
92%
713
81%
806
August16th to endNight
92%
764
45%
1910
31%
764
92%
764
81%
859
September1st to 15thNight
91%
720
41%
1833
33%
720
92%
720
78%
829
September16th to endNight
83%
680
46%
1881
40%
680
88%
680
76%
800
October1st to 15thNight
67%
660
38%
1823
32%
660
74%
660
53%
921
October16th to endNight
68%
704
42%
2144
36%
704
79%
704
53%
984
November1st to 15thNight
62%
700
36%
2275
29%
700
76%
700
53%
1007
November16th to endNight
57%
720
36%
2340
30%
720
69%
720
44%
1129
December1st to 15thNight
50%
720
32%
2340
23%
720
64%
720
34%
1258
December16th to endNight
38%
768
31%
2547
18%
768
56%
768
30%
1360

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
4312212335%68%
48002
Night
4312212335%68%
47035
TransparencyDay
18%36%15%28%27%
47694
Night
18%36%14%26%30%
46844
SeeingDay
6%15%39%29%6%3
5930
Night
5%6%18%31%30%6%
15866

By Month

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
7%5%13313246%60%
1450
16th to endDay
12%6%13312345%54%
1884
February1st to 15thDay
7%5%2331335%6%58%
1751
16th to endDay
12%8%35%213335%50%
1579
March1st to 15thDay
6%4133235%5%8%55%
1800
16th to endDay
6%32442436%8%53%
2211
April1st to 15thDay
7%423312437%59%
2149
16th to endDay
4212112346%68%
2160
May1st to 15thDay
3311212446%67%
2262
16th to endDay
3312212236%70%
2429
June1st to 15thDay
2211112235%74%
2403
16th to endDay
1112287%
2520
July1st to 15thDay
21221223376%
2520
16th to endDay
2111212345%73%
2408
August1st to 15thDay
1111121384%
2160
16th to endDay
122123480%
2292
September1st to 15thDay
111123481%
2127
16th to endDay
111232381%
1871
October1st to 15thDay
6%212213235%68%
1804
16th to endDay
221231232472%
1727
November1st to 15thDay
4313323225%66%
1584
16th to endDay
5%5%13323345%61%
1620
December1st to 15thDay
7%424245%6%8%51%
1620
16th to endDay
12%5%23313446%53%
1671
January1st to 15thNight
7%413322446%58%
2485
16th to endNight
9%5%14312346%55%
2335
February1st to 15thNight
6%5%24413346%58%
2101
16th to endNight
11%6%23433445%50%
1895
March1st to 15thNight
45%1322345%8%57%
2160
16th to endNight
332342446%6%57%
2009
April1st to 15thNight
7%213212327%63%
1799
16th to endNight
232212335%71%
1800
May1st to 15thNight
2212213345%69%
1688
16th to endNight
112212226%75%
1684
June1st to 15thNight
11112226%79%
1552
16th to endNight
1111290%
1440
July1st to 15thNight
111221121479%
1440
16th to endNight
312213245%72%
1754
August1st to 15thNight
111123384%
1800
16th to endNight
2111112284%
1910
September1st to 15thNight
1111113382%
1833
16th to endNight
111122284%
1881
October1st to 15thNight
431321222370%
1823
16th to endNight
231221212474%
2144
November1st to 15thNight
331221324470%
2275
16th to endNight
4413323346%62%
2340
December1st to 15thNight
7%5%14423337%55%
2340
16th to endNight
8%6%24323337%54%
2547

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
25%27%13%25%25%
1450
16th to endDay
31%37%13%21%23%
1884
February1st to 15thDay
25%36%16%25%23%
1751
16th to endDay
35%35%16%27%11%
1579
March1st to 15thDay
25%410%20%21%18%
1800
16th to endDay
25%6%10%22%21%13%
2211
April1st to 15thDay
25%5%8%25%24%10%
2149
16th to endDay
18%39%20%31%15%
2160
May1st to 15thDay
18%410%18%31%17%
2262
16th to endDay
17%38%25%34%11%
2432
June1st to 15thDay
13%27%13%34%28%
2403
16th to endDay
6%136%29%52%
2520
July1st to 15thDay
11%247%25%48%
2371
16th to endDay
13%35%19%30%28%
2260
August1st to 15thDay
6%1310%33%44%
2146
16th to endDay
8%2311%37%36%
2292
September1st to 15thDay
8%25%10%32%40%
2127
16th to endDay
9%1311%34%38%
1871
October1st to 15thDay
20%2416%27%28%
1804
16th to endDay
17%3312%25%37%
1727
November1st to 15thDay
20%3414%29%26%
1584
16th to endDay
23%26%13%24%29%
1620
December1st to 15thDay
26%5%9%16%21%20%
1620
16th to endDay
30%5%7%17%20%18%
1671
January1st to 15thNight
24%36%14%24%26%
2485
16th to endNight
28%28%12%20%27%
2335
February1st to 15thNight
24%36%14%26%24%
2112
16th to endNight
33%5%5%14%25%16%
1895
March1st to 15thNight
22%410%18%23%21%
2160
16th to endNight
22%5%7%22%25%15%
2009
April1st to 15thNight
23%28%24%24%16%
1799
16th to endNight
15%38%22%30%19%
1800
May1st to 15thNight
16%38%20%30%19%
1689
16th to endNight
11%39%23%35%16%
1685
June1st to 15thNight
8%27%15%30%34%
1552
16th to endNight
4146%24%58%
1440
July1st to 15thNight
9%147%19%57%
1360
16th to endNight
12%36%16%26%34%
1640
August1st to 15thNight
6%147%29%50%
1790
16th to endNight
7%139%34%44%
1910
September1st to 15thNight
7%25%7%29%47%
1833
16th to endNight
8%1211%32%43%
1881
October1st to 15thNight
18%4314%31%29%
1823
16th to endNight
16%3211%25%41%
2144
November1st to 15thNight
17%25%13%30%31%
2275
16th to endNight
21%35%15%22%31%
2340
December1st to 15thNight
28%47%14%22%23%
2340
16th to endNight
28%48%14%24%19%
2547

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%24%35%16%1
78
16th to endDay
17%21%37%20%2
282
February1st to 15thDay
12%21%36%24%41
266
16th to endDay
20%23%33%18%3
238
March1st to 15thDay
9%25%33%21%9%
270
16th to endDay
8%22%40%22%5%1
288
April1st to 15thDay
11%24%40%16%41
269
16th to endDay
436%37%17%21
270
May1st to 15thDay
9%21%40%22%33
288
16th to endDay
7%15%43%25%5%2
330
June1st to 15thDay
214%43%30%6%3
315
16th to endDay
16%43%36%6%6%
315
July1st to 15thDay
1236%43%8%7%
305
16th to endDay
2129%50%7%8%
327
August1st to 15thDay
2342%37%7%6%
315
16th to endDay
139%41%10%6%
332
September1st to 15thDay
25%46%35%8%1
315
16th to endDay
28%42%36%8%1
276
October1st to 15thDay
5%18%43%27%31
255
16th to endDay
213%44%27%10%1
239
November1st to 15thDay
215%18%35%23%4
90
16th to endDay
6%22%37%27%41
90
December1st to 15thDay
121%31%32%14%
90
16th to endDay
14%24%35%18%6%
87
January1st to 15thNight
8%10%32%31%13%2
720
16th to endNight
12%9%27%32%15%2
768
February1st to 15thNight
8%8%26%36%17%2
704
16th to endNight
14%9%26%27%18%3
632
March1st to 15thNight
5%10%25%35%19%3
720
16th to endNight
5%9%22%33%25%3
768
April1st to 15thNight
7%8%24%34%21%3
719
16th to endNight
210%27%30%22%6%
720
May1st to 15thNight
46%22%35%26%4
609
16th to endNight
26%20%34%31%4
563
June1st to 15thNight
214%39%40%3
472
16th to endNight
5%37%50%7%
360
July1st to 15thNight
215%67%12%
340
16th to endNight
2224%56%12%
618
August1st to 15thNight
1228%54%12%
717
16th to endNight
2221%55%18%
764
September1st to 15thNight
1328%49%16%
720
16th to endNight
111%27%46%12%
680
October1st to 15thNight
5%5%16%34%32%5%
660
16th to endNight
46%16%32%29%10%
704
November1st to 15thNight
45%23%35%23%6%
700
16th to endNight
5%7%24%34%19%7%
720
December1st to 15thNight
9%9%22%39%18%
720
16th to endNight
11%15%30%31%9%1
768
Page generated at 2017-09-22 04:35:36. Version ac04

Copyright 2017 A. Danko


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