Rock Hill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rock Hill Observatory clear sky chart from 2005-11-05 to 2017-04-30.

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
67%
14808
28%
45652
25%
14773
70%
14773
39%
24892

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
62%
717
20%
2486
22%
716
64%
716
29%
1449
January16th to endNight
55%
768
25%
2496
23%
768
61%
768
27%
1536
February1st to 15thNight
55%
696
23%
2264
21%
696
61%
696
26%
1427
February16th to endNight
52%
632
25%
1895
22%
632
58%
632
27%
1208
March1st to 15thNight
51%
720
15%
2069
14%
720
54%
720
24%
1414
March16th to endNight
52%
768
20%
2051
14%
768
57%
768
29%
1364
April1st to 15thNight
55%
719
19%
1799
11%
719
57%
719
30%
1235
April16th to endNight
63%
716
24%
1790
13%
716
66%
716
43%
1066
May1st to 15thNight
65%
505
30%
1495
22%
505
70%
505
48%
748
May16th to endNight
72%
343
22%
1368
27%
342
74%
342
37%
627
June1st to 15thNight
72%
330
28%
1320
34%
330
79%
330
44%
563
June16th to endNight
84%
330
33%
1320
45%
330
88%
330
63%
457
July1st to 15thNight
95%
310
36%
1240
51%
310
96%
310
74%
384
July16th to endNight
92%
441
38%
1389
40%
411
92%
411
76%
493
August1st to 15thNight
91%
525
40%
1508
33%
522
91%
522
72%
638
August16th to endNight
93%
700
43%
1750
28%
700
94%
700
82%
778
September1st to 15thNight
91%
660
45%
1650
32%
660
93%
660
81%
738
September16th to endNight
84%
656
43%
1779
38%
656
87%
656
68%
818
October1st to 15thNight
72%
660
31%
1980
32%
660
76%
660
48%
994
October16th to endNight
72%
704
35%
2112
35%
704
76%
704
47%
1095
November1st to 15thNight
68%
700
27%
2261
28%
700
72%
700
38%
1222
November16th to endNight
61%
720
24%
2422
25%
720
65%
720
32%
1356
December1st to 15thNight
54%
720
21%
2520
20%
720
59%
720
25%
1527
December16th to endNight
44%
768
22%
2688
19%
768
51%
768
20%
1755

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
11%312212235%61%
46076
Night
13%312212335%58%
45841
TransparencyDay
26%27%18%24%19%
45756
Night
29%37%18%22%18%
45661
SeeingDay
13%9%26%32%13%4
5289
Night
14%29%31%34%7%
14820

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
20%423313336%47%
1450
16th to endDay
23%6%23213335%44%
1728
February1st to 15thDay
22%5%14313335%45%
1592
16th to endDay
24%7%23312346%40%
1579
March1st to 15thDay
23%5%24423347%38%
1890
16th to endDay
21%5%24323348%40%
2172
April1st to 15thDay
20%5%2332345%6%42%
2149
16th to endDay
13%313213346%57%
2150
May1st to 15thDay
6%312212345%65%
2120
16th to endDay
8%324323447%57%
2391
June1st to 15thDay
7%312212246%64%
2310
16th to endDay
2111112382%
2310
July1st to 15thDay
11112285%
2310
16th to endDay
1111121285%
2365
August1st to 15thDay
11112187%
2112
16th to endDay
11112287%
2100
September1st to 15thDay
111113383%
1980
16th to endDay
4121112479%
1848
October1st to 15thDay
8%112112345%66%
1650
16th to endDay
10%31332324460%
1760
November1st to 15thDay
11%314323347%52%
1598
16th to endDay
18%32332433449%
1536
December1st to 15thDay
21%423423436%42%
1440
16th to endDay
25%6%24423235%39%
1536
January1st to 15thNight
18%412313348%46%
2486
16th to endNight
21%5%1432233447%
2496
February1st to 15thNight
21%5%1333345%5%42%
2260
16th to endNight
23%423213445%44%
1895
March1st to 15thNight
23%6%235%23447%38%
2069
16th to endNight
20%5%23323445%45%
2051
April1st to 15thNight
16%5%35%424346%42%
1799
16th to endNight
12%223212346%58%
1790
May1st to 15thNight
7%212222335%64%
1495
16th to endNight
7%11332345%7%59%
1368
June1st to 15thNight
5%312212236%67%
1320
16th to endNight
1112222380%
1320
July1st to 15thNight
1211386%
1320
16th to endNight
111111386%
1493
August1st to 15thNight
21111212380%
1517
16th to endNight
1222385%
1750
September1st to 15thNight
11112385%
1650
16th to endNight
21111223478%
1779
October1st to 15thNight
9%112212335%66%
1980
16th to endNight
9%313223246%62%
2112
November1st to 15thNight
12%313213346%56%
2261
16th to endNight
14%313423345%52%
2422
December1st to 15thNight
24%413313345%44%
2520
16th to endNight
27%5%24313345%40%
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
39%39%20%18%8%
1450
16th to endDay
43%36%15%16%13%
1728
February1st to 15thDay
41%39%19%20%6%
1592
16th to endDay
45%38%27%12%2
1579
March1st to 15thDay
46%311%16%15%6%
1890
16th to endDay
43%413%17%15%4
2172
April1st to 15thDay
42%412%22%14%3
2149
16th to endDay
27%313%24%24%5%
2150
May1st to 15thDay
20%37%29%29%9%
2120
16th to endDay
26%313%28%20%7%
2395
June1st to 15thDay
21%29%21%22%22%
2310
16th to endDay
9%1215%38%32%
2310
July1st to 15thDay
7%128%29%50%
2161
16th to endDay
9%1210%24%51%
2206
August1st to 15thDay
6%1110%29%50%
2096
16th to endDay
5%1111%38%42%
2100
September1st to 15thDay
7%1110%34%43%
1980
16th to endDay
12%1422%34%25%
1848
October1st to 15thDay
19%36%25%27%17%
1650
16th to endDay
27%36%21%24%15%
1760
November1st to 15thDay
30%411%22%20%9%
1598
16th to endDay
38%37%20%22%6%
1536
December1st to 15thDay
44%37%18%22%3
1440
16th to endDay
47%38%14%18%7%
1536
January1st to 15thNight
36%410%19%17%11%
2486
16th to endNight
40%37%13%18%16%
2496
February1st to 15thNight
42%37%18%18%9%
2272
16th to endNight
41%47%24%16%4
1895
March1st to 15thNight
46%410%16%15%6%
2069
16th to endNight
41%5%9%20%16%6%
2051
April1st to 15thNight
43%412%19%14%6%
1799
16th to endNight
28%412%25%22%7%
1790
May1st to 15thNight
21%49%24%26%14%
1496
16th to endNight
23%414%29%19%8%
1368
June1st to 15thNight
19%410%21%22%21%
1320
16th to endNight
10%1414%34%35%
1320
July1st to 15thNight
6%129%29%50%
1240
16th to endNight
7%210%23%54%
1389
August1st to 15thNight
10%1115%24%46%
1508
16th to endNight
6%1111%33%45%
1750
September1st to 15thNight
6%228%38%41%
1650
16th to endNight
11%2419%34%27%
1779
October1st to 15thNight
21%35%23%26%19%
1980
16th to endNight
23%35%22%27%17%
2112
November1st to 15thNight
28%411%23%19%11%
2261
16th to endNight
33%37%22%21%10%
2422
December1st to 15thNight
41%39%17%19%8%
2520
16th to endNight
48%36%14%18%9%
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
43%7%17%17%11%1
78
16th to endDay
28%5%22%26%12%4
256
February1st to 15thDay
25%8%25%26%11%2
239
16th to endDay
30%13%23%21%11%
238
March1st to 15thDay
31%13%20%21%10%3
270
16th to endDay
23%15%30%19%10%1
288
April1st to 15thDay
27%17%26%19%7%1
269
16th to endDay
18%17%29%21%9%2
267
May1st to 15thDay
11%15%37%24%7%3
228
16th to endDay
9%17%16%34%13%6%
266
June1st to 15thDay
5%13%31%35%9%4
255
16th to endDay
45%38%37%9%6%
255
July1st to 15thDay
223%53%14%5%
245
16th to endDay
1127%49%13%7%
271
August1st to 15thDay
2128%46%14%5%
255
16th to endDay
225%47%17%5%
268
September1st to 15thDay
2325%43%20%4
255
16th to endDay
27%29%35%20%3
255
October1st to 15thDay
7%11%29%30%17%4
255
16th to endDay
15%5%25%33%19%
272
November1st to 15thDay
10%6%14%28%29%9%
104
16th to endDay
15%7%23%32%15%3
76
December1st to 15thDay
31%335%16%11%1
60
16th to endDay
26%6%14%21%21%9%
64
January1st to 15thNight
20%28%34%27%6%
720
16th to endNight
23%211%32%24%6%
768
February1st to 15thNight
22%210%35%25%3
704
16th to endNight
24%5%12%31%22%4
632
March1st to 15thNight
24%311%31%25%4
720
16th to endNight
22%413%29%25%4
768
April1st to 15thNight
17%5%12%37%23%3
719
16th to endNight
12%5%12%33%27%8%
716
May1st to 15thNight
8%217%34%32%4
506
16th to endNight
8%36%32%42%5%
343
June1st to 15thNight
6%213%30%43%4
330
16th to endNight
27%34%46%7%
330
July1st to 15thNight
26%62%9%
310
16th to endNight
121%62%13%
441
August1st to 15thNight
2129%54%11%
525
16th to endNight
231%55%9%
700
September1st to 15thNight
1327%54%12%
660
16th to endNight
318%29%40%15%
656
October1st to 15thNight
9%111%30%37%10%
660
16th to endNight
10%39%27%37%11%
704
November1st to 15thNight
13%29%33%30%11%
700
16th to endNight
15%311%35%25%8%
720
December1st to 15thNight
24%310%33%22%5%
720
16th to endNight
28%214%30%20%2
768
Page generated at 2017-04-30 17:39:59. Version ac04

Copyright 2017 A. Danko


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