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 2017-10-31.

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%
15373
28%
47389
26%
15338
71%
15338
40%
25586

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%
720
25%
1800
13%
720
66%
720
43%
1070
May1st to 15thNight
66%
551
29%
1631
21%
551
70%
551
49%
807
May16th to endNight
73%
375
26%
1496
31%
374
75%
374
39%
672
June1st to 15thNight
72%
360
27%
1440
33%
360
78%
360
43%
616
June16th to endNight
86%
360
35%
1440
48%
360
89%
360
64%
493
July1st to 15thNight
95%
340
34%
1360
48%
340
96%
340
75%
417
July16th to endNight
93%
478
40%
1510
43%
448
93%
448
77%
534
August1st to 15thNight
90%
573
38%
1646
31%
570
90%
570
70%
705
August16th to endNight
94%
764
44%
1910
29%
764
94%
764
82%
849
September1st to 15thNight
91%
720
43%
1800
30%
720
92%
720
79%
812
September16th to endNight
82%
716
45%
1941
38%
716
86%
716
68%
892
October1st to 15thNight
73%
720
31%
2160
31%
720
77%
720
51%
1054
October16th to endNight
74%
768
37%
2304
38%
768
78%
768
48%
1172
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%62%
48361
Night
13%312212335%59%
47578
TransparencyDay
25%27%19%24%20%
48041
Night
28%37%18%22%19%
47398
SeeingDay
12%8%25%32%15%4
6020
Night
13%29%31%34%7%
15385

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%58%
2160
May1st to 15thDay
6%312212346%66%
2314
16th to endDay
8%323223446%58%
2615
June1st to 15thDay
7%312212246%63%
2520
16th to endDay
211112383%
2520
July1st to 15thDay
1112286%
2520
16th to endDay
111111286%
2552
August1st to 15thDay
11112286%
2304
16th to endDay
11111288%
2292
September1st to 15thDay
1111123482%
2160
16th to endDay
41211212478%
2016
October1st to 15thDay
7%112112345%67%
1800
16th to endDay
9%313323235%61%
1918
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%
1800
May1st to 15thNight
7%212222346%65%
1631
16th to endNight
7%213323446%60%
1496
June1st to 15thNight
6%312212236%67%
1440
16th to endNight
1112212381%
1440
July1st to 15thNight
1211386%
1440
16th to endNight
11111286%
1614
August1st to 15thNight
21111212379%
1655
16th to endNight
1222384%
1910
September1st to 15thNight
111112384%
1800
16th to endNight
21111222478%
1941
October1st to 15thNight
8%11221223469%
2160
16th to endNight
8%312222245%64%
2304
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%25%24%5%
2160
May1st to 15thDay
19%28%30%29%8%
2314
16th to endDay
25%312%29%22%7%
2619
June1st to 15thDay
22%28%21%23%20%
2520
16th to endDay
8%1215%37%34%
2520
July1st to 15thDay
6%127%28%53%
2371
16th to endDay
8%1210%23%54%
2393
August1st to 15thDay
7%1111%30%47%
2288
16th to endDay
5%1111%37%42%
2292
September1st to 15thDay
7%1213%33%41%
2160
16th to endDay
13%1422%34%23%
2016
October1st to 15thDay
18%36%23%26%22%
1800
16th to endDay
26%36%20%24%18%
1918
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%411%25%22%7%
1800
May1st to 15thNight
20%39%25%27%13%
1632
16th to endNight
22%414%30%20%8%
1496
June1st to 15thNight
19%39%22%23%20%
1440
16th to endNight
10%1414%32%37%
1440
July1st to 15thNight
5%128%27%54%
1360
16th to endNight
7%210%22%57%
1510
August1st to 15thNight
10%1115%25%45%
1646
16th to endNight
6%1112%31%46%
1910
September1st to 15thNight
7%2310%36%40%
1800
16th to endNight
11%2419%35%26%
1941
October1st to 15thNight
20%35%21%25%24%
2160
16th to endNight
22%35%21%27%20%
2304
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%30%21%10%2
270
May1st to 15thDay
9%14%37%25%8%4
288
16th to endDay
10%16%16%33%16%6%
330
June1st to 15thDay
7%13%28%35%10%5%
315
16th to endDay
3432%38%14%7%
315
July1st to 15thDay
120%55%15%7%
305
16th to endDay
126%46%16%8%
327
August1st to 15thDay
2224%45%18%6%
315
16th to endDay
121%44%22%7%
332
September1st to 15thDay
2326%42%20%4
315
16th to endDay
37%30%35%19%3
315
October1st to 15thDay
5%12%29%30%17%4
315
16th to endDay
13%422%32%24%3
336
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%
720
May1st to 15thNight
8%217%34%31%4
552
16th to endNight
8%37%31%42%6%
375
June1st to 15thNight
7%212%28%43%5%
360
16th to endNight
26%32%48%8%
360
July1st to 15thNight
25%63%9%
340
16th to endNight
121%61%14%
478
August1st to 15thNight
2128%55%11%
573
16th to endNight
230%55%10%
764
September1st to 15thNight
1327%55%11%
720
16th to endNight
3110%28%41%14%
716
October1st to 15thNight
8%211%32%36%9%
720
16th to endNight
10%39%26%38%13%
768
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 2017-11-01 14:23:43. Version ac04

Copyright 2017 A. Danko


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