Rolling Hills Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rolling Hills Observatory clear sky chart from 2005-11-05 to 2017-12-02.

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
60%
16249
21%
47835
17%
16207
64%
16207
31%
29729

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
46%
719
21%
2327
16%
716
54%
716
25%
1433
January16th to endNight
44%
768
24%
2451
19%
768
53%
768
28%
1481
February1st to 15thNight
45%
701
25%
2103
16%
698
55%
698
33%
1248
February16th to endNight
44%
631
25%
1831
14%
631
54%
631
33%
1088
March1st to 15thNight
50%
720
30%
1980
18%
720
61%
720
42%
1105
March16th to endNight
57%
768
27%
2112
20%
768
62%
768
42%
1187
April1st to 15thNight
59%
718
24%
1976
17%
718
64%
718
43%
1118
April16th to endNight
60%
720
27%
1840
18%
720
65%
720
44%
1072
May1st to 15thNight
69%
569
26%
1649
19%
569
74%
569
42%
918
May16th to endNight
73%
561
23%
1682
18%
561
75%
561
36%
994
June1st to 15thNight
67%
540
12%
1620
11%
540
67%
540
24%
1115
June16th to endNight
69%
540
8%
1620
8%
540
69%
540
23%
1143
July1st to 15thNight
71%
510
6%
1530
6%
510
71%
510
20%
1144
July16th to endNight
73%
564
7%
1595
7%
531
75%
531
21%
1147
August1st to 15thNight
78%
539
7%
1609
6%
536
78%
536
24%
1108
August16th to endNight
66%
720
9%
2040
9%
720
66%
720
21%
1447
September1st to 15thNight
66%
720
9%
1980
8%
720
66%
720
20%
1443
September16th to endNight
61%
717
14%
1980
13%
717
62%
717
21%
1428
October1st to 15thNight
66%
720
25%
2049
26%
720
68%
720
32%
1273
October16th to endNight
62%
768
29%
2304
28%
768
67%
768
34%
1355
November1st to 15thNight
63%
760
29%
2281
26%
760
71%
760
41%
1259
November16th to endNight
54%
780
30%
2415
24%
780
64%
780
34%
1393
December1st to 15thNight
54%
728
27%
2365
24%
728
60%
728
30%
1377
December16th to endNight
53%
768
24%
2496
23%
768
59%
768
30%
1453

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
8%5%36%6%46%6%6%8%37%
48595
Night
7%5%25%5%35%5%6%9%44%
48044
TransparencyDay
42%7%14%17%13%5%
48296
Night
35%7%15%20%14%6%
47847
SeeingDay
9%211%21%26%28%
6087
Night
9%316%33%28%8%
16256

By Month

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
12%6%25%5%2445%9%41%
1611
16th to endDay
11%5%35%42345%8%45%
1770
February1st to 15thDay
11%6%35%5%245%5%6%44%
1750
16th to endDay
9%425%5%26%446%48%
1640
March1st to 15thDay
6%3235%25%45%8%51%
1980
16th to endDay
8%425%5%3446%6%49%
2111
April1st to 15thDay
6%3145%36%6%5%8%48%
1972
16th to endDay
5%325%5%35%5%6%9%47%
2118
May1st to 15thDay
5%314435%5%6%8%49%
2310
16th to endDay
7%425%6%47%7%8%9%37%
2431
June1st to 15thDay
11%5%47%8%5%7%7%7%9%26%
2340
16th to endDay
8%5%38%9%5%9%7%8%10%24%
2340
July1st to 15thDay
9%6%37%9%6%8%8%8%8%22%
2340
16th to endDay
8%6%5%9%9%5%9%7%7%8%21%
2465
August1st to 15thDay
5%6%37%9%6%9%8%8%11%22%
2340
16th to endDay
10%6%48%9%5%8%7%8%7%22%
2147
September1st to 15thDay
8%6%38%10%6%8%8%6%9%23%
1980
16th to endDay
11%7%28%9%6%7%6%7%9%22%
1980
October1st to 15thDay
8%5%36%8%46%6%6%7%36%
1911
16th to endDay
9%425%435%5%5%8%45%
1920
November1st to 15thDay
5%414435%5%5%7%52%
1907
16th to endDay
8%425%5%35%45%7%45%
1872
December1st to 15thDay
9%6%37%5%2446%8%42%
1632
16th to endDay
7%5%25%5%35%5%5%8%44%
1728
January1st to 15thNight
10%6%35%5%25%5%48%42%
2327
16th to endNight
12%5%2442445%8%44%
2451
February1st to 15thNight
11%6%2442435%5%51%
2103
16th to endNight
8%5%34424448%49%
1831
March1st to 15thNight
5%31442435%7%55%
1980
16th to endNight
5%42432345%7%55%
2112
April1st to 15thNight
6%32341345%9%55%
1976
16th to endNight
6%424324447%56%
1840
May1st to 15thNight
42244345%49%55%
1649
16th to endNight
5%3245%345%7%9%48%
1682
June1st to 15thNight
10%5%247%45%7%8%10%32%
1620
16th to endNight
5%7%37%7%35%6%8%12%31%
1620
July1st to 15thNight
6%6%36%6%47%7%8%13%29%
1620
16th to endNight
5%437%7%48%7%7%11%29%
1703
August1st to 15thNight
3427%7%47%6%8%11%35%
1620
16th to endNight
8%5%36%6%46%6%8%11%32%
2040
September1st to 15thNight
8%5%26%7%46%6%7%11%32%
1980
16th to endNight
9%6%47%8%46%5%6%10%29%
1980
October1st to 15thNight
7%5%25%6%35%5%6%7%44%
2049
16th to endNight
9%4245%24347%50%
2304
November1st to 15thNight
5%41443445%6%54%
2281
16th to endNight
8%424435%5%48%49%
2415
December1st to 15thNight
9%5%24435%35%8%46%
2365
16th to endNight
8%5%25%4245%6%9%44%
2496

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
40%49%20%18%7%
1612
16th to endDay
37%48%17%22%10%
1770
February1st to 15thDay
38%5%7%14%20%14%
1752
16th to endDay
37%39%16%22%10%
1640
March1st to 15thDay
31%410%25%20%8%
1980
16th to endDay
34%411%20%20%9%
2112
April1st to 15thDay
32%5%10%21%21%8%
1972
16th to endDay
32%5%10%21%21%8%
2118
May1st to 15thDay
32%5%12%22%19%8%
2310
16th to endDay
41%5%15%19%14%2
2435
June1st to 15thDay
51%8%16%19%4
2340
16th to endDay
51%10%22%13%2
2340
July1st to 15thDay
54%11%21%10%
2201
16th to endDay
55%11%19%10%1
2310
August1st to 15thDay
50%12%27%9%
2327
16th to endDay
56%11%20%10%1
2147
September1st to 15thDay
55%11%18%10%3
1980
16th to endDay
54%8%16%13%5%2
1980
October1st to 15thDay
44%7%8%17%13%8%
1911
16th to endDay
35%5%7%16%22%12%
1920
November1st to 15thDay
29%49%25%21%9%
1907
16th to endDay
37%48%20%17%10%
1872
December1st to 15thDay
39%411%21%17%5%
1632
16th to endDay
36%413%21%16%8%
1728
January1st to 15thNight
40%410%22%15%7%
2327
16th to endNight
37%49%18%20%9%
2451
February1st to 15thNight
35%38%17%20%14%
2112
16th to endNight
33%5%13%18%22%7%
1831
March1st to 15thNight
27%312%27%21%7%
1980
16th to endNight
27%412%25%20%8%
2112
April1st to 15thNight
26%5%15%24%20%7%
1976
16th to endNight
27%413%25%21%7%
1840
May1st to 15thNight
25%5%15%25%18%8%
1650
16th to endNight
29%7%17%25%17%1
1684
June1st to 15thNight
42%8%21%21%4
1620
16th to endNight
42%11%24%16%4
1620
July1st to 15thNight
43%16%26%12%2
1530
16th to endNight
41%14%28%13%1
1595
August1st to 15thNight
36%15%34%12%
1609
16th to endNight
42%13%27%15%1
2040
September1st to 15thNight
42%15%22%15%3
1980
16th to endNight
47%8%19%17%42
1980
October1st to 15thNight
35%6%12%22%17%6%
2049
16th to endNight
33%48%16%25%10%
2304
November1st to 15thNight
28%311%24%23%8%
2281
16th to endNight
33%48%22%20%11%
2415
December1st to 15thNight
35%411%26%14%6%
2365
16th to endNight
34%5%14%23%14%8%
2496

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
18%333%24%15%4
90
16th to endDay
15%13%31%18%15%5%
96
February1st to 15thDay
6%13%31%16%22%10%
90
16th to endDay
10%7%34%29%17%
141
March1st to 15thDay
7%6%24%37%21%2
270
16th to endDay
9%5%22%27%29%5%
288
April1st to 15thDay
5%5%22%28%27%10%
270
16th to endDay
7%212%28%34%14%
270
May1st to 15thDay
5%110%26%33%22%
288
16th to endDay
6%2419%32%34%
331
June1st to 15thDay
17%2213%24%40%
315
16th to endDay
7%19%21%58%
315
July1st to 15thDay
5%420%67%
305
16th to endDay
10%1210%20%53%
326
August1st to 15thDay
8%1211%19%56%
313
16th to endDay
14%29%20%52%
332
September1st to 15thDay
11%1410%26%44%
315
16th to endDay
13%1114%29%40%
314
October1st to 15thDay
11%38%24%36%14%
315
16th to endDay
10%319%30%27%8%
336
November1st to 15thDay
6%13%36%33%9%
325
16th to endDay
9%118%39%25%5%
252
December1st to 15thDay
10%229%40%15%1
94
16th to endDay
5%410%41%30%8%
96
January1st to 15thNight
13%5%24%37%17%1
720
16th to endNight
14%7%26%36%13%
768
February1st to 15thNight
12%5%30%37%13%1
704
16th to endNight
12%6%31%40%9%
631
March1st to 15thNight
7%5%30%40%14%1
720
16th to endNight
7%325%44%17%1
768
April1st to 15thNight
7%423%43%19%1
718
16th to endNight
7%322%44%20%1
720
May1st to 15thNight
5%114%47%27%3
570
16th to endNight
6%17%36%38%8%
563
June1st to 15thNight
11%1425%42%14%
540
16th to endNight
7%2214%44%28%
540
July1st to 15thNight
9%18%47%32%
510
16th to endNight
4119%51%31%
564
August1st to 15thNight
21110%52%31%
539
16th to endNight
10%1415%42%26%
720
September1st to 15thNight
11%1321%40%20%
720
16th to endNight
11%3424%44%11%
717
October1st to 15thNight
10%110%34%36%6%
720
16th to endNight
10%214%37%30%3
768
November1st to 15thNight
6%219%41%27%3
760
16th to endNight
9%323%42%18%1
780
December1st to 15thNight
9%423%38%22%1
728
16th to endNight
10%5%21%37%21%2
768
Page generated at 2017-12-03 11:16:43. Version ac04

Copyright 2017 A. Danko


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