Red Hill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Red Hill Observatory clear sky chart from 2005-11-05 to 2017-10-06.

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
55%
15326
21%
47099
17%
15292
60%
15292
31%
28197

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%
716
11%
2506
9%
716
45%
716
17%
1746
January16th to endNight
47%
768
14%
2586
12%
768
51%
768
21%
1709
February1st to 15thNight
45%
698
10%
2277
10%
696
48%
696
19%
1588
February16th to endNight
42%
632
14%
1895
10%
632
49%
632
24%
1267
March1st to 15thNight
51%
720
14%
2075
11%
720
55%
720
27%
1342
March16th to endNight
44%
768
17%
2112
11%
768
49%
768
28%
1386
April1st to 15thNight
46%
677
18%
1807
9%
677
51%
677
29%
1194
April16th to endNight
49%
540
25%
1620
16%
540
55%
540
34%
949
May1st to 15thNight
54%
539
20%
1619
14%
539
59%
539
35%
940
May16th to endNight
60%
550
17%
1673
16%
550
63%
550
33%
993
June1st to 15thNight
57%
360
20%
1317
20%
360
66%
360
31%
696
June16th to endNight
71%
360
30%
1340
36%
360
81%
360
54%
533
July1st to 15thNight
83%
340
23%
1360
33%
340
87%
340
46%
566
July16th to endNight
81%
465
32%
1498
36%
436
84%
436
58%
620
August1st to 15thNight
77%
539
30%
1611
24%
536
80%
536
52%
770
August16th to endNight
75%
586
40%
1732
30%
586
78%
586
57%
814
September1st to 15thNight
75%
720
31%
1929
22%
720
79%
720
58%
970
September16th to endNight
71%
716
37%
1980
31%
716
75%
716
50%
1046
October1st to 15thNight
60%
684
28%
1955
21%
684
65%
684
43%
1076
October16th to endNight
62%
704
26%
2205
23%
704
68%
704
35%
1248
November1st to 15thNight
53%
700
23%
2275
21%
700
59%
700
31%
1330
November16th to endNight
52%
780
17%
2400
13%
780
57%
780
27%
1497
December1st to 15thNight
40%
900
9%
2543
6%
900
43%
900
20%
1838
December16th to endNight
37%
864
10%
2784
8%
864
41%
864
14%
2079

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
6%5%2442445%7%51%
48088
Night
7%6%25%42445%7%48%
47280
TransparencyDay
31%6%12%22%18%9%
47767
Night
34%6%13%21%15%8%
47101
SeeingDay
9%7%22%27%22%9%
5571
Night
10%5%21%38%21%2
15339

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
10%10%5%7%6%34448%34%
1432
16th to endDay
12%11%445%35%5%5%6%35%
1636
February1st to 15thDay
8%10%46%425%47%9%35%
1585
16th to endDay
6%10%48%5%26%45%8%37%
1579
March1st to 15thDay
6%8%36%6%45%5%6%9%37%
1884
16th to endDay
10%7%47%5%35%5%6%8%35%
2112
April1st to 15thDay
8%6%25%5%3446%9%42%
2139
16th to endDay
7%6%344235%5%8%48%
2340
May1st to 15thDay
6%41343446%7%52%
2331
16th to endDay
7%6%26%5%246%5%8%43%
2437
June1st to 15thDay
7%423425%5%6%8%51%
2637
16th to endDay
221122336%73%
2613
July1st to 15thDay
22232245%7%66%
2520
16th to endDay
32131435%6%67%
2564
August1st to 15thDay
321231336%6%64%
2340
16th to endDay
1212213236%71%
2468
September1st to 15thDay
321122235%6%68%
2031
16th to endDay
6%312212345%65%
1980
October1st to 15thDay
8%5%2442335%6%52%
1801
16th to endDay
6%425%4245%5%7%51%
1665
November1st to 15thDay
9%7%26%5%24346%47%
1584
16th to endDay
8%9%36%5%345%49%39%
1546
December1st to 15thDay
11%10%38%6%46%5%46%32%
1415
16th to endDay
13%11%5%9%8%35%5%47%25%
1449
January1st to 15thNight
9%11%48%5%3446%8%33%
2506
16th to endNight
10%10%37%433446%40%
2586
February1st to 15thNight
9%9%47%6%45%45%7%35%
2266
16th to endNight
6%8%36%6%36%46%8%37%
1895
March1st to 15thNight
6%6%35%5%45%5%6%8%41%
2075
16th to endNight
10%7%34425%5%6%6%41%
2112
April1st to 15thNight
6%9%35%435%5%5%7%43%
1807
16th to endNight
7%5%3442445%5%51%
1620
May1st to 15thNight
6%5%245%2445%6%51%
1619
16th to endNight
7%5%24435%45%7%47%
1673
June1st to 15thNight
6%225%4245%5%7%52%
1317
16th to endNight
222212335%73%
1340
July1st to 15thNight
11123145%5%8%63%
1440
16th to endNight
211222235%6%69%
1601
August1st to 15thNight
221232445%9%60%
1620
16th to endNight
2213312347%67%
1732
September1st to 15thNight
2212312346%68%
1929
16th to endNight
6%312314335%65%
1980
October1st to 15thNight
7%424223345%59%
1955
16th to endNight
6%414435%5%5%8%51%
2205
November1st to 15thNight
9%5%2432345%8%48%
2275
16th to endNight
6%6%35%5%35%5%5%8%43%
2400
December1st to 15thNight
11%9%47%6%345%6%7%31%
2543
16th to endNight
15%12%49%5%34447%27%
2784

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
48%11%19%16%31
1432
16th to endDay
47%9%19%16%5%1
1636
February1st to 15thDay
43%10%20%20%4
1585
16th to endDay
44%8%17%23%5%1
1579
March1st to 15thDay
41%8%18%24%6%1
1884
16th to endDay
43%8%16%20%9%
2112
April1st to 15thDay
37%5%16%23%15%1
2139
16th to endDay
32%412%28%20%1
2340
May1st to 15thDay
28%6%8%30%22%3
2331
16th to endDay
36%6%12%26%15%2
2440
June1st to 15thDay
29%5%10%26%20%5%
2637
16th to endDay
13%25%19%36%21%
2613
July1st to 15thDay
15%3416%33%26%
2371
16th to endDay
16%3311%23%41%
2404
August1st to 15thDay
17%36%15%25%31%
2325
16th to endDay
14%3420%33%23%
2468
September1st to 15thDay
16%48%18%32%19%
2031
16th to endDay
20%37%29%29%8%
1980
October1st to 15thDay
31%414%29%16%3
1801
16th to endDay
30%6%14%28%18%
1665
November1st to 15thDay
37%6%14%27%11%1
1584
16th to endDay
41%7%21%21%7%
1546
December1st to 15thDay
51%11%19%15%3
1415
16th to endDay
56%8%17%13%3
1449
January1st to 15thNight
46%10%18%19%31
2506
16th to endNight
44%6%19%22%5%1
2586
February1st to 15thNight
46%8%18%20%5%
2277
16th to endNight
40%9%20%23%5%
1895
March1st to 15thNight
37%8%19%24%9%1
2075
16th to endNight
38%7%14%27%10%1
2112
April1st to 15thNight
39%6%13%23%14%2
1807
16th to endNight
33%49%27%24%1
1620
May1st to 15thNight
30%5%9%24%24%4
1620
16th to endNight
33%5%11%27%17%4
1674
June1st to 15thNight
28%6%9%22%25%7%
1317
16th to endNight
13%3413%33%30%
1340
July1st to 15thNight
17%4413%28%31%
1360
16th to endNight
14%239%22%47%
1498
August1st to 15thNight
18%35%16%20%34%
1611
16th to endNight
16%3415%28%32%
1732
September1st to 15thNight
17%36%13%32%26%
1929
16th to endNight
21%4326%29%13%
1980
October1st to 15thNight
27%311%28%22%7%
1955
16th to endNight
28%6%11%29%20%2
2205
November1st to 15thNight
33%5%16%25%16%2
2275
16th to endNight
36%7%19%25%9%1
2400
December1st to 15thNight
48%8%22%16%4
2543
16th to endNight
55%7%16%16%3
2784

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
10%8%31%26%11%11%
60
16th to endDay
27%319%25%20%2
81
February1st to 15thDay
17%428%26%18%7%
100
16th to endDay
15%13%29%26%12%2
238
March1st to 15thDay
11%14%31%27%13%1
270
16th to endDay
13%16%35%24%9%
288
April1st to 15thDay
9%15%33%16%16%7%
269
16th to endDay
10%15%30%24%15%3
270
May1st to 15thDay
6%11%26%31%17%6%
288
16th to endDay
10%9%19%24%20%15%
330
June1st to 15thDay
10%7%22%26%25%7%
432
16th to endDay
3423%30%26%11%
408
July1st to 15thDay
2215%34%33%11%
305
16th to endDay
2414%37%30%11%
327
August1st to 15thDay
5%317%33%30%9%
315
16th to endDay
2312%24%34%22%
332
September1st to 15thDay
35%17%25%28%20%
315
16th to endDay
8%416%26%29%15%
315
October1st to 15thDay
13%320%30%23%8%
203
16th to endDay
14%425%32%17%6%
96
November1st to 15thDay
14%13%34%36%1
90
16th to endDay
20%7%32%28%11%
90
December1st to 15thDay
28%330%29%8%
85
16th to endDay
21%7%18%29%15%6%
64
January1st to 15thNight
13%6%24%37%15%2
720
16th to endNight
16%5%18%36%21%1
768
February1st to 15thNight
13%424%40%17%
704
16th to endNight
11%6%30%36%13%2
632
March1st to 15thNight
9%5%25%41%16%1
720
16th to endNight
13%7%28%36%11%
768
April1st to 15thNight
10%10%24%34%17%2
677
16th to endNight
9%6%28%37%16%1
540
May1st to 15thNight
7%6%25%36%23%1
540
16th to endNight
9%5%19%33%26%5%
552
June1st to 15thNight
7%6%21%40%22%1
360
16th to endNight
4318%43%26%3
360
July1st to 15thNight
217%55%30%2
340
16th to endNight
29%46%37%3
465
August1st to 15thNight
3113%48%31%2
539
16th to endNight
3113%46%30%3
586
September1st to 15thNight
4114%37%33%8%
720
16th to endNight
8%312%33%34%8%
716
October1st to 15thNight
9%319%37%26%3
684
16th to endNight
8%5%17%41%24%3
704
November1st to 15thNight
11%5%21%38%20%2
700
16th to endNight
9%6%24%38%18%2
780
December1st to 15thNight
13%7%25%38%13%1
900
16th to endNight
19%8%21%36%12%1
864
Page generated at 2017-10-07 12:07:51. Version ac04

Copyright 2017 A. Danko


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