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Robert Ferguson Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Robert Ferguson Observatory clear sky chart from 2005-11-05 to 2017-08-12.

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%
15167
26%
46550
22%
15128
68%
15128
37%
25880

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
56%
718
18%
2390
17%
716
61%
716
26%
1465
January16th to endNight
54%
768
25%
2496
23%
768
59%
768
27%
1529
February1st to 15thNight
52%
699
22%
2288
22%
698
57%
698
23%
1462
February16th to endNight
49%
632
22%
1924
17%
632
57%
632
27%
1210
March1st to 15thNight
51%
720
15%
1994
12%
720
54%
720
25%
1363
March16th to endNight
45%
768
21%
2100
14%
768
51%
768
30%
1362
April1st to 15thNight
48%
719
23%
1799
11%
719
53%
719
32%
1160
April16th to endNight
55%
720
26%
1800
12%
720
60%
720
43%
1037
May1st to 15thNight
66%
572
27%
1652
19%
572
70%
572
47%
853
May16th to endNight
71%
390
26%
1513
24%
390
78%
390
39%
694
June1st to 15thNight
71%
360
25%
1440
28%
360
78%
360
40%
635
June16th to endNight
83%
360
34%
1440
44%
360
87%
360
58%
528
July1st to 15thNight
93%
372
32%
1392
40%
372
93%
372
64%
505
July16th to endNight
88%
564
32%
1593
30%
531
89%
531
52%
741
August1st to 15thNight
84%
526
31%
1575
27%
523
85%
523
51%
735
August16th to endNight
87%
691
33%
1741
21%
691
88%
691
59%
904
September1st to 15thNight
88%
660
39%
1650
27%
660
89%
660
69%
802
September16th to endNight
80%
656
38%
1810
34%
656
83%
656
60%
864
October1st to 15thNight
69%
660
30%
1980
29%
660
75%
660
45%
1021
October16th to endNight
69%
704
31%
2112
32%
704
74%
704
40%
1158
November1st to 15thNight
64%
700
27%
2181
23%
700
70%
700
39%
1186
November16th to endNight
59%
720
23%
2472
25%
720
63%
720
30%
1389
December1st to 15thNight
50%
720
19%
2520
17%
720
56%
720
21%
1610
December16th to endNight
48%
768
21%
2688
18%
768
55%
768
23%
1667

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
9%313313336%59%
47428
Night
10%313323346%56%
46736
TransparencyDay
27%49%19%23%14%
47115
Night
29%49%19%22%14%
46551
SeeingDay
11%9%23%32%18%4
5854
Night
11%314%31%32%6%
15176

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
19%6%25%322335%45%
1546
16th to endDay
16%5%25%5%24335%43%
1728
February1st to 15thDay
20%5%25%414345%42%
1576
16th to endDay
20%7%25%423346%39%
1550
March1st to 15thDay
19%6%45%43436%7%34%
1965
16th to endDay
18%5%245%3445%5%41%
2124
April1st to 15thDay
17%5%25%42445%6%40%
2149
16th to endDay
8%422313347%57%
2160
May1st to 15thDay
5%313213347%64%
2295
16th to endDay
5%323322447%59%
2599
June1st to 15thDay
5%423312346%63%
2520
16th to endDay
2111223477%
2520
July1st to 15thDay
1111122481%
2482
16th to endDay
11111135%80%
2468
August1st to 15thDay
111212325%76%
2291
16th to endDay
111112135%78%
2108
September1st to 15thDay
11211226%78%
1980
16th to endDay
421111235%73%
1818
October1st to 15thDay
8%212213336%63%
1650
16th to endDay
10%413212336%59%
1760
November1st to 15thDay
10%2144235%47%53%
1675
16th to endDay
16%42443434448%
1488
December1st to 15thDay
20%8%2432432442%
1440
16th to endDay
23%7%23313245%40%
1536
January1st to 15thNight
16%5%24324448%42%
2390
16th to endNight
19%5%23313436%47%
2496
February1st to 15thNight
17%6%24423446%41%
2276
16th to endNight
16%5%14424347%44%
1924
March1st to 15thNight
16%6%34425%436%41%
1994
16th to endNight
16%6%24422345%47%
2100
April1st to 15thNight
13%424423346%49%
1799
16th to endNight
8%313223346%60%
1800
May1st to 15thNight
4212323347%64%
1652
16th to endNight
322324447%63%
1512
June1st to 15thNight
4213213247%66%
1440
16th to endNight
21211123478%
1440
July1st to 15thNight
111212482%
1474
16th to endNight
11213348%71%
1701
August1st to 15thNight
12223347%70%
1584
16th to endNight
1121335%8%70%
1741
September1st to 15thNight
1212236%77%
1650
16th to endNight
311211236%73%
1810
October1st to 15thNight
5%313313245%63%
1980
16th to endNight
8%212314347%58%
2112
November1st to 15thNight
9%423312449%54%
2181
16th to endNight
12%5%24323236%52%
2472
December1st to 15thNight
21%6%24323346%40%
2520
16th to endNight
21%424323346%43%
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
42%412%16%15%8%
1546
16th to endDay
44%47%12%19%11%
1728
February1st to 15thDay
44%47%18%19%4
1576
16th to endDay
45%6%10%23%10%3
1550
March1st to 15thDay
47%5%11%17%13%4
1965
16th to endDay
42%6%12%18%15%3
2124
April1st to 15thDay
42%6%12%17%17%2
2149
16th to endDay
26%6%14%24%21%6%
2160
May1st to 15thDay
21%49%30%27%7%
2295
16th to endDay
24%6%14%26%20%6%
2603
June1st to 15thDay
23%5%11%23%23%13%
2520
16th to endDay
11%36%17%37%23%
2520
July1st to 15thDay
10%3412%28%39%
2336
16th to endDay
10%46%10%25%41%
2313
August1st to 15thDay
13%45%13%33%29%
2275
16th to endDay
13%35%15%36%25%
2108
September1st to 15thDay
11%35%13%33%31%
1980
16th to endDay
15%36%22%30%20%
1818
October1st to 15thDay
23%48%18%28%15%
1650
16th to endDay
28%48%23%24%10%
1760
November1st to 15thDay
29%6%13%27%13%8%
1675
16th to endDay
39%5%9%18%19%7%
1488
December1st to 15thDay
45%5%7%15%20%4
1440
16th to endDay
46%411%16%14%6%
1536
January1st to 15thNight
39%5%12%18%15%9%
2390
16th to endNight
39%48%14%18%14%
2496
February1st to 15thNight
42%49%17%17%7%
2288
16th to endNight
39%5%12%23%16%3
1924
March1st to 15thNight
44%5%13%15%16%5%
1994
16th to endNight
39%410%20%19%5%
2100
April1st to 15thNight
34%6%14%20%18%5%
1799
16th to endNight
25%411%27%22%8%
1800
May1st to 15thNight
20%6%8%21%30%12%
1653
16th to endNight
20%6%14%29%20%8%
1513
June1st to 15thNight
18%7%11%23%24%15%
1440
16th to endNight
12%25%16%36%25%
1440
July1st to 15thNight
9%3411%28%42%
1392
16th to endNight
15%6%8%11%19%39%
1593
August1st to 15thNight
17%5%8%15%24%29%
1575
16th to endNight
15%5%8%13%29%27%
1741
September1st to 15thNight
11%36%12%32%33%
1650
16th to endNight
16%25%20%32%22%
1810
October1st to 15thNight
22%48%19%25%18%
1980
16th to endNight
25%6%8%22%23%14%
2112
November1st to 15thNight
27%5%14%28%15%8%
2181
16th to endNight
34%39%21%21%9%
2472
December1st to 15thNight
44%49%16%19%6%
2520
16th to endNight
42%410%15%19%7%
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
31%6%23%25%11%1
174
16th to endDay
19%12%23%25%17%3
256
February1st to 15thDay
24%6%24%25%17%1
236
16th to endDay
21%15%23%21%16%1
233
March1st to 15thDay
26%14%23%17%14%3
270
16th to endDay
20%15%30%21%9%2
288
April1st to 15thDay
20%19%28%21%7%2
269
16th to endDay
12%23%28%24%9%2
270
May1st to 15thDay
9%15%34%27%11%1
288
16th to endDay
7%11%23%31%19%5%
330
June1st to 15thDay
7%13%29%34%11%3
315
16th to endDay
2226%41%21%5%
315
July1st to 15thDay
1215%47%25%6%
305
16th to endDay
16%50%21%9%
327
August1st to 15thDay
1418%47%24%4
300
16th to endDay
1125%43%22%5%
268
September1st to 15thDay
1219%45%22%9%
255
16th to endDay
6%6%18%33%25%10%
255
October1st to 15thDay
9%9%24%31%17%7%
255
16th to endDay
16%7%23%29%20%1
272
November1st to 15thDay
11%6%17%24%33%7%
181
16th to endDay
17%10%23%25%22%1
68
December1st to 15thDay
36%15%21%15%11%
60
16th to endDay
20%9%21%25%18%4
64
January1st to 15thNight
18%212%34%25%6%
720
16th to endNight
20%315%29%23%7%
768
February1st to 15thNight
19%5%13%32%25%4
704
16th to endNight
19%5%18%31%20%4
632
March1st to 15thNight
17%417%28%26%4
720
16th to endNight
18%423%28%22%2
768
April1st to 15thNight
14%7%21%32%20%3
719
16th to endNight
9%8%21%29%25%5%
720
May1st to 15thNight
5%220%33%34%4
573
16th to endNight
4317%37%31%5%
391
June1st to 15thNight
4315%39%34%1
360
16th to endNight
39%43%41%2
360
July1st to 15thNight
1328%59%6%
372
16th to endNight
2429%52%10%
564
August1st to 15thNight
26%30%51%8%
526
16th to endNight
15%33%51%7%
691
September1st to 15thNight
16%30%50%10%
660
16th to endNight
419%30%41%12%
656
October1st to 15thNight
7%313%32%33%9%
660
16th to endNight
10%111%30%32%12%
704
November1st to 15thNight
10%216%28%33%8%
700
16th to endNight
14%5%12%31%26%8%
720
December1st to 15thNight
23%413%30%20%7%
720
16th to endNight
23%5%16%33%18%2
768
Page generated at 2017-08-13 11:16:58. Version ac04

Copyright 2017 A. Danko


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