First Colony Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the First Colony 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
54%
15637
25%
47723
19%
15593
60%
15593
31%
28627

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
34%
900
24%
2422
10%
895
45%
895
29%
1563
January16th to endNight
28%
801
25%
2337
11%
801
39%
801
23%
1568
February1st to 15thNight
33%
704
24%
2112
11%
701
45%
701
27%
1323
February16th to endNight
31%
631
25%
1893
12%
631
41%
631
27%
1195
March1st to 15thNight
34%
720
19%
2160
12%
720
41%
720
25%
1386
March16th to endNight
42%
597
25%
1996
19%
597
50%
597
28%
1175
April1st to 15thNight
46%
539
25%
1797
20%
539
55%
539
32%
1006
April16th to endNight
50%
540
26%
1800
23%
540
59%
540
34%
998
May1st to 15thNight
57%
540
21%
1737
17%
540
63%
540
31%
1021
May16th to endNight
70%
561
24%
1682
21%
561
73%
561
37%
974
June1st to 15thNight
77%
540
20%
1561
19%
540
78%
540
37%
938
June16th to endNight
78%
540
24%
1440
20%
540
79%
540
42%
844
July1st to 15thNight
81%
510
19%
1360
17%
510
82%
510
37%
846
July16th to endNight
78%
564
17%
1705
18%
531
79%
531
32%
1033
August1st to 15thNight
82%
539
19%
1788
24%
536
82%
536
34%
1025
August16th to endNight
74%
573
24%
1910
29%
573
75%
573
27%
1176
September1st to 15thNight
68%
558
23%
1818
25%
558
70%
558
30%
1091
September16th to endNight
73%
717
31%
1980
27%
717
74%
717
40%
1152
October1st to 15thNight
68%
720
33%
2006
28%
720
71%
720
43%
1115
October16th to endNight
55%
768
35%
2313
29%
768
62%
768
39%
1269
November1st to 15thNight
53%
760
29%
2471
25%
760
61%
760
34%
1364
November16th to endNight
47%
780
29%
2535
23%
780
57%
780
32%
1427
December1st to 15thNight
41%
728
23%
2365
17%
728
50%
728
27%
1445
December16th to endNight
33%
807
20%
2535
14%
807
41%
807
22%
1693

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%5%25%5%345%5%7%43%
48696
Night
11%42442445%7%48%
47923
TransparencyDay
37%6%11%20%18%4
48399
Night
34%5%10%20%20%7%
47725
SeeingDay
11%415%24%27%17%
5701
Night
13%5%21%30%25%5%
15639

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
19%6%35%422335%42%
1513
16th to endDay
17%6%15%423335%46%
1883
February1st to 15thDay
14%7%36%423346%43%
1750
16th to endDay
17%7%25%423336%43%
1580
March1st to 15thDay
16%6%36%5%2345%6%39%
1800
16th to endDay
12%5%25%6%345%46%43%
2233
April1st to 15thDay
12%41442345%7%47%
2151
16th to endDay
10%4244245%5%7%48%
2160
May1st to 15thDay
13%5%245%345%5%7%41%
2211
16th to endDay
7%425%5%36%5%6%9%42%
2431
June1st to 15thDay
6%4245%45%6%7%11%40%
2394
16th to endDay
5%315%5%36%5%7%10%46%
2520
July1st to 15thDay
8%335%7%47%6%7%10%34%
2520
16th to endDay
6%425%7%47%7%8%9%35%
2339
August1st to 15thDay
6%325%6%47%7%8%11%36%
2160
16th to endDay
11%5%25%5%45%6%7%9%35%
2292
September1st to 15thDay
11%5%25%435%5%7%8%40%
2130
16th to endDay
11%32443445%6%48%
1980
October1st to 15thDay
9%324424446%53%
1951
16th to endDay
10%31431232461%
1911
November1st to 15thDay
9%414423246%56%
1717
16th to endDay
16%413322445%50%
1755
December1st to 15thDay
16%9%35%424345%39%
1632
16th to endDay
21%8%26%423335%38%
1683
January1st to 15thNight
16%5%245%23335%48%
2422
16th to endNight
17%7%35%32443342%
2337
February1st to 15thNight
16%5%24423336%46%
2103
16th to endNight
17%424423345%46%
1893
March1st to 15thNight
16%6%24433446%43%
2160
16th to endNight
13%5%25%323337%49%
1996
April1st to 15thNight
10%42332445%6%52%
1797
16th to endNight
9%41432445%8%52%
1800
May1st to 15thNight
9%5%2443445%8%47%
1736
16th to endNight
5%4134345%7%11%48%
1682
June1st to 15thNight
5%3135%35%5%7%10%48%
1561
16th to endNight
2323425%6%6%12%50%
1440
July1st to 15thNight
4214437%8%7%11%43%
1440
16th to endNight
4315%5%36%7%8%11%43%
1823
August1st to 15thNight
43125%35%7%9%10%47%
1800
16th to endNight
7%325%6%35%5%7%10%43%
1910
September1st to 15thNight
9%42443346%8%46%
1818
16th to endNight
8%42332445%7%53%
1980
October1st to 15thNight
7%313323446%57%
2006
16th to endNight
14%412322225%59%
2313
November1st to 15thNight
11%413423345%55%
2471
16th to endNight
12%5%24323235%53%
2535
December1st to 15thNight
16%6%13423346%46%
2365
16th to endNight
19%7%25%433445%39%
2535

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
44%36%18%22%4
1514
16th to endDay
40%4422%21%6%
1883
February1st to 15thDay
41%38%23%17%4
1752
16th to endDay
44%37%16%23%5%
1580
March1st to 15thDay
44%5%8%18%16%5%
1800
16th to endDay
41%410%22%19%1
2235
April1st to 15thDay
34%5%10%21%19%7%
2151
16th to endDay
33%6%10%23%24%2
2160
May1st to 15thDay
40%6%10%18%20%4
2211
16th to endDay
35%8%15%22%15%1
2435
June1st to 15thDay
34%10%14%23%15%1
2394
16th to endDay
31%8%15%21%18%3
2520
July1st to 15thDay
39%12%17%19%8%3
2371
16th to endDay
39%11%18%20%8%
2194
August1st to 15thDay
36%12%16%19%12%3
2148
16th to endDay
40%11%16%19%8%2
2292
September1st to 15thDay
39%8%13%19%12%5%
2130
16th to endDay
35%5%10%21%18%9%
1980
October1st to 15thDay
31%48%20%23%11%
1951
16th to endDay
28%3417%36%10%
1911
November1st to 15thDay
30%47%20%28%9%
1717
16th to endDay
35%46%18%26%9%
1755
December1st to 15thDay
46%48%19%14%6%
1632
16th to endDay
49%39%18%15%3
1683
January1st to 15thNight
40%36%18%26%4
2422
16th to endNight
46%4416%21%7%
2337
February1st to 15thNight
40%37%19%21%8%
2112
16th to endNight
40%45%19%21%8%
1893
March1st to 15thNight
42%49%17%17%8%
2160
16th to endNight
36%47%23%22%4
1996
April1st to 15thNight
31%49%23%21%9%
1797
16th to endNight
30%5%9%23%23%6%
1800
May1st to 15thNight
34%5%11%19%21%6%
1737
16th to endNight
27%9%15%24%19%4
1684
June1st to 15thNight
28%9%17%22%19%3
1561
16th to endNight
26%7%17%24%21%3
1440
July1st to 15thNight
26%12%18%26%11%4
1360
16th to endNight
30%10%23%22%11%1
1705
August1st to 15thNight
26%11%19%24%14%3
1788
16th to endNight
34%10%16%22%12%4
1910
September1st to 15thNight
34%7%14%22%14%7%
1818
16th to endNight
28%6%9%22%23%9%
1980
October1st to 15thNight
25%5%9%22%22%15%
2006
16th to endNight
30%2414%31%17%
2313
November1st to 15thNight
31%47%18%25%13%
2471
16th to endNight
33%35%18%26%12%
2535
December1st to 15thNight
39%310%21%19%5%
2365
16th to endNight
46%48%17%17%6%
2535

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
20%18%24%24%8%3
90
16th to endDay
19%23%36%14%32
96
February1st to 15thDay
12%21%30%31%5%
90
16th to endDay
19%12%35%25%6%
81
March1st to 15thDay
26%14%36%17%4
90
16th to endDay
17%6%25%31%17%1
231
April1st to 15thDay
13%12%24%24%20%4
270
16th to endDay
12%5%22%30%25%3
270
May1st to 15thDay
17%419%28%22%8%
288
16th to endDay
10%416%30%20%17%
331
June1st to 15thDay
7%8%23%32%26%
369
16th to endDay
5%16%28%33%24%
495
July1st to 15thDay
5%17%25%34%26%
475
16th to endDay
5%413%35%40%
361
August1st to 15thDay
9%5%19%33%30%
313
16th to endDay
13%1417%37%25%
332
September1st to 15thDay
13%8%15%37%23%
315
16th to endDay
8%7%23%39%19%
314
October1st to 15thDay
13%13%30%31%11%
286
16th to endDay
11%429%20%20%13%
144
November1st to 15thDay
14%230%31%19%2
135
16th to endDay
13%11%23%25%17%8%
135
December1st to 15thDay
21%6%37%24%8%2
94
16th to endDay
19%22%25%23%7%1
96
January1st to 15thNight
20%10%31%28%9%
900
16th to endNight
19%10%35%30%3
801
February1st to 15thNight
18%10%32%31%7%
704
16th to endNight
18%10%36%30%4
631
March1st to 15thNight
20%8%31%31%7%
720
16th to endNight
15%6%31%29%16%
597
April1st to 15thNight
10%8%31%32%15%1
539
16th to endNight
9%429%35%18%1
540
May1st to 15thNight
11%222%36%23%3
540
16th to endNight
7%12%34%37%6%
563
June1st to 15thNight
5%6%32%45%8%
540
16th to endNight
37%24%48%14%
540
July1st to 15thNight
3426%50%15%
510
16th to endNight
45%19%48%21%
564
August1st to 15thNight
6%220%50%19%
539
16th to endNight
7%424%47%16%
573
September1st to 15thNight
11%17%27%43%8%
558
16th to endNight
9%8%32%42%5%
717
October1st to 15thNight
9%214%33%35%4
720
16th to endNight
14%5%20%28%27%2
768
November1st to 15thNight
11%5%24%32%22%3
760
16th to endNight
15%7%26%32%17%1
780
December1st to 15thNight
18%7%28%33%10%
728
16th to endNight
24%8%29%29%8%
807
Page generated at 2017-12-03 10:16:37. Version ac04

Copyright 2017 A. Danko


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