Collyer
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Collyer clear sky chart from 2005-11-05 to 2017-09-21.

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
46%
15919
27%
46803
16%
15874
56%
15874
40%
25661

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
41%
900
28%
2506
15%
895
52%
895
40%
1398
January16th to endNight
41%
960
33%
2524
15%
960
53%
960
45%
1383
February1st to 15thNight
33%
736
21%
2148
9%
733
43%
733
30%
1314
February16th to endNight
34%
632
31%
1894
11%
632
50%
632
37%
1020
March1st to 15thNight
41%
672
26%
2112
15%
672
52%
672
37%
1140
March16th to endNight
35%
576
22%
2112
14%
576
47%
576
28%
1138
April1st to 15thNight
29%
539
23%
1800
13%
539
43%
539
29%
1015
April16th to endNight
34%
540
23%
1671
14%
540
48%
540
30%
993
May1st to 15thNight
41%
540
20%
1620
15%
540
50%
540
31%
964
May16th to endNight
39%
562
19%
1685
10%
561
49%
561
33%
981
June1st to 15thNight
44%
540
20%
1514
8%
540
53%
540
44%
816
June16th to endNight
55%
540
26%
1440
13%
540
61%
540
52%
773
July1st to 15thNight
62%
510
19%
1360
12%
510
66%
510
44%
789
July16th to endNight
68%
564
24%
1550
22%
531
71%
531
46%
826
August1st to 15thNight
66%
539
21%
1610
22%
536
69%
536
39%
908
August16th to endNight
66%
573
26%
1876
26%
573
73%
573
42%
976
September1st to 15thNight
55%
540
25%
1902
20%
540
67%
540
38%
972
September16th to endNight
54%
510
34%
1881
29%
510
65%
510
43%
854
October1st to 15thNight
47%
500
33%
1820
27%
500
58%
500
34%
930
October16th to endNight
49%
811
32%
2219
16%
811
57%
811
51%
1153
November1st to 15thNight
53%
875
35%
2275
16%
875
63%
875
55%
1156
November16th to endNight
48%
900
34%
2340
16%
900
58%
900
48%
1271
December1st to 15thNight
41%
900
26%
2340
12%
900
50%
900
40%
1364
December16th to endNight
43%
960
30%
2604
15%
960
52%
960
37%
1527

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
7%42442345%7%54%
48062
Night
7%42432345%7%55%
46987
Cloud CoverDay
7%42432345%7%54%
48060
Night
7%42432335%7%55%
46987
TransparencyDay
28%312%28%20%5%
47749
Night
27%312%26%22%6%
46803
SeeingDay
9%6%26%35%18%3
5898
Night
9%7%32%38%11%
15924

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
45%15%412347%59%
1432
16th to endDay
5%5%25%324347%56%
1697
February1st to 15thDay
5%5%46%5%3435%7%48%
1725
16th to endDay
5%5%24323446%55%
1580
March1st to 15thDay
6%42332445%7%55%
1848
16th to endDay
10%7%23324447%48%
2112
April1st to 15thDay
10%5%2432345%6%51%
2146
16th to endDay
14%6%245%24447%44%
2289
May1st to 15thDay
10%42442445%9%48%
2331
16th to endDay
9%41442445%8%49%
2430
June1st to 15thDay
5%42342345%8%57%
2442
16th to endDay
221232436%9%61%
2520
July1st to 15thDay
4314425%45%9%54%
2520
16th to endDay
5%21342445%9%55%
2509
August1st to 15thDay
8%5%144345%6%8%47%
2340
16th to endDay
5%32342346%8%54%
2324
September1st to 15thDay
9%5%1441345%6%53%
2057
16th to endDay
5%423314337%61%
1871
October1st to 15thDay
13%32313346%56%
1799
16th to endDay
7%5%12212236%63%
1650
November1st to 15thDay
421332235%6%63%
1583
16th to endDay
6%324313235%63%
1620
December1st to 15thDay
6%7%35%423346%52%
1620
16th to endDay
6%5%26%5%33435%51%
1617
January1st to 15thNight
5%5%24423345%58%
2506
16th to endNight
4424214346%60%
2524
February1st to 15thNight
7%6%36%5%34446%47%
2138
16th to endNight
4425%31445%7%55%
1894
March1st to 15thNight
6%5%2432345%7%53%
2112
16th to endNight
9%6%14322348%51%
2112
April1st to 15thNight
11%5%25%32345%8%49%
1800
16th to endNight
13%5%24324347%47%
1671
May1st to 15thNight
9%5%343245%5%7%48%
1619
16th to endNight
10%313335%5%5%9%48%
1683
June1st to 15thNight
431332447%11%52%
1514
16th to endNight
421322336%10%58%
1440
July1st to 15thNight
3424325%5%7%9%50%
1440
16th to endNight
5%31333448%10%52%
1657
August1st to 15thNight
5%3134345%7%10%49%
1620
16th to endNight
332432446%9%57%
1876
September1st to 15thNight
7%21332346%8%54%
1902
16th to endNight
6%213213446%63%
1881
October1st to 15thNight
10%5%13213235%59%
1820
16th to endNight
8%41221114466%
2219
November1st to 15thNight
5%211212346%67%
2275
16th to endNight
5%312323235%64%
2340
December1st to 15thNight
7%424423348%54%
2340
16th to endNight
8%6%24323347%52%
2604

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
4425%312347%59%
1432
16th to endDay
45%34314347%56%
1697
February1st to 15thDay
5%6%45%5%3435%7%48%
1725
16th to endDay
5%5%24424446%56%
1580
March1st to 15thDay
6%4233235%5%7%55%
1848
16th to endDay
10%7%23324447%48%
2110
April1st to 15thDay
10%42432345%6%51%
2146
16th to endDay
14%6%24424446%44%
2289
May1st to 15thDay
10%32432445%8%48%
2331
16th to endDay
9%4144245%5%8%49%
2430
June1st to 15thDay
5%41332345%8%57%
2442
16th to endDay
321232445%8%62%
2520
July1st to 15thDay
43144245%5%10%53%
2520
16th to endDay
5%3135%2445%9%55%
2509
August1st to 15thDay
8%4244345%6%9%47%
2340
16th to endDay
5%31442346%7%55%
2324
September1st to 15thDay
8%5%2432345%7%53%
2057
16th to endDay
5%413313347%61%
1871
October1st to 15thDay
13%42322336%56%
1799
16th to endDay
7%5%1223236%64%
1650
November1st to 15thDay
4323313346%62%
1583
16th to endDay
6%32332333463%
1620
December1st to 15thDay
6%7%35%423246%52%
1620
16th to endDay
7%5%26%5%34446%51%
1617
January1st to 15thNight
5%424423335%58%
2506
16th to endNight
4424214346%60%
2524
February1st to 15thNight
7%6%46%5%24446%47%
2138
16th to endNight
443441445%7%55%
1894
March1st to 15thNight
6%5%2431345%7%53%
2112
16th to endNight
9%6%23323347%51%
2112
April1st to 15thNight
11%414414448%49%
1800
16th to endNight
13%5%24323447%47%
1671
May1st to 15thNight
9%5%243245%5%6%48%
1619
16th to endNight
10%31433446%9%48%
1683
June1st to 15thNight
421332447%11%53%
1514
16th to endNight
421222336%10%59%
1440
July1st to 15thNight
3424325%5%6%10%51%
1440
16th to endNight
5%31432448%10%52%
1657
August1st to 15thNight
5%3144245%6%10%49%
1620
16th to endNight
231432445%9%57%
1876
September1st to 15thNight
7%21232446%8%54%
1902
16th to endNight
5%313213446%63%
1881
October1st to 15thNight
10%5%13212335%59%
1820
16th to endNight
8%312211235%66%
2219
November1st to 15thNight
4211212346%67%
2275
16th to endNight
5%313323235%64%
2340
December1st to 15thNight
7%424423347%55%
2340
16th to endNight
8%5%24323347%53%
2604

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
25%313%33%20%3
1433
16th to endDay
27%312%34%16%4
1697
February1st to 15thDay
35%316%28%11%4
1726
16th to endDay
28%214%25%21%7%
1580
March1st to 15thDay
27%311%29%20%7%
1848
16th to endDay
35%414%24%16%3
2112
April1st to 15thDay
33%413%25%19%4
2146
16th to endDay
39%311%26%16%2
2289
May1st to 15thDay
32%412%31%16%2
2331
16th to endDay
31%7%15%26%15%3
2434
June1st to 15thDay
24%417%28%18%6%
2442
16th to endDay
19%311%31%25%8%
2520
July1st to 15thDay
26%311%29%23%5%
2371
16th to endDay
24%314%31%20%4
2353
August1st to 15thDay
31%5%17%26%14%4
2326
16th to endDay
26%410%28%22%6%
2324
September1st to 15thDay
30%311%25%20%9%
2057
16th to endDay
23%39%33%26%4
1871
October1st to 15thDay
30%39%27%23%6%
1799
16th to endDay
23%18%29%29%7%
1650
November1st to 15thDay
21%210%27%29%9%
1583
16th to endDay
25%19%28%28%7%
1620
December1st to 15thDay
34%214%30%17%1
1620
16th to endDay
34%311%30%17%2
1617
January1st to 15thNight
28%211%29%24%3
2506
16th to endNight
25%211%30%25%4
2524
February1st to 15thNight
38%314%24%14%4
2148
16th to endNight
26%311%28%20%8%
1894
March1st to 15thNight
29%29%24%23%10%
2112
16th to endNight
32%413%25%18%5%
2112
April1st to 15thNight
32%410%27%20%4
1800
16th to endNight
35%415%24%18%2
1671
May1st to 15thNight
33%5%13%22%20%4
1620
16th to endNight
30%6%19%23%15%4
1685
June1st to 15thNight
23%5%20%29%17%4
1514
16th to endNight
19%5%12%27%27%7%
1440
July1st to 15thNight
25%6%14%26%20%6%
1360
16th to endNight
23%5%16%29%19%6%
1550
August1st to 15thNight
28%5%19%28%12%5%
1610
16th to endNight
23%6%13%27%23%6%
1876
September1st to 15thNight
26%5%12%26%20%9%
1902
16th to endNight
22%28%27%31%7%
1881
October1st to 15thNight
28%39%22%26%9%
1820
16th to endNight
22%19%26%29%10%
2219
November1st to 15thNight
18%19%25%31%13%
2275
16th to endNight
23%28%27%26%11%
2340
December1st to 15thNight
29%314%33%17%2
2340
16th to endNight
32%214%25%21%3
2604

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%7%35%35%10%1
90
16th to endDay
14%9%43%22%8%1
96
February1st to 15thDay
8%6%38%34%10%1
90
16th to endDay
317%45%16%16%1
81
March1st to 15thDay
6%12%34%40%6%
90
16th to endDay
14%8%37%22%16%
96
April1st to 15thDay
11%20%39%23%5%
265
16th to endDay
20%13%33%22%8%
399
May1st to 15thDay
12%9%29%31%15%2
468
16th to endDay
15%9%31%31%10%2
517
June1st to 15thDay
6%5%27%39%15%4
495
16th to endDay
3329%40%21%1
495
July1st to 15thDay
5%221%40%24%5%
475
16th to endDay
5%111%43%32%4
515
August1st to 15thDay
10%212%39%31%3
493
16th to endDay
6%123%40%21%5%
364
September1st to 15thDay
6%5%24%38%21%4
212
16th to endDay
9%422%35%22%4
105
October1st to 15thDay
10%232%34%15%5%
90
16th to endDay
7%129%37%21%3
96
November1st to 15thDay
6%421%46%14%6%
90
16th to endDay
24%7%31%21%13%2
90
December1st to 15thDay
14%11%37%23%11%2
90
16th to endDay
13%14%36%28%7%
96
January1st to 15thNight
7%7%36%38%8%1
900
16th to endNight
7%8%38%37%7%
960
February1st to 15thNight
10%7%39%33%7%
740
16th to endNight
7%13%40%31%6%
632
March1st to 15thNight
9%11%34%36%7%
672
16th to endNight
13%11%35%32%6%
576
April1st to 15thNight
14%11%42%28%3
539
16th to endNight
15%13%33%29%7%
540
May1st to 15thNight
12%6%32%37%9%
540
16th to endNight
12%10%34%30%10%
563
June1st to 15thNight
6%6%41%32%12%1
540
16th to endNight
4333%46%11%
540
July1st to 15thNight
6%123%49%18%
510
16th to endNight
6%116%47%26%1
564
August1st to 15thNight
7%15%51%23%
539
16th to endNight
4120%46%23%1
573
September1st to 15thNight
8%229%41%16%1
540
16th to endNight
7%429%40%16%1
510
October1st to 15thNight
14%7%28%35%14%
500
16th to endNight
10%5%31%36%15%
811
November1st to 15thNight
7%8%29%42%11%
875
16th to endNight
8%8%33%38%10%1
900
December1st to 15thNight
11%9%34%38%7%
900
16th to endNight
11%8%32%38%9%
960
Page generated at 2017-09-22 06:35:29. Version ac04

Copyright 2017 A. Danko


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