Brockport State Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Brockport State Observatory clear sky chart from 2005-11-05 to 2018-11-30.

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
27%
16380
13%
51741
7%
16345
33%
16345
15%
37712

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
8%
778
6%
2716
2%
776
13%
776
4%
2307
January16th to endNight
10%
832
7%
2717
2%
832
16%
832
4%
2298
February1st to 15thNight
7%
764
7%
2482
1%
761
14%
761
5%
2059
February16th to endNight
14%
683
8%
2155
3%
683
20%
683
8%
1719
March1st to 15thNight
15%
780
11%
2174
4%
780
22%
780
12%
1734
March16th to endNight
24%
832
16%
2272
7%
832
31%
832
18%
1652
April1st to 15thNight
18%
778
14%
1946
4%
778
24%
778
16%
1489
April16th to endNight
33%
677
18%
1833
7%
677
40%
677
25%
1234
May1st to 15thNight
37%
481
16%
1651
11%
481
45%
481
19%
1091
May16th to endNight
40%
406
16%
1625
14%
406
51%
406
23%
937
June1st to 15thNight
38%
390
14%
1560
13%
390
51%
390
18%
981
June16th to endNight
39%
390
12%
1560
13%
390
48%
390
21%
936
July1st to 15thNight
48%
370
18%
1480
22%
370
54%
370
30%
770
July16th to endNight
55%
472
17%
1605
16%
445
60%
445
30%
901
August1st to 15thNight
54%
575
17%
1715
12%
572
58%
572
32%
1036
August16th to endNight
54%
731
21%
1973
12%
731
58%
731
36%
1207
September1st to 15thNight
48%
780
21%
1950
11%
780
52%
780
31%
1300
September16th to endNight
50%
777
22%
2154
16%
777
53%
777
29%
1385
October1st to 15thNight
33%
780
13%
2340
10%
780
38%
780
18%
1689
October16th to endNight
18%
832
10%
2496
4%
832
25%
832
11%
1950
November1st to 15thNight
25%
820
15%
2757
12%
820
32%
820
14%
1952
November16th to endNight
18%
840
10%
2938
6%
840
24%
840
9%
2258
December1st to 15thNight
9%
780
5%
2730
1%
780
14%
780
5%
2286
December16th to endNight
8%
832
4%
2912
0%
832
12%
832
4%
2541

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
15%9%47%6%3445%6%31%
52568
Night
16%10%47%6%3445%6%30%
51917
Cloud CoverDay
15%9%47%6%3445%6%30%
52578
Night
16%10%47%6%3445%6%30%
51922
TransparencyDay
52%6%11%18%9%
52262
Night
53%6%11%17%9%
51741
SeeingDay
20%16%29%20%9%3
6942
Night
21%16%28%21%9%1
16383

By Month

Percentage Cloud Cover NE (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
15%16%8%12%10%46%45%412%
1552
16th to endDay
12%17%9%14%9%45%435%12%
1859
February1st to 15thDay
16%15%8%13%9%35%5%3414%
1710
16th to endDay
19%14%5%11%10%3445%416%
1604
March1st to 15thDay
15%14%6%12%7%36%33420%
2104
16th to endDay
16%10%47%4335%36%33%
2304
April1st to 15thDay
19%12%5%5%5%24346%30%
2332
16th to endDay
19%8%26%423345%39%
2412
May1st to 15thDay
15%7%26%5%345%5%6%36%
2630
16th to endDay
13%5%25%44445%7%41%
2842
June1st to 15thDay
17%5%345%3445%7%37%
2730
16th to endDay
13%4235%245%7%9%39%
2730
July1st to 15thDay
8%4245%25%5%6%8%46%
2730
16th to endDay
11%425%5%46%6%6%10%36%
2811
August1st to 15thDay
11%5%25%5%35%5%5%8%39%
2487
16th to endDay
12%5%15%5%35%5%5%7%41%
2568
September1st to 15thDay
17%5%245%3446%7%38%
2340
16th to endDay
15%5%2443445%7%40%
2132
October1st to 15thDay
22%7%36%6%24445%31%
1950
16th to endDay
24%11%47%6%44346%22%
2080
November1st to 15thDay
16%12%47%6%335%46%28%
1760
16th to endDay
19%17%49%6%35%35%6%19%
1677
December1st to 15thDay
18%18%8%10%6%23345%16%
1560
16th to endDay
19%20%8%12%6%3444311%
1664
January1st to 15thNight
18%16%7%12%10%45%33414%
2716
16th to endNight
12%16%8%12%11%45%44415%
2717
February1st to 15thNight
15%16%6%12%8%35%445%16%
2480
16th to endNight
14%12%6%12%8%36%45%5%19%
2155
March1st to 15thNight
18%12%5%9%7%3443425%
2162
16th to endNight
16%8%5%7%5%24445%34%
2272
April1st to 15thNight
20%10%37%5%3435%5%30%
1946
16th to endNight
16%7%14435%46%7%39%
1833
May1st to 15thNight
16%5%35%4345%5%7%36%
1651
16th to endNight
11%425%42345%7%46%
1623
June1st to 15thNight
15%4345%245%7%7%38%
1560
16th to endNight
10%5%35%445%46%8%40%
1560
July1st to 15thNight
6%424415%45%8%51%
1560
16th to endNight
9%4133245%6%9%47%
1706
August1st to 15thNight
9%3145%35%45%10%46%
1726
16th to endNight
8%4145%245%6%8%48%
1973
September1st to 15thNight
15%6%25%423447%44%
1950
16th to endNight
15%4144235%6%7%43%
2154
October1st to 15thNight
20%7%36%5%3445%5%33%
2340
16th to endNight
27%11%35%5%33446%24%
2496
November1st to 15thNight
17%10%36%6%25%447%30%
2757
16th to endNight
19%13%48%7%35%446%22%
2938
December1st to 15thNight
19%17%7%10%5%35%445%15%
2730
16th to endNight
19%17%8%11%8%3444412%
2912

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
15%16%7%12%10%37%44313%
1552
16th to endDay
12%17%8%15%9%5%4445%13%
1859
February1st to 15thDay
15%17%7%14%8%35%44314%
1710
16th to endDay
18%14%6%12%9%3445%417%
1604
March1st to 15thDay
16%14%6%12%7%45%33420%
2115
16th to endDay
15%12%47%6%32446%32%
2303
April1st to 15thDay
19%12%46%5%24445%30%
2332
16th to endDay
18%8%25%423445%38%
2412
May1st to 15thDay
14%8%36%5%35%5%5%6%35%
2630
16th to endDay
12%5%35%5%35%46%7%40%
2842
June1st to 15thDay
17%6%35%5%35%45%7%35%
2730
16th to endDay
13%4245%35%5%5%10%38%
2730
July1st to 15thDay
8%425%4346%6%8%44%
2730
16th to endDay
11%436%6%35%6%6%10%34%
2811
August1st to 15thDay
11%6%25%5%35%5%6%8%37%
2487
16th to endDay
12%5%15%5%35%5%6%8%38%
2568
September1st to 15thDay
17%6%25%5%3445%7%37%
2340
16th to endDay
15%5%25%5%3445%8%39%
2132
October1st to 15thDay
22%7%36%6%2345%5%31%
1950
16th to endDay
23%11%48%7%34445%22%
2080
November1st to 15thDay
15%12%47%6%43447%28%
1760
16th to endDay
18%15%5%9%7%35%347%19%
1677
December1st to 15thDay
18%19%7%11%7%23445%16%
1560
16th to endDay
19%19%8%12%7%3344311%
1664
January1st to 15thNight
17%16%6%11%10%45%43414%
2716
16th to endNight
12%16%7%12%10%5%5%43415%
2717
February1st to 15thNight
15%17%7%11%8%35%44417%
2473
16th to endNight
15%12%6%12%9%35%446%19%
2155
March1st to 15thNight
18%12%5%8%7%35%44425%
2174
16th to endNight
16%8%5%7%5%34445%34%
2272
April1st to 15thNight
19%10%46%6%3445%430%
1946
16th to endNight
16%6%2443445%7%39%
1833
May1st to 15thNight
16%5%346%35%45%7%36%
1651
16th to endNight
11%5%25%42345%8%46%
1623
June1st to 15thNight
14%425%5%25%6%7%7%38%
1560
16th to endNight
10%5%25%435%5%7%9%39%
1560
July1st to 15thNight
6%425%5%24448%51%
1560
16th to endNight
9%3234345%6%8%47%
1706
August1st to 15thNight
8%325%435%46%9%45%
1726
16th to endNight
8%4145%245%6%8%48%
1973
September1st to 15thNight
14%5%35%42235%7%44%
1950
16th to endNight
15%415%3245%6%7%43%
2154
October1st to 15thNight
18%8%36%6%24446%33%
2340
16th to endNight
27%10%36%5%3345%6%24%
2496
November1st to 15thNight
17%9%46%5%345%5%6%30%
2757
16th to endNight
19%13%48%6%3445%6%23%
2938
December1st to 15thNight
18%16%7%10%6%35%5%4416%
2730
16th to endNight
20%17%8%12%8%3444412%
2912

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
74%5%7%9%2
1553
16th to endDay
73%6%11%6%1
1859
February1st to 15thDay
72%5%8%10%1
1712
16th to endDay
69%5%8%11%4
1604
March1st to 15thDay
67%49%12%5%
2115
16th to endDay
53%49%20%10%1
2304
April1st to 15thDay
55%5%10%17%10%
2332
16th to endDay
47%47%19%17%2
2412
May1st to 15thDay
45%6%12%22%11%
2630
16th to endDay
40%6%12%24%13%1
2846
June1st to 15thDay
46%5%12%20%13%
2730
16th to endDay
39%7%13%23%14%
2730
July1st to 15thDay
34%7%12%26%19%1
2581
16th to endDay
41%9%15%20%11%
2649
August1st to 15thDay
42%7%16%20%12%
2474
16th to endDay
40%7%13%26%10%1
2568
September1st to 15thDay
44%7%12%23%11%1
2340
16th to endDay
41%6%13%23%13%
2132
October1st to 15thDay
54%5%10%18%10%
1950
16th to endDay
63%5%13%13%3
2080
November1st to 15thDay
56%6%12%15%8%1
1760
16th to endDay
64%6%12%12%3
1677
December1st to 15thDay
70%411%10%2
1560
16th to endDay
76%6%8%6%2
1664
January1st to 15thNight
73%5%8%8%3
2716
16th to endNight
72%5%8%9%3
2717
February1st to 15thNight
69%5%8%12%3
2482
16th to endNight
64%5%10%13%4
2155
March1st to 15thNight
62%5%10%15%6%
2174
16th to endNight
51%5%9%18%13%1
2272
April1st to 15thNight
56%5%8%18%10%
1946
16th to endNight
43%5%11%21%15%3
1833
May1st to 15thNight
45%6%11%19%14%1
1651
16th to endNight
36%7%13%23%17%2
1625
June1st to 15thNight
41%8%11%22%15%
1560
16th to endNight
39%6%12%21%17%2
1560
July1st to 15thNight
30%5%13%26%21%3
1480
16th to endNight
31%7%15%27%15%2
1605
August1st to 15thNight
32%7%17%28%12%
1715
16th to endNight
31%6%13%31%14%1
1973
September1st to 15thNight
38%5%12%26%14%1
1950
16th to endNight
37%7%12%26%16%
2154
October1st to 15thNight
50%7%10%18%12%
2340
16th to endNight
59%6%12%13%5%
2496
November1st to 15thNight
52%6%12%17%9%1
2757
16th to endNight
61%5%13%14%4
2938
December1st to 15thNight
69%7%10%10%2
2730
16th to endNight
75%6%8%7%1
2912

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
15%43%24%12%4
90
16th to endDay
30%30%29%7%1
141
February1st to 15thDay
24%49%20%5%
135
16th to endDay
29%30%30%9%1
185
March1st to 15thDay
22%26%30%15%4
330
16th to endDay
24%20%30%18%41
352
April1st to 15thDay
31%21%27%13%4
330
16th to endDay
23%19%26%18%9%2
319
May1st to 15thDay
23%15%30%17%8%4
348
16th to endDay
14%13%34%24%9%2
395
June1st to 15thDay
21%12%33%24%8%
375
16th to endDay
16%11%35%25%10%1
375
July1st to 15thDay
9%7%27%34%16%5%
365
16th to endDay
11%8%35%28%12%3
390
August1st to 15thDay
13%6%28%29%13%8%
358
16th to endDay
13%6%27%26%17%9%
396
September1st to 15thDay
15%7%22%26%18%9%
375
16th to endDay
16%8%24%21%15%13%
374
October1st to 15thDay
25%13%24%18%11%5%
375
16th to endDay
30%21%30%12%5%
400
November1st to 15thDay
21%20%29%18%8%2
229
16th to endDay
27%28%28%12%2
119
December1st to 15thDay
20%35%20%20%4
90
16th to endDay
34%39%18%7%
96
January1st to 15thNight
26%30%28%12%1
780
16th to endNight
21%30%31%14%3
832
February1st to 15thNight
26%29%31%10%1
764
16th to endNight
23%26%30%17%1
683
March1st to 15thNight
27%20%30%17%3
780
16th to endNight
20%15%34%20%7%1
832
April1st to 15thNight
26%18%31%20%3
778
16th to endNight
20%11%31%27%7%1
677
May1st to 15thNight
19%8%26%29%14%
481
16th to endNight
11%8%33%31%14%
407
June1st to 15thNight
14%8%30%33%12%
390
16th to endNight
11%7%35%35%10%
390
July1st to 15thNight
7%431%32%23%1
370
16th to endNight
10%426%36%18%3
472
August1st to 15thNight
9%227%35%22%3
575
16th to endNight
10%325%31%25%3
731
September1st to 15thNight
17%6%22%27%22%3
780
16th to endNight
16%8%20%24%23%6%
777
October1st to 15thNight
23%12%25%23%13%1
780
16th to endNight
33%16%26%19%3
832
November1st to 15thNight
23%16%28%22%8%1
820
16th to endNight
26%22%26%15%7%
840
December1st to 15thNight
30%24%28%12%3
780
16th to endNight
28%27%28%12%2
832
Page generated at 2018-12-01 11:35:39. Version ac04

Copyright 2018 A. Danko


Brockport State Observatory Clear Sky Chart |Charts Home