Black River Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Black River Observatory 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
36%
15435
14%
46838
9%
15397
42%
15397
20%
32527

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
15%
897
9%
2506
2%
895
22%
895
12%
1995
January16th to endNight
19%
820
10%
2548
4%
820
26%
820
12%
1980
February1st to 15thNight
17%
701
10%
2287
2%
701
26%
701
10%
1763
February16th to endNight
24%
631
13%
1903
5%
631
32%
631
13%
1436
March1st to 15thNight
26%
720
14%
2055
8%
720
31%
720
16%
1518
March16th to endNight
37%
768
17%
2112
11%
768
42%
768
23%
1467
April1st to 15thNight
28%
621
15%
1813
7%
621
35%
621
21%
1265
April16th to endNight
38%
540
20%
1620
9%
540
47%
540
25%
1056
May1st to 15thNight
42%
540
14%
1620
10%
540
47%
540
23%
1112
May16th to endNight
49%
510
16%
1633
13%
510
56%
510
28%
998
June1st to 15thNight
52%
360
16%
1284
16%
360
59%
360
26%
774
June16th to endNight
60%
360
17%
1260
18%
360
66%
360
30%
729
July1st to 15thNight
67%
471
17%
1321
17%
471
69%
471
40%
764
July16th to endNight
66%
564
16%
1525
13%
531
68%
531
36%
906
August1st to 15thNight
66%
539
17%
1609
14%
536
67%
536
34%
947
August16th to endNight
63%
573
23%
1719
17%
573
68%
573
35%
1010
September1st to 15thNight
54%
690
22%
1921
14%
690
59%
690
32%
1200
September16th to endNight
58%
681
21%
1881
16%
681
62%
681
32%
1195
October1st to 15thNight
46%
660
19%
1922
14%
660
51%
660
28%
1257
October16th to endNight
24%
704
12%
2181
6%
704
32%
704
15%
1600
November1st to 15thNight
32%
700
17%
2276
14%
700
38%
700
20%
1529
November16th to endNight
26%
720
12%
2484
8%
720
32%
720
13%
1802
December1st to 15thNight
14%
720
7%
2520
2%
720
21%
720
10%
1918
December16th to endNight
14%
945
7%
2838
2%
945
20%
945
10%
2306

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
13%8%36%6%345%5%7%33%
48008
Night
15%8%36%5%3445%7%35%
47019
Cloud CoverDay
13%8%36%6%35%5%5%7%33%
48018
Night
15%8%36%5%3445%7%35%
47023
TransparencyDay
48%7%13%19%10%1
47707
Night
48%6%12%21%10%1
46838
SeeingDay
15%7%26%26%16%7%
5808
Night
18%8%29%29%12%1
15443

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
17%13%6%9%7%35%5%46%20%
1432
16th to endDay
14%15%9%11%8%45%45%5%16%
1674
February1st to 15thDay
15%14%5%10%9%35%45%5%18%
1575
16th to endDay
13%14%6%9%7%3444425%
1569
March1st to 15thDay
16%10%6%9%7%44445%25%
1894
16th to endDay
17%9%5%9%5%45%45%5%27%
2112
April1st to 15thDay
19%10%45%42445%7%30%
2145
16th to endDay
16%7%35%5%2445%6%37%
2340
May1st to 15thDay
18%6%36%5%34446%34%
2331
16th to endDay
13%6%35%5%2445%6%40%
2479
June1st to 15thDay
9%5%25%5%346%6%7%41%
2673
16th to endDay
9%5%35%6%35%6%6%9%39%
2700
July1st to 15thDay
6%425%6%245%7%8%45%
2555
16th to endDay
8%4245%35%6%7%9%40%
2534
August1st to 15thDay
8%5%25%6%35%6%7%8%38%
2340
16th to endDay
10%6%25%5%345%5%9%40%
2483
September1st to 15thDay
11%6%245%35%6%6%8%40%
2025
16th to endDay
13%5%26%5%2447%8%39%
1872
October1st to 15thDay
13%8%26%6%35%447%38%
1708
16th to endDay
22%8%36%6%33346%30%
1691
November1st to 15thDay
14%7%27%6%35%35%7%34%
1582
16th to endDay
16%10%49%7%4445%6%26%
1473
December1st to 15thDay
16%12%5%8%8%35%445%24%
1440
16th to endDay
20%18%5%8%6%3345%5%17%
1381
January1st to 15thNight
22%11%5%8%7%33345%23%
2506
16th to endNight
14%13%7%10%7%35%445%24%
2548
February1st to 15thNight
15%14%5%8%7%35%445%25%
2285
16th to endNight
15%11%5%9%6%35%445%27%
1903
March1st to 15thNight
16%10%5%7%5%35%346%30%
2043
16th to endNight
15%8%46%5%35%446%36%
2112
April1st to 15thNight
20%8%36%423348%33%
1813
16th to endNight
15%6%25%43446%7%40%
1620
May1st to 15thNight
17%6%26%5%3445%7%36%
1620
16th to endNight
13%424335%447%46%
1631
June1st to 15thNight
9%4336%345%7%8%43%
1284
16th to endNight
8%5%1442445%10%46%
1260
July1st to 15thNight
7%4235%2345%8%53%
1401
16th to endNight
6%314435%45%8%50%
1631
August1st to 15thNight
6%4145%245%7%9%46%
1620
16th to endNight
8%4234245%46%52%
1719
September1st to 15thNight
12%425%43445%7%46%
1921
16th to endNight
11%5%24424447%47%
1881
October1st to 15thNight
14%6%25%424448%42%
1922
16th to endNight
21%8%37%5%245%5%7%29%
2181
November1st to 15thNight
13%8%36%4345%47%36%
2276
16th to endNight
20%10%36%5%24446%29%
2484
December1st to 15thNight
19%12%48%6%35%45%6%24%
2520
16th to endNight
22%13%6%8%6%24445%21%
2838

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
17%14%5%10%7%35%5%45%20%
1432
16th to endDay
14%15%9%10%8%46%44416%
1674
February1st to 15thDay
16%14%5%11%8%45%5%5%5%18%
1575
16th to endDay
14%14%6%8%7%4445%425%
1569
March1st to 15thDay
16%11%5%8%7%34446%26%
1905
16th to endDay
17%10%5%9%5%35%45%6%27%
2111
April1st to 15thDay
19%10%45%424447%30%
2145
16th to endDay
16%7%26%5%2446%6%37%
2340
May1st to 15thDay
18%6%25%6%35%447%34%
2331
16th to endDay
13%5%26%5%345%5%6%40%
2479
June1st to 15thDay
9%5%25%6%345%6%8%40%
2673
16th to endDay
9%5%26%6%35%6%6%9%38%
2700
July1st to 15thDay
7%4246%35%46%9%45%
2555
16th to endDay
8%5%245%35%6%7%9%40%
2534
August1st to 15thDay
8%5%35%6%36%5%7%8%38%
2340
16th to endDay
10%5%25%5%345%6%9%40%
2483
September1st to 15thDay
11%5%246%35%5%7%7%40%
2025
16th to endDay
13%5%26%5%2446%8%39%
1872
October1st to 15thDay
13%7%26%6%35%446%38%
1708
16th to endDay
22%9%36%6%34246%30%
1691
November1st to 15thDay
15%7%37%6%45%447%34%
1582
16th to endDay
15%11%5%8%7%345%5%6%25%
1473
December1st to 15thDay
16%13%5%9%7%35%445%24%
1440
16th to endDay
20%17%6%8%6%33446%17%
1381
January1st to 15thNight
22%11%5%8%7%33345%23%
2506
16th to endNight
14%14%7%10%7%35%446%23%
2548
February1st to 15thNight
14%15%5%8%7%35%435%25%
2278
16th to endNight
15%11%410%6%34445%27%
1903
March1st to 15thNight
16%10%5%6%6%25%446%30%
2055
16th to endNight
16%8%36%5%34446%36%
2112
April1st to 15thNight
20%7%35%42335%8%33%
1813
16th to endNight
15%6%35%43346%7%40%
1620
May1st to 15thNight
16%7%26%5%3345%7%36%
1619
16th to endNight
13%424335%447%46%
1631
June1st to 15thNight
9%4245%35%6%6%8%43%
1284
16th to endNight
8%5%143345%5%10%47%
1260
July1st to 15thNight
7%42442345%7%53%
1401
16th to endNight
6%3135%35%46%8%51%
1631
August1st to 15thNight
6%424435%5%7%10%46%
1620
16th to endNight
8%5%2443445%5%52%
1719
September1st to 15thNight
12%425%43445%6%46%
1921
16th to endNight
11%425%424447%47%
1881
October1st to 15thNight
14%5%25%424448%42%
1922
16th to endNight
21%7%36%5%345%47%29%
2181
November1st to 15thNight
13%9%36%5%345%47%36%
2276
16th to endNight
20%10%36%5%2445%6%29%
2484
December1st to 15thNight
19%12%48%6%3445%6%24%
2520
16th to endNight
22%13%6%8%6%34445%21%
2838

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
65%5%10%13%4
1433
16th to endDay
69%6%9%10%3
1674
February1st to 15thDay
65%6%9%12%4
1577
16th to endDay
60%5%11%14%6%1
1569
March1st to 15thDay
59%6%11%13%7%
1905
16th to endDay
56%6%10%17%7%1
2112
April1st to 15thDay
52%5%11%19%10%
2145
16th to endDay
46%6%15%15%14%2
2340
May1st to 15thDay
48%6%11%20%11%2
2331
16th to endDay
42%7%11%22%14%1
2483
June1st to 15thDay
38%8%14%24%13%1
2673
16th to endDay
40%8%14%22%14%1
2700
July1st to 15thDay
33%6%12%27%17%1
2406
16th to endDay
36%10%15%21%13%2
2377
August1st to 15thDay
38%9%15%22%12%1
2327
16th to endDay
38%8%13%25%12%1
2483
September1st to 15thDay
39%8%15%23%11%
2025
16th to endDay
41%6%13%28%9%
1872
October1st to 15thDay
45%5%12%21%13%1
1708
16th to endDay
55%5%15%17%5%
1691
November1st to 15thDay
49%7%12%20%9%
1582
16th to endDay
57%7%14%15%5%
1473
December1st to 15thDay
62%6%14%12%3
1440
16th to endDay
67%5%12%11%2
1381
January1st to 15thNight
63%411%13%6%
2506
16th to endNight
61%6%13%15%3
2548
February1st to 15thNight
60%6%9%15%7%
2287
16th to endNight
57%6%10%18%6%
1903
March1st to 15thNight
55%5%11%19%7%1
2055
16th to endNight
47%412%23%10%
2112
April1st to 15thNight
49%411%20%12%1
1813
16th to endNight
41%6%10%19%17%3
1620
May1st to 15thNight
46%6%10%21%12%3
1620
16th to endNight
36%6%13%23%16%3
1633
June1st to 15thNight
35%8%12%26%14%1
1284
16th to endNight
32%7%15%23%19%1
1260
July1st to 15thNight
29%49%33%21%2
1321
16th to endNight
29%8%16%24%17%2
1525
August1st to 15thNight
30%8%15%29%13%2
1609
16th to endNight
31%6%11%31%16%1
1719
September1st to 15thNight
35%6%13%29%13%1
1921
16th to endNight
35%7%11%31%13%
1881
October1st to 15thNight
40%6%12%23%15%
1922
16th to endNight
53%6%13%19%6%
2181
November1st to 15thNight
46%6%13%22%9%1
2276
16th to endNight
55%6%15%17%5%
2484
December1st to 15thNight
60%6%15%12%4
2520
16th to endNight
66%5%11%11%4
2838

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
16%15%44%20%21
90
16th to endDay
30%14%36%16%2
96
February1st to 15thDay
24%14%44%16%
90
16th to endDay
11%19%44%19%4
81
March1st to 15thDay
27%14%28%22%7%
195
16th to endDay
23%7%31%23%10%2
288
April1st to 15thDay
25%10%29%20%11%2
270
16th to endDay
20%7%31%18%14%7%
270
May1st to 15thDay
22%6%27%23%14%4
288
16th to endDay
16%6%23%27%17%8%
331
June1st to 15thDay
11%432%31%15%4
468
16th to endDay
10%5%30%30%18%5%
495
July1st to 15thDay
9%322%35%19%10%
475
16th to endDay
8%221%31%24%10%
394
August1st to 15thDay
8%215%33%22%18%
313
16th to endDay
15%316%23%23%18%
332
September1st to 15thDay
11%418%20%27%16%
315
16th to endDay
14%5%14%23%27%13%
275
October1st to 15thDay
14%5%26%28%20%4
255
16th to endDay
24%9%37%22%5%
203
November1st to 15thDay
11%15%31%28%12%1
90
16th to endDay
18%26%32%15%7%
65
December1st to 15thDay
28%23%30%16%1
60
16th to endDay
27%20%44%7%
69
January1st to 15thNight
28%12%34%19%31
900
16th to endNight
18%12%37%25%5%
820
February1st to 15thNight
21%12%40%22%3
704
16th to endNight
20%11%34%28%5%
631
March1st to 15thNight
20%10%34%28%6%
720
16th to endNight
20%7%29%32%9%1
768
April1st to 15thNight
22%9%33%26%6%
621
16th to endNight
17%6%32%30%10%2
540
May1st to 15thNight
18%426%34%14%1
540
16th to endNight
14%227%34%19%2
512
June1st to 15thNight
12%324%41%18%
360
16th to endNight
11%119%45%20%1
360
July1st to 15thNight
10%15%41%27%4
471
16th to endNight
6%117%45%25%3
564
August1st to 15thNight
6%115%38%34%4
539
16th to endNight
11%116%34%29%5%
573
September1st to 15thNight
12%5%20%32%23%6%
690
16th to endNight
13%317%34%26%5%
681
October1st to 15thNight
16%6%25%31%16%2
660
16th to endNight
24%11%35%23%4
704
November1st to 15thNight
17%10%33%23%13%1
700
16th to endNight
24%14%30%22%8%
720
December1st to 15thNight
24%13%40%17%4
720
16th to endNight
28%11%36%20%2
945
Page generated at 2017-09-22 07:35:37. Version ac04

Copyright 2017 A. Danko


Black River Observatory Clear Sky Chart | Charts Home