Bancroft
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bancroft clear sky chart from 2005-11-05 to 2017-11-30.

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
28%
14988
13%
47813
7%
14958
35%
14958
16%
34139

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
13%
720
6%
2506
2%
716
18%
716
6%
2041
January16th to endNight
18%
768
11%
2563
4%
768
27%
768
10%
1992
February1st to 15thNight
13%
703
10%
2287
2%
701
21%
701
10%
1769
February16th to endNight
18%
631
14%
2004
5%
631
29%
631
13%
1469
March1st to 15thNight
17%
720
14%
2025
6%
720
25%
720
14%
1525
March16th to endNight
28%
768
20%
2087
9%
768
37%
768
24%
1410
April1st to 15thNight
20%
718
15%
1796
4%
718
27%
718
19%
1341
April16th to endNight
31%
606
18%
1686
8%
606
38%
606
23%
1171
May1st to 15thNight
36%
399
17%
1479
13%
399
45%
399
19%
955
May16th to endNight
34%
374
15%
1497
10%
374
47%
374
21%
907
June1st to 15thNight
33%
360
9%
1440
6%
360
44%
360
17%
931
June16th to endNight
44%
360
9%
1440
12%
360
49%
360
18%
914
July1st to 15thNight
48%
340
15%
1360
20%
340
55%
340
27%
752
July16th to endNight
46%
376
14%
1418
12%
354
55%
354
26%
800
August1st to 15thNight
55%
535
15%
1606
11%
533
59%
533
31%
1001
August16th to endNight
51%
657
20%
1803
10%
657
57%
657
35%
1106
September1st to 15thNight
44%
720
17%
1800
8%
720
48%
720
30%
1202
September16th to endNight
47%
717
23%
1987
15%
717
51%
717
29%
1292
October1st to 15thNight
29%
720
16%
2160
10%
720
37%
720
19%
1521
October16th to endNight
20%
768
12%
2334
4%
768
29%
768
12%
1811
November1st to 15thNight
28%
760
16%
2599
13%
760
35%
760
15%
1842
November16th to endNight
18%
780
10%
2728
6%
780
25%
780
9%
2119
December1st to 15thNight
13%
720
6%
2520
1%
720
18%
720
6%
2067
December16th to endNight
11%
768
8%
2688
2%
768
18%
768
7%
2201

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
18%10%47%5%34446%30%
48602
Night
16%10%46%5%34446%32%
47983
Cloud CoverDay
18%10%47%6%34446%30%
48612
Night
16%10%46%5%34446%32%
47988
TransparencyDay
53%5%10%18%9%1
48290
Night
51%6%11%19%10%
47813
SeeingDay
23%12%30%20%9%3
5620
Night
22%12%31%22%9%1
14990

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
20%17%7%8%6%23335%21%
1432
16th to endDay
14%14%7%12%8%35%33420%
1659
February1st to 15thDay
13%17%5%12%7%35%335%21%
1575
16th to endDay
16%16%5%10%5%3444425%
1467
March1st to 15thDay
15%12%48%8%34446%26%
1923
16th to endDay
14%10%36%6%2434437%
2136
April1st to 15thDay
22%12%45%424335%31%
2152
16th to endDay
20%9%35%423245%37%
2284
May1st to 15thDay
20%9%36%5%35%346%32%
2472
16th to endDay
15%7%36%5%35%45%7%35%
2618
June1st to 15thDay
23%7%36%5%35%45%7%28%
2520
16th to endDay
16%6%36%5%35%5%6%8%31%
2520
July1st to 15thDay
14%6%35%5%35%5%6%8%36%
2520
16th to endDay
12%6%26%6%46%5%7%8%33%
2654
August1st to 15thDay
13%7%27%7%36%5%5%8%31%
2342
16th to endDay
14%6%26%5%35%5%7%8%35%
2387
September1st to 15thDay
18%6%35%5%3335%7%38%
2160
16th to endDay
15%6%35%434445%41%
1971
October1st to 15thDay
24%9%35%434445%30%
1800
16th to endDay
30%11%36%5%33345%21%
1890
November1st to 15thDay
17%11%37%5%33446%31%
1586
16th to endDay
21%16%6%8%6%33335%21%
1558
December1st to 15thDay
20%18%7%12%7%3224415%
1440
16th to endDay
21%19%7%9%6%3332418%
1536
January1st to 15thNight
19%16%6%9%8%34445%16%
2506
16th to endNight
13%15%6%9%7%45%45%6%21%
2563
February1st to 15thNight
12%15%6%9%7%35%45%6%21%
2285
16th to endNight
14%14%47%5%25%45%7%27%
2004
March1st to 15thNight
17%11%5%8%5%3344431%
2013
16th to endNight
13%8%36%424345%41%
2087
April1st to 15thNight
19%11%35%434435%33%
1796
16th to endNight
16%8%345%25%446%37%
1686
May1st to 15thNight
18%7%25%5%23448%36%
1479
16th to endNight
12%5%245%35%45%7%41%
1495
June1st to 15thNight
17%6%25%5%2445%9%35%
1440
16th to endNight
11%6%35%5%45%6%5%8%37%
1440
July1st to 15thNight
9%4245%34447%48%
1440
16th to endNight
9%3245%3347%9%45%
1514
August1st to 15thNight
8%425%4245%6%8%46%
1616
16th to endNight
8%425%33445%7%50%
1803
September1st to 15thNight
14%5%15%42346%7%44%
1800
16th to endNight
16%6%2432435%5%47%
1987
October1st to 15thNight
20%8%25%5%24447%34%
2160
16th to endNight
22%12%37%5%345%45%24%
2334
November1st to 15thNight
17%10%36%5%34446%32%
2599
16th to endNight
20%14%5%7%6%35%445%22%
2728
December1st to 15thNight
20%19%6%9%5%3435%5%16%
2520
16th to endNight
22%16%8%9%5%2443417%
2688

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
20%17%6%8%5%34235%21%
1432
16th to endDay
15%14%7%12%9%35%335%20%
1659
February1st to 15thDay
13%17%5%12%8%35%43421%
1575
16th to endDay
16%16%5%8%6%3434425%
1467
March1st to 15thDay
15%13%48%8%35%445%26%
1934
16th to endDay
14%10%37%6%2444438%
2135
April1st to 15thDay
21%13%45%323435%30%
2152
16th to endDay
20%9%36%42324438%
2284
May1st to 15thDay
20%8%36%435%435%33%
2472
16th to endDay
15%7%36%5%345%5%7%35%
2618
June1st to 15thDay
23%6%36%6%24448%28%
2520
16th to endDay
17%6%25%5%35%5%7%8%31%
2520
July1st to 15thDay
14%6%25%5%25%5%6%8%35%
2520
16th to endDay
12%6%36%6%36%5%7%9%33%
2654
August1st to 15thDay
12%7%37%7%46%5%6%7%31%
2342
16th to endDay
14%5%36%5%35%5%6%7%35%
2387
September1st to 15thDay
18%6%35%5%24347%38%
2160
16th to endDay
15%6%25%434445%41%
1971
October1st to 15thDay
23%9%36%5%24445%30%
1800
16th to endDay
29%11%45%6%34345%22%
1890
November1st to 15thDay
17%11%28%4345%5%5%31%
1586
16th to endDay
22%16%6%8%5%33435%20%
1558
December1st to 15thDay
21%18%8%11%6%2323415%
1440
16th to endDay
21%18%8%9%6%2422418%
1536
January1st to 15thNight
19%16%6%10%8%35%435%16%
2506
16th to endNight
13%15%6%9%7%35%35%6%21%
2563
February1st to 15thNight
12%16%6%9%7%35%5%5%5%21%
2278
16th to endNight
13%15%47%6%3445%7%27%
2004
March1st to 15thNight
17%11%5%8%6%3343430%
2025
16th to endNight
13%9%46%5%23445%41%
2087
April1st to 15thNight
20%11%35%5%24345%33%
1796
16th to endNight
16%8%35%434446%37%
1686
May1st to 15thNight
18%7%35%5%1335%7%37%
1479
16th to endNight
12%6%25%5%35%45%8%41%
1495
June1st to 15thNight
16%7%26%5%345%5%8%35%
1440
16th to endNight
11%5%35%5%36%6%5%7%37%
1440
July1st to 15thNight
9%5%245%245%5%7%48%
1440
16th to endNight
9%32443446%9%46%
1514
August1st to 15thNight
8%425%44446%8%45%
1616
16th to endNight
8%425%425%45%7%49%
1803
September1st to 15thNight
14%42443346%7%43%
1800
16th to endNight
16%5%2432434447%
1987
October1st to 15thNight
20%7%25%5%24346%35%
2160
16th to endNight
23%12%47%5%3445%6%23%
2334
November1st to 15thNight
18%10%36%5%34446%32%
2599
16th to endNight
20%13%5%7%6%45%435%22%
2728
December1st to 15thNight
20%19%6%8%6%34345%16%
2520
16th to endNight
22%16%7%9%6%2433417%
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
66%410%11%6%
1433
16th to endDay
67%39%10%7%2
1659
February1st to 15thDay
66%5%9%12%5%
1577
16th to endDay
62%48%12%11%
1467
March1st to 15thDay
59%414%13%6%1
1934
16th to endDay
48%47%18%15%4
2136
April1st to 15thDay
56%47%17%11%2
2152
16th to endDay
49%47%21%15%2
2284
May1st to 15thDay
52%6%7%18%13%2
2472
16th to endDay
46%7%10%20%13%1
2622
June1st to 15thDay
53%6%10%19%9%
2520
16th to endDay
47%6%14%19%11%1
2520
July1st to 15thDay
42%7%11%26%11%
2371
16th to endDay
45%8%14%21%9%
2487
August1st to 15thDay
49%8%12%18%10%
2328
16th to endDay
44%7%14%24%9%
2387
September1st to 15thDay
45%5%11%25%11%
2160
16th to endDay
43%5%10%29%10%
1971
October1st to 15thDay
54%5%10%17%10%
1800
16th to endDay
64%6%10%12%5%
1890
November1st to 15thDay
52%7%13%16%9%
1586
16th to endDay
66%5%9%11%5%1
1558
December1st to 15thDay
72%5%9%9%3
1440
16th to endDay
70%47%11%5%
1536
January1st to 15thNight
68%5%10%9%4
2506
16th to endNight
62%6%7%13%9%
2563
February1st to 15thNight
61%6%12%13%6%
2287
16th to endNight
55%5%10%19%9%
2004
March1st to 15thNight
56%5%10%17%9%1
2025
16th to endNight
44%410%21%17%2
2087
April1st to 15thNight
53%47%19%13%2
1796
16th to endNight
45%5%9%21%15%2
1686
May1st to 15thNight
45%5%10%18%16%2
1479
16th to endNight
40%6%11%23%15%2
1497
June1st to 15thNight
44%7%12%21%12%
1440
16th to endNight
43%7%13%23%12%
1440
July1st to 15thNight
32%7%11%28%19%
1360
16th to endNight
33%7%16%29%12%
1418
August1st to 15thNight
33%8%17%27%11%
1606
16th to endNight
32%6%16%32%11%1
1803
September1st to 15thNight
36%8%15%26%11%
1800
16th to endNight
38%5%10%33%10%
1987
October1st to 15thNight
49%5%11%20%12%
2160
16th to endNight
60%6%11%15%6%
2334
November1st to 15thNight
52%6%12%18%9%1
2599
16th to endNight
62%6%11%14%4
2728
December1st to 15thNight
68%7%10%11%2
2520
16th to endNight
70%48%9%6%
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%21%28%11%6%
60
16th to endDay
41%17%27%12%1
85
February1st to 15thDay
36%23%33%5%1
90
16th to endDay
39%16%26%13%3
126
March1st to 15thDay
24%16%32%20%5%
270
16th to endDay
23%15%32%15%9%3
288
April1st to 15thDay
28%16%31%15%7%
270
16th to endDay
26%18%25%17%9%2
270
May1st to 15thDay
33%9%27%17%5%6%
288
16th to endDay
22%12%35%19%8%2
331
June1st to 15thDay
25%9%35%20%9%
315
16th to endDay
17%14%30%23%10%2
315
July1st to 15thDay
15%8%33%24%14%4
305
16th to endDay
13%10%31%27%12%4
326
August1st to 15thDay
13%430%29%14%7%
313
16th to endDay
18%5%25%27%12%10%
332
September1st to 15thDay
17%6%29%18%16%12%
315
16th to endDay
18%8%22%25%15%9%
314
October1st to 15thDay
24%13%28%20%10%2
315
16th to endDay
33%17%30%14%4
328
November1st to 15thDay
25%12%34%21%6%
150
16th to endDay
33%25%31%7%2
90
December1st to 15thDay
35%25%21%16%1
60
16th to endDay
42%29%25%11
64
January1st to 15thNight
29%20%29%14%5%
720
16th to endNight
20%15%36%20%6%
768
February1st to 15thNight
22%19%38%17%2
704
16th to endNight
20%18%37%17%4
631
March1st to 15thNight
27%17%33%18%3
720
16th to endNight
18%16%32%22%9%1
768
April1st to 15thNight
24%16%33%20%5%
718
16th to endNight
20%13%31%23%10%
606
May1st to 15thNight
22%8%28%27%11%1
399
16th to endNight
14%8%37%29%10%
375
June1st to 15thNight
18%10%31%28%10%1
360
16th to endNight
15%7%27%39%9%
360
July1st to 15thNight
8%5%31%36%16%1
340
16th to endNight
8%334%36%15%1
376
August1st to 15thNight
11%421%36%23%3
535
16th to endNight
11%428%31%22%2
657
September1st to 15thNight
16%6%29%26%18%3
720
16th to endNight
20%6%22%25%21%3
717
October1st to 15thNight
24%11%28%21%11%1
720
16th to endNight
31%13%29%18%5%
768
November1st to 15thNight
23%13%30%22%9%1
760
16th to endNight
29%16%28%18%6%1
780
December1st to 15thNight
30%18%31%15%3
720
16th to endNight
32%14%33%15%2
768
Page generated at 2017-12-01 12:13:47. Version ac04

Copyright 2017 A. Danko


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