Bays Mountain Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bays Mountain Park clear sky chart from 2005-11-06 to 2024-01-12.

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
48%
23989
19%
74523
15%
23936
53%
23936
23%
49615

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 10thNight
29%
760
16%
2459
11%
757
37%
757
17%
1721
January11th to 20thNight
30%
728
16%
2365
12%
728
36%
728
14%
1747
January21st to endNight
29%
792
19%
2574
11%
792
39%
792
19%
1741
February1st to 10thNight
33%
720
18%
2282
12%
720
41%
720
19%
1581
February11th to 20thNight
24%
703
15%
2099
9%
700
30%
700
19%
1494
February21st to endNight
24%
592
20%
1776
10%
592
34%
592
18%
1297
March1st to 10thNight
35%
720
22%
2038
14%
720
41%
720
24%
1383
March11th to 20thNight
34%
720
16%
1980
10%
720
38%
720
22%
1399
March21st to endNight
38%
792
16%
2178
10%
792
42%
792
24%
1521
April1st to 10thNight
43%
720
19%
1980
13%
720
48%
720
28%
1274
April11th to 20thNight
45%
596
23%
1736
14%
596
52%
596
28%
1109
April21st to endNight
48%
540
23%
1620
16%
540
53%
540
25%
1077
May1st to 10thNight
49%
540
15%
1620
9%
540
53%
540
24%
1069
May11th to 20thNight
53%
531
14%
1593
10%
531
55%
531
21%
1116
May21st to endNight
62%
582
14%
1744
11%
582
63%
582
26%
1141
June1st to 10thNight
66%
540
14%
1620
13%
540
67%
540
26%
1059
June11th to 20thNight
70%
540
15%
1620
12%
540
72%
540
29%
1032
June21st to endNight
65%
540
16%
1620
13%
540
66%
540
24%
1075
July1st to 10thNight
64%
525
12%
1575
11%
525
65%
525
25%
1067
July11th to 20thNight
70%
522
13%
1566
12%
522
70%
522
27%
1023
July21st to endNight
69%
591
14%
1672
12%
558
71%
558
25%
1128
August1st to 10thNight
66%
537
14%
1600
12%
534
66%
534
26%
1067
August11th to 20thNight
63%
534
16%
1598
16%
534
64%
534
23%
1103
August21st to endNight
69%
625
19%
1907
19%
625
70%
625
29%
1200
September1st to 10thNight
61%
720
20%
1980
18%
720
62%
720
28%
1322
September11th to 20thNight
62%
720
21%
1980
19%
720
62%
720
27%
1321
September21st to endNight
58%
720
25%
1980
20%
720
62%
720
32%
1256
October1st to 10thNight
60%
720
25%
2016
25%
720
62%
720
34%
1255
October11th to 20thNight
51%
720
26%
2160
25%
720
56%
720
30%
1322
October21st to endNight
52%
792
29%
2376
26%
792
58%
792
31%
1448
November1st to 10thNight
58%
740
28%
2338
27%
740
62%
740
32%
1361
November11th to 20thNight
49%
760
26%
2470
22%
760
56%
760
28%
1495
November21st to endNight
47%
760
25%
2470
21%
760
55%
760
28%
1512
December1st to 10thNight
33%
760
16%
2470
12%
760
38%
760
16%
1780
December11th to 20thNight
39%
759
20%
2980
17%
759
47%
759
17%
2014
December21st to endNight
32%
828
11%
4481
11%
817
40%
817
9%
3105

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
14%7%36%6%35%5%6%8%37%
74893
Night
15%7%36%5%345%5%7%39%
74843
TransparencyDay
44%7%12%21%14%3
74616
Night
43%7%11%21%15%3
74639
SeeingDay
17%9%19%23%21%10%
13870
Night
17%6%20%35%19%2
24000

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 10thDay
17%10%310%7%345%46%31%
1706
11th to 20thDay
20%10%5%8%7%34336%29%
1635
21st to endDay
17%10%36%5%35%45%6%36%
1782
February1st to 10thDay
19%11%5%6%5%3445%7%32%
1674
11th to 20thDay
21%9%5%7%6%35%346%30%
1748
21st to endDay
23%8%46%5%34446%33%
1480
March1st to 10thDay
16%7%36%5%3345%7%41%
1921
11th to 20thDay
20%8%37%5%35%5%5%7%32%
1980
21st to endDay
18%9%46%6%3445%5%35%
2178
April1st to 10thDay
12%6%36%5%345%7%8%42%
1980
11th to 20thDay
15%6%25%5%3445%8%43%
2187
21st to endDay
15%6%36%6%35%5%5%8%40%
2340
May1st to 10thDay
14%5%36%7%36%5%6%8%37%
2340
11th to 20thDay
17%7%36%6%46%5%5%7%33%
2301
21st to endDay
12%6%25%7%46%5%7%9%37%
2531
June1st to 10thDay
10%6%26%6%46%6%7%9%39%
2340
11th to 20thDay
8%437%7%5%7%6%7%9%37%
2340
21st to endDay
10%6%35%6%37%7%7%10%36%
2340
July1st to 10thDay
11%6%37%5%47%8%8%10%32%
2340
11th to 20thDay
12%5%35%7%5%6%7%7%11%32%
2340
21st to endDay
11%6%37%7%47%7%8%10%30%
2547
August1st to 10thDay
12%5%37%6%47%7%8%10%30%
2327
11th to 20thDay
12%6%36%7%46%7%9%9%31%
2303
21st to endDay
10%5%26%6%46%6%7%10%38%
2426
September1st to 10thDay
10%5%35%5%35%6%7%8%42%
1980
11th to 20thDay
12%5%26%6%345%6%8%43%
1980
21st to endDay
15%6%245%3445%7%45%
1980
October1st to 10thDay
13%6%15%5%34437%50%
1944
11th to 20thDay
14%5%25%334445%51%
1800
21st to endDay
16%8%35%433445%46%
1980
November1st to 10thDay
11%42443345%6%53%
1736
11th to 20thDay
12%6%25%5%34447%47%
1710
21st to endDay
15%6%35%5%2445%6%44%
1710
December1st to 10thDay
20%11%46%5%34447%32%
1710
11th to 20thDay
17%11%36%4245%5%8%34%
2153
21st to endDay
17%15%46%6%45%5%5%6%27%
3124
January1st to 10thNight
16%10%38%7%44445%34%
2459
11th to 20thNight
20%11%5%7%6%345%45%30%
2365
21st to endNight
17%9%47%6%3445%5%37%
2574
February1st to 10thNight
18%8%46%6%345%5%6%35%
2282
11th to 20thNight
21%9%36%5%25%5%5%5%33%
2098
21st to endNight
22%9%46%5%35%46%5%31%
1776
March1st to 10thNight
16%9%46%434445%42%
2038
11th to 20thNight
19%8%45%6%35%448%35%
1980
21st to endNight
14%7%37%6%36%5%5%7%38%
2178
April1st to 10thNight
12%6%35%445%46%8%43%
1980
11th to 20thNight
13%5%36%5%3446%7%44%
1736
21st to endNight
13%6%36%6%345%5%6%42%
1620
May1st to 10thNight
16%6%35%5%35%5%6%8%39%
1620
11th to 20thNight
15%6%45%6%46%5%6%9%34%
1592
21st to endNight
9%6%37%7%35%5%7%10%38%
1744
June1st to 10thNight
10%5%46%5%35%6%8%10%38%
1620
11th to 20thNight
6%426%6%36%7%7%10%43%
1620
21st to endNight
10%5%36%6%35%5%8%10%39%
1620
July1st to 10thNight
11%6%26%6%45%5%7%10%37%
1620
11th to 20thNight
9%5%26%5%45%7%8%10%39%
1620
21st to endNight
8%436%6%5%8%7%9%10%34%
1771
August1st to 10thNight
11%436%6%35%5%7%9%39%
1611
11th to 20thNight
13%437%7%5%6%6%6%8%37%
1598
21st to endNight
10%5%25%5%36%5%7%10%42%
1907
September1st to 10thNight
12%6%36%6%435%5%6%43%
1980
11th to 20thNight
15%6%25%6%335%6%7%42%
1980
21st to endNight
13%5%346%33347%48%
1980
October1st to 10thNight
13%5%25%5%24446%50%
2016
11th to 20thNight
17%5%34424345%50%
2160
21st to endNight
15%5%25%5%24447%48%
2376
November1st to 10thNight
13%6%24423445%53%
2338
11th to 20thNight
13%9%24433447%46%
2470
21st to endNight
15%8%25%42445%6%45%
2470
December1st to 10thNight
21%10%46%6%445%5%6%31%
2470
11th to 20thNight
17%10%37%5%3445%5%37%
3042
21st to endNight
17%13%46%7%35%5%6%7%26%
4532

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 10thDay
54%5%8%19%10%3
1707
11th to 20thDay
57%5%8%18%11%2
1635
21st to endDay
49%5%8%23%14%1
1782
February1st to 10thDay
54%5%8%19%13%1
1674
11th to 20thDay
57%48%18%12%2
1758
21st to endDay
53%49%15%14%5%
1480
March1st to 10thDay
43%47%23%19%4
1921
11th to 20thDay
51%6%9%18%12%3
1980
21st to endDay
50%5%10%23%10%2
2178
April1st to 10thDay
38%7%12%24%16%3
1980
11th to 20thDay
39%6%9%20%20%6%
2187
21st to endDay
43%7%12%24%12%3
2340
May1st to 10thDay
44%8%12%22%12%2
2340
11th to 20thDay
49%9%13%20%8%2
2305
21st to endDay
41%10%15%23%10%2
2531
June1st to 10thDay
39%9%16%21%13%1
2340
11th to 20thDay
40%11%16%18%13%2
2340
21st to endDay
40%10%14%20%15%2
2340
July1st to 10thDay
42%12%17%17%11%2
2275
11th to 20thDay
42%11%15%17%11%3
2271
21st to endDay
44%12%16%19%9%1
2405
August1st to 10thDay
44%11%18%19%8%
2314
11th to 20thDay
46%10%16%17%11%1
2303
21st to endDay
38%10%16%20%14%2
2426
September1st to 10thDay
36%8%15%21%14%5%
1980
11th to 20thDay
39%8%11%23%18%2
1980
21st to endDay
39%7%12%21%19%4
1980
October1st to 10thDay
36%5%9%23%23%4
1944
11th to 20thDay
36%5%10%24%21%5%
1800
21st to endDay
40%5%6%26%18%5%
1980
November1st to 10thDay
32%48%21%29%5%
1736
11th to 20thDay
38%5%7%24%21%6%
1710
21st to endDay
41%5%8%23%22%3
1710
December1st to 10thDay
54%49%20%11%2
1710
11th to 20thDay
47%5%11%19%16%2
2150
21st to endDay
55%7%8%21%8%
3124
January1st to 10thNight
53%49%18%13%3
2459
11th to 20thNight
56%6%9%14%14%2
2365
21st to endNight
49%5%9%22%15%1
2574
February1st to 10thNight
50%5%10%21%14%1
2282
11th to 20thNight
52%49%20%11%4
2099
21st to endNight
53%5%9%18%11%4
1776
March1st to 10thNight
45%5%8%17%21%3
2038
11th to 20thNight
48%6%10%22%11%2
1980
21st to endNight
45%7%12%21%14%2
2178
April1st to 10thNight
38%7%12%23%16%3
1980
11th to 20thNight
39%6%10%21%18%7%
1736
21st to endNight
43%7%10%26%13%2
1620
May1st to 10thNight
41%8%15%24%9%2
1620
11th to 20thNight
44%11%15%21%8%1
1593
21st to endNight
38%10%17%21%11%2
1745
June1st to 10thNight
38%10%17%19%14%2
1620
11th to 20thNight
33%12%19%22%12%2
1620
21st to endNight
37%13%14%20%13%4
1620
July1st to 10thNight
40%10%17%18%12%2
1575
11th to 20thNight
36%11%19%18%11%5%
1566
21st to endNight
38%13%17%22%10%
1672
August1st to 10thNight
38%12%20%21%9%1
1600
11th to 20thNight
43%10%16%18%12%1
1598
21st to endNight
35%9%17%25%12%1
1907
September1st to 10thNight
39%8%12%20%16%4
1980
11th to 20thNight
39%9%12%20%18%2
1980
21st to endNight
36%7%11%24%18%4
1980
October1st to 10thNight
36%5%10%22%22%5%
2016
11th to 20thNight
36%6%7%25%21%4
2160
21st to endNight
36%5%6%23%24%6%
2376
November1st to 10thNight
34%5%8%22%25%7%
2338
11th to 20thNight
38%47%21%24%6%
2470
21st to endNight
40%38%26%20%3
2470
December1st to 10thNight
54%5%9%18%11%2
2470
11th to 20thNight
50%48%20%16%2
3044
21st to endNight
54%7%11%16%11%
4532

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 10thDay
23%20%31%20%5%1
270
11th to 20thDay
29%18%27%20%7%
245
21st to endDay
24%23%29%17%6%
264
February1st to 10thDay
26%19%25%21%7%1
240
11th to 20thDay
34%24%29%10%3
240
21st to endDay
32%19%30%15%31
198
March1st to 10thDay
20%14%31%26%9%1
361
11th to 20thDay
24%16%26%28%6%
420
21st to endDay
22%15%26%26%10%1
462
April1st to 10thDay
18%16%22%27%15%3
420
11th to 20thDay
16%16%22%25%18%3
412
21st to endDay
20%11%24%23%17%5%
420
May1st to 10thDay
16%15%24%22%17%6%
423
11th to 20thDay
18%6%15%29%23%9%
447
21st to endDay
14%5%15%19%25%21%
485
June1st to 10thDay
13%314%26%29%15%
450
11th to 20thDay
9%414%25%30%19%
450
21st to endDay
13%221%23%27%13%
450
July1st to 10thDay
13%311%19%26%27%
445
11th to 20thDay
12%19%22%32%23%
444
21st to endDay
14%29%24%32%19%
488
August1st to 10thDay
14%413%20%28%21%
446
11th to 20thDay
14%310%22%30%20%
439
21st to endDay
13%38%18%35%23%
495
September1st to 10thDay
10%410%21%35%20%
450
11th to 20thDay
13%311%18%34%21%
450
21st to endDay
18%416%23%29%10%
450
October1st to 10thDay
16%414%26%28%12%
450
11th to 20thDay
14%10%19%29%23%5%
450
21st to endDay
20%8%21%28%19%5%
495
November1st to 10thDay
14%9%23%28%22%5%
334
11th to 20thDay
16%16%23%29%14%3
270
21st to endDay
17%11%28%23%19%3
270
December1st to 10thDay
26%16%26%24%7%1
270
11th to 20thDay
22%16%22%27%11%2
270
21st to endDay
22%16%30%22%8%2
297
January1st to 10thNight
22%13%27%34%4
760
11th to 20thNight
27%10%25%33%5%
728
21st to endNight
19%10%36%33%3
792
February1st to 10thNight
23%10%28%36%3
720
11th to 20thNight
26%12%35%26%2
703
21st to endNight
27%12%32%27%2
592
March1st to 10thNight
19%9%30%38%5%
720
11th to 20thNight
21%11%29%31%8%
720
21st to endNight
17%8%29%37%9%
792
April1st to 10thNight
15%11%26%37%11%
720
11th to 20thNight
14%8%27%37%14%1
596
21st to endNight
15%6%24%44%11%1
540
May1st to 10thNight
16%6%21%39%15%2
540
11th to 20thNight
16%5%18%36%24%2
531
21st to endNight
9%214%33%38%4
584
June1st to 10thNight
10%212%38%34%4
540
11th to 20thNight
7%111%36%40%5%
540
21st to endNight
12%110%37%37%4
540
July1st to 10thNight
13%26%28%45%6%
525
11th to 20thNight
12%16%26%46%8%
522
21st to endNight
10%17%33%42%8%
591
August1st to 10thNight
12%17%29%47%4
537
11th to 20thNight
14%17%33%39%7%
534
21st to endNight
10%18%30%43%8%
625
September1st to 10thNight
14%29%28%42%6%
720
11th to 20thNight
17%38%30%38%5%
720
21st to endNight
15%215%37%28%2
720
October1st to 10thNight
16%414%32%30%4
720
11th to 20thNight
17%5%20%39%18%1
720
21st to endNight
17%7%19%40%15%1
792
November1st to 10thNight
15%5%17%42%18%2
740
11th to 20thNight
17%8%22%42%11%1
760
21st to endNight
19%7%22%41%10%1
760
December1st to 10thNight
25%9%27%34%6%
760
11th to 20thNight
21%8%25%40%7%
760
21st to endNight
24%11%24%35%6%
836
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