B & P Myers Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the B & P Myers Observatory clear sky chart from 2005-11-06 to 2024-01-27.

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%
22840
11%
74961
8%
22799
33%
22799
13%
56000

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
12%
760
7%
2649
4%
757
16%
757
5%
2225
January11th to 20thNight
14%
760
6%
2660
3%
760
17%
760
6%
2249
January21st to endNight
15%
820
8%
2745
3%
820
21%
820
8%
2215
February1st to 10thNight
10%
720
5%
2340
2%
720
15%
720
6%
1980
February11th to 20thNight
12%
703
8%
2220
2%
700
20%
700
8%
1797
February21st to endNight
15%
592
10%
1776
5%
592
22%
592
9%
1429
March1st to 10thNight
18%
720
11%
2160
6%
720
25%
720
12%
1689
March11th to 20thNight
19%
720
13%
1989
6%
720
25%
720
14%
1531
March21st to endNight
22%
792
17%
2052
6%
792
30%
792
16%
1544
April1st to 10thNight
21%
720
13%
1800
4%
720
26%
720
16%
1386
April11th to 20thNight
23%
711
13%
1775
5%
711
27%
711
19%
1361
April21st to endNight
28%
702
15%
1782
6%
702
32%
702
20%
1290
May1st to 10thNight
30%
378
15%
1458
11%
378
38%
378
14%
1008
May11th to 20thNight
35%
354
18%
1416
15%
354
44%
354
18%
866
May21st to endNight
45%
388
13%
1551
14%
388
52%
388
20%
962
June1st to 10thNight
46%
360
13%
1440
15%
360
53%
360
17%
930
June11th to 20thNight
44%
360
13%
1440
17%
360
51%
360
19%
896
June21st to endNight
46%
360
12%
1440
13%
360
54%
360
19%
903
July1st to 10thNight
54%
350
14%
1400
17%
350
59%
350
23%
816
July11th to 20thNight
60%
348
16%
1392
23%
348
63%
348
25%
817
July21st to endNight
55%
394
15%
1486
17%
372
57%
372
23%
880
August1st to 10thNight
56%
441
16%
1505
16%
439
58%
439
24%
942
August11th to 20thNight
52%
596
14%
1660
10%
596
53%
596
24%
1150
August21st to endNight
52%
792
17%
1980
9%
792
54%
792
31%
1323
September1st to 10thNight
49%
720
15%
1800
7%
720
50%
720
29%
1239
September11th to 20thNight
49%
720
22%
1813
14%
720
52%
720
31%
1206
September21st to endNight
43%
720
19%
2007
15%
720
47%
720
25%
1367
October1st to 10thNight
32%
720
12%
2160
10%
720
36%
720
17%
1591
October11th to 20thNight
29%
720
10%
2160
7%
720
34%
720
15%
1629
October21st to endNight
19%
792
9%
2500
5%
792
26%
792
10%
1988
November1st to 10thNight
29%
740
13%
2407
10%
740
33%
740
16%
1731
November11th to 20thNight
22%
760
14%
2560
9%
760
29%
760
12%
1911
November21st to endNight
18%
760
8%
2660
5%
760
22%
760
8%
2127
December1st to 10thNight
13%
760
4%
2660
2%
760
16%
760
5%
2257
December11th to 20thNight
14%
760
5%
3272
3%
759
17%
759
5%
2772
December21st to endNight
10%
827
3%
4846
0%
817
14%
817
3%
3993

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
17%11%5%8%6%35%5%5%6%28%
74854
Night
16%12%5%8%7%45%5%5%6%28%
75186
TransparencyDay
54%7%12%18%9%1
74559
Night
56%7%11%16%8%1
75015
SeeingDay
26%16%27%19%8%3
13560
Night
25%15%27%25%8%1
22850

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 10thDay
12%20%10%12%9%35%5%35%15%
1517
11th to 20thDay
15%19%10%11%9%3435%417%
1520
21st to endDay
11%18%9%13%10%5%5%5%5%416%
1750
February1st to 10thDay
13%17%7%16%10%6%6%44413%
1620
11th to 20thDay
12%17%8%16%9%3344419%
1627
21st to endDay
18%15%6%14%8%5%45%45%16%
1480
March1st to 10thDay
13%14%7%13%8%35%445%24%
1797
11th to 20thDay
13%18%6%10%6%35%445%26%
1970
21st to endDay
19%13%47%7%33435%32%
2304
April1st to 10thDay
18%14%5%7%5%34345%31%
2160
11th to 20thDay
18%11%47%5%33446%35%
2134
21st to endDay
21%12%47%5%35%35%5%30%
2177
May1st to 10thDay
20%11%47%6%34445%32%
2516
11th to 20thDay
17%8%36%5%35%46%7%36%
2478
21st to endDay
16%7%36%5%35%47%9%36%
2725
June1st to 10thDay
20%7%26%6%35%5%6%8%30%
2520
11th to 20thDay
19%7%245%445%6%8%35%
2520
21st to endDay
18%7%37%6%46%5%6%8%31%
2520
July1st to 10thDay
14%6%26%6%36%5%6%8%38%
2520
11th to 20thDay
13%7%26%6%46%5%7%9%35%
2520
21st to endDay
14%6%36%6%47%6%7%8%33%
2744
August1st to 10thDay
14%5%35%6%45%6%7%10%35%
2420
11th to 20thDay
15%6%38%6%36%6%6%9%32%
2223
21st to endDay
15%6%36%5%45%6%6%9%34%
2376
September1st to 10thDay
17%5%25%6%36%5%6%8%37%
2160
11th to 20thDay
16%6%36%4336%5%7%41%
2146
21st to endDay
19%6%36%5%35%5%5%8%36%
1949
October1st to 10thDay
23%9%37%7%35%445%30%
1800
11th to 20thDay
20%11%37%5%445%6%7%27%
1800
21st to endDay
26%13%47%6%36%5%4422%
1854
November1st to 10thDay
13%15%410%7%45%45%5%28%
1671
11th to 20thDay
15%16%5%9%6%35%5%5%6%26%
1618
21st to endDay
18%19%7%9%7%34346%19%
1520
December1st to 10thDay
19%22%9%11%6%35%44413%
1520
11th to 20thDay
19%16%12%14%8%3433414%
1906
21st to endDay
23%19%11%11%7%3432413%
2772
January1st to 10thNight
15%19%8%13%8%45%44415%
2649
11th to 20thNight
14%17%7%13%10%5%6%5%4416%
2660
21st to endNight
11%14%7%14%9%5%6%5%5%5%20%
2745
February1st to 10thNight
13%14%8%15%10%47%45%5%14%
2340
11th to 20thNight
12%11%8%14%10%5%6%5%5%5%19%
2218
21st to endNight
15%13%6%11%9%46%6%5%6%20%
1776
March1st to 10thNight
13%11%6%12%10%45%5%46%25%
2150
11th to 20thNight
14%14%6%8%7%45%446%28%
1988
21st to endNight
16%11%6%8%7%345%5%5%32%
2052
April1st to 10thNight
18%13%6%7%6%3445%6%28%
1800
11th to 20thNight
17%11%36%6%46%447%33%
1775
21st to endNight
18%11%36%6%3445%6%35%
1782
May1st to 10thNight
21%9%37%5%35%5%47%32%
1458
11th to 20thNight
13%9%36%5%445%7%8%38%
1415
21st to endNight
12%6%36%5%35%5%6%8%41%
1550
June1st to 10thNight
17%5%37%5%35%6%6%8%36%
1440
11th to 20thNight
17%6%345%35%5%48%41%
1440
21st to endNight
17%5%25%5%35%46%9%38%
1440
July1st to 10thNight
11%436%6%35%45%8%46%
1440
11th to 20thNight
12%5%245%45%5%5%8%45%
1440
21st to endNight
11%5%35%6%3445%9%44%
1574
August1st to 10thNight
13%6%25%5%445%6%8%43%
1515
11th to 20thNight
14%6%37%6%35%5%6%8%38%
1660
21st to endNight
13%6%245%35%47%7%45%
1980
September1st to 10thNight
14%6%345%25%5%6%7%43%
1800
11th to 20thNight
14%6%36%433445%48%
1813
21st to endNight
17%6%26%5%345%5%8%38%
2007
October1st to 10thNight
21%10%36%6%4445%5%31%
2160
11th to 20thNight
20%9%37%7%45%46%6%30%
2160
21st to endNight
25%12%37%7%4445%6%22%
2500
November1st to 10thNight
15%11%48%8%35%5%46%32%
2407
11th to 20thNight
17%14%5%7%6%35%446%27%
2560
21st to endNight
16%17%6%10%6%46%5%5%6%20%
2660
December1st to 10thNight
18%20%8%11%7%35%45%5%14%
2660
11th to 20thNight
19%17%7%12%7%45%5%4416%
3288
21st to endNight
24%18%9%9%6%34345%14%
4884

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
72%5%9%11%3
1518
11th to 20thDay
71%6%7%9%5%2
1520
21st to endDay
70%6%9%10%5%1
1750
February1st to 10thDay
75%5%8%8%31
1620
11th to 20thDay
69%5%9%12%5%1
1636
21st to endDay
69%6%9%9%6%
1480
March1st to 10thDay
63%5%12%13%6%2
1800
11th to 20thDay
60%6%11%13%9%2
1970
21st to endDay
55%48%15%15%3
2304
April1st to 10thDay
55%5%8%19%11%2
2160
11th to 20thDay
50%6%10%21%12%1
2134
21st to endDay
55%6%9%16%10%3
2177
May1st to 10thDay
54%5%9%18%12%2
2516
11th to 20thDay
47%6%11%24%11%2
2482
21st to endDay
43%9%17%20%10%1
2725
June1st to 10thDay
51%8%12%18%11%
2520
11th to 20thDay
45%8%13%24%9%1
2520
21st to endDay
48%8%15%18%9%1
2520
July1st to 10thDay
41%9%14%23%12%1
2450
11th to 20thDay
42%9%16%27%6%
2445
21st to endDay
43%10%16%21%10%
2591
August1st to 10thDay
41%10%16%22%10%1
2406
11th to 20thDay
46%9%15%22%7%
2223
21st to endDay
42%8%15%26%9%1
2376
September1st to 10thDay
42%8%13%24%12%
2160
11th to 20thDay
40%6%13%27%14%1
2146
21st to endDay
46%7%11%24%11%1
1949
October1st to 10thDay
55%6%11%18%9%1
1800
11th to 20thDay
54%8%14%19%5%1
1800
21st to endDay
63%8%11%10%7%1
1854
November1st to 10thDay
55%7%14%15%9%
1671
11th to 20thDay
58%6%12%14%7%2
1618
21st to endDay
66%7%14%10%4
1520
December1st to 10thDay
75%6%10%7%2
1520
11th to 20thDay
75%6%8%8%3
1906
21st to endDay
77%5%5%10%3
2772
January1st to 10thNight
72%5%8%10%5%
2649
11th to 20thNight
72%7%8%8%41
2660
21st to endNight
66%7%8%13%6%1
2745
February1st to 10thNight
71%7%10%9%4
2340
11th to 20thNight
66%6%9%13%6%
2220
21st to endNight
64%7%11%12%6%
1776
March1st to 10thNight
61%6%11%16%5%1
2160
11th to 20thNight
59%5%10%17%7%1
1989
21st to endNight
54%6%8%17%11%3
2052
April1st to 10thNight
57%5%10%19%8%1
1800
11th to 20thNight
52%8%9%18%12%1
1775
21st to endNight
50%6%12%17%13%3
1782
May1st to 10thNight
52%7%10%15%14%3
1458
11th to 20thNight
42%6%13%22%14%2
1416
21st to endNight
40%9%15%22%12%2
1551
June1st to 10thNight
44%8%14%21%12%1
1440
11th to 20thNight
41%9%14%22%13%2
1440
21st to endNight
43%7%14%25%10%1
1440
July1st to 10thNight
37%7%15%24%16%2
1400
11th to 20thNight
37%7%16%28%12%
1392
21st to endNight
37%8%16%27%11%2
1486
August1st to 10thNight
39%8%15%28%9%1
1505
11th to 20thNight
44%8%15%23%9%
1660
21st to endNight
36%9%15%27%12%
1980
September1st to 10thNight
39%9%14%26%11%1
1800
11th to 20thNight
39%6%11%27%16%1
1813
21st to endNight
42%8%12%25%12%1
2007
October1st to 10thNight
54%6%12%16%11%1
2160
11th to 20thNight
54%9%14%16%6%1
2160
21st to endNight
63%7%11%11%7%1
2500
November1st to 10thNight
52%7%13%16%9%2
2407
11th to 20thNight
56%7%11%15%8%2
2560
21st to endNight
64%8%12%13%31
2660
December1st to 10thNight
72%7%10%9%2
2660
11th to 20thNight
71%8%9%8%4
3288
21st to endNight
72%7%10%9%3
4884

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
32%19%28%16%5%
180
11th to 20thDay
34%28%28%8%11
180
21st to endDay
25%25%34%12%3
241
February1st to 10thDay
43%25%26%5%
240
11th to 20thDay
36%27%32%5%
294
21st to endDay
37%20%29%12%1
346
March1st to 10thDay
30%23%30%15%3
420
11th to 20thDay
29%25%29%13%3
420
21st to endDay
35%22%24%14%5%1
462
April1st to 10thDay
37%19%25%14%5%
420
11th to 20thDay
31%22%21%13%9%3
412
21st to endDay
33%20%27%14%42
420
May1st to 10thDay
31%19%26%14%7%2
423
11th to 20thDay
25%13%31%23%7%2
447
21st to endDay
20%13%29%21%14%2
485
June1st to 10thDay
23%15%30%22%8%2
450
11th to 20thDay
22%12%28%26%9%3
450
21st to endDay
20%14%33%22%8%2
450
July1st to 10thDay
18%9%25%28%17%4
445
11th to 20thDay
17%7%28%32%14%3
444
21st to endDay
16%8%33%30%11%2
488
August1st to 10thDay
15%10%25%28%15%7%
446
11th to 20thDay
17%7%24%31%13%8%
439
21st to endDay
18%13%27%23%14%6%
495
September1st to 10thDay
17%10%26%22%17%8%
450
11th to 20thDay
17%10%25%22%16%9%
450
21st to endDay
20%10%29%23%13%4
450
October1st to 10thDay
29%12%27%16%13%4
450
11th to 20thDay
28%18%27%18%8%1
450
21st to endDay
37%17%22%20%4
432
November1st to 10thDay
27%20%21%23%9%
365
11th to 20thDay
29%26%24%18%31
278
21st to endDay
37%19%28%14%1
180
December1st to 10thDay
36%19%31%11%4
180
11th to 20thDay
33%25%28%13%1
180
21st to endDay
37%22%30%11%
198
January1st to 10thNight
29%23%28%16%3
760
11th to 20thNight
29%22%30%16%3
760
21st to endNight
19%23%35%20%3
820
February1st to 10thNight
26%23%34%17%1
720
11th to 20thNight
25%22%36%14%3
703
21st to endNight
27%22%32%17%2
592
March1st to 10thNight
25%20%33%21%2
720
11th to 20thNight
29%18%30%18%31
720
21st to endNight
25%20%29%19%7%1
792
April1st to 10thNight
27%18%30%23%2
720
11th to 20thNight
25%17%31%20%7%1
711
21st to endNight
27%15%27%24%8%
702
May1st to 10thNight
25%10%28%26%10%
378
11th to 20thNight
19%12%29%33%6%1
354
21st to endNight
15%6%27%37%13%1
389
June1st to 10thNight
19%7%21%43%9%1
360
11th to 20thNight
21%7%22%37%14%
360
21st to endNight
17%5%25%40%12%1
360
July1st to 10thNight
12%5%20%42%21%1
350
11th to 20thNight
14%318%42%22%1
348
21st to endNight
15%320%44%16%1
394
August1st to 10thNight
17%419%39%21%1
441
11th to 20thNight
17%5%17%36%22%3
596
21st to endNight
14%7%19%38%20%1
792
September1st to 10thNight
17%7%22%35%17%2
720
11th to 20thNight
18%6%21%30%20%4
720
21st to endNight
21%9%24%28%16%1
720
October1st to 10thNight
28%12%23%21%15%1
720
11th to 20thNight
28%14%24%27%7%1
720
21st to endNight
34%14%28%21%3
792
November1st to 10thNight
24%14%28%26%8%
740
11th to 20thNight
28%18%27%21%5%1
760
21st to endNight
28%19%29%19%5%
760
December1st to 10thNight
32%21%29%15%3
760
11th to 20thNight
32%20%28%16%31
760
21st to endNight
33%22%28%16%1
836
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