Solebury Mountain Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Solebury Mountain Observatory clear sky chart from 2005-11-06 to 2024-01-10.

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
32%
23189
20%
74580
10%
23144
43%
23144
22%
47340

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
18%
760
23%
2647
8%
757
38%
757
19%
1602
January11th to 20thNight
22%
720
19%
2505
8%
720
38%
720
17%
1625
January21st to endNight
18%
792
22%
2574
7%
792
37%
792
20%
1582
February1st to 10thNight
20%
720
17%
2340
6%
720
35%
720
18%
1531
February11th to 20thNight
13%
703
20%
2131
3%
699
33%
699
16%
1422
February21st to endNight
15%
592
25%
1776
8%
592
36%
592
18%
1160
March1st to 10thNight
22%
720
22%
2160
8%
720
40%
720
22%
1336
March11th to 20thNight
20%
720
21%
1998
8%
720
33%
720
21%
1340
March21st to endNight
20%
792
22%
2039
6%
792
33%
792
25%
1390
April1st to 10thNight
19%
720
19%
1800
3%
720
29%
720
22%
1235
April11th to 20thNight
25%
711
19%
1775
6%
711
31%
711
25%
1228
April21st to endNight
27%
720
19%
1800
5%
720
35%
720
27%
1209
May1st to 10thNight
26%
575
15%
1655
7%
575
33%
575
19%
1165
May11th to 20thNight
28%
354
18%
1416
11%
354
40%
354
17%
901
May21st to endNight
45%
388
15%
1551
14%
388
52%
388
18%
954
June1st to 10thNight
42%
360
17%
1440
15%
360
52%
360
21%
870
June11th to 20thNight
46%
360
15%
1440
14%
360
54%
360
20%
876
June21st to endNight
55%
360
15%
1440
16%
360
61%
360
25%
835
July1st to 10thNight
53%
350
13%
1400
13%
350
58%
350
19%
880
July11th to 20thNight
56%
348
17%
1392
18%
348
61%
348
24%
819
July21st to endNight
53%
398
18%
1490
17%
376
60%
376
25%
858
August1st to 10thNight
59%
537
15%
1600
11%
534
61%
534
28%
1041
August11th to 20thNight
54%
696
15%
1760
9%
696
55%
696
27%
1230
August21st to endNight
53%
792
17%
1980
8%
792
56%
792
30%
1328
September1st to 10thNight
47%
720
20%
1800
10%
720
51%
720
30%
1226
September11th to 20thNight
51%
720
28%
1839
17%
720
57%
720
37%
1137
September21st to endNight
44%
720
24%
1980
16%
720
52%
720
28%
1298
October1st to 10thNight
39%
720
17%
2137
11%
720
47%
720
25%
1391
October11th to 20thNight
39%
720
23%
2160
15%
720
51%
720
29%
1309
October21st to endNight
29%
792
23%
2458
13%
792
43%
792
24%
1551
November1st to 10thNight
37%
740
25%
2407
14%
740
53%
740
29%
1367
November11th to 20thNight
30%
760
25%
2470
13%
760
45%
760
22%
1508
November21st to endNight
27%
760
22%
2584
9%
760
44%
760
22%
1538
December1st to 10thNight
20%
760
19%
2660
7%
760
36%
760
17%
1698
December11th to 20thNight
22%
760
19%
3193
7%
759
38%
759
15%
1948
December21st to endNight
23%
829
13%
4783
7%
817
39%
817
10%
2952

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
16%6%35%5%35%5%5%7%41%
74714
Night
16%6%25%5%3445%7%43%
74949
TransparencyDay
42%6%12%22%16%3
74420
Night
41%6%12%22%16%3
74777
SeeingDay
22%14%29%21%11%3
13841
Night
20%12%31%28%9%1
23197

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
13%6%37%5%3446%6%41%
1509
11th to 20thDay
15%8%37%5%445%6%6%37%
1454
21st to endDay
16%6%36%5%35%45%7%40%
1782
February1st to 10thDay
18%7%27%5%25%46%7%37%
1620
11th to 20thDay
17%8%36%6%34346%39%
1715
21st to endDay
21%8%46%5%24445%37%
1480
March1st to 10thDay
14%6%35%6%3435%6%45%
1797
11th to 20thDay
16%6%36%7%3445%6%39%
1959
21st to endDay
21%7%35%43445%5%39%
2315
April1st to 10thDay
17%7%46%5%2445%6%41%
2160
11th to 20thDay
16%6%35%43445%8%42%
2134
21st to endDay
17%6%26%6%35%46%6%39%
2160
May1st to 10thDay
20%7%26%6%35%5%5%7%35%
2320
11th to 20thDay
20%6%25%5%35%5%5%7%37%
2478
21st to endDay
15%7%35%5%4446%8%40%
2725
June1st to 10thDay
14%5%25%5%45%6%7%9%38%
2520
11th to 20thDay
14%6%26%6%36%5%6%8%37%
2520
21st to endDay
13%4246%45%5%6%9%41%
2520
July1st to 10thDay
13%426%6%46%6%7%8%39%
2520
11th to 20thDay
9%4245%35%5%8%10%43%
2520
21st to endDay
11%6%36%6%46%6%6%9%38%
2736
August1st to 10thDay
11%5%25%6%45%7%7%8%39%
2323
11th to 20thDay
12%6%25%5%45%5%6%9%40%
2126
21st to endDay
14%6%25%445%5%6%8%42%
2376
September1st to 10thDay
15%6%25%5%3446%8%43%
2160
11th to 20thDay
13%42443345%8%50%
2120
21st to endDay
18%6%25%6%44446%41%
1980
October1st to 10thDay
19%6%2343445%7%42%
1819
11th to 20thDay
15%5%34434447%45%
1800
21st to endDay
21%5%3442445%6%42%
1895
November1st to 10thDay
14%6%25%423336%52%
1671
11th to 20thDay
17%5%244345%5%5%48%
1710
21st to endDay
16%5%25%334448%46%
1592
December1st to 10thDay
19%8%25%5%34448%38%
1520
11th to 20thDay
21%7%24434346%43%
1906
21st to endDay
17%6%46%6%46%5%5%6%35%
2772
January1st to 10thNight
15%6%25%5%34446%46%
2647
11th to 20thNight
18%7%26%5%34447%40%
2505
21st to endNight
14%8%35%4245%47%44%
2574
February1st to 10thNight
17%8%35%433446%40%
2340
11th to 20thNight
18%7%35%5%3345%5%41%
2130
21st to endNight
19%8%34423446%43%
1776
March1st to 10thNight
16%5%2443446%7%45%
2150
11th to 20thNight
18%6%26%5%245%45%44%
1997
21st to endNight
19%6%25%5%34446%43%
2039
April1st to 10thNight
17%6%35%5%35%46%6%41%
1800
11th to 20thNight
16%6%25%6%25%5%5%6%41%
1775
21st to endNight
20%6%2342345%7%44%
1800
May1st to 10thNight
20%8%35%5%3446%6%36%
1655
11th to 20thNight
18%6%36%5%3446%6%39%
1415
21st to endNight
15%6%36%5%3446%9%41%
1550
June1st to 10thNight
17%5%25%5%35%45%6%43%
1440
11th to 20thNight
14%5%25%6%45%5%6%9%40%
1440
21st to endNight
11%4245%35%46%9%45%
1440
July1st to 10thNight
11%5%35%6%46%6%6%10%38%
1440
11th to 20thNight
9%425%445%6%7%10%43%
1440
21st to endNight
9%5%25%5%36%5%7%9%44%
1578
August1st to 10thNight
10%5%35%446%6%7%9%42%
1611
11th to 20thNight
11%7%36%6%35%6%6%9%38%
1760
21st to endNight
14%6%25%5%3447%9%41%
1980
September1st to 10thNight
16%6%25%4335%5%5%46%
1800
11th to 20thNight
12%5%24434346%53%
1839
21st to endNight
17%6%245%345%47%43%
1980
October1st to 10thNight
20%6%34424445%44%
2137
11th to 20thNight
16%42442345%6%49%
2160
21st to endNight
19%7%34324345%46%
2458
November1st to 10thNight
12%5%25%423446%53%
2407
11th to 20thNight
18%6%24433345%48%
2470
21st to endNight
14%6%245%35%46%8%45%
2584
December1st to 10thNight
20%6%35%43445%6%40%
2660
11th to 20thNight
18%5%25%5%345%5%6%41%
3288
21st to endNight
19%7%36%5%34446%38%
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
43%312%24%14%4
1510
11th to 20thDay
46%7%13%20%12%3
1454
21st to endDay
43%411%24%15%3
1782
February1st to 10thDay
45%5%14%23%11%2
1620
11th to 20thDay
47%39%23%15%3
1724
21st to endDay
49%5%9%22%13%4
1480
March1st to 10thDay
41%412%25%15%3
1800
11th to 20thDay
45%410%21%15%4
1959
21st to endDay
47%5%9%19%17%5%
2315
April1st to 10thDay
44%5%10%21%15%5%
2160
11th to 20thDay
39%6%11%22%17%4
2134
21st to endDay
44%5%10%19%18%5%
2160
May1st to 10thDay
48%7%9%16%17%3
2320
11th to 20thDay
45%6%11%21%15%2
2482
21st to endDay
42%7%14%20%15%2
2725
June1st to 10thDay
40%9%14%22%14%1
2520
11th to 20thDay
43%8%14%21%11%2
2520
21st to endDay
39%9%14%23%15%1
2520
July1st to 10thDay
42%8%13%21%14%2
2450
11th to 20thDay
34%8%15%25%16%3
2445
21st to endDay
41%7%12%20%17%3
2583
August1st to 10thDay
39%9%14%22%16%1
2310
11th to 20thDay
39%8%15%21%15%2
2126
21st to endDay
40%8%11%20%18%3
2376
September1st to 10thDay
39%7%12%19%20%3
2160
11th to 20thDay
33%5%11%24%24%3
2120
21st to endDay
44%5%9%17%21%3
1980
October1st to 10thDay
42%7%11%21%17%2
1819
11th to 20thDay
38%5%11%24%21%2
1800
21st to endDay
42%5%10%23%18%2
1895
November1st to 10thDay
35%413%25%21%3
1671
11th to 20thDay
38%410%24%21%3
1710
21st to endDay
38%314%30%12%3
1592
December1st to 10thDay
45%5%14%22%12%1
1520
11th to 20thDay
44%414%25%11%2
1906
21st to endDay
47%7%13%23%10%1
2772
January1st to 10thNight
40%5%10%25%16%4
2647
11th to 20thNight
45%5%14%23%10%2
2505
21st to endNight
40%5%11%24%17%3
2574
February1st to 10thNight
44%5%13%23%12%2
2340
11th to 20thNight
45%5%9%19%17%4
2132
21st to endNight
44%48%22%19%4
1776
March1st to 10thNight
38%5%12%24%17%4
2160
11th to 20thNight
43%5%10%21%18%3
1998
21st to endNight
43%5%10%17%19%6%
2039
April1st to 10thNight
42%6%11%20%17%4
1800
11th to 20thNight
42%6%10%20%20%3
1775
21st to endNight
40%6%11%20%19%5%
1800
May1st to 10thNight
49%5%10%17%17%2
1655
11th to 20thNight
46%6%12%16%18%3
1416
21st to endNight
41%8%16%19%13%3
1551
June1st to 10thNight
41%6%12%21%19%1
1440
11th to 20thNight
40%8%14%24%13%1
1440
21st to endNight
34%9%15%26%14%2
1440
July1st to 10thNight
40%11%14%19%15%2
1400
11th to 20thNight
35%9%14%26%14%2
1392
21st to endNight
34%9%16%23%15%3
1490
August1st to 10thNight
38%9%16%21%14%2
1600
11th to 20thNight
42%8%15%20%13%2
1760
21st to endNight
39%7%14%19%19%2
1980
September1st to 10thNight
40%7%12%20%19%2
1800
11th to 20thNight
33%5%11%21%25%4
1839
21st to endNight
41%5%8%22%23%2
1980
October1st to 10thNight
42%5%12%23%15%2
2137
11th to 20thNight
36%5%12%28%17%3
2160
21st to endNight
41%49%26%17%2
2458
November1st to 10thNight
34%412%24%22%4
2407
11th to 20thNight
39%5%9%23%19%5%
2470
21st to endNight
38%413%27%16%2
2584
December1st to 10thNight
46%412%23%14%2
2660
11th to 20thNight
42%6%13%20%16%3
3288
21st to endNight
47%5%12%25%11%1
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
28%24%29%15%21
178
11th to 20thDay
34%26%29%10%2
166
21st to endDay
24%27%34%11%4
264
February1st to 10thDay
34%26%30%8%3
240
11th to 20thDay
30%22%36%11%2
383
21st to endDay
32%21%31%13%3
346
March1st to 10thDay
28%21%31%17%3
420
11th to 20thDay
27%24%32%13%31
420
21st to endDay
28%23%29%13%6%1
462
April1st to 10thDay
28%22%30%13%5%1
420
11th to 20thDay
24%19%32%14%9%2
412
21st to endDay
30%20%30%15%42
420
May1st to 10thDay
30%19%28%14%6%2
423
11th to 20thDay
23%15%33%20%8%1
447
21st to endDay
20%8%25%26%18%3
485
June1st to 10thDay
17%10%32%24%14%3
450
11th to 20thDay
20%12%28%26%12%3
450
21st to endDay
16%9%31%27%13%3
450
July1st to 10thDay
12%5%23%32%21%7%
445
11th to 20thDay
9%425%33%24%5%
444
21st to endDay
14%7%30%31%15%3
488
August1st to 10thDay
11%426%35%18%7%
446
11th to 20thDay
14%421%34%22%6%
439
21st to endDay
14%6%27%28%15%9%
495
September1st to 10thDay
16%8%24%26%17%8%
450
11th to 20thDay
15%7%27%27%15%10%
450
21st to endDay
22%13%24%23%12%6%
450
October1st to 10thDay
24%7%29%19%14%7%
450
11th to 20thDay
18%14%30%26%10%2
450
21st to endDay
25%15%31%17%10%2
453
November1st to 10thDay
21%10%31%24%12%3
365
11th to 20thDay
25%16%32%21%5%1
370
21st to endDay
21%17%40%15%6%
252
December1st to 10thDay
29%24%29%10%8%
180
11th to 20thDay
40%17%27%10%6%
180
21st to endDay
31%17%29%16%7%1
198
January1st to 10thNight
21%18%38%20%3
760
11th to 20thNight
23%15%36%23%3
720
21st to endNight
19%19%40%22%2
792
February1st to 10thNight
24%17%34%23%2
720
11th to 20thNight
25%19%38%16%1
703
21st to endNight
26%18%37%17%2
592
March1st to 10thNight
23%19%33%21%3
720
11th to 20thNight
24%18%36%18%4
720
21st to endNight
21%15%40%19%5%
792
April1st to 10thNight
23%18%37%17%5%
720
11th to 20thNight
19%13%39%23%6%
711
21st to endNight
23%13%34%26%5%
720
May1st to 10thNight
25%14%30%25%6%
575
11th to 20thNight
21%8%37%27%7%
354
21st to endNight
16%6%24%38%13%1
389
June1st to 10thNight
18%6%28%36%13%1
360
11th to 20thNight
13%430%40%12%
360
21st to endNight
11%226%48%13%1
360
July1st to 10thNight
11%5%23%40%20%2
350
11th to 20thNight
11%322%43%20%1
348
21st to endNight
9%425%44%18%
398
August1st to 10thNight
13%117%46%21%2
537
11th to 20thNight
14%220%37%26%2
696
21st to endNight
15%417%41%21%1
792
September1st to 10thNight
17%324%35%18%3
720
11th to 20thNight
15%423%34%20%4
720
21st to endNight
22%5%23%31%18%1
720
October1st to 10thNight
23%7%25%26%16%3
720
11th to 20thNight
17%10%29%33%12%
720
21st to endNight
22%12%33%24%8%1
792
November1st to 10thNight
15%10%33%30%11%1
740
11th to 20thNight
22%15%29%27%7%
760
21st to endNight
19%15%35%25%7%
760
December1st to 10thNight
25%16%31%20%6%1
760
11th to 20thNight
21%15%35%24%5%
760
21st to endNight
23%15%33%26%2
836
Page generated at 2024-01-07 10:06:55. Version ac07

Copyright 2024 Attilla Danko


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