Sullivan Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sullivan Observatory clear sky chart from 2005-11-05 to 2017-10-31.

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
41%
16042
20%
47366
13%
15996
47%
15996
26%
30627

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
22%
900
17%
2506
7%
895
32%
895
20%
1793
January16th to endNight
21%
960
15%
2577
5%
960
29%
960
19%
1879
February1st to 15thNight
24%
779
13%
2187
5%
776
30%
776
18%
1569
February16th to endNight
25%
631
18%
1893
7%
631
34%
631
21%
1252
March1st to 15thNight
25%
720
16%
2160
8%
720
32%
720
19%
1523
March16th to endNight
29%
594
16%
2001
9%
594
39%
594
20%
1335
April1st to 15thNight
32%
539
20%
1797
12%
539
45%
539
24%
1110
April16th to endNight
36%
540
20%
1794
14%
540
45%
540
23%
1163
May1st to 15thNight
40%
540
16%
1620
10%
540
46%
540
23%
1109
May16th to endNight
51%
563
19%
1513
12%
561
55%
561
30%
1010
June1st to 15thNight
61%
540
20%
1440
13%
540
65%
540
39%
860
June16th to endNight
58%
540
21%
1440
15%
540
63%
540
38%
883
July1st to 15thNight
67%
510
19%
1360
16%
510
68%
510
39%
829
July16th to endNight
76%
564
27%
1417
21%
531
79%
531
47%
780
August1st to 15thNight
74%
539
22%
1687
23%
536
76%
536
41%
897
August16th to endNight
74%
573
24%
1910
26%
573
77%
573
37%
1032
September1st to 15thNight
61%
540
28%
1800
28%
540
66%
540
34%
999
September16th to endNight
62%
711
32%
1974
25%
711
66%
711
39%
1141
October1st to 15thNight
53%
720
29%
2079
21%
720
60%
720
35%
1227
October16th to endNight
33%
768
25%
2396
15%
768
44%
768
27%
1467
November1st to 15thNight
37%
700
26%
2276
17%
700
50%
700
29%
1320
November16th to endNight
30%
720
21%
2340
14%
720
40%
720
22%
1508
December1st to 15thNight
25%
891
13%
2511
6%
891
31%
891
18%
1845
December16th to endNight
21%
960
13%
2688
4%
960
28%
960
14%
2096

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%6%35%5%3445%7%39%
48390
Night
14%6%35%424446%42%
47535
Cloud CoverDay
13%6%35%5%3445%7%39%
48398
Night
13%7%35%424446%42%
47540
TransparencyDay
43%5%12%22%13%2
48076
Night
42%411%23%15%2
47367
SeeingDay
14%5%23%27%20%8%
6038
Night
17%7%27%30%15%1
16042

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
16%10%5%9%8%5%433426%
1432
16th to endDay
14%12%6%8%5%25%246%31%
1644
February1st to 15thDay
13%10%5%8%7%3445%7%29%
1675
16th to endDay
13%12%48%6%25%5%46%29%
1580
March1st to 15thDay
17%10%46%5%24446%33%
1790
16th to endDay
17%10%36%5%3445%6%31%
2232
April1st to 15thDay
17%6%35%5%25%45%7%37%
2151
16th to endDay
18%7%35%434346%37%
2166
May1st to 15thDay
21%6%25%5%3445%7%33%
2331
16th to endDay
11%6%35%5%25%6%5%9%39%
2598
June1st to 15thDay
8%4145%246%6%9%45%
2520
16th to endDay
9%425%5%25%5%6%9%43%
2520
July1st to 15thDay
10%324436%6%7%9%42%
2520
16th to endDay
5%214435%6%7%12%45%
2655
August1st to 15thDay
8%3145%3447%11%45%
2261
16th to endDay
7%414435%5%6%8%46%
2292
September1st to 15thDay
13%435%6%24446%45%
2154
16th to endDay
11%314334448%50%
1980
October1st to 15thDay
14%6%1442445%6%45%
1878
16th to endDay
15%6%24423345%45%
1827
November1st to 15thDay
14%5%23323346%49%
1582
16th to endDay
18%8%45%423246%40%
1620
December1st to 15thDay
20%11%5%6%5%35%446%27%
1446
16th to endDay
19%12%6%6%43445%6%26%
1536
January1st to 15thNight
14%9%47%5%35%435%35%
2506
16th to endNight
14%11%5%7%5%34345%33%
2577
February1st to 15thNight
15%9%5%6%5%24446%33%
2185
16th to endNight
16%8%37%423446%39%
1893
March1st to 15thNight
19%9%36%5%24445%35%
2147
16th to endNight
17%7%35%435%45%5%37%
2001
April1st to 15thNight
14%6%25%5%14335%45%
1797
16th to endNight
17%6%26%434345%41%
1794
May1st to 15thNight
18%5%36%5%2335%7%38%
1620
16th to endNight
10%5%25%435%5%5%7%43%
1512
June1st to 15thNight
8%413425%5%5%9%50%
1440
16th to endNight
8%33442446%7%49%
1440
July1st to 15thNight
9%3224345%6%7%50%
1440
16th to endNight
432332346%9%56%
1513
August1st to 15thNight
5%243245%7%11%51%
1696
16th to endNight
6%3134345%5%8%54%
1910
September1st to 15thNight
11%424323347%51%
1800
16th to endNight
8%423423448%53%
1974
October1st to 15thNight
11%42432335%6%51%
2079
16th to endNight
17%5%23323345%47%
2396
November1st to 15thNight
10%5%24324445%51%
2276
16th to endNight
18%8%35%323345%41%
2340
December1st to 15thNight
21%9%36%5%34336%31%
2511
16th to endNight
22%12%47%6%3443427%
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
16%10%6%9%8%5%4335%26%
1432
16th to endDay
14%12%6%8%6%35%346%31%
1644
February1st to 15thDay
13%10%5%8%7%4445%7%28%
1675
16th to endDay
13%12%49%6%25%446%29%
1580
March1st to 15thDay
17%9%46%5%24446%33%
1800
16th to endDay
17%10%46%5%3435%6%31%
2230
April1st to 15thDay
17%6%345%25%45%7%37%
2151
16th to endDay
18%7%35%43345%5%37%
2166
May1st to 15thDay
20%6%25%5%3445%7%33%
2331
16th to endDay
11%6%35%5%246%5%8%38%
2598
June1st to 15thDay
7%5%245%346%6%9%45%
2520
16th to endDay
9%425%435%5%7%9%42%
2520
July1st to 15thDay
9%324435%6%6%9%42%
2520
16th to endDay
5%3145%35%6%7%12%44%
2655
August1st to 15thDay
7%3145%345%7%11%44%
2261
16th to endDay
7%414435%5%6%8%46%
2292
September1st to 15thDay
13%435%5%2435%6%45%
2154
16th to endDay
10%32433445%8%49%
1980
October1st to 15thDay
14%6%14333447%45%
1878
16th to endDay
15%6%25%413445%45%
1827
November1st to 15thDay
14%5%23323346%49%
1582
16th to endDay
18%8%45%32325%6%40%
1620
December1st to 15thDay
20%11%46%5%35%445%27%
1446
16th to endDay
19%12%6%6%43445%6%26%
1536
January1st to 15thNight
14%9%47%5%35%445%35%
2506
16th to endNight
13%11%5%8%5%34335%33%
2577
February1st to 15thNight
15%9%6%6%5%2445%6%33%
2178
16th to endNight
16%8%36%423445%39%
1893
March1st to 15thNight
19%9%36%5%24445%34%
2160
16th to endNight
16%8%35%435%45%5%37%
2001
April1st to 15thNight
14%6%25%5%24345%45%
1797
16th to endNight
17%6%26%424345%41%
1794
May1st to 15thNight
18%6%35%5%2335%7%37%
1619
16th to endNight
9%5%25%5%35%5%5%8%42%
1512
June1st to 15thNight
7%4134245%5%9%49%
1440
16th to endNight
8%4345%2446%8%48%
1440
July1st to 15thNight
8%4234345%5%8%50%
1440
16th to endNight
42233235%6%9%56%
1513
August1st to 15thNight
5%21432447%11%51%
1696
16th to endNight
6%213435%5%5%8%53%
1910
September1st to 15thNight
11%424323437%52%
1800
16th to endNight
8%423423448%53%
1974
October1st to 15thNight
11%41442335%6%51%
2079
16th to endNight
17%6%24323345%47%
2396
November1st to 15thNight
10%5%24324435%51%
2276
16th to endNight
18%8%35%423336%40%
2340
December1st to 15thNight
21%9%36%6%34336%31%
2511
16th to endNight
22%12%47%5%3443427%
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
61%38%17%8%
1433
16th to endDay
55%313%19%6%
1644
February1st to 15thDay
54%412%19%8%
1677
16th to endDay
55%413%20%7%
1580
March1st to 15thDay
51%413%21%7%
1800
16th to endDay
53%413%21%5%
2232
April1st to 15thDay
45%411%24%12%1
2151
16th to endDay
48%412%21%10%2
2166
May1st to 15thDay
49%5%13%20%10%
2331
16th to endDay
41%7%14%17%15%2
2602
June1st to 15thDay
33%7%13%25%18%2
2520
16th to endDay
36%6%15%21%16%3
2520
July1st to 15thDay
37%6%12%24%15%3
2371
16th to endDay
28%9%17%27%15%1
2488
August1st to 15thDay
31%7%14%28%16%2
2246
16th to endDay
32%7%12%25%15%6%
2292
September1st to 15thDay
39%5%7%22%20%4
2154
16th to endDay
33%48%28%22%2
1980
October1st to 15thDay
38%410%26%17%2
1878
16th to endDay
40%211%25%18%1
1827
November1st to 15thDay
36%312%22%20%4
1582
16th to endDay
46%211%24%12%1
1620
December1st to 15thDay
58%311%16%8%
1446
16th to endDay
58%5%9%17%6%1
1536
January1st to 15thNight
51%38%22%13%
2506
16th to endNight
53%313%21%7%
2577
February1st to 15thNight
52%312%19%9%1
2187
16th to endNight
46%314%24%10%
1893
March1st to 15thNight
52%410%20%11%1
2160
16th to endNight
47%413%23%10%1
2001
April1st to 15thNight
41%39%25%17%2
1797
16th to endNight
45%39%22%14%4
1794
May1st to 15thNight
46%5%12%22%12%
1620
16th to endNight
39%7%13%17%18%3
1514
June1st to 15thNight
29%6%12%27%20%3
1440
16th to endNight
33%412%23%21%5%
1440
July1st to 15thNight
30%5%12%28%18%5%
1360
16th to endNight
22%6%15%32%20%2
1417
August1st to 15thNight
24%6%16%26%22%3
1687
16th to endNight
27%6%12%26%20%6%
1910
September1st to 15thNight
32%47%24%24%7%
1800
16th to endNight
29%5%8%26%25%5%
1974
October1st to 15thNight
33%39%26%20%5%
2079
16th to endNight
39%38%27%18%2
2396
November1st to 15thNight
35%38%23%20%7%
2276
16th to endNight
45%210%23%16%
2340
December1st to 15thNight
55%312%17%10%
2511
16th to endNight
61%49%16%7%1
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%12%34%16%5%
90
16th to endDay
11%20%38%26%3
96
February1st to 15thDay
13%22%40%22%2
90
16th to endDay
14%16%34%28%41
81
March1st to 15thDay
30%15%34%15%4
90
16th to endDay
23%12%33%19%8%1
225
April1st to 15thDay
19%12%31%22%12%
270
16th to endDay
22%5%28%26%11%4
270
May1st to 15thDay
19%9%30%27%10%3
288
16th to endDay
14%5%30%27%16%6%
498
June1st to 15thDay
8%221%33%27%7%
495
16th to endDay
11%428%30%16%8%
495
July1st to 15thDay
13%117%32%23%12%
475
16th to endDay
5%12%31%33%16%
515
August1st to 15thDay
10%110%23%36%19%
376
16th to endDay
7%112%28%35%14%
332
September1st to 15thDay
11%113%27%31%13%
315
16th to endDay
11%115%26%28%15%
314
October1st to 15thDay
17%6%23%25%22%5%
213
16th to endDay
20%5%34%29%8%2
144
November1st to 15thDay
14%421%26%20%13%
90
16th to endDay
35%15%23%18%6%
90
December1st to 15thDay
17%14%33%22%7%4
90
16th to endDay
23%18%44%11%1
96
January1st to 15thNight
19%14%37%23%4
900
16th to endNight
19%13%38%25%3
960
February1st to 15thNight
20%14%34%26%3
779
16th to endNight
20%10%37%29%2
631
March1st to 15thNight
24%10%33%25%5%
720
16th to endNight
20%9%35%24%10%
594
April1st to 15thNight
17%12%31%28%8%
539
16th to endNight
21%5%31%30%10%1
540
May1st to 15thNight
20%6%26%35%10%1
540
16th to endNight
11%326%34%20%2
563
June1st to 15thNight
10%120%43%23%
540
16th to endNight
9%122%40%25%1
540
July1st to 15thNight
10%112%37%35%2
510
16th to endNight
5%10%41%37%4
564
August1st to 15thNight
5%12%40%35%5%
539
16th to endNight
5%12%35%39%5%
573
September1st to 15thNight
12%213%35%30%5%
540
16th to endNight
10%415%31%32%6%
711
October1st to 15thNight
14%5%21%34%19%3
720
16th to endNight
21%11%31%26%10%
768
November1st to 15thNight
13%8%35%28%12%
700
16th to endNight
22%13%29%25%7%
720
December1st to 15thNight
27%8%33%23%6%1
891
16th to endNight
29%11%31%23%3
960
Page generated at 2017-11-01 16:23:39. Version ac04

Copyright 2017 A. Danko


Sullivan Observatory Clear Sky Chart |Charts Home