Overstreet Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Overstreet Observatory clear sky chart from 2005-11-06 to 2024-02-20.

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
45%
24272
22%
79524
14%
24171
54%
24171
25%
48911

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
26%
755
28%
3972
9%
737
45%
737
16%
2052
January11th to 20thNight
28%
758
30%
3917
12%
740
45%
740
15%
2058
January21st to endNight
26%
828
19%
4439
13%
814
46%
814
15%
2629
February1st to 10thNight
33%
760
24%
2404
14%
760
46%
760
25%
1451
February11th to 20thNight
22%
740
22%
2213
8%
738
37%
738
22%
1448
February21st to endNight
25%
592
25%
1776
9%
592
42%
592
24%
1140
March1st to 10thNight
32%
720
27%
1990
14%
720
43%
720
29%
1228
March11th to 20thNight
29%
720
21%
1980
10%
720
39%
720
26%
1280
March21st to endNight
30%
792
20%
2178
8%
792
40%
792
25%
1446
April1st to 10thNight
35%
720
24%
1980
11%
720
46%
720
31%
1207
April11th to 20thNight
40%
686
25%
1817
12%
686
49%
686
34%
1106
April21st to endNight
46%
540
30%
1620
19%
540
55%
540
34%
957
May1st to 10thNight
42%
540
20%
1620
10%
540
50%
540
31%
972
May11th to 20thNight
48%
531
14%
1593
8%
531
51%
531
23%
1057
May21st to endNight
58%
582
17%
1744
14%
582
60%
582
27%
1127
June1st to 10thNight
59%
540
15%
1620
12%
540
61%
540
26%
1067
June11th to 20thNight
60%
540
14%
1620
11%
540
61%
540
28%
1057
June21st to endNight
65%
540
14%
1620
11%
540
67%
540
25%
1084
July1st to 10thNight
63%
525
9%
1575
8%
525
63%
525
21%
1117
July11th to 20thNight
70%
522
12%
1566
11%
522
71%
522
27%
1023
July21st to endNight
68%
591
14%
1672
11%
558
69%
558
25%
1111
August1st to 10thNight
64%
537
12%
1600
11%
534
64%
534
23%
1117
August11th to 20thNight
62%
534
16%
1598
14%
534
64%
534
22%
1113
August21st to endNight
63%
679
16%
1947
13%
679
64%
679
25%
1349
September1st to 10thNight
65%
720
20%
1980
16%
720
66%
720
31%
1279
September11th to 20thNight
56%
720
20%
1980
16%
720
59%
720
26%
1364
September21st to endNight
54%
720
23%
1980
17%
720
59%
720
30%
1298
October1st to 10thNight
53%
720
27%
2034
22%
720
59%
720
33%
1238
October11th to 20thNight
49%
720
30%
2160
24%
720
60%
720
34%
1236
October21st to endNight
49%
792
33%
2376
25%
792
62%
792
37%
1323
November1st to 10thNight
49%
740
29%
2240
22%
740
59%
740
34%
1293
November11th to 20thNight
41%
760
28%
2470
19%
760
54%
760
29%
1415
November21st to endNight
43%
760
28%
2470
19%
760
56%
760
28%
1457
December1st to 10thNight
36%
760
25%
2470
15%
760
49%
760
21%
1589
December11th to 20thNight
36%
759
28%
2906
17%
758
50%
758
24%
1633
December21st to endNight
34%
829
16%
4397
14%
817
46%
817
13%
2590

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%5%25%5%35%5%6%7%44%
78762
Night
15%6%25%5%3445%7%44%
80436
TransparencyDay
39%411%22%19%5%
78485
Night
40%410%20%21%6%
80232
SeeingDay
17%8%22%24%19%10%
14131
Night
17%8%22%30%20%3
24299

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%42432335%7%51%
2836
11th to 20thDay
15%6%2442344353%
2840
21st to endDay
27%5%2332324446%
3124
February1st to 10thDay
16%5%25%5%345%5%7%44%
1771
11th to 20thDay
21%6%15%434335%44%
1838
21st to endDay
20%6%25%5%34435%41%
1480
March1st to 10thDay
16%424424345%52%
1969
11th to 20thDay
17%5%25%6%345%5%7%40%
1980
21st to endDay
18%5%25%5%35%5%5%7%41%
2178
April1st to 10thDay
11%4245%25%5%6%9%48%
1980
11th to 20thDay
14%5%145%35%45%7%48%
2105
21st to endDay
12%42343446%8%50%
2340
May1st to 10thDay
10%5%25%5%35%5%6%8%46%
2340
11th to 20thDay
13%5%35%6%35%6%6%8%39%
2301
21st to endDay
11%5%25%5%35%6%7%9%41%
2531
June1st to 10thDay
11%5%26%6%46%6%7%11%36%
2340
11th to 20thDay
7%425%5%47%7%8%11%40%
2340
21st to endDay
7%426%7%37%7%7%9%41%
2340
July1st to 10thDay
7%6%37%7%47%7%8%11%33%
2340
11th to 20thDay
8%5%35%7%5%7%9%8%11%33%
2340
21st to endDay
7%5%36%6%47%7%8%11%36%
2547
August1st to 10thDay
12%6%36%7%5%6%6%8%11%31%
2327
11th to 20thDay
12%6%35%6%5%7%7%8%11%31%
2303
21st to endDay
10%5%27%6%5%6%7%7%9%36%
2385
September1st to 10thDay
8%436%6%45%6%6%9%45%
1980
11th to 20thDay
14%6%25%5%35%45%8%43%
1980
21st to endDay
16%5%34435%45%6%43%
1980
October1st to 10thDay
15%5%13322345%56%
1926
11th to 20thDay
13%423222345%59%
1800
21st to endDay
13%424423335%57%
1980
November1st to 10thDay
14%423323246%56%
1834
11th to 20thDay
15%5%24324435%53%
1710
21st to endDay
17%424324445%50%
1710
December1st to 10thDay
20%7%35%42345%6%40%
1710
11th to 20thDay
18%424323446%50%
2153
21st to endDay
21%6%2342346%6%43%
3124
January1st to 10thNight
18%423433345%51%
4109
11th to 20thNight
13%6%2443445%5%49%
4120
21st to endNight
25%7%23322335%45%
4532
February1st to 10thNight
16%6%24424346%48%
2404
11th to 20thNight
21%6%2443433445%
2213
21st to endNight
18%6%245%3345%6%42%
1776
March1st to 10thNight
15%6%25%424346%50%
1990
11th to 20thNight
18%6%25%43445%8%42%
1980
21st to endNight
15%6%35%5%35%45%6%43%
2178
April1st to 10thNight
13%6%2433445%7%49%
1980
11th to 20thNight
12%5%245%3235%8%50%
1817
21st to endNight
12%435%424345%52%
1620
May1st to 10thNight
10%5%36%6%345%5%9%46%
1620
11th to 20thNight
13%6%26%6%46%6%6%9%37%
1592
21st to endNight
13%5%25%6%36%6%6%9%38%
1744
June1st to 10thNight
11%5%26%7%46%6%9%11%34%
1620
11th to 20thNight
11%5%45%5%5%6%6%7%9%38%
1620
21st to endNight
8%5%26%7%47%7%9%10%35%
1620
July1st to 10thNight
8%7%38%8%5%7%6%8%11%28%
1620
11th to 20thNight
8%5%35%7%5%6%7%9%13%32%
1620
21st to endNight
7%5%26%6%5%7%8%10%13%31%
1771
August1st to 10thNight
12%6%36%6%46%7%9%11%29%
1611
11th to 20thNight
11%7%27%8%5%7%5%7%10%32%
1598
21st to endNight
10%7%36%6%46%6%8%11%32%
1947
September1st to 10thNight
10%5%36%5%35%46%8%44%
1980
11th to 20thNight
16%7%25%5%35%6%6%8%37%
1980
21st to endNight
15%6%35%5%34446%45%
1980
October1st to 10thNight
15%424423337%51%
2034
11th to 20thNight
15%424323347%53%
2160
21st to endNight
13%414323335%58%
2376
November1st to 10thNight
14%5%23422435%55%
2240
11th to 20thNight
15%5%34423346%52%
2470
21st to endNight
16%5%2443445%5%48%
2470
December1st to 10thNight
20%7%245%24445%43%
2470
11th to 20thNight
17%6%24323345%52%
3042
21st to endNight
21%5%244345%5%7%40%
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
35%25%27%24%7%
2837
11th to 20thDay
37%25%17%33%5%
2840
21st to endDay
44%2319%26%7%
3124
February1st to 10thDay
40%37%22%22%5%
1771
11th to 20thDay
44%36%20%21%6%
1848
21st to endDay
47%27%17%20%7%
1480
March1st to 10thDay
37%37%21%23%9%
1969
11th to 20thDay
43%410%19%18%6%
1980
21st to endDay
44%49%22%19%2
2178
April1st to 10thDay
33%49%22%26%6%
1980
11th to 20thDay
37%38%22%21%9%
2105
21st to endDay
34%310%28%20%5%
2340
May1st to 10thDay
36%414%23%19%4
2340
11th to 20thDay
42%5%16%21%15%2
2305
21st to endDay
38%5%14%25%15%1
2531
June1st to 10thDay
41%6%17%25%10%2
2340
11th to 20thDay
35%8%19%24%13%1
2340
21st to endDay
36%9%17%21%14%3
2340
July1st to 10thDay
44%7%20%17%10%3
2275
11th to 20thDay
41%9%23%16%9%2
2271
21st to endDay
39%6%21%22%11%1
2405
August1st to 10thDay
46%7%17%23%8%
2314
11th to 20thDay
45%8%17%19%10%1
2303
21st to endDay
43%6%17%21%9%3
2385
September1st to 10thDay
36%6%14%22%18%4
1980
11th to 20thDay
39%5%12%18%22%3
1980
21st to endDay
42%38%22%18%6%
1980
October1st to 10thDay
33%310%21%28%6%
1926
11th to 20thDay
30%29%25%26%9%
1800
21st to endDay
32%25%22%29%10%
1980
November1st to 10thDay
32%37%19%30%10%
1834
11th to 20thDay
35%35%23%24%9%
1710
21st to endDay
37%37%22%23%8%
1710
December1st to 10thDay
46%36%22%17%6%
1710
11th to 20thDay
38%27%20%23%10%
2150
21st to endDay
43%25%24%23%3
3124
January1st to 10thNight
37%35%20%28%7%
4109
11th to 20thNight
38%35%18%30%7%
4120
21st to endNight
46%2317%25%7%
4532
February1st to 10thNight
40%29%20%23%7%
2404
11th to 20thNight
46%2417%23%8%
2214
21st to endNight
43%39%17%20%8%
1776
March1st to 10thNight
37%38%17%23%12%
1990
11th to 20thNight
41%311%17%20%7%
1980
21st to endNight
43%48%21%20%4
2178
April1st to 10thNight
35%39%19%26%7%
1980
11th to 20thNight
35%27%23%24%9%
1817
21st to endNight
35%38%26%22%5%
1620
May1st to 10thNight
36%414%22%20%3
1620
11th to 20thNight
44%6%14%20%16%1
1593
21st to endNight
41%6%12%25%14%2
1745
June1st to 10thNight
42%7%16%22%11%1
1620
11th to 20thNight
40%7%18%22%11%2
1620
21st to endNight
40%9%17%16%12%4
1620
July1st to 10thNight
48%7%20%14%8%3
1575
11th to 20thNight
38%9%25%19%7%2
1566
21st to endNight
39%10%22%20%7%1
1672
August1st to 10thNight
44%9%20%19%7%
1600
11th to 20thNight
47%7%19%16%10%1
1598
21st to endNight
44%8%18%19%9%3
1947
September1st to 10thNight
37%7%15%20%17%4
1980
11th to 20thNight
44%6%11%18%18%2
1980
21st to endNight
41%5%9%19%20%6%
1980
October1st to 10thNight
36%38%19%28%5%
2034
11th to 20thNight
34%38%25%22%10%
2160
21st to endNight
32%1421%29%12%
2376
November1st to 10thNight
33%46%19%26%12%
2240
11th to 20thNight
37%2418%27%12%
2470
21st to endNight
38%3421%27%7%
2470
December1st to 10thNight
44%37%18%21%6%
2470
11th to 20thNight
37%27%18%27%9%
3044
21st to endNight
45%36%22%20%3
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%16%33%24%4
270
11th to 20thDay
28%15%34%18%5%
270
21st to endDay
25%17%37%16%5%
297
February1st to 10thDay
23%18%33%19%6%1
270
11th to 20thDay
36%15%32%13%3
267
21st to endDay
27%21%34%15%3
198
March1st to 10thDay
20%13%37%22%7%
409
11th to 20thDay
22%14%36%23%5%1
420
21st to endDay
22%13%35%22%7%1
462
April1st to 10thDay
16%14%32%23%13%2
420
11th to 20thDay
15%14%32%24%13%2
412
21st to endDay
16%12%27%25%14%7%
420
May1st to 10thDay
13%12%35%20%15%5%
423
11th to 20thDay
16%6%16%25%26%10%
447
21st to endDay
16%5%16%22%27%14%
485
June1st to 10thDay
12%413%30%27%13%
450
11th to 20thDay
11%410%30%28%18%
450
21st to endDay
10%414%30%25%17%
450
July1st to 10thDay
9%47%25%30%25%
445
11th to 20thDay
8%27%27%34%22%
444
21st to endDay
7%26%34%32%19%
488
August1st to 10thDay
18%211%23%28%18%
446
11th to 20thDay
14%17%28%30%21%
439
21st to endDay
14%28%22%31%24%
495
September1st to 10thDay
11%310%26%31%20%
450
11th to 20thDay
18%213%18%32%17%
450
21st to endDay
21%218%25%26%7%
450
October1st to 10thDay
19%418%26%22%10%
450
11th to 20thDay
14%6%25%27%22%7%
450
21st to endDay
18%9%20%30%18%6%
495
November1st to 10thDay
21%6%22%27%18%5%
432
11th to 20thDay
19%13%34%24%9%1
270
21st to endDay
13%9%32%31%13%3
270
December1st to 10thDay
29%10%33%23%5%
270
11th to 20thDay
25%10%32%24%9%1
270
21st to endDay
27%10%32%20%8%2
297
January1st to 10thNight
22%15%31%27%5%
760
11th to 20thNight
23%14%30%28%5%
760
21st to endNight
21%14%34%28%2
836
February1st to 10thNight
21%13%29%33%4
760
11th to 20thNight
26%14%34%24%2
742
21st to endNight
22%13%36%25%3
592
March1st to 10thNight
18%14%31%32%5%
720
11th to 20thNight
21%13%32%26%8%1
720
21st to endNight
19%11%34%28%8%
792
April1st to 10thNight
17%13%32%29%10%
720
11th to 20thNight
15%11%29%29%15%1
686
21st to endNight
15%5%28%33%18%1
540
May1st to 10thNight
11%8%29%35%16%1
540
11th to 20thNight
15%5%20%33%24%3
531
21st to endNight
17%210%29%35%6%
584
June1st to 10thNight
14%211%33%34%6%
540
11th to 20thNight
13%214%29%32%11%
540
21st to endNight
9%211%35%36%7%
540
July1st to 10thNight
11%27%30%40%11%
525
11th to 20thNight
11%26%25%44%12%
522
21st to endNight
9%27%31%41%9%
591
August1st to 10thNight
16%26%26%39%12%
537
11th to 20thNight
16%16%28%40%8%
534
21st to endNight
13%28%24%44%9%
679
September1st to 10thNight
12%38%28%41%8%
720
11th to 20thNight
19%211%26%35%7%
720
21st to endNight
17%316%32%29%3
720
October1st to 10thNight
17%417%27%29%5%
720
11th to 20thNight
18%5%22%30%22%3
720
21st to endNight
16%7%22%33%20%2
792
November1st to 10thNight
17%6%23%33%19%3
740
11th to 20thNight
18%9%28%32%13%1
760
21st to endNight
18%8%26%34%13%1
760
December1st to 10thNight
24%11%22%35%8%
760
11th to 20thNight
19%10%27%32%11%
760
21st to endNight
27%10%24%32%8%
836
Page generated at 2024-02-17 06:28:36. Version ac07

Copyright 2024 Attilla Danko


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