Covey-Hill
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Covey-Hill clear sky chart from 2005-11-06 to 2024-01-31.

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
20%
22672
13%
74962
6%
22632
30%
22632
13%
54114

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
6%
760
9%
2649
1%
757
16%
757
5%
2154
January11th to 20thNight
9%
760
9%
2660
2%
760
17%
760
6%
2129
January21st to endNight
11%
835
12%
2919
3%
835
22%
835
8%
2195
February1st to 10thNight
6%
720
9%
2352
1%
720
16%
720
6%
1911
February11th to 20thNight
10%
703
11%
2179
2%
700
22%
700
9%
1666
February21st to endNight
13%
592
15%
1776
3%
592
27%
592
11%
1354
March1st to 10thNight
13%
720
14%
2160
5%
720
24%
720
9%
1661
March11th to 20thNight
14%
720
15%
2083
3%
720
25%
720
12%
1551
March21st to endNight
20%
792
19%
1990
5%
792
29%
792
16%
1489
April1st to 10thNight
14%
720
15%
1800
3%
720
21%
720
13%
1402
April11th to 20thNight
20%
711
15%
1775
3%
711
27%
711
17%
1334
April21st to endNight
19%
594
17%
1674
6%
594
27%
594
16%
1206
May1st to 10thNight
22%
419
16%
1499
8%
419
34%
419
14%
1045
May11th to 20thNight
25%
354
20%
1416
13%
354
44%
354
16%
887
May21st to endNight
25%
388
13%
1551
8%
388
37%
388
18%
938
June1st to 10thNight
24%
360
11%
1440
7%
360
38%
360
14%
967
June11th to 20thNight
30%
360
13%
1440
13%
360
42%
360
18%
899
June21st to endNight
29%
360
12%
1440
10%
360
41%
360
17%
925
July1st to 10thNight
35%
350
15%
1400
13%
350
51%
350
25%
782
July11th to 20thNight
39%
348
16%
1392
16%
348
49%
348
25%
772
July21st to endNight
34%
394
16%
1486
12%
372
43%
372
22%
859
August1st to 10thNight
43%
358
18%
1422
15%
356
53%
356
26%
794
August11th to 20thNight
44%
564
18%
1628
10%
564
50%
564
30%
1038
August21st to endNight
37%
792
18%
1980
7%
792
41%
792
31%
1309
September1st to 10thNight
35%
720
15%
1800
5%
720
40%
720
30%
1206
September11th to 20thNight
41%
720
22%
1870
11%
720
47%
720
33%
1185
September21st to endNight
33%
720
21%
1980
13%
720
40%
720
26%
1316
October1st to 10thNight
26%
720
18%
2106
9%
720
35%
720
20%
1424
October11th to 20thNight
22%
720
16%
2182
6%
720
33%
720
15%
1541
October21st to endNight
15%
792
13%
2574
4%
792
25%
792
11%
1929
November1st to 10thNight
16%
740
15%
2407
6%
740
29%
740
13%
1727
November11th to 20thNight
15%
760
16%
2531
8%
760
26%
760
11%
1856
November21st to endNight
14%
760
11%
2660
5%
760
23%
760
8%
2033
December1st to 10thNight
10%
760
8%
2660
2%
760
17%
760
5%
2197
December11th to 20thNight
10%
760
10%
3246
3%
759
19%
759
4%
2593
December21st to endNight
7%
826
5%
4835
1%
817
14%
817
2%
3840

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%10%48%6%45%5%5%6%30%
74906
Night
17%11%5%8%6%45%5%5%6%29%
75224
TransparencyDay
55%310%21%10%1
74611
Night
57%310%19%10%1
75053
SeeingDay
26%18%30%17%7%2
13531
Night
25%19%30%19%6%1
22683

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
14%15%8%13%10%46%44417%
1517
11th to 20thDay
13%17%8%12%10%46%45%419%
1520
21st to endDay
10%14%8%11%10%46%6%5%5%21%
1664
February1st to 10thDay
13%18%7%13%9%46%45%417%
1606
11th to 20thDay
11%14%7%12%9%46%5%5%6%23%
1669
21st to endDay
16%14%6%11%8%45%445%21%
1480
March1st to 10thDay
14%15%6%11%8%345%4425%
1797
11th to 20thDay
15%15%5%8%7%35%45%5%27%
1876
21st to endDay
19%13%5%8%5%34345%32%
2366
April1st to 10thDay
20%15%5%6%5%33445%30%
2160
11th to 20thDay
19%11%5%6%5%34445%35%
2134
21st to endDay
23%11%47%6%34445%31%
2286
May1st to 10thDay
20%9%48%5%345%5%6%32%
2474
11th to 20thDay
17%9%46%43445%7%37%
2478
21st to endDay
18%7%36%5%35%5%6%8%34%
2725
June1st to 10thDay
25%7%35%5%446%6%7%28%
2520
11th to 20thDay
17%7%25%5%45%5%5%9%35%
2520
21st to endDay
20%8%36%7%35%5%5%7%30%
2520
July1st to 10thDay
13%6%36%6%45%5%6%8%39%
2520
11th to 20thDay
14%6%26%5%46%6%7%9%34%
2520
21st to endDay
14%6%36%6%35%6%6%9%36%
2744
August1st to 10thDay
13%7%36%6%47%5%6%8%34%
2506
11th to 20thDay
12%6%26%6%45%7%7%9%37%
2253
21st to endDay
15%6%36%6%35%5%6%7%38%
2376
September1st to 10thDay
15%5%25%5%345%6%8%42%
2160
11th to 20thDay
16%7%24433447%46%
2089
21st to endDay
14%6%36%5%4447%7%39%
1980
October1st to 10thDay
21%8%36%6%45%5%6%7%31%
1852
11th to 20thDay
17%12%47%7%5%5%5%46%29%
1778
21st to endDay
26%14%47%5%3434425%
1782
November1st to 10thDay
17%11%48%7%35%45%8%29%
1671
11th to 20thDay
17%13%6%8%6%45%45%6%26%
1645
21st to endDay
17%15%6%11%8%46%5%5%5%20%
1520
December1st to 10thDay
18%18%8%11%8%445%45%15%
1520
11th to 20thDay
18%15%8%10%6%345%45%21%
1906
21st to endDay
21%17%7%10%7%45%44318%
2772
January1st to 10thNight
13%15%8%12%10%6%7%5%45%15%
2649
11th to 20thNight
13%15%7%12%9%5%7%445%19%
2660
21st to endNight
11%12%6%11%10%5%6%5%6%6%23%
2919
February1st to 10thNight
13%14%6%13%11%5%6%5%5%418%
2352
11th to 20thNight
12%12%6%10%9%5%7%5%5%5%25%
2177
21st to endNight
12%14%6%11%8%45%44427%
1776
March1st to 10thNight
15%14%6%9%9%46%345%25%
2150
11th to 20thNight
16%13%6%8%6%45%445%30%
2082
21st to endNight
18%12%5%7%6%35%44433%
1990
April1st to 10thNight
20%14%5%8%6%445%35%27%
1800
11th to 20thNight
22%9%38%5%35%447%31%
1775
21st to endNight
21%10%46%434446%32%
1674
May1st to 10thNight
23%10%26%6%345%47%31%
1499
11th to 20thNight
17%9%36%5%25%46%7%37%
1415
21st to endNight
15%5%36%5%445%5%8%39%
1550
June1st to 10thNight
22%7%35%5%35%5%5%10%30%
1440
11th to 20thNight
18%6%35%6%345%6%7%38%
1440
21st to endNight
16%6%36%5%36%6%5%7%36%
1440
July1st to 10thNight
10%6%35%5%345%6%9%44%
1440
11th to 20thNight
10%4345%46%6%8%9%41%
1440
21st to endNight
12%6%25%5%35%6%8%9%40%
1574
August1st to 10thNight
12%425%4346%6%9%45%
1432
11th to 20thNight
12%7%36%43445%8%43%
1628
21st to endNight
13%6%26%5%345%6%8%42%
1980
September1st to 10thNight
13%6%35%6%35%46%6%43%
1800
11th to 20thNight
14%6%36%42345%7%46%
1870
21st to endNight
18%6%25%5%2445%7%41%
1980
October1st to 10thNight
20%7%26%5%345%7%6%35%
2106
11th to 20thNight
18%10%36%6%35%5%5%7%30%
2182
21st to endNight
24%13%46%5%3445%5%26%
2574
November1st to 10thNight
17%12%47%6%35%5%5%6%29%
2407
11th to 20thNight
17%11%5%9%6%45%5%45%29%
2531
21st to endNight
17%13%7%10%6%45%5%46%23%
2660
December1st to 10thNight
17%19%7%11%7%5%5%5%45%15%
2660
11th to 20thNight
18%17%7%12%6%35%445%19%
3288
21st to endNight
24%15%6%12%6%3444418%
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
71%38%14%4
1518
11th to 20thDay
71%26%11%9%1
1520
21st to endDay
64%311%13%8%1
1664
February1st to 10thDay
71%25%16%42
1606
11th to 20thDay
64%29%16%8%1
1678
21st to endDay
67%38%13%9%2
1480
March1st to 10thDay
64%29%14%9%2
1800
11th to 20thDay
59%310%13%13%3
1876
21st to endDay
56%16%19%14%3
2366
April1st to 10thDay
58%25%19%13%2
2160
11th to 20thDay
54%16%22%15%2
2134
21st to endDay
57%28%18%12%3
2286
May1st to 10thDay
54%27%20%16%2
2474
11th to 20thDay
49%37%24%16%2
2482
21st to endDay
48%413%21%13%2
2725
June1st to 10thDay
55%39%20%12%1
2520
11th to 20thDay
47%410%25%13%2
2520
21st to endDay
53%311%21%10%1
2520
July1st to 10thDay
42%412%29%12%1
2450
11th to 20thDay
44%413%31%8%
2445
21st to endDay
44%415%27%9%
2591
August1st to 10thDay
48%314%26%9%
2492
11th to 20thDay
43%416%27%10%
2253
21st to endDay
45%312%27%13%1
2376
September1st to 10thDay
41%411%29%14%
2160
11th to 20thDay
40%29%35%14%1
2089
21st to endDay
44%314%28%10%1
1980
October1st to 10thDay
53%49%22%11%
1852
11th to 20thDay
57%314%18%8%1
1778
21st to endDay
65%29%16%7%1
1782
November1st to 10thDay
55%212%21%8%1
1671
11th to 20thDay
60%310%16%9%2
1645
21st to endDay
67%311%13%5%
1520
December1st to 10thDay
72%311%12%2
1520
11th to 20thDay
67%310%15%5%
1906
21st to endDay
72%27%15%4
2772
January1st to 10thNight
72%28%13%5%
2649
11th to 20thNight
69%39%13%6%1
2660
21st to endNight
62%39%15%10%1
2919
February1st to 10thNight
70%38%12%6%1
2352
11th to 20thNight
62%210%16%9%
2179
21st to endNight
61%27%16%12%1
1776
March1st to 10thNight
64%28%15%10%1
2160
11th to 20thNight
59%28%18%10%2
2083
21st to endNight
56%26%20%13%3
1990
April1st to 10thNight
61%27%18%11%2
1800
11th to 20thNight
56%28%21%12%1
1775
21st to endNight
55%28%18%14%3
1674
May1st to 10thNight
55%26%17%16%3
1499
11th to 20thNight
48%28%21%18%3
1416
21st to endNight
44%315%21%15%2
1551
June1st to 10thNight
52%410%22%11%1
1440
11th to 20thNight
46%411%23%14%2
1440
21st to endNight
48%313%25%10%
1440
July1st to 10thNight
37%316%28%16%1
1400
11th to 20thNight
37%414%35%11%
1392
21st to endNight
39%5%17%27%12%1
1486
August1st to 10thNight
37%419%29%12%
1422
11th to 20thNight
41%317%26%13%1
1628
21st to endNight
41%316%28%12%1
1980
September1st to 10thNight
42%312%29%12%1
1800
11th to 20thNight
39%213%34%12%1
1870
21st to endNight
44%313%27%13%1
1980
October1st to 10thNight
48%311%26%11%1
2106
11th to 20thNight
54%213%21%10%
2182
21st to endNight
61%211%16%9%1
2574
November1st to 10thNight
56%211%19%10%1
2407
11th to 20thNight
59%310%18%8%3
2531
21st to endNight
64%313%16%5%
2660
December1st to 10thNight
73%38%13%3
2660
11th to 20thNight
69%37%14%6%
3288
21st to endNight
72%28%14%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
29%21%31%16%21
180
11th to 20thDay
32%27%29%8%3
180
21st to endDay
27%28%32%11%4
196
February1st to 10thDay
36%32%27%4
234
11th to 20thDay
31%27%34%7%1
336
21st to endDay
33%24%32%10%1
346
March1st to 10thDay
32%24%29%11%4
420
11th to 20thDay
29%28%30%10%31
420
21st to endDay
34%21%24%14%6%
462
April1st to 10thDay
35%19%31%11%4
420
11th to 20thDay
33%18%27%15%5%1
412
21st to endDay
32%18%30%14%5%1
420
May1st to 10thDay
31%18%31%13%5%2
423
11th to 20thDay
22%21%32%17%6%2
447
21st to endDay
22%18%32%21%6%2
485
June1st to 10thDay
31%15%31%16%5%2
450
11th to 20thDay
22%15%33%22%7%2
450
21st to endDay
26%15%31%19%7%2
450
July1st to 10thDay
18%10%32%27%10%3
445
11th to 20thDay
16%12%37%25%6%3
444
21st to endDay
15%11%42%22%7%2
488
August1st to 10thDay
17%12%32%25%12%2
446
11th to 20thDay
18%6%35%27%11%4
439
21st to endDay
19%15%28%23%11%4
495
September1st to 10thDay
18%12%34%20%13%4
450
11th to 20thDay
21%10%26%24%14%4
450
21st to endDay
15%17%31%25%9%3
450
October1st to 10thDay
26%16%29%17%11%2
450
11th to 20thDay
28%22%26%14%8%2
439
21st to endDay
38%16%27%15%4
396
November1st to 10thDay
34%19%26%14%6%1
365
11th to 20thDay
34%28%21%10%6%2
305
21st to endDay
33%23%27%12%4
180
December1st to 10thDay
36%22%26%12%4
180
11th to 20thDay
36%29%27%6%3
180
21st to endDay
32%32%21%11%4
198
January1st to 10thNight
27%26%35%9%2
760
11th to 20thNight
28%25%31%12%3
760
21st to endNight
20%26%34%15%5%
835
February1st to 10thNight
24%28%33%13%2
720
11th to 20thNight
23%30%32%14%1
703
21st to endNight
26%26%32%15%2
592
March1st to 10thNight
30%24%27%16%3
720
11th to 20thNight
27%26%28%16%21
720
21st to endNight
29%18%27%20%5%
792
April1st to 10thNight
32%20%29%16%4
720
11th to 20thNight
31%21%25%19%5%
711
21st to endNight
29%16%30%18%6%1
594
May1st to 10thNight
31%14%28%20%6%
419
11th to 20thNight
23%15%31%23%6%1
354
21st to endNight
19%14%37%21%10%1
389
June1st to 10thNight
28%11%31%22%7%1
360
11th to 20thNight
20%10%32%28%9%1
360
21st to endNight
21%10%34%25%10%1
360
July1st to 10thNight
12%11%37%28%10%1
350
11th to 20thNight
9%8%37%34%11%1
348
21st to endNight
15%9%37%29%10%1
394
August1st to 10thNight
14%8%29%34%14%1
358
11th to 20thNight
15%427%35%17%2
564
21st to endNight
17%9%30%29%13%1
792
September1st to 10thNight
17%10%33%28%11%2
720
11th to 20thNight
19%9%27%30%13%3
720
21st to endNight
22%10%29%22%15%2
720
October1st to 10thNight
26%15%28%18%12%1
720
11th to 20thNight
28%18%27%21%6%1
720
21st to endNight
33%19%29%16%4
792
November1st to 10thNight
29%21%28%17%5%1
740
11th to 20thNight
29%22%28%11%7%1
760
21st to endNight
29%25%25%16%5%1
760
December1st to 10thNight
32%24%27%14%3
760
11th to 20thNight
30%27%25%14%31
760
21st to endNight
33%25%26%12%3
836
Page generated at 2024-01-28 05:26:31. Version ac07

Copyright 2024 Attilla Danko


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