Hazard
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hazard clear sky chart from 2005-11-06 to 2024-01-16.

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%
23903
19%
74577
14%
23850
48%
23850
22%
49715

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
19%
760
15%
2459
7%
757
29%
757
12%
1809
January11th to 20thNight
19%
744
15%
2417
9%
744
28%
744
11%
1853
January21st to endNight
19%
792
17%
2574
7%
792
31%
792
15%
1836
February1st to 10thNight
21%
720
14%
2264
6%
720
31%
720
14%
1658
February11th to 20thNight
13%
703
13%
2099
5%
700
21%
700
12%
1587
February21st to endNight
15%
592
16%
1776
7%
592
25%
592
13%
1349
March1st to 10thNight
24%
720
19%
2074
9%
720
32%
720
19%
1442
March11th to 20thNight
24%
720
16%
1980
7%
720
32%
720
19%
1413
March21st to endNight
28%
792
14%
2178
8%
792
32%
792
18%
1583
April1st to 10thNight
34%
720
20%
1980
10%
720
43%
720
25%
1289
April11th to 20thNight
36%
533
23%
1692
14%
533
47%
533
24%
1062
April21st to endNight
34%
540
21%
1620
10%
540
44%
540
25%
1059
May1st to 10thNight
39%
540
15%
1620
9%
540
44%
540
22%
1084
May11th to 20thNight
48%
531
16%
1593
11%
531
51%
531
22%
1090
May21st to endNight
60%
582
17%
1744
13%
582
62%
582
29%
1104
June1st to 10thNight
63%
540
17%
1620
15%
540
65%
540
31%
986
June11th to 20thNight
65%
540
17%
1620
15%
540
67%
540
35%
960
June21st to endNight
60%
540
18%
1620
17%
540
62%
540
29%
1024
July1st to 10thNight
61%
525
13%
1575
12%
525
62%
525
26%
1029
July11th to 20thNight
69%
522
17%
1566
15%
522
71%
522
33%
950
July21st to endNight
65%
591
17%
1672
16%
558
67%
558
29%
1052
August1st to 10thNight
71%
537
19%
1600
18%
534
71%
534
33%
972
August11th to 20thNight
67%
534
19%
1598
18%
534
68%
534
29%
1012
August21st to endNight
69%
594
24%
1908
25%
594
70%
594
33%
1101
September1st to 10thNight
64%
712
22%
1972
19%
712
66%
712
34%
1224
September11th to 20thNight
59%
720
25%
1980
20%
720
61%
720
31%
1271
September21st to endNight
59%
720
27%
1980
22%
720
64%
720
34%
1215
October1st to 10thNight
57%
720
27%
1993
24%
720
60%
720
36%
1196
October11th to 20thNight
45%
720
26%
2160
22%
720
52%
720
29%
1334
October21st to endNight
40%
792
27%
2376
22%
792
50%
792
26%
1514
November1st to 10thNight
46%
740
27%
2401
24%
740
54%
740
30%
1420
November11th to 20thNight
35%
760
26%
2470
17%
760
48%
760
24%
1513
November21st to endNight
39%
760
24%
2470
16%
760
50%
760
24%
1569
December1st to 10thNight
25%
760
15%
2470
8%
760
34%
760
13%
1824
December11th to 20thNight
27%
759
18%
2987
11%
759
36%
759
12%
2103
December21st to endNight
24%
828
10%
4469
9%
817
33%
817
7%
3228

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
15%8%36%6%35%5%6%7%36%
74919
Night
15%8%36%5%345%5%7%38%
74902
TransparencyDay
47%5%10%22%14%2
74642
Night
46%410%21%15%3
74698
SeeingDay
21%12%23%22%15%7%
13782
Night
20%10%21%28%17%3
23914

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%10%6%10%6%3445%6%29%
1706
11th to 20thDay
20%15%6%9%6%3443427%
1671
21st to endDay
16%13%6%7%5%24336%35%
1782
February1st to 10thDay
19%13%5%8%5%2445%6%29%
1692
11th to 20thDay
22%10%5%8%5%35%45%5%28%
1748
21st to endDay
21%12%48%6%34445%30%
1480
March1st to 10thDay
17%11%345%25%45%6%38%
1885
11th to 20thDay
21%8%5%7%6%35%45%6%30%
1980
21st to endDay
19%10%46%5%3445%6%33%
2178
April1st to 10thDay
15%6%36%6%25%46%8%39%
1995
11th to 20thDay
17%7%36%43345%6%42%
2215
21st to endDay
18%6%36%5%35%5%5%7%37%
2340
May1st to 10thDay
17%8%27%7%45%5%6%8%32%
2340
11th to 20thDay
17%7%37%5%46%5%5%6%34%
2301
21st to endDay
12%5%25%6%46%6%7%10%36%
2531
June1st to 10thDay
11%5%35%6%36%7%6%10%38%
2340
11th to 20thDay
8%6%36%6%46%6%7%9%39%
2340
21st to endDay
9%5%36%7%46%5%7%10%38%
2340
July1st to 10thDay
12%5%36%7%46%6%7%8%35%
2340
11th to 20thDay
11%6%26%6%47%6%7%10%34%
2340
21st to endDay
13%6%36%7%46%6%7%9%33%
2547
August1st to 10thDay
11%6%35%7%46%7%8%10%32%
2327
11th to 20thDay
13%5%36%7%47%7%7%9%32%
2303
21st to endDay
10%5%26%6%46%6%7%10%38%
2432
September1st to 10thDay
14%5%245%45%5%6%7%42%
1980
11th to 20thDay
14%5%26%5%35%5%5%7%43%
1980
21st to endDay
17%6%25%5%2445%6%44%
1980
October1st to 10thDay
14%435%5%3445%6%49%
1967
11th to 20thDay
15%5%35%5%3335%6%48%
1800
21st to endDay
19%8%2442335%7%43%
1980
November1st to 10thDay
12%6%34423446%51%
1672
11th to 20thDay
14%10%25%424446%43%
1710
21st to endDay
16%10%45%323446%41%
1710
December1st to 10thDay
21%12%47%6%34446%30%
1710
11th to 20thDay
17%13%38%5%2446%6%33%
2153
21st to endDay
15%18%46%5%46%46%7%24%
3124
January1st to 10thNight
17%12%5%9%6%34435%31%
2459
11th to 20thNight
21%13%6%8%6%345%45%25%
2417
21st to endNight
17%13%5%8%5%34445%33%
2574
February1st to 10thNight
18%11%5%8%6%3445%6%30%
2264
11th to 20thNight
24%11%5%7%5%4444429%
2098
21st to endNight
22%13%47%4345%5%6%26%
1776
March1st to 10thNight
17%11%36%5%35%435%38%
2074
11th to 20thNight
19%10%45%5%25%46%8%32%
1980
21st to endNight
16%10%37%7%35%5%46%33%
2178
April1st to 10thNight
13%7%25%5%35%45%7%44%
1980
11th to 20thNight
15%7%25%5%345%5%8%41%
1692
21st to endNight
16%7%25%5%35%46%7%40%
1620
May1st to 10thNight
17%6%35%7%345%6%8%37%
1620
11th to 20thNight
15%6%35%6%35%6%7%9%36%
1592
21st to endNight
8%5%26%6%45%5%8%11%40%
1744
June1st to 10thNight
9%425%5%346%9%10%43%
1620
11th to 20thNight
5%325%6%45%7%7%10%46%
1620
21st to endNight
9%436%5%35%6%7%11%41%
1620
July1st to 10thNight
11%6%26%5%45%7%6%9%38%
1620
11th to 20thNight
6%425%5%45%6%8%12%43%
1620
21st to endNight
10%426%6%47%6%6%10%39%
1771
August1st to 10thNight
10%5%25%5%35%5%7%10%44%
1611
11th to 20thNight
11%426%5%45%6%8%10%39%
1598
21st to endNight
9%435%5%25%5%7%9%47%
1908
September1st to 10thNight
11%5%36%43447%8%46%
1972
11th to 20thNight
13%6%36%5%3445%8%45%
1980
21st to endNight
12%5%245%245%6%6%49%
1980
October1st to 10thNight
13%42442345%7%52%
1993
11th to 20thNight
18%7%24423345%47%
2160
21st to endNight
18%7%245%34446%44%
2376
November1st to 10thNight
14%7%35%433346%50%
2401
11th to 20thNight
16%7%34424447%44%
2470
21st to endNight
15%9%35%33445%6%43%
2470
December1st to 10thNight
21%13%5%8%4245%5%5%28%
2470
11th to 20thNight
19%13%5%8%5%24445%32%
3042
21st to endNight
18%15%47%6%45%5%5%8%21%
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
57%38%18%13%2
1707
11th to 20thDay
63%28%16%9%1
1671
21st to endDay
53%28%22%13%1
1782
February1st to 10thDay
57%47%18%13%1
1692
11th to 20thDay
59%36%19%11%2
1758
21st to endDay
58%37%16%11%4
1480
March1st to 10thDay
48%29%22%16%3
1885
11th to 20thDay
56%48%18%11%3
1980
21st to endDay
51%49%25%11%1
2178
April1st to 10thDay
43%411%24%15%4
1995
11th to 20thDay
43%38%21%20%5%
2215
21st to endDay
47%410%25%12%2
2340
May1st to 10thDay
50%411%22%10%2
2340
11th to 20thDay
51%6%12%21%9%1
2305
21st to endDay
40%9%15%24%11%2
2531
June1st to 10thDay
41%7%12%24%14%1
2340
11th to 20thDay
41%7%14%19%17%2
2340
21st to endDay
40%7%13%20%17%3
2340
July1st to 10thDay
45%7%13%19%14%1
2275
11th to 20thDay
41%9%15%20%13%3
2271
21st to endDay
45%7%14%23%10%1
2405
August1st to 10thDay
44%8%17%20%10%
2314
11th to 20thDay
47%7%13%22%11%1
2303
21st to endDay
41%7%13%22%14%2
2432
September1st to 10thDay
40%6%12%22%15%5%
1980
11th to 20thDay
41%5%11%25%17%2
1980
21st to endDay
40%38%24%22%2
1980
October1st to 10thDay
37%410%22%23%3
1967
11th to 20thDay
39%39%24%22%4
1800
21st to endDay
44%26%26%18%4
1980
November1st to 10thDay
35%38%25%25%5%
1672
11th to 20thDay
44%25%24%19%5%
1710
21st to endDay
45%38%22%18%3
1710
December1st to 10thDay
58%38%20%10%1
1710
11th to 20thDay
53%310%17%16%2
2150
21st to endDay
60%38%22%7%
3124
January1st to 10thNight
59%37%17%12%2
2459
11th to 20thNight
63%27%14%11%2
2417
21st to endNight
55%39%21%10%2
2574
February1st to 10thNight
56%410%18%10%1
2264
11th to 20thNight
60%36%17%11%3
2099
21st to endNight
60%38%15%11%3
1776
March1st to 10thNight
50%37%17%20%3
2074
11th to 20thNight
52%310%22%11%2
1980
21st to endNight
52%5%9%20%11%2
2178
April1st to 10thNight
41%5%10%24%18%3
1980
11th to 20thNight
42%39%21%17%7%
1692
21st to endNight
44%412%26%12%1
1620
May1st to 10thNight
46%6%14%20%12%2
1620
11th to 20thNight
44%9%13%24%10%1
1593
21st to endNight
37%8%15%25%14%2
1745
June1st to 10thNight
34%8%18%23%16%3
1620
11th to 20thNight
30%8%20%23%17%2
1620
21st to endNight
36%8%15%23%15%4
1620
July1st to 10thNight
41%7%14%22%13%3
1575
11th to 20thNight
33%7%20%21%15%4
1566
21st to endNight
37%7%17%26%12%1
1672
August1st to 10thNight
35%6%19%25%14%1
1600
11th to 20thNight
38%7%17%23%14%1
1598
21st to endNight
32%6%14%29%17%2
1908
September1st to 10thNight
35%5%14%22%18%6%
1972
11th to 20thNight
38%6%9%23%22%2
1980
21st to endNight
34%5%8%25%24%3
1980
October1st to 10thNight
33%410%23%23%6%
1993
11th to 20thNight
40%37%24%22%4
2160
21st to endNight
42%35%23%21%5%
2376
November1st to 10thNight
38%37%22%25%6%
2401
11th to 20thNight
41%37%21%22%6%
2470
21st to endNight
43%37%26%17%3
2470
December1st to 10thNight
59%38%17%10%2
2470
11th to 20thNight
56%27%19%14%2
3044
21st to endNight
62%39%15%11%1
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
26%29%27%14%41
270
11th to 20thDay
39%25%21%12%2
257
21st to endDay
32%28%27%9%4
264
February1st to 10thDay
33%26%26%12%21
240
11th to 20thDay
44%28%20%8%1
240
21st to endDay
39%24%29%7%1
198
March1st to 10thDay
29%22%31%15%3
325
11th to 20thDay
27%24%28%17%31
420
21st to endDay
32%17%27%16%7%
462
April1st to 10thDay
27%16%27%19%9%1
420
11th to 20thDay
23%16%30%19%9%2
412
21st to endDay
25%17%27%18%9%3
420
May1st to 10thDay
27%15%26%18%8%5%
423
11th to 20thDay
19%13%26%24%13%5%
447
21st to endDay
14%7%23%24%20%12%
485
June1st to 10thDay
13%6%25%27%19%10%
450
11th to 20thDay
10%8%22%26%24%10%
450
21st to endDay
9%5%32%24%20%10%
450
July1st to 10thDay
15%5%17%26%20%18%
445
11th to 20thDay
8%6%16%32%22%16%
444
21st to endDay
13%5%15%31%24%11%
488
August1st to 10thDay
15%416%27%25%12%
446
11th to 20thDay
15%418%26%27%10%
439
21st to endDay
12%313%30%28%15%
495
September1st to 10thDay
15%413%24%32%12%
450
11th to 20thDay
16%211%27%29%14%
450
21st to endDay
18%8%19%28%20%8%
450
October1st to 10thDay
17%8%18%26%22%9%
450
11th to 20thDay
18%11%27%25%15%4
450
21st to endDay
27%11%25%23%11%3
495
November1st to 10thDay
20%14%30%21%11%4
270
11th to 20thDay
26%14%33%16%10%1
270
21st to endDay
24%16%30%20%7%1
270
December1st to 10thDay
32%20%28%15%41
270
11th to 20thDay
28%17%29%19%7%1
270
21st to endDay
33%20%29%13%5%
297
January1st to 10thNight
28%21%28%20%4
760
11th to 20thNight
32%20%24%20%4
744
21st to endNight
25%18%33%22%2
792
February1st to 10thNight
26%18%30%24%2
720
11th to 20thNight
34%19%31%14%1
703
21st to endNight
35%17%29%16%2
592
March1st to 10thNight
27%16%29%23%4
720
11th to 20thNight
26%17%29%21%7%1
720
21st to endNight
22%16%28%26%8%
792
April1st to 10thNight
22%15%26%28%9%
720
11th to 20thNight
20%11%28%27%12%1
533
21st to endNight
20%7%33%30%9%1
540
May1st to 10thNight
19%9%26%30%14%2
540
11th to 20thNight
18%5%21%34%20%2
531
21st to endNight
9%318%34%27%8%
584
June1st to 10thNight
11%414%38%29%4
540
11th to 20thNight
6%216%38%32%6%
540
21st to endNight
10%217%37%29%5%
540
July1st to 10thNight
15%29%30%36%8%
525
11th to 20thNight
8%211%30%43%6%
522
21st to endNight
13%28%33%38%7%
591
August1st to 10thNight
11%38%31%40%7%
537
11th to 20thNight
13%18%35%36%7%
534
21st to endNight
10%29%30%39%10%
594
September1st to 10thNight
13%310%30%38%6%
712
11th to 20thNight
15%212%30%35%5%
720
21st to endNight
14%417%35%26%4
720
October1st to 10thNight
14%6%17%30%28%5%
720
11th to 20thNight
22%8%19%33%16%2
720
21st to endNight
22%9%23%30%14%1
792
November1st to 10thNight
17%10%22%32%16%3
740
11th to 20thNight
20%15%25%30%10%1
760
21st to endNight
23%12%23%31%11%
760
December1st to 10thNight
30%16%24%24%5%
760
11th to 20thNight
24%18%25%27%6%1
760
21st to endNight
29%17%24%27%4
836
Page generated at 2024-01-13 19:28:29. Version ac07

Copyright 2024 Attilla Danko


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