Hale Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hale Observatory clear sky chart from 2005-11-06 to 2024-01-14.

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
60%
24635
20%
74517
16%
24582
64%
24582
29%
46987

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
49%
758
22%
2459
17%
757
58%
757
30%
1431
January11th to 20thNight
50%
736
26%
2391
20%
736
60%
736
31%
1396
January21st to endNight
44%
792
24%
2488
18%
792
52%
792
28%
1522
February1st to 10thNight
46%
720
22%
2160
16%
720
53%
720
30%
1342
February11th to 20thNight
51%
700
26%
2098
18%
699
60%
699
38%
1158
February21st to endNight
53%
592
31%
1650
21%
592
61%
592
41%
930
March1st to 10thNight
53%
720
32%
1980
20%
720
63%
720
48%
1053
March11th to 20thNight
55%
720
30%
1980
19%
720
64%
720
42%
1115
March21st to endNight
57%
792
31%
2178
22%
792
64%
792
45%
1198
April1st to 10thNight
59%
720
24%
1980
19%
720
63%
720
45%
1085
April11th to 20thNight
57%
711
21%
1927
15%
711
62%
711
40%
1138
April21st to endNight
60%
720
29%
1800
18%
720
65%
720
45%
1062
May1st to 10thNight
68%
658
28%
1738
20%
658
72%
658
48%
959
May11th to 20thNight
72%
531
15%
1592
12%
531
74%
531
33%
991
May21st to endNight
72%
582
21%
1744
18%
582
74%
582
32%
1098
June1st to 10thNight
67%
540
13%
1620
12%
540
67%
540
23%
1141
June11th to 20thNight
70%
540
10%
1620
10%
540
70%
540
24%
1144
June21st to endNight
73%
540
8%
1620
8%
540
73%
540
21%
1184
July1st to 10thNight
70%
525
4%
1575
4%
525
70%
525
21%
1180
July11th to 20thNight
75%
522
5%
1566
6%
522
75%
522
20%
1180
July21st to endNight
73%
591
7%
1672
7%
558
73%
558
20%
1261
August1st to 10thNight
77%
537
5%
1600
5%
534
77%
534
23%
1140
August11th to 20thNight
73%
594
4%
1730
5%
594
73%
594
22%
1231
August21st to endNight
60%
792
6%
2178
6%
792
60%
792
17%
1668
September1st to 10thNight
63%
720
6%
1980
6%
720
64%
720
17%
1506
September11th to 20thNight
58%
720
6%
1980
7%
720
58%
720
19%
1476
September21st to endNight
58%
720
14%
1980
12%
720
59%
720
21%
1426
October1st to 10thNight
61%
720
20%
1998
19%
720
64%
720
27%
1335
October11th to 20thNight
66%
720
26%
2160
28%
720
69%
720
33%
1312
October21st to endNight
62%
792
27%
2376
25%
792
67%
792
35%
1382
November1st to 10thNight
57%
740
26%
2221
21%
740
64%
740
34%
1302
November11th to 20thNight
57%
760
28%
2280
25%
760
63%
760
33%
1366
November21st to endNight
55%
760
28%
2320
24%
760
63%
760
33%
1362
December1st to 10thNight
59%
760
27%
2470
25%
760
66%
760
34%
1404
December11th to 20thNight
55%
760
24%
2938
22%
758
60%
758
25%
1686
December21st to endNight
53%
830
14%
4468
20%
817
59%
817
16%
2823

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
8%5%37%7%5%6%6%7%9%37%
74873
Night
8%5%36%6%35%5%6%9%43%
74894
TransparencyDay
41%8%15%18%13%5%
74596
Night
36%8%16%20%14%5%
74690
SeeingDay
8%316%24%25%23%
14515
Night
9%318%34%28%9%
24648

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
9%5%46%5%345%7%8%44%
1706
11th to 20thDay
7%425%5%45%5%7%10%47%
1647
21st to endDay
11%6%35%5%345%6%8%43%
1863
February1st to 10thDay
11%6%26%5%35%5%6%8%45%
1800
11th to 20thDay
5%425%5%35%6%6%6%54%
1748
21st to endDay
8%5%26%5%46%45%8%48%
1605
March1st to 10thDay
43135%36%6%5%8%56%
1980
11th to 20thDay
7%3245%45%6%5%8%51%
1980
21st to endDay
6%3245%35%5%6%7%53%
2178
April1st to 10thDay
5%4246%46%6%7%9%48%
1980
11th to 20thDay
7%5%26%7%5%7%6%7%9%39%
1982
21st to endDay
5%414445%6%7%9%49%
2160
May1st to 10thDay
5%3245%35%5%6%9%54%
2235
11th to 20thDay
8%5%27%7%5%6%8%6%8%38%
2301
21st to endDay
7%5%48%8%5%7%7%7%9%35%
2531
June1st to 10thDay
12%9%49%8%5%8%7%8%9%21%
2340
11th to 20thDay
8%6%39%9%6%8%7%8%11%26%
2340
21st to endDay
8%7%39%9%6%8%8%7%9%25%
2340
July1st to 10thDay
9%6%310%10%5%9%8%8%9%24%
2340
11th to 20thDay
6%6%49%10%6%9%8%8%12%22%
2340
21st to endDay
8%6%38%10%6%10%8%8%10%23%
2547
August1st to 10thDay
6%439%9%6%9%9%10%11%25%
2327
11th to 20thDay
5%5%37%11%7%8%9%9%12%23%
2145
21st to endDay
9%8%410%9%6%7%7%8%10%22%
2178
September1st to 10thDay
7%7%48%8%6%7%8%9%11%24%
1980
11th to 20thDay
9%7%49%10%6%7%9%8%10%22%
1980
21st to endDay
8%7%39%8%5%7%7%7%9%28%
1980
October1st to 10thDay
9%6%37%7%46%6%7%8%36%
1960
11th to 20thDay
6%5%35%7%47%6%5%9%42%
1800
21st to endDay
8%5%25%6%445%6%10%46%
1980
November1st to 10thDay
7%435%5%45%46%9%48%
1857
11th to 20thDay
9%5%27%5%46%5%6%8%42%
1900
21st to endDay
8%6%36%5%36%5%6%9%43%
1856
December1st to 10thDay
6%436%7%46%5%6%8%45%
1710
11th to 20thDay
10%6%36%7%35%45%8%43%
2153
21st to endDay
10%7%47%8%46%7%6%7%34%
3124
January1st to 10thNight
9%6%25%4345%6%9%46%
2459
11th to 20thNight
9%6%25%435%5%6%10%46%
2391
21st to endNight
11%6%35%5%45%5%6%7%45%
2488
February1st to 10thNight
10%6%36%5%3446%8%45%
2160
11th to 20thNight
8%5%2443446%8%53%
2098
21st to endNight
5%5%2443446%10%52%
1650
March1st to 10thNight
431443445%8%59%
1980
11th to 20thNight
5%425%42445%8%56%
1980
21st to endNight
5%32442445%8%58%
2178
April1st to 10thNight
5%3235%2446%9%56%
1980
11th to 20thNight
5%425%5%345%7%10%50%
1927
21st to endNight
5%32343446%7%57%
1800
May1st to 10thNight
432442446%7%61%
1738
11th to 20thNight
7%425%5%46%5%7%9%46%
1592
21st to endNight
6%5%26%6%46%5%5%10%44%
1744
June1st to 10thNight
10%7%28%7%46%6%8%10%32%
1620
11th to 20thNight
6%6%37%8%5%6%8%8%13%30%
1620
21st to endNight
6%5%37%8%5%6%7%8%11%33%
1620
July1st to 10thNight
8%8%5%7%7%47%6%8%12%28%
1620
11th to 20thNight
5%5%38%8%5%8%8%8%13%31%
1620
21st to endNight
5%6%39%9%5%7%8%8%12%28%
1771
August1st to 10thNight
6%5%36%7%5%7%6%9%13%34%
1611
11th to 20thNight
6%437%8%5%6%8%8%13%32%
1730
21st to endNight
9%8%39%7%5%7%6%8%10%28%
2178
September1st to 10thNight
7%6%37%8%47%9%9%12%28%
1980
11th to 20thNight
9%7%49%9%6%6%6%8%10%28%
1980
21st to endNight
11%8%38%7%5%6%6%7%8%32%
1980
October1st to 10thNight
10%7%26%6%36%5%7%8%40%
1998
11th to 20thNight
7%6%35%5%345%5%8%48%
2160
21st to endNight
9%5%25%43445%9%50%
2376
November1st to 10thNight
9%5%245%445%5%8%50%
2221
11th to 20thNight
8%5%35%6%35%5%5%8%48%
2280
21st to endNight
9%6%26%5%345%6%9%45%
2320
December1st to 10thNight
6%435%5%35%5%6%8%50%
2470
11th to 20thNight
12%6%245%3445%8%47%
3042
21st to endNight
11%7%37%6%45%6%6%8%36%
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
36%6%9%23%19%8%
1707
11th to 20thDay
31%5%8%26%21%8%
1647
21st to endDay
39%49%19%20%9%
1863
February1st to 10thDay
37%5%10%20%20%9%
1800
11th to 20thDay
28%5%9%23%23%12%
1758
21st to endDay
34%5%10%17%25%9%
1605
March1st to 10thDay
26%5%11%25%24%9%
1980
11th to 20thDay
30%5%10%27%19%9%
1980
21st to endDay
29%49%26%22%9%
2178
April1st to 10thDay
30%6%17%24%17%6%
1980
11th to 20thDay
40%6%12%18%19%5%
1982
21st to endDay
30%7%10%22%23%8%
2160
May1st to 10thDay
27%5%13%22%24%9%
2235
11th to 20thDay
40%7%15%20%16%2
2305
21st to endDay
45%7%13%19%14%1
2531
June1st to 10thDay
58%7%17%14%4
2340
11th to 20thDay
49%10%21%16%2
2340
21st to endDay
53%11%22%12%21
2340
July1st to 10thDay
53%13%26%7%2
2275
11th to 20thDay
52%12%26%9%1
2271
21st to endDay
52%12%24%11%1
2405
August1st to 10thDay
46%13%32%9%1
2314
11th to 20thDay
48%14%27%10%1
2145
21st to endDay
54%13%22%9%2
2178
September1st to 10thDay
48%14%22%14%1
1980
11th to 20thDay
54%13%20%11%3
1980
21st to endDay
49%12%16%13%9%1
1980
October1st to 10thDay
42%9%14%18%12%6%
1960
11th to 20thDay
38%6%10%23%19%4
1800
21st to endDay
34%6%11%19%21%10%
1980
November1st to 10thDay
32%7%11%20%18%11%
1857
11th to 20thDay
38%7%9%22%17%8%
1900
21st to endDay
37%6%11%21%19%7%
1856
December1st to 10thDay
35%5%14%24%18%5%
1710
11th to 20thDay
38%5%10%20%16%11%
2150
21st to endDay
46%6%11%17%15%4
3124
January1st to 10thNight
35%5%12%21%19%8%
2459
11th to 20thNight
34%5%9%27%18%6%
2391
21st to endNight
39%410%21%16%9%
2488
February1st to 10thNight
38%5%12%18%19%9%
2160
11th to 20thNight
28%5%9%23%24%10%
2099
21st to endNight
27%5%14%21%27%6%
1650
March1st to 10thNight
22%5%13%30%23%8%
1980
11th to 20thNight
26%5%13%30%18%7%
1980
21st to endNight
24%6%12%28%23%8%
2178
April1st to 10thNight
24%5%19%29%16%7%
1980
11th to 20thNight
28%7%16%23%21%5%
1927
21st to endNight
26%6%12%26%24%6%
1800
May1st to 10thNight
23%5%12%28%23%9%
1738
11th to 20thNight
33%8%21%23%12%1
1593
21st to endNight
35%8%17%22%18%1
1745
June1st to 10thNight
45%9%23%18%5%
1620
11th to 20thNight
42%12%27%17%3
1620
21st to endNight
42%15%24%14%5%
1620
July1st to 10thNight
46%13%30%10%1
1575
11th to 20thNight
43%17%28%11%1
1566
21st to endNight
45%15%27%12%1
1672
August1st to 10thNight
38%16%34%12%
1600
11th to 20thNight
40%15%36%8%1
1730
21st to endNight
48%15%24%11%1
2178
September1st to 10thNight
45%18%24%11%2
1980
11th to 20thNight
49%12%23%15%2
1980
21st to endNight
48%9%18%15%9%1
1980
October1st to 10thNight
39%9%14%19%13%5%
1998
11th to 20thNight
33%7%12%22%22%4
2160
21st to endNight
31%6%12%20%21%10%
2376
November1st to 10thNight
32%6%11%21%21%9%
2221
11th to 20thNight
33%7%10%26%16%8%
2280
21st to endNight
34%5%10%22%22%6%
2320
December1st to 10thNight
31%5%14%28%16%6%
2470
11th to 20thNight
36%5%11%21%16%12%
3044
21st to endNight
45%7%13%16%14%5%
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
10%8%39%29%13%2
270
11th to 20thDay
7%10%30%33%15%6%
249
21st to endDay
15%9%42%24%9%
264
February1st to 10thDay
8%10%28%32%18%4
240
11th to 20thDay
7%5%29%32%20%8%
240
21st to endDay
9%424%33%25%4
323
March1st to 10thDay
4433%37%19%3
420
11th to 20thDay
8%6%25%29%26%5%
420
21st to endDay
5%424%34%27%6%
462
April1st to 10thDay
47%29%34%21%5%
420
11th to 20thDay
6%6%23%35%21%9%
412
21st to endDay
6%218%34%27%13%
420
May1st to 10thDay
4216%28%36%14%
423
11th to 20thDay
9%113%25%30%21%
447
21st to endDay
8%19%18%33%30%
485
June1st to 10thDay
15%113%17%26%28%
450
11th to 20thDay
10%25%14%31%39%
450
21st to endDay
6%1411%24%54%
450
July1st to 10thDay
7%1310%19%60%
445
11th to 20thDay
41212%23%57%
444
21st to endDay
8%1415%19%53%
488
August1st to 10thDay
6%1412%25%53%
446
11th to 20thDay
5%38%25%59%
439
21st to endDay
9%18%15%24%42%
495
September1st to 10thDay
6%35%14%24%48%
450
11th to 20thDay
8%28%14%32%37%
450
21st to endDay
9%15%19%36%30%
450
October1st to 10thDay
10%312%32%33%11%
450
11th to 20thDay
5%416%31%31%14%
450
21st to endDay
7%316%31%34%8%
495
November1st to 10thDay
7%6%19%31%29%9%
455
11th to 20thDay
13%5%20%33%25%3
460
21st to endDay
11%322%36%24%4
416
December1st to 10thDay
6%6%29%32%18%10%
270
11th to 20thDay
10%6%27%34%19%4
270
21st to endDay
9%6%25%33%21%5%
297
January1st to 10thNight
11%7%26%40%16%1
760
11th to 20thNight
10%5%27%43%13%1
736
21st to endNight
14%6%31%38%10%1
792
February1st to 10thNight
13%5%28%39%14%
720
11th to 20thNight
9%7%27%41%15%1
703
21st to endNight
8%329%45%14%
592
March1st to 10thNight
45%33%44%13%1
720
11th to 20thNight
7%5%28%42%18%1
720
21st to endNight
6%427%46%17%1
792
April1st to 10thNight
5%425%47%18%
720
11th to 20thNight
6%328%45%17%1
711
21st to endNight
6%325%44%21%
720
May1st to 10thNight
5%218%50%24%2
658
11th to 20thNight
8%111%42%34%5%
531
21st to endNight
6%210%32%45%6%
584
June1st to 10thNight
11%17%28%44%9%
540
11th to 20thNight
6%15%17%46%24%
540
21st to endNight
7%1314%45%31%
540
July1st to 10thNight
8%129%46%33%
525
11th to 20thNight
6%1210%43%39%
522
21st to endNight
5%311%44%36%
591
August1st to 10thNight
6%138%47%35%
537
11th to 20thNight
5%239%45%36%
594
21st to endNight
12%17%20%36%24%
792
September1st to 10thNight
9%16%17%40%27%
720
11th to 20thNight
10%28%22%41%18%
720
21st to endNight
14%28%23%40%13%
720
October1st to 10thNight
13%213%38%28%6%
720
11th to 20thNight
9%213%36%35%4
720
21st to endNight
10%220%39%27%3
792
November1st to 10thNight
10%223%37%25%3
740
11th to 20thNight
9%422%41%23%2
760
21st to endNight
11%224%44%17%1
760
December1st to 10thNight
8%423%38%26%1
760
11th to 20thNight
10%423%38%23%2
760
21st to endNight
9%5%25%39%21%1
836
Page generated at 2024-01-11 13:32:01. Version ac07

Copyright 2024 Attilla Danko


Hale Observatory Clear Sky Chart |Charts Home