Hale Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hale Observatory clear sky chart from 2005-11-05 to 2017-09-24.

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
61%
16046
20%
47023
16%
16006
65%
16006
30%
29694

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
50%
717
20%
2327
16%
716
58%
716
27%
1423
January16th to endNight
48%
768
25%
2439
19%
768
56%
768
30%
1452
February1st to 15thNight
47%
701
23%
2103
16%
698
55%
698
33%
1274
February16th to endNight
50%
631
28%
1809
17%
631
61%
631
39%
1016
March1st to 15thNight
53%
720
31%
1980
18%
720
63%
720
44%
1093
March16th to endNight
58%
768
27%
2112
20%
768
63%
768
42%
1185
April1st to 15thNight
62%
718
23%
1976
19%
718
66%
718
44%
1092
April16th to endNight
62%
720
28%
1842
17%
720
67%
720
44%
1082
May1st to 15thNight
69%
617
27%
1697
19%
617
73%
617
42%
983
May16th to endNight
77%
561
21%
1682
17%
561
78%
561
35%
1023
June1st to 15thNight
68%
540
10%
1620
9%
540
68%
540
21%
1170
June16th to endNight
71%
540
7%
1620
7%
540
71%
540
21%
1204
July1st to 15thNight
70%
510
6%
1530
6%
510
70%
510
20%
1165
July16th to endNight
75%
564
7%
1595
7%
531
75%
531
20%
1186
August1st to 15thNight
78%
539
5%
1609
6%
536
77%
536
25%
1113
August16th to endNight
63%
747
6%
2073
5%
747
63%
747
18%
1548
September1st to 15thNight
61%
720
5%
1980
6%
720
61%
720
16%
1512
September16th to endNight
58%
693
11%
1914
10%
693
59%
693
19%
1404
October1st to 15thNight
68%
660
24%
1881
25%
660
70%
660
32%
1174
October16th to endNight
61%
704
26%
2112
24%
704
66%
704
32%
1279
November1st to 15thNight
63%
700
31%
2101
28%
700
69%
700
38%
1172
November16th to endNight
56%
720
30%
2185
26%
720
64%
720
34%
1273
December1st to 15thNight
57%
720
25%
2340
24%
720
62%
720
29%
1407
December16th to endNight
57%
768
22%
2496
22%
768
62%
768
31%
1464

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%46%6%6%8%35%
47888
Night
7%5%25%5%35%5%6%9%43%
47232
TransparencyDay
44%7%13%16%12%5%
47589
Night
35%7%16%20%14%5%
47035
SeeingDay
9%111%20%25%30%
5886
Night
9%215%33%29%9%
16055

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 15thDay
10%5%36%5%346%7%8%37%
1611
16th to endDay
9%4245%3446%8%45%
1782
February1st to 15thDay
10%5%25%5%245%5%5%46%
1750
16th to endDay
7%426%5%45%45%6%47%
1663
March1st to 15thDay
5%3136%36%5%5%7%51%
1980
16th to endDay
7%325%5%35%5%5%8%47%
2111
April1st to 15thDay
5%4146%46%6%7%9%42%
1972
16th to endDay
6%415%5%46%6%6%7%44%
2118
May1st to 15thDay
5%325%5%46%6%5%7%45%
2262
16th to endDay
6%438%8%5%7%6%7%8%33%
2431
June1st to 15thDay
12%8%49%8%5%7%6%7%8%21%
2340
16th to endDay
8%7%39%9%6%8%7%6%9%22%
2340
July1st to 15thDay
8%6%411%10%5%9%7%7%7%19%
2340
16th to endDay
9%6%38%11%6%9%7%7%9%19%
2465
August1st to 15thDay
6%5%39%10%5%9%8%8%10%22%
2340
16th to endDay
10%7%39%9%6%7%8%7%9%20%
2113
September1st to 15thDay
8%7%48%9%5%7%8%7%9%22%
1980
16th to endDay
10%8%310%8%5%7%7%7%8%20%
1905
October1st to 15thDay
8%5%26%7%47%6%6%8%36%
1747
16th to endDay
8%425%6%45%5%5%7%43%
1760
November1st to 15thDay
5%335%5%46%5%6%8%47%
1757
16th to endDay
7%5%27%5%36%5%5%7%43%
1773
December1st to 15thDay
9%6%46%6%45%447%39%
1620
16th to endDay
6%435%5%446%6%8%43%
1728
January1st to 15thNight
8%6%26%5%35%5%6%9%40%
2327
16th to endNight
10%5%2443445%8%44%
2439
February1st to 15thNight
10%435%5%2445%6%47%
2103
16th to endNight
5%41442446%9%51%
1809
March1st to 15thNight
431443445%7%55%
1980
16th to endNight
5%31441345%8%56%
2112
April1st to 15thNight
42135%2446%8%56%
1976
16th to endNight
5%31342446%8%54%
1842
May1st to 15thNight
3314425%45%7%56%
1697
16th to endNight
5%3145%36%5%7%10%45%
1682
June1st to 15thNight
8%7%27%7%5%6%7%9%11%27%
1620
16th to endNight
6%5%38%7%5%6%7%7%10%30%
1620
July1st to 15thNight
7%6%47%7%46%6%8%10%30%
1620
16th to endNight
5%438%8%47%8%7%13%28%
1703
August1st to 15thNight
5%425%6%36%6%8%13%35%
1620
16th to endNight
10%6%37%6%45%6%7%12%29%
2073
September1st to 15thNight
7%6%37%8%46%7%8%11%27%
1980
16th to endNight
9%7%28%8%5%6%6%7%8%29%
1914
October1st to 15thNight
8%5%15%5%35%46%7%45%
1881
16th to endNight
10%5%2442345%8%47%
2112
November1st to 15thNight
5%4245%24448%51%
2101
16th to endNight
7%425%5%2445%9%47%
2185
December1st to 15thNight
8%5%25%5%35%46%8%44%
2340
16th to endNight
6%425%5%35%5%6%8%46%
2496

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
40%6%8%20%18%4
1612
16th to endDay
36%37%20%21%9%
1782
February1st to 15thDay
37%47%16%20%13%
1752
16th to endDay
35%410%17%20%11%
1663
March1st to 15thDay
30%5%10%25%19%8%
1980
16th to endDay
35%39%21%21%8%
2112
April1st to 15thDay
35%5%13%21%18%5%
1972
16th to endDay
36%5%9%17%22%7%
2118
May1st to 15thDay
35%412%20%19%7%
2262
16th to endDay
45%7%12%19%12%1
2435
June1st to 15thDay
57%7%17%13%3
2340
16th to endDay
55%10%18%12%2
2340
July1st to 15thDay
58%12%19%7%1
2201
16th to endDay
55%12%20%9%1
2310
August1st to 15thDay
51%11%27%9%
2327
16th to endDay
56%13%20%7%1
2113
September1st to 15thDay
53%12%21%10%2
1980
16th to endDay
57%10%16%9%41
1905
October1st to 15thDay
42%7%10%17%15%6%
1747
16th to endDay
39%5%8%13%21%10%
1760
November1st to 15thDay
33%5%8%21%20%10%
1757
16th to endDay
37%6%8%18%16%12%
1773
December1st to 15thDay
43%411%17%17%5%
1620
16th to endDay
35%5%11%21%17%7%
1728
January1st to 15thNight
38%5%12%22%15%5%
2327
16th to endNight
36%49%23%17%8%
2439
February1st to 15thNight
36%38%17%21%12%
2112
16th to endNight
27%5%13%22%22%8%
1809
March1st to 15thNight
26%312%30%20%7%
1980
16th to endNight
26%5%13%25%20%8%
2112
April1st to 15thNight
24%5%16%25%20%6%
1976
16th to endNight
26%5%12%25%23%6%
1842
May1st to 15thNight
27%5%13%27%19%6%
1698
16th to endNight
31%7%19%24%16%
1684
June1st to 15thNight
46%10%22%16%4
1620
16th to endNight
44%14%23%14%3
1620
July1st to 15thNight
45%14%26%11%2
1530
16th to endNight
43%15%27%13%
1595
August1st to 15thNight
36%15%38%9%
1609
16th to endNight
45%15%28%9%1
2073
September1st to 15thNight
47%15%22%11%2
1980
16th to endNight
49%10%20%15%41
1914
October1st to 15thNight
35%6%13%19%19%5%
1881
16th to endNight
34%6%10%15%23%9%
2112
November1st to 15thNight
29%49%25%22%8%
2101
16th to endNight
32%5%8%22%19%11%
2185
December1st to 15thNight
36%5%12%24%14%6%
2340
16th to endNight
33%6%14%21%17%7%
2496

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
23%437%16%12%5%
90
16th to endDay
12%11%33%22%16%3
96
February1st to 15thDay
6%14%24%28%17%7%
90
16th to endDay
12%428%35%18%
164
March1st to 15thDay
4425%37%22%4
270
16th to endDay
9%320%28%31%6%
288
April1st to 15thDay
3221%32%29%10%
270
16th to endDay
7%213%29%26%20%
270
May1st to 15thDay
6%10%23%34%24%
288
16th to endDay
7%6%17%33%33%
331
June1st to 15thDay
16%9%11%20%40%
315
16th to endDay
8%17%22%59%
315
July1st to 15thDay
7%6%16%68%
305
16th to endDay
11%39%15%59%
326
August1st to 15thDay
7%116%18%63%
313
16th to endDay
12%38%18%56%
332
September1st to 15thDay
12%148%23%49%
315
16th to endDay
11%29%37%39%
287
October1st to 15thDay
10%7%29%35%17%
255
16th to endDay
10%116%27%32%11%
272
November1st to 15thDay
6%211%33%32%13%
265
16th to endDay
8%218%36%28%4
243
December1st to 15thDay
7%234%42%12%1
90
16th to endDay
7%311%34%35%8%
96
January1st to 15thNight
10%5%23%40%19%1
720
16th to endNight
12%429%38%14%
768
February1st to 15thNight
13%427%40%13%
704
16th to endNight
8%428%44%13%
631
March1st to 15thNight
45%30%42%16%
720
16th to endNight
7%225%45%18%
768
April1st to 15thNight
5%223%45%21%1
718
16th to endNight
7%221%43%24%
720
May1st to 15thNight
6%114%48%26%2
618
16th to endNight
6%6%36%42%7%
563
June1st to 15thNight
9%324%46%14%
540
16th to endNight
8%112%46%30%
540
July1st to 15thNight
8%26%48%33%
510
16th to endNight
6%36%43%39%
564
August1st to 15thNight
7%15%46%38%
539
16th to endNight
12%15%14%36%29%
747
September1st to 15thNight
10%15%15%41%25%
720
16th to endNight
13%422%43%15%
693
October1st to 15thNight
11%8%35%37%6%
660
16th to endNight
12%214%34%30%4
704
November1st to 15thNight
6%217%41%28%3
700
16th to endNight
9%222%43%20%1
720
December1st to 15thNight
11%319%41%23%
720
16th to endNight
6%422%38%26%2
768
Page generated at 2017-09-25 09:02:19. Version ac04

Copyright 2017 A. Danko


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