Hale Mountain Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hale Mountain Observatory clear sky chart from 2005-11-05 to 2017-09-23.

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
37%
15746
25%
46948
14%
15699
48%
15699
30%
27814

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
20%
900
27%
2327
7%
895
35%
895
28%
1441
January16th to endNight
23%
960
30%
2496
8%
960
37%
960
31%
1526
February1st to 15thNight
20%
880
21%
2288
5%
876
30%
876
26%
1456
February16th to endNight
18%
597
26%
1859
6%
597
35%
597
24%
1100
March1st to 15thNight
24%
540
22%
1980
10%
540
39%
540
20%
1234
March16th to endNight
24%
576
18%
2112
12%
576
34%
576
18%
1353
April1st to 15thNight
22%
539
22%
1860
9%
539
41%
539
23%
1095
April16th to endNight
24%
540
21%
1794
9%
540
43%
540
25%
1087
May1st to 15thNight
31%
539
22%
1619
14%
539
44%
539
26%
1041
May16th to endNight
42%
563
19%
1685
13%
561
52%
561
30%
1040
June1st to 15thNight
57%
540
22%
1620
18%
540
63%
540
43%
855
June16th to endNight
63%
540
25%
1620
19%
540
70%
540
46%
836
July1st to 15thNight
67%
510
18%
1530
17%
510
71%
510
37%
879
July16th to endNight
78%
564
28%
1594
31%
531
80%
531
47%
826
August1st to 15thNight
73%
539
26%
1610
29%
536
76%
536
41%
879
August16th to endNight
67%
573
26%
1863
26%
573
72%
573
35%
1048
September1st to 15thNight
60%
540
27%
1854
27%
540
66%
540
34%
1012
September16th to endNight
58%
516
33%
1903
28%
516
67%
516
33%
974
October1st to 15thNight
42%
656
29%
1976
17%
656
52%
656
35%
1128
October16th to endNight
38%
704
31%
2112
16%
704
50%
704
36%
1166
November1st to 15thNight
35%
700
31%
2100
14%
700
49%
700
33%
1168
November16th to endNight
26%
870
28%
2310
10%
870
39%
870
28%
1449
December1st to 15thNight
25%
900
23%
2340
7%
900
36%
900
27%
1533
December16th to endNight
23%
960
25%
2496
8%
960
35%
960
24%
1688

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
11%6%25%5%2445%7%43%
47954
Night
10%5%24424446%51%
47144
TransparencyDay
39%5%10%23%16%3
47654
Night
33%5%10%24%20%5%
46949
SeeingDay
14%9%26%28%17%3
5778
Night
15%12%30%26%12%1
15747

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
11%8%35%313335%49%
1611
16th to endDay
12%6%34423336%50%
1728
February1st to 15thDay
13%8%45%5%23335%44%
1575
16th to endDay
12%8%36%433445%43%
1624
March1st to 15thDay
15%8%25%424345%40%
1980
16th to endDay
18%8%36%6%34335%36%
2110
April1st to 15thDay
14%6%25%5%24446%42%
2086
16th to endDay
16%9%36%6%3434437%
2164
May1st to 15thDay
16%6%37%5%35%445%37%
2331
16th to endDay
11%6%36%6%46%5%5%7%36%
2430
June1st to 15thDay
8%425%5%35%6%6%9%41%
2340
16th to endDay
6%4235%36%6%7%10%43%
2340
July1st to 15thDay
9%5%25%5%37%5%6%11%36%
2340
16th to endDay
5%2246%46%6%7%11%43%
2466
August1st to 15thDay
6%4235%36%7%8%10%41%
2340
16th to endDay
7%425%5%45%6%5%8%43%
2337
September1st to 15thDay
13%5%25%32445%7%46%
2103
16th to endDay
8%2144345%6%8%49%
1885
October1st to 15thDay
13%6%24323435%50%
1650
16th to endDay
10%5%2341223458%
1760
November1st to 15thDay
9%5%34222346%55%
1758
16th to endDay
13%9%35%313235%49%
1648
December1st to 15thDay
14%7%35%5%23346%44%
1620
16th to endDay
14%9%35%5%13335%43%
1728
January1st to 15thNight
12%5%25%323335%52%
2327
16th to endNight
11%5%3432333454%
2496
February1st to 15thNight
12%7%25%313345%48%
2278
16th to endNight
10%5%24425%345%49%
1859
March1st to 15thNight
14%8%35%42435%5%42%
1980
16th to endNight
16%5%25%434445%43%
2112
April1st to 15thNight
10%5%24424345%49%
1860
16th to endNight
12%7%25%423346%46%
1794
May1st to 15thNight
11%5%24425%5%5%7%46%
1619
16th to endNight
8%5%25%5%25%47%8%44%
1683
June1st to 15thNight
421442445%8%58%
1620
16th to endNight
4124145%6%10%57%
1620
July1st to 15thNight
6%313325%5%7%12%48%
1620
16th to endNight
321332446%11%56%
1702
August1st to 15thNight
3213425%46%10%54%
1620
16th to endNight
43144346%6%8%52%
1863
September1st to 15thNight
9%5%2432335%6%53%
1854
16th to endNight
7%31432335%6%56%
1903
October1st to 15thNight
10%313323446%56%
1976
16th to endNight
10%5%2322244458%
2112
November1st to 15thNight
8%5%2331333459%
2100
16th to endNight
13%6%2442323352%
2310
December1st to 15thNight
12%7%25%424446%45%
2340
16th to endNight
13%9%46%42334442%
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
38%38%26%20%3
1612
16th to endDay
35%47%28%20%3
1728
February1st to 15thDay
42%310%23%15%2
1576
16th to endDay
43%37%23%16%4
1624
March1st to 15thDay
43%49%19%15%6%
1980
16th to endDay
50%49%20%13%1
2112
April1st to 15thDay
41%5%10%21%17%3
2086
16th to endDay
50%5%7%17%16%2
2164
May1st to 15thDay
50%48%18%16%1
2331
16th to endDay
45%7%12%20%12%
2434
June1st to 15thDay
37%8%12%25%15%
2340
16th to endDay
34%8%14%25%16%2
2340
July1st to 15thDay
38%9%14%27%9%
2201
16th to endDay
32%8%15%29%12%1
2311
August1st to 15thDay
32%10%14%22%17%2
2326
16th to endDay
37%8%14%21%15%3
2337
September1st to 15thDay
37%5%10%22%15%9%
2103
16th to endDay
29%7%10%25%22%5%
1885
October1st to 15thDay
37%48%21%21%7%
1650
16th to endDay
31%28%25%24%7%
1760
November1st to 15thDay
30%38%28%19%8%
1758
16th to endDay
39%27%22%24%4
1648
December1st to 15thDay
40%411%23%17%3
1620
16th to endDay
42%38%24%16%3
1728
January1st to 15thNight
35%38%25%23%4
2327
16th to endNight
33%37%25%24%4
2496
February1st to 15thNight
36%49%28%16%4
2288
16th to endNight
35%410%25%18%5%
1859
March1st to 15thNight
42%5%9%17%19%5%
1980
16th to endNight
42%6%8%23%15%3
2112
April1st to 15thNight
37%49%21%20%6%
1860
16th to endNight
38%49%23%19%3
1794
May1st to 15thNight
39%6%9%20%20%3
1620
16th to endNight
33%8%18%24%14%1
1685
June1st to 15thNight
23%5%14%31%22%1
1620
16th to endNight
21%5%15%30%21%5%
1620
July1st to 15thNight
27%8%15%28%19%1
1530
16th to endNight
20%7%13%37%19%2
1594
August1st to 15thNight
23%8%14%30%20%3
1610
16th to endNight
28%7%14%25%19%4
1863
September1st to 15thNight
30%49%26%18%10%
1854
16th to endNight
27%6%8%25%26%6%
1903
October1st to 15thNight
29%5%10%20%22%11%
1976
16th to endNight
28%36%23%27%10%
2112
November1st to 15thNight
29%48%25%23%9%
2100
16th to endNight
38%26%21%25%6%
2310
December1st to 15thNight
39%410%21%18%5%
2340
16th to endNight
43%38%19%19%4
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
27%22%37%7%4
90
16th to endDay
11%40%32%13%2
96
February1st to 15thDay
24%25%37%11%1
90
16th to endDay
28%28%32%8%2
81
March1st to 15thDay
36%16%40%6%
90
16th to endDay
28%22%31%15%2
96
April1st to 15thDay
22%21%30%17%6%
205
16th to endDay
28%15%32%14%7%1
274
May1st to 15thDay
19%16%36%19%6%
468
16th to endDay
18%10%37%22%8%2
517
June1st to 15thDay
11%327%37%17%2
495
16th to endDay
8%426%34%22%3
495
July1st to 15thDay
12%222%38%20%3
475
16th to endDay
5%10%36%38%8%
515
August1st to 15thDay
6%115%40%31%4
493
16th to endDay
10%116%41%24%6%
377
September1st to 15thDay
11%313%35%30%5%
258
16th to endDay
1129%35%25%6%
111
October1st to 15thDay
8%13%36%25%11%4
90
16th to endDay
19%343%25%6%2
96
November1st to 15thDay
11%8%44%20%14%1
90
16th to endDay
35%27%18%16%1
90
December1st to 15thDay
21%26%34%11%42
90
16th to endDay
20%28%41%8%1
96
January1st to 15thNight
20%20%35%17%4
900
16th to endNight
17%19%37%21%3
960
February1st to 15thNight
21%20%36%19%2
880
16th to endNight
18%21%39%17%2
597
March1st to 15thNight
21%15%36%23%3
540
16th to endNight
18%19%35%20%5%
576
April1st to 15thNight
16%22%37%19%4
539
16th to endNight
17%13%42%17%8%
540
May1st to 15thNight
15%10%39%24%9%
540
16th to endNight
12%8%31%30%14%1
563
June1st to 15thNight
6%425%43%18%2
540
16th to endNight
5%125%38%25%3
540
July1st to 15thNight
7%118%42%26%3
510
16th to endNight
5%17%38%41%4
564
August1st to 15thNight
5%114%38%34%5%
539
16th to endNight
7%118%40%27%4
573
September1st to 15thNight
13%216%39%25%2
540
16th to endNight
9%423%36%22%4
516
October1st to 15thNight
12%9%32%24%17%2
656
16th to endNight
15%11%32%27%12%
704
November1st to 15thNight
13%15%32%26%10%
700
16th to endNight
24%17%31%20%6%
870
December1st to 15thNight
21%17%34%22%4
900
16th to endNight
23%18%32%20%3
960
Page generated at 2017-09-24 08:15:57. Version ac04

Copyright 2017 A. Danko


Hale Mountain Observatory Clear Sky Chart | Charts Home