Mount Hamilton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mount Hamilton clear sky chart from 2005-11-05 to 2017-05-01.

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
66%
15017
29%
45690
25%
14981
70%
14981
39%
24903

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
60%
716
20%
2395
20%
716
63%
716
29%
1414
January16th to endNight
57%
768
25%
2496
25%
768
61%
768
27%
1526
February1st to 15thNight
55%
700
25%
2270
24%
700
60%
700
26%
1410
February16th to endNight
51%
632
25%
1895
21%
632
57%
632
27%
1202
March1st to 15thNight
52%
720
19%
2025
17%
720
55%
720
26%
1349
March16th to endNight
49%
768
21%
2076
15%
768
55%
768
30%
1337
April1st to 15thNight
49%
719
22%
1799
12%
719
54%
719
29%
1205
April16th to endNight
53%
720
26%
1800
11%
720
59%
720
41%
1071
May1st to 15thNight
67%
598
30%
1594
19%
598
71%
598
54%
817
May16th to endNight
69%
344
26%
1370
24%
344
77%
344
41%
601
June1st to 15thNight
70%
330
31%
1320
32%
330
79%
330
45%
554
June16th to endNight
87%
330
36%
1320
44%
330
91%
330
67%
436
July1st to 15thNight
93%
331
36%
1261
45%
331
95%
331
70%
428
July16th to endNight
93%
522
35%
1467
31%
489
94%
489
67%
622
August1st to 15thNight
92%
531
40%
1514
32%
528
93%
528
69%
652
August16th to endNight
93%
700
42%
1750
28%
700
93%
700
78%
808
September1st to 15thNight
91%
660
44%
1650
33%
660
92%
660
77%
773
September16th to endNight
83%
656
43%
1789
38%
656
86%
656
63%
849
October1st to 15thNight
72%
660
31%
1980
31%
660
77%
660
45%
1015
October16th to endNight
71%
704
35%
2112
36%
704
76%
704
46%
1094
November1st to 15thNight
67%
700
29%
2199
28%
700
71%
700
40%
1168
November16th to endNight
62%
720
26%
2400
27%
720
66%
720
33%
1336
December1st to 15thNight
54%
720
22%
2520
21%
720
60%
720
24%
1538
December16th to endNight
47%
768
21%
2688
20%
768
53%
768
21%
1698

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%413313335%61%
46069
Night
9%413313346%57%
45878
TransparencyDay
26%36%18%25%19%
45755
Night
27%46%17%23%20%
45691
SeeingDay
11%10%24%32%16%3
5447
Night
10%5%10%28%32%11%
15027

By Month

Percentage Cloud Cover SW (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
14%6%35%423346%45%
1540
16th to endDay
18%8%23414335%44%
1728
February1st to 15thDay
18%7%35%314246%42%
1594
16th to endDay
20%8%25%324335%38%
1579
March1st to 15thDay
16%9%26%5%3436%8%33%
1932
16th to endDay
14%8%45%5%34446%39%
2148
April1st to 15thDay
16%7%25%5%23347%41%
2149
16th to endDay
8%5%22313336%58%
2160
May1st to 15thDay
4312313346%64%
2036
16th to endDay
6%414213347%59%
2386
June1st to 15thDay
4312213237%65%
2310
16th to endDay
1111122482%
2310
July1st to 15thDay
111121386%
2284
16th to endDay
111122384%
2286
August1st to 15thDay
1111386%
2107
16th to endDay
1111387%
2100
September1st to 15thDay
1112386%
1980
16th to endDay
311212235%74%
1838
October1st to 15thDay
5%313213347%63%
1650
16th to endDay
7%413422345%61%
1760
November1st to 15thDay
10%5%23324347%51%
1659
16th to endDay
14%5%33323345%49%
1557
December1st to 15thDay
17%8%36%422335%41%
1440
16th to endDay
20%7%35%423346%37%
1536
January1st to 15thNight
14%5%23425%45%7%45%
2395
16th to endNight
16%6%3332445%5%44%
2496
February1st to 15thNight
16%6%24424447%40%
2259
16th to endNight
17%6%24423347%42%
1895
March1st to 15thNight
16%8%34424337%41%
2025
16th to endNight
14%6%245%2435%8%43%
2076
April1st to 15thNight
13%5%25%425%45%6%42%
1799
16th to endNight
7%5%23324247%56%
1800
May1st to 15thNight
3313313248%64%
1594
16th to endNight
42123224411%61%
1370
June1st to 15thNight
2213312337%67%
1320
16th to endNight
1111112383%
1320
July1st to 15thNight
111122482%
1343
16th to endNight
1112136%79%
1575
August1st to 15thNight
1111226%81%
1523
16th to endNight
11112484%
1750
September1st to 15thNight
1111112383%
1650
16th to endNight
211212226%76%
1789
October1st to 15thNight
6%323313347%61%
1980
16th to endNight
6%213313345%62%
2112
November1st to 15thNight
8%413313448%55%
2199
16th to endNight
9%6%245%24347%50%
2400
December1st to 15thNight
16%7%245%2335%5%43%
2520
16th to endNight
19%7%24323435%41%
2688

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
39%49%20%17%9%
1540
16th to endDay
42%4415%19%13%
1728
February1st to 15thDay
43%37%19%20%6%
1594
16th to endDay
48%27%21%15%3
1579
March1st to 15thDay
46%49%17%15%6%
1932
16th to endDay
43%6%10%18%16%4
2148
April1st to 15thDay
42%410%20%19%3
2149
16th to endDay
26%411%24%24%8%
2160
May1st to 15thDay
19%36%27%33%9%
2036
16th to endDay
24%410%27%25%7%
2390
June1st to 15thDay
19%48%22%25%19%
2310
16th to endDay
8%1316%35%34%
2310
July1st to 15thDay
6%217%28%53%
2137
16th to endDay
7%239%28%48%
2131
August1st to 15thDay
6%2112%28%47%
2091
16th to endDay
5%111%38%41%
2100
September1st to 15thDay
7%2112%36%40%
1980
16th to endDay
12%3223%34%22%
1838
October1st to 15thDay
21%37%22%24%20%
1650
16th to endDay
26%36%20%26%17%
1760
November1st to 15thDay
32%48%21%23%9%
1659
16th to endDay
35%47%18%28%5%
1557
December1st to 15thDay
46%37%16%20%6%
1440
16th to endDay
46%39%15%17%7%
1536
January1st to 15thNight
36%410%19%19%9%
2395
16th to endNight
38%5%8%12%17%18%
2496
February1st to 15thNight
41%27%19%19%8%
2270
16th to endNight
40%49%23%16%5%
1895
March1st to 15thNight
43%49%17%16%9%
2025
16th to endNight
39%411%18%17%8%
2076
April1st to 15thNight
39%5%9%21%19%4
1799
16th to endNight
27%49%23%24%10%
1800
May1st to 15thNight
18%47%21%32%15%
1595
16th to endNight
20%49%23%32%9%
1370
June1st to 15thNight
16%5%9%18%22%27%
1320
16th to endNight
8%2213%30%42%
1320
July1st to 15thNight
6%31425%58%
1261
16th to endNight
9%429%24%48%
1467
August1st to 15thNight
8%5%11%28%46%
1514
16th to endNight
6%39%35%43%
1750
September1st to 15thNight
8%227%28%51%
1650
16th to endNight
13%4119%32%30%
1789
October1st to 15thNight
22%45%21%23%22%
1980
16th to endNight
23%3420%28%18%
2112
November1st to 15thNight
26%49%20%25%12%
2199
16th to endNight
32%47%20%23%11%
2400
December1st to 15thNight
41%37%16%20%9%
2520
16th to endNight
42%5%9%15%17%9%
2688

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
26%15%25%20%10%1
168
16th to endDay
21%10%26%21%16%3
256
February1st to 15thDay
22%13%23%24%15%1
239
16th to endDay
22%15%27%22%10%1
238
March1st to 15thDay
21%16%24%20%12%4
270
16th to endDay
21%17%29%21%8%1
288
April1st to 15thDay
21%22%28%18%8%
269
16th to endDay
15%21%31%20%9%
270
May1st to 15thDay
11%13%37%28%5%2
229
16th to endDay
9%16%25%31%13%3
266
June1st to 15thDay
5%14%33%30%12%3
255
16th to endDay
2332%40%14%6%
255
July1st to 15thDay
1115%49%27%4
245
16th to endDay
12%53%25%7%
271
August1st to 15thDay
1120%41%27%6%
255
16th to endDay
1115%48%24%8%
268
September1st to 15thDay
317%47%23%8%
255
16th to endDay
6%7%16%43%21%4
255
October1st to 15thDay
8%10%26%36%14%3
255
16th to endDay
11%7%32%33%15%
272
November1st to 15thDay
10%9%17%23%31%7%
165
16th to endDay
11%12%27%36%7%3
79
December1st to 15thDay
25%23%15%26%10%
60
16th to endDay
20%12%10%26%25%4
64
January1st to 15thNight
15%410%29%27%12%
720
16th to endNight
19%5%9%28%24%12%
768
February1st to 15thNight
20%410%29%25%9%
704
16th to endNight
18%9%13%30%20%6%
632
March1st to 15thNight
18%8%12%27%27%7%
720
16th to endNight
16%9%17%28%24%4
768
April1st to 15thNight
15%11%15%30%22%4
719
16th to endNight
8%10%20%26%24%9%
720
May1st to 15thNight
45%18%32%30%9%
599
16th to endNight
5%5%15%31%35%7%
345
June1st to 15thNight
2415%35%34%7%
330
16th to endNight
26%37%44%7%
330
July1st to 15thNight
1228%52%14%
331
16th to endNight
117%56%22%
522
August1st to 15thNight
1228%50%17%
531
16th to endNight
1225%56%14%
700
September1st to 15thNight
11324%52%16%
660
16th to endNight
326%27%42%17%
656
October1st to 15thNight
7%48%30%32%15%
660
16th to endNight
9%210%26%30%20%
704
November1st to 15thNight
9%411%30%29%13%
700
16th to endNight
10%411%31%29%12%
720
December1st to 15thNight
18%7%9%31%25%8%
720
16th to endNight
20%11%12%28%22%5%
768
Page generated at 2017-05-02 05:43:31. Version ac04

Copyright 2017 A. Danko


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