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Mount Hopkins
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mount Hopkins clear sky chart from 2005-11-05 to 2018-03-11.

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
72%
16284
35%
49044
30%
16244
77%
16244
50%
23985

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
70%
779
32%
2522
32%
776
76%
776
48%
1207
January16th to endNight
62%
832
35%
2704
32%
832
72%
832
40%
1395
February1st to 15thNight
68%
757
36%
2375
33%
756
78%
756
51%
1113
February16th to endNight
59%
684
37%
1976
32%
684
67%
684
45%
1045
March1st to 15thNight
63%
764
39%
2101
29%
764
72%
764
55%
1046
March16th to endNight
67%
768
38%
2112
26%
768
76%
768
57%
1033
April1st to 15thNight
62%
688
35%
1947
23%
688
72%
688
54%
956
April16th to endNight
66%
540
44%
1800
36%
540
78%
540
66%
676
May1st to 15thNight
68%
539
40%
1623
29%
539
78%
539
69%
654
May16th to endNight
73%
561
43%
1684
33%
561
81%
561
73%
667
June1st to 15thNight
81%
540
35%
1620
30%
540
83%
540
68%
676
June16th to endNight
83%
540
29%
1620
25%
540
84%
540
58%
750
July1st to 15thNight
80%
510
17%
1530
16%
510
81%
510
37%
879
July16th to endNight
78%
564
13%
1593
11%
531
77%
531
25%
1054
August1st to 15thNight
83%
539
23%
1611
21%
536
83%
536
36%
919
August16th to endNight
80%
603
27%
1890
27%
603
80%
603
35%
1075
September1st to 15thNight
74%
720
26%
1980
22%
720
75%
720
38%
1190
September16th to endNight
83%
716
43%
1980
34%
716
87%
716
65%
921
October1st to 15thNight
76%
720
39%
2091
29%
720
83%
720
63%
952
October16th to endNight
82%
768
44%
2304
39%
768
86%
768
67%
981
November1st to 15thNight
76%
760
41%
2280
34%
760
82%
760
62%
994
November16th to endNight
68%
780
40%
2462
37%
780
73%
780
50%
1171
December1st to 15thNight
67%
780
36%
2535
36%
780
71%
780
45%
1239
December16th to endNight
63%
832
35%
2704
35%
832
69%
832
41%
1392

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
4313323445%61%
49573
Night
3313313346%65%
49248
TransparencyDay
23%35%11%26%28%
49268
Night
20%36%13%28%28%
49054
SeeingDay
8%9%22%31%21%7%
5996
Night
5%313%34%35%8%
16295

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
5%32342334460%
1746
16th to endDay
6%423223445%61%
1872
February1st to 15thDay
6%412212235%65%
1809
16th to endDay
6%6%13412335%60%
1782
March1st to 15thDay
4413313345%63%
2095
16th to endDay
331322225%71%
2112
April1st to 15thDay
3212223445%68%
2000
16th to endDay
12121112380%
2160
May1st to 15thDay
111211233475%
2325
16th to endDay
1121222382%
2429
June1st to 15thDay
21121235%77%
2340
16th to endDay
3213323435%66%
2340
July1st to 15thDay
6%426%8%5%7%7%7%8%34%
2340
16th to endDay
10%6%38%8%5%8%8%7%9%22%
2467
August1st to 15thDay
8%5%37%7%48%8%6%7%33%
2340
16th to endDay
5%426%7%46%6%7%7%41%
2305
September1st to 15thDay
8%6%26%6%46%45%6%42%
1980
16th to endDay
432324445%64%
1980
October1st to 15thDay
211221323473%
1869
16th to endDay
112212235%74%
1920
November1st to 15thDay
222213245%71%
1909
16th to endDay
4312312235%69%
1826
December1st to 15thDay
7%413323346%58%
1755
16th to endDay
6%5%2321345%6%58%
1872
January1st to 15thNight
5%31331434463%
2522
16th to endNight
6%414324435%58%
2704
February1st to 15thNight
3312223336%66%
2372
16th to endNight
45%23323335%60%
1976
March1st to 15thNight
4312312246%66%
2101
16th to endNight
231231233470%
2112
April1st to 15thNight
231232323469%
1947
16th to endNight
21111112381%
1800
May1st to 15thNight
1121234477%
1623
16th to endNight
1111222284%
1684
June1st to 15thNight
211111213478%
1620
16th to endNight
121221335%6%68%
1620
July1st to 15thNight
33135%36%6%9%11%45%
1620
16th to endNight
5%325%6%37%9%11%15%29%
1701
August1st to 15thNight
32135%26%6%7%10%50%
1620
16th to endNight
5%314435%6%6%10%47%
1890
September1st to 15thNight
5%4245%3446%6%51%
1980
16th to endNight
321112335%73%
1980
October1st to 15thNight
21221322476%
2091
16th to endNight
12211213477%
2304
November1st to 15thNight
213112345%72%
2280
16th to endNight
5%314212235%66%
2462
December1st to 15thNight
6%413213346%61%
2535
16th to endNight
7%5%24313335%60%
2704

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
25%25%11%28%26%
1747
16th to endDay
25%1415%27%25%
1872
February1st to 15thDay
21%312%29%31%
1809
16th to endDay
25%1312%28%27%
1782
March1st to 15thDay
22%137%33%31%
2095
16th to endDay
17%139%37%30%
2112
April1st to 15thDay
16%236%39%31%
2000
16th to endDay
11%127%29%48%
2160
May1st to 15thDay
12%128%28%47%
2325
16th to endDay
9%125%32%47%
2432
June1st to 15thDay
10%125%25%53%
2340
16th to endDay
19%337%21%44%
2340
July1st to 15thDay
39%10%13%13%13%9%
2201
16th to endDay
52%12%18%11%4
2312
August1st to 15thDay
44%10%9%14%16%4
2325
16th to endDay
37%9%12%16%14%9%
2305
September1st to 15thDay
38%6%8%14%18%11%
1980
16th to endDay
21%35%11%32%24%
1980
October1st to 15thDay
15%3411%32%32%
1869
16th to endDay
13%1310%30%40%
1920
November1st to 15thDay
14%1213%35%31%
1909
16th to endDay
19%1311%29%35%
1826
December1st to 15thDay
25%2415%31%20%
1755
16th to endDay
25%27%15%31%18%
1872
January1st to 15thNight
22%25%12%31%26%
2522
16th to endNight
27%2414%29%21%
2704
February1st to 15thNight
19%25%14%25%33%
2383
16th to endNight
25%2313%31%24%
1976
March1st to 15thNight
19%1310%30%34%
2101
16th to endNight
17%1410%34%30%
2112
April1st to 15thNight
19%1210%38%27%
1947
16th to endNight
9%129%30%47%
1800
May1st to 15thNight
9%139%31%44%
1624
16th to endNight
7%126%35%45%
1685
June1st to 15thNight
11%12424%55%
1620
16th to endNight
15%347%22%45%
1620
July1st to 15thNight
25%10%19%18%14%11%
1530
16th to endNight
35%13%26%17%5%1
1593
August1st to 15thNight
25%11%15%21%19%6%
1611
16th to endNight
29%7%16%18%18%9%
1890
September1st to 15thNight
30%6%12%19%21%10%
1980
16th to endNight
13%25%15%38%25%
1980
October1st to 15thNight
13%2415%31%32%
2091
16th to endNight
11%1413%28%40%
2304
November1st to 15thNight
13%1318%31%30%
2280
16th to endNight
21%1310%28%33%
2462
December1st to 15thNight
24%1415%32%21%
2535
16th to endNight
26%26%15%28%20%
2704

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
14%8%17%34%22%2
135
16th to endDay
9%6%23%31%22%6%
144
February1st to 15thDay
8%11%22%29%20%5%
234
16th to endDay
11%24%28%24%8%1
290
March1st to 15thDay
9%16%28%26%13%4
312
16th to endDay
425%29%22%12%4
288
April1st to 15thDay
5%18%36%24%10%3
269
16th to endDay
422%38%21%9%3
270
May1st to 15thDay
421%35%22%11%4
288
16th to endDay
212%36%34%11%3
330
June1st to 15thDay
5%7%32%38%13%3
315
16th to endDay
420%44%23%6%
315
July1st to 15thDay
6%111%41%30%7%
305
16th to endDay
17%26%29%30%14%
327
August1st to 15thDay
10%6%32%33%15%
315
16th to endDay
6%6%36%34%15%
332
September1st to 15thDay
15%112%38%24%7%
315
16th to endDay
7%5%21%34%23%7%
315
October1st to 15thDay
38%23%33%19%11%
204
16th to endDay
4115%27%38%13%
144
November1st to 15thDay
5%11%18%36%23%5%
135
16th to endDay
7%8%20%32%25%5%
135
December1st to 15thDay
12%6%20%28%30%2
135
16th to endDay
15%8%18%26%24%7%
144
January1st to 15thNight
6%214%40%29%5%
780
16th to endNight
8%316%40%25%5%
832
February1st to 15thNight
45%16%37%29%6%
764
16th to endNight
6%8%20%43%19%2
684
March1st to 15thNight
5%6%19%38%25%4
764
16th to endNight
35%17%38%29%5%
768
April1st to 15thNight
45%20%44%22%1
688
16th to endNight
36%21%39%25%3
540
May1st to 15thNight
15%22%35%30%3
540
16th to endNight
1318%38%34%2
563
June1st to 15thNight
2210%44%37%2
540
16th to endNight
216%32%49%7%
540
July1st to 15thNight
5%321%58%11%
510
16th to endNight
6%113%58%20%
564
August1st to 15thNight
5%113%56%23%
539
16th to endNight
7%114%53%22%
603
September1st to 15thNight
7%5%21%50%15%
720
16th to endNight
38%34%40%12%
716
October1st to 15thNight
3213%35%36%8%
720
16th to endNight
119%34%40%12%
768
November1st to 15thNight
3313%35%37%7%
760
16th to endNight
6%315%34%32%8%
780
December1st to 15thNight
8%413%39%26%6%
780
16th to endNight
9%415%38%24%7%
832
Page generated at 2018-03-12 10:28:14. Version ac04

Copyright 2018 A. Danko


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