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Hale Hill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hale Hill Observatory clear sky chart from 2005-11-05 to 2019-01-28.

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
38%
17702
19%
52452
12%
17659
44%
17659
23%
34935

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%
1050
15%
2926
6%
1045
29%
1045
15%
2200
January16th to endNight
17%
1076
13%
3016
4%
1076
24%
1076
16%
2255
February1st to 15thNight
17%
763
13%
2292
4%
761
25%
761
14%
1688
February16th to endNight
19%
683
15%
2049
7%
683
26%
683
15%
1496
March1st to 15thNight
21%
780
15%
2340
8%
780
27%
780
17%
1647
March16th to endNight
28%
741
16%
2204
8%
741
37%
741
19%
1562
April1st to 15thNight
30%
584
20%
1947
12%
584
42%
584
21%
1271
April16th to endNight
34%
579
20%
1850
12%
579
43%
579
24%
1183
May1st to 15thNight
36%
585
15%
1755
10%
585
41%
585
22%
1214
May16th to endNight
51%
609
16%
1762
12%
609
54%
609
27%
1163
June1st to 15thNight
57%
585
19%
1560
14%
585
60%
585
37%
952
June16th to endNight
61%
585
20%
1560
15%
585
65%
585
38%
954
July1st to 15thNight
66%
555
20%
1480
15%
555
69%
555
39%
896
July16th to endNight
73%
612
25%
1574
20%
579
76%
579
44%
899
August1st to 15thNight
71%
575
23%
1766
21%
572
73%
572
37%
1006
August16th to endNight
70%
621
23%
2070
23%
621
74%
621
36%
1125
September1st to 15thNight
61%
637
26%
2002
24%
637
65%
637
32%
1177
September16th to endNight
58%
777
28%
2145
21%
777
62%
777
36%
1289
October1st to 15thNight
50%
780
30%
2155
20%
780
57%
780
34%
1310
October16th to endNight
31%
832
22%
2664
15%
832
41%
832
25%
1652
November1st to 15thNight
34%
820
25%
2666
17%
820
47%
820
24%
1640
November16th to endNight
29%
840
20%
2730
12%
840
40%
840
18%
1825
December1st to 15thNight
22%
913
13%
2803
7%
913
29%
913
15%
2069
December16th to endNight
16%
1120
12%
3136
3%
1120
25%
1120
13%
2462

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
15%7%35%5%3445%7%38%
53134
Night
15%7%35%423446%40%
52624
Cloud CoverDay
15%7%35%5%3445%7%38%
53143
Night
15%8%35%424446%40%
52629
TransparencyDay
44%5%11%21%13%2
52824
Night
44%5%10%22%14%2
52452
SeeingDay
18%9%26%23%15%6%
7592
Night
19%10%27%26%14%1
17705

By Month

Percentage Cloud Cover NE (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
20%11%48%5%24445%28%
1672
16th to endDay
13%14%5%7%5%33335%34%
1823
February1st to 15thDay
16%12%5%8%5%23446%30%
1900
16th to endDay
16%13%47%5%34446%29%
1710
March1st to 15thDay
21%9%36%5%24345%34%
1940
16th to endDay
19%9%36%5%3345%6%31%
2382
April1st to 15thDay
18%8%35%424446%38%
2331
16th to endDay
19%6%25%5%34445%38%
2385
May1st to 15thDay
20%7%35%6%245%46%33%
2526
16th to endDay
13%6%26%6%445%6%6%36%
2702
June1st to 15thDay
10%42443445%9%45%
2730
16th to endDay
10%425%435%5%5%10%41%
2730
July1st to 15thDay
10%5%25%6%35%5%6%9%40%
2730
16th to endDay
7%325%6%46%5%7%9%41%
2847
August1st to 15thDay
8%3145%35%6%7%10%42%
2433
16th to endDay
8%425%436%5%6%8%44%
2484
September1st to 15thDay
13%5%24435%5%5%7%43%
2274
16th to endDay
12%3145%24446%49%
2145
October1st to 15thDay
15%424434446%44%
2132
16th to endDay
17%6%2432445%5%42%
1911
November1st to 15thDay
14%6%34424436%46%
1852
16th to endDay
19%8%45%323345%38%
1890
December1st to 15thDay
21%12%47%5%23335%30%
1813
16th to endDay
22%12%47%5%23346%28%
1792
January1st to 15thNight
19%10%5%8%5%23435%31%
2926
16th to endNight
16%12%6%7%5%33345%29%
3016
February1st to 15thNight
17%11%5%8%5%33345%30%
2290
16th to endNight
18%11%47%5%24345%32%
2049
March1st to 15thNight
18%9%35%5%24445%35%
2327
16th to endNight
19%8%35%5%24446%35%
2204
April1st to 15thNight
17%8%35%433345%41%
1947
16th to endNight
15%6%35%42445%6%41%
1850
May1st to 15thNight
17%6%26%5%2445%7%36%
1755
16th to endNight
10%436%5%35%5%7%8%40%
1760
June1st to 15thNight
9%425%5%2345%9%48%
1560
16th to endNight
8%3133346%6%10%47%
1560
July1st to 15thNight
7%5%133236%7%8%49%
1560
16th to endNight
5%31342445%8%55%
1672
August1st to 15thNight
5%31443445%9%52%
1777
16th to endNight
5%32442445%8%53%
2070
September1st to 15thNight
11%5%14323447%50%
2002
16th to endNight
10%423423436%52%
2145
October1st to 15thNight
11%5%13323347%50%
2155
16th to endNight
17%6%24323346%44%
2664
November1st to 15thNight
15%6%34423346%45%
2666
16th to endNight
18%10%44422336%38%
2730
December1st to 15thNight
20%12%5%7%5%13345%30%
2803
16th to endNight
24%12%5%6%42444426%
3136

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
20%11%48%5%34445%28%
1672
16th to endDay
13%14%5%7%5%33335%33%
1823
February1st to 15thDay
15%12%5%8%5%34345%30%
1900
16th to endDay
16%13%48%5%34446%29%
1710
March1st to 15thDay
21%8%36%5%23445%33%
1950
16th to endDay
19%8%46%5%3445%6%31%
2381
April1st to 15thDay
18%7%35%43335%6%38%
2331
16th to endDay
18%6%25%6%34446%38%
2385
May1st to 15thDay
20%7%36%6%24446%33%
2526
16th to endDay
13%6%26%6%45%5%6%7%36%
2702
June1st to 15thDay
10%4245%35%36%8%45%
2730
16th to endDay
10%5%25%436%46%9%41%
2730
July1st to 15thDay
10%425%5%345%6%9%40%
2730
16th to endDay
7%425%6%46%6%6%9%41%
2847
August1st to 15thDay
8%315%5%36%5%7%10%42%
2433
16th to endDay
8%425%435%5%6%8%43%
2484
September1st to 15thDay
13%5%245%35%5%5%7%43%
2274
16th to endDay
12%4145%24346%49%
2145
October1st to 15thDay
15%5%25%434446%43%
2132
16th to endDay
17%6%2432445%5%42%
1911
November1st to 15thDay
13%6%35%324445%45%
1852
16th to endDay
19%8%45%423445%37%
1890
December1st to 15thDay
21%11%47%423335%30%
1813
16th to endDay
23%11%47%424336%28%
1792
January1st to 15thNight
19%11%5%7%6%23445%30%
2926
16th to endNight
16%12%6%7%5%34345%29%
3016
February1st to 15thNight
17%11%5%8%5%33345%30%
2283
16th to endNight
18%11%47%5%34335%32%
2049
March1st to 15thNight
18%9%35%5%24445%35%
2340
16th to endNight
19%8%35%434446%35%
2204
April1st to 15thNight
16%8%35%433345%41%
1947
16th to endNight
14%7%35%424346%41%
1850
May1st to 15thNight
17%5%35%5%2445%7%36%
1754
16th to endNight
9%5%36%435%5%7%8%40%
1760
June1st to 15thNight
8%425%5%2345%8%49%
1560
16th to endNight
8%414325%6%6%10%47%
1560
July1st to 15thNight
7%412325%5%7%8%50%
1560
16th to endNight
5%2135%2445%8%55%
1672
August1st to 15thNight
5%31443445%9%53%
1777
16th to endNight
6%32442445%8%53%
2070
September1st to 15thNight
10%5%14423447%50%
2002
16th to endNight
10%424423347%51%
2145
October1st to 15thNight
11%5%13324347%50%
2155
16th to endNight
17%7%25%313346%44%
2664
November1st to 15thNight
15%7%24333346%45%
2666
16th to endNight
18%10%35%423236%38%
2730
December1st to 15thNight
20%12%5%8%423345%29%
2803
16th to endNight
24%12%46%5%2443426%
3136

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
57%49%16%10%
1673
16th to endDay
53%411%23%6%
1823
February1st to 15thDay
54%5%11%19%7%1
1902
16th to endDay
54%410%21%7%
1710
March1st to 15thDay
52%5%10%21%10%
1950
16th to endDay
52%5%11%21%7%1
2382
April1st to 15thDay
46%5%11%22%13%
2331
16th to endDay
47%48%21%11%5%
2385
May1st to 15thDay
51%6%12%18%11%
2526
16th to endDay
44%8%12%17%14%2
2706
June1st to 15thDay
34%7%11%26%16%3
2730
16th to endDay
36%8%14%21%15%3
2730
July1st to 15thDay
39%7%11%21%16%3
2581
16th to endDay
35%7%15%25%13%1
2682
August1st to 15thDay
34%8%13%23%17%2
2420
16th to endDay
35%7%12%22%16%5%
2484
September1st to 15thDay
39%5%11%22%16%4
2274
16th to endDay
36%49%24%23%2
2145
October1st to 15thDay
40%5%9%24%18%1
2132
16th to endDay
42%310%24%16%
1911
November1st to 15thDay
39%411%22%16%5%
1852
16th to endDay
48%48%23%14%1
1890
December1st to 15thDay
57%49%17%9%
1813
16th to endDay
57%411%20%5%1
1792
January1st to 15thNight
56%47%18%11%1
2926
16th to endNight
56%312%19%7%
3016
February1st to 15thNight
55%412%18%7%1
2292
16th to endNight
54%5%11%18%9%
2049
March1st to 15thNight
50%49%20%11%2
2340
16th to endNight
49%5%13%22%7%1
2204
April1st to 15thNight
45%48%24%15%1
1947
16th to endNight
42%48%22%14%6%
1850
May1st to 15thNight
45%7%12%21%12%
1755
16th to endNight
38%8%13%18%15%4
1762
June1st to 15thNight
32%5%12%25%21%2
1560
16th to endNight
29%7%15%22%19%5%
1560
July1st to 15thNight
29%7%15%23%19%4
1480
16th to endNight
24%6%12%34%18%3
1574
August1st to 15thNight
28%6%14%24%21%3
1766
16th to endNight
26%7%12%26%19%5%
2070
September1st to 15thNight
33%5%10%22%20%6%
2002
16th to endNight
32%5%10%21%25%5%
2145
October1st to 15thNight
32%5%9%25%20%5%
2155
16th to endNight
41%39%26%17%2
2664
November1st to 15thNight
40%48%21%19%5%
2666
16th to endNight
48%39%23%14%
2730
December1st to 15thNight
57%310%17%10%
2803
16th to endNight
61%5%8%16%7%
3136

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
36%17%28%13%3
180
16th to endDay
23%25%42%8%
180
February1st to 15thDay
27%27%34%8%1
135
16th to endDay
29%20%36%11%1
120
March1st to 15thDay
28%21%41%8%
135
16th to endDay
26%16%32%17%5%1
345
April1st to 15thDay
24%16%31%19%8%
330
16th to endDay
23%11%28%19%13%2
319
May1st to 15thDay
24%10%31%18%10%3
348
16th to endDay
19%5%28%23%14%9%
458
June1st to 15thDay
11%427%33%17%5%
570
16th to endDay
12%7%30%26%16%7%
570
July1st to 15thDay
14%321%25%21%13%
550
16th to endDay
8%217%33%23%13%
563
August1st to 15thDay
11%112%29%30%14%
358
16th to endDay
10%319%25%28%11%
396
September1st to 15thDay
14%414%27%26%12%
375
16th to endDay
14%5%17%25%27%9%
374
October1st to 15thDay
16%7%29%27%15%4
362
16th to endDay
24%11%40%21%2
192
November1st to 15thDay
25%17%25%20%7%3
180
16th to endDay
26%16%36%17%2
180
December1st to 15thDay
24%28%28%12%5%
180
16th to endDay
35%17%39%6%1
192
January1st to 15thNight
25%17%32%20%3
1050
16th to endNight
23%20%34%20%1
1076
February1st to 15thNight
23%17%36%20%1
764
16th to endNight
24%18%35%19%2
683
March1st to 15thNight
25%14%35%21%2
780
16th to endNight
22%13%31%24%7%
741
April1st to 15thNight
21%14%29%26%7%
584
16th to endNight
18%8%33%27%11%
579
May1st to 15thNight
17%8%30%30%12%
585
16th to endNight
11%426%31%21%4
611
June1st to 15thNight
10%223%41%21%
585
16th to endNight
9%222%37%27%1
585
July1st to 15thNight
8%116%35%32%5%
555
16th to endNight
7%10%38%34%7%
612
August1st to 15thNight
6%112%36%36%6%
575
16th to endNight
5%115%33%39%4
621
September1st to 15thNight
14%214%33%29%5%
637
16th to endNight
14%417%27%31%5%
777
October1st to 15thNight
15%6%23%29%21%4
780
16th to endNight
19%12%34%23%9%
832
November1st to 15thNight
17%12%30%25%12%1
820
16th to endNight
24%16%25%24%8%
840
December1st to 15thNight
29%14%30%19%6%1
913
16th to endNight
31%13%33%18%4
1120
Page generated at 2019-01-28 21:54:06. Version ac04

Copyright 2019 A. Danko


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