Hillsman's Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hillsman's Observatory clear sky chart from 2005-11-06 to 2024-01-16.

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
42%
24479
23%
74752
14%
24417
50%
24417
30%
45495

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 10thNight
29%
950
22%
2458
7%
946
41%
946
30%
1592
January11th to 20thNight
24%
930
22%
2418
8%
930
34%
930
25%
1656
January21st to endNight
26%
990
22%
2574
7%
990
35%
990
27%
1720
February1st to 10thNight
22%
900
16%
2340
5%
900
29%
900
24%
1654
February11th to 20thNight
25%
879
18%
2274
6%
875
32%
875
26%
1528
February21st to endNight
22%
564
24%
1748
8%
564
36%
564
24%
1103
March1st to 10thNight
28%
540
25%
1980
12%
540
45%
540
26%
1139
March11th to 20thNight
32%
540
19%
1980
13%
540
41%
540
19%
1254
March21st to endNight
25%
594
13%
2178
7%
594
33%
594
15%
1515
April1st to 10thNight
33%
540
23%
1846
14%
540
47%
540
29%
1038
April11th to 20thNight
35%
533
23%
1775
18%
533
46%
533
26%
1071
April21st to endNight
32%
540
21%
1729
12%
540
47%
540
26%
1082
May1st to 10thNight
38%
540
18%
1620
13%
540
47%
540
25%
1052
May11th to 20thNight
47%
531
19%
1594
17%
531
52%
531
28%
1004
May21st to endNight
50%
584
20%
1604
13%
582
56%
582
30%
1016
June1st to 10thNight
69%
540
23%
1440
15%
540
72%
540
46%
797
June11th to 20thNight
64%
540
24%
1440
16%
540
67%
540
43%
838
June21st to endNight
64%
540
27%
1440
17%
540
68%
540
52%
761
July1st to 10thNight
72%
525
19%
1485
17%
525
73%
525
40%
852
July11th to 20thNight
75%
522
24%
1566
22%
522
78%
522
49%
786
July21st to endNight
71%
591
24%
1673
25%
558
74%
558
42%
900
August1st to 10thNight
78%
537
23%
1601
28%
534
80%
534
45%
850
August11th to 20thNight
71%
534
29%
1600
32%
534
75%
534
42%
885
August21st to endNight
75%
594
29%
1966
34%
594
77%
594
44%
970
September1st to 10thNight
65%
540
27%
1800
30%
540
68%
540
37%
968
September11th to 20thNight
64%
540
31%
1899
29%
540
71%
540
36%
976
September21st to endNight
60%
566
30%
2006
26%
566
68%
566
38%
1017
October1st to 10thNight
54%
720
27%
2160
20%
720
58%
720
39%
1186
October11th to 20thNight
35%
720
29%
2160
16%
720
46%
720
36%
1229
October21st to endNight
34%
792
26%
2376
12%
792
45%
792
29%
1438
November1st to 10thNight
41%
740
31%
2220
17%
740
53%
740
38%
1206
November11th to 20thNight
35%
893
27%
2550
12%
893
48%
893
34%
1488
November21st to endNight
31%
950
23%
2660
9%
950
42%
950
29%
1673
December1st to 10thNight
30%
950
21%
2660
8%
950
40%
950
28%
1700
December11th to 20thNight
30%
949
22%
3135
9%
948
40%
948
24%
1952
December21st to endNight
24%
1041
13%
4797
8%
1026
36%
1026
12%
3599

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
12%7%35%5%3445%7%44%
74659
Night
12%7%35%43445%7%48%
75155
TransparencyDay
40%5%13%26%15%2
74382
Night
37%411%27%18%3
74953
SeeingDay
16%7%26%28%18%5%
14505
Night
15%7%30%33%14%1
24484

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 10thDay
13%7%36%5%35%5%37%42%
1707
11th to 20thDay
15%10%47%6%34445%39%
1670
21st to endDay
13%10%47%5%35%45%6%38%
1782
February1st to 10thDay
15%11%6%6%5%23347%36%
1620
11th to 20thDay
14%9%47%5%4445%6%40%
1574
21st to endDay
14%10%36%5%3335%6%41%
1522
March1st to 10thDay
12%11%36%6%2445%5%42%
1980
11th to 20thDay
21%9%47%5%33346%35%
1980
21st to endDay
22%11%47%5%34445%30%
2178
April1st to 10thDay
14%7%36%5%3346%6%43%
2112
11th to 20thDay
16%9%25%5%34446%40%
2134
21st to endDay
21%6%37%5%35%446%35%
2227
May1st to 10thDay
18%7%46%6%35%45%6%37%
2340
11th to 20thDay
17%7%35%6%3445%7%41%
2302
21st to endDay
14%6%36%6%45%6%6%8%34%
2668
June1st to 10thDay
7%4244346%7%10%49%
2520
11th to 20thDay
8%425%5%45%5%5%9%48%
2520
21st to endDay
6%324436%5%6%10%52%
2520
July1st to 10thDay
10%4244245%6%11%46%
2426
11th to 20thDay
4324435%5%7%10%53%
2340
21st to endDay
8%5%346%36%5%6%9%45%
2546
August1st to 10thDay
7%5%25%5%35%5%7%11%45%
2328
11th to 20thDay
8%425%5%36%5%6%9%47%
2301
21st to endDay
8%4245%3445%10%53%
2390
September1st to 10thDay
11%5%2443345%7%52%
2160
11th to 20thDay
10%42342445%9%53%
2057
21st to endDay
8%425%42445%7%56%
1936
October1st to 10thDay
12%5%2442335%7%53%
1800
11th to 20thDay
13%6%34323436%53%
1800
21st to endDay
18%8%36%423345%45%
1980
November1st to 10thDay
10%7%24323447%53%
1858
11th to 20thDay
15%7%24423346%50%
1626
21st to endDay
16%8%45%423336%46%
1520
December1st to 10thDay
11%8%46%5%34347%45%
1520
11th to 20thDay
12%9%5%7%5%3435%5%42%
1918
21st to endDay
16%15%7%10%6%34445%27%
2797
January1st to 10thNight
10%10%36%434345%47%
2458
11th to 20thNight
13%8%46%6%345%5%6%40%
2418
21st to endNight
11%9%47%5%3435%6%42%
2574
February1st to 10thNight
13%10%47%6%4445%6%36%
2340
11th to 20thNight
13%8%47%434347%42%
2273
21st to endNight
14%9%45%424445%45%
1748
March1st to 10thNight
12%6%45%5%24347%48%
1980
11th to 20thNight
17%8%36%42445%6%40%
1980
21st to endNight
21%10%35%435%5%5%6%32%
2178
April1st to 10thNight
11%7%3432335%6%51%
1846
11th to 20thNight
14%7%35%423446%46%
1775
21st to endNight
17%5%36%42436%7%42%
1729
May1st to 10thNight
16%6%35%5%35%46%7%42%
1620
11th to 20thNight
15%5%245%345%47%47%
1593
21st to endNight
11%426%5%35%5%6%9%44%
1603
June1st to 10thNight
6%31332448%10%55%
1440
11th to 20thNight
5%424435%5%8%12%50%
1440
21st to endNight
42134345%7%8%60%
1440
July1st to 10thNight
8%2245%345%7%10%51%
1529
11th to 20thNight
43134245%6%9%59%
1620
21st to endNight
7%3244345%6%11%51%
1772
August1st to 10thNight
42135%345%6%10%57%
1611
11th to 20thNight
7%4235%25%5%47%58%
1600
21st to endNight
6%324424448%60%
1966
September1st to 10thNight
10%5%1442445%6%56%
1800
11th to 20thNight
10%41342346%7%55%
1899
21st to endNight
7%4245%3345%6%58%
2006
October1st to 10thNight
10%42342445%6%57%
2160
11th to 20thNight
14%5%24313346%55%
2160
21st to endNight
17%6%2442343451%
2376
November1st to 10thNight
11%424323336%59%
2220
11th to 20thNight
11%5%35%424346%53%
2550
21st to endNight
16%7%25%423335%49%
2660
December1st to 10thNight
13%8%3443445%5%46%
2660
11th to 20thNight
13%7%36%424447%45%
3279
21st to endNight
19%16%5%8%5%3444428%
4852

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 10thDay
42%410%25%17%1
1708
11th to 20thDay
49%310%25%12%1
1670
21st to endDay
46%415%22%11%2
1782
February1st to 10thDay
50%312%22%11%2
1620
11th to 20thDay
46%313%21%14%2
1583
21st to endDay
45%312%23%15%2
1522
March1st to 10thDay
45%311%24%14%3
1980
11th to 20thDay
51%5%9%22%11%2
1980
21st to endDay
56%412%18%8%1
2178
April1st to 10thDay
42%412%25%16%1
2112
11th to 20thDay
45%413%23%14%1
2134
21st to endDay
50%411%24%11%
2227
May1st to 10thDay
48%6%12%23%11%1
2340
11th to 20thDay
44%5%13%25%13%
2306
21st to endDay
46%6%14%21%11%2
2668
June1st to 10thDay
27%8%17%33%14%1
2520
11th to 20thDay
33%7%13%28%18%1
2520
21st to endDay
27%6%16%32%15%4
2520
July1st to 10thDay
32%6%17%26%16%3
2362
11th to 20thDay
25%7%17%30%18%3
2271
21st to endDay
34%6%12%32%15%1
2405
August1st to 10thDay
32%6%19%27%14%1
2314
11th to 20thDay
32%7%13%31%16%2
2301
21st to endDay
28%5%14%26%20%6%
2390
September1st to 10thDay
32%412%28%18%6%
2160
11th to 20thDay
28%6%12%26%26%2
2057
21st to endDay
28%410%31%23%3
1936
October1st to 10thDay
32%312%27%22%3
1800
11th to 20thDay
34%37%30%22%4
1800
21st to endDay
43%38%22%19%5%
1980
November1st to 10thDay
31%413%28%19%5%
1858
11th to 20thDay
37%310%25%22%3
1626
21st to endDay
43%38%27%19%1
1520
December1st to 10thDay
41%312%30%13%1
1520
11th to 20thDay
45%313%27%9%2
1915
21st to endDay
61%410%16%8%1
2797
January1st to 10thNight
40%213%26%17%2
2458
11th to 20thNight
45%412%26%13%1
2418
21st to endNight
43%313%25%14%2
2574
February1st to 10thNight
48%411%21%13%2
2340
11th to 20thNight
43%412%21%18%3
2274
21st to endNight
43%310%22%17%5%
1748
March1st to 10thNight
38%310%25%19%4
1980
11th to 20thNight
45%49%23%15%4
1980
21st to endNight
52%5%12%20%10%1
2178
April1st to 10thNight
35%311%27%20%4
1846
11th to 20thNight
39%39%27%17%4
1775
21st to endNight
41%411%27%16%1
1729
May1st to 10thNight
42%5%13%24%15%1
1620
11th to 20thNight
38%6%13%25%17%1
1594
21st to endNight
38%6%15%26%13%2
1604
June1st to 10thNight
23%7%18%33%17%3
1440
11th to 20thNight
26%7%14%28%22%3
1440
21st to endNight
20%5%15%34%21%5%
1440
July1st to 10thNight
27%7%14%32%16%4
1485
11th to 20thNight
20%5%14%36%22%3
1566
21st to endNight
26%5%13%37%17%1
1673
August1st to 10thNight
21%8%19%34%16%3
1601
11th to 20thNight
26%5%10%33%24%1
1600
21st to endNight
23%411%28%26%7%
1966
September1st to 10thNight
30%412%27%21%7%
1800
11th to 20thNight
28%5%10%28%25%4
1899
21st to endNight
27%48%29%28%4
2006
October1st to 10thNight
29%310%27%25%6%
2160
11th to 20thNight
33%26%29%22%8%
2160
21st to endNight
38%39%23%24%4
2376
November1st to 10thNight
29%312%28%23%6%
2220
11th to 20thNight
33%38%27%24%5%
2550
21st to endNight
40%38%28%18%3
2660
December1st to 10thNight
40%412%27%15%1
2660
11th to 20thNight
41%310%31%14%1
3281
21st to endNight
59%5%8%18%9%2
4852

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 10thDay
22%12%35%24%7%
270
11th to 20thDay
31%14%40%14%2
257
21st to endDay
19%13%45%19%3
264
February1st to 10thDay
26%13%42%14%4
240
11th to 20thDay
23%19%37%15%6%1
240
21st to endDay
23%22%37%14%41
198
March1st to 10thDay
20%13%47%16%5%
240
11th to 20thDay
28%11%36%21%41
240
21st to endDay
37%15%30%14%41
264
April1st to 10thDay
20%14%35%22%9%
372
11th to 20thDay
20%14%32%25%8%1
412
21st to endDay
24%13%31%23%9%1
487
May1st to 10thDay
18%11%35%25%10%1
603
11th to 20thDay
20%6%28%29%13%3
625
21st to endDay
18%5%25%26%19%6%
679
June1st to 10thDay
7%218%35%27%10%
630
11th to 20thDay
10%223%35%25%6%
630
21st to endDay
8%329%35%21%4
630
July1st to 10thDay
14%110%26%32%17%
621
11th to 20thDay
6%117%35%30%11%
618
21st to endDay
9%112%35%33%10%
684
August1st to 10thDay
7%114%40%31%7%
626
11th to 20thDay
9%114%36%32%8%
615
21st to endDay
10%111%28%38%13%
509
September1st to 10thDay
14%212%37%26%9%
450
11th to 20thDay
7%217%37%30%8%
347
21st to endDay
9%6%24%32%23%6%
270
October1st to 10thDay
15%7%27%27%16%9%
270
11th to 20thDay
13%14%41%23%7%
270
21st to endDay
26%12%34%23%5%
297
November1st to 10thDay
16%9%35%26%9%5%
270
11th to 20thDay
19%16%30%24%10%2
270
21st to endDay
24%11%34%24%7%
270
December1st to 10thDay
12%15%37%26%7%3
270
11th to 20thDay
23%14%33%23%7%1
270
21st to endDay
23%19%40%18%1
297
January1st to 10thNight
15%11%38%29%7%
950
11th to 20thNight
17%13%39%26%5%1
930
21st to endNight
15%12%41%29%4
990
February1st to 10thNight
17%11%42%25%4
900
11th to 20thNight
18%13%38%28%3
879
21st to endNight
20%13%41%22%4
564
March1st to 10thNight
15%11%42%26%6%
540
11th to 20thNight
20%9%34%30%6%1
540
21st to endNight
27%9%35%25%4
594
April1st to 10thNight
16%9%37%31%6%
540
11th to 20thNight
20%9%31%30%9%1
533
21st to endNight
19%6%36%31%8%
540
May1st to 10thNight
17%6%30%38%9%1
540
11th to 20thNight
16%5%26%36%17%1
531
21st to endNight
13%424%34%21%3
584
June1st to 10thNight
8%216%43%29%3
540
11th to 20thNight
6%121%46%24%2
540
21st to endNight
4224%50%18%2
540
July1st to 10thNight
9%28%42%36%4
525
11th to 20thNight
6%111%44%34%3
522
21st to endNight
10%210%41%36%2
591
August1st to 10thNight
5%18%47%37%2
537
11th to 20thNight
7%111%43%34%4
534
21st to endNight
7%111%38%39%4
594
September1st to 10thNight
13%113%41%28%4
540
11th to 20thNight
11%216%40%25%6%
540
21st to endNight
7%423%40%23%4
566
October1st to 10thNight
12%323%38%20%3
720
11th to 20thNight
16%6%37%33%8%1
720
21st to endNight
21%8%33%28%10%
792
November1st to 10thNight
13%7%34%35%11%
740
11th to 20thNight
14%10%36%29%10%
893
21st to endNight
20%8%36%29%6%
950
December1st to 10thNight
16%9%38%29%6%1
950
11th to 20thNight
20%7%36%32%4
950
21st to endNight
20%14%36%26%4
1045
Page generated at 2024-01-13 18:28:32. Version ac07

Copyright 2024 Attilla Danko


Hillsman's Observatory Clear Sky Chart |Charts Home