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 2005-11-05 to 2017-10-06.

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
44%
15941
23%
47157
15%
15894
52%
15894
32%
28355

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
31%
900
23%
2327
9%
895
42%
895
33%
1451
January16th to endNight
29%
960
25%
2496
9%
960
39%
960
31%
1587
February1st to 15thNight
24%
879
16%
2288
6%
875
30%
875
24%
1596
February16th to endNight
28%
672
24%
1934
7%
672
40%
672
29%
1196
March1st to 15thNight
35%
540
21%
1980
14%
540
45%
540
24%
1191
March16th to endNight
30%
576
15%
2112
10%
576
38%
576
17%
1400
April1st to 15thNight
34%
539
22%
1827
15%
539
47%
539
29%
1043
April16th to endNight
38%
540
22%
1752
17%
540
50%
540
26%
1093
May1st to 15thNight
45%
539
19%
1620
15%
539
52%
539
26%
1049
May16th to endNight
49%
563
20%
1589
15%
561
55%
561
31%
993
June1st to 15thNight
66%
540
21%
1440
13%
540
70%
540
43%
824
June16th to endNight
65%
540
25%
1440
15%
540
69%
540
51%
772
July1st to 15thNight
69%
510
19%
1470
16%
510
70%
510
40%
833
July16th to endNight
77%
564
25%
1594
25%
531
80%
531
49%
799
August1st to 15thNight
81%
539
25%
1610
30%
536
81%
536
46%
850
August16th to endNight
72%
573
27%
1842
32%
573
75%
573
40%
975
September1st to 15thNight
64%
540
27%
1807
29%
540
67%
540
35%
1001
September16th to endNight
62%
555
30%
1998
25%
555
71%
555
35%
1041
October1st to 15thNight
49%
684
28%
2052
20%
684
54%
684
36%
1169
October16th to endNight
40%
704
28%
2112
15%
704
50%
704
35%
1201
November1st to 15thNight
40%
724
29%
2151
15%
724
52%
724
35%
1218
November16th to endNight
33%
900
24%
2520
10%
900
44%
900
30%
1552
December1st to 15thNight
29%
900
19%
2520
8%
900
38%
900
26%
1676
December16th to endNight
29%
960
20%
2676
8%
960
39%
960
23%
1845

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%6%25%42445%7%43%
48032
Night
11%5%24424447%48%
47352
TransparencyDay
39%413%25%14%2
47732
Night
35%312%27%17%3
47157
SeeingDay
13%5%22%29%21%6%
5965
Night
14%6%28%33%15%1
15943

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
12%5%36%5%245%26%45%
1611
16th to endDay
13%8%45%5%34436%40%
1728
February1st to 15thDay
13%9%5%6%5%2335%6%37%
1575
16th to endDay
13%9%35%5%32346%41%
1548
March1st to 15thDay
12%11%36%5%2435%6%37%
1980
16th to endDay
22%8%36%424335%33%
2110
April1st to 15thDay
16%8%35%5%23345%41%
2120
16th to endDay
21%6%36%5%34446%33%
2205
May1st to 15thDay
18%6%36%6%2435%5%37%
2331
16th to endDay
14%5%35%5%35%5%5%8%37%
2523
June1st to 15thDay
9%425%4345%6%9%44%
2520
16th to endDay
6%213336%5%7%10%48%
2520
July1st to 15thDay
8%424425%5%6%10%46%
2397
16th to endDay
5%3245%36%5%6%9%47%
2466
August1st to 15thDay
8%4145%25%46%10%46%
2340
16th to endDay
7%3245%35%45%9%48%
2360
September1st to 15thDay
11%42432345%7%50%
2151
16th to endDay
8%3244235%5%8%50%
1950
October1st to 15thDay
15%5%14313346%49%
1706
16th to endDay
13%5%25%41334451%
1760
November1st to 15thDay
12%5%13323437%52%
1706
16th to endDay
17%7%34323235%46%
1440
December1st to 15thDay
15%9%46%5%23346%38%
1440
16th to endDay
15%9%47%423345%39%
1545
January1st to 15thNight
10%7%34423346%49%
2327
16th to endNight
9%6%36%423346%47%
2496
February1st to 15thNight
12%8%46%6%24446%38%
2278
16th to endNight
12%7%34324346%47%
1934
March1st to 15thNight
13%6%35%5%24346%44%
1980
16th to endNight
20%7%3432445%7%35%
2112
April1st to 15thNight
12%7%24322346%50%
1827
16th to endNight
17%6%35%31335%6%42%
1752
May1st to 15thNight
13%5%3443445%6%42%
1619
16th to endNight
13%3244245%5%7%46%
1587
June1st to 15thNight
5%312435%48%10%51%
1440
16th to endNight
321232347%11%57%
1440
July1st to 15thNight
8%2125%235%6%8%51%
1560
16th to endNight
5%2133135%6%11%54%
1702
August1st to 15thNight
42124245%5%9%58%
1620
16th to endNight
7%314423447%57%
1842
September1st to 15thNight
9%5%1432445%6%52%
1807
16th to endNight
7%3135%3345%7%54%
1998
October1st to 15thNight
13%313323245%54%
2052
16th to endNight
12%41341333456%
2112
November1st to 15thNight
11%323313335%55%
2151
16th to endNight
15%6%24313335%50%
2520
December1st to 15thNight
16%8%34424345%42%
2520
16th to endNight
16%10%36%423336%39%
2676

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
41%311%25%17%1
1612
16th to endDay
45%315%23%11%1
1728
February1st to 15thDay
47%315%23%9%
1576
16th to endDay
44%214%23%13%1
1548
March1st to 15thDay
47%311%24%9%1
1980
16th to endDay
55%312%18%8%1
2112
April1st to 15thDay
44%311%24%13%1
2120
16th to endDay
51%312%19%11%
2205
May1st to 15thDay
48%5%11%23%9%
2331
16th to endDay
43%5%15%22%11%1
2527
June1st to 15thDay
35%6%13%29%14%1
2520
16th to endDay
27%6%17%30%15%2
2520
July1st to 15thDay
33%5%16%29%12%2
2258
16th to endDay
29%6%14%32%15%1
2311
August1st to 15thDay
31%5%17%28%15%1
2326
16th to endDay
32%6%13%24%18%5%
2360
September1st to 15thDay
33%411%26%19%4
2151
16th to endDay
30%5%12%31%18%2
1950
October1st to 15thDay
35%210%26%20%4
1706
16th to endDay
36%39%27%19%4
1760
November1st to 15thDay
32%312%25%20%5%
1706
16th to endDay
40%29%28%18%
1440
December1st to 15thDay
47%313%25%10%
1440
16th to endDay
47%315%21%10%2
1545
January1st to 15thNight
36%214%27%17%1
2327
16th to endNight
38%314%26%16%1
2496
February1st to 15thNight
47%311%22%12%1
2288
16th to endNight
38%313%24%18%2
1934
March1st to 15thNight
41%310%25%15%3
1980
16th to endNight
47%5%12%22%10%1
2112
April1st to 15thNight
36%210%27%19%3
1827
16th to endNight
41%310%26%15%1
1752
May1st to 15thNight
40%6%12%24%15%1
1620
16th to endNight
36%6%14%26%14%1
1589
June1st to 15thNight
25%6%15%32%17%2
1440
16th to endNight
20%5%16%31%23%3
1440
July1st to 15thNight
29%412%33%16%3
1470
16th to endNight
20%415%38%19%1
1594
August1st to 15thNight
21%6%15%34%19%2
1610
16th to endNight
27%39%26%25%6%
1842
September1st to 15thNight
31%310%25%20%7%
1807
16th to endNight
28%410%31%21%3
1998
October1st to 15thNight
32%29%26%22%6%
2052
16th to endNight
32%29%28%21%5%
2112
November1st to 15thNight
31%311%23%22%7%
2151
16th to endNight
38%28%29%18%2
2520
December1st to 15thNight
44%313%25%12%
2520
16th to endNight
47%411%21%12%3
2676

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%10%40%20%3
90
16th to endDay
23%13%38%16%6%1
96
February1st to 15thDay
14%18%36%23%6%
90
16th to endDay
20%19%35%12%8%2
81
March1st to 15thDay
25%12%45%12%4
90
16th to endDay
29%10%33%18%8%
96
April1st to 15thDay
17%12%32%27%10%
239
16th to endDay
25%8%27%25%11%1
315
May1st to 15thDay
17%8%32%25%13%2
468
16th to endDay
18%427%29%14%5%
517
June1st to 15thDay
9%222%36%20%7%
495
16th to endDay
7%327%31%23%6%
495
July1st to 15thDay
14%113%33%28%8%
475
16th to endDay
47%32%41%13%
515
August1st to 15thDay
6%9%34%38%9%
493
16th to endDay
9%11%33%35%10%
400
September1st to 15thDay
10%211%35%31%8%
306
16th to endDay
5%220%40%22%8%
135
October1st to 15thDay
14%5%30%27%14%7%
107
16th to endDay
12%437%36%9%
96
November1st to 15thDay
8%5%22%31%16%15%
90
16th to endDay
35%16%24%16%5%1
90
December1st to 15thDay
20%11%38%18%6%4
90
16th to endDay
22%16%40%16%3
96
January1st to 15thNight
14%11%38%28%7%
900
16th to endNight
13%10%40%30%5%
960
February1st to 15thNight
15%10%40%29%3
880
16th to endNight
17%9%40%27%4
672
March1st to 15thNight
16%9%35%30%6%1
540
16th to endNight
22%8%34%27%6%
576
April1st to 15thNight
17%8%35%30%8%
539
16th to endNight
20%5%28%32%11%
540
May1st to 15thNight
14%427%38%13%1
540
16th to endNight
14%425%35%17%3
563
June1st to 15thNight
7%119%45%24%1
540
16th to endNight
3124%45%22%2
540
July1st to 15thNight
9%110%46%28%2
510
16th to endNight
6%17%39%42%2
564
August1st to 15thNight
36%43%43%2
539
16th to endNight
7%110%37%36%5%
573
September1st to 15thNight
12%212%39%27%5%
540
16th to endNight
8%218%37%25%6%
555
October1st to 15thNight
16%325%33%18%3
684
16th to endNight
15%5%33%30%13%
704
November1st to 15thNight
13%7%32%31%13%
724
16th to endNight
18%9%35%28%8%
900
December1st to 15thNight
20%9%35%28%4
900
16th to endNight
20%8%34%30%4
960
Page generated at 2017-10-07 13:07:48. Version ac04

Copyright 2017 A. Danko


Hillsman's Observatory Clear Sky Chart | Charts Home