PS-191 Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the PS-191 Observatory clear sky chart from 2005-11-05 to 2017-09-22.

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
46%
15426
23%
47003
16%
15384
55%
15384
28%
28774

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
23%
720
22%
2327
10%
716
39%
716
19%
1522
January16th to endNight
25%
768
24%
2436
12%
768
39%
768
21%
1569
February1st to 15thNight
27%
702
24%
2112
10%
700
40%
700
25%
1329
February16th to endNight
21%
631
23%
1893
10%
631
33%
631
21%
1243
March1st to 15thNight
30%
720
22%
2094
12%
720
39%
720
24%
1367
March16th to endNight
36%
768
21%
2112
13%
768
41%
768
27%
1367
April1st to 15thNight
42%
581
26%
1839
16%
581
55%
581
35%
1014
April16th to endNight
43%
540
26%
1719
18%
540
54%
540
33%
990
May1st to 15thNight
50%
540
21%
1620
12%
540
57%
540
32%
982
May16th to endNight
64%
561
21%
1683
15%
561
68%
561
33%
1002
June1st to 15thNight
69%
540
16%
1620
13%
540
71%
540
36%
948
June16th to endNight
79%
540
19%
1620
16%
540
80%
540
39%
914
July1st to 15thNight
69%
510
15%
1530
13%
510
71%
510
31%
944
July16th to endNight
71%
564
20%
1595
17%
531
73%
531
35%
928
August1st to 15thNight
75%
539
20%
1663
20%
536
76%
536
32%
998
August16th to endNight
68%
573
21%
1910
20%
573
70%
573
27%
1165
September1st to 15thNight
64%
672
19%
1932
17%
672
66%
672
28%
1252
September16th to endNight
61%
685
27%
1892
20%
685
66%
685
34%
1158
October1st to 15thNight
54%
660
35%
1815
27%
660
61%
660
39%
1054
October16th to endNight
49%
704
32%
2139
24%
704
60%
704
35%
1209
November1st to 15thNight
46%
700
31%
2276
24%
700
58%
700
34%
1234
November16th to endNight
35%
720
27%
2340
16%
720
50%
720
27%
1396
December1st to 15thNight
30%
720
22%
2340
15%
720
41%
720
22%
1503
December16th to endNight
27%
768
20%
2496
12%
768
37%
768
19%
1686

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%5%25%5%35%5%5%7%40%
47877
Night
11%5%2442445%7%44%
47201
TransparencyDay
41%411%21%17%3
47578
Night
38%411%22%19%4
47004
SeeingDay
15%7%18%23%22%12%
5311
Night
14%8%22%29%20%3
15430

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
18%8%35%5%2344438%
1611
16th to endDay
17%5%26%5%2343443%
1786
February1st to 15thDay
16%8%36%5%22446%38%
1750
16th to endDay
16%7%37%5%34346%38%
1580
March1st to 15thDay
17%7%35%434347%37%
1866
16th to endDay
15%7%2443445%6%40%
2111
April1st to 15thDay
12%5%24435%5%5%6%43%
2118
16th to endDay
11%5%25%6%35%446%43%
2240
May1st to 15thDay
12%5%26%5%345%5%6%42%
2331
16th to endDay
9%426%6%35%5%7%8%39%
2431
June1st to 15thDay
7%425%6%37%6%8%10%37%
2340
16th to endDay
5%3245%36%7%8%11%39%
2340
July1st to 15thDay
9%5%36%6%48%7%7%10%29%
2340
16th to endDay
7%5%25%6%5%8%7%9%10%30%
2465
August1st to 15thDay
6%415%7%47%7%8%11%35%
2284
16th to endDay
12%5%27%6%5%6%6%7%9%29%
2292
September1st to 15thDay
13%5%26%5%445%7%9%35%
2016
16th to endDay
14%425%5%2435%7%45%
1881
October1st to 15thDay
11%413324335%56%
1815
16th to endDay
12%42432234455%
1730
November1st to 15thDay
12%5%13423335%54%
1582
16th to endDay
16%6%23323336%47%
1620
December1st to 15thDay
17%8%36%5%34446%37%
1620
16th to endDay
22%9%35%5%2333436%
1728
January1st to 15thNight
17%6%345%35%445%39%
2327
16th to endNight
16%7%25%5%24445%40%
2436
February1st to 15thNight
14%6%25%424336%44%
2103
16th to endNight
16%6%25%6%34445%39%
1893
March1st to 15thNight
14%7%35%43445%7%41%
2094
16th to endNight
12%6%36%5%2435%5%44%
2112
April1st to 15thNight
11%413324348%51%
1839
16th to endNight
10%425%324447%49%
1719
May1st to 15thNight
10%425%4345%5%7%46%
1619
16th to endNight
7%324426%5%5%10%45%
1682
June1st to 15thNight
5%3145%36%6%7%12%43%
1620
16th to endNight
3313435%5%7%12%47%
1620
July1st to 15thNight
8%325%5%37%6%7%11%39%
1620
16th to endNight
6%324435%6%8%14%40%
1703
August1st to 15thNight
5%315%5%35%7%7%11%42%
1674
16th to endNight
9%5%24445%5%8%9%38%
1910
September1st to 15thNight
10%4246%346%8%9%38%
1932
16th to endNight
9%5%145%2445%8%47%
1892
October1st to 15thNight
10%413423236%56%
1815
16th to endNight
10%5%25%32233357%
2139
November1st to 15thNight
12%423312236%56%
2276
16th to endNight
14%5%25%42333449%
2340
December1st to 15thNight
16%7%25%5%24446%39%
2340
16th to endNight
20%9%345%23445%35%
2496

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
47%36%19%19%2
1612
16th to endDay
44%28%23%17%4
1786
February1st to 15thDay
47%27%23%17%2
1752
16th to endDay
47%26%20%18%3
1580
March1st to 15thDay
47%37%18%18%4
1866
16th to endDay
44%312%24%14%1
2112
April1st to 15thDay
39%310%24%17%4
2118
16th to endDay
41%37%24%18%4
2240
May1st to 15thDay
40%412%23%15%3
2331
16th to endDay
39%5%15%22%14%3
2435
June1st to 15thDay
37%6%18%24%11%1
2340
16th to endDay
33%6%16%23%15%3
2340
July1st to 15thDay
42%8%17%18%9%3
2201
16th to endDay
41%7%19%19%11%1
2310
August1st to 15thDay
38%8%16%22%12%1
2271
16th to endDay
47%5%14%17%11%2
2292
September1st to 15thDay
42%7%12%18%13%4
2016
16th to endDay
38%310%20%22%4
1881
October1st to 15thDay
31%37%21%27%8%
1815
16th to endDay
33%15%22%29%7%
1730
November1st to 15thDay
33%25%19%31%7%
1582
16th to endDay
39%25%22%25%5%
1620
December1st to 15thDay
48%37%20%16%3
1620
16th to endDay
52%19%17%15%2
1728
January1st to 15thNight
46%36%19%19%3
2327
16th to endNight
45%26%22%18%4
2436
February1st to 15thNight
42%28%22%19%5%
2112
16th to endNight
46%26%23%18%2
1893
March1st to 15thNight
43%38%19%18%6%
2094
16th to endNight
41%310%27%15%2
2112
April1st to 15thNight
31%211%26%22%5%
1839
16th to endNight
34%310%25%21%5%
1719
May1st to 15thNight
35%416%21%19%2
1620
16th to endNight
33%5%17%25%15%2
1684
June1st to 15thNight
30%6%22%26%12%1
1620
16th to endNight
26%7%21%23%16%4
1620
July1st to 15thNight
34%7%18%23%12%3
1530
16th to endNight
31%6%22%22%14%2
1595
August1st to 15thNight
31%8%18%24%14%2
1663
16th to endNight
37%7%17%20%14%1
1910
September1st to 15thNight
37%8%16%18%14%4
1932
16th to endNight
34%410%22%22%5%
1892
October1st to 15thNight
31%28%21%26%9%
1815
16th to endNight
33%1320%29%11%
2139
November1st to 15thNight
31%2421%28%11%
2276
16th to endNight
39%1421%25%6%
2340
December1st to 15thNight
45%29%18%19%3
2340
16th to endNight
50%29%18%15%2
2496

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
24%16%33%13%11%1
90
16th to endDay
20%29%42%5%2
96
February1st to 15thDay
28%26%35%7%1
90
16th to endDay
32%19%29%18%
81
March1st to 15thDay
21%21%31%18%5%
156
16th to endDay
19%11%35%20%12%1
288
April1st to 15thDay
18%11%28%24%14%2
270
16th to endDay
15%426%27%21%4
270
May1st to 15thDay
13%11%25%23%13%12%
288
16th to endDay
12%319%29%20%14%
331
June1st to 15thDay
9%27%29%28%22%
315
16th to endDay
9%211%25%26%24%
315
July1st to 15thDay
10%29%24%30%21%
305
16th to endDay
11%15%19%30%31%
326
August1st to 15thDay
11%27%30%28%19%
313
16th to endDay
17%16%24%31%18%
332
September1st to 15thDay
15%28%22%31%20%
315
16th to endDay
15%310%26%30%12%
278
October1st to 15thDay
15%221%30%24%5%
255
16th to endDay
15%424%25%26%3
231
November1st to 15thDay
24%10%23%23%16%2
90
16th to endDay
15%15%33%21%14%
90
December1st to 15thDay
25%21%35%11%5%1
90
16th to endDay
33%21%29%12%3
96
January1st to 15thNight
21%18%31%20%6%
720
16th to endNight
20%16%33%26%3
768
February1st to 15thNight
18%14%36%27%2
704
16th to endNight
22%17%34%22%3
631
March1st to 15thNight
19%13%33%27%6%
720
16th to endNight
16%13%28%28%12%
768
April1st to 15thNight
13%10%31%33%10%
581
16th to endNight
11%7%32%34%13%
540
May1st to 15thNight
11%427%32%21%3
540
16th to endNight
7%314%36%31%5%
563
June1st to 15thNight
6%111%35%36%8%
540
16th to endNight
416%32%42%12%
540
July1st to 15thNight
11%6%29%40%10%
510
16th to endNight
7%17%22%46%13%
564
August1st to 15thNight
8%431%44%10%
539
16th to endNight
10%27%29%38%10%
573
September1st to 15thNight
12%28%29%39%7%
672
16th to endNight
12%113%33%35%3
685
October1st to 15thNight
12%5%21%29%25%5%
660
16th to endNight
14%6%24%32%20%2
704
November1st to 15thNight
14%9%24%32%18%2
700
16th to endNight
19%12%28%26%12%
720
December1st to 15thNight
22%14%27%26%8%
720
16th to endNight
25%13%30%25%5%
768
Page generated at 2017-09-23 06:43:41. Version ac04

Copyright 2017 A. Danko


PS-191 Observatory Clear Sky Chart | Charts Home