Shepherd Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Shepherd Observatory clear sky chart from 2005-11-05 to 2017-09-21.

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
50%
15256
24%
47019
17%
15213
58%
15213
29%
28589

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
29%
720
25%
2318
11%
716
45%
716
24%
1412
January16th to endNight
27%
768
26%
2304
11%
768
40%
768
23%
1511
February1st to 15thNight
31%
704
26%
2112
11%
701
44%
701
27%
1297
February16th to endNight
29%
631
25%
1893
12%
631
41%
631
26%
1178
March1st to 15thNight
31%
720
21%
2158
11%
720
40%
720
26%
1355
March16th to endNight
40%
699
24%
2043
13%
699
50%
699
31%
1226
April1st to 15thNight
41%
539
25%
1797
17%
539
53%
539
30%
1034
April16th to endNight
47%
540
28%
1800
20%
540
59%
540
35%
971
May1st to 15thNight
51%
540
22%
1659
14%
540
60%
540
31%
1016
May16th to endNight
69%
561
23%
1682
19%
561
73%
561
36%
991
June1st to 15thNight
73%
540
15%
1620
14%
540
73%
540
30%
1004
June16th to endNight
77%
540
18%
1620
17%
540
78%
540
34%
977
July1st to 15thNight
74%
510
14%
1530
13%
510
75%
510
30%
982
July16th to endNight
75%
564
15%
1648
16%
531
77%
531
29%
1052
August1st to 15thNight
76%
539
17%
1788
20%
536
77%
536
28%
1099
August16th to endNight
68%
573
19%
1910
24%
573
68%
573
24%
1249
September1st to 15thNight
64%
615
21%
1875
21%
615
65%
615
26%
1213
September16th to endNight
66%
681
28%
1881
23%
681
69%
681
36%
1131
October1st to 15thNight
58%
660
34%
1815
26%
660
65%
660
42%
1020
October16th to endNight
54%
704
34%
2114
28%
704
62%
704
37%
1183
November1st to 15thNight
52%
700
30%
2276
25%
700
61%
700
37%
1205
November16th to endNight
41%
720
28%
2340
19%
720
54%
720
30%
1348
December1st to 15thNight
38%
720
23%
2340
17%
720
47%
720
26%
1445
December16th to endNight
31%
768
20%
2496
14%
768
39%
768
19%
1690

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%41%
47831
Night
11%5%2442445%7%46%
47223
TransparencyDay
40%6%11%18%17%5%
47538
Night
35%6%10%19%20%7%
47021
SeeingDay
13%5%18%23%24%14%
5173
Night
13%7%22%28%23%5%
15258

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
19%7%2332333444%
1619
16th to endDay
17%6%34323245%45%
1920
February1st to 15thDay
16%7%25%424335%43%
1750
16th to endDay
19%6%24424335%42%
1580
March1st to 15thDay
17%7%26%423246%42%
1800
16th to endDay
14%5%25%434347%43%
2189
April1st to 15thDay
13%5%245%24447%44%
2151
16th to endDay
9%424436%45%7%46%
2160
May1st to 15thDay
13%425%5%245%48%43%
2292
16th to endDay
9%5%26%5%36%5%5%7%41%
2431
June1st to 15thDay
8%5%26%7%46%7%6%9%34%
2340
16th to endDay
6%325%6%36%6%7%10%41%
2340
July1st to 15thDay
10%425%8%5%8%8%7%11%27%
2340
16th to endDay
7%5%26%7%48%8%8%9%30%
2404
August1st to 15thDay
8%415%7%47%7%9%10%32%
2160
16th to endDay
11%6%26%7%48%7%7%8%28%
2292
September1st to 15thDay
12%5%26%6%45%46%7%36%
2073
16th to endDay
12%5%246%24446%46%
1872
October1st to 15thDay
10%5%1342445%7%50%
1815
16th to endDay
11%413412335%58%
1753
November1st to 15thDay
13%423213335%54%
1582
16th to endDay
13%6%24423345%50%
1620
December1st to 15thDay
18%6%25%324346%42%
1620
16th to endDay
21%10%46%323236%35%
1728
January1st to 15thNight
15%7%2421335%6%46%
2318
16th to endNight
18%7%35%433435%41%
2304
February1st to 15thNight
15%6%24224346%47%
2103
16th to endNight
16%5%25%423335%47%
1893
March1st to 15thNight
16%5%1432345%6%44%
2158
16th to endNight
10%42341445%7%49%
2043
April1st to 15thNight
10%42442445%7%49%
1797
16th to endNight
9%31342345%6%54%
1800
May1st to 15thNight
9%4245%3445%8%47%
1658
16th to endNight
5%2145%345%7%10%48%
1682
June1st to 15thNight
4315%6%36%6%8%10%42%
1620
16th to endNight
33145%36%5%7%13%44%
1620
July1st to 15thNight
6%435%5%46%6%7%9%40%
1620
16th to endNight
4335%5%36%6%8%11%40%
1760
August1st to 15thNight
5%4245%35%6%9%12%39%
1800
16th to endNight
8%6%247%45%5%6%10%38%
1910
September1st to 15thNight
9%425%6%35%5%5%8%42%
1875
16th to endNight
8%42442435%7%51%
1881
October1st to 15thNight
8%423313345%58%
1815
16th to endNight
12%5%1322233458%
2114
November1st to 15thNight
10%423312348%56%
2276
16th to endNight
12%42432335%5%52%
2340
December1st to 15thNight
16%6%24323336%45%
2340
16th to endNight
20%7%35%42335%5%37%
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
43%46%14%24%6%
1620
16th to endDay
41%36%18%23%7%
1920
February1st to 15thDay
43%36%22%19%5%
1752
16th to endDay
45%35%14%23%6%
1580
March1st to 15thDay
44%39%17%19%5%
1800
16th to endDay
41%411%19%20%3
2190
April1st to 15thDay
38%48%19%20%7%
2151
16th to endDay
34%7%10%19%25%3
2160
May1st to 15thDay
39%6%10%17%21%4
2292
16th to endDay
39%7%13%23%13%3
2435
June1st to 15thDay
42%10%14%19%11%1
2340
16th to endDay
33%9%17%22%13%3
2340
July1st to 15thDay
44%11%17%16%7%1
2201
16th to endDay
42%13%18%15%8%
2254
August1st to 15thDay
41%11%17%17%9%3
2148
16th to endDay
48%11%13%15%9%2
2292
September1st to 15thDay
44%9%12%15%13%4
2073
16th to endDay
39%6%10%19%18%6%
1872
October1st to 15thDay
32%5%11%16%23%11%
1815
16th to endDay
31%3416%33%12%
1753
November1st to 15thDay
32%36%17%28%11%
1582
16th to endDay
35%47%16%25%10%
1620
December1st to 15thDay
43%48%19%16%6%
1620
16th to endDay
52%37%17%14%4
1728
January1st to 15thNight
38%46%18%25%6%
2318
16th to endNight
44%3416%21%8%
2304
February1st to 15thNight
38%35%20%20%10%
2112
16th to endNight
39%35%18%23%8%
1893
March1st to 15thNight
39%49%18%19%8%
2158
16th to endNight
33%6%9%23%22%4
2043
April1st to 15thNight
32%5%10%21%20%9%
1797
16th to endNight
28%5%10%24%23%7%
1800
May1st to 15thNight
34%7%11%17%23%6%
1659
16th to endNight
28%9%15%26%15%5%
1684
June1st to 15thNight
32%10%18%21%15%1
1620
16th to endNight
28%11%18%21%17%3
1620
July1st to 15thNight
34%10%20%22%9%2
1530
16th to endNight
32%12%23%20%11%
1648
August1st to 15thNight
31%12%17%22%12%3
1788
16th to endNight
39%10%16%17%13%2
1910
September1st to 15thNight
37%9%14%18%13%6%
1875
16th to endNight
32%5%10%22%21%7%
1881
October1st to 15thNight
28%39%19%24%15%
1815
16th to endNight
30%3410%32%18%
2114
November1st to 15thNight
28%37%17%28%15%
2276
16th to endNight
34%47%16%24%13%
2340
December1st to 15thNight
40%49%18%21%5%
2340
16th to endNight
48%47%17%16%6%
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
21%17%34%16%8%1
90
16th to endDay
23%19%47%5%12
96
February1st to 15thDay
17%28%32%20%1
90
16th to endDay
27%9%39%23%
81
March1st to 15thDay
24%24%33%13%4
90
16th to endDay
18%7%32%22%17%
288
April1st to 15thDay
18%12%27%20%19%1
270
16th to endDay
10%6%28%28%21%5%
270
May1st to 15thDay
12%7%23%27%20%9%
288
16th to endDay
11%319%26%21%17%
331
June1st to 15thDay
12%10%23%31%21%
315
16th to endDay
8%9%21%31%27%
315
July1st to 15thDay
6%15%21%35%29%
305
16th to endDay
6%15%19%31%35%
326
August1st to 15thDay
12%15%20%35%24%
313
16th to endDay
14%15%25%31%21%
332
September1st to 15thDay
11%28%26%30%19%
315
16th to endDay
12%110%33%28%13%
275
October1st to 15thDay
13%5%14%29%30%5%
255
16th to endDay
14%5%20%29%22%8%
162
November1st to 15thDay
22%5%35%25%10%1
90
16th to endDay
13%12%40%18%14%1
90
December1st to 15thDay
25%15%36%16%41
90
16th to endDay
32%11%32%17%6%
96
January1st to 15thNight
20%14%31%24%8%
720
16th to endNight
19%14%33%26%5%
768
February1st to 15thNight
19%12%33%29%5%
704
16th to endNight
18%13%35%26%5%
631
March1st to 15thNight
19%12%33%27%7%
720
16th to endNight
13%10%31%28%15%
699
April1st to 15thNight
11%9%34%26%16%1
539
16th to endNight
10%6%30%31%18%2
540
May1st to 15thNight
9%427%30%23%3
540
16th to endNight
6%14%35%36%6%
563
June1st to 15thNight
6%7%35%40%9%
540
16th to endNight
416%24%47%16%
540
July1st to 15thNight
7%5%26%42%16%
510
16th to endNight
5%16%21%44%20%
564
August1st to 15thNight
7%425%47%14%
539
16th to endNight
10%7%26%39%15%
573
September1st to 15thNight
12%110%26%37%11%
615
16th to endNight
10%112%33%35%5%
681
October1st to 15thNight
11%321%29%30%3
660
16th to endNight
13%7%20%30%25%3
704
November1st to 15thNight
13%6%23%31%21%4
700
16th to endNight
14%12%27%31%13%1
720
December1st to 15thNight
20%9%26%30%11%
720
16th to endNight
25%11%28%25%8%
768
Page generated at 2017-09-22 06:35:35. Version ac04

Copyright 2017 A. Danko


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