Sheep Hill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sheep Hill Observatory clear sky chart from 2005-11-05 to 2018-03-11.

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
32%
15717
20%
49103
9%
15686
43%
15686
23%
31165

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
22%
780
20%
2716
8%
776
38%
776
18%
1678
January16th to endNight
17%
832
21%
2798
6%
832
37%
832
18%
1763
February1st to 15thNight
18%
764
17%
2431
4%
761
34%
761
18%
1595
February16th to endNight
20%
683
26%
2049
8%
683
42%
683
21%
1301
March1st to 15thNight
19%
764
19%
2270
7%
764
35%
764
20%
1500
March16th to endNight
23%
768
23%
2001
8%
768
35%
768
25%
1311
April1st to 15thNight
22%
718
17%
1796
4%
718
29%
718
25%
1229
April16th to endNight
27%
717
18%
1797
4%
717
35%
717
26%
1227
May1st to 15thNight
26%
483
19%
1563
8%
483
38%
483
19%
1041
May16th to endNight
39%
374
15%
1497
13%
374
47%
374
19%
921
June1st to 15thNight
40%
360
14%
1440
11%
360
52%
360
18%
900
June16th to endNight
52%
360
15%
1440
15%
360
61%
360
26%
810
July1st to 15thNight
49%
340
13%
1360
15%
340
54%
340
21%
825
July16th to endNight
55%
376
16%
1418
17%
354
62%
354
24%
819
August1st to 15thNight
55%
557
18%
1628
11%
555
59%
555
31%
1004
August16th to endNight
53%
764
19%
1910
10%
764
55%
764
31%
1287
September1st to 15thNight
46%
720
23%
1800
12%
720
51%
720
32%
1170
September16th to endNight
51%
717
26%
1962
19%
717
56%
717
34%
1212
October1st to 15thNight
37%
720
21%
2121
14%
720
46%
720
26%
1366
October16th to endNight
30%
768
24%
2388
12%
768
46%
768
27%
1441
November1st to 15thNight
32%
760
22%
2472
11%
760
47%
760
24%
1508
November16th to endNight
28%
780
22%
2604
11%
780
44%
780
21%
1592
December1st to 15thNight
25%
780
15%
2730
7%
780
37%
780
16%
1790
December16th to endNight
19%
832
19%
2912
5%
832
36%
832
17%
1875

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
16%5%25%43445%7%39%
49528
Night
16%6%24424447%42%
49273
Cloud CoverDay
16%5%25%43445%7%40%
49537
Night
16%5%24424446%43%
49279
TransparencyDay
43%5%11%22%15%2
49216
Night
41%412%23%16%2
49103
SeeingDay
21%11%28%22%11%3
6292
Night
20%11%30%26%9%
15718

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
14%6%25%5%35%445%42%
1552
16th to endDay
14%7%35%4245%5%7%40%
1775
February1st to 15thDay
16%7%26%5%345%46%37%
1760
16th to endDay
17%5%26%5%25%446%39%
1710
March1st to 15thDay
16%7%345%3445%7%36%
1914
16th to endDay
17%7%35%424346%41%
2221
April1st to 15thDay
18%7%35%423337%41%
2152
16th to endDay
16%5%245%23447%42%
2163
May1st to 15thDay
22%5%25%5%34446%34%
2397
16th to endDay
17%6%36%425%45%8%35%
2618
June1st to 15thDay
19%5%24435%5%6%9%33%
2520
16th to endDay
13%5%25%6%46%5%5%8%36%
2520
July1st to 15thDay
12%5%36%6%45%5%7%9%34%
2520
16th to endDay
11%5%35%5%36%6%6%9%35%
2654
August1st to 15thDay
14%425%5%36%5%6%7%36%
2307
16th to endDay
14%5%25%5%3446%7%40%
2292
September1st to 15thDay
15%42442445%6%43%
2160
16th to endDay
14%5%25%5%24346%45%
1998
October1st to 15thDay
18%5%14424447%40%
1836
16th to endDay
18%5%24324346%44%
1836
November1st to 15thDay
19%5%24323345%44%
1716
16th to endDay
16%5%2431335%6%45%
1683
December1st to 15thDay
17%6%25%4245%5%6%39%
1560
16th to endDay
19%8%2342445%7%36%
1664
January1st to 15thNight
16%6%24433446%42%
2716
16th to endNight
15%8%24424446%41%
2798
February1st to 15thNight
15%7%36%5%35%35%5%39%
2430
16th to endNight
16%6%34423346%44%
2049
March1st to 15thNight
18%6%24423346%42%
2257
16th to endNight
16%7%23323346%45%
2001
April1st to 15thNight
16%6%245%25%45%7%39%
1796
16th to endNight
18%5%245%23346%42%
1797
May1st to 15thNight
18%7%25%5%24446%38%
1563
16th to endNight
18%4243235%5%7%41%
1495
June1st to 15thNight
18%5%235%24348%40%
1440
16th to endNight
10%4244345%6%9%45%
1440
July1st to 15thNight
11%425%5%2447%10%40%
1440
16th to endNight
9%4145%346%7%12%40%
1514
August1st to 15thNight
10%4235%2446%9%44%
1638
16th to endNight
13%4245%25%447%43%
1910
September1st to 15thNight
16%414423445%47%
1800
16th to endNight
13%5%25%423337%49%
1962
October1st to 15thNight
18%6%24323336%44%
2121
16th to endNight
17%6%14312346%48%
2388
November1st to 15thNight
16%5%24323346%47%
2472
16th to endNight
17%5%2442435%6%43%
2604
December1st to 15thNight
18%6%25%5%3445%7%35%
2730
16th to endNight
17%6%24434447%40%
2912

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
14%6%24435%45%6%42%
1552
16th to endDay
15%6%25%424446%42%
1775
February1st to 15thDay
17%6%25%5%34446%39%
1760
16th to endDay
17%5%25%4245%5%5%40%
1710
March1st to 15thDay
17%7%26%5%25%448%36%
1924
16th to endDay
17%6%34424345%43%
2220
April1st to 15thDay
18%7%24422346%42%
2152
16th to endDay
16%5%25%423447%43%
2163
May1st to 15thDay
22%5%25%434347%34%
2397
16th to endDay
17%5%15%5%2445%8%37%
2618
June1st to 15thDay
19%425%435%5%5%9%34%
2520
16th to endDay
13%5%25%5%45%5%6%8%37%
2520
July1st to 15thDay
12%5%26%7%36%5%5%9%35%
2520
16th to endDay
10%435%5%36%6%7%9%36%
2654
August1st to 15thDay
13%425%5%36%6%6%9%36%
2307
16th to endDay
14%425%435%46%7%41%
2292
September1st to 15thDay
15%424434447%43%
2160
16th to endDay
14%5%25%5%33345%45%
1998
October1st to 15thDay
18%5%15%32345%6%41%
1836
16th to endDay
19%5%13324336%45%
1836
November1st to 15thDay
19%5%14323346%44%
1716
16th to endDay
16%42432335%6%46%
1683
December1st to 15thDay
16%8%2442445%7%40%
1560
16th to endDay
18%7%3442345%7%37%
1664
January1st to 15thNight
17%5%3442445%6%43%
2716
16th to endNight
15%8%25%5%24336%42%
2798
February1st to 15thNight
14%8%35%434445%40%
2423
16th to endNight
17%5%35%322345%45%
2049
March1st to 15thNight
17%8%24423246%42%
2270
16th to endNight
16%7%23223346%46%
2001
April1st to 15thNight
17%5%24415%45%7%40%
1796
16th to endNight
18%5%235%24246%43%
1797
May1st to 15thNight
18%6%25%423346%39%
1563
16th to endNight
18%5%2442345%7%41%
1495
June1st to 15thNight
19%4344245%47%39%
1440
16th to endNight
9%41443446%9%46%
1440
July1st to 15thNight
11%4245%45%6%6%8%40%
1440
16th to endNight
9%4145%26%5%8%10%40%
1514
August1st to 15thNight
11%4145%3445%8%46%
1638
16th to endNight
12%5%25%6%2435%8%43%
1910
September1st to 15thNight
16%4235%23446%47%
1800
16th to endNight
13%5%14323346%49%
1962
October1st to 15thNight
18%6%24422246%44%
2121
16th to endNight
18%424313346%48%
2388
November1st to 15thNight
16%6%24323335%48%
2472
16th to endNight
17%42442445%6%43%
2604
December1st to 15thNight
19%6%35%4345%46%36%
2730
16th to endNight
18%6%1443445%5%41%
2912

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
42%413%23%12%4
1553
16th to endDay
42%313%24%14%2
1775
February1st to 15thDay
45%5%11%22%12%2
1763
16th to endDay
43%411%25%13%1
1710
March1st to 15thDay
46%413%21%11%1
1924
16th to endDay
44%310%20%17%3
2221
April1st to 15thDay
43%310%22%15%4
2152
16th to endDay
40%49%21%20%3
2163
May1st to 15thDay
49%38%19%15%2
2397
16th to endDay
45%6%13%20%13%1
2622
June1st to 15thDay
46%6%13%21%11%
2520
16th to endDay
42%5%13%23%13%1
2520
July1st to 15thDay
44%6%10%22%15%1
2371
16th to endDay
40%7%13%22%12%2
2487
August1st to 15thDay
41%8%13%19%16%
2293
16th to endDay
40%5%9%24%18%2
2292
September1st to 15thDay
39%5%10%20%22%1
2160
16th to endDay
40%48%21%22%3
1998
October1st to 15thDay
42%412%21%17%2
1836
16th to endDay
40%39%26%17%1
1836
November1st to 15thDay
41%312%20%18%2
1716
16th to endDay
38%311%28%15%2
1683
December1st to 15thDay
44%416%19%13%1
1560
16th to endDay
46%414%20%12%
1664
January1st to 15thNight
41%413%22%14%3
2716
16th to endNight
43%311%24%15%2
2798
February1st to 15thNight
45%412%21%13%2
2431
16th to endNight
41%37%26%17%3
2049
March1st to 15thNight
44%412%22%13%3
2270
16th to endNight
40%411%21%18%4
2001
April1st to 15thNight
42%411%22%15%2
1796
16th to endNight
42%48%20%20%3
1797
May1st to 15thNight
46%5%9%19%16%2
1563
16th to endNight
41%6%15%18%15%2
1497
June1st to 15thNight
44%5%13%19%15%1
1440
16th to endNight
33%7%15%27%15%
1440
July1st to 15thNight
38%8%13%22%15%1
1360
16th to endNight
34%9%16%23%13%2
1418
August1st to 15thNight
35%6%14%25%16%2
1628
16th to endNight
39%5%11%20%20%1
1910
September1st to 15thNight
38%411%24%19%1
1800
16th to endNight
36%38%23%27%1
1962
October1st to 15thNight
41%410%24%16%2
2121
16th to endNight
37%312%28%16%1
2388
November1st to 15thNight
39%311%22%18%4
2472
16th to endNight
40%312%26%14%2
2604
December1st to 15thNight
47%414%20%11%
2730
16th to endNight
44%5%12%22%12%1
2912

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
25%23%33%13%4
90
16th to endDay
22%18%40%13%3
122
February1st to 15thDay
29%25%30%14%
186
16th to endDay
23%18%36%18%2
291
March1st to 15thDay
27%18%30%18%3
312
16th to endDay
24%17%32%18%6%1
288
April1st to 15thDay
25%13%34%16%7%1
270
16th to endDay
23%10%37%16%8%3
270
May1st to 15thDay
36%13%22%16%9%1
288
16th to endDay
19%9%25%29%13%1
331
June1st to 15thDay
20%9%29%24%13%1
315
16th to endDay
17%9%33%26%11%1
315
July1st to 15thDay
16%5%26%29%17%3
305
16th to endDay
12%5%24%32%21%3
326
August1st to 15thDay
16%322%31%16%8%
313
16th to endDay
14%321%28%22%8%
332
September1st to 15thDay
16%10%25%23%13%10%
315
16th to endDay
17%5%21%26%14%14%
314
October1st to 15thDay
23%5%24%25%17%3
315
16th to endDay
20%15%29%20%11%1
315
November1st to 15thDay
24%10%27%24%10%2
280
16th to endDay
18%22%29%22%42
213
December1st to 15thDay
31%21%27%11%8%
90
16th to endDay
31%23%38%6%
96
January1st to 15thNight
21%15%36%21%4
780
16th to endNight
21%17%37%21%1
832
February1st to 15thNight
21%15%39%22%1
764
16th to endNight
23%17%35%20%3
683
March1st to 15thNight
25%17%34%19%3
764
16th to endNight
20%16%35%20%5%1
768
April1st to 15thNight
20%16%36%21%4
718
16th to endNight
20%13%33%24%6%
717
May1st to 15thNight
22%11%33%24%7%
483
16th to endNight
20%7%25%34%12%1
375
June1st to 15thNight
21%5%27%32%13%
360
16th to endNight
10%425%45%13%
360
July1st to 15thNight
14%325%39%17%
340
16th to endNight
11%221%42%18%2
376
August1st to 15thNight
14%122%38%22%1
557
16th to endNight
15%316%38%24%3
764
September1st to 15thNight
17%5%23%34%18%1
720
16th to endNight
16%421%31%22%4
717
October1st to 15thNight
23%7%26%25%14%2
720
16th to endNight
21%11%33%24%8%
768
November1st to 15thNight
21%11%28%24%12%1
760
16th to endNight
19%16%30%24%7%1
780
December1st to 15thNight
24%13%30%25%5%
780
16th to endNight
23%15%37%21%2
832
Page generated at 2018-03-12 13:28:04. Version ac04

Copyright 2018 A. Danko


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