Spring Hill School Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Spring Hill School Observatory clear sky chart from 2005-11-05 to 2017-09-24.

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
35%
14925
15%
46720
10%
14889
41%
14889
19%
32510

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
14%
716
10%
2410
5%
716
21%
716
8%
1923
January16th to endNight
15%
768
10%
2496
4%
768
23%
768
10%
1964
February1st to 15thNight
17%
701
8%
2287
3%
701
24%
701
9%
1794
February16th to endNight
23%
631
12%
1980
4%
631
31%
631
12%
1491
March1st to 15thNight
24%
720
13%
1995
7%
720
30%
720
16%
1522
March16th to endNight
32%
768
20%
2112
11%
768
40%
768
23%
1443
April1st to 15thNight
28%
706
15%
1838
7%
706
33%
706
21%
1323
April16th to endNight
40%
540
21%
1620
10%
540
48%
540
26%
1042
May1st to 15thNight
43%
540
16%
1620
11%
540
49%
540
24%
1071
May16th to endNight
47%
387
17%
1510
15%
387
57%
387
24%
874
June1st to 15thNight
47%
360
13%
1440
13%
360
55%
360
22%
840
June16th to endNight
52%
360
16%
1265
17%
360
59%
360
27%
750
July1st to 15thNight
63%
340
18%
1265
22%
340
68%
340
36%
636
July16th to endNight
63%
564
15%
1595
13%
531
65%
531
33%
936
August1st to 15thNight
68%
539
18%
1609
15%
536
70%
536
34%
957
August16th to endNight
64%
600
24%
1746
17%
600
68%
600
36%
1030
September1st to 15thNight
55%
720
22%
1859
13%
720
59%
720
33%
1195
September16th to endNight
58%
693
22%
1914
16%
693
60%
693
32%
1195
October1st to 15thNight
44%
660
19%
1974
16%
660
49%
660
25%
1299
October16th to endNight
25%
704
14%
2112
8%
704
33%
704
16%
1547
November1st to 15thNight
36%
700
18%
2345
16%
700
42%
700
20%
1537
November16th to endNight
25%
720
11%
2520
7%
720
30%
720
11%
1885
December1st to 15thNight
16%
720
6%
2520
2%
720
20%
720
8%
2025
December16th to endNight
12%
768
7%
2688
2%
768
17%
768
6%
2231

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
15%9%37%6%35%45%7%31%
48200
Night
15%8%46%5%3445%7%34%
46899
Cloud CoverDay
14%9%37%6%35%5%5%7%31%
48210
Night
14%8%46%5%3445%7%34%
46903
TransparencyDay
50%7%12%18%9%
47898
Night
48%6%12%20%11%1
46720
SeeingDay
17%7%26%24%16%7%
5603
Night
18%9%28%28%12%1
14933

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
19%13%5%10%7%35%446%18%
1525
16th to endDay
13%17%6%12%9%45%445%15%
1728
February1st to 15thDay
15%16%6%10%7%45%5%5%6%18%
1575
16th to endDay
16%13%5%10%7%46%45%6%21%
1491
March1st to 15thDay
15%13%5%9%7%35%35%7%24%
1953
16th to endDay
15%9%5%7%6%3445%6%31%
2112
April1st to 15thDay
18%10%47%5%34447%28%
2122
16th to endDay
18%9%25%5%23346%38%
2340
May1st to 15thDay
17%7%35%6%35%447%34%
2331
16th to endDay
13%5%25%5%45%447%40%
2604
June1st to 15thDay
14%6%245%245%5%9%37%
2520
16th to endDay
12%415%5%35%5%7%9%37%
2691
July1st to 15thDay
8%5%25%6%45%5%7%9%40%
2613
16th to endDay
9%5%25%6%36%6%6%9%36%
2465
August1st to 15thDay
10%425%6%35%7%7%8%37%
2340
16th to endDay
11%5%26%6%35%5%5%8%38%
2444
September1st to 15thDay
13%6%25%7%3446%8%37%
2100
16th to endDay
14%5%25%5%345%6%7%39%
1905
October1st to 15thDay
19%6%27%5%35%346%33%
1656
16th to endDay
24%10%37%6%3445%6%23%
1760
November1st to 15thDay
13%8%47%6%3446%7%32%
1509
16th to endDay
18%14%5%6%6%45%46%7%19%
1440
December1st to 15thDay
17%17%6%10%7%35%45%5%16%
1440
16th to endDay
19%15%7%11%7%45%45%5%11%
1536
January1st to 15thNight
20%12%6%10%6%35%45%6%19%
2410
16th to endNight
14%13%7%11%7%3445%6%20%
2496
February1st to 15thNight
15%13%6%10%6%46%5%46%21%
2285
16th to endNight
15%10%5%8%7%4446%7%25%
1980
March1st to 15thNight
18%9%37%5%345%5%6%28%
1983
16th to endNight
15%8%46%423345%40%
2112
April1st to 15thNight
19%8%35%5%23446%35%
1838
16th to endNight
11%7%25%6%2445%7%40%
1620
May1st to 15thNight
16%5%26%43445%7%38%
1620
16th to endNight
11%42442445%8%47%
1508
June1st to 15thNight
11%4245%345%6%9%42%
1440
16th to endNight
10%4145%335%5%8%46%
1265
July1st to 15thNight
5%22342337%9%56%
1341
16th to endNight
8%22443446%9%48%
1703
August1st to 15thNight
6%314435%5%7%8%49%
1620
16th to endNight
8%324424347%53%
1746
September1st to 15thNight
12%42342445%6%49%
1859
16th to endNight
11%4245%3445%8%46%
1914
October1st to 15thNight
17%6%25%424347%41%
1974
16th to endNight
22%7%36%5%35%5%47%28%
2112
November1st to 15thNight
14%7%26%5%35%46%7%36%
2345
16th to endNight
19%10%46%7%35%45%7%25%
2520
December1st to 15thNight
19%14%6%7%6%35%5%5%6%18%
2520
16th to endNight
20%13%8%11%7%35%445%15%
2688

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%13%5%9%7%445%47%18%
1525
16th to endDay
13%17%7%12%9%35%5%36%16%
1728
February1st to 15thDay
15%15%6%10%7%35%46%6%18%
1575
16th to endDay
16%13%5%9%7%46%445%22%
1491
March1st to 15thDay
16%13%5%8%6%35%35%6%24%
1964
16th to endDay
15%9%5%7%6%35%346%31%
2111
April1st to 15thDay
18%10%47%5%34447%28%
2122
16th to endDay
18%9%25%5%23346%37%
2340
May1st to 15thDay
16%7%36%5%3445%7%34%
2331
16th to endDay
12%6%25%5%35%45%7%39%
2604
June1st to 15thDay
14%6%25%5%345%6%9%37%
2520
16th to endDay
12%425%6%35%6%6%10%37%
2691
July1st to 15thDay
8%5%246%36%6%6%9%40%
2613
16th to endDay
8%6%26%5%46%6%7%10%36%
2465
August1st to 15thDay
9%5%26%6%45%6%7%9%36%
2340
16th to endDay
12%5%25%5%345%5%8%38%
2444
September1st to 15thDay
12%7%26%6%3445%8%36%
2100
16th to endDay
14%5%25%5%345%5%7%39%
1905
October1st to 15thDay
18%7%46%5%34446%33%
1656
16th to endDay
24%10%37%6%35%5%46%23%
1760
November1st to 15thDay
13%8%37%6%345%6%8%32%
1509
16th to endDay
19%14%48%6%445%5%8%20%
1440
December1st to 15thDay
17%16%6%9%8%3345%6%16%
1440
16th to endDay
20%15%7%10%8%35%45%5%12%
1536
January1st to 15thNight
20%12%6%9%7%34446%20%
2410
16th to endNight
14%14%7%10%7%3445%6%20%
2496
February1st to 15thNight
14%13%6%9%7%36%5%5%5%22%
2278
16th to endNight
15%10%5%8%7%3445%7%25%
1980
March1st to 15thNight
18%9%37%5%35%5%5%6%28%
1995
16th to endNight
15%9%35%423345%40%
2112
April1st to 15thNight
19%9%36%424446%34%
1838
16th to endNight
11%7%25%6%25%45%8%40%
1620
May1st to 15thNight
15%5%36%42445%8%38%
1619
16th to endNight
11%42442445%8%46%
1508
June1st to 15thNight
10%424436%47%9%41%
1440
16th to endNight
9%4245%25%46%8%45%
1265
July1st to 15thNight
5%22432345%9%55%
1341
16th to endNight
7%32443445%10%47%
1703
August1st to 15thNight
5%324435%5%8%9%49%
1620
16th to endNight
8%324424446%53%
1746
September1st to 15thNight
12%5%14434446%48%
1859
16th to endNight
11%3245%3445%7%46%
1914
October1st to 15thNight
16%5%26%434347%41%
1974
16th to endNight
21%8%46%6%345%47%28%
2112
November1st to 15thNight
14%7%35%5%345%6%7%36%
2345
16th to endNight
20%10%46%5%25%45%7%25%
2520
December1st to 15thNight
20%15%48%5%35%5%46%19%
2520
16th to endNight
21%13%7%10%7%35%5%5%5%15%
2688

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
65%6%9%12%4
1526
16th to endDay
70%6%9%9%3
1728
February1st to 15thDay
65%6%10%13%4
1577
16th to endDay
63%411%14%41
1491
March1st to 15thDay
60%5%12%15%5%
1964
16th to endDay
53%5%11%17%10%1
2112
April1st to 15thDay
55%5%12%17%9%
2122
16th to endDay
47%410%20%14%2
2340
May1st to 15thDay
48%6%12%21%11%
2331
16th to endDay
42%6%13%21%13%2
2608
June1st to 15thDay
42%7%13%23%12%1
2520
16th to endDay
40%8%14%22%12%
2691
July1st to 15thDay
36%7%13%23%16%1
2461
16th to endDay
40%8%15%21%11%2
2310
August1st to 15thDay
40%9%16%20%11%1
2327
16th to endDay
41%7%14%23%12%1
2444
September1st to 15thDay
43%7%13%22%11%
2100
16th to endDay
42%7%13%26%9%
1905
October1st to 15thDay
50%5%12%17%12%1
1656
16th to endDay
60%7%14%12%4
1760
November1st to 15thDay
47%8%15%18%8%
1509
16th to endDay
61%7%12%14%4
1440
December1st to 15thDay
66%9%12%9%2
1440
16th to endDay
72%7%8%9%1
1536
January1st to 15thNight
64%6%9%11%7%
2410
16th to endNight
62%6%11%14%4
2496
February1st to 15thNight
63%6%11%13%5%
2287
16th to endNight
56%8%11%16%7%
1980
March1st to 15thNight
54%7%10%19%6%
1995
16th to endNight
46%410%22%14%2
2112
April1st to 15thNight
50%410%21%12%
1838
16th to endNight
40%5%10%20%19%3
1620
May1st to 15thNight
43%6%10%25%12%2
1620
16th to endNight
35%8%13%25%14%3
1510
June1st to 15thNight
37%7%11%25%15%1
1440
16th to endNight
35%7%13%23%18%1
1265
July1st to 15thNight
25%6%12%29%23%3
1265
16th to endNight
31%7%15%24%17%3
1595
August1st to 15thNight
28%9%15%30%13%2
1609
16th to endNight
30%6%11%30%17%2
1746
September1st to 15thNight
36%6%12%27%15%1
1859
16th to endNight
35%6%13%29%14%
1914
October1st to 15thNight
42%5%10%25%15%
1974
16th to endNight
53%5%13%18%7%
2112
November1st to 15thNight
44%6%14%19%13%1
2345
16th to endNight
56%7%14%15%6%
2520
December1st to 15thNight
63%8%12%10%3
2520
16th to endNight
69%7%10%10%2
2688

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
18%26%38%410%1
75
16th to endDay
38%15%33%12%
96
February1st to 15thDay
21%18%48%11%
90
16th to endDay
25%19%35%17%1
81
March1st to 15thDay
22%11%34%24%6%
254
16th to endDay
24%7%31%25%8%2
288
April1st to 15thDay
24%12%28%21%11%1
270
16th to endDay
21%10%27%20%14%6%
270
May1st to 15thDay
19%7%27%22%14%7%
288
16th to endDay
14%6%29%26%15%7%
331
June1st to 15thDay
19%6%23%31%16%4
315
16th to endDay
13%8%29%28%14%4
486
July1st to 15thDay
9%5%21%29%23%9%
398
16th to endDay
9%321%29%23%11%
326
August1st to 15thDay
9%120%24%25%18%
313
16th to endDay
15%218%19%24%19%
332
September1st to 15thDay
11%316%23%29%15%
315
16th to endDay
16%314%22%22%19%
287
October1st to 15thDay
18%7%24%27%17%5%
255
16th to endDay
26%8%31%27%4
272
November1st to 15thDay
15%12%29%25%11%3
77
16th to endDay
28%16%31%15%6%1
60
December1st to 15thDay
31%23%31%8%5%
60
16th to endDay
26%28%37%6%1
64
January1st to 15thNight
25%17%34%17%4
720
16th to endNight
22%12%37%23%4
768
February1st to 15thNight
22%17%34%22%3
704
16th to endNight
22%11%34%26%5%
631
March1st to 15thNight
23%11%33%25%6%
720
16th to endNight
17%10%33%27%10%
768
April1st to 15thNight
24%12%29%27%5%
706
16th to endNight
13%7%32%33%11%1
540
May1st to 15thNight
16%5%27%33%15%1
540
16th to endNight
12%429%33%18%1
388
June1st to 15thNight
11%5%27%40%14%
360
16th to endNight
10%326%43%15%
360
July1st to 15thNight
324%47%22%1
340
16th to endNight
8%220%43%22%2
564
August1st to 15thNight
6%116%45%27%3
539
16th to endNight
10%116%35%32%3
600
September1st to 15thNight
13%419%31%25%4
720
16th to endNight
12%318%29%28%6%
693
October1st to 15thNight
19%6%23%28%18%3
660
16th to endNight
25%10%33%24%5%
704
November1st to 15thNight
16%9%33%26%12%2
700
16th to endNight
25%15%27%21%9%
720
December1st to 15thNight
29%15%31%19%3
720
16th to endNight
26%13%36%18%4
768
Page generated at 2017-09-25 09:02:24. Version ac04

Copyright 2017 A. Danko


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