Scott's Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Scott's Observatory clear sky chart from 2005-11-05 to 2017-12-02.

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
64%
16190
20%
47866
17%
16151
67%
16151
30%
29968

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
51%
717
18%
2327
14%
716
57%
716
24%
1463
January16th to endNight
49%
768
24%
2381
19%
768
55%
768
29%
1451
February1st to 15thNight
51%
701
24%
2105
18%
699
57%
699
33%
1270
February16th to endNight
54%
631
24%
1859
16%
631
62%
631
35%
1079
March1st to 15thNight
54%
720
29%
1980
16%
720
64%
720
43%
1099
March16th to endNight
61%
768
26%
2112
21%
768
64%
768
39%
1220
April1st to 15thNight
65%
718
22%
1976
17%
718
68%
718
44%
1109
April16th to endNight
63%
717
27%
1890
19%
717
67%
717
42%
1124
May1st to 15thNight
79%
539
28%
1619
25%
539
81%
539
45%
863
May16th to endNight
76%
561
24%
1683
20%
561
78%
561
37%
987
June1st to 15thNight
73%
540
11%
1620
10%
540
74%
540
24%
1115
June16th to endNight
79%
540
9%
1620
9%
540
79%
540
24%
1128
July1st to 15thNight
76%
510
6%
1530
6%
510
76%
510
19%
1151
July16th to endNight
78%
564
7%
1595
7%
531
79%
531
22%
1138
August1st to 15thNight
80%
539
4%
1691
5%
536
80%
536
24%
1167
August16th to endNight
69%
696
8%
2033
8%
696
69%
696
19%
1505
September1st to 15thNight
68%
720
7%
1980
8%
720
68%
720
17%
1492
September16th to endNight
65%
717
12%
1980
12%
717
65%
717
20%
1431
October1st to 15thNight
72%
720
24%
2007
23%
720
74%
720
34%
1229
October16th to endNight
58%
768
26%
2304
24%
768
64%
768
33%
1382
November1st to 15thNight
65%
760
29%
2281
26%
760
71%
760
39%
1273
November16th to endNight
56%
780
28%
2432
25%
780
63%
780
35%
1401
December1st to 15thNight
55%
728
23%
2365
22%
728
60%
728
28%
1428
December16th to endNight
58%
768
24%
2496
25%
768
61%
768
30%
1463

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
7%5%25%6%46%6%7%8%38%
48566
Night
6%4245%35%5%6%9%44%
48072
TransparencyDay
40%10%15%16%13%5%
48267
Night
33%9%17%19%14%5%
47875
SeeingDay
9%211%22%27%25%
6044
Night
8%216%33%28%10%
16199

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
11%6%36%5%335%6%10%38%
1611
16th to endDay
10%42442346%7%47%
1841
February1st to 15thDay
11%6%244245%5%6%46%
1750
16th to endDay
7%4145%2435%9%51%
1613
March1st to 15thDay
43143245%5%8%55%
1980
16th to endDay
8%3244245%5%8%50%
2111
April1st to 15thDay
6%4244345%6%9%46%
1972
16th to endDay
6%3145%345%6%8%49%
2079
May1st to 15thDay
4313425%46%8%54%
2331
16th to endDay
7%425%6%47%7%7%9%38%
2431
June1st to 15thDay
10%6%37%7%5%7%7%7%10%26%
2340
16th to endDay
6%6%36%8%6%9%9%9%9%24%
2340
July1st to 15thDay
8%5%38%8%7%10%9%7%9%20%
2340
16th to endDay
7%6%48%8%5%9%9%9%10%20%
2465
August1st to 15thDay
6%6%37%8%6%10%10%9%11%19%
2253
16th to endDay
10%6%38%8%5%8%8%7%9%22%
2154
September1st to 15thDay
9%6%37%9%6%8%7%8%10%21%
1980
16th to endDay
8%7%49%9%6%7%7%7%9%23%
1980
October1st to 15thDay
5%426%8%45%6%6%8%39%
1952
16th to endDay
9%6%25%435%45%7%46%
1920
November1st to 15thDay
44145%45%5%6%7%50%
1907
16th to endDay
8%4245%345%5%6%49%
1856
December1st to 15thDay
9%5%25%5%35%47%9%40%
1632
16th to endDay
7%5%25%5%2445%9%47%
1728
January1st to 15thNight
9%5%35%5%35%5%6%9%39%
2327
16th to endNight
10%6%25%43446%8%43%
2381
February1st to 15thNight
11%5%24433347%47%
2103
16th to endNight
7%323425%47%8%48%
1859
March1st to 15thNight
43144245%6%8%54%
1980
16th to endNight
6%3145%3345%6%55%
2112
April1st to 15thNight
42133245%5%9%54%
1976
16th to endNight
4414425%45%9%52%
1890
May1st to 15thNight
321333435%10%58%
1619
16th to endNight
4315%425%47%9%51%
1682
June1st to 15thNight
9%5%25%5%46%6%7%11%35%
1620
16th to endNight
45%25%6%46%7%9%12%36%
1620
July1st to 15thNight
5%5%35%6%46%8%8%13%32%
1620
16th to endNight
3325%7%49%7%10%14%29%
1703
August1st to 15thNight
5%3246%45%7%10%14%36%
1702
16th to endNight
7%5%25%7%5%7%6%8%12%31%
2033
September1st to 15thNight
6%5%27%9%5%8%8%8%10%28%
1980
16th to endNight
8%7%36%7%46%6%8%9%30%
1980
October1st to 15thNight
44245%346%6%10%46%
2007
16th to endNight
7%5%2443435%8%47%
2304
November1st to 15thNight
4324425%45%7%53%
2281
16th to endNight
6%425%5%2445%8%49%
2432
December1st to 15thNight
9%435%5%25%45%8%45%
2365
16th to endNight
6%435%5%26%46%9%46%
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
40%5%11%21%16%4
1612
16th to endDay
34%5%9%20%22%7%
1841
February1st to 15thDay
36%5%9%15%19%13%
1752
16th to endDay
31%6%12%17%22%10%
1613
March1st to 15thDay
26%5%12%25%22%8%
1980
16th to endDay
31%5%12%21%21%7%
2112
April1st to 15thDay
31%8%15%18%19%6%
1972
16th to endDay
31%7%12%18%24%6%
2079
May1st to 15thDay
25%7%14%24%20%7%
2331
16th to endDay
38%11%14%19%14%1
2435
June1st to 15thDay
50%11%18%16%3
2340
16th to endDay
49%16%21%11%1
2340
July1st to 15thDay
55%18%19%5%1
2201
16th to endDay
50%17%21%9%
2310
August1st to 15thDay
50%18%23%7%
2240
16th to endDay
53%16%20%9%
2154
September1st to 15thDay
53%15%18%9%2
1980
16th to endDay
52%12%15%13%41
1980
October1st to 15thDay
38%9%12%14%16%7%
1952
16th to endDay
36%6%9%15%19%12%
1920
November1st to 15thDay
29%6%10%23%22%7%
1907
16th to endDay
33%6%9%18%19%12%
1856
December1st to 15thDay
38%6%14%18%16%5%
1632
16th to endDay
34%5%13%20%19%6%
1728
January1st to 15thNight
39%7%12%23%13%3
2327
16th to endNight
37%5%11%18%19%7%
2381
February1st to 15thNight
35%48%17%21%12%
2112
16th to endNight
29%6%14%19%21%7%
1859
March1st to 15thNight
25%5%14%27%20%6%
1980
16th to endNight
28%6%11%24%20%8%
2112
April1st to 15thNight
24%6%19%24%19%6%
1976
16th to endNight
27%6%13%23%23%5%
1890
May1st to 15thNight
21%7%14%30%19%7%
1620
16th to endNight
27%9%18%25%17%1
1684
June1st to 15thNight
39%12%23%18%6%
1620
16th to endNight
35%17%25%16%5%
1620
July1st to 15thNight
40%20%28%8%1
1530
16th to endNight
37%18%31%12%
1595
August1st to 15thNight
32%19%36%10%
1691
16th to endNight
43%15%26%12%1
2033
September1st to 15thNight
45%16%22%13%2
1980
16th to endNight
44%12%21%14%41
1980
October1st to 15thNight
29%10%15%19%18%7%
2007
16th to endNight
33%6%11%16%22%10%
2304
November1st to 15thNight
27%5%11%23%22%9%
2281
16th to endNight
31%5%12%21%17%11%
2432
December1st to 15thNight
36%6%13%23%16%4
2365
16th to endNight
33%6%13%21%18%7%
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
22%8%23%25%15%4
90
16th to endDay
11%16%34%23%11%2
96
February1st to 15thDay
10%13%25%28%17%4
90
16th to endDay
12%34%35%17%
114
March1st to 15thDay
5%331%35%21%2
270
16th to endDay
9%5%22%33%25%3
288
April1st to 15thDay
7%421%31%30%5%
270
16th to endDay
8%112%35%29%12%
270
May1st to 15thDay
6%211%28%31%18%
288
16th to endDay
6%16%21%32%32%
331
June1st to 15thDay
16%16%16%26%32%
315
16th to endDay
7%119%26%53%
315
July1st to 15thDay
6%1323%63%
305
16th to endDay
11%39%23%51%
326
August1st to 15thDay
9%36%23%56%
313
16th to endDay
10%149%27%47%
332
September1st to 15thDay
10%1414%26%41%
315
16th to endDay
7%118%37%33%
314
October1st to 15thDay
6%110%31%36%13%
315
16th to endDay
13%316%30%25%9%
336
November1st to 15thDay
6%14%35%35%8%
325
16th to endDay
8%221%37%25%4
236
December1st to 15thDay
10%430%36%17%1
94
16th to endDay
6%6%11%33%37%5%
96
January1st to 15thNight
11%5%23%39%18%1
720
16th to endNight
11%6%27%38%15%
768
February1st to 15thNight
13%5%25%41%13%
704
16th to endNight
7%427%43%15%
631
March1st to 15thNight
6%431%43%13%1
720
16th to endNight
7%321%45%19%1
768
April1st to 15thNight
5%221%45%23%
718
16th to endNight
7%220%45%22%
717
May1st to 15thNight
5%11%45%34%3
540
16th to endNight
419%35%40%9%
563
June1st to 15thNight
10%1220%48%16%
540
16th to endNight
5%212%43%35%
540
July1st to 15thNight
6%17%41%41%
510
16th to endNight
428%43%41%
564
August1st to 15thNight
6%16%41%43%
539
16th to endNight
10%5%13%39%30%
696
September1st to 15thNight
9%5%18%43%22%
720
16th to endNight
12%5%25%41%14%
717
October1st to 15thNight
8%9%39%35%5%
720
16th to endNight
11%119%35%28%3
768
November1st to 15thNight
6%119%44%24%2
760
16th to endNight
6%325%43%19%1
780
December1st to 15thNight
11%222%40%22%
728
16th to endNight
7%422%41%22%1
768
Page generated at 2017-12-03 11:16:39. Version ac04

Copyright 2017 A. Danko


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