Mt. Cuba Astronomical Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mt. Cuba Astronomical Observatory clear sky chart from 2005-11-05 to 2017-08-12.

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
38%
14981
20%
46505
11%
14946
48%
14946
25%
29497

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
25%
719
20%
2506
10%
716
40%
716
20%
1580
January16th to endNight
23%
768
23%
2505
8%
768
41%
768
23%
1562
February1st to 15thNight
22%
704
17%
2269
6%
701
36%
701
21%
1447
February16th to endNight
20%
631
25%
1893
8%
631
40%
631
24%
1183
March1st to 15thNight
27%
720
20%
2079
8%
720
40%
720
26%
1329
March16th to endNight
28%
768
21%
2040
9%
768
38%
768
27%
1360
April1st to 15thNight
27%
718
19%
1796
5%
718
34%
718
29%
1203
April16th to endNight
38%
720
18%
1800
7%
720
43%
720
30%
1206
May1st to 15thNight
33%
520
16%
1600
9%
520
41%
520
20%
1096
May16th to endNight
51%
374
15%
1497
14%
374
56%
374
19%
934
June1st to 15thNight
51%
360
16%
1440
17%
360
58%
360
21%
868
June16th to endNight
60%
360
16%
1440
20%
360
63%
360
26%
831
July1st to 15thNight
57%
340
12%
1360
15%
340
58%
340
18%
873
July16th to endNight
63%
430
15%
1468
15%
404
68%
404
28%
855
August1st to 15thNight
66%
560
18%
1608
14%
557
67%
557
31%
1017
August16th to endNight
62%
700
16%
1750
9%
700
63%
700
34%
1150
September1st to 15thNight
57%
660
25%
1650
14%
660
61%
660
35%
1078
September16th to endNight
55%
657
24%
1782
19%
657
58%
657
33%
1145
October1st to 15thNight
47%
660
21%
1980
17%
660
54%
660
28%
1237
October16th to endNight
37%
704
26%
2133
16%
704
51%
704
32%
1263
November1st to 15thNight
36%
700
23%
2277
13%
700
50%
700
26%
1385
November16th to endNight
33%
720
20%
2424
12%
720
45%
720
22%
1528
December1st to 15thNight
26%
720
17%
2520
7%
720
39%
720
18%
1652
December16th to endNight
24%
768
21%
2688
7%
768
41%
768
19%
1715

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
14%5%245%35%5%5%7%40%
47469
Night
15%5%2442445%7%43%
46681
Cloud CoverDay
14%5%24435%5%5%7%40%
47478
Night
15%5%2442445%7%43%
46686
TransparencyDay
40%6%12%22%15%2
47162
Night
40%5%12%22%16%2
46505
SeeingDay
17%6%23%26%18%6%
5590
Night
17%7%30%30%12%1
14983

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
15%6%345%3445%6%40%
1432
16th to endDay
15%6%24425%5%45%42%
1719
February1st to 15thDay
15%6%34435%45%6%40%
1592
16th to endDay
13%7%35%6%35%35%6%38%
1580
March1st to 15thDay
15%6%245%35%446%41%
1868
16th to endDay
19%5%245%24446%40%
2184
April1st to 15thDay
15%5%345%23446%44%
2152
16th to endDay
16%425%3245%5%7%43%
2160
May1st to 15thDay
18%6%245%35%45%7%36%
2358
16th to endDay
16%5%24435%46%8%38%
2618
June1st to 15thDay
12%6%335%35%5%7%10%36%
2520
16th to endDay
10%5%25%5%36%5%6%10%38%
2520
July1st to 15thDay
9%425%6%46%6%6%9%37%
2520
16th to endDay
6%425%6%48%7%7%10%36%
2598
August1st to 15thDay
11%415%6%446%6%9%38%
2244
16th to endDay
9%6%25%435%5%7%9%41%
2100
September1st to 15thDay
14%3244245%5%7%45%
1980
16th to endDay
15%5%245%34347%40%
1846
October1st to 15thDay
16%4144335%5%6%44%
1650
16th to endDay
18%414323446%46%
1738
November1st to 15thDay
15%5%3431344447%
1581
16th to endDay
18%5%23324446%45%
1533
December1st to 15thDay
17%325%4245%47%41%
1440
16th to endDay
19%6%25%32445%7%37%
1536
January1st to 15thNight
17%6%24434346%41%
2506
16th to endNight
16%5%2342435%6%43%
2505
February1st to 15thNight
14%8%35%43445%5%41%
2268
16th to endNight
16%5%24324445%45%
1893
March1st to 15thNight
16%5%2342435%7%44%
2067
16th to endNight
16%5%345%23336%44%
2040
April1st to 15thNight
15%6%2442445%7%42%
1796
16th to endNight
17%42443345%6%43%
1800
May1st to 15thNight
18%6%25%425%446%38%
1600
16th to endNight
15%5%26%42436%8%40%
1495
June1st to 15thNight
13%6%145%3335%9%42%
1440
16th to endNight
9%5%25%4245%6%11%41%
1440
July1st to 15thNight
9%5%35%7%36%6%7%9%35%
1440
16th to endNight
7%425%435%5%6%11%41%
1568
August1st to 15thNight
8%4245%345%5%9%45%
1619
16th to endNight
11%424435%45%7%46%
1750
September1st to 15thNight
14%5%23323448%47%
1650
16th to endNight
14%5%25%42435%7%45%
1782
October1st to 15thNight
18%5%1332335%6%45%
1980
16th to endNight
16%413322336%51%
2133
November1st to 15thNight
13%7%35%323335%48%
2277
16th to endNight
17%5%244245%6%6%40%
2424
December1st to 15thNight
18%5%35%5%2445%6%38%
2520
16th to endNight
17%6%2442345%7%39%
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
15%5%335%35%45%6%41%
1432
16th to endDay
14%7%24325%5%45%42%
1719
February1st to 15thDay
15%6%34425%5%45%41%
1592
16th to endDay
14%7%36%5%2445%6%38%
1580
March1st to 15thDay
15%6%25%445%437%40%
1878
16th to endDay
19%5%25%424445%41%
2183
April1st to 15thDay
15%5%25%423447%43%
2152
16th to endDay
16%4244245%5%7%42%
2160
May1st to 15thDay
17%6%245%35%46%6%36%
2358
16th to endDay
15%5%244345%6%8%38%
2618
June1st to 15thDay
12%6%34436%5%7%9%37%
2520
16th to endDay
11%425%5%35%5%6%10%39%
2520
July1st to 15thDay
9%5%25%6%36%6%6%9%37%
2520
16th to endDay
6%425%6%47%7%7%10%36%
2598
August1st to 15thDay
11%415%7%35%5%7%8%38%
2244
16th to endDay
10%5%244345%8%8%41%
2100
September1st to 15thDay
13%42442445%7%45%
1980
16th to endDay
15%5%25%434447%41%
1846
October1st to 15thDay
16%41442346%5%45%
1650
16th to endDay
17%5%13423446%46%
1738
November1st to 15thDay
15%6%34314345%47%
1581
16th to endDay
18%424323346%45%
1533
December1st to 15thDay
16%425%4345%46%41%
1440
16th to endDay
19%6%243335%5%7%37%
1536
January1st to 15thNight
17%6%24424446%42%
2506
16th to endNight
17%5%24424346%43%
2505
February1st to 15thNight
14%8%35%434446%41%
2261
16th to endNight
15%6%2342345%5%46%
1893
March1st to 15thNight
16%5%24424347%44%
2079
16th to endNight
16%6%245%23436%44%
2040
April1st to 15thNight
16%6%24424447%42%
1796
16th to endNight
17%42433445%7%43%
1800
May1st to 15thNight
17%7%35%5%145%47%37%
1600
16th to endNight
14%5%26%33435%8%40%
1495
June1st to 15thNight
13%6%2443335%9%42%
1440
16th to endNight
9%5%25%5%245%6%11%42%
1440
July1st to 15thNight
9%5%25%6%47%6%6%8%36%
1440
16th to endNight
7%425%436%47%10%42%
1568
August1st to 15thNight
8%3246%25%5%5%9%46%
1619
16th to endNight
11%5%15%4345%48%46%
1750
September1st to 15thNight
14%5%2342345%6%47%
1650
16th to endNight
13%6%25%423348%44%
1782
October1st to 15thNight
18%5%14323346%45%
1980
16th to endNight
16%314313336%51%
2133
November1st to 15thNight
13%6%35%32333449%
2277
16th to endNight
17%5%2442446%7%40%
2424
December1st to 15thNight
18%5%25%5%24446%38%
2520
16th to endNight
17%6%25%32445%7%39%
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
42%5%14%21%12%4
1433
16th to endDay
41%412%24%13%2
1719
February1st to 15thDay
42%5%12%24%12%2
1595
16th to endDay
44%5%12%24%11%2
1580
March1st to 15thDay
43%412%24%13%2
1878
16th to endDay
43%5%9%20%18%2
2184
April1st to 15thDay
41%411%22%15%4
2152
16th to endDay
39%6%10%17%21%5%
2160
May1st to 15thDay
45%7%10%19%14%2
2358
16th to endDay
40%8%13%22%13%2
2622
June1st to 15thDay
40%9%12%24%11%1
2520
16th to endDay
37%9%13%21%16%1
2520
July1st to 15thDay
39%8%13%21%14%3
2371
16th to endDay
37%8%13%24%13%1
2435
August1st to 15thDay
39%7%14%20%16%1
2231
16th to endDay
36%8%11%22%17%4
2100
September1st to 15thDay
36%6%12%19%22%2
1980
16th to endDay
40%5%9%19%23%2
1846
October1st to 15thDay
38%5%13%22%17%2
1650
16th to endDay
38%410%26%18%1
1738
November1st to 15thDay
38%412%21%18%3
1581
16th to endDay
39%49%28%14%2
1533
December1st to 15thDay
40%6%15%23%11%1
1440
16th to endDay
44%5%15%21%12%1
1536
January1st to 15thNight
42%5%12%20%15%3
2506
16th to endNight
41%411%26%15%1
2505
February1st to 15thNight
42%412%23%13%2
2269
16th to endNight
39%410%23%18%3
1893
March1st to 15thNight
39%413%23%16%2
2079
16th to endNight
42%5%11%20%17%3
2040
April1st to 15thNight
40%411%21%18%4
1796
16th to endNight
40%5%10%18%20%5%
1800
May1st to 15thNight
45%8%9%17%16%3
1600
16th to endNight
41%8%14%15%16%2
1497
June1st to 15thNight
39%7%12%21%17%
1440
16th to endNight
34%7%14%26%15%1
1440
July1st to 15thNight
42%10%15%17%12%2
1360
16th to endNight
33%8%19%23%14%1
1468
August1st to 15thNight
33%9%13%22%19%1
1608
16th to endNight
36%6%13%21%19%2
1750
September1st to 15thNight
35%6%11%21%22%2
1650
16th to endNight
37%48%20%25%3
1782
October1st to 15thNight
39%412%22%17%2
1980
16th to endNight
34%49%28%19%2
2133
November1st to 15thNight
39%410%21%16%7%
2277
16th to endNight
41%5%11%23%16%2
2424
December1st to 15thNight
45%5%12%21%12%1
2520
16th to endNight
42%6%13%23%11%1
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
16%26%38%13%31
60
16th to endDay
24%13%33%26%2
95
February1st to 15thDay
20%21%35%21%1
109
16th to endDay
16%14%43%21%4
239
March1st to 15thDay
18%15%30%27%8%
270
16th to endDay
22%9%33%22%9%2
288
April1st to 15thDay
21%9%33%23%9%2
270
16th to endDay
20%8%25%26%16%3
270
May1st to 15thDay
30%11%23%20%11%2
288
16th to endDay
19%316%27%26%6%
331
June1st to 15thDay
15%5%22%26%20%8%
315
16th to endDay
13%322%35%19%6%
315
July1st to 15thDay
15%17%31%26%8%
305
16th to endDay
7%111%34%32%12%
326
August1st to 15thDay
12%213%28%29%13%
297
16th to endDay
10%19%27%29%21%
268
September1st to 15thDay
13%318%24%25%14%
255
16th to endDay
22%114%30%16%15%
254
October1st to 15thDay
23%316%26%21%9%
255
16th to endDay
15%6%30%28%16%1
268
November1st to 15thDay
19%329%27%18%1
235
16th to endDay
19%10%35%19%13%1
153
December1st to 15thDay
20%16%28%18%15%1
60
16th to endDay
39%6%31%18%4
64
January1st to 15thNight
19%11%38%24%5%
720
16th to endNight
20%11%40%26%1
768
February1st to 15thNight
18%13%41%25%1
704
16th to endNight
18%14%43%21%2
631
March1st to 15thNight
20%12%36%24%5%
720
16th to endNight
19%8%40%23%7%
768
April1st to 15thNight
18%10%39%25%5%
718
16th to endNight
18%6%31%33%10%
720
May1st to 15thNight
19%5%35%30%8%
520
16th to endNight
16%421%39%18%1
375
June1st to 15thNight
16%122%41%17%
360
16th to endNight
8%120%50%18%
360
July1st to 15thNight
13%117%44%23%
340
16th to endNight
7%114%44%28%3
430
August1st to 15thNight
11%10%48%27%2
560
16th to endNight
15%211%37%30%3
700
September1st to 15thNight
15%216%37%25%2
660
16th to endNight
17%217%32%26%4
657
October1st to 15thNight
21%421%31%18%2
660
16th to endNight
18%6%33%30%10%
704
November1st to 15thNight
17%6%33%28%12%1
700
16th to endNight
19%8%33%27%10%
720
December1st to 15thNight
21%10%33%24%9%1
720
16th to endNight
20%10%39%26%2
768
Page generated at 2017-08-13 14:16:21. Version ac04

Copyright 2017 A. Danko


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