This page made possible by the sponsorship of: Jeff Dutton (DRAACO).

DRAACO
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the DRAACO clear sky chart from 2005-11-05 to 2017-09-10.

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
37%
14755
14%
46817
9%
14722
42%
14722
18%
32849

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
15%
719
7%
2506
3%
716
20%
716
7%
2021
January16th to endNight
21%
768
10%
2508
3%
768
27%
768
9%
1989
February1st to 15thNight
16%
701
9%
2287
3%
701
22%
701
10%
1795
February16th to endNight
23%
631
12%
2015
5%
631
33%
631
14%
1480
March1st to 15thNight
25%
720
13%
1992
6%
720
32%
720
16%
1497
March16th to endNight
34%
768
21%
2109
10%
768
43%
768
26%
1412
April1st to 15thNight
34%
718
15%
1796
5%
718
39%
718
24%
1309
April16th to endNight
42%
597
20%
1677
9%
597
49%
597
29%
1104
May1st to 15thNight
50%
447
15%
1527
14%
447
54%
447
22%
1007
May16th to endNight
53%
374
17%
1497
18%
374
61%
374
25%
842
June1st to 15thNight
51%
360
12%
1440
13%
360
59%
360
21%
892
June16th to endNight
56%
360
11%
1440
16%
360
59%
360
22%
848
July1st to 15thNight
69%
340
16%
1360
24%
340
71%
340
34%
692
July16th to endNight
67%
436
16%
1473
19%
409
69%
409
31%
835
August1st to 15thNight
66%
539
16%
1609
12%
536
69%
536
33%
961
August16th to endNight
63%
648
22%
1794
13%
648
66%
648
35%
1084
September1st to 15thNight
55%
700
19%
1750
10%
700
59%
700
34%
1159
September16th to endNight
54%
657
20%
1831
15%
657
57%
657
29%
1191
October1st to 15thNight
39%
660
17%
1980
13%
660
45%
660
20%
1393
October16th to endNight
27%
704
11%
2112
7%
704
33%
704
14%
1606
November1st to 15thNight
37%
700
18%
2386
15%
700
44%
700
19%
1616
November16th to endNight
25%
720
10%
2520
6%
720
31%
720
11%
1902
December1st to 15thNight
16%
720
5%
2520
2%
720
20%
720
8%
2023
December16th to endNight
15%
768
6%
2688
2%
768
20%
768
7%
2191

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%8%36%5%35%45%7%34%
47815
Night
16%8%36%5%3445%6%35%
46993
Cloud CoverDay
14%7%36%5%35%45%7%34%
47825
Night
15%8%36%5%3445%6%35%
46998
TransparencyDay
46%8%14%19%10%1
47509
Night
48%7%12%18%10%1
46817
SeeingDay
17%5%24%29%17%5%
5357
Night
19%7%27%28%14%1
14760

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
17%14%6%8%5%3435%6%24%
1432
16th to endDay
13%15%5%10%8%45%445%20%
1714
February1st to 15thDay
14%13%5%11%9%44445%21%
1575
16th to endDay
17%12%6%8%6%24435%27%
1458
March1st to 15thDay
15%10%48%7%345%46%29%
1957
16th to endDay
16%9%35%423346%39%
2115
April1st to 15thDay
19%8%37%6%2445%5%31%
2152
16th to endDay
18%6%25%434445%40%
2294
May1st to 15thDay
15%6%35%5%35%5%5%6%36%
2422
16th to endDay
12%5%25%435%5%6%8%40%
2618
June1st to 15thDay
17%5%25%435%5%6%8%35%
2520
16th to endDay
13%424436%47%9%39%
2520
July1st to 15thDay
9%414426%46%10%44%
2520
16th to endDay
8%5%245%45%7%7%9%39%
2592
August1st to 15thDay
8%5%25%6%35%6%6%7%42%
2340
16th to endDay
10%5%243245%6%8%44%
2396
September1st to 15thDay
15%5%14435%45%7%41%
2098
16th to endDay
13%5%25%425%448%42%
1797
October1st to 15thDay
19%8%26%5%35%45%5%34%
1650
16th to endDay
22%10%37%6%3445%5%27%
1760
November1st to 15thDay
15%10%36%5%35%45%7%32%
1469
16th to endDay
18%12%46%6%25%5%5%5%26%
1440
December1st to 15thDay
18%13%5%9%6%25%5%36%21%
1440
16th to endDay
20%13%7%8%6%25%5%45%20%
1536
January1st to 15thNight
21%13%6%7%7%3444423%
2506
16th to endNight
14%13%6%8%6%46%436%24%
2508
February1st to 15thNight
14%14%6%8%6%36%445%26%
2285
16th to endNight
15%10%38%6%3445%6%30%
2015
March1st to 15thNight
19%8%47%5%3444433%
1980
16th to endNight
14%6%35%5%3423444%
2109
April1st to 15thNight
19%6%35%435%446%36%
1796
16th to endNight
13%7%35%424446%44%
1677
May1st to 15thNight
15%4246%35%5%5%8%37%
1527
16th to endNight
12%42342445%7%48%
1495
June1st to 15thNight
12%5%345%35%6%5%8%39%
1440
16th to endNight
11%5%25%5%25%45%8%42%
1440
July1st to 15thNight
6%32432445%8%54%
1440
16th to endNight
8%323425%5%5%9%48%
1574
August1st to 15thNight
8%4144245%7%8%48%
1620
16th to endNight
7%424434446%52%
1794
September1st to 15thNight
14%5%13324446%47%
1750
16th to endNight
14%6%23423446%46%
1831
October1st to 15thNight
18%6%26%5%33446%38%
1980
16th to endNight
21%7%36%6%345%5%6%29%
2112
November1st to 15thNight
16%7%35%43445%7%36%
2386
16th to endNight
21%9%36%4345%5%8%25%
2520
December1st to 15thNight
20%13%47%5%34446%23%
2520
16th to endNight
22%11%5%7%6%35%5%5%6%19%
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
16%14%5%8%5%43446%25%
1432
16th to endDay
13%14%6%9%9%45%45%5%21%
1714
February1st to 15thDay
13%13%6%11%8%36%45%5%21%
1575
16th to endDay
16%12%5%7%6%34335%28%
1458
March1st to 15thDay
15%9%48%7%25%5%46%29%
1968
16th to endDay
16%8%36%423445%39%
2114
April1st to 15thDay
20%8%36%5%2446%5%32%
2152
16th to endDay
18%6%35%43444440%
2294
May1st to 15thDay
15%6%35%5%35%5%6%6%36%
2422
16th to endDay
11%5%25%5%35%5%6%8%40%
2618
June1st to 15thDay
17%6%25%4345%7%8%35%
2520
16th to endDay
13%5%24435%5%6%9%39%
2520
July1st to 15thDay
8%424436%47%10%44%
2520
16th to endDay
8%425%6%45%6%7%9%39%
2592
August1st to 15thDay
8%5%25%6%35%6%6%8%41%
2340
16th to endDay
10%5%24335%5%6%10%43%
2396
September1st to 15thDay
14%5%24435%45%7%41%
2098
16th to endDay
13%5%25%425%447%43%
1797
October1st to 15thDay
19%7%25%5%35%45%5%34%
1650
16th to endDay
21%9%48%5%34345%27%
1760
November1st to 15thDay
14%9%46%5%45%45%7%32%
1469
16th to endDay
18%11%47%6%345%46%25%
1440
December1st to 15thDay
18%12%5%10%6%44445%22%
1440
16th to endDay
20%12%6%9%5%36%5%36%20%
1536
January1st to 15thNight
20%13%5%8%6%35%345%23%
2506
16th to endNight
14%12%6%8%6%35%5%45%25%
2508
February1st to 15thNight
13%13%5%8%6%36%5%45%25%
2278
16th to endNight
15%9%47%6%3445%5%31%
2015
March1st to 15thNight
20%8%47%6%34345%32%
1992
16th to endNight
15%6%345%34345%44%
2109
April1st to 15thNight
19%6%35%435%446%36%
1796
16th to endNight
13%6%25%424346%44%
1677
May1st to 15thNight
15%5%15%6%445%5%8%36%
1527
16th to endNight
12%5%2342345%7%47%
1495
June1st to 15thNight
12%5%35%5%35%5%6%7%39%
1440
16th to endNight
11%5%36%425%45%9%42%
1440
July1st to 15thNight
5%4144235%6%8%54%
1440
16th to endNight
7%413425%46%10%48%
1574
August1st to 15thNight
8%41443446%8%49%
1620
16th to endNight
7%425%43445%6%52%
1794
September1st to 15thNight
14%5%1342445%6%47%
1750
16th to endNight
13%6%24423437%47%
1831
October1st to 15thNight
18%6%26%6%33446%38%
1980
16th to endNight
21%7%36%7%35%5%46%29%
2112
November1st to 15thNight
15%8%35%5%3445%8%36%
2386
16th to endNight
22%9%46%5%345%6%7%25%
2520
December1st to 15thNight
20%13%47%6%34446%23%
2520
16th to endNight
21%11%5%7%6%36%5%5%6%19%
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
59%9%13%12%4
1433
16th to endDay
67%8%9%9%5%
1714
February1st to 15thDay
63%9%10%13%3
1577
16th to endDay
58%6%12%14%7%
1458
March1st to 15thDay
54%6%13%16%7%
1968
16th to endDay
46%5%9%19%16%2
2115
April1st to 15thDay
51%5%11%17%12%1
2152
16th to endDay
43%6%10%21%14%2
2294
May1st to 15thDay
44%7%12%20%13%1
2422
16th to endDay
38%7%15%23%12%2
2622
June1st to 15thDay
42%8%15%22%10%
2520
16th to endDay
36%9%17%21%13%
2520
July1st to 15thDay
30%8%15%28%16%1
2371
16th to endDay
35%10%17%24%10%1
2430
August1st to 15thDay
36%8%17%22%13%1
2327
16th to endDay
32%8%17%29%11%1
2396
September1st to 15thDay
38%8%16%25%10%
2098
16th to endDay
38%8%13%27%10%
1797
October1st to 15thDay
49%8%11%20%9%1
1650
16th to endDay
56%8%16%13%4
1760
November1st to 15thDay
48%10%13%17%8%1
1469
16th to endDay
58%8%14%13%5%
1440
December1st to 15thDay
63%9%15%10%1
1440
16th to endDay
66%9%11%10%2
1536
January1st to 15thNight
64%8%11%10%3
2506
16th to endNight
61%8%10%12%5%
2508
February1st to 15thNight
61%7%11%14%4
2287
16th to endNight
54%6%14%17%6%
2015
March1st to 15thNight
55%5%12%19%6%
1992
16th to endNight
42%5%8%23%17%2
2109
April1st to 15thNight
48%5%10%18%15%1
1796
16th to endNight
40%5%10%20%19%2
1677
May1st to 15thNight
43%7%12%18%15%2
1527
16th to endNight
34%7%13%25%16%2
1497
June1st to 15thNight
40%8%11%22%15%1
1440
16th to endNight
38%6%13%22%16%1
1440
July1st to 15thNight
26%6%14%26%24%1
1360
16th to endNight
31%7%14%25%18%2
1473
August1st to 15thNight
30%9%18%26%13%1
1609
16th to endNight
32%6%13%30%15%1
1794
September1st to 15thNight
36%6%16%25%13%1
1750
16th to endNight
38%6%9%29%14%
1831
October1st to 15thNight
47%7%10%21%12%
1980
16th to endNight
54%8%13%14%7%
2112
November1st to 15thNight
45%8%14%18%12%1
2386
16th to endNight
56%9%15%12%5%
2520
December1st to 15thNight
62%10%14%10%2
2520
16th to endNight
65%8%12%9%3
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%25%31%15%8%1
60
16th to endDay
28%12%32%22%3
94
February1st to 15thDay
17%22%46%12%1
90
16th to endDay
26%11%35%23%3
117
March1st to 15thDay
23%11%33%24%6%
270
16th to endDay
23%434%26%9%2
288
April1st to 15thDay
21%7%31%28%9%1
270
16th to endDay
21%331%27%11%4
270
May1st to 15thDay
21%322%28%17%6%
288
16th to endDay
12%221%35%22%5%
331
June1st to 15thDay
20%119%34%21%1
315
16th to endDay
17%217%35%22%5%
315
July1st to 15thDay
9%15%34%30%9%
305
16th to endDay
9%118%38%24%7%
326
August1st to 15thDay
9%212%36%29%10%
313
16th to endDay
12%114%28%28%13%
332
September1st to 15thDay
13%317%26%27%10%
294
16th to endDay
17%417%31%19%8%
254
October1st to 15thDay
19%327%26%18%5%
255
16th to endDay
24%12%29%26%6%
272
November1st to 15thDay
15%330%39%8%1
114
16th to endDay
23%10%28%28%10%
60
December1st to 15thDay
13%20%43%13%8%1
60
16th to endDay
29%18%39%12%
64
January1st to 15thNight
26%17%34%15%5%
720
16th to endNight
21%12%35%24%4
768
February1st to 15thNight
21%15%41%18%4
704
16th to endNight
21%11%34%27%4
631
March1st to 15thNight
24%10%33%27%4
720
16th to endNight
18%7%32%26%12%1
768
April1st to 15thNight
21%7%32%30%8%
718
16th to endNight
15%5%29%33%14%1
597
May1st to 15thNight
19%122%36%18%2
447
16th to endNight
13%121%36%24%1
375
June1st to 15thNight
13%124%40%18%1
360
16th to endNight
11%118%44%23%1
360
July1st to 15thNight
7%115%48%24%3
340
16th to endNight
10%14%41%28%3
436
August1st to 15thNight
10%113%38%30%5%
539
16th to endNight
10%215%34%32%5%
648
September1st to 15thNight
16%417%30%26%4
700
16th to endNight
15%418%26%27%6%
657
October1st to 15thNight
24%5%24%25%17%2
660
16th to endNight
24%9%32%25%7%
704
November1st to 15thNight
20%7%27%29%12%1
700
16th to endNight
26%12%29%22%8%1
720
December1st to 15thNight
29%12%36%18%3
720
16th to endNight
27%12%36%19%2
768
Page generated at 2017-09-11 19:35:24. Version ac04

Copyright 2017 A. Danko


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