Danville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Danville clear sky chart from 2005-11-05 to 2017-09-23.

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%
15891
19%
46895
11%
15850
43%
15850
21%
31206

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
19%
900
15%
2506
5%
895
27%
895
16%
1850
January16th to endNight
19%
960
13%
2634
4%
960
26%
960
14%
1984
February1st to 15thNight
22%
737
12%
2148
4%
737
28%
737
14%
1552
February16th to endNight
23%
631
17%
1893
8%
631
32%
631
16%
1317
March1st to 15thNight
22%
720
14%
2160
6%
720
29%
720
16%
1531
March16th to endNight
24%
645
16%
2019
7%
645
33%
645
17%
1386
April1st to 15thNight
27%
539
18%
1797
10%
539
40%
539
18%
1176
April16th to endNight
29%
540
18%
1744
10%
540
40%
540
18%
1161
May1st to 15thNight
32%
540
15%
1620
7%
540
39%
540
19%
1127
May16th to endNight
40%
561
18%
1551
8%
561
47%
561
24%
1017
June1st to 15thNight
47%
540
18%
1440
10%
540
54%
540
30%
888
June16th to endNight
49%
540
19%
1440
11%
540
55%
540
30%
907
July1st to 15thNight
58%
510
18%
1360
12%
510
62%
510
34%
832
July16th to endNight
64%
564
26%
1417
18%
531
72%
531
43%
781
August1st to 15thNight
67%
539
22%
1650
21%
536
71%
536
34%
928
August16th to endNight
66%
573
23%
1910
21%
573
72%
573
32%
1070
September1st to 15thNight
58%
564
27%
1824
26%
564
63%
564
31%
1061
September16th to endNight
58%
689
29%
1903
20%
689
63%
689
32%
1157
October1st to 15thNight
50%
660
30%
1864
22%
660
57%
660
33%
1104
October16th to endNight
30%
704
20%
2236
12%
704
39%
704
21%
1429
November1st to 15thNight
32%
700
26%
2276
17%
700
46%
700
25%
1341
November16th to endNight
24%
720
19%
2340
10%
720
36%
720
16%
1569
December1st to 15thNight
20%
855
11%
2475
5%
855
27%
855
14%
1880
December16th to endNight
15%
960
11%
2688
2%
960
23%
960
10%
2158

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%7%36%5%3445%7%37%
48011
Night
14%7%35%434446%40%
47063
Cloud CoverDay
14%7%35%5%3445%7%37%
48020
Night
14%7%35%434446%40%
47068
TransparencyDay
45%5%11%21%13%2
47697
Night
44%410%22%14%2
46895
SeeingDay
14%13%22%22%18%7%
5912
Night
15%20%23%26%13%1
15896

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%12%5%8%7%34336%24%
1432
16th to endDay
14%14%6%9%5%33346%27%
1587
February1st to 15thDay
14%11%5%9%7%34445%29%
1711
16th to endDay
15%12%47%6%44436%29%
1580
March1st to 15thDay
18%10%5%7%5%3445%5%29%
1790
16th to endDay
16%10%47%5%25%347%30%
2214
April1st to 15thDay
18%7%35%5%24447%38%
2151
16th to endDay
19%8%25%5%33347%35%
2214
May1st to 15thDay
20%8%36%5%34447%31%
2331
16th to endDay
12%6%26%5%45%46%7%38%
2561
June1st to 15thDay
9%5%15%5%3446%8%44%
2520
16th to endDay
9%435%5%35%5%6%9%40%
2520
July1st to 15thDay
9%425%5%35%6%6%9%40%
2520
16th to endDay
5%3246%35%6%8%10%42%
2655
August1st to 15thDay
6%4245%346%6%9%46%
2296
16th to endDay
7%4245%35%5%7%8%45%
2292
September1st to 15thDay
11%5%245%45%5%47%44%
2124
16th to endDay
12%4244235%5%6%48%
1894
October1st to 15thDay
14%6%1443446%6%43%
1765
16th to endDay
17%7%25%424436%40%
1634
November1st to 15thDay
16%5%24323336%48%
1582
16th to endDay
19%7%45%5%24445%37%
1620
December1st to 15thDay
21%12%47%5%34446%26%
1482
16th to endDay
21%14%5%6%6%24336%23%
1536
January1st to 15thNight
16%11%48%6%2334433%
2506
16th to endNight
15%12%5%8%5%34435%31%
2634
February1st to 15thNight
17%11%46%5%34346%31%
2146
16th to endNight
15%9%48%43345%6%35%
1893
March1st to 15thNight
19%8%45%433445%34%
2147
16th to endNight
16%7%37%424447%35%
2019
April1st to 15thNight
14%7%25%43445%5%41%
1797
16th to endNight
16%6%35%425%5%5%5%38%
1744
May1st to 15thNight
18%6%26%425%45%7%36%
1620
16th to endNight
10%5%344445%5%9%42%
1549
June1st to 15thNight
9%415%325%45%8%49%
1440
16th to endNight
6%415%445%5%7%9%45%
1440
July1st to 15thNight
7%4225%2446%9%48%
1440
16th to endNight
43133234411%56%
1513
August1st to 15thNight
43145%3447%9%51%
1659
16th to endNight
6%3135%4445%8%52%
1910
September1st to 15thNight
10%5%2442335%6%50%
1824
16th to endNight
9%42443445%7%49%
1903
October1st to 15thNight
12%413323346%53%
1864
16th to endNight
17%7%24424335%43%
2236
November1st to 15thNight
11%5%24333445%49%
2276
16th to endNight
18%9%26%42325%5%37%
2340
December1st to 15thNight
21%10%48%5%34345%28%
2475
16th to endNight
25%12%47%6%25%33423%
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%12%5%7%7%34336%25%
1432
16th to endDay
14%14%6%9%5%33346%27%
1587
February1st to 15thDay
14%11%5%9%6%44445%29%
1711
16th to endDay
15%13%47%6%43436%30%
1580
March1st to 15thDay
19%9%5%7%5%24445%29%
1800
16th to endDay
16%10%5%7%5%24347%31%
2213
April1st to 15thDay
18%7%3442345%7%38%
2151
16th to endDay
19%7%35%5%33346%35%
2214
May1st to 15thDay
20%8%36%5%3445%7%31%
2331
16th to endDay
12%6%36%6%35%46%7%38%
2561
June1st to 15thDay
10%5%15%5%335%5%8%45%
2520
16th to endDay
9%435%5%35%5%7%9%40%
2520
July1st to 15thDay
10%5%15%5%35%6%6%8%41%
2520
16th to endDay
6%3245%446%8%10%42%
2655
August1st to 15thDay
7%4146%246%6%10%46%
2296
16th to endDay
8%4245%25%5%7%8%45%
2292
September1st to 15thDay
11%5%14445%5%5%6%44%
2124
16th to endDay
12%41342345%7%48%
1894
October1st to 15thDay
14%5%245%2445%6%43%
1765
16th to endDay
18%7%244235%45%40%
1634
November1st to 15thDay
16%5%24323335%48%
1582
16th to endDay
19%7%45%5%24446%37%
1620
December1st to 15thDay
21%11%47%5%34446%26%
1482
16th to endDay
22%14%5%6%5%25%345%23%
1536
January1st to 15thNight
16%12%47%6%2334433%
2506
16th to endNight
15%12%5%7%5%34335%31%
2634
February1st to 15thNight
17%11%46%5%34346%32%
2139
16th to endNight
15%9%47%5%33446%34%
1893
March1st to 15thNight
19%8%45%5%33446%34%
2160
16th to endNight
16%7%37%424347%35%
2019
April1st to 15thNight
15%7%25%5%3445%6%41%
1797
16th to endNight
16%6%25%425%5%45%38%
1744
May1st to 15thNight
19%7%25%5%25%45%7%36%
1619
16th to endNight
11%5%25%5%3445%9%42%
1549
June1st to 15thNight
9%414425%45%8%50%
1440
16th to endNight
7%3245%35%5%6%10%45%
1440
July1st to 15thNight
7%423425%46%9%49%
1440
16th to endNight
5%21322345%10%56%
1513
August1st to 15thNight
5%3235%245%6%8%51%
1659
16th to endNight
6%323444447%53%
1910
September1st to 15thNight
10%425%42345%6%51%
1824
16th to endNight
10%424424447%49%
1903
October1st to 15thNight
12%413324346%53%
1864
16th to endNight
17%7%24424335%44%
2236
November1st to 15thNight
12%5%25%433445%49%
2276
16th to endNight
19%8%26%43335%5%37%
2340
December1st to 15thNight
21%10%48%5%34345%28%
2475
16th to endNight
25%12%5%7%6%3433423%
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
62%310%14%8%
1433
16th to endDay
58%413%17%5%
1587
February1st to 15thDay
57%412%15%8%1
1713
16th to endDay
56%411%20%6%
1580
March1st to 15thDay
56%5%12%18%6%
1800
16th to endDay
53%413%20%6%1
2214
April1st to 15thDay
46%5%10%22%14%1
2151
16th to endDay
50%411%19%10%4
2214
May1st to 15thDay
52%6%11%20%9%
2331
16th to endDay
45%6%10%17%16%3
2565
June1st to 15thDay
36%6%10%25%18%2
2520
16th to endDay
39%6%13%20%16%3
2520
July1st to 15thDay
39%7%10%23%16%2
2371
16th to endDay
32%8%16%27%13%1
2488
August1st to 15thDay
32%7%13%26%18%1
2281
16th to endDay
34%6%11%25%15%6%
2292
September1st to 15thDay
38%6%9%22%17%5%
2124
16th to endDay
34%5%10%25%21%2
1894
October1st to 15thDay
41%49%25%16%2
1765
16th to endDay
45%412%22%13%1
1634
November1st to 15thDay
39%411%21%18%4
1582
16th to endDay
50%310%21%12%1
1620
December1st to 15thDay
59%49%17%7%
1482
16th to endDay
63%5%9%14%5%
1536
January1st to 15thNight
54%49%19%11%
2506
16th to endNight
56%412%18%7%
2634
February1st to 15thNight
54%413%17%9%1
2148
16th to endNight
50%411%22%9%
1893
March1st to 15thNight
51%410%20%10%1
2160
16th to endNight
49%413%22%8%1
2019
April1st to 15thNight
43%5%9%23%15%2
1797
16th to endNight
46%5%9%19%13%5%
1744
May1st to 15thNight
48%5%11%21%12%
1620
16th to endNight
38%6%14%18%17%3
1551
June1st to 15thNight
33%5%11%27%20%2
1440
16th to endNight
34%6%12%23%17%5%
1440
July1st to 15thNight
31%6%13%25%19%4
1360
16th to endNight
22%5%15%33%19%3
1417
August1st to 15thNight
27%7%12%27%21%2
1650
16th to endNight
30%6%11%24%20%6%
1910
September1st to 15thNight
33%48%23%21%7%
1824
16th to endNight
34%47%25%23%4
1903
October1st to 15thNight
32%49%27%22%3
1864
16th to endNight
44%39%23%16%2
2236
November1st to 15thNight
36%38%24%20%6%
2276
16th to endNight
48%310%21%14%
2340
December1st to 15thNight
59%310%16%9%
2475
16th to endNight
65%48%14%7%
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
27%14%34%16%5%1
90
16th to endDay
17%17%43%17%3
96
February1st to 15thDay
22%18%40%16%2
90
16th to endDay
20%11%37%20%8%1
81
March1st to 15thDay
32%17%33%14%2
90
16th to endDay
25%19%28%17%8%
258
April1st to 15thDay
18%23%24%19%11%1
270
16th to endDay
22%16%25%18%11%4
270
May1st to 15thDay
21%17%25%22%8%4
288
16th to endDay
16%16%26%20%12%6%
461
June1st to 15thDay
10%15%20%27%20%4
495
16th to endDay
10%17%28%24%13%5%
495
July1st to 15thDay
13%10%18%25%20%11%
475
16th to endDay
5%13%13%26%25%14%
515
August1st to 15thDay
8%7%8%22%34%18%
341
16th to endDay
7%7%11%23%35%14%
332
September1st to 15thDay
14%6%11%24%30%13%
315
16th to endDay
12%10%7%20%31%17%
283
October1st to 15thDay
10%11%20%26%23%7%
205
16th to endDay
20%8%39%27%4
96
November1st to 15thDay
7%10%21%25%25%10%
90
16th to endDay
33%11%31%15%8%
90
December1st to 15thDay
22%10%43%16%6%1
90
16th to endDay
27%16%42%13%
96
January1st to 15thNight
18%25%30%22%2
900
16th to endNight
17%26%29%23%3
960
February1st to 15thNight
19%26%26%22%4
740
16th to endNight
19%23%28%24%3
631
March1st to 15thNight
20%25%29%20%4
720
16th to endNight
16%22%31%21%6%1
645
April1st to 15thNight
15%25%27%23%8%
539
16th to endNight
17%22%27%23%8%
540
May1st to 15thNight
17%20%25%27%9%
540
16th to endNight
11%20%21%30%14%1
563
June1st to 15thNight
11%18%17%35%16%
540
16th to endNight
7%18%18%37%18%
540
July1st to 15thNight
9%12%15%35%24%2
510
16th to endNight
417%8%33%32%4
564
August1st to 15thNight
5%9%7%40%31%5%
539
16th to endNight
6%8%10%29%40%3
573
September1st to 15thNight
11%10%13%32%26%3
564
16th to endNight
11%11%11%28%33%3
689
October1st to 15thNight
13%13%19%32%18%3
660
16th to endNight
18%18%30%23%8%
704
November1st to 15thNight
12%21%29%23%11%1
700
16th to endNight
20%26%24%20%7%
720
December1st to 15thNight
24%23%24%20%6%
855
16th to endNight
26%25%25%18%3
960
Page generated at 2017-09-24 08:15:44. Version ac04

Copyright 2017 A. Danko


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