De Kalb
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the De Kalb clear sky chart from 2005-11-05 to 2017-09-16.

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%
15974
18%
46836
11%
15932
45%
15932
25%
30807

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
4%
895
29%
895
20%
1790
January16th to endNight
22%
960
13%
2634
4%
960
29%
960
18%
1932
February1st to 15thNight
22%
821
14%
2232
4%
821
30%
821
20%
1571
February16th to endNight
28%
631
18%
1893
7%
631
37%
631
19%
1305
March1st to 15thNight
30%
720
15%
2160
8%
720
35%
720
20%
1472
March16th to endNight
30%
597
15%
2004
10%
597
37%
597
19%
1367
April1st to 15thNight
30%
539
15%
1797
10%
539
40%
539
20%
1194
April16th to endNight
34%
540
19%
1755
12%
540
45%
540
23%
1155
May1st to 15thNight
36%
540
16%
1566
7%
540
44%
540
23%
1079
May16th to endNight
47%
562
18%
1498
10%
561
53%
561
33%
957
June1st to 15thNight
53%
540
16%
1440
10%
540
57%
540
36%
897
June16th to endNight
53%
540
17%
1440
10%
540
57%
540
32%
935
July1st to 15thNight
64%
510
17%
1360
11%
510
66%
510
42%
810
July16th to endNight
70%
564
22%
1417
17%
531
73%
531
43%
820
August1st to 15thNight
74%
539
22%
1575
20%
536
75%
536
43%
850
August16th to endNight
66%
573
21%
1910
22%
573
70%
573
35%
1049
September1st to 15thNight
64%
540
29%
1800
29%
540
69%
540
38%
941
September16th to endNight
59%
647
26%
1812
19%
647
64%
647
37%
1072
October1st to 15thNight
46%
660
26%
1924
19%
660
53%
660
33%
1147
October16th to endNight
30%
704
19%
2222
10%
704
39%
704
22%
1430
November1st to 15thNight
32%
700
24%
2276
15%
700
44%
700
25%
1398
November16th to endNight
27%
787
17%
2407
9%
787
36%
787
20%
1623
December1st to 15thNight
23%
900
13%
2520
5%
900
29%
900
17%
1854
December16th to endNight
18%
960
11%
2688
3%
960
25%
960
12%
2159

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
13%8%36%5%35%45%7%36%
47934
Night
13%8%35%5%24446%40%
47004
Cloud CoverDay
13%7%36%5%35%45%7%36%
47942
Night
14%7%35%5%24447%40%
47009
TransparencyDay
45%5%13%22%11%1
47620
Night
43%412%23%14%2
46836
SeeingDay
15%6%25%27%18%6%
5988
Night
17%7%28%30%13%1
15978

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
14%11%6%7%7%35%5%5%8%24%
1432
16th to endDay
12%14%6%9%6%44445%26%
1589
February1st to 15thDay
13%13%6%8%5%35%446%28%
1629
16th to endDay
14%9%5%7%6%345%47%31%
1580
March1st to 15thDay
15%10%37%5%245%5%6%33%
1790
16th to endDay
17%8%46%5%35%45%6%30%
2229
April1st to 15thDay
17%9%5%6%6%24446%29%
2151
16th to endDay
19%8%35%5%24347%33%
2204
May1st to 15thDay
18%8%46%6%35%45%7%28%
2384
16th to endDay
12%7%35%5%35%5%5%8%37%
2617
June1st to 15thDay
10%5%25%5%25%5%5%8%42%
2520
16th to endDay
8%5%25%5%36%5%7%9%38%
2520
July1st to 15thDay
6%4245%36%7%6%8%45%
2520
16th to endDay
6%5%25%6%35%5%6%10%41%
2655
August1st to 15thDay
6%435%5%346%6%9%43%
2373
16th to endDay
10%5%25%5%35%46%8%43%
2292
September1st to 15thDay
12%31442445%6%49%
2160
16th to endDay
9%6%35%5%2445%8%45%
1825
October1st to 15thDay
14%5%26%323446%44%
1705
16th to endDay
18%8%35%5%24446%36%
1650
November1st to 15thDay
13%9%35%5%34446%40%
1582
16th to endDay
17%11%46%5%23336%35%
1551
December1st to 15thDay
16%13%6%7%5%35%347%27%
1440
16th to endDay
20%13%6%7%7%34435%22%
1536
January1st to 15thNight
15%10%5%6%6%34445%33%
2506
16th to endNight
12%10%7%9%6%34446%29%
2634
February1st to 15thNight
14%11%5%6%5%24345%36%
2230
16th to endNight
14%11%46%42435%6%35%
1893
March1st to 15thNight
16%10%35%5%34335%38%
2147
16th to endNight
16%8%46%5%345%46%32%
2004
April1st to 15thNight
18%8%35%424446%36%
1797
16th to endNight
18%8%26%424346%39%
1755
May1st to 15thNight
16%6%246%25%5%6%7%34%
1566
16th to endNight
9%6%24425%5%7%9%42%
1496
June1st to 15thNight
10%424424447%48%
1440
16th to endNight
7%435%5%36%6%7%8%42%
1440
July1st to 15thNight
6%3134245%5%10%51%
1440
16th to endNight
6%223435%47%11%49%
1513
August1st to 15thNight
33134345%7%9%54%
1584
16th to endNight
9%41442345%9%50%
1910
September1st to 15thNight
9%413323346%57%
1800
16th to endNight
9%41442445%7%50%
1812
October1st to 15thNight
12%4245%23445%50%
1924
16th to endNight
18%8%24323246%41%
2222
November1st to 15thNight
13%7%245%23336%46%
2276
16th to endNight
16%8%46%424346%37%
2407
December1st to 15thNight
19%10%38%6%3335%5%30%
2520
16th to endNight
21%14%5%8%6%25%335%21%
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%11%5%8%6%25%6%48%25%
1432
16th to endDay
12%14%6%10%6%34445%26%
1589
February1st to 15thDay
13%13%6%8%5%36%445%28%
1629
16th to endDay
14%10%46%6%3445%6%32%
1580
March1st to 15thDay
15%9%37%42445%6%33%
1800
16th to endDay
17%8%47%5%36%45%6%30%
2227
April1st to 15thDay
17%10%46%6%34446%29%
2151
16th to endDay
20%8%25%5%34446%34%
2204
May1st to 15thDay
18%9%36%5%45%5%5%7%28%
2384
16th to endDay
13%6%25%5%35%5%5%9%37%
2617
June1st to 15thDay
11%425%5%25%46%7%43%
2520
16th to endDay
9%5%25%5%36%6%7%9%38%
2520
July1st to 15thDay
7%3235%35%6%6%8%44%
2520
16th to endDay
6%5%26%5%35%6%6%9%42%
2655
August1st to 15thDay
7%425%6%35%5%7%8%43%
2373
16th to endDay
11%5%246%35%5%5%9%42%
2292
September1st to 15thDay
12%3234345%5%6%49%
2160
16th to endDay
9%6%26%42445%8%45%
1825
October1st to 15thDay
14%5%25%423446%44%
1705
16th to endDay
18%7%345%24446%37%
1650
November1st to 15thDay
12%10%35%5%2445%5%41%
1582
16th to endDay
18%11%46%5%23335%35%
1551
December1st to 15thDay
16%14%5%8%5%35%346%28%
1440
16th to endDay
21%13%5%7%6%335%45%22%
1536
January1st to 15thNight
16%11%47%5%24435%34%
2506
16th to endNight
12%9%7%9%6%34446%29%
2634
February1st to 15thNight
14%11%5%6%423345%36%
2223
16th to endNight
15%11%46%5%24347%35%
1893
March1st to 15thNight
17%9%45%5%33335%38%
2160
16th to endNight
17%8%46%5%25%45%6%32%
2004
April1st to 15thNight
19%8%344245%46%36%
1797
16th to endNight
18%7%25%424346%39%
1755
May1st to 15thNight
16%7%245%25%5%6%7%34%
1565
16th to endNight
10%5%25%5%236%7%9%42%
1496
June1st to 15thNight
10%425%424447%48%
1440
16th to endNight
7%425%5%36%5%6%8%42%
1440
July1st to 15thNight
6%313425%46%9%51%
1440
16th to endNight
5%2234345%7%10%49%
1513
August1st to 15thNight
33134335%6%9%54%
1584
16th to endNight
9%4134235%5%9%50%
1910
September1st to 15thNight
9%413323346%58%
1800
16th to endNight
9%4234235%5%7%50%
1812
October1st to 15thNight
12%41442335%5%50%
1924
16th to endNight
18%8%24423346%42%
2222
November1st to 15thNight
14%7%34423336%47%
2276
16th to endNight
16%8%46%424346%37%
2407
December1st to 15thNight
19%10%38%6%2335%6%30%
2520
16th to endNight
22%14%5%8%5%34435%21%
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
55%414%15%9%
1433
16th to endDay
58%314%14%8%
1589
February1st to 15thDay
56%412%18%8%1
1631
16th to endDay
51%5%13%20%8%1
1580
March1st to 15thDay
51%5%13%20%7%
1800
16th to endDay
51%5%14%21%6%1
2229
April1st to 15thDay
53%410%22%8%
2151
16th to endDay
50%413%18%11%2
2204
May1st to 15thDay
54%5%11%22%6%
2384
16th to endDay
42%6%13%21%13%1
2621
June1st to 15thDay
37%5%12%26%16%1
2520
16th to endDay
39%7%13%22%15%2
2520
July1st to 15thDay
33%7%13%28%14%2
2371
16th to endDay
34%6%18%24%13%3
2488
August1st to 15thDay
35%6%13%28%14%1
2358
16th to endDay
36%5%13%25%16%2
2292
September1st to 15thDay
33%5%10%26%20%4
2160
16th to endDay
36%410%29%17%1
1825
October1st to 15thDay
39%5%11%27%15%1
1705
16th to endDay
47%414%22%10%2
1650
November1st to 15thDay
43%311%24%13%2
1582
16th to endDay
51%413%23%6%
1551
December1st to 15thDay
57%313%17%7%
1440
16th to endDay
62%411%11%7%
1536
January1st to 15thNight
51%311%20%11%
2506
16th to endNight
54%315%16%9%
2634
February1st to 15thNight
50%312%21%11%
2232
16th to endNight
49%412%22%8%2
1893
March1st to 15thNight
49%313%19%11%2
2160
16th to endNight
50%313%20%10%1
2004
April1st to 15thNight
47%310%21%14%1
1797
16th to endNight
45%310%24%10%4
1755
May1st to 15thNight
46%5%12%23%11%
1566
16th to endNight
35%6%15%21%18%2
1498
June1st to 15thNight
34%412%24%20%2
1440
16th to endNight
36%7%12%21%19%2
1440
July1st to 15thNight
29%413%29%20%2
1360
16th to endNight
26%6%16%27%18%4
1417
August1st to 15thNight
24%5%15%32%19%2
1575
16th to endNight
30%5%13%27%18%4
1910
September1st to 15thNight
27%49%29%26%3
1800
16th to endNight
31%411%32%18%2
1812
October1st to 15thNight
34%410%27%21%2
1924
16th to endNight
45%310%25%13%1
2222
November1st to 15thNight
40%39%24%18%3
2276
16th to endNight
47%412%23%11%
2407
December1st to 15thNight
55%310%21%8%
2520
16th to endNight
65%39%13%6%
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
22%6%40%26%4
90
16th to endDay
21%7%33%26%9%2
96
February1st to 15thDay
16%13%50%17%2
90
16th to endDay
24%12%29%20%12%
81
March1st to 15thDay
34%13%28%16%5%1
90
16th to endDay
25%7%33%20%10%2
225
April1st to 15thDay
21%10%31%24%10%
270
16th to endDay
22%10%23%27%10%4
270
May1st to 15thDay
23%9%28%23%11%3
341
16th to endDay
17%8%26%25%15%5%
517
June1st to 15thDay
10%329%32%19%4
495
16th to endDay
10%7%30%30%13%6%
495
July1st to 15thDay
9%321%33%21%11%
475
16th to endDay
6%321%31%26%10%
515
August1st to 15thDay
8%315%31%26%14%
427
16th to endDay
10%315%27%29%13%
332
September1st to 15thDay
11%313%31%29%9%
315
16th to endDay
10%5%20%28%28%7%
257
October1st to 15thDay
11%6%24%26%23%6%
145
16th to endDay
25%7%34%28%5%
96
November1st to 15thDay
6%7%27%30%21%6%
90
16th to endDay
37%5%34%13%7%1
90
December1st to 15thDay
22%12%32%25%7%
90
16th to endDay
29%13%51%42
96
January1st to 15thNight
20%11%40%21%6%
900
16th to endNight
17%11%36%28%4
960
February1st to 15thNight
20%10%37%25%5%
824
16th to endNight
20%12%32%27%6%
631
March1st to 15thNight
21%9%32%27%7%
720
16th to endNight
20%8%33%27%8%1
597
April1st to 15thNight
23%10%32%27%5%
539
16th to endNight
23%6%32%27%9%
540
May1st to 15thNight
19%7%30%32%10%
540
16th to endNight
12%428%35%18%
563
June1st to 15thNight
11%323%46%14%
540
16th to endNight
8%227%41%17%2
540
July1st to 15thNight
8%118%39%30%2
510
16th to endNight
6%14%47%27%4
564
August1st to 15thNight
49%48%30%5%
539
16th to endNight
9%213%36%34%3
573
September1st to 15thNight
11%216%34%29%4
540
16th to endNight
11%418%36%25%4
647
October1st to 15thNight
14%6%26%32%18%2
660
16th to endNight
23%8%32%24%10%
704
November1st to 15thNight
17%9%34%25%11%1
700
16th to endNight
20%13%31%25%7%
787
December1st to 15thNight
25%11%32%24%5%
900
16th to endNight
28%11%31%24%3
960
Page generated at 2017-09-17 11:05:45. Version ac04

Copyright 2017 A. Danko


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