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Edward Knight Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Edward Knight Observatory clear sky chart from 2005-11-05 to 2019-09-17.

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
28%
17380
18%
54713
8%
17348
40%
17348
21%
35600

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
17%
840
20%
2926
6%
836
35%
836
16%
1865
January16th to endNight
14%
896
18%
3136
4%
896
33%
896
15%
2026
February1st to 15thNight
17%
824
18%
2573
5%
821
33%
821
16%
1736
February16th to endNight
17%
735
21%
2205
6%
735
35%
735
17%
1470
March1st to 15thNight
18%
840
18%
2520
6%
840
32%
840
16%
1749
March16th to endNight
21%
896
22%
2363
6%
896
35%
896
21%
1600
April1st to 15thNight
21%
838
19%
2096
4%
838
30%
838
21%
1483
April16th to endNight
22%
685
17%
1931
4%
685
32%
685
20%
1316
May1st to 15thNight
24%
630
14%
1890
6%
630
32%
630
17%
1330
May16th to endNight
26%
472
11%
1786
7%
471
34%
471
15%
1182
June1st to 15thNight
31%
420
13%
1680
9%
420
44%
420
16%
1107
June16th to endNight
40%
420
12%
1680
12%
420
48%
420
21%
1033
July1st to 15thNight
48%
400
14%
1600
16%
400
55%
400
23%
934
July16th to endNight
49%
440
16%
1674
16%
418
55%
418
23%
991
August1st to 15thNight
49%
568
18%
1799
13%
566
53%
566
27%
1122
August16th to endNight
51%
846
21%
2184
10%
846
55%
846
35%
1403
September1st to 15thNight
41%
840
19%
2166
8%
840
47%
840
33%
1396
September16th to endNight
45%
782
26%
2159
16%
782
53%
782
34%
1326
October1st to 15thNight
36%
780
22%
2179
10%
780
47%
780
27%
1399
October16th to endNight
24%
832
17%
2704
7%
832
38%
832
20%
1736
November1st to 15thNight
31%
820
21%
2667
11%
820
45%
820
21%
1708
November16th to endNight
24%
840
21%
2730
8%
840
39%
840
19%
1736
December1st to 15thNight
22%
840
18%
2929
6%
840
38%
840
17%
1889
December16th to endNight
16%
896
18%
3136
4%
896
33%
896
16%
2063

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
17%6%25%43445%6%39%
55985
Night
17%6%24424446%41%
54883
Cloud CoverDay
17%6%25%43445%6%39%
55995
Night
17%6%24424446%41%
54888
TransparencyDay
43%5%11%21%15%2
55673
Night
43%5%11%22%15%2
54713
SeeingDay
22%14%31%19%8%2
8410
Night
21%13%32%24%7%
17380

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
16%6%25%5%3345%5%41%
1672
16th to endDay
15%6%2342445%6%43%
1792
February1st to 15thDay
17%7%26%5%345%5%6%34%
1943
16th to endDay
15%8%25%5%34345%39%
1840
March1st to 15thDay
21%8%35%5%24346%35%
2090
16th to endDay
17%7%25%423445%41%
2564
April1st to 15thDay
18%6%26%5%34347%36%
2512
16th to endDay
20%5%2442445%6%40%
2634
May1st to 15thDay
25%7%25%434445%32%
2722
16th to endDay
17%425%5%3435%7%39%
3043
June1st to 15thDay
23%425%42445%8%34%
2940
16th to endDay
16%5%25%5%35%5%7%7%34%
2940
July1st to 15thDay
11%425%5%35%5%6%7%42%
2940
16th to endDay
12%6%245%35%5%6%9%39%
3102
August1st to 15thDay
11%416%5%46%6%6%8%38%
2719
16th to endDay
10%315%5%35%46%8%44%
2720
September1st to 15thDay
15%6%244245%5%6%44%
2454
16th to endDay
15%424323436%49%
2156
October1st to 15thDay
21%4145%2445%5%40%
2110
16th to endDay
18%5%25%4245%45%43%
1872
November1st to 15thDay
20%7%24323245%44%
1851
16th to endDay
17%6%25%433335%44%
1890
December1st to 15thDay
17%6%25%424446%40%
1687
16th to endDay
22%7%25%324346%37%
1792
January1st to 15thNight
16%7%335%24346%41%
2926
16th to endNight
15%9%35%5%23346%39%
3136
February1st to 15thNight
15%8%35%5%35%446%38%
2572
16th to endNight
17%8%25%424445%40%
2205
March1st to 15thNight
19%7%35%424446%36%
2507
16th to endNight
15%6%35%423345%44%
2363
April1st to 15thNight
18%6%25%5%3435%6%37%
2096
16th to endNight
22%6%14423345%40%
1931
May1st to 15thNight
21%6%25%435%35%6%34%
1890
16th to endNight
19%5%15%434448%36%
1784
June1st to 15thNight
22%6%25%424446%36%
1680
16th to endNight
15%4244245%6%7%40%
1680
July1st to 15thNight
11%5%25%435%45%6%45%
1680
16th to endNight
11%4246%35%45%8%42%
1770
August1st to 15thNight
9%415%5%45%5%6%8%43%
1809
16th to endNight
12%324335%45%8%45%
2184
September1st to 15thNight
14%5%1433335%7%47%
2166
16th to endNight
15%413223345%51%
2159
October1st to 15thNight
19%41342335%5%45%
2179
16th to endNight
20%6%1442345%5%41%
2704
November1st to 15thNight
18%6%24333445%44%
2667
16th to endNight
18%6%24323445%43%
2730
December1st to 15thNight
18%8%34423446%38%
2929
16th to endNight
18%7%25%43345%6%38%
3136

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%6%25%424445%41%
1672
16th to endDay
15%6%2443445%5%43%
1792
February1st to 15thDay
17%7%26%425%5%5%6%34%
1943
16th to endDay
16%8%25%5%34445%39%
1840
March1st to 15thDay
22%7%35%434345%34%
2100
16th to endDay
17%7%25%423445%41%
2564
April1st to 15thDay
17%7%35%5%34346%36%
2512
16th to endDay
20%42442445%6%39%
2634
May1st to 15thDay
25%7%25%42435%6%31%
2722
16th to endDay
17%435%5%34347%40%
3043
June1st to 15thDay
23%5%244245%5%8%33%
2940
16th to endDay
16%426%5%35%5%6%7%34%
2940
July1st to 15thDay
11%4245%35%5%6%8%41%
2940
16th to endDay
11%5%25%5%35%5%6%9%39%
3102
August1st to 15thDay
11%425%5%36%6%5%8%39%
2719
16th to endDay
10%425%435%46%8%44%
2720
September1st to 15thDay
15%6%24424446%44%
2454
16th to endDay
15%424323345%48%
2156
October1st to 15thDay
20%5%14424445%40%
2110
16th to endDay
17%425%433445%43%
1872
November1st to 15thDay
20%6%2332333443%
1851
16th to endDay
17%6%35%333435%43%
1890
December1st to 15thDay
17%6%26%424436%40%
1687
16th to endDay
22%8%24324335%37%
1792
January1st to 15thNight
16%8%25%423445%41%
2926
16th to endNight
16%8%35%423346%39%
3136
February1st to 15thNight
16%7%35%5%34445%38%
2565
16th to endNight
17%9%25%423445%39%
2205
March1st to 15thNight
19%8%35%435%346%36%
2520
16th to endNight
15%7%35%423335%44%
2362
April1st to 15thNight
17%7%25%5%44346%37%
2096
16th to endNight
21%6%25%323336%40%
1931
May1st to 15thNight
21%6%25%5%2445%6%34%
1890
16th to endNight
19%426%4345%48%35%
1784
June1st to 15thNight
22%6%2442335%7%35%
1680
16th to endNight
14%5%34325%5%5%9%39%
1680
July1st to 15thNight
11%4245%25%45%8%44%
1680
16th to endNight
11%5%245%445%5%7%42%
1770
August1st to 15thNight
8%4145%35%5%6%8%44%
1809
16th to endNight
12%323425%46%8%45%
2184
September1st to 15thNight
14%5%14423446%47%
2166
16th to endNight
14%5%24223345%50%
2159
October1st to 15thNight
19%41342335%6%44%
2179
16th to endNight
19%5%245%2335%5%41%
2704
November1st to 15thNight
18%6%2442334444%
2667
16th to endNight
19%6%24322346%43%
2730
December1st to 15thNight
18%8%25%424346%39%
2929
16th to endNight
18%8%345%2335%6%38%
3136

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
43%5%10%24%13%2
1673
16th to endDay
41%5%13%24%14%1
1792
February1st to 15thDay
47%6%12%19%11%1
1946
16th to endDay
46%5%9%20%14%3
1840
March1st to 15thDay
50%411%18%11%2
2100
16th to endDay
44%49%19%16%6%
2564
April1st to 15thDay
48%49%19%14%3
2512
16th to endDay
44%5%7%19%19%3
2634
May1st to 15thDay
53%48%18%13%2
2722
16th to endDay
43%7%12%21%13%2
3047
June1st to 15thDay
47%6%13%18%12%1
2940
16th to endDay
44%8%12%19%14%
2940
July1st to 15thDay
38%7%11%24%17%1
2791
16th to endDay
39%7%16%21%13%2
2935
August1st to 15thDay
39%8%14%23%12%1
2705
16th to endDay
35%7%12%25%17%1
2720
September1st to 15thDay
39%6%10%23%18%2
2454
16th to endDay
37%48%23%23%2
2156
October1st to 15thDay
44%410%23%13%3
2110
16th to endDay
41%5%10%24%15%2
1872
November1st to 15thDay
44%312%23%15%1
1851
16th to endDay
42%413%21%16%2
1890
December1st to 15thDay
44%5%14%17%17%
1687
16th to endDay
48%5%11%19%12%1
1792
January1st to 15thNight
44%412%23%13%2
2926
16th to endNight
46%411%19%14%2
3136
February1st to 15thNight
46%5%12%20%12%2
2573
16th to endNight
46%39%22%14%3
2205
March1st to 15thNight
48%5%9%20%12%2
2520
16th to endNight
43%49%17%21%4
2363
April1st to 15thNight
46%49%18%17%2
2096
16th to endNight
46%410%18%16%4
1931
May1st to 15thNight
49%6%10%17%13%2
1890
16th to endNight
46%7%13%19%11%1
1786
June1st to 15thNight
47%6%11%21%11%1
1680
16th to endNight
40%7%12%22%15%1
1680
July1st to 15thNight
36%7%13%25%16%1
1600
16th to endNight
38%6%14%27%11%1
1674
August1st to 15thNight
35%9%14%24%15%1
1799
16th to endNight
35%5%11%26%19%
2184
September1st to 15thNight
37%5%13%24%18%
2166
16th to endNight
34%48%24%25%1
2159
October1st to 15thNight
40%413%23%14%3
2179
16th to endNight
43%412%24%13%
2704
November1st to 15thNight
42%5%10%21%17%2
2667
16th to endNight
42%412%22%15%2
2730
December1st to 15thNight
45%414%22%12%
2929
16th to endNight
46%5%12%21%14%
3136

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
23%29%29%14%4
120
16th to endDay
27%27%33%11%
128
February1st to 15thDay
30%21%34%12%2
317
16th to endDay
21%24%36%13%3
343
March1st to 15thDay
29%20%32%13%2
390
16th to endDay
21%25%34%10%6%1
416
April1st to 15thDay
26%22%30%12%7%
390
16th to endDay
27%16%31%16%5%2
379
May1st to 15thDay
34%16%27%13%5%1
408
16th to endDay
22%11%38%21%41
459
June1st to 15thDay
22%12%36%19%8%
435
16th to endDay
19%12%38%21%5%2
435
July1st to 15thDay
15%6%27%32%15%2
425
16th to endDay
15%6%29%31%13%3
454
August1st to 15thDay
13%9%29%28%17%2
418
16th to endDay
11%5%33%27%15%6%
460
September1st to 15thDay
22%8%27%21%14%6%
435
16th to endDay
21%8%26%17%13%12%
378
October1st to 15thDay
26%8%25%21%13%4
374
16th to endDay
24%17%27%22%8%
336
November1st to 15thDay
28%11%30%18%9%2
325
16th to endDay
26%17%27%17%7%1
330
December1st to 15thDay
20%29%26%16%6%
127
16th to endDay
25%32%29%11%
128
January1st to 15thNight
21%18%37%19%3
840
16th to endNight
23%18%36%18%2
896
February1st to 15thNight
21%17%38%21%1
824
16th to endNight
24%19%33%18%3
735
March1st to 15thNight
25%17%35%18%2
840
16th to endNight
21%20%32%20%6%
896
April1st to 15thNight
22%18%34%20%4
838
16th to endNight
24%18%31%19%5%
685
May1st to 15thNight
26%12%31%23%5%
630
16th to endNight
21%10%36%25%5%
472
June1st to 15thNight
24%6%33%27%7%
420
16th to endNight
17%334%36%7%
420
July1st to 15thNight
11%428%43%11%1
400
16th to endNight
12%127%42%14%
440
August1st to 15thNight
11%428%41%12%1
568
16th to endNight
12%326%38%16%2
846
September1st to 15thNight
17%5%31%30%14%1
840
16th to endNight
17%5%27%25%20%3
782
October1st to 15thNight
22%9%26%26%12%2
780
16th to endNight
24%13%33%21%6%
832
November1st to 15thNight
20%14%30%23%9%1
820
16th to endNight
24%16%30%20%7%1
840
December1st to 15thNight
23%16%33%21%5%
840
16th to endNight
23%18%36%18%2
896
Page generated at 2019-09-17 21:12:18. Version ac04

Copyright 2019 A. Danko


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