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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 2020-06-03.

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
27%
18360
19%
57775
8%
18328
40%
18328
20%
37666

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%
900
19%
3136
5%
896
34%
896
16%
2011
January16th to endNight
15%
960
19%
3360
4%
960
34%
960
15%
2162
February1st to 15thNight
17%
884
17%
2761
5%
881
32%
881
16%
1878
February16th to endNight
17%
791
23%
2373
7%
791
36%
791
18%
1576
March1st to 15thNight
18%
900
17%
2700
6%
900
31%
900
15%
1869
March16th to endNight
20%
960
22%
2531
6%
960
34%
960
20%
1729
April1st to 15thNight
20%
898
18%
2246
4%
898
29%
898
20%
1590
April16th to endNight
22%
734
19%
2070
4%
734
32%
734
20%
1408
May1st to 15thNight
23%
675
14%
2025
6%
675
31%
675
17%
1421
May16th to endNight
26%
506
12%
1916
8%
505
35%
505
16%
1264
June1st to 15thNight
31%
425
13%
1701
9%
425
44%
425
16%
1117
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%
837
27%
2310
17%
837
54%
837
35%
1400
October1st to 15thNight
35%
840
21%
2346
10%
840
45%
840
25%
1537
October16th to endNight
24%
896
17%
2912
6%
896
38%
896
20%
1896
November1st to 15thNight
30%
880
22%
2862
11%
880
44%
880
21%
1824
November16th to endNight
23%
900
21%
2925
8%
900
39%
900
19%
1863
December1st to 15thNight
22%
900
18%
3138
6%
900
37%
900
16%
2040
December16th to endNight
16%
960
19%
3360
4%
960
34%
960
16%
2202

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%
58646
Night
17%6%24424446%41%
57945
Cloud CoverDay
17%6%25%43445%6%39%
58656
Night
17%6%24424446%41%
57950
TransparencyDay
43%5%11%21%15%2
58334
Night
43%5%11%21%15%2
57775
SeeingDay
23%15%31%19%8%2
9273
Night
21%13%32%24%7%
18360

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%25%5%3345%5%40%
1792
16th to endDay
15%6%3342445%5%43%
1920
February1st to 15thDay
18%7%26%5%345%5%6%33%
2085
16th to endDay
15%9%25%5%34345%39%
1980
March1st to 15thDay
20%7%35%5%24446%35%
2240
16th to endDay
17%7%35%423445%41%
2748
April1st to 15thDay
18%7%36%5%34346%36%
2692
16th to endDay
20%5%2442445%6%38%
2825
May1st to 15thDay
23%7%35%434445%33%
2917
16th to endDay
16%425%5%3435%7%40%
3266
June1st to 15thDay
23%425%42445%8%33%
2968
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
14%414323436%51%
2310
October1st to 15thDay
22%5%245%24445%39%
2273
16th to endDay
18%6%25%4245%45%42%
2016
November1st to 15thDay
19%7%24322245%44%
1986
16th to endDay
18%6%25%423335%44%
2025
December1st to 15thDay
18%7%25%424446%39%
1808
16th to endDay
22%7%25%324346%37%
1920
January1st to 15thNight
16%7%345%24446%40%
3136
16th to endNight
15%9%35%5%23446%39%
3360
February1st to 15thNight
15%8%35%5%35%446%37%
2760
16th to endNight
17%8%25%424445%40%
2373
March1st to 15thNight
19%7%35%424446%36%
2687
16th to endNight
16%7%35%424345%43%
2531
April1st to 15thNight
18%7%25%5%3435%6%37%
2246
16th to endNight
21%7%14423345%41%
2070
May1st to 15thNight
21%6%35%43445%6%34%
2025
16th to endNight
19%5%26%434448%36%
1914
June1st to 15thNight
22%5%25%424446%37%
1701
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
14%414223345%52%
2310
October1st to 15thNight
20%5%14423345%43%
2346
16th to endNight
20%6%1442345%5%40%
2912
November1st to 15thNight
18%6%24333445%44%
2862
16th to endNight
18%6%24323445%43%
2925
December1st to 15thNight
19%8%34424446%38%
3138
16th to endNight
18%7%25%42345%6%38%
3360

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%7%25%424445%41%
1792
16th to endDay
14%6%2443445%5%43%
1920
February1st to 15thDay
18%7%26%5%35%5%5%6%33%
2085
16th to endDay
15%8%26%5%34445%40%
1980
March1st to 15thDay
21%7%35%43445%5%35%
2250
16th to endDay
18%8%25%423335%41%
2748
April1st to 15thDay
18%8%35%5%34346%36%
2692
16th to endDay
20%5%2443445%6%38%
2825
May1st to 15thDay
24%7%25%5%2445%6%32%
2917
16th to endDay
16%435%5%34447%41%
3266
June1st to 15thDay
23%5%244245%5%8%33%
2968
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
14%424323345%50%
2310
October1st to 15thDay
21%6%25%424445%39%
2273
16th to endDay
17%6%25%433445%42%
2016
November1st to 15thDay
20%6%2432323444%
1986
16th to endDay
18%6%25%323445%43%
2025
December1st to 15thDay
17%6%26%423446%40%
1808
16th to endDay
22%7%24324335%37%
1920
January1st to 15thNight
16%8%25%5%23445%41%
3136
16th to endNight
15%8%35%433346%39%
3360
February1st to 15thNight
16%8%35%5%34445%37%
2753
16th to endNight
17%9%25%423445%39%
2373
March1st to 15thNight
18%8%35%435%346%36%
2700
16th to endNight
16%8%35%42333443%
2530
April1st to 15thNight
18%7%25%5%34346%37%
2246
16th to endNight
21%6%25%323336%40%
2070
May1st to 15thNight
21%6%25%5%24446%34%
2025
16th to endNight
19%426%434448%35%
1914
June1st to 15thNight
22%5%2442335%7%36%
1701
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
13%423223345%51%
2310
October1st to 15thNight
20%5%1342335%6%43%
2346
16th to endNight
20%6%245%2335%5%40%
2912
November1st to 15thNight
18%5%2432334444%
2862
16th to endNight
19%6%24323346%43%
2925
December1st to 15thNight
19%8%25%424346%38%
3138
16th to endNight
18%8%345%2435%6%38%
3360

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%23%13%2
1793
16th to endDay
40%5%13%23%15%2
1920
February1st to 15thDay
49%6%12%19%11%1
2088
16th to endDay
46%5%9%20%15%3
1980
March1st to 15thDay
49%412%18%12%3
2250
16th to endDay
45%48%18%16%6%
2748
April1st to 15thDay
48%49%19%14%3
2692
16th to endDay
45%5%7%19%19%3
2825
May1st to 15thDay
52%48%17%14%2
2917
16th to endDay
42%6%12%21%14%2
3270
June1st to 15thDay
47%6%13%18%12%1
2968
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
35%38%25%24%2
2310
October1st to 15thDay
46%5%9%23%12%3
2273
16th to endDay
43%5%10%23%15%2
2016
November1st to 15thDay
43%312%23%14%2
1986
16th to endDay
42%412%22%15%2
2025
December1st to 15thDay
45%413%17%17%
1808
16th to endDay
48%5%11%19%13%1
1920
January1st to 15thNight
44%5%11%22%12%2
3136
16th to endNight
45%411%19%15%2
3360
February1st to 15thNight
47%5%12%19%12%2
2761
16th to endNight
45%39%22%15%3
2373
March1st to 15thNight
48%5%9%19%13%3
2700
16th to endNight
44%48%16%20%5%
2531
April1st to 15thNight
47%49%19%17%2
2246
16th to endNight
46%49%18%16%5%
2070
May1st to 15thNight
49%6%9%17%14%3
2025
16th to endNight
46%7%13%19%11%1
1916
June1st to 15thNight
47%6%11%21%11%1
1701
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
33%48%25%26%1
2310
October1st to 15thNight
41%413%22%14%3
2346
16th to endNight
44%412%24%13%
2912
November1st to 15thNight
41%5%10%21%17%2
2862
16th to endNight
43%412%22%15%2
2925
December1st to 15thNight
46%413%21%12%
3138
16th to endNight
46%5%11%21%13%
3360

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
26%27%32%11%3
150
16th to endDay
24%27%32%13%1
160
February1st to 15thDay
33%21%31%11%2
369
16th to endDay
22%23%36%13%3
399
March1st to 15thDay
28%22%33%13%2
450
16th to endDay
24%23%34%10%5%1
480
April1st to 15thDay
27%24%29%11%6%
450
16th to endDay
29%18%30%14%42
439
May1st to 15thDay
33%17%29%12%41
468
16th to endDay
20%11%39%21%5%1
523
June1st to 15thDay
21%12%36%19%8%
443
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
19%10%27%19%12%11%
434
October1st to 15thDay
28%9%24%20%12%3
434
16th to endDay
25%17%27%21%7%
384
November1st to 15thDay
28%12%29%19%8%1
370
16th to endDay
28%17%28%16%7%1
375
December1st to 15thDay
21%28%27%17%5%
158
16th to endDay
24%32%30%11%1
160
January1st to 15thNight
21%19%37%18%3
900
16th to endNight
23%17%36%18%3
960
February1st to 15thNight
22%16%38%21%1
884
16th to endNight
24%18%34%18%3
791
March1st to 15thNight
25%18%34%18%2
900
16th to endNight
22%19%32%19%5%
960
April1st to 15thNight
23%18%34%19%4
898
16th to endNight
24%18%32%19%5%
734
May1st to 15thNight
26%13%32%22%5%
675
16th to endNight
21%10%35%26%5%
506
June1st to 15thNight
24%6%34%27%7%
425
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
16%5%28%26%19%3
837
October1st to 15thNight
23%10%26%26%11%1
840
16th to endNight
25%13%32%21%6%
896
November1st to 15thNight
21%13%31%23%8%1
880
16th to endNight
25%16%30%20%6%1
900
December1st to 15thNight
24%16%32%21%4
900
16th to endNight
23%18%36%18%2
960
Page generated at 2020-06-04 03:18:55. Version ac04

Copyright 2020 A. Danko


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