Eisenhower Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Eisenhower Observatory clear sky chart from 2005-11-05 to 2017-09-24.

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
33%
16149
16%
46867
8%
16103
41%
16103
24%
31338

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
25%
900
13%
2506
5%
895
32%
895
18%
1824
January16th to endNight
20%
960
12%
2540
3%
960
27%
960
16%
1921
February1st to 15thNight
26%
879
13%
2288
4%
875
32%
875
22%
1649
February16th to endNight
27%
756
16%
2018
4%
756
35%
756
22%
1396
March1st to 15thNight
30%
576
14%
2016
9%
576
36%
576
19%
1336
March16th to endNight
31%
576
15%
2100
13%
576
39%
576
17%
1422
April1st to 15thNight
31%
539
18%
1797
12%
539
42%
539
21%
1172
April16th to endNight
27%
540
17%
1665
10%
540
37%
540
18%
1175
May1st to 15thNight
30%
540
15%
1500
6%
540
37%
540
23%
1035
May16th to endNight
39%
562
16%
1498
6%
561
45%
561
29%
992
June1st to 15thNight
43%
540
13%
1440
4%
540
48%
540
33%
914
June16th to endNight
52%
540
17%
1354
6%
540
56%
540
43%
813
July1st to 15thNight
53%
510
16%
1357
7%
510
56%
510
43%
780
July16th to endNight
56%
564
20%
1439
10%
531
60%
531
44%
819
August1st to 15thNight
60%
539
23%
1610
18%
536
65%
536
39%
904
August16th to endNight
52%
573
23%
1788
18%
573
61%
573
36%
1004
September1st to 15thNight
53%
540
23%
1800
19%
540
63%
540
36%
962
September16th to endNight
37%
557
20%
1913
11%
557
49%
557
28%
1119
October1st to 15thNight
35%
660
23%
1980
13%
660
43%
660
29%
1196
October16th to endNight
31%
704
15%
2120
8%
704
38%
704
21%
1437
November1st to 15thNight
29%
834
20%
2410
8%
834
38%
834
24%
1581
November16th to endNight
26%
900
15%
2520
7%
900
32%
900
18%
1839
December1st to 15thNight
22%
900
10%
2520
3%
900
28%
900
15%
1898
December16th to endNight
17%
960
11%
2688
3%
960
26%
960
12%
2150

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%8%36%5%3445%7%36%
48037
Night
12%8%36%5%24446%40%
47038
Cloud CoverDay
26%7%25%5%23346%31%
48048
Night
25%6%25%423335%35%
47042
Cloud CoverDay
14%8%36%5%3445%7%36%
48046
Night
12%8%36%5%34446%40%
47042
TransparencyDay
46%5%14%23%9%
47726
Night
44%5%13%24%11%1
46867
SeeingDay
17%10%31%25%12%2
6155
Night
16%10%32%28%10%
16151

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
9%12%7%8%9%35%445%27%
1432
16th to endDay
9%15%6%9%6%47%5%5%7%22%
1683
February1st to 15thDay
8%12%7%8%7%45%45%5%30%
1575
16th to endDay
10%11%49%5%45%45%6%30%
1454
March1st to 15thDay
14%12%5%7%5%3435%6%31%
1944
16th to endDay
18%9%36%6%35%347%30%
2123
April1st to 15thDay
15%9%36%5%23446%37%
2151
16th to endDay
23%10%36%5%24345%29%
2292
May1st to 15thDay
20%7%26%6%34446%33%
2450
16th to endDay
16%7%35%5%245%5%7%36%
2617
June1st to 15thDay
15%5%25%4245%7%8%38%
2520
16th to endDay
10%425%5%35%5%6%9%39%
2578
July1st to 15thDay
8%414435%45%9%48%
2520
16th to endDay
7%414435%47%9%46%
2628
August1st to 15thDay
9%425%6%37%5%5%8%40%
2340
16th to endDay
12%41442445%7%47%
2414
September1st to 15thDay
10%425%43445%7%46%
2160
16th to endDay
17%5%2442445%7%41%
1891
October1st to 15thDay
16%7%25%5%23346%43%
1650
16th to endDay
19%9%35%423345%36%
1752
November1st to 15thDay
11%11%5%5%42435%5%39%
1447
16th to endDay
15%9%36%6%25%35%8%31%
1440
December1st to 15thDay
16%11%6%8%8%45%435%25%
1440
16th to endDay
19%15%8%10%8%2323421%
1536
January1st to 15thNight
10%9%6%9%6%35%446%32%
2506
16th to endNight
11%12%6%10%6%35%45%6%28%
2540
February1st to 15thNight
8%11%5%8%6%35%435%37%
2285
16th to endNight
9%8%36%6%35%5%5%6%37%
2018
March1st to 15thNight
12%9%46%5%3445%5%39%
2004
16th to endNight
15%10%47%5%24347%34%
2100
April1st to 15thNight
16%9%44414346%39%
1797
16th to endNight
23%8%35%433436%33%
1665
May1st to 15thNight
19%6%25%425%337%39%
1500
16th to endNight
10%5%26%5%26%5%48%42%
1496
June1st to 15thNight
12%434325%46%8%45%
1440
16th to endNight
6%32433345%8%54%
1354
July1st to 15thNight
43233245%5%9%55%
1437
16th to endNight
5%31432447%8%55%
1537
August1st to 15thNight
6%3243245%5%7%53%
1620
16th to endNight
9%414323446%55%
1788
September1st to 15thNight
7%314434347%55%
1800
16th to endNight
12%424424346%49%
1913
October1st to 15thNight
13%5%24422336%49%
1980
16th to endNight
19%9%25%423345%39%
2120
November1st to 15thNight
14%7%36%424445%43%
2410
16th to endNight
14%11%47%6%34446%33%
2520
December1st to 15thNight
12%12%49%7%35%445%30%
2520
16th to endNight
17%14%6%10%7%24445%23%
2688

Percentage Cloud Cover SW (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
22%9%5%7%7%35%345%24%
1432
16th to endDay
24%14%48%6%35%346%18%
1683
February1st to 15thDay
23%10%5%7%6%3433426%
1575
16th to endDay
24%9%47%5%35%346%25%
1454
March1st to 15thDay
28%9%46%423345%28%
1955
16th to endDay
30%7%36%5%34346%26%
2123
April1st to 15thDay
29%8%25%423335%31%
2151
16th to endDay
37%9%25%42334423%
2292
May1st to 15thDay
33%6%25%5%33335%27%
2450
16th to endDay
30%6%24423346%30%
2617
June1st to 15thDay
30%5%2432345%6%31%
2520
16th to endDay
25%4145%3445%7%32%
2578
July1st to 15thDay
23%31342335%7%40%
2520
16th to endDay
23%31433346%8%37%
2628
August1st to 15thDay
17%4245%35%5%5%7%37%
2340
16th to endDay
19%414422446%45%
2414
September1st to 15thDay
17%41442445%6%43%
2160
16th to endDay
23%5%14423446%39%
1891
October1st to 15thDay
23%5%24422345%40%
1650
16th to endDay
26%8%25%423345%34%
1752
November1st to 15thDay
24%9%25%423345%36%
1447
16th to endDay
29%8%25%5%23337%28%
1440
December1st to 15thDay
30%9%48%7%35%33420%
1440
16th to endDay
31%13%6%9%7%1222318%
1536
January1st to 15thNight
23%7%38%6%34335%28%
2506
16th to endNight
25%11%49%5%24445%23%
2540
February1st to 15thNight
23%10%46%5%3423432%
2278
16th to endNight
22%7%36%6%34345%33%
2018
March1st to 15thNight
25%8%25%42334434%
2016
16th to endNight
29%8%35%422345%31%
2100
April1st to 15thNight
30%7%24312335%34%
1797
16th to endNight
37%6%24323335%26%
1665
May1st to 15thNight
33%41431423434%
1499
16th to endNight
26%425%5%24436%35%
1496
June1st to 15thNight
27%32332435%6%38%
1440
16th to endNight
22%213332346%45%
1354
July1st to 15thNight
20%213323446%46%
1437
16th to endNight
21%21322345%6%46%
1537
August1st to 15thNight
15%31332345%7%49%
1620
16th to endNight
16%313222336%53%
1788
September1st to 15thNight
15%313334246%50%
1800
16th to endNight
19%323423435%47%
1913
October1st to 15thNight
21%5%23422235%45%
1980
16th to endNight
27%7%1441233437%
2120
November1st to 15thNight
25%6%15%32233439%
2410
16th to endNight
27%9%36%5%23335%29%
2520
December1st to 15thNight
27%9%38%6%3433425%
2520
16th to endNight
30%12%5%9%6%2233420%
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
9%12%8%8%8%36%445%27%
1432
16th to endDay
9%15%5%9%7%47%45%7%22%
1683
February1st to 15thDay
8%11%8%8%7%45%446%30%
1575
16th to endDay
10%11%5%9%6%36%45%6%30%
1454
March1st to 15thDay
15%11%6%7%43435%7%31%
1955
16th to endDay
17%9%37%5%35%446%31%
2121
April1st to 15thDay
16%9%36%5%23346%37%
2151
16th to endDay
23%10%36%5%24445%29%
2292
May1st to 15thDay
20%7%35%6%34446%32%
2450
16th to endDay
16%7%35%5%245%5%8%36%
2617
June1st to 15thDay
16%5%25%42447%8%38%
2520
16th to endDay
10%425%5%35%6%6%9%39%
2578
July1st to 15thDay
8%41443446%9%48%
2520
16th to endDay
7%314435%5%6%9%46%
2628
August1st to 15thDay
9%425%5%46%6%5%8%40%
2340
16th to endDay
12%414423447%48%
2414
September1st to 15thDay
10%425%43445%8%46%
2160
16th to endDay
17%6%15%42445%7%41%
1891
October1st to 15thDay
16%6%35%423445%43%
1650
16th to endDay
19%10%35%433345%36%
1752
November1st to 15thDay
11%10%46%5%23446%39%
1447
16th to endDay
15%9%36%6%24448%32%
1440
December1st to 15thDay
16%11%5%9%8%45%445%25%
1440
16th to endDay
19%15%8%10%8%2323321%
1536
January1st to 15thNight
9%9%5%9%6%36%446%32%
2506
16th to endNight
11%12%6%10%6%35%5%46%28%
2540
February1st to 15thNight
8%11%5%8%6%35%345%37%
2278
16th to endNight
9%8%46%6%45%5%5%6%38%
2018
March1st to 15thNight
12%9%46%5%3445%5%38%
2016
16th to endNight
16%9%47%5%23446%35%
2100
April1st to 15thNight
17%9%35%414446%39%
1797
16th to endNight
23%8%35%424446%32%
1665
May1st to 15thNight
19%5%35%425%336%39%
1499
16th to endNight
10%5%26%5%26%448%42%
1496
June1st to 15thNight
12%424325%46%8%45%
1440
16th to endNight
6%32343345%8%53%
1354
July1st to 15thNight
4223425%5%5%8%55%
1437
16th to endNight
6%3143235%6%8%55%
1537
August1st to 15thNight
6%3243345%5%8%52%
1620
16th to endNight
9%324323446%55%
1788
September1st to 15thNight
7%414434347%55%
1800
16th to endNight
12%424424446%49%
1913
October1st to 15thNight
14%5%24423346%49%
1980
16th to endNight
19%9%25%423345%39%
2120
November1st to 15thNight
14%7%26%423445%43%
2410
16th to endNight
14%10%47%6%34446%33%
2520
December1st to 15thNight
13%11%49%8%35%345%30%
2520
16th to endNight
17%14%6%9%7%34435%23%
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
57%411%18%7%
1433
16th to endDay
60%6%13%16%3
1683
February1st to 15thDay
54%414%19%6%
1576
16th to endDay
53%6%12%22%5%
1454
March1st to 15thDay
53%5%15%19%6%
1955
16th to endDay
53%414%23%3
2123
April1st to 15thDay
47%412%22%10%1
2151
16th to endDay
57%312%17%7%1
2292
May1st to 15thDay
51%5%13%20%7%
2450
16th to endDay
46%6%12%22%11%1
2621
June1st to 15thDay
40%6%16%27%8%1
2520
16th to endDay
38%6%15%27%10%1
2578
July1st to 15thDay
32%5%15%29%15%1
2371
16th to endDay
32%7%16%25%16%1
2463
August1st to 15thDay
38%6%14%28%9%2
2326
16th to endDay
34%5%16%29%13%1
2414
September1st to 15thDay
35%5%15%31%11%
2160
16th to endDay
41%5%14%31%7%
1891
October1st to 15thDay
42%312%27%12%
1650
16th to endDay
49%413%24%7%
1752
November1st to 15thDay
45%413%22%12%1
1447
16th to endDay
51%5%19%15%7%
1440
December1st to 15thDay
61%7%13%13%4
1440
16th to endDay
68%310%12%5%
1536
January1st to 15thNight
52%5%12%21%7%
2506
16th to endNight
56%415%16%6%
2540
February1st to 15thNight
49%414%22%8%
2288
16th to endNight
45%5%13%24%9%
2018
March1st to 15thNight
47%415%22%10%
2016
16th to endNight
50%412%25%6%
2100
April1st to 15thNight
46%39%25%14%1
1797
16th to endNight
51%5%9%18%12%2
1665
May1st to 15thNight
45%5%13%19%12%2
1500
16th to endNight
39%6%11%24%15%2
1498
June1st to 15thNight
35%6%15%28%13%1
1440
16th to endNight
27%5%15%30%17%3
1354
July1st to 15thNight
26%5%14%33%17%2
1357
16th to endNight
24%6%14%30%18%4
1439
August1st to 15thNight
27%5%13%32%17%3
1610
16th to endNight
29%5%14%28%17%3
1788
September1st to 15thNight
29%413%32%19%
1800
16th to endNight
35%5%14%30%14%
1913
October1st to 15thNight
37%311%29%15%2
1980
16th to endNight
47%414%21%11%
2120
November1st to 15thNight
42%413%23%14%1
2410
16th to endNight
52%5%15%17%8%
2520
December1st to 15thNight
56%5%13%19%5%
2520
16th to endNight
64%411%14%4
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%13%32%26%7%1
90
16th to endDay
29%9%32%22%5%1
96
February1st to 15thDay
14%17%43%20%4
90
16th to endDay
20%16%32%23%6%1
81
March1st to 15thDay
21%16%38%20%3
90
16th to endDay
25%14%34%19%4
107
April1st to 15thDay
19%16%33%21%8%
270
16th to endDay
29%12%32%17%7%
402
May1st to 15thDay
23%15%32%18%7%1
468
16th to endDay
20%10%32%22%10%2
517
June1st to 15thDay
16%9%32%28%11%2
495
16th to endDay
10%13%34%25%12%2
495
July1st to 15thDay
9%6%31%29%16%6%
475
16th to endDay
8%7%30%32%17%3
515
August1st to 15thDay
10%6%24%33%21%3
493
16th to endDay
15%7%26%29%15%5%
454
September1st to 15thDay
10%9%27%31%16%4
315
16th to endDay
22%6%31%24%13%2
150
October1st to 15thDay
6%16%32%21%20%3
90
16th to endDay
27%15%27%22%7%
96
November1st to 15thDay
8%443%28%12%2
90
16th to endDay
38%8%40%7%4
90
December1st to 15thDay
21%15%32%24%6%
90
16th to endDay
34%18%36%8%2
96
January1st to 15thNight
13%15%35%27%7%1
900
16th to endNight
17%13%38%25%4
960
February1st to 15thNight
14%12%36%27%7%1
880
16th to endNight
12%14%38%24%9%
756
March1st to 15thNight
15%11%35%28%8%
576
16th to endNight
18%12%31%23%11%2
576
April1st to 15thNight
21%11%30%28%7%
539
16th to endNight
27%8%32%23%7%
540
May1st to 15thNight
22%9%34%27%5%
540
16th to endNight
12%8%32%31%14%1
563
June1st to 15thNight
13%433%38%9%
540
16th to endNight
7%5%30%42%13%
540
July1st to 15thNight
5%332%35%22%
510
16th to endNight
6%329%41%16%1
564
August1st to 15thNight
7%322%40%22%2
539
16th to endNight
9%328%31%23%1
573
September1st to 15thNight
8%5%28%35%16%4
540
16th to endNight
13%10%34%22%17%1
557
October1st to 15thNight
17%12%31%24%12%1
660
16th to endNight
24%11%27%27%9%
704
November1st to 15thNight
18%13%32%26%8%
834
16th to endNight
19%18%30%23%7%
900
December1st to 15thNight
20%12%37%24%5%
900
16th to endNight
23%14%30%24%6%
960
Page generated at 2017-09-25 08:02:20. Version ac04

Copyright 2017 A. Danko


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