Elk Creek Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Elk Creek Observatory clear sky chart from 2005-11-05 to 2017-12-02.

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
37%
16232
20%
47985
12%
16185
45%
16185
32%
28529

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
30%
900
21%
2327
9%
895
38%
895
33%
1473
January16th to endNight
25%
960
20%
2496
8%
960
33%
960
33%
1567
February1st to 15thNight
24%
880
15%
2288
5%
876
31%
876
23%
1613
February16th to endNight
24%
669
19%
1931
5%
669
35%
669
30%
1193
March1st to 15thNight
31%
540
20%
1980
12%
540
41%
540
25%
1141
March16th to endNight
25%
576
14%
2112
9%
576
34%
576
19%
1352
April1st to 15thNight
27%
539
18%
1881
11%
539
40%
539
26%
1084
April16th to endNight
23%
540
16%
1653
9%
540
33%
540
24%
1081
May1st to 15thNight
34%
539
16%
1620
13%
539
40%
539
25%
1045
May16th to endNight
36%
563
14%
1684
10%
561
41%
561
32%
1029
June1st to 15thNight
49%
540
17%
1482
10%
540
53%
540
40%
852
June16th to endNight
50%
540
19%
1526
11%
540
54%
540
51%
782
July1st to 15thNight
60%
510
16%
1530
12%
510
62%
510
41%
832
July16th to endNight
58%
564
21%
1594
19%
531
65%
531
45%
839
August1st to 15thNight
69%
539
22%
1610
25%
536
72%
536
43%
868
August16th to endNight
64%
573
25%
1776
26%
573
68%
573
40%
956
September1st to 15thNight
55%
540
23%
1899
24%
540
60%
540
33%
1036
September16th to endNight
54%
537
26%
1980
21%
537
65%
537
36%
982
October1st to 15thNight
41%
686
26%
2126
18%
686
47%
686
31%
1254
October16th to endNight
38%
768
28%
2304
13%
768
50%
768
39%
1243
November1st to 15thNight
37%
884
27%
2404
13%
884
47%
884
40%
1364
November16th to endNight
30%
975
23%
2652
8%
975
41%
975
36%
1560
December1st to 15thNight
27%
910
16%
2547
7%
910
35%
910
27%
1653
December16th to endNight
27%
960
20%
2583
8%
960
36%
960
26%
1730

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
23%5%14423346%39%
48450
Night
22%413323335%44%
48181
Cloud CoverDay
11%6%25%42445%7%45%
48448
Night
10%5%24424347%50%
48181
TransparencyDay
37%6%13%24%15%2
48148
Night
33%5%13%26%18%3
47986
SeeingDay
13%7%27%30%17%3
6155
Night
12%8%31%34%12%
16233

By Month

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
24%5%15%333446%37%
1611
16th to endDay
25%8%25%41334435%
1728
February1st to 15thDay
25%7%26%424346%33%
1575
16th to endDay
24%6%36%42323437%
1553
March1st to 15thDay
25%7%25%423445%32%
1980
16th to endDay
31%8%24422245%31%
2112
April1st to 15thDay
29%6%2442333335%
2067
16th to endDay
32%7%25%424445%27%
2305
May1st to 15thDay
28%5%145%24345%33%
2331
16th to endDay
29%425%423446%33%
2430
June1st to 15thDay
23%415%424445%38%
2472
16th to endDay
19%21332445%8%44%
2428
July1st to 15thDay
23%3134245%5%7%37%
2340
16th to endDay
22%21343445%8%41%
2466
August1st to 15thDay
15%3134245%5%8%44%
2340
16th to endDay
15%314423348%46%
2426
September1st to 15thDay
17%415%433346%44%
2058
16th to endDay
15%313423446%49%
1980
October1st to 15thDay
20%42432233447%
1821
16th to endDay
17%313313335%52%
1920
November1st to 15thDay
20%413312235%50%
1783
16th to endDay
26%5%13311335%44%
1636
December1st to 15thDay
27%8%25%42344432%
1450
16th to endDay
26%8%37%22224433%
1638
January1st to 15thNight
22%5%2443333441%
2327
16th to endNight
23%6%25%41233440%
2496
February1st to 15thNight
23%7%26%5%3333434%
2278
16th to endNight
23%6%24323336%40%
1931
March1st to 15thNight
25%5%2442333440%
1980
16th to endNight
30%7%14322345%33%
2112
April1st to 15thNight
25%5%24412336%41%
1881
16th to endNight
31%5%25%323235%33%
1653
May1st to 15thNight
27%424423345%38%
1619
16th to endNight
26%413413347%38%
1683
June1st to 15thNight
22%212323346%47%
1482
16th to endNight
18%12223349%52%
1526
July1st to 15thNight
22%2231335%8%46%
1620
16th to endNight
20%11232335%9%44%
1702
August1st to 15thNight
12%2133135%5%9%52%
1620
16th to endNight
13%223322245%56%
1776
September1st to 15thNight
17%313323447%47%
1899
16th to endNight
14%312223345%54%
1980
October1st to 15thNight
21%41321313449%
2126
16th to endNight
16%41221322457%
2304
November1st to 15thNight
19%313222235%52%
2404
16th to endNight
25%3222233448%
2652
December1st to 15thNight
27%7%1442333437%
2547
16th to endNight
27%8%3431123437%
2583

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%5%25%43445%7%45%
1611
16th to endDay
10%8%36%424445%43%
1728
February1st to 15thDay
11%8%47%5%2435%6%38%
1575
16th to endDay
9%7%37%424446%44%
1553
March1st to 15thDay
12%8%35%5%25%5%5%6%39%
1980
16th to endDay
17%10%45%5%2335%5%35%
2110
April1st to 15thDay
14%6%25%5%3434443%
2067
16th to endDay
19%7%25%5%3445%6%34%
2305
May1st to 15thDay
15%6%35%6%25%45%6%37%
2331
16th to endDay
13%6%35%5%245%6%7%40%
2430
June1st to 15thDay
8%5%25%5%35%5%5%7%45%
2472
16th to endDay
5%214435%5%6%10%50%
2428
July1st to 15thDay
8%424435%6%7%9%44%
2340
16th to endDay
6%314435%46%9%49%
2466
August1st to 15thDay
8%3234346%6%9%47%
2340
16th to endDay
9%4245%24449%48%
2426
September1st to 15thDay
10%425%5%24447%48%
2058
16th to endDay
7%31442445%8%53%
1980
October1st to 15thDay
13%5%24322446%51%
1821
16th to endDay
11%414413335%55%
1920
November1st to 15thDay
8%5%13324236%57%
1783
16th to endDay
12%6%34422346%50%
1636
December1st to 15thDay
12%8%26%5%35%45%6%40%
1450
16th to endDay
12%9%5%7%42435%7%37%
1638
January1st to 15thNight
7%6%245%34446%49%
2327
16th to endNight
9%6%26%323446%50%
2496
February1st to 15thNight
10%9%47%5%34445%39%
2278
16th to endNight
8%6%34424447%48%
1931
March1st to 15thNight
9%6%24424445%49%
1980
16th to endNight
18%8%2442345%6%38%
2112
April1st to 15thNight
11%5%25%5%23346%49%
1881
16th to endNight
17%6%26%323346%42%
1653
May1st to 15thNight
12%6%25%425%45%7%42%
1619
16th to endNight
10%42442445%9%48%
1683
June1st to 15thNight
6%31333436%7%55%
1482
16th to endNight
31232336%11%60%
1526
July1st to 15thNight
6%21342346%10%53%
1620
16th to endNight
4214325%5%6%10%53%
1702
August1st to 15thNight
421441445%10%56%
1620
16th to endNight
6%323423346%58%
1776
September1st to 15thNight
10%42342335%7%52%
1899
16th to endNight
7%31222445%6%57%
1980
October1st to 15thNight
14%5%13323335%52%
2126
16th to endNight
10%422213225%60%
2304
November1st to 15thNight
7%423222347%57%
2404
16th to endNight
11%423223345%55%
2652
December1st to 15thNight
11%7%25%5%24346%45%
2547
16th to endNight
14%9%35%313347%43%
2583

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
37%5%15%26%14%1
1612
16th to endDay
40%5%15%24%12%1
1728
February1st to 15thDay
44%6%16%22%8%2
1576
16th to endDay
40%413%24%14%2
1553
March1st to 15thDay
44%5%11%23%13%1
1980
16th to endDay
50%5%13%20%8%1
2112
April1st to 15thDay
42%6%12%21%16%
2067
16th to endDay
48%7%11%21%10%
2305
May1st to 15thDay
46%7%10%21%12%
2331
16th to endDay
41%8%15%21%11%1
2434
June1st to 15thDay
35%7%13%25%15%1
2472
16th to endDay
26%7%18%28%16%2
2428
July1st to 15thDay
32%8%14%28%13%2
2201
16th to endDay
27%7%15%29%16%2
2311
August1st to 15thDay
29%8%15%26%17%1
2326
16th to endDay
32%6%11%24%18%5%
2426
September1st to 15thDay
35%5%13%21%18%5%
2058
16th to endDay
28%7%11%29%21%
1980
October1st to 15thDay
34%5%9%23%22%3
1821
16th to endDay
30%411%26%21%5%
1920
November1st to 15thDay
28%412%26%22%5%
1783
16th to endDay
34%49%29%20%1
1636
December1st to 15thDay
43%5%16%23%10%
1450
16th to endDay
46%5%14%21%10%1
1638
January1st to 15thNight
35%415%26%17%
2327
16th to endNight
34%5%14%26%15%3
2496
February1st to 15thNight
46%6%11%22%11%2
2288
16th to endNight
35%5%12%23%18%3
1931
March1st to 15thNight
35%6%12%24%17%3
1980
16th to endNight
45%5%14%21%10%2
2112
April1st to 15thNight
35%410%26%19%2
1881
16th to endNight
42%5%12%22%15%
1653
May1st to 15thNight
40%6%13%22%16%1
1620
16th to endNight
33%7%19%23%15%1
1685
June1st to 15thNight
26%7%16%31%14%3
1482
16th to endNight
18%6%14%34%23%3
1526
July1st to 15thNight
24%6%15%31%17%4
1530
16th to endNight
24%414%32%22%1
1594
August1st to 15thNight
22%7%17%30%18%2
1610
16th to endNight
26%5%10%27%22%7%
1776
September1st to 15thNight
31%412%25%19%7%
1899
16th to endNight
25%5%12%28%24%2
1980
October1st to 15thNight
34%48%23%23%5%
2126
16th to endNight
28%210%28%26%4
2304
November1st to 15thNight
27%413%25%22%7%
2404
16th to endNight
31%310%31%19%2
2652
December1st to 15thNight
40%5%13%27%12%
2547
16th to endNight
41%5%13%24%12%2
2583

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%13%43%15%41
90
16th to endDay
17%14%39%23%4
96
February1st to 15thDay
13%21%44%15%5%
90
16th to endDay
12%19%45%9%12%
81
March1st to 15thDay
13%23%42%20%1
90
16th to endDay
25%16%38%15%4
96
April1st to 15thDay
19%10%32%27%8%
186
16th to endDay
24%13%35%17%7%1
415
May1st to 15thDay
17%11%31%25%11%1
468
16th to endDay
19%7%33%27%9%2
517
June1st to 15thDay
8%429%34%19%4
495
16th to endDay
5%433%35%17%4
495
July1st to 15thDay
10%218%39%24%4
475
16th to endDay
7%111%42%32%4
515
August1st to 15thDay
7%115%40%30%3
493
16th to endDay
10%216%36%27%6%
466
September1st to 15thDay
7%225%33%23%7%
213
16th to endDay
9%228%42%12%4
135
October1st to 15thDay
16%10%31%28%48%
135
16th to endDay
10%12%38%25%11%1
144
November1st to 15thDay
15%5%28%32%13%3
135
16th to endDay
24%14%37%15%8%
135
December1st to 15thDay
12%19%45%15%33
94
16th to endDay
26%20%31%19%2
96
January1st to 15thNight
11%12%37%30%7%
900
16th to endNight
13%10%41%29%5%
960
February1st to 15thNight
15%11%38%30%3
880
16th to endNight
13%11%41%27%5%
669
March1st to 15thNight
12%10%37%32%7%
540
16th to endNight
23%9%37%23%5%
576
April1st to 15thNight
14%11%38%30%5%
539
16th to endNight
19%11%35%25%7%
540
May1st to 15thNight
13%10%31%34%10%
540
16th to endNight
11%6%34%34%12%
563
June1st to 15thNight
8%225%43%18%
540
16th to endNight
4229%46%16%
540
July1st to 15thNight
7%117%47%25%1
510
16th to endNight
415%51%27%
564
August1st to 15thNight
412%51%30%1
539
16th to endNight
6%215%40%31%4
573
September1st to 15thNight
12%319%37%23%3
540
16th to endNight
8%326%37%22%2
537
October1st to 15thNight
17%6%29%29%16%1
686
16th to endNight
13%7%34%32%10%
768
November1st to 15thNight
10%10%33%34%10%
884
16th to endNight
14%10%37%28%8%
975
December1st to 15thNight
17%11%35%28%5%
910
16th to endNight
19%8%34%30%6%
960
Page generated at 2017-12-03 10:16:39. Version ac04

Copyright 2017 A. Danko


Elk Creek Observatory Clear Sky Chart |Charts Home