Engle Ridge Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Engle Ridge 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%
15926
11%
47015
8%
15884
36%
15884
16%
35717

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
15%
900
3%
2506
1%
895
16%
895
4%
2292
January16th to endNight
15%
960
4%
2688
2%
960
17%
960
6%
2429
February1st to 15thNight
17%
754
5%
2285
2%
754
19%
754
7%
1991
February16th to endNight
22%
631
7%
1893
4%
631
25%
631
9%
1582
March1st to 15thNight
30%
720
13%
2136
8%
720
34%
720
17%
1579
March16th to endNight
37%
726
17%
2070
12%
726
42%
726
21%
1467
April1st to 15thNight
31%
539
13%
1794
9%
539
37%
539
17%
1266
April16th to endNight
39%
540
19%
1620
12%
540
45%
540
24%
1095
May1st to 15thNight
40%
540
13%
1620
9%
540
45%
540
21%
1126
May16th to endNight
49%
562
14%
1503
8%
561
54%
561
31%
985
June1st to 15thNight
46%
447
13%
1347
9%
447
49%
447
25%
887
June16th to endNight
56%
456
13%
1356
10%
456
58%
456
29%
848
July1st to 15thNight
65%
510
15%
1360
10%
510
67%
510
39%
813
July16th to endNight
60%
564
15%
1417
10%
531
62%
531
36%
886
August1st to 15thNight
66%
539
18%
1557
14%
536
68%
536
34%
924
August16th to endNight
58%
573
17%
1788
15%
573
60%
573
28%
1108
September1st to 15thNight
54%
604
16%
1864
14%
604
57%
604
28%
1171
September16th to endNight
52%
693
19%
1914
15%
693
54%
693
29%
1257
October1st to 15thNight
38%
660
16%
1873
11%
660
42%
660
20%
1376
October16th to endNight
25%
704
8%
2288
6%
704
28%
704
10%
1823
November1st to 15thNight
26%
700
14%
2276
11%
700
30%
700
13%
1727
November16th to endNight
17%
744
6%
2400
5%
744
19%
744
7%
2066
December1st to 15thNight
10%
900
2%
2700
1%
900
11%
900
3%
2502
December16th to endNight
11%
960
3%
2760
1%
960
13%
960
5%
2517

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
15%10%47%6%34446%32%
47907
Night
15%12%5%8%7%34445%28%
47183
Cloud CoverDay
15%9%47%6%34446%32%
47916
Night
16%12%5%8%6%34345%29%
47188
TransparencyDay
52%6%12%18%9%
47593
Night
57%6%11%16%8%
47015
SeeingDay
19%6%25%28%16%5%
6034
Night
20%8%27%30%11%1
15930

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%18%10%14%11%5%43238%
1432
16th to endDay
12%16%11%17%12%5%7%4337%
1536
February1st to 15thDay
12%14%9%14%14%46%34312%
1575
16th to endDay
12%16%8%13%10%36%345%13%
1580
March1st to 15thDay
12%10%411%8%45%5%45%27%
1814
16th to endDay
14%10%5%7%5%24446%31%
2163
April1st to 15thDay
20%12%34434345%33%
2154
16th to endDay
17%10%35%42435%6%35%
2340
May1st to 15thDay
16%7%36%5%3445%5%36%
2331
16th to endDay
11%6%2433445%8%44%
2610
June1st to 15thDay
14%6%24425%45%8%41%
2607
16th to endDay
12%5%245%345%6%9%40%
2597
July1st to 15thDay
11%313425%45%7%47%
2520
16th to endDay
11%413325%46%10%45%
2655
August1st to 15thDay
9%425%5%345%6%7%45%
2394
16th to endDay
15%5%25%42435%7%42%
2413
September1st to 15thDay
16%425%424447%42%
2083
16th to endDay
16%5%243245%5%8%40%
1905
October1st to 15thDay
22%9%26%6%33446%30%
1757
16th to endDay
28%13%37%7%245%46%16%
1584
November1st to 15thDay
16%15%6%6%5%2445%6%25%
1582
16th to endDay
17%26%8%9%6%2333413%
1555
December1st to 15thDay
17%21%10%16%10%242328%
1260
16th to endDay
18%22%12%11%9%343239%
1460
January1st to 15thNight
17%16%9%16%10%5%432211%
2506
16th to endNight
12%17%9%14%11%5%5%34411%
2688
February1st to 15thNight
11%15%10%12%13%5%5%33314%
2283
16th to endNight
14%15%6%13%9%46%34417%
1893
March1st to 15thNight
12%10%5%8%6%35%445%34%
2123
16th to endNight
14%9%47%5%2445%6%34%
2070
April1st to 15thNight
21%11%36%41335%5%31%
1794
16th to endNight
17%9%25%423436%40%
1620
May1st to 15thNight
15%6%35%6%36%5%5%6%34%
1620
16th to endNight
12%6%334245%5%9%41%
1501
June1st to 15thNight
12%5%25%6%35%5%5%6%41%
1347
16th to endNight
10%435%4245%5%9%43%
1356
July1st to 15thNight
10%41432445%9%49%
1440
16th to endNight
8%4145%25%45%7%50%
1513
August1st to 15thNight
7%415%4245%6%8%48%
1566
16th to endNight
14%5%14424346%47%
1788
September1st to 15thNight
14%7%24413345%47%
1864
16th to endNight
17%434433348%44%
1914
October1st to 15thNight
21%8%36%5%13345%34%
1873
16th to endNight
25%12%37%6%34446%21%
2288
November1st to 15thNight
16%15%5%7%6%33445%27%
2276
16th to endNight
19%22%6%10%7%4333414%
2400
December1st to 15thNight
17%23%11%14%9%342328%
2700
16th to endNight
16%21%10%13%8%343339%
2760

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%18%11%13%11%5%43239%
1432
16th to endDay
12%17%10%17%11%5%5%4327%
1536
February1st to 15thDay
12%14%9%14%14%46%33412%
1575
16th to endDay
12%16%9%12%9%46%43414%
1580
March1st to 15thDay
12%9%5%10%8%35%5%45%27%
1824
16th to endDay
15%10%5%6%6%3445%6%32%
2162
April1st to 15thDay
20%12%34423445%33%
2154
16th to endDay
17%10%35%424346%36%
2340
May1st to 15thDay
16%7%36%5%2445%6%36%
2331
16th to endDay
12%5%2442445%7%44%
2610
June1st to 15thDay
14%5%24425%46%8%41%
2607
16th to endDay
13%425%4335%6%8%41%
2597
July1st to 15thDay
11%31343445%7%48%
2520
16th to endDay
11%32332446%9%46%
2655
August1st to 15thDay
9%4146%345%6%8%45%
2394
16th to endDay
16%5%24424447%43%
2413
September1st to 15thDay
17%424434347%43%
2083
16th to endDay
16%42442446%8%40%
1905
October1st to 15thDay
23%8%26%6%33346%30%
1757
16th to endDay
29%13%37%6%34445%16%
1584
November1st to 15thDay
16%16%5%6%5%25%446%25%
1582
16th to endDay
18%26%7%10%5%2333313%
1555
December1st to 15thDay
18%20%11%17%9%232228%
1260
16th to endDay
19%22%11%12%8%332239%
1460
January1st to 15thNight
17%16%9%16%10%4422211%
2506
16th to endNight
13%17%9%14%11%5%433311%
2688
February1st to 15thNight
12%15%9%13%13%45%33314%
2276
16th to endNight
15%14%7%13%9%45%33417%
1893
March1st to 15thNight
13%10%5%8%6%34445%33%
2136
16th to endNight
15%9%47%5%2445%6%34%
2070
April1st to 15thNight
21%11%35%5%2335%5%32%
1794
16th to endNight
17%9%35%423446%40%
1620
May1st to 15thNight
15%6%35%6%36%5%5%6%34%
1619
16th to endNight
13%6%3343445%9%41%
1501
June1st to 15thNight
12%426%5%35%5%47%41%
1347
16th to endNight
11%425%42446%8%43%
1356
July1st to 15thNight
10%31442445%9%50%
1440
16th to endNight
8%324425%35%8%50%
1513
August1st to 15thNight
7%3244246%6%7%49%
1566
16th to endNight
14%5%245%33245%47%
1788
September1st to 15thNight
15%6%24422345%47%
1864
16th to endNight
17%433432348%44%
1914
October1st to 15thNight
22%9%36%5%23345%34%
1873
16th to endNight
26%11%37%7%34346%21%
2288
November1st to 15thNight
17%15%47%5%24445%27%
2276
16th to endNight
19%22%7%10%6%33335%14%
2400
December1st to 15thNight
18%24%11%13%9%332228%
2700
16th to endNight
17%22%10%13%7%343339%
2760

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
81%6%5%5%1
1433
16th to endDay
83%45%5%
1536
February1st to 15thDay
76%5%8%8%
1577
16th to endDay
72%6%8%9%2
1580
March1st to 15thDay
58%6%12%16%5%
1824
16th to endDay
51%7%13%20%5%1
2163
April1st to 15thDay
52%411%22%9%
2154
16th to endDay
48%5%12%15%15%2
2340
May1st to 15thDay
48%410%22%10%3
2331
16th to endDay
38%6%13%25%14%1
2614
June1st to 15thDay
39%6%13%25%13%
2607
16th to endDay
39%8%16%22%12%1
2597
July1st to 15thDay
33%5%14%29%16%1
2371
16th to endDay
34%7%15%25%16%1
2488
August1st to 15thDay
35%7%15%28%11%
2379
16th to endDay
40%6%13%24%14%1
2413
September1st to 15thDay
40%6%14%25%12%
2083
16th to endDay
40%7%17%24%10%
1905
October1st to 15thDay
54%6%9%21%7%
1757
16th to endDay
67%7%12%8%2
1584
November1st to 15thDay
57%6%12%16%6%
1582
16th to endDay
75%5%10%6%1
1555
December1st to 15thDay
84%45%4
1260
16th to endDay
81%47%41
1460
January1st to 15thNight
80%5%5%6%1
2506
16th to endNight
77%7%7%6%1
2688
February1st to 15thNight
74%5%7%9%1
2285
16th to endNight
69%5%10%10%3
1893
March1st to 15thNight
53%6%12%17%9%
2136
16th to endNight
50%412%21%10%
2070
April1st to 15thNight
53%49%21%10%1
1794
16th to endNight
45%5%10%20%16%2
1620
May1st to 15thNight
48%5%12%20%10%3
1620
16th to endNight
38%5%14%24%13%2
1503
June1st to 15thNight
41%7%11%24%14%
1347
16th to endNight
36%7%15%24%15%
1356
July1st to 15thNight
30%5%13%28%19%2
1360
16th to endNight
33%6%15%27%16%1
1417
August1st to 15thNight
30%7%17%30%12%
1557
16th to endNight
38%6%15%24%15%1
1788
September1st to 15thNight
38%6%13%24%16%
1864
16th to endNight
40%5%16%28%8%
1914
October1st to 15thNight
52%5%9%21%10%
1873
16th to endNight
63%7%12%12%4
2288
November1st to 15thNight
58%7%11%15%7%
2276
16th to endNight
73%5%10%7%2
2400
December1st to 15thNight
82%6%5%4
2700
16th to endNight
79%6%7%41
2760

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%11%38%26%4
90
16th to endDay
31%6%26%31%5%
96
February1st to 15thDay
18%15%42%21%2
90
16th to endDay
23%11%35%20%8%
81
March1st to 15thDay
21%15%23%25%13%
114
16th to endDay
26%5%23%28%14%1
288
April1st to 15thDay
26%7%27%25%10%2
270
16th to endDay
24%7%29%21%15%2
270
May1st to 15thDay
22%7%26%25%13%4
288
16th to endDay
15%6%33%25%14%4
510
June1st to 15thDay
17%5%28%30%14%3
495
16th to endDay
13%5%28%34%15%3
495
July1st to 15thDay
14%321%31%21%6%
475
16th to endDay
11%323%34%20%6%
515
August1st to 15thDay
12%115%33%26%10%
367
16th to endDay
20%315%26%22%10%
332
September1st to 15thDay
19%217%24%21%15%
315
16th to endDay
16%316%32%25%6%
287
October1st to 15thDay
26%6%22%28%13%2
244
16th to endDay
32%6%37%18%5%
96
November1st to 15thDay
21%10%22%32%13%1
90
16th to endDay
31%19%24%16%8%
83
December1st to 15thDay
36%25%23%11%11
60
16th to endDay
27%24%40%6%1
83
January1st to 15thNight
24%12%32%24%5%
900
16th to endNight
19%12%34%26%6%
960
February1st to 15thNight
17%10%37%28%5%
757
16th to endNight
22%10%30%27%8%
631
March1st to 15thNight
17%10%33%28%9%
720
16th to endNight
19%6%28%34%10%1
726
April1st to 15thNight
25%9%28%28%7%
539
16th to endNight
21%5%30%32%10%1
540
May1st to 15thNight
18%5%30%34%11%
540
16th to endNight
14%425%38%16%
563
June1st to 15thNight
15%325%39%14%1
447
16th to endNight
12%221%41%21%1
456
July1st to 15thNight
11%116%41%25%3
510
16th to endNight
10%120%39%25%2
564
August1st to 15thNight
8%215%44%27%2
539
16th to endNight
16%115%39%24%2
573
September1st to 15thNight
18%318%32%21%5%
604
16th to endNight
19%417%32%21%4
693
October1st to 15thNight
26%5%21%31%14%
660
16th to endNight
33%10%25%24%5%
704
November1st to 15thNight
26%10%31%24%7%
700
16th to endNight
29%14%30%21%3
744
December1st to 15thNight
26%15%37%17%3
900
16th to endNight
24%11%37%21%31
960
Page generated at 2017-09-25 09:02:26. Version ac04

Copyright 2017 A. Danko


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