Cordell-Lorenz Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cordell-Lorenz Observatory clear sky chart from 2005-11-06 to 2024-01-12.

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
45%
23567
21%
74509
15%
23507
52%
23507
24%
47588

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 10thNight
21%
760
20%
2459
9%
757
34%
757
16%
1658
January11th to 20thNight
21%
725
17%
2354
8%
725
32%
725
13%
1712
January21st to endNight
22%
792
25%
2426
10%
792
37%
792
19%
1622
February1st to 10thNight
24%
720
20%
2160
10%
720
33%
720
19%
1495
February11th to 20thNight
18%
703
16%
2098
6%
699
27%
699
15%
1512
February21st to endNight
18%
592
19%
1776
7%
592
27%
592
14%
1298
March1st to 10thNight
28%
720
20%
2160
11%
720
36%
720
21%
1430
March11th to 20thNight
28%
720
17%
2022
8%
720
35%
720
18%
1417
March21st to endNight
31%
766
18%
2152
9%
766
38%
766
22%
1469
April1st to 10thNight
42%
540
25%
1800
16%
540
53%
540
26%
1065
April11th to 20thNight
38%
533
27%
1775
17%
533
53%
533
28%
1023
April21st to endNight
44%
540
23%
1733
16%
540
52%
540
27%
1037
May1st to 10thNight
45%
540
22%
1620
12%
540
54%
540
31%
999
May11th to 20thNight
52%
531
18%
1593
12%
531
56%
531
26%
1023
May21st to endNight
63%
582
18%
1744
16%
582
64%
582
30%
1083
June1st to 10thNight
63%
540
17%
1620
14%
540
65%
540
28%
1028
June11th to 20thNight
79%
540
20%
1620
17%
540
81%
540
44%
867
June21st to endNight
71%
540
17%
1620
14%
540
73%
540
36%
946
July1st to 10thNight
64%
525
13%
1575
11%
525
65%
525
26%
1033
July11th to 20thNight
71%
522
17%
1566
15%
522
73%
522
32%
948
July21st to endNight
70%
591
18%
1672
16%
558
71%
558
30%
1067
August1st to 10thNight
76%
537
18%
1666
18%
534
76%
534
30%
1020
August11th to 20thNight
68%
534
16%
1776
18%
534
69%
534
26%
1094
August21st to endNight
69%
594
19%
1980
23%
594
69%
594
26%
1233
September1st to 10thNight
68%
596
21%
1856
22%
596
69%
596
32%
1118
September11th to 20thNight
60%
720
23%
1980
19%
720
62%
720
32%
1267
September21st to endNight
63%
720
30%
1980
22%
720
68%
720
37%
1169
October1st to 10thNight
57%
720
33%
1980
26%
720
63%
720
42%
1116
October11th to 20thNight
43%
720
29%
1999
19%
720
53%
720
31%
1248
October21st to endNight
46%
792
29%
2520
25%
792
55%
792
29%
1505
November1st to 10thNight
48%
740
26%
2406
23%
740
56%
740
29%
1379
November11th to 20thNight
37%
760
28%
2470
18%
760
52%
760
27%
1435
November21st to endNight
37%
760
24%
2470
17%
760
47%
760
22%
1563
December1st to 10thNight
28%
760
19%
2470
12%
760
37%
760
15%
1752
December11th to 20thNight
33%
759
22%
2958
16%
758
43%
758
17%
1893
December21st to endNight
26%
833
12%
4453
11%
817
35%
817
8%
3064

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
13%7%36%6%45%5%6%7%37%
74834
Night
13%7%36%5%345%5%7%42%
74880
TransparencyDay
44%7%11%20%16%3
74557
Night
41%6%10%21%18%4
74676
SeeingDay
20%12%23%22%16%7%
13491
Night
18%11%20%27%20%4
23573

By Month

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 10thDay
18%8%5%6%5%45%45%7%34%
1706
11th to 20thDay
23%10%37%5%24345%32%
1629
21st to endDay
16%8%46%433446%42%
1926
February1st to 10thDay
20%11%48%434445%34%
1800
11th to 20thDay
22%9%47%5%3445%5%32%
1748
21st to endDay
22%9%46%5%34445%35%
1480
March1st to 10thDay
17%8%35%5%3445%7%39%
1800
11th to 20thDay
20%8%37%6%35%445%34%
1936
21st to endDay
16%10%37%6%35%5%5%7%33%
2218
April1st to 10thDay
13%6%25%5%45%5%5%7%43%
2160
11th to 20thDay
13%8%27%5%3345%7%43%
2134
21st to endDay
13%7%35%6%4445%8%40%
2227
May1st to 10thDay
13%7%35%4445%6%7%42%
2340
11th to 20thDay
12%8%47%7%46%5%5%6%37%
2301
21st to endDay
9%5%37%7%5%6%6%6%10%37%
2531
June1st to 10thDay
9%6%37%6%5%6%6%6%10%35%
2340
11th to 20thDay
7%435%5%46%7%9%11%40%
2340
21st to endDay
7%5%26%6%47%7%8%11%37%
2340
July1st to 10thDay
9%7%38%8%5%8%7%8%10%29%
2340
11th to 20thDay
10%5%36%9%5%9%7%8%8%30%
2340
21st to endDay
10%5%36%8%5%8%8%8%10%29%
2547
August1st to 10thDay
9%6%37%8%5%8%7%8%11%29%
2256
11th to 20thDay
9%7%36%7%6%7%8%7%10%30%
2125
21st to endDay
12%7%36%8%5%7%7%7%8%31%
2376
September1st to 10thDay
11%6%37%6%5%6%5%7%8%35%
2084
11th to 20thDay
11%7%37%6%35%5%6%8%40%
1980
21st to endDay
11%5%25%6%35%5%6%6%46%
1980
October1st to 10thDay
11%5%25%5%34445%53%
1980
11th to 20thDay
12%6%24434447%52%
1959
21st to endDay
14%6%25%4235%5%6%48%
1832
November1st to 10thDay
11%6%245%24435%56%
1672
11th to 20thDay
12%7%36%42445%5%47%
1710
21st to endDay
17%8%25%4245%46%42%
1710
December1st to 10thDay
20%11%37%5%235%5%5%33%
1710
11th to 20thDay
14%10%48%6%445%45%36%
2153
21st to endDay
16%12%7%7%5%3445%7%30%
3124
January1st to 10thNight
19%9%46%5%23445%38%
2459
11th to 20thNight
21%11%5%7%6%35%45%5%30%
2354
21st to endNight
15%10%46%5%35%335%40%
2426
February1st to 10thNight
19%10%48%5%23436%37%
2160
11th to 20thNight
22%10%47%6%25%33435%
2098
21st to endNight
25%11%35%5%24445%32%
1776
March1st to 10thNight
17%7%35%435%46%6%40%
2160
11th to 20thNight
16%10%37%6%3435%7%36%
2022
21st to endNight
13%10%36%5%44446%39%
2152
April1st to 10thNight
12%6%35%445%448%47%
1800
11th to 20thNight
15%6%2432446%8%47%
1775
21st to endNight
12%6%25%4245%6%7%45%
1733
May1st to 10thNight
12%5%2442446%7%49%
1620
11th to 20thNight
11%6%35%6%35%6%7%8%42%
1592
21st to endNight
7%5%26%5%46%6%7%10%42%
1744
June1st to 10thNight
7%5%36%5%5%5%5%7%10%40%
1620
11th to 20thNight
4213425%6%7%13%53%
1620
21st to endNight
6%424425%6%7%11%48%
1620
July1st to 10thNight
8%5%37%7%46%5%8%9%38%
1620
11th to 20thNight
8%425%5%35%6%8%11%43%
1620
21st to endNight
7%5%36%6%36%8%9%11%38%
1771
August1st to 10thNight
6%3345%46%7%9%12%40%
1677
11th to 20thNight
8%5%36%6%45%6%8%9%41%
1776
21st to endNight
8%7%36%5%35%6%8%9%40%
1980
September1st to 10thNight
9%6%25%5%346%6%9%45%
1856
11th to 20thNight
9%6%26%5%35%5%6%7%46%
1980
21st to endNight
8%5%24435%45%6%53%
1980
October1st to 10thNight
11%414422446%58%
1980
11th to 20thNight
14%5%35%434445%49%
1999
21st to endNight
14%8%24423346%49%
2520
November1st to 10thNight
12%6%24433446%52%
2406
11th to 20thNight
12%8%3442335%7%49%
2470
21st to endNight
15%10%35%434445%43%
2470
December1st to 10thNight
21%10%5%6%5%34445%34%
2470
11th to 20thNight
16%9%46%424445%40%
3042
21st to endNight
16%13%7%7%6%35%5%5%7%27%
4532

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 10thDay
50%37%18%18%3
1707
11th to 20thDay
55%37%17%16%3
1629
21st to endDay
44%38%23%19%3
1926
February1st to 10thDay
53%46%18%16%3
1800
11th to 20thDay
54%45%18%14%4
1758
21st to endDay
53%37%14%18%6%
1480
March1st to 10thDay
45%5%8%17%20%7%
1800
11th to 20thDay
52%5%9%15%15%4
1936
21st to endDay
50%6%10%21%12%1
2218
April1st to 10thDay
40%5%11%22%18%4
2160
11th to 20thDay
41%5%7%19%24%5%
2134
21st to endDay
42%6%9%27%15%2
2227
May1st to 10thDay
40%7%11%26%13%3
2340
11th to 20thDay
46%7%14%20%12%
2305
21st to endDay
41%8%14%22%14%1
2531
June1st to 10thDay
42%9%15%20%13%1
2340
11th to 20thDay
33%9%18%24%14%2
2340
21st to endDay
38%9%19%19%12%3
2340
July1st to 10thDay
45%9%16%19%8%2
2275
11th to 20thDay
44%11%18%15%9%3
2271
21st to endDay
43%12%17%20%7%1
2405
August1st to 10thDay
44%12%16%20%8%1
2243
11th to 20thDay
44%11%13%18%11%2
2125
21st to endDay
47%11%12%18%10%3
2376
September1st to 10thDay
43%8%12%19%14%4
2084
11th to 20thDay
41%7%11%20%19%2
1980
21st to endDay
36%6%10%23%19%6%
1980
October1st to 10thDay
34%5%8%21%26%6%
1980
11th to 20thDay
33%49%21%24%9%
1959
21st to endDay
37%46%22%24%7%
1832
November1st to 10thDay
33%37%20%30%7%
1672
11th to 20thDay
39%35%22%23%7%
1710
21st to endDay
42%46%21%23%4
1710
December1st to 10thDay
53%45%19%15%3
1710
11th to 20thDay
48%5%8%15%20%4
2150
21st to endDay
52%5%9%19%13%3
3124
January1st to 10thNight
50%47%18%18%4
2459
11th to 20thNight
56%46%16%14%3
2354
21st to endNight
48%36%22%18%4
2426
February1st to 10thNight
50%38%18%17%3
2160
11th to 20thNight
55%35%17%15%5%
2099
21st to endNight
55%5%5%15%14%5%
1776
March1st to 10thNight
44%5%8%15%19%9%
2160
11th to 20thNight
49%5%8%19%16%3
2022
21st to endNight
46%410%23%14%2
2152
April1st to 10thNight
37%5%11%23%21%3
1800
11th to 20thNight
34%5%9%21%23%8%
1775
21st to endNight
37%6%12%27%17%2
1733
May1st to 10thNight
35%6%12%24%21%2
1620
11th to 20thNight
37%9%17%23%13%1
1593
21st to endNight
35%8%17%24%14%3
1745
June1st to 10thNight
37%8%16%23%13%3
1620
11th to 20thNight
22%8%20%33%14%2
1620
21st to endNight
28%9%20%25%14%4
1620
July1st to 10thNight
38%10%19%19%11%2
1575
11th to 20thNight
31%10%21%21%12%5%
1566
21st to endNight
34%11%19%24%11%2
1672
August1st to 10thNight
30%12%19%27%11%
1666
11th to 20thNight
35%10%20%18%14%2
1776
21st to endNight
37%9%17%22%12%3
1980
September1st to 10thNight
35%6%17%21%16%5%
1856
11th to 20thNight
35%8%13%20%22%3
1980
21st to endNight
30%6%10%24%23%7%
1980
October1st to 10thNight
27%48%26%25%9%
1980
11th to 20thNight
37%47%22%21%9%
1999
21st to endNight
37%3422%26%8%
2520
November1st to 10thNight
34%5%6%21%25%9%
2406
11th to 20thNight
36%36%20%25%9%
2470
21st to endNight
44%35%19%22%6%
2470
December1st to 10thNight
53%5%6%17%16%3
2470
11th to 20thNight
45%5%6%15%24%5%
3044
21st to endNight
55%5%8%18%12%2
4532

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 10thDay
34%22%31%11%2
270
11th to 20thDay
37%23%24%12%4
243
21st to endDay
27%32%31%8%2
264
February1st to 10thDay
34%24%30%10%1
240
11th to 20thDay
48%22%24%5%
240
21st to endDay
42%24%28%5%1
198
March1st to 10thDay
30%24%36%8%2
240
11th to 20thDay
30%26%22%17%5%1
376
21st to endDay
32%18%29%13%8%
462
April1st to 10thDay
24%17%29%20%10%1
420
11th to 20thDay
24%17%28%21%10%1
412
21st to endDay
25%13%29%22%8%2
420
May1st to 10thDay
21%15%30%20%10%4
423
11th to 20thDay
13%10%30%25%15%8%
447
21st to endDay
15%5%20%30%18%13%
485
June1st to 10thDay
16%6%19%26%19%14%
450
11th to 20thDay
8%5%15%30%22%20%
450
21st to endDay
12%422%26%21%15%
450
July1st to 10thDay
13%314%24%28%18%
445
11th to 20thDay
14%311%22%29%21%
444
21st to endDay
11%39%26%31%19%
488
August1st to 10thDay
14%413%24%30%15%
446
11th to 20thDay
14%313%31%31%8%
439
21st to endDay
17%38%26%32%14%
495
September1st to 10thDay
12%413%29%29%13%
450
11th to 20thDay
14%5%14%26%29%11%
450
21st to endDay
14%6%16%29%30%4
450
October1st to 10thDay
14%8%23%28%21%7%
450
11th to 20thDay
16%12%31%26%13%3
450
21st to endDay
23%10%30%24%12%1
347
November1st to 10thDay
18%12%34%26%8%1
270
11th to 20thDay
18%20%40%21%2
270
21st to endDay
24%17%37%12%9%1
270
December1st to 10thDay
37%16%28%13%5%
270
11th to 20thDay
28%23%32%11%6%
270
21st to endDay
33%20%32%12%2
297
January1st to 10thNight
28%21%26%20%5%
760
11th to 20thNight
28%22%25%20%5%
725
21st to endNight
22%18%34%23%3
792
February1st to 10thNight
26%17%27%25%4
720
11th to 20thNight
30%22%27%19%3
703
21st to endNight
34%17%28%18%2
592
March1st to 10thNight
22%18%27%28%4
720
11th to 20thNight
22%17%27%26%8%
720
21st to endNight
22%16%26%26%10%
766
April1st to 10thNight
17%11%27%32%12%1
540
11th to 20thNight
20%11%28%27%13%2
533
21st to endNight
17%8%26%33%13%2
540
May1st to 10thNight
15%7%27%29%20%3
540
11th to 20thNight
15%6%19%32%22%5%
531
21st to endNight
11%213%34%33%6%
584
June1st to 10thNight
11%211%34%36%6%
540
11th to 20thNight
5%19%34%38%13%
540
21st to endNight
8%211%30%41%9%
540
July1st to 10thNight
10%28%25%44%11%
525
11th to 20thNight
10%26%25%40%16%
522
21st to endNight
10%15%24%47%13%
591
August1st to 10thNight
9%1425%49%13%
537
11th to 20thNight
10%36%30%43%8%
534
21st to endNight
12%35%28%43%9%
594
September1st to 10thNight
12%38%29%41%9%
596
11th to 20thNight
14%5%13%27%35%6%
720
21st to endNight
11%413%34%34%4
720
October1st to 10thNight
13%6%19%27%28%7%
720
11th to 20thNight
17%10%23%28%20%2
720
21st to endNight
20%9%19%34%15%2
792
November1st to 10thNight
16%9%21%31%19%3
740
11th to 20thNight
17%16%26%27%13%1
760
21st to endNight
23%13%22%29%12%1
760
December1st to 10thNight
28%16%23%27%6%
760
11th to 20thNight
24%15%24%28%8%1
760
21st to endNight
28%17%24%25%5%
836
Page generated at 2024-01-08 22:31:23. Version ac07

Copyright 2024 Attilla Danko


Cordell-Lorenz Observatory Clear Sky Chart |Charts Home