Ladd Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ladd Observatory clear sky chart from 2005-11-05 to 2018-04-23.

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
23%
15807
18%
49485
7%
15775
36%
15775
18%
32546

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
13%
780
19%
2716
6%
776
30%
776
14%
1723
January16th to endNight
12%
832
18%
2912
3%
832
32%
832
12%
1912
February1st to 15thNight
14%
764
17%
2349
4%
761
30%
761
14%
1600
February16th to endNight
13%
683
23%
2049
6%
683
33%
683
15%
1368
March1st to 15thNight
15%
780
17%
2337
5%
780
30%
780
14%
1603
March16th to endNight
18%
832
23%
2200
6%
832
32%
832
18%
1494
April1st to 15thNight
16%
778
17%
1946
3%
778
25%
778
16%
1391
April16th to endNight
18%
620
19%
1734
3%
620
28%
620
18%
1197
May1st to 15thNight
19%
540
15%
1620
5%
540
28%
540
13%
1142
May16th to endNight
20%
432
10%
1554
6%
431
28%
431
13%
1057
June1st to 15thNight
29%
360
12%
1440
9%
360
38%
360
13%
971
June16th to endNight
33%
360
12%
1440
10%
360
43%
360
19%
876
July1st to 15thNight
37%
340
12%
1360
11%
340
45%
340
18%
835
July16th to endNight
39%
376
15%
1418
14%
354
48%
354
18%
886
August1st to 15thNight
38%
518
16%
1589
10%
516
43%
516
24%
999
August16th to endNight
47%
735
21%
1881
11%
735
52%
735
32%
1218
September1st to 15thNight
38%
720
19%
1863
9%
720
43%
720
29%
1240
September16th to endNight
41%
717
24%
1980
14%
717
49%
717
27%
1263
October1st to 15thNight
32%
720
23%
1996
10%
720
44%
720
24%
1307
October16th to endNight
23%
768
19%
2496
7%
768
39%
768
19%
1607
November1st to 15thNight
23%
760
19%
2472
9%
760
37%
760
18%
1601
November16th to endNight
20%
780
23%
2535
8%
780
39%
780
18%
1577
December1st to 15thNight
17%
780
18%
2686
5%
780
33%
780
13%
1757
December16th to endNight
12%
832
20%
2912
3%
832
31%
832
12%
1922

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%2442445%7%40%
50039
Night
16%6%25%424446%41%
49655
Cloud CoverDay
17%6%2442445%7%39%
50049
Night
17%7%25%424446%40%
49660
TransparencyDay
43%6%11%21%15%2
49727
Night
44%5%11%21%15%2
49485
SeeingDay
20%21%29%18%7%2
6620
Night
19%24%28%20%6%
15807

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%5%26%324446%43%
1552
16th to endDay
16%6%245%22445%45%
1664
February1st to 15thDay
18%7%24426%447%37%
1838
16th to endDay
16%6%23425%5%46%41%
1710
March1st to 15thDay
20%7%2442345%7%37%
1943
16th to endDay
16%6%35%423345%42%
2374
April1st to 15thDay
19%6%35%424446%37%
2332
16th to endDay
18%424423447%42%
2341
May1st to 15thDay
26%7%24423345%34%
2332
16th to endDay
16%5%2443445%7%40%
2571
June1st to 15thDay
23%6%2442445%8%32%
2520
16th to endDay
13%5%25%5%45%5%6%9%37%
2520
July1st to 15thDay
13%5%15%5%35%5%7%9%35%
2520
16th to endDay
13%5%26%5%36%5%6%9%35%
2654
August1st to 15thDay
13%5%26%5%35%5%6%7%37%
2346
16th to endDay
11%5%26%4345%5%7%42%
2318
September1st to 15thDay
14%5%1442445%5%46%
2097
16th to endDay
15%5%24223345%49%
1980
October1st to 15thDay
20%5%14323435%44%
1962
16th to endDay
16%324424446%45%
1728
November1st to 15thDay
22%6%23323345%41%
1716
16th to endDay
16%5%24324446%45%
1755
December1st to 15thDay
18%7%15%323446%41%
1602
16th to endDay
20%7%24425%346%37%
1664
January1st to 15thNight
17%8%25%424335%42%
2716
16th to endNight
17%9%35%42334440%
2912
February1st to 15thNight
17%7%35%5%24445%39%
2348
16th to endNight
16%7%35%42433442%
2049
March1st to 15thNight
18%7%245%3445%6%37%
2324
16th to endNight
16%7%34423345%42%
2200
April1st to 15thNight
16%8%35%5%35%445%37%
1946
16th to endNight
20%6%25%5%23336%40%
1734
May1st to 15thNight
21%6%445%24345%36%
1620
16th to endNight
18%5%25%6%25%45%8%34%
1552
June1st to 15thNight
21%5%36%42335%6%36%
1440
16th to endNight
15%424425%5%6%9%40%
1440
July1st to 15thNight
12%6%344245%7%9%39%
1440
16th to endNight
11%5%35%5%36%6%5%10%36%
1514
August1st to 15thNight
8%6%35%435%46%8%42%
1599
16th to endNight
11%4244235%5%7%46%
1881
September1st to 15thNight
14%4245%2445%6%44%
1863
16th to endNight
14%7%24323335%47%
1980
October1st to 15thNight
17%6%23423336%45%
1996
16th to endNight
18%5%14424446%42%
2496
November1st to 15thNight
17%6%2442344443%
2472
16th to endNight
17%6%24323446%44%
2535
December1st to 15thNight
19%7%25%433445%39%
2686
16th to endNight
18%8%35%42335%6%38%
2912

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%6%25%324346%43%
1552
16th to endDay
16%6%34422446%44%
1664
February1st to 15thDay
18%7%24435%5%47%36%
1838
16th to endDay
16%7%33424445%41%
1710
March1st to 15thDay
20%8%2442435%7%36%
1953
16th to endDay
16%8%34424335%42%
2374
April1st to 15thDay
19%7%25%424447%36%
2332
16th to endDay
18%5%14423447%42%
2341
May1st to 15thDay
26%7%34323346%33%
2332
16th to endDay
16%5%2442445%7%39%
2571
June1st to 15thDay
24%6%2442445%7%32%
2520
16th to endDay
13%5%26%5%35%5%7%8%36%
2520
July1st to 15thDay
13%5%35%6%35%5%7%9%35%
2520
16th to endDay
13%5%25%6%36%6%7%8%35%
2654
August1st to 15thDay
13%6%25%6%45%5%6%7%37%
2346
16th to endDay
11%5%25%5%345%5%8%41%
2318
September1st to 15thDay
14%5%25%5%24446%45%
2097
16th to endDay
15%6%14323345%49%
1980
October1st to 15thDay
20%5%24323345%44%
1962
16th to endDay
15%5%24424446%44%
1728
November1st to 15thDay
22%7%13324335%41%
1716
16th to endDay
16%5%24423446%45%
1755
December1st to 15thDay
19%7%25%323346%41%
1602
16th to endDay
21%7%345%24346%36%
1664
January1st to 15thNight
17%8%24423235%42%
2716
16th to endNight
17%10%35%423345%40%
2912
February1st to 15thNight
16%8%36%433445%38%
2341
16th to endNight
18%7%35%424335%41%
2049
March1st to 15thNight
18%8%2443445%6%37%
2337
16th to endNight
16%8%345%24345%42%
2199
April1st to 15thNight
17%8%25%435%45%6%36%
1946
16th to endNight
21%5%35%42333441%
1734
May1st to 15thNight
22%6%35%424436%35%
1620
16th to endNight
18%6%26%5%35%5%5%7%34%
1552
June1st to 15thNight
21%6%35%4345%46%35%
1440
16th to endNight
15%425%325%5%6%8%40%
1440
July1st to 15thNight
12%6%34425%6%6%9%38%
1440
16th to endNight
11%5%35%5%36%6%5%10%35%
1514
August1st to 15thNight
9%6%26%445%46%8%41%
1599
16th to endNight
12%4144335%6%7%46%
1881
September1st to 15thNight
14%4235%245%46%45%
1863
16th to endNight
15%7%25%323335%47%
1980
October1st to 15thNight
18%5%24323336%45%
1996
16th to endNight
17%6%24424346%42%
2496
November1st to 15thNight
17%6%25%423445%43%
2472
16th to endNight
18%5%24323346%43%
2535
December1st to 15thNight
20%7%25%423345%39%
2686
16th to endNight
18%8%35%42335%7%37%
2912

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
41%6%10%24%13%4
1553
16th to endDay
41%5%11%25%15%1
1664
February1st to 15thDay
46%5%12%19%13%2
1841
16th to endDay
43%5%11%21%15%2
1710
March1st to 15thDay
46%5%12%22%10%3
1953
16th to endDay
44%48%20%16%5%
2374
April1st to 15thDay
47%5%9%19%15%2
2332
16th to endDay
41%6%8%20%18%4
2341
May1st to 15thDay
51%5%9%16%14%2
2332
16th to endDay
41%7%14%20%13%2
2575
June1st to 15thDay
50%7%10%20%10%1
2520
16th to endDay
40%8%13%22%13%1
2520
July1st to 15thDay
42%8%11%21%14%1
2371
16th to endDay
41%9%14%20%11%3
2487
August1st to 15thDay
42%7%14%19%14%1
2332
16th to endDay
38%6%10%24%18%2
2318
September1st to 15thDay
38%6%11%20%21%2
2097
16th to endDay
36%46%22%26%2
1980
October1st to 15thDay
42%410%23%16%2
1962
16th to endDay
40%412%23%17%2
1728
November1st to 15thDay
45%411%20%15%1
1716
16th to endDay
40%411%24%16%2
1755
December1st to 15thDay
44%5%14%17%17%1
1602
16th to endDay
50%5%12%18%11%1
1664
January1st to 15thNight
45%311%22%14%2
2716
16th to endNight
47%410%19%15%2
2912
February1st to 15thNight
47%5%11%20%13%2
2349
16th to endNight
46%49%20%17%2
2049
March1st to 15thNight
46%6%10%20%13%2
2337
16th to endNight
45%38%18%19%4
2200
April1st to 15thNight
47%5%9%18%15%2
1946
16th to endNight
46%47%19%15%5%
1734
May1st to 15thNight
50%5%10%15%14%3
1620
16th to endNight
47%8%16%16%8%2
1554
June1st to 15thNight
50%6%12%17%12%
1440
16th to endNight
40%7%13%23%14%1
1440
July1st to 15thNight
39%8%12%24%14%
1360
16th to endNight
40%9%13%24%9%2
1418
August1st to 15thNight
38%6%14%23%14%2
1589
16th to endNight
34%7%11%27%17%
1881
September1st to 15thNight
38%6%11%23%18%
1863
16th to endNight
39%46%21%26%1
1980
October1st to 15thNight
41%410%22%17%3
1996
16th to endNight
41%6%11%23%15%1
2496
November1st to 15thNight
43%5%11%20%16%2
2472
16th to endNight
41%411%25%15%2
2535
December1st to 15thNight
46%413%20%13%
2686
16th to endNight
47%411%21%13%
2912

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%33%30%12%2
90
16th to endDay
22%22%40%13%
96
February1st to 15thDay
27%27%33%8%2
292
16th to endDay
19%28%36%11%3
291
March1st to 15thDay
29%26%29%12%2
330
16th to endDay
20%29%32%11%5%1
352
April1st to 15thDay
24%27%31%10%6%
330
16th to endDay
20%26%27%19%43
289
May1st to 15thDay
34%25%20%13%41
288
16th to endDay
19%19%35%21%5%
331
June1st to 15thDay
25%21%27%17%6%
315
16th to endDay
16%20%34%20%6%1
315
July1st to 15thDay
17%13%32%24%10%
305
16th to endDay
12%16%29%27%11%2
326
August1st to 15thDay
14%11%29%29%12%2
313
16th to endDay
11%10%30%25%15%6%
332
September1st to 15thDay
15%14%24%25%16%3
315
16th to endDay
21%9%29%17%10%10%
314
October1st to 15thDay
22%14%24%22%10%4
315
16th to endDay
16%22%28%21%9%1
288
November1st to 15thDay
25%20%27%15%8%2
280
16th to endDay
20%27%29%14%7%1
285
December1st to 15thDay
25%26%25%14%8%
132
16th to endDay
31%31%29%6%2
96
January1st to 15thNight
19%32%31%13%2
780
16th to endNight
21%31%30%14%1
832
February1st to 15thNight
20%29%31%17%
764
16th to endNight
21%31%30%14%2
683
March1st to 15thNight
22%30%28%14%2
780
16th to endNight
19%30%27%17%4
832
April1st to 15thNight
19%32%30%15%3
778
16th to endNight
19%29%30%15%5%
620
May1st to 15thNight
22%27%28%17%4
540
16th to endNight
20%24%29%20%4
432
June1st to 15thNight
20%21%25%27%5%
360
16th to endNight
15%18%29%30%6%
360
July1st to 15thNight
13%14%30%31%10%
340
16th to endNight
11%17%24%37%7%1
376
August1st to 15thNight
12%12%29%35%10%
518
16th to endNight
12%11%21%36%15%1
735
September1st to 15thNight
16%12%28%30%11%
720
16th to endNight
19%14%19%25%16%4
717
October1st to 15thNight
20%15%28%23%10%1
720
16th to endNight
20%20%32%17%8%
768
November1st to 15thNight
19%25%27%18%8%
760
16th to endNight
17%30%27%17%5%
780
December1st to 15thNight
24%26%27%16%4
780
16th to endNight
22%32%29%14%1
832
Page generated at 2018-04-24 10:02:59. Version ac04

Copyright 2018 A. Danko


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